6.3 Energy flows through an ecosystem

Learning intentions

By the end of this topic, you will be able to: • define the terms

‘herbivore’,

‘carnivore’ and omnivore’ • describe how energy flows through an ecosystem.

Figure 1 Plants use energy from the Sun to grow and repair.

photosynthesis a chemical process used by plants to make glucose and oxygen from carbon dioxide, sunlight and water

omnivore an animal that eats both plants and animals

herbivore an animal that eats only plants

carnivore an animal that eats other animals

Key ideas

• 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 humans, are called omnivores. • Microorganisms obtain energy by breaking down dead organisms.

Energy transfer

All food chains show the transfer of energy from the organism that is eaten to the consumer. This transfer of energy is shown by the direction of the arrow in the food chain or web. The source of energy in most food webs is light energy from the sun. Even in caves, where there is no sunlight, there may be energy from dead plants and animals, which originally obtained their energy from the Sun. An exception is chemosynthetic bacteria on the ocean oor and in the craters of volcanoes – these bacteria trap the energy from chemicals and chemical reactions occurring under the Earth’s crust. What is photosynthesis?

Top consumer Secondary consumersDRAFT Living things need energy to grow and repair, to defend themselves, and to move around. Plants, some algae and some bacteria are able to transform the light energy from the sun into chemical energy through a process called photosynthesis . In this process, the plant takes in water from the roots and carbon dioxide through their leaves. The water is transported to the leaves, where it is combined with the carbon dioxide to make glucose (a sugar) and oxygen. This can be shown by a word equation for photosynthesis: carbon dioxide + water → glucose + oxygen Sugars like glucose provide chemical energy that plants can use to make new leaves and stems. Animals that eat plants are called rst order consumers or herbivores. The chemical energy in the plant is used by the animal to move and grow. Some of the energy is stored in the muscles and fat of the animal. When a second-order consumer or carnivore such as a dog eats the herbivore, it is able to use the energy in the fat and muscle to keep hunting. Humans eat both meat and plants, making them omnivores . Every time the plants and animals grow and move, the chemical energy is transferred to movement energy.

Primary consumers

Producers

Sun

Figure 2 An example of the movement of energy through an ecosystem, where each green arrow represents the transfer of energy

Some microorganisms decompose organic matter

simpler particles. Plant roots can then absorb the nutrients and the cycle starts again. Imagine what life would be like without decomposers!

As well as energy, 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 breaks down the dead organisms and prevents them from piling up. Instead, the chemical energy in the dead organism’s muscle and fat are used for energy by the decomposers. When another organism eats a decomposer, the particles (atoms) that make up the nutrients once again become part of the food chain. The nutrients that pass through Wetlands and forests help the decomposers as waste end up in the soil as clean water If you poured dirty water through a lter, you would expect cleaner water to come out. A similar thing happens in nature when water passes through a forest or wetland ecosystem. By slowing the ow of water, the plants and bacteria trap some of the pollutants and sediments. But plants are not the only living things that clean water. Aquatic animals, such as freshwater clams, pump water through their Figure 2 Decomposers recycle important bodies to lter out food for themselves and, in nutrients in an ecosystem. so doing, clean the water they live in.

Figure 3 Mushrooms (fungi) are decomposers. They get the nutrients they need by feeding on dead things, such as rotting logs. Figure 4 Forested water catchment areas are vital for keeping Queensland’s water supplies clean.

Retrieve 1 Identify the term used to describe animals that eat both meat and plants. 2 Identify the following as either an input or an output of photosynthesis. a carbon dioxide b glucose c water Comprehend 3 Describe one consequence that may occur if decomposers did not exist. Analyse 4 Compare the similarities between the following terms: producer, rst order consumer, second-order consumer, herbivore, carnivore, photosynthesising organism.

6.3 Check your learning Apply 5 We get the energy we need by eating other living organisms. Determine the source of energy for the following organisms. a Plants b Herbivores c Decomposers 6 ‘Photosynthesis is the most important metabolic process on Earth.’ Evaluate the above statement by: a describing why photosynthesis is important in an ecosystem b describing what would happen if photosynthesis was not able to occur c deciding whether the statement is correct.

decomposer an organism that gains nutrients by breaking down dead organisms into simpler nutrients

DRAFT

Quiz me Complete the Quiz me to check how well you’ve mastered the learning intentions and to be assigned a worksheet at your level.