Download Wk15 Chemical Coordination

Wk15 Chemical Coordination
Endocrine Glands - hormones
A hormone from an endocrine cell is secreted into the blood, which carries it to its target cell.
[Exocrine glands secrete products into a duct e.g. saliva, sweat]
Hormones Vs Nerves
Hormonal system
Nervous system
Chemical communication
Nervous communication
Transmission by blood
Transmission by neurones
Transmission relatively slow
Transmission very rapid
Hormones travel throughout body but
only target responds
Nerve impulse specifically targeted
Response is widespread
Response is localised
Response slow
Response rapid
Response longer lasting
Response short lived
Effect may be permanent & irreversible Effect is temporary
Chemical mediators
Chemicals released and active in their immediate vicinity
Histamine
Chemical released by:
Basophil white cells;
Mast cells (in connective and mucus tissues);
Trigger for release:
Antigens;
Effect:
Histamine receptors in smooth muscle
leads to dilation of small arteries & arterioles;
Increases capillary permeability to white cells
and proteins;
Redness, swelling and itching.
[Note: histamine has a number of other roles including as a neurotransmitter]
Chemical mediators
Prostaglandins
A number of fatty acid derived compounds with various effects
Released by:
most cells;
Triggered by:
tissue damage;
Effect:
In response to injury
dilation of arterioles;
increased capillary permeability;
increased sensitivity to pain;
Other roles:
relaxation of smooth muscle in the gut;
promotion of muscle contraction during birth.
Plant Growth Factors
Tropisms:
A growth movement of a plant
in response to a stimulus
Phototropism
Geotropism
Hydrotropism
The Evidence
Control of tropisms
IAA (indoleacetic acid )
[Sometimes referred to as Auxin, which refers to a group of plant growth factors including IAA]
Control of tropisms by IAA (indoleacetic acid )
Positive phototropism: growth of a coleoptile towards the direction of a light source.
In roots IAA decreases cell elongation
Control of Tropisms
Experiments
Control of Growth in Plants
Phototropism:
Darwin noticed germinating oat seedlings grew toward light.
He and his son investigated how this
happened.
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Control of Growth in Plants
Phototropism:
Darwin (1880):
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Control of Growth in Plants
Phototropism:
Darwin (1880):
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Control of Growth in Plants
Phototropism:
Darwin (1880):
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Control of Growth in Plants
Phototropism:
Darwin (1880):
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Control of Growth in Plants
Phototropism:
Darwin (1880):
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Control of Growth in Plants
Phototropism:
Darwin (1880):
Conclusion:
•coleoptile tip acts as light receptor;
•message sent to stem.
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Control of Growth in Plants
Phototropism:
Boysen-Jensen (1913):
Coleoptile tip sends messenger substance to
encourage growth on darker side.
Q. What sort of messenger might this be?
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Control of Growth in Plants
Phototropism:
Paal (1919):
Result suggested differential diffusion of
hormone.
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Control of Growth in Plants
Phototropism:
Went (1928):
Was able to collect hormone then named AUXIN in agar.
Degree of curvature directly related to auxin concentration.
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