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1. Which statement best represents a key principle of modern cell theory?
ⓐ. New cells originate only from non-living material under special conditions
ⓑ. Every organism is made of cells, but cells need not be the basic unit of life
ⓒ. All cells arise from pre-existing cells through cell division
ⓓ. Cells can be formed spontaneously inside tissues when nutrients are abundant
Correct Answer: All cells arise from pre-existing cells through cell division
Explanation: Modern cell theory emphasizes continuity of life at the cellular level: a cell does not appear “from nothing,” but is produced when an existing cell divides. This explains how genetic information, cellular organization, and metabolism are maintained across generations. It also rules out spontaneous generation for routine formation of living cells in organisms. The principle fits observations of growth, repair, and reproduction, where division produces daughter cells. It supports heredity because DNA is passed from parent cell to daughter cells during division. Hence, cell division from pre-existing cells is a core modern statement.
2. A bacterial cell lacks a true nucleus mainly because:
ⓐ. Its DNA is not enclosed by a nuclear envelope
ⓑ. Its DNA is absent and genetic information is in ribosomes
ⓒ. Its DNA is always linear and attached to histones
ⓓ. Its DNA is stored inside mitochondria for protection
Correct Answer: Its DNA is not enclosed by a nuclear envelope
Explanation: In bacteria, genetic material is present in a nucleoid region, where DNA lies in the cytoplasm without being surrounded by a nuclear membrane. The absence of a nuclear envelope is the defining reason it is not a “true” nucleus. This organization allows transcription and translation to be closely coupled in prokaryotes because there is no membrane barrier between DNA and ribosomes. Although bacteria may have additional DNA in plasmids, the main chromosome still remains unenclosed. Therefore, the lack of a nuclear envelope around DNA explains the absence of a true nucleus.
3. Why do most cells remain microscopic rather than growing indefinitely in size?
ⓐ. Large cells cannot synthesize proteins due to lack of ribosomes
ⓑ. Cytoplasm becomes acidic in bigger cells, stopping metabolism
ⓒ. Large cells always lose DNA during growth, causing cell death
ⓓ. As cell size increases, surface area becomes too small relative to volume for exchange
Correct Answer: As cell size increases, surface area becomes too small relative to volume for exchange
Explanation: As a cell grows, its volume increases faster than its surface area, reducing the surface area-to-volume ratio. Since exchange of nutrients, gases, and wastes largely occurs across the plasma membrane, insufficient surface area limits the rate at which materials can enter and leave. Meanwhile, a larger volume demands more resources and produces more waste, increasing the transport load. Diffusion distances inside the cell also increase, slowing internal distribution. These combined constraints make very large single cells inefficient for maintaining homeostasis. Hence, surface area-to-volume limitations keep most cells microscopic.
4. In microscopy, “resolution” primarily refers to:
ⓐ. The total magnification achieved by objective × eyepiece
ⓑ. The ability to distinguish two closely placed points as separate
ⓒ. The brightness of the image produced by the light source
ⓓ. The thickness of the specimen that can be observed clearly
Correct Answer: The ability to distinguish two closely placed points as separate
Explanation: Resolution is the measure of image clarity in terms of how well a microscope can separate two nearby points into distinct images. Even very high magnification is not useful if resolution is poor, because the image becomes a larger blur rather than revealing detail. Resolution depends on factors such as the wavelength of radiation used and the numerical aperture of the lens system. Shorter wavelengths improve resolving power, which is why electron microscopes can reveal much finer structures than visible-light microscopes. Therefore, resolution is fundamentally about distinguishing closely spaced details.
5. The fluid mosaic model of the plasma membrane is best supported by the idea that:
ⓐ. Membrane proteins are arranged in rigid repeating rows
ⓑ. The membrane is made only of phospholipids with no proteins
ⓒ. Carbohydrates form the main structural framework of the membrane
ⓓ. Lipids form a dynamic bilayer with proteins embedded and able to move laterally
Correct Answer: Lipids form a dynamic bilayer with proteins embedded and able to move laterally
Explanation: The fluid mosaic model describes the membrane as a phospholipid bilayer that is not static but remains fluid, allowing components to shift within the plane of the membrane. Proteins are embedded within or associated with this bilayer, creating a “mosaic” pattern, and many can move laterally depending on interactions and membrane composition. This dynamic nature explains processes like membrane transport, cell signaling, endocytosis, and membrane fusion. It also accounts for differences in permeability and the presence of channels, carriers, and receptors. Thus, a fluid lipid bilayer with mobile proteins is central to the model.
6. Which statement about ribosomes is correct in the context of cell organization?
ⓐ. They are sites of protein synthesis and occur in both prokaryotes and eukaryotes
ⓑ. They are membrane-bound organelles responsible for lipid synthesis
ⓒ. They contain DNA and serve as the genetic control centers of cells
ⓓ. They are present only in animal cells and absent in plants
Correct Answer: They are sites of protein synthesis and occur in both prokaryotes and eukaryotes
Explanation: Ribosomes are the universal protein-synthesizing machines of cells, translating mRNA into polypeptide chains. They are found in both prokaryotic and eukaryotic cells, reflecting the fundamental and conserved nature of translation across life forms. Ribosomes may be free in the cytosol or attached to rough endoplasmic reticulum in eukaryotes, depending on the destination of the proteins produced. Prokaryotic ribosomes are typically 70S and eukaryotic cytosolic ribosomes are typically 80S, but the function remains the same. Hence, ribosomes are present in all cells and are the sites of protein synthesis.
7. A correct match of cell wall component with organism group is:
ⓐ. Cellulose — bacteria
ⓑ. Peptidoglycan — bacteria
ⓒ. Chitin — plants
ⓓ. Pectin — fungi
Correct Answer: Peptidoglycan — bacteria
Explanation: Bacterial cell walls are primarily made of peptidoglycan, a mesh-like polymer of sugars cross-linked by short peptides that provides strength and shape. This component is characteristic of most bacteria and is a major reason bacterial walls respond to certain antibiotics that target peptidoglycan synthesis. In contrast, plant cell walls mainly contain cellulose, and fungal cell walls primarily contain chitin. Correct identification of peptidoglycan with bacteria helps distinguish bacterial cells from plant and fungal cells in structure and drug sensitivity. Therefore, peptidoglycan is the correct bacterial cell wall component.
8. Which set includes only components of the endomembrane system?
ⓐ. Mitochondria, chloroplasts, ribosomes, lysosomes
ⓑ. Nucleus, mitochondria, Golgi apparatus, peroxisomes
ⓒ. Endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles
ⓓ. Chloroplasts, endoplasmic reticulum, ribosomes, centrosome
Correct Answer: Endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles
Explanation: The endomembrane system is a functionally connected group of membranous organelles involved mainly in synthesis, modification, packaging, transport, and digestion. It includes structures like the endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles, which coordinate the flow of proteins and lipids via vesicles. Organelles such as mitochondria and chloroplasts are excluded because they are semi-autonomous and have distinct origins and functions. Ribosomes are also excluded because they are not membrane-bound. Hence, ER, Golgi, lysosomes, and vacuoles correctly represent the endomembrane system.
9. Lysosomal enzymes function optimally because lysosomes:
ⓐ. Maintain an acidic internal pH that activates acid hydrolases
ⓑ. Contain chlorophyll that supplies energy for enzyme action
ⓒ. Have a neutral pH to prevent damage to cellular components
ⓓ. Lack membranes, allowing enzymes to mix freely with cytoplasm
Correct Answer: Maintain an acidic internal pH that activates acid hydrolases
Explanation: Lysosomes contain hydrolytic enzymes (acid hydrolases) designed to break down macromolecules, worn-out organelles, and foreign material. These enzymes work best at an acidic pH, which is maintained inside lysosomes by proton pumps in the lysosomal membrane. The membrane not only helps create this acidic environment but also isolates potentially destructive enzymes from the rest of the cell. This compartmentalization ensures digestion occurs safely within the lysosome without harming cytosolic structures. Therefore, acidic internal pH is essential for lysosomal enzyme activity and is a defining functional feature.
10. In animal cells, centrioles are most directly associated with:
ⓐ. ATP synthesis during aerobic respiration
ⓑ. Detoxification of drugs via membrane-bound enzymes
ⓒ. Protein packaging and secretion into vesicles
ⓓ. Organization of microtubules during spindle formation in cell division
Correct Answer: Organization of microtubules during spindle formation in cell division
Explanation: Centrioles, typically present as a pair within the centrosome of animal cells, act as key microtubule-organizing structures. During cell division, they help organize the spindle apparatus by directing microtubule arrangement, which is essential for accurate separation of chromosomes. Their structural pattern supports microtubule nucleation and alignment, contributing to orderly mitosis and meiosis. While some plant cells lack centrioles, animals commonly use them in centrosome-based spindle organization. Thus, the most direct role of centrioles is microtubule organization for spindle formation during division.
11. Robert Hooke is credited with coining the term “cell” after observing:
ⓐ. Living bacteria moving in pond water
ⓑ. Box-like compartments in a thin slice of cork
ⓒ. Membrane-bound nucleus in onion epidermis
ⓓ. Chromosomes separating during cell division
Correct Answer: Box-like compartments in a thin slice of cork
Explanation: Robert Hooke examined a very thin section of cork under a compound microscope and saw numerous tiny, empty, box-like chambers arranged in a honeycomb pattern. These compartments reminded him of small rooms, so he used the term “cells” to describe them. Cork is made of dead tissue, so he was mainly seeing the rigid boundaries rather than living contents. His observation was important because it introduced the idea that plant materials could be made of repeated structural units. This naming later became foundational when scientists discovered living cell contents in other tissues.
12. What did Hooke actually observe in cork that led him to describe “cells”?
ⓐ. Cytoplasm actively streaming inside compartments
ⓑ. Chloroplasts arranged along the cell periphery
ⓒ. A clearly visible nucleus in each unit
ⓓ. Rigid cell walls forming empty chamber-like boxes
Correct Answer: Rigid cell walls forming empty chamber-like boxes
Explanation: In cork, the protoplasm is absent because the cells are dead at maturity, leaving behind only the thick, rigid boundaries. Hooke’s microscope revealed these boundaries as a network of small, box-like compartments, which he described as “cells.” He did not observe cytoplasm, nuclei, or other organelles in cork, because these structures are not preserved in dead cork tissue. The visible feature was the wall pattern that outlines each unit. This is why his “cells” looked empty and chamber-like rather than filled with living material.
13. The honeycomb-like appearance described by Hooke was mainly due to:
ⓐ. Regular arrangement of dead cork cells with thick boundaries
ⓑ. Spiral thickening of xylem vessels in cork tissue
ⓒ. Stacked thylakoids forming repetitive disc-like units
ⓓ. Circular movement of cytoplasm producing optical patterns
Correct Answer: Regular arrangement of dead cork cells with thick boundaries
Explanation: Cork tissue consists of tightly packed cells that, when cut in a thin section, show a repeated pattern of compartments separated by thick walls. Because the cells are dead, the internal living contents are missing, so the walls stand out prominently. This creates a regular, lattice-like pattern that resembles a honeycomb. The geometry is a natural result of closely packed units in plant tissue. Hooke’s description was based on this visible structural organization, not on moving cytoplasm or organelles. Thus, the honeycomb appearance reflects the wall-bounded arrangement of cork cells.
14. The term “cell” was used by Hooke primarily because the structures resembled:
ⓐ. Tiny bubbles formed in sap-filled tissue
ⓑ. Grain-like bodies seen in cytoplasm
ⓒ. Small rooms or chambers like those in a monastery
ⓓ. Circular discs similar to red blood cells
Correct Answer: Small rooms or chambers like those in a monastery
Explanation: Hooke chose the word “cell” because the compartments he saw reminded him of small rooms or chambers, similar to the tiny living spaces used by monks. His microscope showed many repeated box-like spaces, and the visual similarity guided his naming. The term was based on appearance rather than an understanding of cell function or internal components. This historical naming is significant because it introduced a word that later became central to biology. As microscopy improved, scientists found that living cells contain active material and organelles, but the name “cell” remained rooted in Hooke’s original comparison.
15. Hooke published his observations on cork “cells” in the book:
ⓐ. Origin of Species
ⓑ. Micrographia
ⓒ. Systema Naturae
ⓓ. De Humani Corporis Fabrica
Correct Answer: Micrographia
Explanation: Hooke documented many microscopic observations, including the cork “cells,” in his famous book Micrographia. This work helped popularize microscopy and showed that microscopic structures could be studied systematically. In Micrographia, he included detailed drawings and descriptions that allowed others to understand what he saw. The cork observation was particularly influential because it provided a clear structural pattern and introduced the term “cell.” Although Hooke did not describe living cell contents from cork, the publication inspired further microscopic studies. Therefore, Micrographia is directly associated with Hooke’s cork observations and the naming of cells.
16. A key limitation of Hooke’s cork observation was that it did not reveal:
ⓐ. Living protoplasm and cell organelles inside the compartments
ⓑ. The presence of rigid boundaries around each compartment
ⓒ. The repeated structural units in plant tissue
ⓓ. The honeycomb-like arrangement of the compartments
Correct Answer: Living protoplasm and cell organelles inside the compartments
Explanation: Cork is composed of dead cells, so the living contents (protoplasm) are absent and cannot be seen even with careful observation. Hooke mainly observed the empty, wall-bounded chambers and could not describe organelles like nucleus, mitochondria, or cytoplasm. This limitation meant his “cells” were structural outlines rather than functioning living units. Later scientists examined living tissues and microorganisms to understand cell contents and activity. The cork observation still remained historically important because it highlighted repeated units in biological material. However, it did not provide information about the living nature and internal organization of cells.
17. Which statement best distinguishes Hooke’s cork “cells” from a typical living plant cell?
ⓐ. Cork “cells” lack a cell wall, while living plant cells have one
ⓑ. Cork “cells” contain chloroplasts, while living plant cells do not
ⓒ. Cork “cells” appear empty because the protoplasm is absent in dead tissue
ⓓ. Cork “cells” have a nuclear envelope, while living plant cells lack it
Correct Answer: Cork “cells” appear empty because the protoplasm is absent in dead tissue
Explanation: Hooke’s cork compartments looked empty because cork cells are dead and do not retain active protoplasm. In a typical living plant cell, the interior contains cytoplasm, membranes, and often a nucleus and vacuole, making it a functional unit of life. Cork, being protective tissue, develops thick walls and loses its living contents at maturity. Therefore, what Hooke saw was mainly the wall framework rather than the living machinery. This distinction explains why later observations of living cells provided far more information about cell function and internal structures. The apparent emptiness is a consequence of tissue state, not a general property of all cells.
18. The instrument most directly associated with Hooke’s cork observation was a:
ⓐ. Electron microscope
ⓑ. Phase-contrast microscope
ⓒ. Dissecting microscope
ⓓ. Compound light microscope
Correct Answer: Compound light microscope
Explanation: Hooke used an early compound microscope that employed multiple lenses to magnify small objects. This allowed him to observe a thin slice of cork and identify the repeating compartment-like units. Electron microscopes did not exist in his time, and phase-contrast methods were developed much later to improve viewing of transparent living cells. A dissecting microscope provides low magnification for larger specimens and is not suited for revealing tiny cork compartments. Hooke’s compound microscope, although limited compared to modern instruments, was sufficient to show the wall-bounded honeycomb pattern. Hence, the compound light microscope is the correct instrument associated with his discovery.
19. Which observation would you most likely expect if you repeat Hooke’s cork experiment properly today?
ⓐ. Rapid cytoplasmic streaming inside each compartment
ⓑ. Empty, box-like chambers bounded by thick walls
ⓒ. Chloroplasts aligned along the inner membrane surface
ⓓ. Amoeboid movement of the compartment contents
Correct Answer: Empty, box-like chambers bounded by thick walls
Explanation: A thin cork section will still show a network of empty compartments because cork cells are dead and the protoplasm is not present. The thick, rigid walls remain and form clear boundaries that appear as box-like or polygonal chambers. Features like cytoplasmic streaming, chloroplast placement, or amoeboid movement require living cells with active contents, which cork does not provide. The repeated pattern arises from the structural packing of cells in the cork tissue. Therefore, the expected observation is the honeycomb-like array of wall-bounded empty chambers, matching Hooke’s classic description.
20. Hooke’s cork observation is historically significant mainly because it:
ⓐ. Introduced the term “cell” and highlighted repeated structural units in organisms
ⓑ. Proved that all cells have nuclei visible under light microscopes
ⓒ. Established that cell membranes are made of a lipid bilayer
ⓓ. Demonstrated that mitochondria are the energy centers of cells
Correct Answer: Introduced the term “cell” and highlighted repeated structural units in organisms
Explanation: Hooke’s work provided one of the earliest clear demonstrations that biological material can have a repeated, organized microscopic structure. By naming the compartments “cells,” he introduced a term that later became central to understanding life’s organization. Although he did not explain cell functions or internal structures, his observation encouraged further microscopy and systematic study of tissues. The concepts of nuclei, lipid bilayers, and mitochondria were discovered much later with improved techniques. Hooke’s contribution was primarily conceptual and historical: recognizing and naming a basic structural unit. This milestone helped set the stage for later development of cell theory and modern biology.
21. Antonie van Leeuwenhoek is best known in cell discovery history for:
ⓐ. Naming “cells” after seeing empty chambers in cork
ⓑ. Proposing that cells arise spontaneously from non-living matter
ⓒ. First observing living microscopic organisms using improved microscopes
ⓓ. Demonstrating the lipid nature of the plasma membrane experimentally
Correct Answer: First observing living microscopic organisms using improved microscopes
Explanation: Leeuwenhoek used finely crafted lenses to observe living microscopic forms in natural samples like water and scrapings, describing them as “animalcules.” Unlike earlier observations limited to dead plant tissue outlines, his work revealed that microscopic life is active and diverse. This was crucial because it showed that living units could be directly seen rather than inferred from structure alone. His observations expanded the biological world to include microorganisms, shaping how scientists understood life’s scale. It also encouraged systematic microscopy to study cells and living contents. Therefore, his key contribution was the first clear observation of living microscopic organisms.
22. Leeuwenhoek’s “animalcules” were most accurately described as:
ⓐ. Microorganisms such as protozoa and bacteria observed in water samples
ⓑ. Empty air-filled chambers inside cork tissue seen under magnification
ⓒ. Protein granules released from broken plant cells during sectioning
ⓓ. Crystal-like bodies produced when salts precipitate in plant sap
Correct Answer: Microorganisms such as protozoa and bacteria observed in water samples
Explanation: The term “animalcules” was used by Leeuwenhoek to describe tiny moving living forms he saw in samples like pond water and other infusions. These were not empty structures but active organisms capable of locomotion and behavior under the microscope. Many of these observations correspond to protozoa and bacteria as understood today. His descriptions emphasized movement, life-like activity, and abundance, which distinguished them from non-living particles. This was a major shift because it revealed a previously unseen living world. Hence, “animalcules” refers to microorganisms such as protozoa and bacteria.
23. Leeuwenhoek’s observation of bacteria is most commonly associated with:
ⓐ. Thin slices of cork observed as box-like units
ⓑ. Human blood cells observed as colored discs
ⓒ. Plant epidermal peel showing a nucleus
ⓓ. Scrapings from teeth or infusions showing tiny moving forms
Correct Answer: Scrapings from teeth or infusions showing tiny moving forms
Explanation: Leeuwenhoek reported extremely small, actively moving organisms in materials such as dental scrapings and various infusions, which are now recognized as bacteria. These samples contain dense microbial populations, making them suitable for early microscopy. His accounts focused on their minute size, large numbers, and lively motion in a drop of fluid. This differs from cork observations, which show dead wall compartments without living content. By seeing such tiny living forms, he provided early evidence that life exists at microscopic scales beyond direct human vision. Therefore, bacteria are linked to observations from dental scrapings or infusions.
24. Which contrast between Hooke and Leeuwenhoek is scientifically accurate?
ⓐ. Hooke observed living bacteria, while Leeuwenhoek observed only dead cork tissue
ⓑ. Hooke used electron microscopy, while Leeuwenhoek used phase-contrast microscopy
ⓒ. Hooke mainly saw dead cell walls in cork, while Leeuwenhoek saw living cells/organisms
ⓓ. Hooke discovered mitochondria, while Leeuwenhoek discovered ribosomes
Correct Answer: Hooke mainly saw dead cell walls in cork, while Leeuwenhoek saw living cells/organisms
Explanation: Hooke examined cork and described “cells” as empty, box-like compartments because cork tissue is dead and largely shows only rigid walls. Leeuwenhoek, in contrast, examined fresh samples containing living microscopic forms and reported their movement and behavior. This difference is central to why Leeuwenhoek’s work expanded understanding from structural compartments to living units. It also helped shift scientific attention toward protoplasm and life processes at the microscopic level. The contrast does not involve modern microscopes or organelles discovered later. Hence, Hooke saw dead wall outlines, whereas Leeuwenhoek saw living cells/organisms.
25. Leeuwenhoek achieved high magnification primarily using:
ⓐ. A simple microscope with a single, finely polished small lens
ⓑ. A compound microscope with multiple objectives and eyepieces
ⓒ. A fluorescent microscope with dye-based imaging
ⓓ. An electron microscope with electromagnetic lenses
Correct Answer: A simple microscope with a single, finely polished small lens
Explanation: Leeuwenhoek’s instruments were simple microscopes that used a single, very small, carefully shaped lens. Despite being “simple” in design, the lens quality and short focal length allowed impressive magnification and clarity for that era. This design differs from compound microscopes that use multiple lenses, which at the time often suffered from poorer optics. His approach enabled him to observe living microscopic forms in drops of water and other samples. The strength of his microscopy lay in lens craftsmanship rather than complex instrument architecture. Therefore, a single finely polished lens in a simple microscope best explains his high magnification.
26. A sample most consistent with Leeuwenhoek’s reports of “animalcules” would be:
ⓐ. Dry cork scrapings mounted without any liquid
ⓑ. Pond water containing visible moving microscopic organisms
ⓒ. A thick stem piece viewed without slicing
ⓓ. A mineral crystal slide with no biological material
Correct Answer: Pond water containing visible moving microscopic organisms
Explanation: Leeuwenhoek repeatedly examined natural water samples and described numerous tiny moving forms within them. Pond water commonly contains protozoa and other microorganisms that can be seen as active “animalcules” under sufficient magnification. Such a sample provides living content, motion, and variety—key features of his classic observations. Dry cork or thick unsliced tissues are far less suitable for observing active microscopic life, and mineral crystals are non-living. The hallmark of his work was viewing living organisms in fluid samples. Hence, pond water with moving microscopic organisms best matches his “animalcules.”
27. Leeuwenhoek made an important observation that contributed to understanding reproduction by describing:
ⓐ. Chloroplast division in leaf cells
ⓑ. Sperm cells as microscopic motile units in semen
ⓒ. DNA molecules directly as helical threads
ⓓ. Ribosomes attached to rough endoplasmic reticulum
Correct Answer: Sperm cells as microscopic motile units in semen
Explanation: Leeuwenhoek observed tiny motile cells in semen and described them as living moving units, now recognized as sperm cells. This finding was significant because it supported the idea that reproduction involves specialized microscopic cells rather than purely visible fluids. It also emphasized that essential biological processes can depend on structures not detectable without magnification. His observation highlighted cell-level participation in reproduction, aligning with later advances in cell biology and gamete concepts. While his interpretations were limited by the science of the time, the direct observation of motile sperm was a key milestone. Therefore, his description of sperm cells as microscopic motile units is the correct contribution.
28. Leeuwenhoek’s work most directly expanded biology by:
ⓐ. Proving that viruses are visible with light microscopes
ⓑ. Establishing that all cells have cell walls
ⓒ. Demonstrating a vast diversity of microscopic living organisms
ⓓ. Showing that chromosomes are the carriers of genes
Correct Answer: Demonstrating a vast diversity of microscopic living organisms
Explanation: By observing many forms of “animalcules” in different samples, Leeuwenhoek revealed that living organisms exist far below the scale of unaided vision. This discovery transformed biological thinking by adding microorganisms as a major component of life on Earth. It also set the stage for later developments in microbiology, disease understanding, and cell-based explanations of life processes. His observations demonstrated not just existence but abundance and variation of microscopic life. This was a conceptual leap beyond earlier structural observations of dead tissues. Hence, his most direct impact was demonstrating the diversity of microscopic living organisms.
29. Which statement best links Leeuwenhoek’s observations to the development of cell theory?
ⓐ. They showed that living units can be directly observed and studied microscopically
ⓑ. They established that cell walls are made of cellulose in all organisms
ⓒ. They proved that cells are formed only inside nuclei
ⓓ. They demonstrated that mitochondria are present in all living cells
Correct Answer: They showed that living units can be directly observed and studied microscopically
Explanation: Cell theory required reliable evidence that living organisms are composed of fundamental units that can be examined scientifically. Leeuwenhoek’s observations provided direct viewing of living microscopic entities, showing that life exists at the cellular scale and can be investigated with microscopes. This strengthened the idea that understanding life demands studying these small units rather than only whole organisms. His work complemented later studies of tissues and cells in plants and animals by confirming that living, active microscopic forms are real and abundant. It helped normalize microscopy as a core biological method. Therefore, his observations supported cell theory by demonstrating that living units can be directly observed and studied.
30. One major reason Leeuwenhoek could see living microorganisms better than many contemporaries was:
ⓐ. He used chemical stains that selectively colored nuclei and membranes
ⓑ. He built high-quality small lenses that provided sharper images at high magnification
ⓒ. He used ultraviolet light sources to improve resolution beyond visible limits
ⓓ. He used vacuum chambers to prevent light scattering in specimens
Correct Answer: He built high-quality small lenses that provided sharper images at high magnification
Explanation: Leeuwenhoek’s advantage came from exceptional lens making, producing small, well-shaped lenses that yielded high magnification and comparatively clear images. Better lens quality reduces optical distortions and improves detail, which is essential when observing tiny living organisms in fluid. Many early compound microscopes of the period often had poorer optics, limiting clarity even when magnification increased. His careful craftsmanship, along with suitable illumination and specimen handling, enabled observation of moving microorganisms. This practical improvement made living microscopic life visible and convincing to science. Hence, sharper images from high-quality small lenses were a key reason for his success.
31. In the development of cell theory, who concluded that all plants are made of cells?
ⓐ. Robert Hooke
ⓑ. Antonie van Leeuwenhoek
ⓒ. Matthias Schleiden
ⓓ. Rudolf Virchow
Correct Answer: Matthias Schleiden
Explanation: Matthias Schleiden, after studying plant tissues under the microscope, proposed that the plant body is composed of cells and that the cell is the basic structural unit in plants. His conclusions came from observing repeated cellular organization across different plant parts rather than a single specimen. This idea helped shift biology toward a cell-based explanation of plant structure and growth. Although later refinements corrected some of his interpretations, his plant-focused generalization became a cornerstone in forming the broader cell theory. His work directly paired with later animal studies to build a unified view of living organization.
32. Who generalized the cellular basis of life to animals, complementing Schleiden’s plant conclusions?
ⓐ. Theodor Schwann
ⓑ. Louis Pasteur
ⓒ. Gregor Mendel
ⓓ. Robert Brown
Correct Answer: Theodor Schwann
Explanation: Theodor Schwann examined a wide range of animal tissues and recognized that animals, like plants, are composed of cells and cell products. By comparing animal tissues with plant tissues, he strengthened the idea that the cell is a universal structural unit across living organisms. This unification was essential because it extended the “cell as a unit” concept beyond plants into the animal kingdom. Schwann’s generalization supported the emerging view that common organizational principles underlie diverse life forms. Together with Schleiden’s plant work, it formed the early framework of cell theory.
33. The correct chronological sequence of proposals related to early cell theory is:
ⓐ. Schwann (1838) → Schleiden (1839)
ⓑ. Virchow (1838) → Schwann (1839)
ⓒ. Hooke (1838) → Schleiden (1839)
ⓓ. Schleiden (1838) → Schwann (1839)
Correct Answer: Schleiden (1838) → Schwann (1839)
Explanation: Schleiden presented his conclusions about plants being composed of cells in 1838, and Schwann extended the cellular principle to animals in 1839. This timeline matters because it shows how the idea matured from a plant-based generalization to a broader biological principle. The sequence reflects a logical expansion: first recognizing cellular organization consistently in plant tissues, then confirming similar cellular organization in animal tissues. These steps collectively strengthened the argument that cells are fundamental units in living organisms. Later scientists refined the theory further, but the 1838–1839 progression is the key early milestone.
34. Which statement best captures the shared core conclusion from Schleiden and Schwann’s work?
ⓐ. Cells are the basic structural unit of living organisms
ⓑ. Proteins are the genetic material in all organisms
ⓒ. Cells arise spontaneously from non-living materials
ⓓ. All enzymes are found only inside the nucleus
Correct Answer: Cells are the basic structural unit of living organisms
Explanation: The main shared outcome of Schleiden’s and Schwann’s studies was the recognition that cells form the basic structural framework of living bodies. Their observations across plant and animal tissues supported a unified idea: organisms are built from repeated cellular units, and tissues can be understood as cellular assemblies or products. This shifted biology toward explaining structure and function at the cellular level rather than only at the whole-organism level. While later improvements clarified how new cells form, the structural-unit concept remained central and enduring. This foundational conclusion directly enabled modern cell-based understanding of growth, repair, and organization.
35. A known limitation in the early views of Schleiden and Schwann was the idea that:
ⓐ. Cells are made only of proteins and lipids
ⓑ. New cells can form by “free cell formation” in a fluid
ⓒ. The nucleus is absent in all plant cells
ⓓ. Only animal tissues contain true cells
Correct Answer: New cells can form by “free cell formation” in a fluid
Explanation: In early cell theory development, Schleiden and Schwann associated new cell appearance with a concept often described as free cell formation, where cells were thought to arise within a formative fluid rather than strictly by division of existing cells. This idea reflected limitations of microscopy and incomplete understanding of cell division mechanisms at the time. Later advances in observing mitosis and cellular reproduction showed that cells originate from pre-existing cells, correcting this earlier view. Recognizing this limitation is important because it highlights how scientific theories evolve with improved evidence. The correction strengthened cell theory by making it consistent with heredity and continuity of cellular organization.
36. Schwann’s comparative studies helped clarify a key difference between typical plant and animal cells by emphasizing that animal cells:
ⓐ. Always have chloroplasts for photosynthesis
ⓑ. Possess a rigid cellulose cell wall in all tissues
ⓒ. Lack a true nucleus in most cases
ⓓ. Commonly lack a cell wall but have a plasma membrane
Correct Answer: Commonly lack a cell wall but have a plasma membrane
Explanation: Schwann’s animal tissue studies reinforced that animal cells do not generally possess a rigid cell wall, unlike most plant cells, yet they are still bounded by a functional plasma membrane. This helped correct the misconception that a “cell wall-like” boundary is required for something to be a cell. By establishing that cellular boundaries and organization exist in both kingdoms, even with structural differences, Schwann strengthened the universality of the cell concept. This comparison supported the broader claim that cells are fundamental units across plants and animals. It also helped focus attention on the plasma membrane as a common boundary of living cells.
37. Which pair is correctly associated with proposing the early cell theory based on plant and animal studies?
ⓐ. Hooke and Brown
ⓑ. Darwin and Wallace
ⓒ. Schleiden and Schwann
ⓓ. Pasteur and Mendel
Correct Answer: Schleiden and Schwann
Explanation: Schleiden and Schwann are directly linked with proposing the early form of cell theory by combining evidence from plant tissues (Schleiden) and animal tissues (Schwann). Their combined conclusions established that organisms share a common cellular organization, making the cell a central biological unit for explaining structure. This collaboration of ideas was pivotal because it unified two major branches of biology under one principle. While other scientists contributed related discoveries, the plant–animal synthesis is the defining hallmark of their role. Their work set the stage for later refinements about how new cells arise.
38. Which statement is attributed to later refinement (not originally emphasized by Schleiden and Schwann) that strengthened cell theory?
ⓐ. Cells contain hereditary information in chromosomes
ⓑ. Cells arise from pre-existing cells by cell division
ⓒ. Cells are surrounded by a non-living wall in all organisms
ⓓ. Cells can develop only inside specialized organs
Correct Answer: Cells arise from pre-existing cells by cell division
Explanation: The statement that new cells arise from pre-existing cells through cell division is a critical refinement that addressed weaknesses in earlier ideas about cell origin. It made cell theory consistent with observed reproduction, growth, and tissue repair, where division produces daughter cells with continuity of organization and genetic material. This principle also helped eliminate explanations suggesting routine spontaneous formation of cells within organisms. With improved microscopy and better understanding of cell division, scientists could directly observe the process supporting this refinement. The addition strengthened cell theory by emphasizing biological continuity from one cell generation to the next.
39. In the context of cell theory development, Schleiden’s main evidence was primarily derived from:
ⓐ. Comparative study of animal tissues like cartilage and nerve
ⓑ. Observation of microbes in pond water and dental scrapings
ⓒ. Microscopic examination of diverse plant tissues and organs
ⓓ. Chemical isolation of DNA from cell nuclei in the lab
Correct Answer: Microscopic examination of diverse plant tissues and organs
Explanation: Schleiden’s conclusions were driven by repeated microscopic observations across many kinds of plant tissues, showing consistent cellular organization. By examining different plant parts and recognizing that the plant body is composed of similar basic units, he proposed that the cell is fundamental to plant structure. This approach relied on anatomical microscopy rather than microbiological sampling or molecular extraction methods. His plant-focused generalization was essential because it provided a broad structural principle rather than an isolated observation. When Schwann later extended a similar principle to animals, the combined evidence supported a unified cell theory framework for living organisms.
40. Which sequence best describes how the early cell theory was built from observations across kingdoms?
ⓐ. Virchow (plants) → Schwann (animals)
ⓑ. Hooke (animals) → Schleiden (plants)
ⓒ. Brown (animals) → Leeuwenhoek (plants)
ⓓ. Schleiden (plants) → Schwann (animals)
Correct Answer: Schleiden (plants) → Schwann (animals)
Explanation: Early cell theory emerged by first establishing broad cellular organization in plants through Schleiden’s plant tissue studies, followed by Schwann’s extension of the cellular principle to animals. This order reflects how evidence accumulated from plant anatomy to animal histology to form a general biological principle. The logic was persuasive because it showed that two major groups of organisms share a common structural plan based on cells. Once both kingdoms were covered, the cell could be treated as a universal unit of structure in living bodies. This progression was foundational before later refinements clarified the precise mechanism of new cell formation.
41. Virchow’s addition to cell theory is best summarized as:
ⓐ. Cells develop only inside the nucleus during body growth
ⓑ. Cells appear from a formative fluid present in tissues
ⓒ. Cells arise from pre-existing cells
ⓓ. Cells are empty wall-bounded chambers seen in cork tissue
Correct Answer: Cells arise from pre-existing cells
Explanation: Virchow emphasized that a new cell is produced only when an existing cell divides, making cell lineage continuous through time. This corrected earlier views that suggested routine “free” formation of cells inside a fluid. The idea explains why growth, repair, and reproduction always involve cell division and why living organization is maintained rather than appearing suddenly. It also aligns with heredity because cellular contents, including genetic material, pass from a parent cell to daughter cells. By making cell origin dependent on prior cells, the theory became biologically consistent and testable. This statement is therefore Virchow’s key contribution to strengthening cell theory.
42. Virchow’s statement most directly challenged the earlier idea of:
ⓐ. Free cell formation in a fluid
ⓑ. Tissue growth needing oxygen supply
ⓒ. Cells having a boundary surface
ⓓ. Plants being made of cells
Correct Answer: Free cell formation in a fluid
Explanation: Earlier interpretations proposed that cells could originate “freely” within a formative fluid inside tissues, without a parent cell. Virchow’s addition rejected that concept by insisting that cell division is the only reliable route for producing new cells. This was important because it removed a major inconsistency in early cell theory regarding cell origin. Once cell division became central, growth and repair could be explained as an increase in cell number rather than sudden appearance of new units. It also provided continuity between generations of cells, supporting stable biological organization. Thus, Virchow directly opposed the idea of free cell formation.
43. The scientist associated with the statement “Omnis cellula e cellula” is:
ⓐ. Matthias Jakob Schleiden
ⓑ. Theodor Schwann
ⓒ. Antonie van Leeuwenhoek
ⓓ. Rudolf Virchow
Correct Answer: Rudolf Virchow
Explanation: Rudolf Virchow is credited with stating “Omnis cellula e cellula,” which conveys that every cell comes from a pre-existing cell. This statement served as a decisive refinement to early cell theory by explaining how new cells originate in organisms. It shifted attention toward cell division as the basis for growth and regeneration, replacing earlier unclear ideas about spontaneous cell origin within tissues. The principle also fits with the observation that living systems maintain continuity across time. Because it clarified cell origin, it became a foundational line in modern cell theory. Hence, Virchow is the correct association.
44. A wound heals mainly because new skin cells are produced by:
ⓐ. Spontaneous appearance of cells in tissue fluid
ⓑ. Division of existing cells
ⓒ. Transformation of proteins directly into new cells
ⓓ. Entry of external cells through the skin surface
Correct Answer: Division of existing cells
Explanation: Healing requires an increase in cell number to replace damaged cells, and this occurs by division of cells already present near the wound. This directly reflects Virchow’s principle that new cells arise from pre-existing cells, not by sudden formation from non-living material. During repair, surviving cells proliferate, producing daughter cells that migrate and differentiate to rebuild tissue architecture. The process is orderly because division preserves cellular organization and passes essential internal components into new cells. This explains why tissue repair follows biological rules rather than random “cell appearance.” Therefore, cell division of existing cells is the correct mechanism.
45. Virchow’s addition most strongly supports which biological phenomenon?
ⓐ. Growth by increase in cell number
ⓑ. Photosynthesis in chloroplasts
ⓒ. Protein folding in cytosol
ⓓ. Osmosis across membranes
Correct Answer: Growth by increase in cell number
Explanation: Virchow’s statement makes growth a cellular process that occurs through production of new cells from existing ones. In multicellular organisms, overall growth largely results from repeated cell division, increasing the number of cells while maintaining continuity of structure. This view explains development from a single fertilized cell into many cells through successive divisions. It also supports tissue maintenance, where old or damaged cells are replaced by newly divided cells. The principle removes ambiguity about where new cells come from during growth. Thus, growth by increasing cell number is the phenomenon most directly supported.
46. The reproduction of Amoeba by binary fission is best explained by Virchow’s idea because:
ⓐ. A nucleus forms first and then creates a new cell around it
ⓑ. New cells appear from cytoplasmic fluid without any parent cell
ⓒ. Cell walls split to generate two completely new cells from non-living parts
ⓓ. Binary fission forms new cells
Correct Answer: Binary fission forms new cells
Explanation: Binary fission is a direct example of producing new living units by division of an existing cell, matching Virchow’s principle. In Amoeba, one parent cell duplicates essential components and then divides to give two daughter cells, each capable of independent life. This shows that cell origin is linked to a prior cell rather than sudden formation in a fluid. The process demonstrates continuity because the daughter cells inherit cellular organization and genetic material from the parent. It also illustrates how unicellular reproduction is fundamentally a cell-division event. Therefore, binary fission forming new cells best reflects Virchow’s idea.
47. Virchow’s key statement reinforcing cell theory is commonly dated to:
ⓐ. 1665 (Hooke’s cork observations)
ⓑ. 1839 (animal tissue generalization)
ⓒ. 1855
ⓓ. 1883 (chromosome behavior described)
Correct Answer: 1855
Explanation: Virchow’s refinement that every cell arises from a pre-existing cell is commonly associated with the year 1855. This date is important in the historical sequence because it comes after the plant and animal generalizations of Schleiden and Schwann and resolves the debated question of cell origin. By emphasizing cell division as the source of new cells, the theory became stronger and more consistent with observed growth and repair. The statement also aligned with emerging evidence from microscopic observation of dividing cells. It marks a major consolidation point in the development of cell theory. Hence, 1855 is the commonly cited date for Virchow’s addition.
48. Which observation would most directly validate Virchow’s claim in a laboratory?
ⓐ. Seeing cork compartments that look like empty boxes
ⓑ. Watching a single cell divide into two daughter cells under a microscope
ⓒ. Measuring the salt concentration outside a cell in different solutions
ⓓ. Noting that cells vary in shape across different tissues
Correct Answer: Watching a single cell divide into two daughter cells under a microscope
Explanation: Virchow’s claim is about the origin of new cells, so the most direct validation is to observe a parent cell undergoing division to form daughter cells. Microscopic visualization of division provides immediate evidence that new cells come from existing cells rather than appearing independently. Such observation can be repeated across many cell types, reinforcing the universality of the principle. It also links cell origin to continuity of internal organization and genetic material transfer during division. This kind of evidence is stronger than structural observations or measurements unrelated to cell birth. Therefore, directly watching cell division is the best validating observation.
49. Virchow’s addition aligns most closely with which broader biological principle?
ⓐ. Biogenesis as life from life
ⓑ. Spontaneous generation as life from non-life
ⓒ. Chemosynthesis as energy from inorganic reactions
ⓓ. Homeostasis as constant internal conditions
Correct Answer: Biogenesis as life from life
Explanation: By stating that cells arise only from pre-existing cells, Virchow reinforced the broader idea that living units originate from living sources. This supports biogenesis because it rejects routine formation of living cells from non-living materials within organisms. The concept also strengthens continuity in living systems, where each new cell has a cellular ancestor. It makes biological growth and reproduction explainable through observable processes like cell division rather than unexplained appearance. This alignment with life-from-life thinking helped make cell theory more coherent and scientifically grounded. Therefore, Virchow’s addition fits most closely with biogenesis.
50. A concise modern summary combining Schleiden–Schwann with Virchow is:
ⓐ. Cells are only structural units, but can arise freely in tissues
ⓑ. Cells occur only in plants, while animals are made of cell products
ⓒ. Cells are basic units, but new cells form mainly from non-living fluids
ⓓ. Organisms are cellular; cells arise from cells
Correct Answer: Organisms are cellular; cells arise from cells
Explanation: Schleiden and Schwann established that living organisms are composed of cells, making the cell the core unit of structure and organization across plants and animals. Virchow added the crucial origin rule that new cells come only from existing cells, providing continuity and a mechanism for growth and repair. Together, these ideas explain how organisms are built from cellular units and how those units increase in number through division. This combined summary also fits observations from development, tissue maintenance, and reproduction. It removes earlier confusion about cell origin by focusing on a repeatable biological process. Hence, the integrated statement “organisms are cellular; cells arise from cells” captures the modern combined view.
51. In a typical prokaryotic cell, the nucleoid is best described as:
ⓐ. A membrane-bound region with pores and a nucleolus
ⓑ. A DNA-filled organelle with double membranes and enzymes
ⓒ. A DNA region in cytoplasm without envelope
ⓓ. A vacuole-like space storing RNA and proteins in sacs
Correct Answer: A DNA region in cytoplasm without envelope
Explanation: The nucleoid is the region where the prokaryotic chromosome is located, but it is not separated from the cytoplasm by a nuclear membrane. Because there is no nuclear envelope, the genetic material lies in an irregularly shaped area and is directly surrounded by cytosol. This arrangement is a key structural marker that distinguishes prokaryotes from eukaryotes. It also helps explain why many gene-expression steps occur without the barrier of a nucleus. The term “nucleoid” indicates a nucleus-like area, not a true nucleus. Hence, it is correctly defined as cytoplasmic DNA without an envelope.
52. A defining structural feature of a true eukaryotic nucleus is:
ⓐ. DNA enclosed by a nuclear envelope
ⓑ. DNA attached to a plasma membrane fold in loops
ⓒ. DNA packed in a nucleoid without any boundary
ⓓ. DNA stored inside chloroplasts for protection and control
Correct Answer: DNA enclosed by a nuclear envelope
Explanation: A true nucleus is characterized by the presence of a nuclear envelope that separates the genetic material from the cytoplasm. This membrane barrier allows regulated exchange through nuclear pores and enables distinct nuclear processes such as RNA processing before export. The separation creates a clear division between transcription in the nucleus and translation in the cytoplasm. It also supports higher-order regulation of gene expression by controlling molecular traffic. This organization is a hallmark of eukaryotic cells and is absent in prokaryotes. Therefore, DNA enclosed by a nuclear envelope defines a true nucleus.
53. Which group of organelles is typically absent in prokaryotic cells?
ⓐ. Ribosomes and cytosol with dissolved enzymes
ⓑ. Cell wall and plasma membrane with transport proteins
ⓒ. Flagella and pili with surface attachment proteins
ⓓ. ER, Golgi and mitochondria as compartments
Correct Answer: ER, Golgi and mitochondria as compartments
Explanation: Prokaryotic cells do not possess membrane-bound organelles that create internal compartments like endoplasmic reticulum, Golgi apparatus, and mitochondria. Instead, most metabolic pathways occur in the cytosol or are associated with the plasma membrane. The absence of these compartments is a major reason prokaryotes have simpler internal organization compared with eukaryotes. It also means functions such as protein modification and energy generation are not separated into distinct organelle spaces. This feature is a core criterion used to distinguish prokaryotic from eukaryotic cellular architecture. Hence, ER, Golgi, and mitochondria are typically absent in prokaryotes.
54. A direct consequence of lacking a nuclear envelope in prokaryotes is that:
ⓐ. DNA cannot be copied before cell division occurs
ⓑ. Transcription and translation can occur together
ⓒ. Ribosomes are absent and proteins form only in nuclei
ⓓ. Cell walls become the main site of genetic information storage
Correct Answer: Transcription and translation can occur together
Explanation: In prokaryotes, DNA is not separated from ribosomes by a nuclear membrane, so mRNA can be translated while it is still being transcribed. This coupling is possible because the cytoplasm is the shared space for both processes. It enables rapid protein synthesis and quick cellular responses to environmental changes. The mechanism fits the prokaryotic organization where genetic material is accessible directly in the cytosol. It also contrasts with eukaryotes, where transcription occurs in the nucleus and translation occurs in the cytoplasm. Therefore, the absence of a nuclear envelope allows transcription and translation to occur together.
55. The typical genetic organization of most bacteria is best described as:
ⓐ. One circular DNA chromosome in nucleoid
ⓑ. Many linear DNA chromosomes inside a nucleus
ⓒ. Many circular chromosomes inside mitochondria only
ⓓ. Two linear DNA sets stored in nucleolus region
Correct Answer: One circular DNA chromosome in nucleoid
Explanation: Most bacteria possess a single, long, circular double-stranded DNA molecule that forms the main chromosome. This chromosome is located in the nucleoid region rather than inside a membrane-bound nucleus. The circular nature helps avoid end problems seen in linear DNA and suits compact packing in a small cell volume. This organization is a classic structural and genetic feature used to describe bacterial cells. While bacteria may also carry extra DNA elements, the main genome is typically one circular chromosome. Hence, one circular DNA chromosome in the nucleoid is the correct description.
56. In prokaryotes, plasmids are best defined as:
ⓐ. Membrane-bound sacs storing enzymes for digestion
ⓑ. Protein filaments that maintain cell shape and rigidity
ⓒ. Small circular DNA pieces independent of chromosome
ⓓ. Lipid droplets storing energy for starvation conditions
Correct Answer: Small circular DNA pieces independent of chromosome
Explanation: Plasmids are extra-chromosomal DNA molecules, usually small and circular, that replicate independently of the main bacterial chromosome. They often carry genes that can provide advantages under specific conditions, such as resistance traits or specialized metabolic functions. Because they are separate from the primary genome, they can be gained or lost without necessarily killing the cell. Their independent replication helps maintain copy number within the cell. This property also makes plasmids important in gene transfer and genetic studies. Therefore, plasmids are correctly defined as small circular DNA pieces independent of the chromosome.
57. The ribosomes typically found in prokaryotic cells are:
ⓐ. 80S ribosomes attached to rough ER membranes
ⓑ. 70S ribosomes in cytosol and near membrane
ⓒ. 60S ribosomes with 40S units in nucleoplasm
ⓓ. 90S ribosomes present only during mitotic division
Correct Answer: 70S ribosomes in cytosol and near membrane
Explanation: Prokaryotic ribosomes are characteristically 70S, composed of 50S and 30S subunits, and they function as the sites of protein synthesis. Because prokaryotes lack rough endoplasmic reticulum, these ribosomes are found free in the cytosol and can also associate with the plasma membrane during synthesis of certain proteins. This ribosomal type is a classic marker distinguishing prokaryotic translation machinery from eukaryotic cytosolic 80S ribosomes. The 70S form supports efficient protein production in the simpler prokaryotic cellular organization. It is also consistent with the absence of a nuclear envelope, enabling rapid gene expression. Hence, 70S ribosomes in the cytosol and near the membrane is correct.
58. A key reason prokaryotes do not have a nucleolus is that they:
ⓐ. Lack a true nucleus with nuclear envelope
ⓑ. Lack DNA entirely and use RNA as genetic material
ⓒ. Lack ribosomes so rRNA is not needed
ⓓ. Lack cytoplasm so internal organization cannot occur
Correct Answer: Lack a true nucleus with nuclear envelope
Explanation: The nucleolus is a specialized region within the nucleus where rRNA synthesis and ribosome assembly steps are organized. Prokaryotes do not have a membrane-bound nucleus, so they cannot form a nucleolus as a nuclear substructure. Instead, rRNA is transcribed in the cytoplasm, and ribosomal subunits assemble without a nucleolar compartment. This reflects the broader absence of nuclear compartmentalization in prokaryotic cells. The lack of a nucleolus does not mean prokaryotes lack ribosomes; they simply organize these processes differently. Therefore, the correct reason is the absence of a true nucleus with a nuclear envelope.
59. The presence of membrane-bound organelles in eukaryotic cells mainly enables:
ⓐ. Direct coupling of transcription and translation in one space
ⓑ. Storage of DNA in a nucleoid with no boundary
ⓒ. Elimination of internal transport between cell regions
ⓓ. Compartmentalized metabolism with specialized functions
Correct Answer: Compartmentalized metabolism with specialized functions
Explanation: Membrane-bound organelles separate cellular processes into distinct compartments, allowing specialized conditions and reactions to occur efficiently. For example, energy conversion, protein modification, and breakdown reactions can proceed in different organelles without interfering with each other. This compartmentalization improves regulation by controlling what enters and exits each organelle, and it supports complex cellular functions. It also helps coordinate multiple pathways simultaneously by spatially organizing enzymes and substrates. Such internal division of labor is a defining feature of eukaryotic cells compared with prokaryotes. Hence, membrane organelles mainly enable compartmentalized metabolism with specialized functions.
60. Compared with eukaryotic nuclear DNA, prokaryotic chromosomal DNA is typically:
ⓐ. Surrounded by a double membrane with nuclear pores
ⓑ. Organized into chromatin with abundant true histones
ⓒ. Not enclosed by a nuclear envelope in cytoplasm
ⓓ. Split into many linear chromosomes within a nucleus
Correct Answer: Not enclosed by a nuclear envelope in cytoplasm
Explanation: Prokaryotic chromosomal DNA remains in the nucleoid region and is not separated from the cytoplasm by a nuclear envelope. This structural feature is central to the prokaryote–eukaryote distinction and affects gene expression organization within the cell. Without a nuclear membrane, DNA-related processes occur in the same general compartment where ribosomes operate, supporting rapid cellular responses. In contrast, eukaryotic DNA is enclosed within a nucleus and is separated from cytosolic translation machinery. This difference also underlies many downstream differences in regulation and RNA processing. Therefore, prokaryotic chromosomal DNA is correctly described as not enclosed by a nuclear envelope in the cytoplasm.
61. Which feature most reliably indicates a true nucleus in a cell?
ⓐ. Single membrane around DNA region
ⓑ. DNA region in cytoplasm without envelope
ⓒ. Double membrane with nuclear pores
ⓓ. Protein coat around DNA for stability
Correct Answer: Double membrane with nuclear pores
Explanation: A true nucleus is defined by a nuclear envelope that encloses the genetic material and separates it from the cytoplasm. This envelope is typically a double membrane and contains nuclear pores that regulate movement of RNAs, proteins, and other molecules. The pores enable controlled exchange rather than free mixing, supporting complex gene regulation. This compartment also allows RNA processing steps to occur before export to the cytoplasm. Such organization is a hallmark of eukaryotic cells and is absent in prokaryotes. Therefore, a double membrane with nuclear pores is the most reliable indicator of a true nucleus.
62. Membrane-bound organelles in eukaryotes primarily allow:
ⓐ. Compartmentalized reactions in organelles
ⓑ. All reactions to occur only on cell wall
ⓒ. No internal membranes inside cytoplasm
ⓓ. Protein synthesis only inside the nucleus
Correct Answer: Compartmentalized reactions in organelles
Explanation: Membrane-bound organelles create distinct internal compartments that specialize in specific biochemical tasks. This separation allows incompatible reactions to proceed simultaneously and efficiently under optimized conditions, such as different pH or enzyme sets. It also improves regulation because membranes control what enters and leaves each compartment. As a result, eukaryotic cells can support complex processes like secretion, energy conversion, and intracellular digestion with better coordination. Compartmentalization also reduces unwanted cross-reactions and increases metabolic efficiency. Hence, the major advantage is compartmentalized reactions within organelles.
63. In eukaryotic cells, the organelle most directly responsible for aerobic ATP production is:
ⓐ. Golgi apparatus for packaging enzymes
ⓑ. Smooth ER for lipid synthesis and transport
ⓒ. Lysosome for intracellular digestion
ⓓ. Mitochondria make ATP aerobically
Correct Answer: Mitochondria make ATP aerobically
Explanation: Mitochondria are the primary sites of aerobic respiration in eukaryotic cells, where energy from food molecules is converted into ATP. Their inner membrane houses the electron transport chain and ATP synthase, enabling efficient oxidative phosphorylation. This membrane-based energy system is a key eukaryotic feature because it localizes high-yield ATP production within a dedicated compartment. By isolating these reactions, the cell can regulate energy output according to demand. This specialization supports high-energy activities in multicellular organisms. Therefore, mitochondria are directly responsible for aerobic ATP production.
64. A key functional advantage of a nucleus in eukaryotes is:
ⓐ. Immediate translation on DNA templates
ⓑ. RNA processing before export
ⓒ. DNA mixing freely with cytosolic enzymes
ⓓ. Protein storage inside nuclear sap
Correct Answer: RNA processing before export
Explanation: The nucleus separates transcription from translation, allowing eukaryotic cells to process RNA before it enters the cytoplasm. Newly formed RNA can undergo modifications such as capping, splicing, and polyadenylation, improving stability and translation readiness. This separation also provides additional checkpoints for regulating gene expression, ensuring only properly processed transcripts are exported. Nuclear pores then control the selective movement of mature RNAs and proteins between nucleus and cytoplasm. This layered control supports complex development and cell specialization. Hence, RNA processing before export is a major functional advantage of having a nucleus.
65. The secretory pathway for many proteins in eukaryotes mainly involves:
ⓐ. Ribosome to nucleolus direct transfer
ⓑ. Mitochondria to lysosome direct fusion
ⓒ. ER to Golgi vesicle traffic
ⓓ. Nucleus to cell wall diffusion only
Correct Answer: ER to Golgi vesicle traffic
Explanation: Many secreted and membrane proteins are synthesized on ribosomes associated with rough endoplasmic reticulum and enter the ER for initial folding and modification. They are then transported in vesicles to the Golgi apparatus, where further processing and sorting occur. From the Golgi, vesicles deliver proteins to the plasma membrane, lysosomes, or outside the cell. This organelle-based routing depends on membrane-bound compartments, a defining eukaryotic feature absent in prokaryotes. The pathway ensures accurate targeting and efficient secretion. Therefore, ER to Golgi vesicle traffic is central to the secretory route.
66. Which membrane-bound organelle is most directly involved in intracellular digestion in many eukaryotic cells?
ⓐ. Centriole organizing microtubules in division
ⓑ. Ribosome translating mRNA in cytoplasm
ⓒ. Nucleolus assembling rRNA components
ⓓ. Lysosomes digest macromolecules
Correct Answer: Lysosomes digest macromolecules
Explanation: Lysosomes contain hydrolytic enzymes that break down macromolecules, damaged organelles, and engulfed particles within a membrane-bound compartment. Their internal environment is maintained acidic, which supports enzyme activity while keeping the cytoplasm safe from uncontrolled digestion. This compartmentalization allows the cell to recycle building blocks and maintain cellular cleanliness. Such membrane-bound digestive structures are a key feature of many eukaryotic cells and reflect advanced internal organization. By isolating degradative reactions, lysosomes protect other cellular components. Hence, lysosomes are most directly involved in intracellular digestion.
67. In photosynthetic eukaryotic cells, the organelle that converts light energy into chemical energy is:
ⓐ. Chloroplasts in photosynthetic eukaryotes
ⓑ. Mitochondria in all cells for glycolysis only
ⓒ. Golgi bodies for vesicle formation and export
ⓓ. Lysosomes for oxidation and detox reactions
Correct Answer: Chloroplasts in photosynthetic eukaryotes
Explanation: Chloroplasts are membrane-bound organelles where photosynthesis occurs in algae and plant cells. They contain pigments that capture light energy and internal membranes that organize the reactions converting this energy into chemical forms used to build sugars. This organelle-based system allows photosynthesis to be efficiently compartmentalized and regulated. Chloroplasts also illustrate how eukaryotic cells can host specialized energy-transforming compartments beyond the nucleus. Their presence distinguishes photosynthetic eukaryotes from non-photosynthetic cells. Therefore, chloroplasts are the organelles responsible for converting light energy into chemical energy.
68. Which organelle is most associated with hydrogen peroxide breakdown in eukaryotic cells?
ⓐ. Golgi stacks sorting secretory proteins
ⓑ. Nucleus controlling transcriptional activity
ⓒ. Peroxisomes detoxify H2O2
ⓓ. Ribosomes assembling polypeptide chains
Correct Answer: Peroxisomes detoxify H2O2
Explanation: Peroxisomes are membrane-bound organelles that contain enzymes involved in oxidative reactions, including the breakdown of hydrogen peroxide. Because hydrogen peroxide can be harmful, isolating these reactions inside peroxisomes protects the rest of the cell. Enzymes within peroxisomes convert hydrogen peroxide into less reactive products, helping maintain cellular stability. This detox role is part of the broader theme of eukaryotic compartmentalization, where risky chemistry is confined to specific organelles. Such internal membranes are typically absent in prokaryotes. Hence, peroxisomes are most associated with hydrogen peroxide breakdown.
69. A student says, “Both nucleoid and nucleus are membrane-bound.” The correct correction is:
ⓐ. Nucleoid is not membrane-bound; nucleus is
ⓑ. Both are membrane-bound in all cell types
ⓒ. Nucleus is not membrane-bound; nucleoid is
ⓓ. Both lack DNA and contain only proteins
Correct Answer: Nucleoid is not membrane-bound; nucleus is
Explanation: The nucleoid is a region in prokaryotic cells where the main DNA is located, but it lacks a surrounding nuclear envelope. In contrast, the nucleus in eukaryotic cells is enclosed by a nuclear envelope that separates DNA from the cytoplasm. This distinction is central to how cells are classified as prokaryotic or eukaryotic and influences how gene expression is organized. Membrane separation supports RNA processing and regulated transport through pores in eukaryotes. Prokaryotes do not have this nuclear compartment. Therefore, the correct statement is that nucleoid is not membrane-bound, while the nucleus is.
70. A cell shows rough ER, Golgi stacks, and a membrane-bound nucleus. This cell is:
ⓐ. A typical bacterium with nucleoid region
ⓑ. A prokaryote with internal compartments
ⓒ. A cyanobacterium with true nucleus
ⓓ. A eukaryote with organelles
Correct Answer: A eukaryote with organelles
Explanation: Rough endoplasmic reticulum and Golgi stacks are membrane-bound organelles that form part of the internal compartment system characteristic of eukaryotic cells. The presence of a membrane-bound nucleus further confirms eukaryotic organization because prokaryotes lack a nuclear envelope. Together, these features indicate advanced compartmentalization for protein synthesis, processing, and transport. Such structures enable specialized cellular workflows like secretion and targeted delivery of proteins. Prokaryotic cells may have membranes, but they generally do not have these discrete organelles. Hence, a cell with rough ER, Golgi stacks, and a membrane-bound nucleus is a eukaryote with organelles.
71. Which ribosome type is typically found in bacteria?
ⓐ. 80S ribosome
ⓑ. 70S ribosome
ⓒ. 90S ribosome
ⓓ. 60S ribosome
Correct Answer: 70S ribosome
Explanation: Bacterial ribosomes are characteristically 70S, made of 50S and 30S subunits, and they perform translation in the cytoplasm. This 70S type is a standard marker used to distinguish prokaryotic protein-synthesis machinery from eukaryotic cytosolic ribosomes. Because bacteria lack membrane-bound organelles like rough ER, these ribosomes are not ER-bound but are free or membrane-associated. The 70S ribosome supports rapid protein production needed for fast growth and quick responses. This feature is broadly conserved across most bacteria. Therefore, the typical bacterial ribosome is 70S.
72. Which ribosome type is typical for the cytosol of eukaryotic cells?
ⓐ. 70S cytosolic ribosome
ⓑ. 60S cytosolic ribosome
ⓒ. 50S cytosolic ribosome
ⓓ. 80S cytosolic ribosome
Correct Answer: 80S cytosolic ribosome
Explanation: Eukaryotic cells generally contain 80S ribosomes in the cytosol, formed by 60S and 40S subunits, and these carry out translation for most cellular proteins. This ribosomal type is a key distinction from prokaryotes, which typically use 70S ribosomes. The 80S ribosome works in coordination with mRNA processing that occurs in the nucleus before export to the cytoplasm. Because eukaryotes have compartmentalization, translation is mainly cytosolic (or on rough ER) rather than being directly coupled to transcription. The 80S designation refers to sedimentation behavior and is a standard textbook feature of eukaryotic cytosol. Hence, the typical eukaryotic cytosolic ribosome is 80S.
73. Which statement correctly matches prokaryotic ribosomal subunits with their complete ribosome?
ⓐ. 50S + 30S gives 70S
ⓑ. 60S + 40S gives 70S
ⓒ. 50S + 30S gives 80S
ⓓ. 60S + 40S gives 80S
Correct Answer: 50S + 30S gives 70S
Explanation: In prokaryotes, the functional ribosome is 70S and is assembled from a large 50S subunit and a small 30S subunit. This pairing is a fundamental classification point used in cell biology to separate prokaryotic translation machinery from eukaryotic cytosolic translation machinery. The subunits cooperate during initiation, elongation, and termination to translate mRNA into polypeptides. Their sizes are defined by sedimentation behavior, which reflects mass and shape. Recognizing the 50S and 30S combination is also useful for understanding why certain antibiotics can selectively disrupt bacterial translation. Therefore, 50S + 30S correctly gives a 70S ribosome.
74. In eukaryotic cells, 70S-type ribosomes are typically found in:
ⓐ. Nucleus and nucleolus regions
ⓑ. Golgi stacks and lysosomes only
ⓒ. Mitochondria and chloroplasts
ⓓ. Endoplasmic reticulum and Golgi
Correct Answer: Mitochondria and chloroplasts
Explanation: In eukaryotic cells, the main protein-synthesizing ribosomes in the cytosol are 80S, but certain organelles retain a prokaryote-like translation system. Mitochondria and chloroplasts have their own genetic material and their own ribosomes, which are commonly described as 70S-type due to their evolutionary origin. Chloroplast ribosomes are characteristically 70S, and mitochondrial ribosomes are also prokaryote-like in nature (even though exact sedimentation can vary among organisms). This is why some inhibitors of bacterial translation can affect organelle protein synthesis. Hence, 70S-type ribosomes are typically found in mitochondria and chloroplasts.
75. Many antibiotics show selective action on bacteria mainly because:
ⓐ. They target the 70S ribosome
ⓑ. They target the 80S cytosol ribosome
ⓒ. They cannot bind any ribosome
ⓓ. They act only on nuclear pores
Correct Answer: They target the 70S ribosome
Explanation: A common basis for selective antibacterial action is that bacterial translation uses 70S ribosomes, which differ structurally from the 80S ribosomes in the eukaryotic cytosol. When an antibiotic specifically interferes with a 70S ribosomal site or step, it can strongly inhibit bacterial protein synthesis while having comparatively less effect on host cytosolic translation. This selectivity is rooted in ribosome architecture differences, not in the presence of a nucleus. Because protein synthesis is essential for growth and survival, blocking 70S ribosomes can rapidly limit bacterial proliferation. The concept is widely used to explain why translation is a major antimicrobial target. Therefore, targeting the 70S ribosome is a key reason for bacterial selectivity.
76. In a eukaryotic cell, the nucleolus is most directly linked to:
ⓐ. Nucleolus makes ATP for division
ⓑ. Nucleolus forms nuclear pores
ⓒ. Nucleolus makes rRNA subunits
ⓓ. Nucleolus stores lipids for membrane
Correct Answer: Nucleolus makes rRNA subunits
Explanation: The nucleolus is a specialized nuclear region where rRNA is synthesized and ribosomal subunits are assembled before export to the cytoplasm. This is possible because eukaryotes have a true nucleus that separates transcription-related processes from cytosolic translation. The nucleolus organizes rRNA production and combines rRNA with ribosomal proteins to form subunits efficiently. These subunits then exit through nuclear pores to participate in building functional 80S ribosomes in the cytosol. This role connects nuclear compartmentalization directly to ribosome biogenesis and controlled gene expression. Hence, the nucleolus is most directly linked to making rRNA and assembling ribosomal subunits.
77. In a typical eukaryotic cell, where are 70S-type ribosomes most likely located?
ⓐ. In animal cytosol as free ribosomes
ⓑ. On rough ER for secretory proteins
ⓒ. Inside nucleus for chromatin work
ⓓ. In mitochondria and chloroplasts
Correct Answer: In mitochondria and chloroplasts
Explanation: A typical eukaryotic cell uses 80S ribosomes in the cytosol for most protein synthesis, including proteins made on free ribosomes and on rough ER. However, mitochondria and chloroplasts have their own translation machinery and contain prokaryote-like ribosomes often referred to as 70S-type in standard biology. This reflects their evolutionary origin and the fact that these organelles can synthesize some proteins internally. The nucleus is not a site where such ribosomes operate for translation, and rough ER–bound ribosomes are still 80S. Therefore, the most likely location for 70S-type ribosomes is inside mitochondria and chloroplasts.
78. A cell shows 80S ribosomes and a membrane-bound nucleus. It is most likely:
ⓐ. A prokaryotic bacterium
ⓑ. A eukaryotic cell
ⓒ. A typical virus particle
ⓓ. An infectious prion protein
Correct Answer: A eukaryotic cell
Explanation: The combination of 80S ribosomes (for cytosolic translation) and a membrane-bound nucleus (for compartmentalized genetic control) is characteristic of eukaryotic cells. A true nucleus indicates DNA is enclosed by a nuclear envelope with regulated transport, which prokaryotes lack. The 80S ribosome type further supports eukaryotic cellular machinery for protein synthesis in the cytoplasm. Together, these features reflect internal compartmentalization, coordinated gene expression, and complex cellular organization. This pairing is a core diagnostic for identifying eukaryotic cells in basic cell biology. Hence, the cell is most likely eukaryotic.
79. Why does 50S + 30S form 70S rather than “80S”?
ⓐ. S units add like normal numbers
ⓑ. 30S dissolves to make 70S
ⓒ. S units are not additive
ⓓ. 70S has less mass than 30S
Correct Answer: S units are not additive
Explanation: The “S” values are sedimentation coefficients that depend on mass, shape, and density, so they do not add arithmetically like ordinary numbers. When ribosomal subunits associate, the combined particle sediments based on its overall properties, not the simple sum of two independent values. The interaction changes shape and hydrodynamic behavior, which alters sedimentation. This is why 50S and 30S together form a 70S ribosome, and 60S and 40S together form an 80S ribosome. Understanding this avoids a common misconception in exam questions about ribosome notation. Therefore, the reason is that S units are not additive.
80. Prokaryotes can often couple transcription and translation mainly because:
ⓐ. No nuclear envelope enables coupled gene expression
ⓑ. Nuclear pores block ribosomes during translation
ⓒ. Mitochondria stop transcription in cytosol always
ⓓ. Golgi stacks control DNA replication directly
Correct Answer: No nuclear envelope enables coupled gene expression
Explanation: In prokaryotes, DNA lies in the nucleoid without a nuclear membrane, so newly made mRNA is immediately accessible to ribosomes in the same compartment. This allows translation to begin while transcription is still ongoing, enabling rapid protein production. Such coupling supports fast responses to environmental changes because gene products can be produced quickly. The arrangement reflects the absence of a true nucleus and the lack of compartmental separation between gene transcription and protein synthesis. This property is a key functional difference from eukaryotes, where the nuclear envelope separates these steps. Hence, the absence of a nuclear envelope enables coupled gene expression in prokaryotes.
81. In many bacteria, the glycocalyx is best described as:
ⓐ. A rigid layer made of cellulose fibers
ⓑ. A double membrane around DNA region
ⓒ. A protein sheath inside cell wall
ⓓ. A polysaccharide coat outside wall
Correct Answer: A polysaccharide coat outside wall
Explanation: The glycocalyx is an outer, sticky covering present outside the cell wall in many bacteria, typically made of polysaccharides (and sometimes polypeptides). It may appear as a well-organized capsule or a loose slime layer, but in both forms it lies external to the wall. This coating helps cells adhere to surfaces and to each other, aiding colonization and biofilm formation. It also reduces water loss and offers protection against unfavorable conditions by acting as a barrier. In host-associated bacteria, a capsule can help resist removal by host defenses. Hence, a polysaccharide coat outside the wall correctly describes the glycocalyx.
82. The correct outside-to-inside order of bacterial cell envelope layers is:
ⓐ. Cell wall → membrane → glycocalyx
ⓑ. Membrane → cell wall → glycocalyx
ⓒ. Glycocalyx → wall → membrane
ⓓ. Wall → glycocalyx → membrane
Correct Answer: Glycocalyx → wall → membrane
Explanation: In bacteria with a complete envelope, the glycocalyx forms the outermost covering, lying outside the cell wall. Beneath it is the cell wall, which provides shape and mechanical strength and helps prevent osmotic bursting. The innermost boundary of the envelope is the plasma membrane, a selectively permeable barrier that controls transport and hosts key metabolic functions. Remembering the “coat–wall–membrane” sequence helps avoid mixing up protective external layers with the living membrane boundary. This layered arrangement is a major structural theme in prokaryotic cells. Therefore, the correct order is glycocalyx, then wall, then membrane.
83. A major feature of Gram-positive bacterial cell wall is:
ⓐ. Outer membrane with lipopolysaccharide layer
ⓑ. Thick peptidoglycan with teichoic acids
ⓒ. No peptidoglycan and no rigid wall layer
ⓓ. Thin peptidoglycan with wide periplasm
Correct Answer: Thick peptidoglycan with teichoic acids
Explanation: Gram-positive bacteria characteristically possess a thick peptidoglycan (murein) layer that forms the main structural component of their cell wall. Teichoic acids are commonly associated with this wall and contribute to wall rigidity and overall surface properties. The thick peptidoglycan provides strong mechanical support and helps the cell resist osmotic stress. This structural pattern also explains why Gram-positive cells retain certain stains more strongly during Gram staining. Recognizing the thick peptidoglycan–teichoic acid combination is a standard way to identify Gram-positive wall architecture. Hence, thick peptidoglycan with teichoic acids is the correct feature.
84. The presence of an outer membrane containing lipopolysaccharide is typical of:
ⓐ. Gram-positive bacteria with thick peptidoglycan
ⓑ. Plant cells with cellulose wall and plasmodesmata
ⓒ. Fungal cells with chitin-rich wall layer
ⓓ. Gram-negative bacteria with outer membrane
Correct Answer: Gram-negative bacteria with outer membrane
Explanation: Gram-negative bacteria are defined by a more complex envelope that includes an outer membrane external to a thin peptidoglycan layer. Lipopolysaccharide (LPS) is a key component of this outer membrane and contributes to the barrier nature of Gram-negative cells. The outer membrane reduces permeability to many substances and alters how these bacteria interact with their environment. This organization is also linked to the periplasmic region found between membranes in Gram-negative bacteria. The presence of LPS in an outer membrane is therefore a hallmark of Gram-negative envelope design. Hence, Gram-negative bacteria with an outer membrane is the correct choice.
85. A capsule in bacteria most directly helps the cell by:
ⓐ. Preventing drying and aiding attachment
ⓑ. Making ATP in place of mitochondria
ⓒ. Replicating DNA like a nuclear envelope
ⓓ. Forming microtubules for cell division
Correct Answer: Preventing drying and aiding attachment
Explanation: A bacterial capsule is a well-organized form of glycocalyx that provides a protective outer covering. By holding water and creating a hydrated barrier, it reduces desiccation and supports survival in dry or harsh conditions. The capsule also increases adhesion to surfaces, which helps bacteria colonize tissues or inert surfaces and can support biofilm development. Because it sits outside the wall, it can reduce the impact of environmental stress and improve persistence. In some host settings, it can also make bacterial cells harder to clear by host defenses. Therefore, preventing drying and aiding attachment captures a core capsule benefit.
86. In bacteria, the plasma membrane is especially important because it:
ⓐ. Stores chromosomes inside a membrane-bound nucleus
ⓑ. Contains cellulose strands that form rigid wall plates
ⓒ. Hosts respiration enzymes for ATP formation
ⓓ. Replaces glycocalyx in all bacterial species
Correct Answer: Hosts respiration enzymes for ATP formation
Explanation: Bacteria lack mitochondria, so many steps of aerobic respiration and electron transport are associated with the plasma membrane. Enzyme complexes embedded in the membrane generate a proton gradient that drives ATP synthesis, making the membrane a central energy platform. This also fits with the membrane’s role in selective transport, since ions and molecules must be controlled to maintain gradients. The same membrane can host transporters, receptors, and metabolic enzymes, reflecting efficient use of limited cellular space. This is a major functional difference from eukaryotic cells, where mitochondria handle most aerobic ATP production. Hence, hosting respiration enzymes for ATP formation is a key plasma membrane role in bacteria.
87. Which prokaryote is known for lacking a cell wall and showing only a flexible membrane boundary?
ⓐ. Nostoc in gelatinous colonies
ⓑ. Mycoplasma in small pleomorphic forms
ⓒ. Anabaena with heterocyst formation
ⓓ. Bacillus with thick endospore coat
Correct Answer: Mycoplasma in small pleomorphic forms
Explanation: Mycoplasma is notable for lacking a rigid cell wall, making it naturally pleomorphic and more flexible in shape. Without a wall, the plasma membrane becomes the primary boundary that maintains cellular integrity. This feature also affects how such cells respond to osmotic stress, since the wall normally provides strong protection against bursting. The absence of peptidoglycan is a key diagnostic point for Mycoplasma-like forms in basic microbiology. It also helps explain why wall-targeting mechanisms may be ineffective against them. Therefore, Mycoplasma lacking a cell wall is the correct identification.
88. In Gram-negative bacteria, the periplasm is best described as:
ⓐ. Space inside nucleus between chromatin fibers
ⓑ. Layer outside capsule where pili are anchored
ⓒ. Channel through cell wall for plasmid transfer
ⓓ. Space between outer and inner membranes
Correct Answer: Space between outer and inner membranes
Explanation: Gram-negative bacteria have both an outer membrane and an inner (plasma) membrane, creating a distinct region between them. This region, called the periplasm, contains the thin peptidoglycan layer and various enzymes and binding proteins. Because it is physically separated by membranes, it can support specialized reactions and processing steps without mixing freely with the cytosol or the external environment. The periplasm also contributes to the barrier function and overall envelope complexity of Gram-negative cells. Recognizing this “between two membranes” location is essential for correctly mapping Gram-negative envelope structure. Hence, the periplasm is the space between outer and inner membranes.
89. Which structure is NOT considered a part of the bacterial cell envelope?
ⓐ. Nucleoid containing chromosomal DNA
ⓑ. Cell wall providing mechanical strength
ⓒ. Plasma membrane as selective barrier
ⓓ. Glycocalyx as outer protective coat
Correct Answer: Nucleoid containing chromosomal DNA
Explanation: The bacterial cell envelope refers to the layers that surround the cytoplasm and form the boundary of the cell, typically including glycocalyx (when present), the cell wall, and the plasma membrane. The nucleoid is an internal region where the main DNA is located and is not a boundary layer. It has no surrounding nuclear envelope and lies within the cytoplasm, making it part of the cell’s interior organization rather than its envelope. This distinction is important because “envelope” is about protective and selective covering layers, not genetic location. Confusing nucleoid with an envelope layer is a common misconception in classification questions. Therefore, the nucleoid is not part of the bacterial cell envelope.
90. In many animal cells, the carbohydrate-rich coat on the outer surface of the plasma membrane is called:
ⓐ. Cellulose wall with middle lamella
ⓑ. Peptidoglycan wall with teichoic acids
ⓒ. Glycocalyx on membrane surface
ⓓ. Periplasm between two membranes
Correct Answer: Glycocalyx on membrane surface
Explanation: Animal cells do not have a rigid cell wall, but many have a carbohydrate-rich coating on the external face of the plasma membrane formed by glycoproteins and glycolipids. This coating is termed the glycocalyx and plays roles in cell recognition, adhesion, and protection of the cell surface. It also contributes to how cells interact with the extracellular environment by providing binding sites and a hydrated surface layer. Although bacteria also use the term glycocalyx for an outer coating, in animals it is directly associated with the membrane surface rather than a wall-external layer. This concept connects membrane structure to cell communication and tissue organization. Hence, the correct term is glycocalyx on the membrane surface.
91. A microbiologist calls a bacterial surface layer a “capsule” rather than a slime layer when it is:
ⓐ. Always made only of protein and never sugars
ⓑ. Present only in Gram-positive bacteria
ⓒ. Well organized and firmly attached
ⓓ. Present only during spore formation stage
Correct Answer: Well organized and firmly attached
Explanation: A capsule is defined by its distinct, well-organized nature and its firm attachment to the bacterial cell surface, making it appear as a clear, discrete layer. This organization helps the bacterium maintain a stable protective coat that can reduce dehydration and improve persistence on surfaces. Because it is tightly bound, it contributes effectively to adhesion and can make cells harder to remove from host tissues or inert materials. The capsule can also act as a barrier that limits harmful environmental exposure at the surface. In contrast, a slime layer is typically loose and easily removable. Therefore, “well organized and firmly attached” best supports calling it a capsule.
92. The bacterial cell wall is most critical for survival in hypotonic conditions because it:
ⓐ. Limits osmotic lysis
ⓑ. Makes ATP for the cell
ⓒ. Stores DNA in a safe place
ⓓ. Builds ribosomes for proteins
Correct Answer: Limits osmotic lysis
Explanation: In hypotonic surroundings, water tends to enter the cell, raising internal pressure against the boundary. The bacterial cell wall provides mechanical strength that resists this pressure and prevents the cell from bursting. This role is especially important because many bacteria live in environments where water movement can be significant. The wall maintains cell shape and integrity even when osmotic gradients favor inflow. Without a strong wall, membrane stretching alone would be insufficient to prevent rupture. Thus, the wall’s key protective value here is limiting osmotic lysis.
93. In Gram-negative bacteria, the peptidoglycan layer is typically located:
ⓐ. Inside nucleoid only
ⓑ. Outside glycocalyx always
ⓒ. As thick outer sheet
ⓓ. In periplasm region
Correct Answer: In periplasm region
Explanation: Gram-negative bacteria have a more complex envelope with an outer membrane and an inner plasma membrane. The peptidoglycan is relatively thin and lies in the space between these two membranes, commonly referred to as the periplasmic region. This placement helps explain why Gram-negative cells have a distinct envelope architecture compared with Gram-positive cells. The periplasm also contains enzymes and binding proteins that work alongside the thin wall layer. Because the peptidoglycan is not the outermost barrier, the outer membrane adds an additional protective layer. Therefore, “in periplasm region” correctly identifies the typical location.
94. Teichoic acids are most closely associated with Gram-positive bacteria because they:
ⓐ. Form nuclear pores
ⓑ. Add wall strength
ⓒ. Make outer membrane
ⓓ. Store cell DNA
Correct Answer: Add wall strength
Explanation: Teichoic acids are commonly found in the thick cell wall of Gram-positive bacteria and contribute to the wall’s overall stability and surface properties. Their presence supports rigidity and helps maintain wall organization along with the extensive peptidoglycan network. This association is a standard feature used to describe Gram-positive envelope structure. Because Gram-positive cells lack an outer membrane, the wall becomes the dominant external structural barrier, and teichoic acids contribute to its effectiveness. These molecules also influence interactions at the cell surface by affecting charge and binding behavior. Hence, adding wall strength is the best-linked role in this context.
95. The outer membrane of Gram-negative bacteria mainly acts as:
ⓐ. Extra barrier layer
ⓑ. Main DNA container
ⓒ. Site of mitosis
ⓓ. Cell wall substitute
Correct Answer: Extra barrier layer
Explanation: Gram-negative bacteria possess an outer membrane external to the thin peptidoglycan layer, which provides an added protective boundary. This outer membrane limits entry of many harmful substances and contributes to overall envelope selectivity, making the cell less permeable to certain chemicals. It also works with transport proteins that regulate what can pass inward, strengthening control over the cell’s internal environment. Because the peptidoglycan is thin, the outer membrane becomes especially important as a defensive layer. This layered envelope design is a key reason Gram-negative cells often show different sensitivity patterns compared with Gram-positive cells. Therefore, its main role here is as an extra barrier layer.
96. Lysozyme weakens many bacterial cell walls by breaking:
ⓐ. Peptide bonds only
ⓑ. Lipid bilayer tails
ⓒ. DNA phosphates
ⓓ. β-1,4 linkages
Correct Answer: β-1,4 linkages
Explanation: Lysozyme targets the sugar backbone of peptidoglycan by cleaving the β-1,4 glycosidic linkages that connect key sugar units in the wall framework. When these bonds are cut, the peptidoglycan mesh loses strength and cannot resist internal osmotic pressure effectively. This makes the wall less rigid and can lead to cell damage, especially in hypotonic conditions. The action is focused on the structural carbohydrate component that supports the wall’s integrity. Because the wall is a major protective feature in many bacteria, disrupting these links has a strong weakening effect. Hence, breaking β-1,4 linkages explains lysozyme’s wall-damaging action.
97. A prokaryote that can show irregular shape mainly because it lacks a cell wall is:
ⓐ. Bacillus
ⓑ. Nostoc
ⓒ. Mycoplasma
ⓓ. Anabaena
Correct Answer: Mycoplasma
Explanation: Mycoplasma is known for lacking a rigid cell wall, so it does not maintain a fixed shape and can appear pleomorphic. Without a wall, the plasma membrane becomes the main boundary, and shape depends more on membrane flexibility and external conditions. This feature is commonly used to distinguish Mycoplasma from typical bacteria that rely on peptidoglycan walls for structural stability. The absence of a wall also increases vulnerability to osmotic stress, so these organisms often require protective environments. Their flexible form is therefore directly linked to missing wall support. Hence, Mycoplasma best fits the description.
98. In many bacteria, enzymes for aerobic respiration are mainly found in the:
ⓐ. Nucleoid region
ⓑ. Plasma membrane
ⓒ. Glycocalyx coat
ⓓ. Cell wall mesh
Correct Answer: Plasma membrane
Explanation: Bacteria lack mitochondria, so the plasma membrane commonly serves as the site where key respiration-related enzyme complexes are arranged. These membrane-associated systems help generate ion gradients that drive ATP synthesis, making the membrane central to energy production in aerobic conditions. This placement also supports efficient coupling between transport and metabolism, since the membrane controls entry and exit of ions and molecules. The membrane’s role is therefore not only as a barrier but also as an active metabolic platform. This is a standard prokaryotic adaptation to simpler internal organization. Hence, plasma membrane is the correct location for many aerobic respiration enzymes.
99. The glycocalyx most directly helps bacteria establish biofilms by:
ⓐ. Improving adhesion
ⓑ. Making ATP faster
ⓒ. Packing DNA tighter
ⓓ. Forming ribosomes
Correct Answer: Improving adhesion
Explanation: Biofilm formation begins when bacterial cells attach to surfaces and to one another, and the glycocalyx supports this process through its sticky, surface-binding properties. By acting as an adhesive coat, it increases the ability of bacteria to remain anchored under fluid flow and environmental stress. The glycocalyx also helps create a protective microenvironment around clustered cells, supporting stable community growth. This surface layer can trap water and nutrients, improving survival and persistence in challenging conditions. Because adhesion is the first major step in biofilm development, the glycocalyx has a direct enabling role. Therefore, improving adhesion is the key contribution.
100. The term “cell envelope” in many bacteria commonly includes:
ⓐ. Wall only and nothing else
ⓑ. Membrane only and nothing else
ⓒ. Nucleoid with cytosol
ⓓ. Coat wall membrane
Correct Answer: Coat wall membrane
Explanation: The bacterial cell envelope refers to the boundary layers that surround the cytoplasm, typically including the outer coat (glycocalyx when present), the cell wall, and the plasma membrane. These layers together provide protection, shape, and selective control over movement of substances into and out of the cell. The wall contributes mechanical strength, the membrane regulates transport and hosts key metabolic functions, and the coat often supports adhesion and protection. Thinking of it as “coat–wall–membrane” helps map the outside-to-inside organization used in many textbook descriptions. This layered concept is central to comparing prokaryotic structure with eukaryotic cells. Hence, “coat wall membrane” correctly captures common envelope layers.