8.2
All organisms have a role in an ecosystem In this topic, you will learn that:
• animals that only eat plants are called herbivores • animals that only eat other animals are called carnivores • animals that eat both plants and animals, like many humans, are called omnivores • decomposers obtain energy by breaking down dead organisms.
carnivore an animal that eats other animals omnivore an animal that eats both plants and animals
Insects, birds and bats pollinate plants
Plants and animals interact in their search for food. Bees and other insects, as well as some birds and bats, transfer pollen from plant to plant. While stopping at a flower for a sip of nectar, the animals or insects get dusted with pollen.
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decomposer an organism that gains nutrients by breaking down dead organisms into simpler nutrients
Figure 1 Some plants use bats to transfer pollen from one plant to another.
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When the animals or insects fly to another flower of the same or similar species, some of that pollen brushes off and the pollinated flowers are then able to produce seeds. Pollination is important not only for wild plants but also for crop plants. More than 70 per cent of plant species worldwide, including fruits and vegetables, are pollinated by animals, insects or birds.
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herbivore an animal that eats only plants
There are many different organisms in an ecosystem that are interdependent on one another. That is, they each have a role in maintaining the survival of one another. While plants convert the energy from the Sun into new leaves and stems, the herbivores that eat the plants use this stored energy to move and grow. Carnivores such as dogs eat the herbivores as part of their meat diet. Most humans eat both meat and plants, making them omnivores.
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Video 8.2 Ants and caterpillars
Some organisms decompose organic matter Locked inside all organisms is an enormous amount of nutrients. All organisms in a food web end up passing these nutrients and energy on to decomposers. Decomposers – such as bacteria, fungi and invertebrates (slugs and worms) – get the food they need by feeding on dead things. This prevents the dead organisms from piling up. Instead, the nutrients stored in the dead organisms are used for energy by the decomposers. When another organism eats a decomposer, the nutrients once again become part of the food chain. The nutrients that pass through the decomposers as waste end up in the soil in simpler forms. Plant roots can then absorb the nutrients and the cycle starts again. Imagine what life would be like without decomposers!
Figure 2 Insects, such as bees, are important pollinators of plants. Figure 3 Decomposers recycle important nutrients in an ecosystem.
OXFORD UNIVERSITY PRESS OXFORD SCIENCE 7: VICTORIAN CURRICULUM No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means.
