How to Analyse Chemical Composition?
Living organisms and the non-living world share the same basic inventory of elements — but the proportions tell a different story. This quiz tests your understanding of elemental analysis applied to plant, animal and microbial tissue, the comparison with the earth’s crust, and the laboratory procedure of grinding tissue in trichloroacetic acid.
What you will practise
- Interpreting the results of elemental analysis on living vs non-living matter
- Identifying which elements show higher relative abundance in living organisms
- Recalling the role of trichloroacetic acid, mortar and pestle
- Distinguishing the filtrate (acid-soluble pool) from the retentate (acid-insoluble fraction)
Work carefully — several questions test the reasoning behind the procedure, not just the names.
Q1. When elemental analysis is performed on a plant tissue, an animal tissue or a microbial paste, what is obtained?
Elemental analysis of living tissue yields a list of elements such as carbon, hydrogen, oxygen and several others, together with their respective content per unit mass of living tissue.
Q2. If the same elemental analysis is performed on a piece of earth's crust, the list of elements obtained is:
The lesson states that analysis of earth's crust as an example of non-living matter gives a similar list of elements to that from living tissue.
Q3. Comparing the two elemental lists in absolute terms, what conclusion does the lesson draw?
In absolute terms no differences could be made out: all the elements present in a sample of earth's crust are also present in a sample of living tissue.
Q4. Which statement correctly describes the relationship between the elements of earth's crust and those of living tissue?
The lesson states clearly that all the elements present in a sample of earth's crust are also present in a sample of living tissue.
Q5. On closer examination, which difference between living organisms and earth's crust is revealed?
A closer examination reveals that the relative abundance of carbon and hydrogen with respect to other elements is higher in any living organism than in earth's crust (Table 9.1).
Q6. According to Table 9.1 comparison, the key distinction between living matter and non-living matter lies mainly in:
The difference is one of proportion, not of kind: the same elements occur in both, but carbon and hydrogen are relatively more abundant in living organisms.
Q7. Which pair of elements is specifically named as having higher relative abundance in living organisms than in earth's crust?
The lesson specifically states that the relative abundance of carbon and hydrogen with respect to other elements is higher in any living organism than in earth's crust.
Q8. To begin a chemical analysis of living tissue, the tissue is ground in which substance?
The lesson states that living tissue is ground in trichloroacetic acid, ##\ce{Cl3CCOOH}##.
Q9. Which chemical formula correctly represents trichloroacetic acid as given in the lesson?
The lesson writes trichloroacetic acid as ##\ce{Cl3CCOOH}##, i.e. three chlorine atoms on the carbon bearing the carboxyl group.
Q10. Which apparatus is used to grind the living tissue in trichloroacetic acid?
The lesson specifies grinding the tissue in trichloroacetic acid using a mortar and a pestle, producing a thick slurry.
Q11. After grinding the tissue in trichloroacetic acid, what is obtained before straining?
Grinding the tissue in trichloroacetic acid with a mortar and pestle gives a thick slurry, which is then strained.
Q12. The thick slurry is strained through which material to obtain two fractions?
The lesson states that if the slurry is strained through a cheesecloth or cotton, two fractions are obtained.
Q13. The filtrate obtained after straining the slurry is technically called the:
The filtrate is more technically called the acid-soluble pool; the retentate is the acid-insoluble fraction.
Q14. The retentate obtained after straining the slurry is known as the:
The retentate is called the acid-insoluble fraction, while the filtrate is the acid-soluble pool.
Q15. What have scientists found in the acid-soluble pool?
The lesson states that scientists have found thousands of organic compounds in the acid-soluble pool.