NCERT Book Class 11 Biology Chapter 9 Biomolecules

104 BIOLOGY

C HAPTER 9
B IOMOLECULES
9.1 How to Analyse There is a wide diversity in living organisms in our biosphere. Now a
Chemical question that arises in our minds is: Are all living organisms made of the
Composition? same chemicals, i.e., elements and compounds? You have learnt in
9.2 Primary and chemistry how elemental analysis is performed. If we perform such an
Secondary analysis on a plant tissue, animal tissue or a microbial paste, we obtain a
Metabolites list of elements like carbon, hydrogen, oxygen and several others and
9.3 Biomacromolecules their respective content per unit mass of a living tissue. If the same analysis
9.4 Proteins
is performed on a piece of earth’s crust as an example of non-living matter,
we obtain a similar list. What are the differences between the two lists? In
9.5 Polysaccharides
absolute terms, no such differences could be made out. All the elements
9.6 Nucleic Acids present in a sample of earth’s crust are also present in a sample of living
9.7 Structure of tissue. However, a closer examination reveals that the relative abundance
Proteins of carbon and hydrogen with respect to other elements is higher in any
9.8 Enzymes living organism than in earth’s crust (Table 9.1).

9.1 HO W TO ANALYSE CHEMICAL COMPOSITION?
We can continue asking in the same way, what type of organic compounds
are found in living organisms? How does one go about finding the answer?
To get an answer, one has to perform a chemical analysis. We can take any
living tissue (a vegetable or a piece of liver, etc.) and grind it in trichloroacetic
acid (Cl3CCOOH) using a mortar and a pestle. We obtain a thick slurry. If
we were to strain this through a cheesecloth or cotton we would obtain two
fractions. One is called the filtrate or more technically, the acid-soluble
pool, and the second, the retentate or the acid-insoluble fraction. Scientists
have found thousands of organic compounds in the acid-soluble pool.