coordination and response Flashcards
define homeostasis
the maintenance of a constant internal environment.
what does a co-ordinated response require?
a stimulus, a receptor and an effector
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Explain how auxins cause a positive phototropism.
- Auxin diffuses from the tip to the shaded side, causing elongation
- Therefore the shaded side is longer, causing the stem to bend towards the light.
How do shoots respond to gravity?
They grow up (negative geotropism).
When a plant is laid on its side, the auxins produced collect in the lower side of the stem. Auxins sped up growth in the lower side of the shoot, so the shoot curves up.
How do roots respond to gravity?
They grow down (positive geotropism)
If a plant is laid on its side, the auxins produced collect in the lower side of the root. Auxins slow down growth on the lower side of the root, so the root curves down.
describe nervous coordination
coordination from a nervous system involving a network of nerve cells that carry impulses between parts of body.
describe hormonal coordination
coordination from an endocrine system involving glands that produce and secrete hormones to stimulate change in the body
describe two differences between hormonal and nervous coordination
- Nervous communication is electrical, hormonal communication is chemical
- Nervous Communication is faster, hormonal communication is slower
what does the central nervous system consist of?
the brain and the spinal cord
give two adaptations of a nerve cell
- long fibre (axon) which is insulated by a fatty sheath
- tiny branches (dendrons) which branch further as dendrites at each end
Name the neurones going into the coordination centres
Sensory neurones
Name the neurones going out of the coordination centre
Motor neurones
Describe how a normal response works
Stimulus -> receptor -> (sensory neurone) -> coordination centre -> (motor neurone) -> effector -> response
What is a synapse
The gap between where one neurone ends and another begins
Describe the 4 stages of electrical impulses crossing synapses.
- An impulse arrives at the synapse, vesicles containing neurotransmitters move to the membrane.
- The vesicles release the neurotransmitters into the gap.
- The neurotransmitter crosses the synapse and binds to receptors in the end of the next neurone, beginning a new electrical impulse
- The neurotransmitter is broken down by enzymes in the second neurone
Describe the reflex arc
- Sensory receptors
- Impulse in sensory neurone travels to grey matter of spinal cord
- Sensory -> relay neurone
- Relay -> motor
- Effector
Function of cornea.
The transparent lens that refracts light as it enters the eye.
Function of iris.
Controls how much light enters the pupil.
Function of lens.
The transparent disc that can change shape to focus light onto the retina.