energy transfers starter: write a list of the food you have eaten so far today. where does all of...

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?

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

All food chains begin with energy from the sun.

So you are (indirectly) solar powered!

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

Answers1. 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?

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 used for growth (output)efficiency =

energy supplied (input)

100 – 60 – 34efficiency =

100

Q: What is the efficiency of farming cows for food?

= 6 / 100= 0.06= 6%

A:

Q: What is the efficiency of this plant?

A: 5% (of the light energy is converted into chemical energy in glucose)

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?

CO2 + H2O C6H12O6 + O26 66light

Carbon dioxide + Water Glucose + Oxygen

Can you balance it?

What does photosynthesis require?

Photosynthesis requires:

1. Carbon dioxide

2. Water

3. Sunlight

4. Chlorophyll contained in the chloroplasts of the plant cells.

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).

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

1 Choose from the following list the correct products of photosynthesis.A water and carbon dioxide B glucose and carbon dioxideC glucose and oxygenD water and carbon dioxide

Plenary Quiz

1 Choose from the following list the correct products of photosynthesis.A water and carbon dioxide B glucose and carbon dioxideC glucose and oxygenD water and carbon dioxide

2 In plants starch is used:A to make flowers colourful.B as a store of energy.C to absorb water from the soil.D to make leaves green.

2 In plants starch is used:A to make flowers colourful.B as a store of energy.C to absorb water from the soil.D to make leaves green.

3 Starch is part of a balanced diet because:A it is needed for strong bones and teeth.B it helps the digestive system remain healthy.C it is a source of energy.D it is needed for growth and repair of cells.

3 Starch is part of a balanced diet because:A it is needed for strong bones and teeth.B it helps the digestive system remain healthy.C it is a source of energy.D it is needed for growth and repair of cells.