Ecosystems, Year 8: more practice

It will fall

提示Follow the change along the chain, one step at a time.

为什么Fewer 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

提示Think about real animals' diets.

为什么A web shows all the feeding links, so you can predict what happens if one species disappears.

The number of organisms at that level

提示It is a count, not a mass or energy.

为什么Each bar stands for one feeding level. A wider bar means there are more individual organisms at that level.

500

提示Find 10% of the amount.

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

They make their own food by photosynthesis

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

为什么Producers make glucose from carbon dioxide and water using light. All the other organisms in the chain depend on them.

Oxygen

提示Animals need this gas to breathe.

为什么Photosynthesis makes glucose and oxygen. Some of the oxygen is used by the plant and the rest is released into the air.

Bacteria and fungi

提示One group includes moulds and mushrooms.

为什么Both 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

提示Think about conditions the microbes like.

为什么Warmth and moisture help bacteria and fungi grow and reproduce, so they break down material more quickly.

800

提示Multiply the average per square by the number of squares that fit.

为什么Daisies per m² × area of the field = 4 × 200 = 800.

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

提示Think about luck.

为什么A single square might fall on an unusually crowded or empty patch. Averaging many random squares evens that out.