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Food

Webs:

·

Autotrophs produce food

·

Organisms classified into three

groups producers, consumers and decomposers

·

Producers:

- Convert simple inorganic chemicals to complex organic molecules

(food)

- Use solar radiation as an energy source

- Productivity: amount of energy fixed in organic compounds; measured

by increase of biomass per unit time.

- Temperature influences the rate at which chemical reactions take

place

- Production of glucose by plants and its conversion into other

organic compounds is influenced by season, latitude and altitude

- Productivity is also influenced by other factors such as soil

mineral availability and water.

- The total amount of organic matter in an ecosystem, which is

produced as a result of photosynthesis, is termed gross primary production,

whereas the amount of this energy available for herbivores is termed net

primary production

·

Consumers:

- Use food produced by other organisms as their energy source

- First order consumers are herbivores

- Second order are carnivores that eat herbivores

- Third – and high-order consumers are carnivores that eat other

carnivores

- Latter carnivores may be either predators (killing other animals for

food), parasites or scavengers (eating animals they have not themselves

killed.)

- Omnivore may occupy different levels simultaneously

·

Decomposers:

- Simple life forms (bacteria, fungi and some protozoans)

- Have external digestion and break down the dead bodies and waste

products of other living things

- Convert complex molecules into simple inorganic chemicals which are released

into the environment and can be reused

·

Trophic

Levels of Organisms:

·

Trophic feeding levels describe

the relative positions of producers and consumers in a food chain

·

Each organism in the series

feeds on, and therefore derives energy from, the preceding one.

·

Very rarely more than six links

in any food chain; usually only three or four

·

Much energy lost to the

environment in the form of heat at each level of the food chain

·

Estimated that energy transfer

between any two levels of the food chain is only 5-20 percent efficient

·

Closer a consumer is to the

producer, the more efficient is the energy transfer.

·

Levels:

1. Sun – energy transfer

Ø First energy/trophic level - Energy transfer 0.2% efficient

2. Producer – plants

Ø Second energy/trophic level - Energy transfer 5-20% efficient

3. Consumer 1 – herbivores

Ø Third energy/trophic level - Energy transfer 5-20% efficient

4. Consumer 2 – carnivore that eat herbivores

Ø Fourth energy/trophic level - Energy transfer 5-20% efficient

5. Consumer 3 – carnivore eats carnivore

Ø Fifth energy/trophic level - Energy transfer 5-20% efficient