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From where are hormones released?
How are hormones transmitted
They are carried in the bloodstream
What functions do hormones serve?
They change the physiological activities of a target organ by binding to specific receptors in the membrane of its cells
Give four characteristics of the endocrine system
Long lasting response
Effects are sometimes irreversible or permanent
Give 4 characteristics of the nervous system
Short lived response
Reversible and temporary effects
What are chemical mediators?
Chemicals released by some mammalian cells that only affect cells in the immediate area
How are chemical mediators different from hormones?
They are not distributed around the body in the bloodstream
They are not secreted from glands
What is histamine
A chemical mediator released by white blood cells following injury or response to an allergen
Causes dilation of arterioles and increases permeability of capillaries
What are prostoglandins?
Mediators released from most cells following injury
Causes increased permeability of capillaries, blood clotting and blood pressure regulation
What are plant growth factors?
Chemicals, such as IAA, that result in a change in growth causing a tropism
How do growth factors respond to stimuli?
They are transported to one side of the stem or root
This causes the side to grow more or less than the other
The effect of this unequal growth is bending of the root or stem towards or away from the stimulus
Give an example of a tropism caused by growth factors
IAA is transported to the shaded side of them stem
This causes more growth to occur on that side
The increased growth makes the stem bend towards the light
How are growth factors affected by gravity?
They are transported to the lower side of the root
This causes growth inhibition on that side
This results in the downward bending of the root with the force of gravity
Biology Hormones camturnbull
AQA BIOL5 Hormones