Enhancement of Food Production — BIOLOGY STD 12 Science — Question

Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs, what are microbes referred to as? How do the microbes fulfil their energy requirements?

Draw the diagram of a microsporangium and label its wall layers. Write briefly on the role of the endothecium.

In ecosystem the movement of nutrients is called cycling while the term 'flow' used for energy. Why?

In the following table of interspecific interactions, fill the blanks with (+) sign for beneficient interaction, (-) sign for detrimental and 0 for neutral interaction.

Species A	Species B	Name of Interaction
+		Mutualism
	-	Competition
	-	Predation
+		Parasitism
+		Commensalism
	0	Amensalism

With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain.

Describe the process of oogenesis in human female.

Trophoblast of blastocyst.

The cytological observations made in a number of insects led to the development of the concept of genetic/ chromosomal basis of sex-determination mechanism. Honey bee is an interesting example to study the mechanism of sex-determination. Study the schematic cross between the male and the female honey bees given below and answer the questions that follow:

1. Identify the cell divisions ‘A’ and ‘B’ that lead to gamete formation in female and male honey bees respectively.
2. Name the process ‘C’ that leads to the development of male honey bee (drone).

How do biofertilisers enrich the fertility of the soil?