A.

Oxaloacetic acid

In C₄ Plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of CO₂ i.e. phosphoenol pyruvate (PEP) combines with CO₂ in the presence of PEP carboxylase or PEPcase to form oxaloacetic acid, which is the first stable carbon dioxide fixation product in C₄ pathway.

A.

Cycas

Roots in Cycas are of two types- normal and coralloid roots. Coralloid roots are irregular, negatively geotropic, dichotomously branched coral like roots which do not possess root hairs and root caps. Coralloid roots have a symbiotic association with blue-green algae like Nostoc and Anabaena species

C.

insulin

Cholesterol is a precursor of most steroid hormones like progesterone, estradiol, aldosterone, cortisol etc. Cholesterol forms vitamin D on UV exposure  and it also helps in forming bile salt

B.

A-(4), B-(1), C-(2), D-(3)

D.

Phaeophyceae only

Alginic acid(or algin or alginate) is an anionic polysccharide distributed widely in the cell walls of many brown algae (Phaeophyceae). It is a phycocolloid which is obtained commercially from Laminaria, Macrocystis, Nereocystis, Fucus, Sagrassum etc.