Q5. The answer is because there is a large decrease in the amount of energy or biomass as you move from one trophic level up to the next.

Organisms from the higher trophic levels consume organisms from the lower trophic levels. During this process, energy is lost as metabolic heat. Primary producers on the first trophic level contain the greatest amount of energy originally from the sunlight. The next trophic level belongs to primary consumers that consume primary producers which result in less energy. Similarly, secondary consumers eat primary consumers, and energy is lost again. The highest trophic level is tertiary consumers and they contain the least amount of energy.

Q6. The answer is Elements continuously cycle between the physical environment and living organisms.

Biogeochemical
cycles are pathways by which chemical substances move through biosphere and
geosphere (lithosphere), as well as atmosphere and hydrosphere. In these cycles
elements are recycled, they are not lost. They continuously cycle between the physical environment and living organisms.

Q7. The answer is grass, grasshopper, snake, hawk.

Figure 3-4 is not attached, however, the logic food web among all choices wood be: grass, grasshopper, snake, hawk.

Grass belong to the producents. Grasshopper is a primary consumer and it eats producent grass. Snake, as a secondary consumer, eats the primary consumer grasshopper. A terciary consumer hawk eats the secondary consumer snake.