OCR Biology A2 Unit 1 Notes-Communication and Homeostasis

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STIMULUS-any change in the environment that causes a response.

RESPONSE-a change in behaviour or physiology as a result of a change in the environment.

Good communication system: covers whole body, cell communication, rapid and specific communication, short and long term responses.

CELL SIGNALLING-one cell releases a chemical detected by another cell and the chain continues.

Neuronal system: neurones signal to each other across synapses.

Hormonal system: uses blood to transport signals-cells release hormones in the blood-it is carried all over the body and recognised by target cells.

HOMEOSTASIS-the maintenance of a constant internal environment, despite external changes. e.g. body temperature, blood glucose, blood salt, water potential of blood, blood pressure, CO2 concentration.

NEGATIVE FEEDBACK-the reversal of a change in the internal environment to return to its steady state/optimum position.

Pathway: stimulus-->receptor-->communication pathway (cell signalling)-->effector-->response.

POSITIVE FEEDBACK-a process that increases any change detected by receptors. It tends to be harmful and does not lead to homeostasis.

Structures for pathway: sensory receptors, communication systems, effector cells.

Examples of positive feedback: when body gets too cold, oxytocin: brings about dilation of the cervix, change sent to anterior pituitary gland-secretes oxytocin, which increases uterine contractions, stretching the cervix more, releasing more oxytocin etc.

ECTOTHERMS-organisms that rely on external sources of heat to regulate their body temperature.

Advantages of being an ectotherm: use less food in respiration, need to find less food, can survive for longer periods without eating, more energy can be used for growth and less for regulating body temperature.

Disadvantages: less active in cooler temperatures, may not be capable of activity in winter.

Adaptations: expose body to sun, orientate body to sun, orientate body away from sun, hide in burrow, alter body shape, breathing.

ENDOTHERMS-organisms that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain their body temperature.

Advantages of being an endotherm: a fairly constant body temperature despite external changes, when temperatures are cold activity is still possible, ability to inhabit cooler parts of the world.

Disadvantages: energy intake is used to maintain body temperature in the cold, food is required for growth and temperature regulation.

Adaptations: sweat glands, lungs, mouth, nose, hair on skin, arterioles leading to capillaries in skin, liver cells, skeletal muscles.

Endotherms monitor the temperature of their blood in teh hypothalamus of the brain. If core temperature drops the hypothalamus sends signals to reverse the changes-increases metabolism and muscle contraction or vv.

Peripheral temperature receptors in the skin monitor temperatures in the extremities, and can feed information to the thermoregulatory centre in the hypothalamus, signalling to initiate behavioural mechanisms for maintaining body temperature. This is an early warning that helps the hypothalamus to respond quickly and avoid too much temperature variation.

SENSORY RECEPTORS-specialised cells that can detect changes in our surroundings. They convert one form of energy to another and so act as transducers.

POLARISED-has a potential difference across it. This is known as the resting potential of -60mv, with the inside of the cell being more negative in comparison to the…




The first one I have seen with proper explanations!! :D

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