Question

Sporopollenin is chemically
(a)Homopolysaccharide
(b)Heteropolysaccharide
(c)Protein
(d)Fatty substance

Answer 1

Sporopollenin is the most resistant known biological material that is found in the exine of the pollen grains. Sporopollenin is resistant to chemical and microbial decomposition. The pollens are well preserved and conserved due to this during fossilization.

Complete answer:
The sporopollenin is a major component of the tough outer (exine) walls of plant spores and pollen grains, it can be said as one of the most chemically inert biological polymers and also chemically it is very stable and is usually well preserved in soils and sediments. The exine layer provides useful information to palynologists about plant and fungal populations in the past as it is often intricately sculptured in species-specific patterns, allowing material recovered from lake sediments and also in the field of paleoclimatology and also found in the cell walls of several taxa of the green alga, including Phycopeltis (an ulvophyceae) and Chlorella. Due to the unusual chemical stability and resistance to degradation by enzymes and strong chemical reagent, the chemical composition of sporopollenin has long been elusive, and it’s analyses have revealed that it is a mixture of biopolymers, containing mainly long-chain fatty acids, phenylpropanoids, phenolics, and traces of carotenoids. Sporopollenin likely derives from several precursors that are chemically cross-linked to form a rigid structure

Additional information:

1. It has been determined via thioacidolysis degradation and solid-state NMR the molecular structure of pine sporopollenin by the researchers at MIT in 2019, finding it primarily composed of polyvinyl alcohol units alongside other aliphatic monomers, all crosslinked through a series of acetal linkages.
2. Sporopollenin has been found chemically intact in sedimentary rocks some 500 million years old and it is a highly cross-linked polymer composed of carbon, hydrogen, and oxygen that is extraordinarily stable.
3. To degrade the sporopollenin of some Brassicaceae family members catalase enzymes (all at high levels at the pollination interface) to be experimentally sufficient.

So, the correct answer is, ‘Fatty substances.’

Note: It has been observed that sporopollenin covered all land plant spores whereas algae only have heavy-walled zygotes that germinate via meiosis, hence to land plants, sporopollenin coated spores are an innovation specific.