Importance of Photosynthesis in Plants

1. Starter Activity: Name three uses of bacteria which help humans.

2. Key area 6 Photosynthesis

3. Photosynthesis and its Limiting Factors Learning Intention: To understand the importance of plants making their own food. Success Criteria: Be able to describe how plants make food. Be able to state the overall word equation for photosynthesis.

4. Watch and Listen • Plants are Amazing!

5. Photosynthesis • Plants make their own food, called glucose. • They make it in a process called photosynthesis. • Photosynthesis takes place in the leaves of green plants.

6. Photosynthesis • There are many different things a plant needs before it can photosynthesise. • Listen to the photosynthesis song and see if you can work out what a plant needs.

7. Watch and Listen

8. Photosynthesis in green plants

9. Photosynthesis • Plants need light, water and carbon dioxide to photosynthesise. • They produce glucose (their food) and oxygen. • The oxygen is released into the air for us to breathe in. • The glucose can be stored as starch.

10. Photosynthesis in a leaf

11. Photosynthesis Light energy Carbon Dioxide + Water Glucose + Oxygen Raw Materials Products

12. Watch and Listen • Photosynthesis Video Clip

13. Starter Activity: Answer the following questions What gas do plants take in and use for photosynthesis? What gas, made in photosynthesis, do plants release into the air? Why is this useful for animals? When do plants not photosynthesise?

14. Photosynthesis and its Limiting Factors Learning Intention: To understand the importance of light Success Criteria: Be able to state the source of light Be able to carry out investigations to see the effect of light on photosynthesis

15. Light • A green plant needs light to allow it to photosynthesise. • Plants obtain light from the sun . • We will carry out an experiment to prove that plants need light to photosynthesise.

16. Light and photosynthesis. • The glucose made in photosynthesis is made into starch and stored in the leaves of plants. • We can test a plant that has been in the light and one that has been in the dark, to see if there is starch present in their leaves. • This will tell us if the plant has photosynthesised.

17. Activity 1 - Testing a leaf for starch Important Points: 1) We boil the leaf to remove the waxy coating so our stain can get inside the leaf. 2) We place the leaf in ethanol to remove the green colour so we can see the colour change.

18. Testing a Leaf for Starch 1 6 2 5 4 3

19. Method • Place four leaf discs from a plant in a beaker of water on a tripod stand. • Use a bunsen burner to heat the water and allow to boil for 2 minutes. • TURN OFF THE BUNSEN BURNER. • Using a spatula, remove the leaf discs. • Place the discs in a boiling tube and cover with ethanol. • Place the boiling tube into the beaker of hot water. • Once the ethanol has turned green, transfer the leaf discs into the beaker of hot water. • Put leaf discs on a spotting tile and test for the presence of starch using iodine solution.

20. Conclusion • The plant in the dark did not turn blue/black when tested with iodine. • This means it had no starch, so had not photosynthesised. • The plant in the light did turn blue/black. • This means it contained starch, so it had photosynthesised.

21. Starter Activity: Think about how you could investigate whether a plant needs carbon dioxide to photosynthesise. What kind of experiment would you set up?

22. Photosynthesis and its Limiting Factors Learning Intention: To understand the importance of carbon dioxide Success Criteria: Be able to state the source of carbon dioxide Be able to carry out investigations to see the effect of carbon dioxide on photosynthesis

23. Carbon Dioxide • A plant needs carbon dioxide to photosynthesise. • It obtains carbon dioxide from the air around it . • We will carry out an experiment to prove that plants need carbon dioxide to photosynthesise.

24. Activity 2 - Carbon dioxide and photosynthesis • The plant on the left has no carbon dioxide because the chemical absorbs it from the air. • The plant on the right does have carbon dioxide because the candle releases it. • We can test the leaves of these two plants for starch, to find out if they have been carrying out photosynthesis. Candle to provide carbon dioxide Chemical to absorb carbon dioxide

25. Method • Place four leaf discs from a plant in a beaker of water on a tripod stand. • Use a bunsen burner to heat the water and allow to boil for 2 minutes. • TURN OFF THE BUNSEN BURNER. • Using a spatula, remove the leaf discs. • Place the discs in a boiling tube and cover with ethanol. • Place the boiling tube into the beaker of hot water. • Once the ethanol has turned green, transfer the leaf discs into the beaker of hot water. • Put leaf discs on a spotting tile and test for the presence of starch using iodine solution.

26. Conclusion • The plant with no carbon dioxide did not turn blue/black when tested with iodine. • This means it did not contain starch, so it was not photosynthesising. • The plant with carbon dioxide did turn blue/black. • This means it did have starch, so it was photosynthesising.

27. Starter Activity: Name two substances needed by a plant for photosynthesis.

28. Photosynthesis and its Limiting Factors Learning Intention: To understand the importance of chlorophyll Success Criteria: Be able to explain what chlorophyll is Be able to carry out an investigation to see the effect of chlorophyll on photosynthesis

29. Chlorophyll • Chlorophyll is a pigment found in plants. It is found in the chloroplasts of plant cells. • It makes plants appear green. • Chlorophyll’s function is to trap the light from the sun so the plant can carry out photosynthesis.

30. Activity 3 – importance of chlorophyll • We are going to prove that chlorophyll is needed for plants to photosynthesise. • To prove this, we are going to test a variegated leaf. • A variegated plant is one which has green parts and white parts on its leaves.

31. Method • Place a small piece of leaf from a variegated plant in a beaker of water on a tripod stand. • Use a bunsen burner to heat the water and allow to boil for 5 minutes. • TURN OFF THE BUNSEN BURNER. • Using a spatula, remove the leaf. • Place the leaf in a boiling tube and cover with ethanol. • Place the boiling tube into the beaker of hot water. • Once the ethanol has turned green, transfer the leaf into the beaker of hot water. • Put leaf on a spotting tile and test for the presence of starch using iodine solution.

32. Photosynthesis • The green parts of the variegated leaf contain chlorophyll. • These parts turned blue/black when tested with iodine. • This white parts of the leaf remained orange when tested with iodine. • This proves that chlorophyll is needed for photosynthesis .

33. Starter Activity: Answer the following questions When testing a leaf for starch, why is the leaf boiled in water? Why is the leaf heated in alcohol? What is put onto the leaf at the end to test for starch? What colour does it turn if starch is present?

34. Photosynthesis and its Limiting Factors Learning Intention: to state the limiting factors of photosynthesis and the effects of these on the rate of photosynthesis Success Criteria: Be able to name the limiting factors of photosynthesis Be able to carry out an investigation to see the effect of limiting factors on photosynthesis

35. Limiting Factor • A limiting factor is something that limits the rate of a reaction. • We already learned about limiting factors in respiration, like oxygen and temperature. • We will now look at limiting factors in photosynthesis.

36. Limiting factors in photosynthesis Photosynthesis cannot work without: • Carbon dioxide • Water • Light • A suitable temperature If any of these are in short supply, they are called limiting factors.

37. Measuring the rate of photosynthesis • Water plants produce oxygen bubbles when they are photosynthesising. • You can measure the rate of photosynthesis in pond plants by counting the number of bubbles released per minute.

38. Pondweed Cabomba Elodea • These plants are often used in fish tanks. They produce tiny oxygen bubbles which are released into the water. • This is good for the fish in a fish tank! What do the plants get from the fish in return?

39. Activity 4 - Elodea bubbler Used to measure the rate of photosynthesis oxygen collects at top Water containing a chemical to provide CO2 lamp or oxygen released as bubbles

40. Elodea Bubbler • We can vary the light intensity by moving the lamp closer or further away. • The less light on the Elodea, the less bubbles released. • The more light on the Elodea, the more bubbles released.

41. Other limiting factors This animation helps demonstrate how other limiting factors affect the rate of photosynthesis. http://www.kscience.co.uk/animations/photolab.htm

42. Elodea Bubbler What happens as light intensity increases? The rate of photosynthesis increases then levels off. Why does it level off? Another limiting factor must be in short supply.

43. Photosynthesis and its Limiting Factors Learning Intention: To understand the effects of limiting factors on plant growth. Success Criteria: Describe ways of overcoming limiting factors in horticulture. Be able to state that faster growth can be achieved in plants if the rate of photosynthesis is high.

44. Growing plants • Some people grow plants commercially to supply garden centres and supermarkets. • This is usually done in large greenhouses. • This is known as horticulture.

45. Making the most of photosynthesis – Reducing limiting factors By reducing the limiting factors for photosynthesis, plant growers can increase the rate of photosynthesis in their plants. The plants will then grow faster. They can therefore grow larger plants with more fruit or bigger flowers. Farmers also can do this to produce bigger and better crops of cabbages, potatoes or wheat.

46. Polytunnels • By covering outdoor plants with polythene tunnels, the temperatureis raised and the plants are protected from damaging wind and pests. • This increases their growth rate.

47. Greenhouses • Greenhouses also increase the temperature for plants and protect them from frost and pests. • If a paraffin stove is burned, this increases the temperature and has the added benefit of providing them with extra carbon dioxide. • Both of these will make the plants grow faster.

48. Greenhouse lights • Artificial lights in greenhouses can provide extra light and warmth for plants, which increases the growth rate of the plants.

49. Greenhouse heaters and lights • Greenhouse heaters and lights help to increase the rate of photosynthesis, and this makes the plants grow faster. • However, heating and lighting costs lots of money, so may not be cost effective for a farmer or plant grower.