Zoology MCQs for NEET — Practice Questions with Answers

(b) The major portion of the dry weight plants comprises carbon, nitrogen, oxygen, hydrogen.

(b) is incorrect with respect to enzyme action because addition of a lot of succinate reverse the inhibition of succinic dehydrogenase by malonate. If substrate succinate concentration is increased, it will remove malonate from its active site and thus succinate reverses the inhibition of dehydrogenase.

Inhibition of succinic dehydrogenase by malonate is an example of competitive inhibition.Competitive inhibition occurs when enzyme and inhibitor both have more or less similar structure and are present in higher concentration. Thus, both enzyme and inhibitor for compete for the active site of enzyme resulting in the decrease of the enzymatic activity. 

Two free ribonucleotide units are linked together by a phosphodiester bond. This bond is formed by the condensation reaction between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of another nucleotide, with the elimination of a water molecule.

(b) Bacteria are prokaryotic organisms. They possess a double stranded DNA molecule as it's genetic material. Polyamines like spermidine and cadaverine (instead of histones) are associated with DNA packaging in bacteria.

(a) Starch and glycogen are storage polysaccharide and cellulose is a structural polysaccharide. Starch has straight chain of 1,4 $\mathrm{\alpha }$-D pyranose glucose units and side chains or amylopectin part of 2-200 thousand glucose units that are attached to straight chains by 1,6 $\mathrm{\alpha }$-D glycosidic bonds.

Glycogen is a long chain branched polymer of 5-300 thousand glucose units, straight chain linked by $\mathrm{\alpha }$-D 1-4 glycosidic bonds and side chains through $\mathrm{\alpha }$-D 1$\to$6 glycosidic bonds.  

Cellulose, a fibrous polysaccharide has a linear chain of 6-10 thousand 1$\to$4 linked $\mathrm{\beta }$-pyranose glucose chain.

Km is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax.

(b) Cellulose is fibrous polysaccharide that forms the structural component of plant cell wall, some primitive fungi and tunic of ascidians. Cellulose is the most abundant organic substance on earth. It can be digested by only a few microbes present in the gut of ruminants and white ants.

Answer 3. Read page 144, XI NCERT

Answer 2. Read page 144, XI NCERT

Answer 3. Reas page 150, XI NCERT