Edexcel IGCSE Biology

Revision Notes

1.1.4 Living Organisms: Response to Surroundings

Response to Surroundings

  • The sensitivity of an organism refers to its ability to detect and respond to stimuli in its surroundings
  • Responding to the environment around them gives an organism the best chances of survival

Sensitivity responses in animals

  • In humans, the nervous system provides a complex system of receptors, neurones and effectors which detect and respond to different stimuli using electrical impulses
  • The endocrine system also allows a response to stimuli using chemical messengers, which travel in the blood, called hormones

Sensitivity in Humans, IGCSE & GCSE Biology revision notes
The nervous system and endocrine system allow humans to respond to their environment

Sensitivity responses in plants

  • In plants, responses are controlled by chemicals and are usually much slower
    • Geotropism describes a plants response to gravity which causes the roots to grow down into the soil
    • Phototropism describes a plant’s response to light which causes shoots to grow towards sunlight

Sensitivity in Plants, IGCSE & GCSE Physics revision notes
Phototropism and geotropism allow plants to respond to their environment

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