Survival and response (A-level only) Flashcards
Detecting change
Organisms can detect changes in:
External environment (e.g. temperature of surroundings).
Internal environment (e.g. blood glucose concentration).
Coordinating responses
Coordinating a response to the environment involves three components:
Stimulus - change in the environment.
Receptors - detect the change in the environment.
Effectors - initiate the response.
Trophisms
Directional growth responses
Phototrophism in plants
Phototropism is growth in response to direction of light:
Shoots are positively phototropic - they grow towards light.
Roots are negatively phototropic - they grow away from light.
Gravitrophism in plants
Gravitropism is growth in response to direction of gravity:
Shoots are negatively gravitropic - they grow upwards (away from the gravitational pull).
Roots are positively gravitropic - they grow downwards (towards the gravitational pull).
Indoleacetic acid (IAA)
IAA is a type of auxin that controls the tropic response in plants.
Distribution of IAA
IAA can be transported over short distances (by diffusion or active transport) and longer distances (in the phloem) around the plant.
When a plant detects directional stimuli, IAA is transported to different parts of the plant.
This creates an uneven distribution of IAA.
Where the distribution of IAA is uneven, a directional growth response occurs.
IAA phototrophism- shoots
Shoots are positively phototropic.
If a shoot is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts cause cells in the shaded area to elongate.
Cell elongation causes the shoot to bend towards the light.
IAA phototrophism- roots
Roots are negatively phototropic.
If a root is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts inhibits cell elongation on the shaded part.
The root bends away from the light.
IAA gravitrophism- shoots
Shoots are negatively gravitropic.
If a shoot is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside cause cells in the underside to elongate.
Cell elongation causes the shoot to bend away from the gravitational pull.
IAA gravitrophism- roots
Roots are positively gravitropic.
If a root is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside inhibits cell elongation on the lower side.
The root bends towards the gravitational pull.
Tactic animal responses- taxes
The stimulus is positively or negatively directional, e.g. light.
E.g. Woodlice move away from a light source.
Dark environments (e.g. under stones) are favourable for woodlice to protect them from predators.
Being able to detect the direction of light and move away helps woodlice locate a more favourable habitat.
Kinetic animal responses- Kinesis
The stimulus is non-directional, e.g. humidity.
E.g. Woodlice move more slowly and turn less in high humidity but move faster and turn more in low humidity.
Damp environments are favourable for woodlice to reduce water loss.
When woodlice detect a drier environment they move more.
This increases the chance woodlice will find a more favourable habitat.
When woodlice detect a damper environment they move less.
This ensures the woodlice stay in the more favourable habitat.
Choice chambers
Choice chambers can be used to study how animals respond to environmental stimuli.
4 stages of choice chambers
Build
Add woodlice
Collect results
Repeat
