Flashcards · 8461 · Topic 5

Homeostasis and response flashcards

16 cards on Topic 5, subtopics 4.5.1 to 4.5.4. Pick a subtopic or study them all.

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Homeostasis: The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes. In humans: blood glucose, body temperature and water levels.
The three parts of an automatic control system: Receptors detect stimuli; coordination centres (such as the brain, spinal cord and pancreas) receive and process the information; effectors (muscles or glands) bring about responses that restore optimum levels.
Why is homeostasis important, and what does it control in humans?: It maintains optimal conditions for enzyme action and all cell functions. In the human body it includes control of blood glucose concentration, body temperature and water levels.

The reflex arc, in order: Stimulus → receptor → sensory neurone → synapse → relay neurone (CNS) → synapse → motor neurone → effector (muscle contracts or gland secretes). Reflexes are automatic and rapid.
Accommodation: focusing on a near object vs a distant object: Near: ciliary muscles contract, suspensory ligaments slacken, lens thicker, refracts more. Distant: ciliary muscles relax, suspensory ligaments tighten, lens thinner, refracts less.
Myopia vs hyperopia, and the lens used to correct each: Myopia (short sight): image forms in front of the retina; concave lens. Hyperopia (long sight): image forms behind the retina; convex lens.
Body temperature: responses when too hot and when too cold: Monitored by the thermoregulatory centre in the brain. Too hot: vasodilation, sweating. Too cold: vasoconstriction, sweating stops, shivering.
Cerebral cortex, cerebellum and medulla: roles: Cerebral cortex: consciousness, intelligence, memory and language. Cerebellum: coordination of muscular activity. Medulla: unconscious activities such as heartbeat and breathing.

Type 1 vs Type 2 diabetes: Type 1: the pancreas makes too little insulin; treated with insulin injections. Type 2: body cells no longer respond to insulin; treated with a carbohydrate-controlled diet and exercise. Obesity is a risk factor.
Negative feedback in blood glucose controlHigher: Glucose too high: the pancreas releases insulin, glucose moves into cells and is stored as glycogen. Glucose too low: the pancreas releases glucagon, glycogen → glucose, released into the blood.
ADH and water balanceHigher: Blood too concentrated → the pituitary releases more ADH → kidney tubules become more permeable → more water reabsorbed → blood less concentrated (negative feedback).
FSH, LH, oestrogen and progesterone: gland and role: FSH (pituitary): egg matures in the ovary. LH (pituitary): egg released (ovulation). Oestrogen (ovary): main female hormone; uterus lining. Progesterone (ovary): maintains the uterus lining.
Hormonal vs non-hormonal contraception: Hormonal: the pill (inhibits FSH), progesterone injection, implant or patch. Non-hormonal: condom, diaphragm, spermicide, an IUD that only prevents implantation, abstinence at fertile times, sterilisation.

Auxin and tropisms: Unequal distribution of auxin causes unequal growth. Shoots bend towards light (phototropism); roots grow down (gravitropism). Auxin collects on the shaded side of a shoot.
Uses of auxin, ethene and gibberellinsHigher: Auxin: weed killers, rooting powder, tissue culture. Ethene: control ripening of fruit in storage and transport. Gibberellins: end seed dormancy, promote flowering, increase fruit size.
Required practical 8: effect of light or gravity on seedlings: Grow seedlings from cress or mung beans in dishes, with light from one side or the dish turned on its side, and a control. After a few days measure and record the direction and length of shoot and root growth.