Energy in an Ecosystem

8.2 A Local Ecosystem

In this presentation, we will be covering the following:

We will be learning about:

8.2.1 The distribution, diversity and numbers of plants and animals found in ecosystems are determined by biotic and abiotic factors.

Energy and MatterWork is done when energy is released. There are many different types of energy such as heat, light, kinetic (energy of motion) and potential (stored) energy. Energy cannot be created and it can not be destroyed. However, energy can be converted into other types of energy.

Energy is important to organisms. Food provides a source of chemical energy. This chemical energy can be converted into other forms of energy useful to the organism such as heat energy and kinetic energy (for movement.)

Matter is the word we use to refer to the stuff from which things are made. Matter has mass. Within food webs, matter (food) moves from one organism to another. We can also measure biomass, the mass of living matter. For example, the biomass of plants in a particular area is generally much higher than the biomass of herbivores that feed upon the plants.

Energy and Matter flow in an EcosystemTASK 1:

Before we begin, define the following terms in your workbook:

- Autotroph

- Heterotroph

- Primary producer

- Secondary producer

- Herbivore

- Carnivore

- Omnivore

- Decomposer

- Biomass

- Trophic

Food ChainsThink about the food you ate last night. All of the food we consume comes from other living things, like plants (carrots, celery) and other animals (cows, sheep). The food we consume (eat) can be placed into two different categories - producers and consumers.!Producers are living things that produce their own food through the process of photosynthesis - they use the energy of the sun and carbon dioxide in the air to make their own energy. Plants are producers.List all the producers you ate during dinner last night.!!Consumers are living things that cannot make their own food - they must consume (eat) other plants and animals to gain energy. Cats are consumers because they eat fish to get their energy.List all the consumers you ate during dinner last night.!!Decomposers are living things that get their energy from decaying matter, such as dead plants and animals. They break down dead things, and release nutrients back into the soil, which can then be used by plants.Fungi are a type of decomposer. Can you think of a decomposer you might have eaten?!!!

Food ChainsTASK 2:

Open the ziplock bag you have been given. Remove all of the pictures of living things (leave the arrows behind).

Look at the pictures of living things. decide which things are

- producers

- consumers

- decomposers

!Draw a table into you workbook and use it to record your results (like the table below).

Every living thing needs energy in order to survive. Every time a living thing (like a plant or animal) moves or grows, it requires energy. Animals get their energy from the food they eat. Plants get their energy through the process of photosynthesis (using the Sun’s energy and carbon dioxide). Energy is essential for living things to grow and develop.!A food chain shows how each living thing gets food, and how energy is passed from creature to creature. Food chains begin with plant life (producers) and end with animal life. Some animals eat plants, and some animals eat other animals.!A simple food chain is shown below. Note the direction of the arrows - these show where the energy (food) is being transferred to.

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Food Chains

Food ChainsTASK 3:

Read the information below to construct a food chain. You can use the images and arrows in the ziplock bag to help you.!

Rabbits are herbivores - they eat lots of grass to get their energy. Grass is a producer as it gets its energy through the process of photosynthesis - it uses the Sun’s energy to make its own food. When rabbits eat the grass, they absorb energy from the grass. Sometimes, foxes hunt rabbits and eat them for food too

!Draw a simple food chain in your workbook, based on the paragraph you just read.!Referring to your food chain, answer the following questions (in your workbook)1. Who are the producers?2. Who are the consumers?3. What is a predator? Who is the predator in your food chain?4. What is prey? Who is they prey in your food chain?

Food WebsFood chains are simple ways of showing energy relationships between living things. However, Food relationships can be much more complex. We combine food chains to create food webs.!Look at the food chains below. They show the food relationships occurring in a garden.

To get a more complete picture of the feeding relationships in the garden, these food chains can be combined to give a food web. For example, you can see from the food web below that frogs eat beetles as well as bugs, but lizards eat bugs only.

Food WebsTASK 4:

Collect the second ziplock bag from your teacher. Read the information below to construct a food web.!

The Great Barrier Reef Food WebMarine algae is a producer, who uses the Sun’s energy to produce its own food. Plankton, krill and Giant clams all feed on the marine algae. Krill is consumed by Sea Horses, Whale sharks and Box jellyfish. Box Jellyfish also consume Giant clams and Molluscs. Molluscs get eaten by clown fish, which are then eaten by Sea Eagles. Sea turtles love eating plankton and Box Jellyfish. Dugongs enjoy eating clown fish. Tiger sharks eat Sea eagles and Clown fish. The Humpback Whale also eats plankton and krill.

!HINT: use a spare sheet of A3 paper when planning your food web, and draw your energy arrows in pencil, so you can easily rub them out if you make an error.!Once you are happy with your Food Web, draw it in your workbook. Check your answer with your teacher.

Food WebsTASK 4 continued:

Consider the food web you just constructed. Use your web to answer the questions below (write your answers in your workbook).!1. Who are the producers?2. Who are the consumers?3. Who are the predators? 4. Who are the prey?5. Who are the herbivores?6. Who are the carnivores?7. Who are the first order consumers?8. Who are the second order consumers?9. Imagine all of the molluscs contract a disease and died. What effect could this have on the food

web?10. Can an organism be both a first order consumer and a second order consumer?!

Biomass Pyramids

Biomass is the total living mass of organisms. Biomass can be used to refer to the total mass of a species, or group of organisms in an area. Ecologists can determine the total biomass of all organisms in an area or the biomass of a single species.

If you estimated the biomass of herbivores, carnivores and primary producers in a community, a pyramid like the one below could be drawn.

This biomass pyramid is based on qualitative data. It simply shows that the total living mass (biomass) of top-order consumers is less than that of carnivores. The biomass of carnivores is less than the biomass of herbivores. The biomass of herbivores is less than the biomass of primary producers upon which they feed.

If a quantitative study was made a biomass pyramid could provide more detail:

What information can you obtain from the above energy pyramid?

Energy pyramids!Only about 10% of all the energy stored by the primary producers is passed on to the herbivores. Likewise, only 10% of total herbivore energy is passed to the carnivores, and only 10% of total carnivore energy reaches the top-order consumers.Let’s look at this in a different way. Of all the energy available in primary producers:

10% of this reaches herbivores 1% reaches carnivores 0.1% reaches top-order consumers.

The figure below shows reduction of energy passed along the food chain.

Number of organisms or biomassEnergy transfer

Only 10% is passed on

to the next trophic

level

Need a lot of producers to

support only a few top

consumers

Think about the producers and herbivores. Producers use much of the energy stored in their cells in respiration and growth. This energy used by the producers cannot be passed on to herbivores.

The herbivores eat the producers, but they do not eat all the producers. Some producers remain uneaten and will eventually die and decay.

The energy used by the producers and the uneaten individuals accounts for about 90% of all the energy available in producer cells. This is why only 10% of the total energy is passed on to herbivores.

A careful quantitative study of a community could produce an energy pyramid such as this:

Trophic levelsWhen referring to organisms as primary producers, herbivores, carnivores and top-order consumers or producers, herbivores, first order carnivores and second order carnivores, we are really dividing living things into trophic levels.

A trophic level is the relative position of an organism in a food chain. (Trophic comes from the Greek word trophos meaning ‘food’.)

Plants which are able to convert light energy from the sun into chemical energy are at the bottom trophic level of all food chains because they support all of the other trophic levels. All these other trophic levels obtain energy by obtaining chemicals from the bodies of lower trophic levels.

The energy flows in one direction only from producers to herbivores to carnivores.

The energy is not recycled. No energy is returned to the sun. However, energy from the sun can be trapped and stored, unused in fossil fuels such as coal and oil, for hundreds of millions of years.

TASK 5:

1. Construct and annotate a biomass pyramid in your workbook.

2. You are about to eat a buffet lunch that has a variety of food including salads, chicken, beef, seafood and dessert. Make a list of these foods and identify the possible trophic levels of each.

The sun is essential to life on Earth. The sun provides the light energy that is converted into chemical energy for use by living things in the process of photosynthesis. As we will see in another module, photosynthesis:

• has been important in the development of our current atmosphere

• is a factor in the carbon/oxygen cycle.

Photosynthesis is important because it is the main process by which raw materials (abiotic factors) can be made into high-energy compounds that can provide a food source for organisms. Light energy is converted into chemical energy during photosynthesis. The low-energy compounds water and carbon dioxide are changed into high-energy sugars in the process. The word equation for photosynthesis is given below. The equation should be familiar to you already since you had the opportunity to study it earlier in this module.

Primary producers start each food chain. It is the energy from the sugars created in photosynthesis that is passed along food chains. What is the ultimate source of the energy of sugars made by photosynthesis?

Photosynthesis

PhotosynthesisTASK 6:

In your workbook, answer the following questions

1. What is the source of energy in almost all ecosystems?

2. How does this energy move through and ecosystem?

3. What is photosynthesis?

4. What is the role of photosynthesis in an ecosystem?

5. Explain why plants are called “autotrophs”.

Respiration is the process by which energy is released from food. It is a chemical process that occurs in all cells of all living things. When respiration stops, life stops. A word equation for the process of respiration is given below.!!Mainly chemical energy and heat energy are released in this process. Food is a high-energy reactant. Carbon dioxide and water are two low–energy products.

Respiration is more complex than the word equation above indicates. The process does not release energy in a single step. Respiration is a reaction with many steps. Each step releases a little energy. One of the advantages of this is that the rate of energy release can be better controlled to prevent overheating of cells.

Respiration is important in ecosystems because of the by-products, carbon dioxide and water. The global rate of carbon dioxide production must be equal to the global rate of oxygen release by photosynthesis. If an imbalance occurs the levels of oxygen and carbon dioxide in the atmosphere will change, with potentially disastrous consequences for ecosystems.

Respiration

RespirationTASK 7:

In your workbook, answer the following questions

1. Write a general word equation for the process of respiration.

2. Why is this equation known as a general or overall equation?

3. Why is the process of respiration important to plants and animals?

4. What is the difference between normal breathing “respiration” and cellular respiration?

5. Distinguish between anaerobic and aerobic respiration.

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