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Flashcards · J247 · Topic 3

Organism level systems flashcards

36 cards on Topic 3, subtopics B3.1 to B3.3. Pick a subtopic or study them all.

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B3.1 Coordination and control – the nervous system

The pathway of a nervous response
Stimulus → receptor → sensory neurone → CNS (brain and spinal cord) → motor neurone → effector (muscle or gland) → response.
How is a neurone adapted to carry impulses?
A long axon carries impulses over long distances; the myelin sheath insulates it and speeds up the impulse; branched endings pass the signal on.
What happens at a synapse, and why is it one-way?
The impulse reaches the end of a neurone; a transmitter chemical is released, diffuses across the gap and binds to receptors on the next neurone, starting a new impulse. Receptors are only on the receiving side.
Why is a reflex faster than a voluntary response?
It has a short pathway with few neurones and synapses (receptor, sensory, relay, motor, effector) and needs no conscious decision. Reflexes protect the body from harm.
A ruler is caught after falling 22 cm. Reaction time? (t = √(2d/g), g = 9.8 m/s²)
d = 0.22 m. t = √(2 × 0.22 ÷ 9.8) = √0.0449 = 0.21 s.
Functions of the cornea, iris, lens and retina
Cornea: transparent front; refracts light and does most of the focusing. Iris: muscle that changes pupil size. Lens: fine focusing onto the retina. Retina: rods (dim light) and cones (colour) change light into impulses.
The iris reflex in bright light and in dim light
Bright: circular muscles contract, radial muscles relax, pupil smaller. Dim: circular muscles relax, radial muscles contract, pupil larger.
Accommodation: focusing on a near object vs a distant object
Near: ciliary muscle contracts (shortens), tension in suspensory ligaments low, lens fatter, light bent more. Distant: ciliary muscle relaxes, ligaments taut, lens slimmer, light bent less.
Short-sightedness vs long-sightedness: cause and correction
Short-sight: eyeball too long or lens too strong; focus in front of the retina; concave lens. Long-sight: eyeball too short or lens too weak; focus behind the retina; convex lens. Laser surgery can also be used.
Functions of the cerebrum, cerebellum, medulla, hypothalamus and pituitary
Cerebrum: conscious thought, memory, language, voluntary movement. Cerebellum: coordination and balance. Medulla: unconscious actions such as heart and breathing rate. Hypothalamus: body temperature and water balance. Pituitary: releases hormones.
Why is brain function difficult to investigate?Higher
The brain is delicate and inside the skull, so it cannot be examined safely while working. Case studies rely on rare, different injuries (small samples); other areas may compensate; and there are ethical limits on consent and harm.
Why is damage to the nervous system hard to treat?Higher
Damaged neurones in the brain and spinal cord are not readily replaced; surgery or radiation can harm healthy tissue around the damage; and the skull and backbone make deep parts hard and risky to reach.

B3.2 Coordination and control – the endocrine system

Hormone, and why only some cells respond to it
A chemical messenger secreted by an endocrine gland directly into the blood, carried in the plasma to all parts of the body. Only target cells respond, because only they have receptors that fit that hormone.
Which gland makes FSH and LH, thyroxine, adrenaline, oestrogen and progesterone, and testosterone?
Pituitary: FSH and LH. Thyroid: thyroxine. Adrenal glands: adrenaline. Ovaries: oestrogen and progesterone. Testes: testosterone.
Thyroxine and negative feedbackHigher
Thyroxine (thyroid gland) controls metabolic rate. When its level falls, more is released; when it rises, less is released. The response reverses the change: negative feedback.
Effects of adrenalineHigher
Released by the adrenal glands in fear or excitement ("fight or flight"): faster, stronger heartbeat, faster breathing, glucose released from the liver, more blood to the muscles, so muscles get more oxygen and glucose.
Roles of FSH, oestrogen and progesterone in the menstrual cycle
FSH (pituitary): an egg matures in the ovary, and the ovary makes oestrogen. Oestrogen: thickens the uterus lining. Progesterone (after ovulation): maintains the lining. Ovulation is at about day 14.
How do FSH, oestrogen, LH and progesterone interact?Higher
FSH matures an egg and stimulates oestrogen. Oestrogen inhibits FSH and stimulates an LH surge, which triggers ovulation. The empty follicle makes progesterone, which keeps the lining thick and inhibits FSH and LH.
How do the combined pill and progesterone-only methods prevent pregnancy?
Combined pill (oestrogen and progesterone): inhibits FSH, so no egg matures or is released. Progesterone-only methods: thicken cervical mucus so sperm cannot reach the egg, and may stop ovulation.
Non-hormonal contraception, and which method protects against infection
Condoms, diaphragm or cap, copper coil (IUD), natural family planning, sterilisation, abstinence. Only condoms give some protection from infection.
IVF in stepsHigher
FSH and LH are given so several eggs mature; eggs are collected; mixed with sperm in a dish; embryos grow for a few days; one or two are placed in the uterus. Drawbacks: cost, strain, not guaranteed, multiple births.
Auxin: why shoots grow up and roots grow down when laid on their side
Auxin collects on the lower side of both. In shoots it promotes elongation, so the lower side grows more and the shoot bends up. In roots high auxin inhibits elongation, so the root bends down.
Effects of gibberellins and etheneHigher
Gibberellins: stem growth, germination (enzymes break down stored food), can promote flowering. Ethene (a gas): fruit ripening and shedding of leaves.
Commercial uses of auxin, ethene and gibberellinsHigher
Auxin: rooting powder; selective herbicides (synthetic auxin kills broad-leaved weeds, not grasses); seedless fruit. Ethene: ripening fruit on demand. Gibberellins: end dormancy; seedless fruit.

B3.3 Maintaining internal environments

Homeostasis, and why body temperature matters
Keeping the internal environment constant despite internal and external change. Metabolic reactions are enzyme-controlled: too cold and they are too slow; too hot and enzymes denature. Core temperature is kept near 37 °C.
Negative feedback in four steps
A receptor detects a change; a control centre (brain or pancreas) processes it; an effector responds; the response reverses the change, so the level returns towards normal.
Responses when the body is too hot
Sweat glands release sweat, which evaporates and transfers energy from the skin. Arterioles to the skin widen (vasodilation), so more blood flows near the surface and more heat is transferred to the surroundings.
Responses when the body is too cold
Shivering (rapid muscle contraction; respiration releases heat); vasoconstriction (arterioles to the skin narrow, less heat transferred); less sweat.
How insulin lowers blood glucose after a meal
The pancreas detects the rise and secretes insulin into the blood. Target cells, mainly in the liver and muscles, take up glucose; the liver converts it to glycogen. Blood glucose falls and insulin release falls.
Glucagon vs insulinHigher
Glucagon is released by the pancreas when blood glucose is low; it acts on the liver, which converts glycogen to glucose and releases it, so blood glucose rises. Insulin and glucagon are an antagonistic pair.
Type 1 vs type 2 diabetes
Type 1: too little insulin made; treated with insulin injections or a pump (insulin is a protein, so a tablet would be digested). Type 2: cells respond poorly to insulin; diet, exercise, weight loss, medicines. Obesity is a risk factor.
What happens to an animal cell in a solution with a higher water potential than the cell?
Water enters by osmosis; the cell swells and may burst (lysis), because it has no cell wall. In a lower water potential it shrinks.
The parts of a kidney tubule and their jobs
Bowman's capsule: filtration under pressure (water, glucose, urea, ions; no cells or proteins). Proximal convoluted tubule: selective reabsorption of all glucose, much water, many ions. Loop of Henlé: more water reabsorbed. Collecting duct: final water adjustment.
Water gained is 2400 cm³ and water lost other than in urine is 1100 cm³. Urine volume for balance?
2400 − 1100 = 1300 cm³. Water is gained from drinks, food and respiration, and lost in urine, sweat, breath and faeces.
ADH negative feedback when the blood is too concentratedHigher
Blood water potential falls; the hypothalamus detects it; the pituitary releases more ADH; the collecting duct becomes more permeable, so more water is reabsorbed; blood returns to normal; less ADH is released.
Responses to heavy sweating and to drinking too much waterHigher
Heavy sweating: blood more concentrated, so thirst, more ADH, a small volume of concentrated urine. Drinking too much: blood more dilute, so less ADH, a large volume of dilute urine.

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