A-Level Notes > Leicester High A-Level Notes > OCR Biology Module 1 - homeostasis and nerves (F214) Notes

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CHAPTER 1- COMMUNICATION (a) outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to co-ordinate the activities of different organs; (b) state that cells need to communicate with each other by a process called cell signalling; (c) state that neuronal and hormonal systems are examples of cell signalling; (d) define the terms negative feedback, positive feedback and homeostasis; (e) explain the principles of homeostasis in terms of receptors, effectors and negative feedback; (f) describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.

Different parts of the organism perform different functions- important that information can pass between these different parts Organisms need to respond to external stimuli e.g. temperature In plants and animals, chemicals known as hormones (or in plants known as plant growth regulators) help to transfer information from one part to another In many animals, nerves transfer information in the form of electrical impulses

Homeostasis: the maintenance of a stable internal environment (conditions inside the body) 1- Temperature: low temperatures slow down metabolic reactions, high temperatures can cause proteins to denature, causing damages to enzymes and to cell membrane 2- Amount of water- lack of water in tissue fluid causes water to move out of the cell by osmosis, too much water causes water to move into the cell via osmosis 3- Concentration of glucose- glucose is need for respiration, so lack of it will cause respiration to slow down and the cells have no energy.
 Mammals can control core body temperature- whatever the temperature of the environment outside the body; the cells are kept at a temperature of 37°C. One mechanism, negative feedback (process in which any change in a parameter brings about the reversal of that change so that the parameter is kept fairly constant), detects the external change (stimuli), communicating with other cells, and reversing the change (response).

The receptor monitors the factor that is being controlled (temperature) If the value is not within a suitable range, the receptor communicates with the effector Effector causes an action that brings the factor back towards the normal

Positive feedback: a process in which may change in a parameter brings about an increase in change

Temperature Regulation
    Endotherms: organisms which can use physiological mechanisms to regulate internal body temperature independently of the environment
  Endotherms monitor blood temperature (core temperature) using the hypothalamus- should remain 37°C.
  Hypothalamus received information about temperature from other sources e.g. the skin contain receptors that monitor the change in skin temperature
  The peripheral receptors are able to give early warning about a possible change in core temperature Temperature change in endotherms: Temperature rises Physiological Behaviour al Arterioles supplying blood Move into to the skin dilate as the shade or smooth muscle in their hide in walls relaxes-vasodilation. barrow This allows more blood to flow close to the skin surface, so that head can radiate from it or be conducted to the air

Temperature falls Physiological Behavioural Vasoconstriction reduces the flow of blood through the capillaries near the skin surface, so less heat is loss to the surroundings by radiation from the warm blood at the surface of the skin

Move into sunlight

Sweat glands secrete more sweat, as it lies on the surface of the skin, water evaporates. Water has a high latent heat of vaporisation and as it changes from liquid to gas it absorbs heat from the skin

Orientate body to decrease surface area exposed to sun

Less sweat is secreted, so less water evaporates, and so less loss of latent heat

Oreinetate body to increase surface area exposed to sun

Hair lies flat, providing little insulation, meaning heat can be lost through convection and radiation

Remain inactive and spread out limbs to increase surface area

Erector muscle each attached to the base of a hair follicle contract and pull the hair up on ends. This traps a layer of air, insulating the skin and reducing heat loss

Move about to generate heat in muscle

No panting, less water evaporates, and n loss of latent heat

Put on more clothes, increasing insulation of the body surface.

Panting increases water evaporation from lungs, tongue and moist surface, doing this has the same effect as sweating

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