Unit 1 Food Chains and Food Webs

What is the source of energy for all living things?

Sun

What do the arrows in a food chain show?

• Direction of energy flow

• What each organism feeds on or consumes

What is the order in a food chain?

Producer, primary consumer, secondary consumer, tertiary consumer

What is a trophic level?

The feeding stage or level e.g producers are trophic level 1

Why are plants called producers?

• They can make their own food through P/S

• They provide food and energy for the rest of the food chain

What is a pyramid of numbers?

A diagram showing the number of organisms at each trophic level

What is a pyramid of biomass?

A diagram showing the mass of living tissue or organisms at each trophic level

Give one advantage and one disadvantage of pyramid of numbers

Adv: easy to collect data for

Disadv: they do not take into account the size of organisms

Give one advantage and one disadvantage of pyramids of biomass

Adv: they take into account the size of the organisms

Disadv: difficult to measure, may involve killing organisms and may damage habitat

Is energy recycled?

Energy flows between organisms

No - continuously supplied by the sun

Give egs of how energy is lost as it passes from sun to producers

• Reflected by leaves

• Passes through leaves (misses chloroplasts)

• Absorbed by clouds

• Doesn’t hit the plants

Give egs of how energy is lost as it passes from producers to consumers (food chain)

• Energy is lost to resp/heat

• Egestion (energy lost in faeces) - these are inedible parts e.g most consumers do not eat hair or bone

• Excretion

How do we calculate the % of energy available at any particular point in a food chain?

Energy gained by trophic level ÷ energy in previous trophic level

×100

Why are food chains rarely mire than 3 or 4 trophic levels?

• Short food chains are more efficient as there are fewer stages at which energy may be lost

• May not be enough energy left to support another trophic level

Explain in terms of energy, why it would be better for humans to eat a crop like barley, wheat, rather than meat

• Human would be acting as a primary consumer rather than a secondary consumer

• A shorter food chain has fewer steps and therefore less energy losses between trophic levels

• More energy available to the humans

• More efficient