Communication & Homeostasis Basics

The basics of communication & homeostasis. OCR A2 Biology. Unit 4

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Responding to Environment = Survival

Plants & Animals - increase chances of survival by responding to external environment changes & internal environment. e.g. temp
Means conditions optimal for metabolism (chem reactions).
Stimulus - any change in internal/external.

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  • Receptors detect stimuli.
  • Specific - detect one particular stimulus. e.g. light, pressure etc.
  • Many different types for different stimuli.
  • Some are cells e.g photoreceptors connect to nervous system.
  • some are proteins on cell surface membranes e.g. glucose receptors on pancreatic cells.
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  • bring a response to stimulus
  • produce an effect
  • e.g. muscle cells, cells in glands (pancreas)
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Nerve & Hormone Communiction

  • Receptors communicate with effectors via nervous / hormonal system or both.
  • Both are examples of cell signalling.
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Changes in external envir. can affect internal. e.g. blood + tissue fluid
Homeostasis - involves control systems
                       - keeps internal envir constant which is vital to function normally + to stop damage.

- maintaining core body temp as it affects enzyme activity. Enzymes control rate of metabolic reactions.

  • Body temp too high (e.g. 40°C) - enzymes denature (molecules vibrate too much, breaks H bonds which holds 3D shape, active site changed + no longer works as catalyst). Metabolic reactions less efficient.
  • Body temp too low - enzyme activity reduced. Rate of metabolic reactions slowed down.
  • Highest rate of enzyme activity - optimum temp (about 30°C)

Important - maintaining glucose concentration in blood for respiration

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Negative Feedback

  • mechanism that restores to around norm.
  • e.g. body temp kept within 0.5°C above/below 37°C
  • change can't be too big b/c effectors can't counteract
  • e.g. big body temp drop from prolonged cold weather - too big a change to counteract
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Positive Feedback

  • Amplifies change
  • Effectors increase level away from norm
  • Rapidly activates something

e.g. blood clot:

  • Platelets activiated
  • Release chemical
  • More platelets activated
  • Platelets quickly form blood clot at injury
  • Negative feedback - body detects blood clot has formed.

Positive feedback - not involved in homeostasis b/c doesn't keep internal envir. constant.

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Homeostatic systems - receptor, communication system, effector.
Receptor - detect too high/low
Communication system - sends stimulus from receptor to effector by hormonal/nervous sys.
Effector - respond to counteract change to norm.
Enzyme conditions - need to be kept constant to be optimum.
Negative feedback - mechanism that restores back to norm.
Positive feedback - amplifies change.

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