Hormone control of growth

1. Hormone control of growth List two hormones the pituitary gland (in the brain) produces that controls human growth and development. Growth hormone (GH) Thyroid stimulating hormone (TSH) Explain how each one is involved in growth and development of a human. GH - This hormone makes soft tissue like muscle and also into bone. These amino acids can be used by the muscle and bone tissue to grow. TSH – This hormone enters the blood and is taken to the thyroid gland and stimulates it to produce thyroxine hormone. This thyroxine regulates the metabolic activity which in turn regulates growth and development.

2. Plant growth substances Where is the plant growth substance,called IAA, produced? In the shoot and root tip How does it affect the cells in these regions? IAA stimulates cell division ( mitosis ) IAA stimulates cell elongation by increasing the plasticity of the plant cell wall so the cell can take in more water IAA is necessary for undifferentiated cells to become differentiated in the region of cell differentiation in shoot and root tips

3. How does IAA move down the plant? First by diffusion – short distances Uses phloem for longer distances. IAA is involved in the growth of organs in the plant and not just cells. Explain the term phototropism and the role of IAA. Phototropism is the directional growth of a plant organ (eg stem) to light coming from ONE direction.

4. Explain why a plant shoot will bend towards light shining from the right hand side ie directional light? The right side of the stem gets more light so produces less IAA so grows less and the darker, left side of the stem produces more IAA so the cells on the darker side grow more. How does phototropism help the plant survive? The stem now bends towards the light and gains more light for photosynthesis so makes more glucose (food).

5. IAA has other roles Apical dominance AS IAA moves down the stem it inhibits the lateral buds from growing so the plant grows taller and not as bushy ie IAA dominates over the lateral the buds. Leaf abscission (fall) In Autumn the IAA concentration decreases and this makes a thin layer, called the absission layer, to form in the stalk (petiole) of the leaf. The leaf falls off! Fruit formation After fertilisation, in a flower, the production of IAA changes the ovary wall into the fruit coat.

6. Gibberellic acid (GA) on plant growth The role of GA in germinating barley grains. Which part of the seed makes GA? The embryo What concentration is produced – a high or low concentration? Low concentration Which tissue of the seed does the GA affect? The GA affects the aleurone layer What does this tissue do when when GA is present in the seed? The aleurone tissue produces a amylase enzyme. Why is this important to the barley grain? This enzyme breaks down the starch to maltose so the embryo has a supply of sugar. SAM memory aid

7. The role of GA has in producing dwarf and tall plants as in peas. Where does the GA affect the growth of plants? In the internode cells of the stem How does it affect the growth? GA increase elongation of the cell in the internode. Why are some plants tall and some dwarf? The dwarf plants have a mutated gene so produces Less GA so less elongation in the cells of the internode so less growth Tall plants produce sufficient GA so have full elongation – full growth.

8. The role of GA has in bud dormancy • Explain the role of GA in bid dormancy. • In the spring the plant begins to make GA and this breaks dormancy by stimulating the buds to grow. • List two practical applications of plant growth substances? • Can be used as a herbicide and kill of plants we do not want • Can be used as a rooting powder and stimulate roots to grow in cuttings