1. Living systems are built from atoms and molecules that are not living by themselves. Which statement best explains how these components contribute to life?
ⓐ. They become living as soon as they enter any aqueous solution.
ⓑ. Their organised interactions and chemical reactions generate living-system properties.
ⓒ. They acquire life only when each molecule can reproduce independently.
ⓓ. Their presence proves that living matter contains elements absent from non-living matter.
Correct Answer: Their organised interactions and chemical reactions generate living-system properties.
Explanation: Atoms, ions and molecules such as water, proteins and sugars do not independently display the complete characteristics of life. In a cell, however, these components are arranged in an organised system and participate in coordinated reactions. Their structures determine how they interact, while continuous chemical transformations supply materials, release or use energy and maintain cellular organisation. Life is an emergent property of the organised system rather than a separate property added to every molecule. Dissolving a compound in water does not make it living, and an isolated biomolecule does not reproduce as an autonomous organism. The chemical basis of life lies in organisation, interaction and regulated transformation of non-living components.
2. Evaluate the following statements about the chemical basis of living systems.
I. The atoms present in a cell are individually non-living.
II. Cellular organisation influences the biological effects of molecules.
III. Continuous chemical transformations are essential to living activity.
IV. An isolated biomolecule need not display all properties of a living organism.
ⓐ. I and II only
ⓑ. II and III only
ⓒ. I, III and IV only
ⓓ. I, II, III and IV
Correct Answer: I, II, III and IV
Explanation: Each statement addresses a different part of the same central idea. The atoms and molecules of a cell are ordinary chemical entities and are not independently alive. Their arrangement within membranes, complexes and reaction networks determines where and how they act. Living cells also maintain a continuous flow of chemical reactions, allowing synthesis, breakdown, energy transfer and regulation. Removing one biomolecule from this organisation does not produce a miniature living organism; the molecule may retain a chemical function but not the integrated properties of life. The valid set is all four statements. The reasoning avoids treating life as a special element or as an intrinsic property of every compound isolated from living tissue.
3. Elemental analysis of a tissue sample and a rock sample detects carbon, hydrogen, oxygen, nitrogen, sulphur and several mineral elements in both. Their percentages differ markedly. What is the strongest inference?
ⓐ. Similar elements may occur in both, but their relative abundances differ.
ⓑ. Detection of carbon alone is sufficient to identify a sample as living tissue.
ⓒ. Every element must occur in equal proportion in tissue and rock.
ⓓ. Elements lose their chemical identity when incorporated into living matter.
Correct Answer: Similar elements may occur in both, but their relative abundances differ.
Explanation: The observation supplies two kinds of evidence: a similar qualitative list of elements and a different quantitative composition. Qualitative analysis asks which elements are present, whereas quantitative analysis compares how much of each is present. Since carbon, hydrogen, oxygen and mineral elements can occur in both tissue and rock, mere detection of one of them cannot establish that the sample is living. The marked percentage differences are the biologically useful distinction. Living systems concentrate some elements through their molecular composition and organisation, while earth's crust contains other elements at much higher proportions. The data support similarity in elemental kinds combined with disparity in relative abundance, not equality of composition or a change in the identity of the elements. A proper observation-to-inference step must retain both findings: overlap in what is present and contrast in how much is present.
4. Assertion: The presence of carbon in a tissue sample does not show that carbon is an element exclusive to living matter.
Reason: Elemental analysis shows that earth's crust lacks carbon and other elements commonly detected in living tissues.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain Assertion
ⓒ. Assertion is true and Reason is false; therefore Reason cannot explain Assertion
ⓓ. Assertion is false and Reason is true; therefore Reason cannot explain Assertion
Correct Answer: Assertion is true and Reason is false; therefore Reason cannot explain Assertion
Explanation: The Assertion is valid: carbon occurs in living tissues, but it also occurs in non-living matter. An element does not become unique to life merely through its presence in cells. The Reason is false since elemental analysis of earth's crust and living tissue yields broadly overlapping element lists, even though the proportions differ greatly. The correct explanation for the Assertion is this qualitative overlap, not an alleged absence of carbon from the crust. The reasoning separates mere presence from relative abundance. Carbon is greatly enriched in the human body relative to earth's crust, yet enrichment is a quantitative relation and does not establish exclusivity. Hence the Assertion remains true while the stated Reason fails.
5. Study the elemental records from two samples.
| Element | Sample P: tissue | Sample Q: crustal material |
|---|
| Carbon | Detected | Detected |
| Oxygen | Detected | Detected |
| Calcium | Detected | Detected |
| Magnesium | Detected | Detected |
No abundance values were measured. Which conclusion is justified by these records?
ⓐ. The two samples have identical chemical composition.
ⓑ. Shared elements do not establish equal abundances.
ⓒ. Sample P must contain less carbon than Sample Q.
ⓓ. Sample Q cannot contain biologically important elements.
Correct Answer: Shared elements do not establish equal abundances.
Explanation: Every table entry reports only whether an element was detected. This establishes that the selected elements occur in both samples and supports qualitative similarity. The table gives no percentages, masses or concentration values, so it cannot compare relative abundance. Identical presence records are compatible with very different proportions; carbon, for example, is far more abundant in the human body than in earth's crust, while some mineral elements show the opposite pattern. A valid inference must stay within the information measured. The table neither proves identical composition nor permits a greater-than or less-than comparison for any element. It demonstrates why presence data and abundance data provide different kinds of analytical information. To test quantitative similarity, the investigator would need a second table containing percentages or another common measure for both samples. Without that measurement, the direction of enrichment remains unknown.
6. An investigator records only the presence or absence of elements in living tissue and nearby soil. The two lists are almost the same. What change would most directly reveal the major chemical distinction emphasised by such a comparison?
ⓐ. Measure the percentage contribution of each detected element in both samples.
ⓑ. Rename the elements according to the sample from which they were obtained.
ⓒ. Test whether carbon from tissue has a different atomic number from carbon in soil.
ⓓ. Remove every element that occurs in both lists before comparing the samples.
Correct Answer: Measure the percentage contribution of each detected element in both samples.
Explanation: A presence-or-absence record is qualitative. It can reveal whether an element is detectable, but it cannot show that carbon and hydrogen are enriched in living tissue or that silicon is abundant in crustal material. Measuring the percentage contribution converts the comparison into a quantitative one and exposes differences in relative abundance. The atomic number and chemical identity of carbon do not change with its source, so renaming or retesting its identity would add no relevant distinction. Removing shared elements would also discard the very elements whose proportions differ most informatively. The improved measurement targets the decisive variable: how much of each common element contributes to the total sample. This change preserves the shared element list while adding the information needed to distinguish the two materials.
7. The following values compare selected elements by mass.
| Element | Human body | Earth's crust |
|---|
| Carbon | \(18.5\%\) | \(0.03\%\) |
| Oxygen | \(65.0\%\) | \(46.6\%\) |
| Silicon | Negligible | \(27.7\%\) |
| Sodium | \(0.2\%\) | \(2.8\%\) |
Which synthesis best represents the data?
ⓐ. Oxygen is exclusive to the human body, while silicon is exclusive to all non-living matter.
ⓑ. Every element is more abundant in the body than in the crust.
ⓒ. Similar element lists require similar percentage composition.
ⓓ. Carbon is enriched in the body, whereas silicon is enriched in the crust.
Correct Answer: Carbon is enriched in the body, whereas silicon is enriched in the crust.
Explanation: The decisive comparison uses both direction and magnitude. Carbon contributes \(18.5\%\) of human-body mass but only \(0.03\%\) of earth's crust, showing very strong enrichment in the body. Silicon contributes \(27.7\%\) of the crust and is negligible in the body, giving the reverse pattern. Oxygen occurs substantially in both, while sodium is more abundant in the crust than in the body. These values demonstrate quantitative differentiation rather than a universal rule that all elements are enriched in living tissue. The term negligible also should not be expanded into an absolute claim that silicon can never occur in any living organism. The table supports contrasting relative-abundance patterns for the compared materials. It also shows why a single universal statement such as “minerals belong to crust and carbon belongs to life” would be inaccurate: the distinction appears in proportions, not in completely separate element categories.
8. Carbon forms \(18.5\%\) of human-body mass but \(0.03\%\) of earth's crust. Approximately how many times greater is the carbon percentage in the body than in the crust?
ⓐ. \(6.2\) times
ⓑ. \(62\) times
ⓒ. \(617\) times
ⓓ. \(6167\) times
Correct Answer: \(617\) times
Explanation: The required comparison is a fold ratio, so the percentage in the body is divided by the percentage in the crust. The common percentage unit cancels: \[\frac{18.5}{0.03}=616.67\] Rounding to the nearest whole-number estimate gives about \(617\) times. This calculation does not mean that carbon is absent from earth's crust; it shows that its relative contribution to human-body mass is enormously greater. A value near \(62\) would result from shifting the decimal place incorrectly, while \(6167\) would introduce an extra factor of \(10\). The biological interpretation is enrichment: living tissue contains many carbon-rich organic compounds, so carbon forms a much larger mass fraction than it does in crustal material. The ratio compares percentages on the same basis and should not be read as the number of carbon atoms in one body or one crust sample. Because both entries are percentages of their respective total masses, no further unit conversion is needed before division. The quotient is dimensionless and expresses relative enrichment rather than absolute carbon mass.
9. Consider the following comparisons between the human body and earth's crust.
I. Hydrogen, carbon and oxygen are relatively more abundant in the body.
II. Silicon is abundant in the crust but negligible in the body.
III. The main distinction is quantitative rather than the presence of an entirely unique set of elements.
IV. Sodium forms a greater percentage of the body than of the crust.
ⓐ. I, II and III only
ⓑ. I and IV only
ⓒ. II, III and IV only
ⓓ. I, II, III and IV
Correct Answer: I, II and III only
Explanation: Hydrogen, carbon and oxygen contribute larger percentages to the human body than to earth's crust, so Statement I is valid. Silicon shows the opposite extreme, reaching a large crustal percentage while being negligible in the body; Statement II is also valid. Since many elements occur in both materials, the important distinction lies in proportion, supporting Statement III. Sodium does not follow the proposed direction: it contributes about \(0.2\%\) to the body and \(2.8\%\) to the crust, making Statement IV false. The accepted combination is the first three statements. This pattern also warns against assuming that every biologically important element must be more abundant in living tissue. Sodium, calcium and magnesium are biologically important despite having lower listed percentages in the body than in the crust.
10. A dry sample contains carbon, hydrogen, oxygen, sodium, calcium and magnesium. Quantitative analysis shows high carbon and hydrogen percentages, a high oxygen percentage and very little silicon. Which interpretation is most defensible?
ⓐ. The sample is certainly alive at the moment of analysis.
ⓑ. The sample must lack all inorganic constituents.
ⓒ. The element list alone proves that it came from an organism.
ⓓ. Biological origin is plausible; current life is uncertain.
Correct Answer: Biological origin is plausible; current life is uncertain.
Explanation: The case supplies more than an element list: it gives a pattern of relative abundance. Enrichment of carbon and hydrogen together with very low silicon resembles the comparison reported for living material rather than earth's crust. That evidence can support an origin or composition inference, but it cannot establish that the sample is currently alive. Dried or dead biological material may retain the same elemental pattern, and living tissues also contain inorganic ions and salts. The strongest conclusion must match both the evidence and its limit. Relative abundance is informative for distinguishing chemical composition, while the complete property of life depends on organised structures and ongoing processes that elemental analysis does not measure. A stronger claim about present life would require evidence such as cellular organisation or active metabolism, neither of which is supplied.
11. A plant tissue sample shows an unexpectedly high silicon percentage after being collected with adhering soil particles. Which conclusion should be drawn first?
ⓐ. Silicon has become an element unique to living tissue.
ⓑ. Mineral contamination may have altered the measured abundance pattern.
ⓒ. The tissue cannot contain carbon-rich biomolecules.
ⓓ. Qualitative elemental similarity between living and non-living matter is disproved.
Correct Answer: Mineral contamination may have altered the measured abundance pattern.
Explanation: Silicon is abundant in earth's crust, so adhering soil can contribute a large amount of silicon to the analysed mass. The measured percentage would then describe a mixture of tissue and crustal material rather than uncontaminated tissue. The first inference should address this sampling condition and call for cleaning or a suitable control before interpreting the composition. A high silicon reading does not create a unique biological element, remove carbon compounds or disprove the overlap of element lists. It shows how relative abundance can be distorted when the analysed sample includes material from two sources. Sound interpretation links the unexpected value to the collection condition instead of treating one measurement as an absolute boundary between living and non-living matter.
12. In the human body and earth's crust, carbon percentages are \(18.5\%\) and \(0.03\%\), while oxygen percentages are \(65.0\%\) and \(46.6\%\), respectively. The carbon enrichment factor in the body is approximately how many times the oxygen enrichment factor?
ⓐ. \(4.4\) times
ⓑ. \(44\) times
ⓒ. \(4.4\times10^2\) times
ⓓ. \(4.4\times10^3\) times
Correct Answer: \(4.4\times10^2\) times
Explanation: Two enrichment factors must be calculated before they are compared. For carbon, the body-to-crust factor is \[\frac{18.5}{0.03}\approx616.7\] For oxygen, the corresponding factor is \[\frac{65.0}{46.6}\approx1.39\] The ratio of these factors is \[\frac{616.7}{1.39}\approx443\approx4.4\times10^2\] The result means that carbon is enriched in the body relative to the crust far more strongly than oxygen is. Oxygen is already abundant in both materials, so its body-to-crust ratio is close to \(1\). Carbon is scarce in the crustal percentage table but abundant in biological material, producing the much larger comparative enrichment. The two-stage calculation is essential: comparing the raw body percentages alone would not reveal how strongly each element is enriched relative to its own crustal baseline. Both denominators must remain matched to the same element. A useful check is that dividing \(616.7\) by a value slightly greater than \(1\) should give a result somewhat below \(616.7\), which is consistent with approximately \(443\). This confirms the order of magnitude.
13. Arrange the steps used to begin compound analysis of living tissue.
P. Add trichloroacetic acid to the tissue.
Q. Grind the tissue with a mortar and pestle to form a slurry.
R. Pass the slurry through cheesecloth or cotton.
S. Collect the filtrate and the retained material as separate fractions.
ⓐ. Q → P → S → R
ⓑ. P → R → Q → S
ⓒ. R → P → Q → S
ⓓ. P → Q → R → S
Correct Answer: P → Q → R → S
Explanation: The reagent must first be present during homogenisation, so tissue is combined with trichloroacetic acid, \(\mathrm{Cl_3CCOOH}\). Grinding then disrupts the tissue and produces a slurry in which soluble constituents can enter the liquid phase while insoluble material remains suspended. Filtration is meaningful only after this preparation. Passing the slurry through cheesecloth or cotton separates liquid that passes through from material retained on the filter. These products are collected as the acid-soluble pool and acid-insoluble fraction. The sequence follows procedural dependency: a slurry must exist before it can be filtered, and the two fractions can be collected only after the filter has separated them. Reversing grinding and filtration would leave much intracellular material unextracted, while collecting named fractions before filtration would have no physical basis. The order is tied to the purpose of each stage, not merely to a memorised list.
14. Two equal tissue samples are treated with the same volume of trichloroacetic acid. Sample P is thoroughly ground before filtration, whereas Sample Q is filtered without grinding. Which result is most likely?
ⓐ. Sample Q releases fewer intracellular solutes into the filtrate.
ⓑ. Sample Q converts insoluble macromolecules into soluble monomers.
ⓒ. Sample P prevents all inorganic ions from entering the filtrate.
ⓓ. Sample P changes the elemental identity of the tissue compounds.
Correct Answer: Sample Q releases fewer intracellular solutes into the filtrate.
Explanation: Grinding mechanically disrupts tissue architecture, breaks many cells and increases contact between intracellular contents and the extraction medium. In Sample P, small soluble compounds can move into the trichloroacetic-acid phase before filtration. Without grinding, many cells in Sample Q remain intact, trapping soluble intracellular molecules behind membranes and within tissue pieces. Its filtrate would underrepresent the acid-soluble pool. Homogenisation does not hydrolyse every macromolecule into monomers, selectively exclude all ions or change one element into another. The predicted difference comes from access and release: identical reagent volume cannot compensate for failure to disrupt the tissue adequately. The retentate from Sample Q would be expected to retain more intact cellular material along with soluble substances that never reached the extracting liquid. Comparing equal tissue masses and reagent volumes isolates grinding as the meaningful changed condition.
15. Assess the following statements about preparing a tissue extract with trichloroacetic acid.
I. Grinding increases contact between tissue contents and the extraction medium.
II. The product before filtration is a slurry.
III. Filtration directly reveals the molecular formula of each separated compound.
IV. The preparation enables separation into operationally soluble and insoluble fractions.
ⓐ. I and III only
ⓑ. II and IV only
ⓒ. I, II and IV only
ⓓ. I, II, III and IV
Correct Answer: I, II and IV only
Explanation: Grinding disrupts tissue and disperses its contents in trichloroacetic acid, so Statement I is valid. The heterogeneous mixture produced is described as a slurry, making Statement II valid. Filtration then divides the mixture according to whether material passes through or remains on the filter under the stated conditions, which supports Statement IV. It does not identify the molecular formula or probable structure of each compound; those conclusions require later separation, isolation, purification and analytical methods. Statement III confuses fractionation with chemical identification. The accepted set includes the preparation and separation statements but excludes the claim that a simple filter provides molecular-level structural information. Filtration sorts material by behaviour in the prepared mixture; analytical identification is a later operation performed on separated and purified compounds.
16. A researcher grinds tissue thoroughly in distilled water and filters the mixture. The liquid and residue are then labelled “acid-soluble pool” and “acid-insoluble fraction.” What is the main methodological problem?
ⓐ. Grinding cannot be performed in any liquid medium.
ⓑ. The labels require trichloroacetic-acid extraction, which was not used.
ⓒ. Filtration can separate elements but never compounds.
ⓓ. Distilled water reproduces the same acid-dependent fractionation as trichloroacetic acid.
Correct Answer: The labels require trichloroacetic-acid extraction, which was not used.
Explanation: Solubility depends on the extraction conditions. The terms acid-soluble pool and acid-insoluble fraction refer to the fractions obtained after homogenising tissue in trichloroacetic acid and then filtering. Water may dissolve or retain a different set of compounds, so a water filtrate and residue cannot automatically receive the same operational labels. Grinding and filtration are still possible in water, but the resulting fractions measure a different experimental property. No conversion of biomolecules into inorganic substances is implied. The methodological error is not the physical act of filtering; it is assigning conclusions tied to a reagent that was never present. Proper interpretation must preserve the connection between treatment and fraction name. Repeating the procedure with trichloroacetic acid would be needed before the standard acid-soluble and acid-insoluble terminology could be applied. The case illustrates that a fraction is defined jointly by the material recovered and the conditions used to recover it.
17. After a tissue slurry in trichloroacetic acid is filtered, the liquid passes through the cloth while particulate material remains on it. The two products are identified, respectively, as:
ⓐ. acid-soluble pool and acid-insoluble fraction
ⓑ. acid-insoluble fraction and acid-soluble pool
ⓒ. ash and dry organic matter
ⓓ. purified biomolecules and isolated elements
Correct Answer: acid-soluble pool and acid-insoluble fraction
Explanation: Filtration separates the prepared slurry according to passage through the filter. Dissolved and sufficiently small soluble constituents move with the liquid into the filtrate, which is called the acid-soluble pool. Cellular debris and other material that does not dissolve under the extraction conditions remain on the cheesecloth or cotton as the acid-insoluble fraction. These names describe experimental behaviour in trichloroacetic acid; they do not mean that every substance in one fraction belongs to a single chemical class. Nor does filtration itself purify each compound or produce ash. The mapping follows the physical locations created by the procedure: filtrate below the filter and retained material on the filter.
18. A text-described filtration setup has Region P as the clear liquid collected below a cotton filter and Region Q as the material remaining on the cotton after a trichloroacetic-acid tissue slurry is poured through it. Which labelling is appropriate?
ⓐ. P is dry weight; Q is wet weight.
ⓑ. P is inorganic ash; Q is volatilised organic matter.
ⓒ. P is acid-insoluble; Q is acid-soluble.
ⓓ. P is acid-soluble; Q is acid-insoluble.
Correct Answer: P is acid-soluble; Q is acid-insoluble.
Explanation: The spatial description fully determines the labels. Region P lies below the filter and contains the liquid that passed through, so it is the filtrate or acid-soluble pool. Region Q remains on the cotton and represents the retentate or acid-insoluble fraction. The terms wet weight, dry weight and ash belong to a different destructive-analysis sequence involving drying and burning, not to this filtration diagram. The direction of movement matters: soluble constituents travel with the extracting liquid through the cotton, while insoluble material is physically retained. Translating the described positions into the filtration process gives the P-soluble and Q-insoluble assignment. The cotton acts as the physical boundary: passage with the liquid identifies the filtrate, while failure to pass identifies the retained fraction. No unseen diagram is needed once the orientation and locations are stated.
19. The relative recovery of two substances after trichloroacetic-acid extraction is shown below.
| Substance | Filtrate | Retentate |
|---|
| Free amino acids | High | Low |
| Intact proteins | Low | High |
Which interpretation best uses the complete pattern?
ⓐ. Both are mainly acid-soluble after extraction.
ⓑ. Both are mainly acid-insoluble after extraction.
ⓒ. Amino acids are mainly acid-soluble; intact proteins are mainly acid-insoluble.
ⓓ. Amino acids are mainly acid-insoluble; intact proteins are mainly acid-soluble.
Correct Answer: Amino acids are mainly acid-soluble; intact proteins are mainly acid-insoluble.
Explanation: The table must be read across both rows and both fractions. High recovery of free amino acids in the filtrate indicates that these small molecules are predominantly soluble under the extraction conditions. Intact proteins show the complementary pattern, with high recovery in the retentate, placing them mainly in the acid-insoluble fraction. The result reflects molecular size, solubility and the behaviour of cellular material during extraction; it does not indicate chemical conversion between amino acids and proteins. The word “mainly” is important since experimental recovery need not be absolute. The combined pattern supports classification of the free monomers in the soluble pool and the macromolecular protein in the insoluble fraction. The inference uses relative recovery rather than a single cell in the table. It also remains limited to the stated extraction method, since changing solvent or treatment could alter solubility behaviour.
20. An acid-insoluble retentate is ground again with fresh trichloroacetic acid and refiltered. Only traces of intact protein appear in the second filtrate. What is the strongest conclusion?
ⓐ. The first filtration destroyed all protein molecules.
ⓑ. Intact proteins remain largely insoluble under the repeated extraction conditions.
ⓒ. Trichloroacetic acid changes proteins into mineral ions that pass through the filter.
ⓓ. The second extraction proves that the retentate contains no other substances.
Correct Answer: Intact proteins remain largely insoluble under the repeated extraction conditions.
Explanation: Re-extraction tests whether poor initial contact or incomplete washing caused protein to remain in the retentate. Even after renewed grinding and fresh reagent, only traces enter the filtrate. This repeated observation supports the inference that intact proteins are largely insoluble under these conditions and belong mainly to the acid-insoluble fraction. The evidence does not show destruction or conversion into ions, since the measured substance is still intact protein. It also cannot establish that the retentate contains nothing else; many macromolecules and cellular structures may remain there. The experiment strengthens a solubility conclusion while preserving the limit of inference: it concerns protein behaviour in this extraction system, not the complete chemical identity of the retentate. Fresh reagent and renewed grinding reduce the chance that the first result arose merely from poor mixing. A repeated result under improved contact provides stronger evidence for persistent insolubility.
