201. Why are living root cells especially important for active mineral absorption?
ⓐ. They provide metabolic energy and functional membrane carriers for ion uptake
ⓑ. They allow xylem vessels to perform photosynthesis in the cortex
ⓒ. They convert all absorbed ions directly into sugars
ⓓ. They stop water from entering through root hairs
Correct Answer: They provide metabolic energy and functional membrane carriers for ion uptake
Explanation: Active mineral absorption requires more than just physical contact with soil water. The root cells involved must be alive so that they can respire, generate ATP, and maintain functioning membrane proteins for selective ion transport. Dead cells cannot sustain this kind of controlled uphill movement because they lack the metabolic machinery needed for it. This is why living root hairs and cortical cells are essential in nutrient uptake. The selectivity and accumulation of ions depend strongly on active membranes. Therefore, living root cells are important because they provide both metabolic energy and functional membrane carriers for ion uptake.
202. Which statement best explains why mineral ion uptake may still occur passively under certain conditions?
ⓐ. Root cells can always force every ion inward by respiration alone
ⓑ. Some ions can enter when the external conditions already favor their inward movement
ⓒ. Passive absorption requires stronger ATP supply than active absorption
ⓓ. Passive absorption occurs only after all stomata are closed
Correct Answer: Some ions can enter when the external conditions already favor their inward movement
Explanation: Passive absorption does not require the plant to spend energy forcing ions inward. Instead, it occurs when the surrounding conditions already permit the ions to move into the root along a favorable gradient. In such situations, the root benefits from the natural tendency of the ions to move inward. This explains why not all mineral uptake must always be active. Depending on the ion and the conditions in the soil and root tissues, passive entry may contribute to total uptake. The plant therefore uses both passive and active modes in different circumstances. Hence, mineral ion uptake may still occur passively when external conditions already favor inward movement.
203. A root is placed in a solution containing potassium ions at a lower concentration than that already present inside the root cells, yet the cells continue to absorb potassium. This uptake is best explained by:
ⓐ. passive diffusion through dead cell walls
ⓑ. active absorption using energy-dependent membrane transport
ⓒ. evaporation-driven movement through stomata
ⓓ. downward translocation through phloem tissues
Correct Answer: active absorption using energy-dependent membrane transport
Explanation: In this situation, potassium ions are entering the root cells even though their concentration is already higher inside than outside. Such movement is against the concentration gradient and cannot be explained by passive diffusion. The root must therefore use metabolic energy to move the ions inward. This is done by living membrane systems with specific transport proteins. The example is a classic case of active mineral absorption by roots. It shows that the plant can accumulate needed ions even from dilute external solutions. Therefore, the uptake is best explained by active absorption using energy-dependent membrane transport.
204. Which observation would best indicate that a particular mineral ion is being absorbed passively by roots?
ⓐ. Its uptake falls sharply when ATP production is blocked
ⓑ. Its uptake continues efficiently in dead root tissue
ⓒ. Its inward movement occurs mainly when the external concentration is higher and favors entry
ⓓ. Its concentration inside the root becomes much higher than outside
Correct Answer: Its inward movement occurs mainly when the external concentration is higher and favors entry
Explanation: Passive absorption depends on favorable conditions that allow ions to move into the root without direct expenditure of metabolic energy. If the ion enters mainly when its external concentration is higher or otherwise favors inward movement, that fits the idea of passive uptake. Such entry follows the natural direction of the gradient. It does not require the cell to push the ion uphill against its tendency. By contrast, sharp dependence on ATP or strong accumulation against the gradient would suggest active absorption. Therefore, uptake occurring when external conditions already favor entry is the best sign of passive absorption.
205. A student says, "If a membrane protein is involved, the process must be active absorption." What is the best correction?
ⓐ. Membrane proteins can participate in both passive and active uptake, depending on whether energy is required
ⓑ. All membrane proteins in roots function only after photosynthesis in leaves
ⓒ. Membrane proteins are used only for water absorption, not for mineral ions
ⓓ. Presence of a membrane protein proves that uptake occurs only in dead cells
Correct Answer: Membrane proteins can participate in both passive and active uptake, depending on whether energy is required
Explanation: The presence of a membrane protein alone does not prove that the process is active. Some proteins allow substances to move passively when the gradient already favors entry, while others use metabolic energy to transport ions against a gradient. The key distinction is therefore not simply whether a protein is present, but whether ATP-dependent work is required. This is an important misconception in transport biology. Roots use membranes and proteins in both passive and active forms of ion uptake. Therefore, the correct correction is that membrane proteins can take part in both passive and active uptake, depending on the role of energy.
206. Which experimental result would most strongly support the idea that mineral ion absorption by roots is selective?
ⓐ. Every ion enters at exactly the same rate under all conditions
ⓑ. One ion is absorbed readily, while another similar ion is taken up poorly by the same root system
ⓒ. All dissolved substances pass through the root surface without restriction
ⓓ. Mineral ions move into the root only after water loss from leaves begins
Correct Answer: One ion is absorbed readily, while another similar ion is taken up poorly by the same root system
Explanation: Selective absorption means that roots do not take up all ions equally. Instead, the membranes and transport systems of root cells show preference for certain ions over others. If one ion is absorbed efficiently while another similar one is not, that strongly indicates selective uptake. This kind of result is consistent with the presence of specific carrier systems and controlled membrane transport. It also explains why plants can regulate internal mineral composition rather than absorbing everything indiscriminately. Therefore, the contrasting uptake of two similar ions best supports the idea that mineral absorption is selective.
207. When the soil around roots becomes waterlogged and oxygen supply falls, mineral ion uptake often decreases mainly because:
ⓐ. root hairs turn into xylem vessels
ⓑ. ions stop dissolving in the soil solution entirely
ⓒ. transpiration converts mineral salts into gases
ⓓ. respiration declines and less ATP becomes available for active absorption
Correct Answer: respiration declines and less ATP becomes available for active absorption
Explanation: Waterlogged soil reduces the amount of air available around the roots, and this lowers the oxygen supply to living root cells. Since respiration depends on oxygen, ATP production may fall under such conditions. Active absorption of mineral ions requires ATP to drive transport against gradients. When ATP becomes limited, the energy-dependent part of ion uptake decreases. This is why poor soil aeration can strongly reduce mineral nutrition in plants. The effect is especially important for actively absorbed ions. Therefore, the decrease occurs mainly because respiration declines and less ATP becomes available for active absorption.
208. Which of the following is the best non-example of mineral ion absorption by roots?
ⓐ. nitrate ions entering a root hair cell from the soil solution
ⓑ. potassium ions being accumulated by living epidermal cells
ⓒ. phosphate ions moving from soil water into root tissues
ⓓ. dissolved calcium ions being carried upward in the xylem after uptake
Correct Answer: dissolved calcium ions being carried upward in the xylem after uptake
Explanation: Mineral ion absorption by roots refers specifically to the entry of ions from the soil solution into the root tissues. Once the ions have already entered the root and are being carried upward through xylem, the process is no longer absorption. It has become long-distance transport within the plant. This distinction is important because uptake and conduction are related but not identical processes. The first three options describe entry from soil into root tissues, which fits the idea of absorption. The fourth describes movement after uptake has already occurred. Therefore, upward xylem transport of calcium after entry is the best non-example of mineral ion absorption by roots.
209. A plant is transferred to a dilute nutrient solution containing a required ion, and after some time the root concentration of that ion becomes much higher than the surrounding solution. Which conclusion is most reasonable?
ⓐ. The ion must have entered only by passive absorption
ⓑ. The concentration inside and outside must actually be equal
ⓒ. The root likely used active absorption to accumulate the ion
ⓓ. The ion could not have crossed the root surface at all
Correct Answer: The root likely used active absorption to accumulate the ion
Explanation: If the concentration of an ion becomes much higher inside the root than in the surrounding solution, the plant has accumulated the ion against a concentration gradient. Passive absorption alone cannot account for such buildup because passive movement follows a favorable gradient rather than creating an unfavorable one. This suggests that the root has used living membrane transport systems with metabolic energy to bring the ion inward. Such accumulation is a common sign of active mineral uptake. The result also shows that the root is regulating its internal composition actively. Therefore, the most reasonable conclusion is that the root used active absorption to accumulate the ion.
210. Which statement best compares mineral ion uptake with water absorption by roots?
ⓐ. Water absorption always requires ATP, but ion uptake never does
ⓑ. Mineral ion uptake may be passive or active, whereas water absorption is mainly explained by water potential difference
ⓒ. Mineral ion uptake occurs only through hydathodes, whereas water absorption occurs only through stomata
ⓓ. Both processes are identical because both always move against a gradient
Correct Answer: Mineral ion uptake may be passive or active, whereas water absorption is mainly explained by water potential difference
Explanation: Water absorption by roots is primarily understood in terms of water potential difference, with water moving from higher to lower water potential. Mineral ion uptake is more varied because some ions may enter passively when conditions favor their movement, while others are absorbed actively against their gradient using energy. This makes ion uptake more dependent on metabolic transport systems than ordinary water entry. The two processes are related because both occur at the root surface, but they are not identical in mechanism. Understanding this comparison helps separate osmotic water movement from nutrient absorption. Therefore, the best comparison is that mineral ion uptake may be passive or active, whereas water absorption is mainly explained by water potential difference.
211. Which statement best defines translocation in xylem?
ⓐ. Movement of manufactured food from leaves to storage organs through living sieve tubes
ⓑ. Long-distance transport of water and dissolved minerals from roots to aerial parts through xylem tissue
ⓒ. Diffusion of gases through intercellular spaces of leaves and stems
ⓓ. Active movement of sugars into companion cells using ATP
Correct Answer: Long-distance transport of water and dissolved minerals from roots to aerial parts through xylem tissue
Explanation: Translocation in xylem refers to the movement of water along with dissolved mineral substances through the xylem conducting tissue of the plant. This transport connects the absorbing parts of the root with the stem, leaves, and other aerial organs. It is essential because water and minerals taken up from the soil must reach distant tissues for metabolism and growth. The process is long-distance in nature and is distinct from phloem transport of food. Xylem therefore acts as the main conducting pathway for the upward transport stream. The term does not refer to gaseous diffusion or sugar loading. Hence, the best definition is long-distance transport of water and dissolved minerals through xylem.
212. The main substances transported through xylem are:
ⓐ. sucrose and amino acids
ⓑ. oxygen and carbon dioxide
ⓒ. water and mineral ions
ⓓ. starch grains and proteins
Correct Answer: water and mineral ions
Explanation: Xylem is specialized for conducting water absorbed by the roots and the mineral ions dissolved in that water. These substances move together as part of the transpiration stream toward the stem and leaves. The xylem does not mainly transport prepared organic food such as sucrose, because that is the function of phloem. Gases also do not move chiefly by xylem conduction in this context. The dissolved mineral substances include nitrates, phosphates, potassium, calcium, and similar ions. Their upward movement depends on the water stream in xylem. Therefore, the main substances transported through xylem are water and mineral ions.
213. The direction of transport in xylem is generally:
ⓐ. mainly upward from roots toward stems and leaves
ⓑ. equally upward and downward in the same vessel at all times
ⓒ. mainly downward from leaves to roots
ⓓ. restricted only to lateral movement between cortical cells
Correct Answer: mainly upward from roots toward stems and leaves
Explanation: Xylem transport is generally unidirectional in the sense that it mainly carries water and dissolved minerals from the roots to the upper parts of the plant. This reflects the fact that water is absorbed from the soil by roots and is then needed in stems and leaves. The driving forces involved in ascent of sap support this upward movement. Although some local lateral movement into surrounding tissues can occur, the main long-distance direction is upward. This is different from phloem, where transport may occur in more than one direction depending on source and sink. Thus, the usual direction in xylem is from roots toward aerial parts. Hence, the correct answer is mainly upward transport.
214. Which xylem elements are chiefly responsible for conduction of water over long distances?
ⓐ. guard cells and epidermal cells
ⓑ. vessels and tracheids
ⓒ. companion cells and sieve tubes
ⓓ. cork cells and lenticels
Correct Answer: vessels and tracheids
Explanation: Vessels and tracheids are the conducting elements of xylem that form elongated channels for water movement. Their structure is highly suited for long-distance transport because they are hollow at maturity and have thick walls that help maintain the pathway. Vessels form continuous tube-like channels, while tracheids conduct through overlapping cells with pits. Together, they provide the main route for water and dissolved minerals. Other listed cells serve different functions in the plant body. The conducting role of xylem is therefore centered on these elements. Hence, vessels and tracheids are chiefly responsible for long-distance water conduction.
215. Which feature makes xylem well suited for transport of water and minerals?
ⓐ. Presence of soft cytoplasm filling the conducting cavity
ⓑ. Thin unlignified walls that collapse easily under tension
ⓒ. Hollow continuous conducting elements with strong lignified walls
ⓓ. Numerous chloroplasts for active pumping of water
Correct Answer: Hollow continuous conducting elements with strong lignified walls
Explanation: Xylem is structurally adapted for conduction because its main transporting elements become hollow and form long pathways with little obstruction to water flow. Their lignified walls give strength and prevent collapse while water is being pulled upward under tension. This makes xylem an efficient conducting tissue for long-distance movement. The absence of living protoplasm in the lumen also reduces resistance to the movement of water. Such a design is ideal for the transport stream linking roots and leaves. Therefore, xylem is well suited for conduction because of its hollow continuous elements with strong lignified walls.
216. The liquid moving through xylem is often called:
ⓐ. phloem sap
ⓑ. cell sap
ⓒ. xylem sap
ⓓ. latex
Correct Answer: xylem sap
Explanation: The water along with dissolved mineral substances that moves through xylem is commonly referred to as xylem sap. This term emphasizes that the transported fluid is not just pure water but also includes inorganic solutes absorbed from the soil. Xylem sap is therefore the medium by which mineral nutrients are distributed to aerial tissues. It differs from phloem sap, which is rich in sugars and other organic substances. The composition of xylem sap reflects the nutritional and transport role of the xylem pathway. This term is widely used in plant transport studies. Hence, the correct name for the fluid moving through xylem is xylem sap.
217. After mineral ions are absorbed by root cells, they are transported to the shoot mainly because they:
ⓐ. evaporate from the root surface into the stem
ⓑ. move with the transpiration stream in the xylem
ⓒ. diffuse through phloem from sink to source
ⓓ. are carried upward only by growing cortical cells
Correct Answer: move with the transpiration stream in the xylem
Explanation: Once mineral ions enter the root tissues, they reach the xylem and then travel upward dissolved in the water stream. This movement is strongly associated with the transpiration stream, which carries both water and minerals toward the shoot. The ions do not rise by evaporation from roots or by phloem food transport. Their distribution depends on their dissolution in the xylem sap and the upward movement of that sap. This is why transpiration is important not only for water movement but also for mineral supply to leaves and growing regions. The minerals are therefore transported as part of the xylem stream. Hence, they move with the transpiration stream in the xylem.
218. Which statement correctly compares xylem transport with phloem transport?
ⓐ. Xylem mainly carries water and minerals, whereas phloem mainly carries organic food
ⓑ. Xylem mainly transports sugars, whereas phloem mainly transports water
ⓒ. Both tissues carry exactly the same substances in the same direction
ⓓ. Xylem functions only in roots, whereas phloem functions only in leaves
Correct Answer: Xylem mainly carries water and minerals, whereas phloem mainly carries organic food
Explanation: Xylem and phloem are both conducting tissues, but they transport different kinds of materials. Xylem mainly conducts water and dissolved mineral substances absorbed from the soil. Phloem mainly carries organic nutrients such as sugars produced in photosynthetic tissues. This functional distinction is one of the most important in plant transport biology. The two tissues may work together in the same plant, but their transported contents are not the same. Recognizing this difference helps explain how plants distribute both inorganic and organic materials. Therefore, the correct comparison is that xylem carries water and minerals, whereas phloem carries organic food.
219. Why is long-distance transport of minerals through xylem important to the plant?
ⓐ. It allows mineral nutrients absorbed by roots to reach leaves and growing tissues
ⓑ. It converts mineral salts directly into glucose inside the vessels
ⓒ. It stops water from entering leaf cells during transpiration
ⓓ. It keeps all minerals permanently stored in the root cortex
Correct Answer: It allows mineral nutrients absorbed by roots to reach leaves and growing tissues
Explanation: Mineral ions are taken up from the soil mainly by roots, but many of their important functions are required in distant tissues such as leaves, shoot tips, flowers, and developing organs. Long-distance transport through xylem ensures that these minerals are delivered where they are needed. This supply supports enzyme activity, chlorophyll formation, growth, and many other physiological processes. Without such transport, nutrients absorbed by roots would remain localized and could not support the whole plant. The xylem therefore connects nutrient uptake with nutrient use. Hence, long-distance transport in xylem is important because it carries mineral nutrients to leaves and growing tissues.
220. Which statement best explains why xylem transport is considered part of long-distance transport in plants?
ⓐ. It occurs only between neighboring cortical cells over a very short path
ⓑ. It links root absorption zones with distant aerial organs through a continuous conducting system
ⓒ. It depends only on random diffusion inside one leaf
ⓓ. It transports substances only within a single guard cell
Correct Answer: It links root absorption zones with distant aerial organs through a continuous conducting system
Explanation: Long-distance transport means movement of substances across relatively large distances within the plant body rather than only from one nearby cell to another. Xylem fulfills this role by forming a continuous conducting network from the roots to the stem, leaves, and other aerial organs. Water and minerals absorbed in one region can therefore reach tissues far away from the point of uptake. This makes xylem essential for whole-plant integration. The process is very different from local diffusion across short cellular distances. Thus, xylem transport is considered long-distance because it connects root absorption zones with distant aerial parts through one conducting system. Therefore, that statement best explains its long-distance nature.
