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Higher Biology

Higher Biology. Hormonal Control of Growth in Plants -part 2. Hormonal Control of Growth 2. By the end of this lesson you should be able to:. Know the name of a 2nd plant growth substance. Know the effects of GA: on cells on stems on dormancy in inducing a -amylase in barley grains

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Higher Biology

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  1. Higher Biology Hormonal Control of Growth in Plants -part 2

  2. Hormonal Control of Growth 2 By the end of this lesson you should be able to: • Know the name of a 2nd plant growth substance. • Know the effects of GA: • on cells • on stems • on dormancy • in inducing a-amylase in barley grains • Describe practical applications of plant growth substances.

  3. Introduction • In the 1920s Japanese rice farmers noticed that some of their rice seedlings started to grow abnormally tall. • It was found that these plants were infected with a fungus which secreted substances. • They called these substances gibberellins. • It is now known that there are more than 70 different types of gibberellin- many of them occurring naturally in plants.

  4. Gibberellic Acid (GA) • GA is the most important gibberellin. • GA (like IAA) promotes cell elongation, but only in the stems of plants. • Low concentrations of GA have this effect. • It does this by increasing the length of the internodes (not their number). • GA and internodes • An internode is a space between 2 sets of leaves on a stem.

  5. Effect of GA on germination • internal structure of barley grain • Copy this diagram and label: • Starchy endosperm • Embryo (young plant) • Aleurone layer • Cotyledon

  6. Gibberellic Acid (GA) & Germination • Read pages 257-258, “Effect of GA on germinating barley grains” of Torrance, then answer the following questions: • What carbohydrate is found in the endosperm? • What carbohydrate is required for barley seeds to germinate? • What enzyme converts the carbohydrate in the endosperm into the carbohydrate needed for germination?

  7. Gibberellic Acid (GA) & Germination Stages in GA action: • Water is absorbed by the seed. • The embryo produces GA which diffuses to the aleurone layer. • GA stimulates the aleurone layer to synthesise and secrete a-amylase into the endosperm. • a-amylase breaks down the starch in the endosperm to maltose. • Maltose diffuses into the embryo and is used for respiration.

  8. Summary Put the following stages into the correct order: GA stimulates the aleurone layer cells to synthesise a-amylase GA is transported to the aleurone layer a-amylase breaks down starch to maltose GA is transported to the aleurone layer a-amylase travels to the endosperm GA is produced by the embryo a-amylase travels to the endosperm GA stimulates the aleurone layer cells to synthesise a-amylase GA is produced by the embryo a-amylase breaks down starch to maltose

  9. Gibberellic Acid (GA) & Germination • Insert and complete the “Germination” summary into your notes.

  10. Bud Dormancy Read pages 258-259 on “GA and Bud Dormancy” in Torrance, and then answer the following questions: • What is meant by “bud dormancy”? • What effect does GA have on dormant buds? • When would this effect normally happen?

  11. Rooting Powder Read page 255 on “Rooting Powders” in Torrance, and then answer the following questions: • What is present in rooting powder? • What effect does this have on the roots?

  12. Herbicides Read page 256 on “Herbicides” in Torrance, and then answer the following questions: • Explain how auxins are used to kill weeds. • Explain why auxins can be used as selective weedkillers on lawns. • Insert and complete the “IAA v GA” summary.

  13. Practice Questions • Torrance • TYK page 259 Q1 and 2 • AYK pages 260-262 Q2,3 and 7 • You will need graph paper for Q2 on page 260!

  14. Hormonal Control of Growth 2 Can you do it? • Know the name of a 2nd plant growth substance. • Know the effects of GA: • on cells • on stems • on dormancy • in inducing a-amylase in barley grains • Describe practical applications of plant growth substances.

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