IGCSE Biology Paper-2: Specimen Questions with Answers 188 - 189 of 203

The diagram shows a food web.

Which arrow does not show the direction of energy flow?

Answer

c.

Explanation

• The energy flow in an ecosystem is from the producer level to the consumer level. At each trophic level, 80 to 90 % of energy is lost. Hence, the amount of energy decreases from the producer level to the consumer level that is unidirectional flow.
• Pyramid of energy is always upright because during the flow of energy from one trophic level to the next one, there always occurs a loss of energy.
• 10 per cent Law: Only 10 % of the total energy stored in a trophic level is transferred to the next trophic level of a food chain. Lindeman (1942) gave this law.

The diagram shows a cross-section of a flower.

Where does pollen formation takes place take place?

Answer

a.

Explanation

Stamen

• Stamen is the male reproductive unit of angiosperms.
• Stamen consists of anther, connective and fi lament.
• The long and slender stalk called as fi lament and the terminal structure is known as anther.
• Typically, angiospermic anther is bilobed which is connected by connective and dithecous i.e.. , each lobe has two theca. The bilobed structure of the anther is tetrasporangiate (four sporangia) . In transverse section, it appears as four sided tetragonal structure consisting of two microsporangia in each lobe.
• Microsporangia develop into pollen sac filled with pollen grains.
• The number, form, and length of stamen vary from species to species.