Movement of energy and matter in ecosystemsCHAPTER 21

Input from sunlightFood chains and food webs demonstrate that all consumers depend ultimately on producer organisms – photosynthetic plants and algae. Producers convert sunlight energy into chemical energy which is then stored in the plants cells and tissues. Herbivores and consumers get their energy first, second, third and even fourth hand. The flow of energy along a food chain is therefore a fundamental process in an ecosystem.

Primary productivity:

Primary productivity is the rate at which producers convert light energy to chemical energy as new cell growth. In photosynthetic plants some of the energy is used up in cellular respiration. What is left accumulates in the plants tissues .

Biomass is an estimate of the amount of matter in a given

population of organisms. It is the amount of material

resulting from primary productivity that is available for eating

in an ecosystem.

Biomass for different trophic levels is compared in a biomass

pyramid. A biomass pyramid shows how the quantity of

matter in living things changes along a food chain.

Biomass

Biomass Pyramid

At each level in the pyramid biomass is smaller than in the trophic level below. At each level biomass is lost.

An energy pyramid shows the total energy in trophic

levels and how that energy is lost along a food chain.

Energy pyramid

The Carbon Cycle

The Carbon Cycle

Carbon dioxide added to the air by respiration of animals, plants and microorganisms and by the combustion of fossil fuels.

Photosynthesis takes place on such a large scale that it re-uses, on a daily basis, as much carbon dioxide that is released.

The Nitrogen Cycle

The Nitrogen CycleNitrogen is needed to make amino acids, proteins and

nucleic acids.

Animals and plants are unable to use nitrogen gas (N2), but instead plants take in nitrogen via nitrates in solution through their roots.

This nitrogen is transferred through the food chain and any bodies must be decomposed in order to release these minerals back into the soil!

The Phosphorus Cycle

The phosphorus cycle is long and slow, but it is an important part of the environment. It helps plants grow, and is used by farmers to fertilize them. When animals eat the plants, they absorb phosphates. Phosphates are used for DNA backbones in animals.When the animals die, their body decays and the phosphorus is absorbed into the soil, where it re-enters plants. What isn’t absorbed by plants ends up in rock, and may stay there for millions of years, slowly being released as the rocks weather.

The Phosphorus Cycle

The Water Cycle

The Water Cycle• During part of the water cycle, the sun heats up liquid water

and changes it to a gas by the process of evaporation. Water that evaporates from Earth’s oceans, lakes, rivers, and moist soil rises up into the atmosphere.• The process of evaporation from plants is called transpiration. (In other words, it’s like plants sweating.)

• As water (in the form of gas) rises higher in the atmosphere, it starts to cool and become a liquid again. This process is called condensation. When a large amount of water vapor condenses, it results in the formation of clouds.

• When the water in the clouds gets too heavy, the water falls back to the earth. This is called precipitation.

• When rain falls on the land, some of the water is absorbed into the ground forming pockets of water called groundwater. Most groundwater eventually returns to the ocean. Other precipitation runs directly into streams or rivers. Water that collects in rivers, streams, and oceans is called runoff.