Energy transfers Starter: Write a list of the food you have eaten so far today. Where does all of the energy in your food originally come from?

The Sun

Learning outcomes State that the energy in food originated from the sun. Describe how energy is lost at every stage of a food chain. Explain why glucose made in photosynthesis is stored as starch

Key words Energy Food chain Respiration Movement Waste Urea Faeces Efficiency Photosynthesis Chlorophyll Chloroplast Chemical energy Glucose Starch

Specification a) Radiation from the Sun is the source of energy for most communities of living organisms. Green plants and algae absorb a small amount of the light that reaches them. The transfer from light energy to chemical energy occurs during photosynthesis. This energy is stored in the substances that make up the cells of the plants.

Specification 2 c) The amounts of material and energy contained in the biomass of organisms is reduced at each successive stage in a food chain because: – some materials and energy are always lost in the organisms’ waste materials – respiration supplies all the energy needs for living processes, including movement. Much of this energy is eventually transferred to the surroundings.

All food chains begin with energy from the sun. So you are (indirectly) solar powered! Solar powered people

The sun is not usually included in food chains so the previous diagram becomes: Food chains

Copy the diagram above and answer the following questions: 1.Which direction are the arrows pointing? 2.What is this showing about how energy is transferred in this food chain? 3.What are the arrows that split off from the food chain showing about the energy transfer at each stage? Food chain questions

Answers 1.The arrows are pointing right. 2.This shows that energy is passed along the food chain. 3.The arrows that split off from the food chain show that energy is lost at every stage of the food chain.

Why is energy lost at every stage of the food chain?

Cows are 6% efficient All animals lose energy in: 1.Respiration (which includes movement and keeping warm in warm blooded animals) 2.Excretion of urea in urine and undigested food in faeces Energy transfer efficiency diagrams

energy used for growth (output) efficiency = energy supplied (input) 100 – 60 – 34 efficiency = 100 Cows are 6% efficient Q: What is the efficiency of farming cows for food? Energy transfer efficiency diagrams = 6 / 100 = 0.06 = 6% A:

Wasted energy What processes do you think result in wasted energy? Not all food can be digested so energy is left in faeces or as urea in urine (waste) Some energy is used for respiration and movement Some energy is used to keep animals warm.

Plants are 5% efficient Q: What is the efficiency of this plant? A: 5% (of the light energy is converted into chemical energy in glucose) Efficiency of photosynthesis 5% of the light is converted into glucose 95% of the light is reflected.

Why are plant leaves only 5% efficient?

Q: Why are plant leaves only 5% efficient? A: Approx. 95% of the energy hitting the plant is reflected. The rest of the wasted energy in plants: – heats up leaves – is absorbed by non-photosynthetic parts – is transmitted through leaves

How does the plant convert light energy to chemical energy?

Q: How does the plant convert light energy to chemical energy? A: Through the process of photosynthesis

What is the equation for photosynthesis? CO 2 + H 2 O C 6 H 12 O 6 + O light Carbon dioxide + Water  Glucose + Oxygen Can you balance it?

Photosynthesis Carbon dioxide + Water  Glucose + Oxygen CO 2 + H 2 O  C 6 H 12 O 6 + O 2 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

What does photosynthesis require? Photosynthesis requires: 1.Carbon dioxide 2.Water 3.Sunlight 4.Chlorophyll contained in the chloroplasts of the plant cells.

Photosynthesis is a process by which plants make food - carbohydrates. To make this food they need light, a green colour called chlorophyll, the gas carbon dioxide and water. The green colour is needed to absorb the light energy to join together the carbon dioxide and water to make glucose. Glucose is rapidly changed into starch. The gas oxygen is also given out. Photosynthesis occurs where ever the plant is green i.e. Stem and leaves.

Storing the chemical energy The glucose made in photosynthesis is used for growth, repair and respiration by the plant. Extra glucose is stored as starch. This is what we usually eat (e.g. potato, rice, wheat).

The fate of glucose

How does photosynthesis relate to respiration? Respiration is the opposite to photosynthesis, releasing energy from glucose and oxygen: Photosynthesis: Carbon dioxide + Water  Glucose + Oxygen Respiration: Glucose + Oxygen  Carbon dioxide + Water energy in energy out

Past paper questions Answer the past paper questions

1Choose from the following list the correct products of photosynthesis. Awater and carbon dioxide Bglucose and carbon dioxide Cglucose and oxygen Dwater and carbon dioxide Plenary Quiz

1Choose from the following list the correct products of photosynthesis. Awater and carbon dioxide Bglucose and carbon dioxide Cglucose and oxygen Dwater and carbon dioxide

2In plants starch is used: Ato make flowers colourful. Bas a store of energy. Cto absorb water from the soil. Dto make leaves green.

2In plants starch is used: Ato make flowers colourful. Bas a store of energy. Cto absorb water from the soil. Dto make leaves green.

3Starch is part of a balanced diet because: Ait is needed for strong bones and teeth. Bit helps the digestive system remain healthy. Cit is a source of energy. Dit is needed for growth and repair of cells.

3Starch is part of a balanced diet because: Ait is needed for strong bones and teeth. Bit helps the digestive system remain healthy. Cit is a source of energy. Dit is needed for growth and repair of cells.