1. Revision: B4 Photosynthesis PEHN

2. Section of a leaf

3. Key 1. Waxy cuticle, this gives the leaf a waterproof layer, which lets in light. 2. Upper epidermis - provides an upper surface. 3. Palisade cells, which are packed full of chloroplasts. 4. Spongy mesophyll. Collection of damp, loosely packed cells. 5. Lower epidermis is the layer of cells on the lower surface. 6. Air space inside the leaf, allows contact between air and moist cell surfaces. 7. Stoma, a hole in the leaf which gases diffuse through. 8. Guard cells, which change shape to close the stoma.

7. Plants use the green dye (or pigment) called chlorophyll to pick up the energy from the sunlight. Plants make sugar and use some of it for energy to keep them alive (respiration) but they also use some for growth and repair by making fats and proteins. However, it is not always sunny so plants need to be able to store some of the sugar they make, so they convert it to a storage carbohydrate.

9. Method for starch test: 1) Cover up part of the leaf using black card What effect does this have on the plant? 2) Boil the leaf for a few minutes What does this do to the leaf? 3)Soak the leaves in alcohol What effect does this have on the leaf? 4) Dip the leaves in water What effect does this have? 5) Drop some iodine onto the leaf What do you see? Draw and explain your results

10. Factors effecting Photosynthesis

12. Exercise 1: Leaf Structure 1. ___________ 2. ___________ 3. ______________________ 5. _____________________ 7. __________ 6. ________ 4. __________ Waxy cuticle Epidermis Palisade mesophyll layer Spongy mesophyll layer Epidermis Stomata Air space

13. Exercise 2: Link the Boxes Waxy cuticle Stoma Air spaces Waterproof layer atop the epidermis Pores that allow gaseous exchange Found in the spongy mesophyll layer, enable gases to reach the leaf cells

14. Exercise 3: Link the Boxes Epidermis Palisade mesophyll cell Spongy mesophyll cell Contain numerous chloroplasts and are densely packed, where most of the photosynthesis occurs Loosely packed cells that do not contain as many chloroplasts as palisade cells One-cell thick outer layer of cells that prevent water loss from the leaf

15. Exercise 4: Short Questions - Leaf 1.What do we call the continuation of the leaf stalk into the leaf- blade? 2.What do we call the specially adapted cells that form holes in the leaves to allow gaseous exchange? 3.What are these holes/pores called? 4. What is the name of the waxy waterproof layer found on top of the epidermis? 5.What is the lamina? Midrib Guard cells Stoma Cuticle The leaf-blade

16. Exercise 5: Short Questions - Leaf 1.What do we call the outer one-cell thick layer of cells that contain no chloroplasts? 2.What is the function of this layer? 3.What are two differences between palisade mesophyll cells (PMC) and spongy mesophyll cells (SMC)? 4. By what process does carbon dioxide enter and leave leaves? The epidermis To prevent water loss and to stop substances and organisms entering the leaf SMC – more loosely packed, less chloroplasts Diffusion PMC – more densely packed, more chloroplasts

17. Exercise 6: Insert the Missing Words Chloroplasts __________ of plant cells that contain a green substance called __________. Scientists believe chlorophyll absorbs _____ energy and this energy is then used to make _____. The raw materials of photosynthesis are carbon dioxide and _____. This waste product of this reaction is _______. The carbon dioxide required is absorbed through the ______ in the leaves – this is how the oxygen is also removed. The water required is absorbed by the _____. rootsorganelles lightfood water chlorophyll oxygenstoma organelles chlorophyll light food wateroxygen stoma roots

18. Exercise 7: Short Questions - Photosynthesis 1.Which organelles in plant cells contain a green substance called chlorophyll? 2.Which two raw materials are required by green plants for photosynthesis? 3.What is the waste product of photosynthesis? 4. How does this waste product leave the plant during the day? 5.What process requires this waste product to enable green plants to release energy from their food? Chloroplasts Water and carbon dioxide Oxygen Through the stoma Respiration

19. Exercise 8: Short Questions – Plant Nutrition 1.What do we call the process whereby green plants make glucose using light energy and the raw materials carbon dioxide and water? 2.During the night many green plants perform another process whereby they release the energy from their food they have made. What do we call this process? 3.The sugar glucose, the product of photosynthesis, is changed to starch when it is being stored by the plant. Why? 4. What is the chemical formula of glucose? Photosynthesis Respiration Glucose is soluble in water, starch is insoluble in water. By storing the food starch it means it is easier for the plant to keep the food in the required place C 6 H 12 O 6

20. Exercise 9: Short Questions – Plant Nutrition 1.What is the word equation for photosynthesis? 2.What is the chemical equation for photosynthesis? 3.Name the arrowed organelle. 4. Which substance does this organelle contain that allows green plants to absorb the Sun’s light energy for the process of photosynthesis? 6H 2 O + 6CO 2  C 6 H 12 O 6 + 6O 2 Chloroplast Chlorophyll

21. Exercise 10: Variegated Leaf A destarched variegated plant was left in a sunny garden during the day for several hours. At the end of this period a leaf was taken from the plant and tested for starch. The results are shown below… Variegated leaf before starch test Variegated leaf after starch test Explain the result observed (8 marks)

22. Exercise 11: Products of Photosynthesis Some destarched pondweed was set-up as below. A bright lamp was placed nearby for two hours. Before lamp turned on After six hours of lamp shining Explain the result observed (6 marks) The following results were observed at the end of this period.

23. Exercise 12: Short Questions 1.What is a variegated leaf? 2.Draw a diagram of a variegated leaf. 3.What is the chemical test for starch? 4.How do you destarch a green plant? Parts of the leaf do not contain chlorophyll, other parts do Starch turns orange/brown iodine solution purple/black You leave it in the dark for several days so that its food stores (starch) are exhausted

24. Self test (foundation & extension) http://www.bbc.co.uk/apps/ifl/schools/gcse bitesize/biology/quizengine?quiz=photosy nthesisf&templateStyle=biologyhttp://www.bbc.co.uk/apps/ifl/schools/gcse bitesize/biology/quizengine?quiz=photosy nthesisf&templateStyle=biology http://www.bbc.co.uk/apps/ifl/schools/gcse bitesize/biology/quizengine?quiz=photosy nthesish&templateStyle=biologyhttp://www.bbc.co.uk/apps/ifl/schools/gcse bitesize/biology/quizengine?quiz=photosy nthesish&templateStyle=biology