Biology Topic 6

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How does responding to the environment help organisms survive?
Increases their chance of survival, by respondin to changes in their external environment. They respond to changes in their internal environment to ensure that the conditions are always right for metabolism.
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What does a receptor do?
Detects stimuli. Receptors in the sense organs are groups of cells that detect external stimuli.
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What are effectors?
Effectors are cells that bring about a response to the stimuli. They include muscle cells and cells found in glands. They respond in different ways- muscle cells contract, whereas glands secrete hormones.
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What are receptors?
Receptors communicate with effectors via the nervous system, the hormonal system or sometimes both.
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How does the Central Nervous System work?
It is made up of neurones. There are three main types of neurones (sensory, relay, motor). The CNS consists of the brain, and spinal cord. When receptors detect a stimulus, they send electrical impulses along sensory neurones to the CNS.
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How does the Central Nervous System work? (2)
CNS sends electrical impulses to effector along motor neurone.The effector responds.CNS coordinates the response.Coordinated responses always need a stimulus+receptor+effector. Neurones transmit info via high speed electrical impulses,rapid responsce
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How do reflexes help to prevent injury?
Reflexes are automatic responses to certain stimuli. The route taken by the information in a reflex is called a reflex arc. If there is too much light, you're pupils get smaller, stopping the light entering.
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Diagram of the reflex arc.
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Block diagram to represent a reflex arc.
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Diagram of the eye.
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How does the iris reflex work?
Very bright light can damage the retina. It makes the pupil smaller, allowing less light in. In dim light, the brain tells the radial muscles to contract, making the pupil bigger.
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What happens if you focus on near objects?
The ciliary muscles contract, which slackens the suspensory ligaments. The lens becomes fat.
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What happens if you focus on distant objects?
The ciliary muscles reflex allows the suspensory ligaments to pull tight. This makes the lens go thin.
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Why are long-sighted people unable to focus on near objects?
The cornea or lens doesn't bend the light enough or the eyeball is too short. The images of near objects are brought into focus behind the retina.
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Why are short-sighted people unable to focus on distant objects?
The cornea or lens bends the light too much or the eyeball is too long. The images of distant objects are brought into focus in front of the retina.
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What are hormones?
They are chemicals released directly into the blood. They're carried in the blood plasma to other parts of the body, but only affect particular cells (target cells). They control things in organs and cells that need constant adjustment. Glands.
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What is the source, role and effect of ADH?
Pituitary gland (in the brain), controls water content, increases the permeability of the kidney tubules to water.
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What is the source, role and effect of Adrenaline?
Adrenal glands (top of kidneys), readies the body for fight or flight response, increases heart rate, blood flow to muscles and blood sugar level.
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What is the source, role and effect of Insulin?
Pancreas, helps control the blood sugar level, stimulates the liver to turn glucose into glycogen for storage.
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What is the source, role and effect of Testosterone?
Testes, main male sex hormone, promotes male secondary sexual characteristics.
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What is the source, role and effect of Progesterone?
Ovaries, supports pregnancy, maintains the lining of the uterus.
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What is the source, role and effect of Oestrogen?
Ovaries, main female sex hormone, controls the menstrual cycle and promotes female secondary sexual characteristics.
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What are the characteristics of nerves?
Very fast message, act for a very short time, act on a very precise area.
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What are the characteristics of hormones?
Slower message, act for a long time, act in a more general way.
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What is homeostasis?
The maintenance of a constant internal environment.
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How is water lost from the body in various ways?
Through the skin as sweat, via the lungs in breath, via the kidneys as urine.
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Why is body temperature kept at 37 degrees?
All enzymes work best at a certain optimum temperature. The enzymes in the body work best at this temperature.
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How does the skin help to maintain body temperature?
When you're too hot, you swear- evaporate, transfers heat. Blood vessels widen- vasodilation. Hairs lie flat. Cold- little sweat, vasoconstriction, shiver, hairs on ends.
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Why can smaller organisms cool down quicker?
They have bigger surface area to volume ratios. They lose heat more easily in hot climates, but are more vulnerable in cold areas.
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How do plants respond to stimuli?
They sense the direction of light and grow towards it. Sense gravity, roots grow in the right direction. Respond to the presence of predators to avoid being eaten. Plants are more likely to survive if they respond to abiotic stress.
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What are auxins?
Plant hormones which control growth at the tips of shoots and roots. They move through the plant in solution. It is produced in the tips and diffuses backwards to stimulate the cell elongation process. Promotes growth in the shoot, inhibits it though
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How do auxins change the direction of root and shoot growth?
Shoots are positively phototropic. When a shoot tip is exposed to light, it accumulates more auxin on the side that's in the shade than the side that's in the light. This makes the cells elongate faster, shaded side, so the shoot goes towards light.
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How do auxins change the direction of root and shoot growth? (2)
Shoots are negatively geotropic. When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side. Lower side grows faster, bending shoot upwards.
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How do auxins change the direction of root and shoot growth? (3)
Roots are positively geotropic. A root growing sideways will also have more auxin on its lower side. The extra auxin inhibits growth, cells on top elongate faster, root bends downwards.
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Card 2

Front

What does a receptor do?

Back

Detects stimuli. Receptors in the sense organs are groups of cells that detect external stimuli.

Card 3

Front

What are effectors?

Back

Preview of the front of card 3

Card 4

Front

What are receptors?

Back

Preview of the front of card 4

Card 5

Front

How does the Central Nervous System work?

Back

Preview of the front of card 5
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