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Leaves

Leaves. B4a. Results of mustard seed experiment. What differences can you see between the two sets? Suggest why a lack of light caused these differences.

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Leaves

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  1. Leaves B4a

  2. Results of mustard seed experiment • What differences can you see between the two sets? • Suggest why a lack of light caused these differences. • Suggest what would happen to the cress seedlings if they were left in the dark for another 2 weeks. Give an explanation for your suggestion.

  3. Objectives Key Objective • Describe the role of leaves in aiding photosynthesis • Describe how the main features of the plant are linked to photosynthesis (E-G) • Explain how leaves are adapted for efficient photosynthesis (C/D) • Explain how the structure of a leaf palisade cell is related to its function (C/D) • Identify the process by which gases travel in and out of the plant (C/D) • Explain how the cellular structure of a leaf is adapted for efficient photosynthesis (A/B)

  4. Experiment • What do you see on the upper and lower leaf surfaces? • Suggest an explanation for your observations. • Pour some hot water into the beaker. • Hold the stalk of a large leaf with a pair of forceps and lower it into the hot water. • Watch what happens to the upper and lower surfaces.

  5. STOMATA

  6. While you are waiting for the varnish to dry complete w/s B4a4 using the blue OCR book Practicals - tearing leaves painting leaves You will need: • lettuce or privet leaf • glass slides • cover slips • microscope Method • Take a leaf such as a lettuce or privet leaf. • Tear it across so that a strip of lower epidermis is removed. • Put a small piece of the torn strip onto a glass slide. • Add a drop of water and a cover slip. • Look at it under the microscope. • Repeat the procedure with a strip torn off the upper epidermis. You will need: • lettuce or privet leaf • forceps • clear nail varnish • glass slides • cover slips • microscope Method • Paint the upper and lower surfaces of a leaf with a thin layer of clear nail varnish. Allow it to dry. • Using forceps, peel off the dried nail varnish. • Put a piece from each surface on a microscope slide. • Add a drop of water and a cover slip. • Look at it under a microscope.

  7. For G-E: • Identify the chloroplasts, vacuole and cell wall in a plant cell. • State that chloroplasts absorb light energy for photosynthesis. • State that photosynthesis occurs mainly in the leaves. • Describe the entry points of materials required for photosynthesis: • water through roots; • carbon dioxide through leaf pores. • Describe the exit point of materials produced in photosynthesis: • oxygen through leaf pores. KEY WORDS: • chlorophyll; cuticle; guard cell; lower epidermis; palisade mesophyll; spongy mesophyll; stomata; upper epidermis; vein

  8. For C/D • Name and locate the parts of a leaf: • cuticle; • upper and lower epidermis; • palisade and spongy mesophyll layers; • stomata and guard cells; • veins. • Explain how leaves are adapted for efficient photosynthesis: • broad so large surface area; • thin so short distance for gases to travel; • contain chlorophyll to absorb light; • have a network of veins for support and transport; • stomata for gas exchange. • State that the exchange of gases is by diffusion. • Explain how the structure of a leaf palisade cell is related to its function: • contains many chloroplasts.

  9. For A*-B: • Explain how the cellular structure of a leaf is adapted for efficient photosynthesis: • epidermis is transparent; • palisade layer at the top containing most of the chloroplasts; • air spaces in the spongy mesophyll allow diffusion between stomata and photosynthesising cells; • internal surface area / volume ratio very large.

  10. Leaves are designed for one thing only – making food • In order to do this they must be able to draw in water and carbon dioxide gas. • They must also be able to trap sunlight.

  11. How leaves are suited to photosynthesis • Leaves are broad and flat, to absorb as much light as possible.

  12. They have ‘holes’ in the leaves to allow carbon dioxide in and oxygen out. These are STOMATA.

  13. There are veins in the leaves to transport water and sugar around.

  14. Many of the cells are packed with chloroplasts which contain a light trapping pigment- chlorophyll.

  15. There is a waxy layer on top to stop water being lost from the leaf.

  16. Plenary • Draw this diagram of a Marram grass leaf.

  17. Marram grass is found on sand dunes. • Add the two missing labels (D) • What does the waxy cuticle do? (C) • How does the position of the stomata help this plant? (C) • Why are there no stomata on the outer surface of the leaf? (B) • Explain the function of the hairs on the inner surface of the leaves? (A) • Explain how having sunken stomata will affect gaseous exchange in the plant, and why this would be an advantage to the plant. (A*)

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