Ecosystems, Year 8: more practice

It will fall

HintFollow the change along the chain, one step at a time.

The whyFewer owls means fewer mice are eaten, so mouse numbers rise and more seeds are eaten.

Most organisms eat more than one thing and are eaten by more than one

HintThink about real animals' diets.

The whyA web shows all the feeding links, so you can predict what happens if one species disappears.

The number of organisms at that level

HintIt is a count, not a mass or energy.

The whyEach bar stands for one feeding level. A wider bar means there are more individual organisms at that level.

500

HintFind 10% of the amount.

The why10% of 5000 is 5000 ÷ 10 = 500 kJ. The rest is lost as heat, movement and waste.

They make their own food by photosynthesis

HintWhere does a plant's energy for growing come from, if it never eats?

The whyProducers make glucose from carbon dioxide and water using light. All the other organisms in the chain depend on them.

Oxygen

HintAnimals need this gas to breathe.

The whyPhotosynthesis makes glucose and oxygen. Some of the oxygen is used by the plant and the rest is released into the air.

Bacteria and fungi

HintOne group includes moulds and mushrooms.

The whyBoth feed on dead plants and animals. They release nutrients back into the soil for plants to use.

Decomposers work faster when it is warm and moist

HintThink about conditions the microbes like.

The whyWarmth and moisture help bacteria and fungi grow and reproduce, so they break down material more quickly.

800

HintMultiply the average per square by the number of squares that fit.

The whyDaisies per m² × area of the field = 4 × 200 = 800.

One sample might not be typical, so more samples give a more reliable estimate

HintThink about luck.

The whyA single square might fall on an unusually crowded or empty patch. Averaging many random squares evens that out.