C.

Crenation

When the external water potential is more negative than that of the cell, the cell lose water by osmosis. Such phenomenon in red blood cell is called crenation.

Flaccid cell in botany, is a cell in which the plasma membrane is not pressed tightly against the cell wall.

Bursting of cell occurs due to an osmotic imbalance that has caused excess water to diffuse into the cell.

Tonicity is a measure of the effective osmotic pressure gradient.

B.

1, 3, 7 and 9

Purines are 9-membered double rings with nitrogen at 1, 3, 7 and 9 positions. DNA has two types of purines namely Adenine (A) and Guanine (G).

A.

Anatropous ovule

Anatropous ovule is a completely inverted ovule turned back 180 degrees on its stalk. It is the most common type of ovule in angiosperms.

Campylotropous ovule refers to the body of the ovule that is curved or bent round so that the micropyle and chalaza so not lie in the same straight line.

Hemitropous ovule refers to the body of the ovule is placed transversely at right angles to the funicle. The micropyle and chalaza lie in one straight line.

D.

I, III

I and III reactions in which water is removed, but NAD⁺ is not reduced.

(I) Succinic acid $\to$Fumaric acid

       NAD+         $\to$ FADH⁺ + H₂O

(III) 2- Phosphoglycerate $\to$2- Phosphoenol pyruvic acid + H₂O

The II and IV reaction occur in the following way:

(II) Malic acid $\to$Oxaloacetic acid

NAD⁺ + H₂O + NADH

(IV) Pyruvic acid $\to$Acetyl Co- A

          NAD⁺       $\to$NAD⁺ + CO₂ + H₂

D.

Stenoteles

Stenoteles or penetrants are the largest type of nematocysts in Hydra. The thread tube is open at the end. When discharged, it release thread tube by which a poisnous fluid, hypotoxin is injected paralysing the prey.