Transcript Hormone control of growth

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.
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
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.
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).
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.
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
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.
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?
1. Can be used as a herbicide and kill of plants we do not want
2. Can be used as a rooting powder and stimulate roots to
grow in cuttings