survival and response Flashcards
What do organisms gain by responding to changes in their environment?
An increased chance of survival
Stimulus
A detectable change in the internal/external environment of an organism that leads to a response
Receptor
Detects a stimulus
(specific to one type of stimulus)
Coordinator
Formulates a suitable response to a stimulus
Effector
Produces a response to a stimulus
What is the reflex arc? [7]
stimulus → receptor → sensory neurone → coordinator (CNS / relay neurone) → motor neurone → effector → response
Why is a simple reflex important? [3]
- Rapid (short pathway) because only 3 neurones and few synapses (synaptic transmission is slow)
- Autonomic because doesn’t involve passage to brain, and doesn’t have to be learnt
- Protect from harmful stimuli e.g. escape from predator / prevents damage to body tissues
Taxes
Directional responses by simple motile organisms who move towards a favourable stimulus (positive taxis) or away from an unfavourable one (negative taxis
Give an example of taxes
Woodlice show a tactic response to light
Moving away from light keeps woodlice concealed under stones and away from predators improving chances of survival
Kineses
Non-directional, behavioural responses by simple motile organisms who change the speed of movement or the rate of direction change, in response to a non-directional stimulus
Give an example of Kineses
Woodlice show a kinetic response to humidity.
Moving faster / changing direction more often when air drier increases chances of moving to an area of higher humidity where woodlice will lose less water, improving chances of survival
Tropism
Growth of a part of a plant in response to a directional stimulus
Positive tropism - growth towards stimulus
Negative tropism - growth away from stimulus
What do plant responses to external stimuli involve?
growth factors (hormone-like growth substances)
What do growth factors do?
Growth factors move from growing regions (e.g. shoot tips / leaves where they are produced) to other tissues, where they regulate growth in response to directional stimuli (e.g. Auxins, such as IAA)
What is IAA?
An auxin (indoleacetic acid
What effect do auxins have on plant growth in the shoots and the roots?
Auxins in the shoots promote cell elongation
Auxins in the roots inhibit cell elongation
What is Phototropism?
Phototropism is a directional response to sunlight
What is Gravitropism? (aka geotropism)
Gravitropism is a plant response to the stimulus of gravity
Responses [4]
Phototropism
Shoots - Positive
Roots - Negative
Gravitropism
Shoots - Negative
Roots - Positive
What response do plant shoots show to sunlight and why? [3]
- Plant shoots show positive phototropism
- Promoting cell elongation and growing towards the sun
- Maximising the amount of light they can absorb for photosynthesis
What response do plant roots show to sunlight and why? [3]
- Plant roots show negative phototropism
- Inhibiting cell elongation and growing away from the sun
- Growing deeper into the soil, maximising water uptake
How do auxins result in phototropism in the shoots? [5]
- Cells in tip of shoot produce IAA
- Which initially is evenly transported down the shoot
- IAA concentration increases on the shaded side
- Promoting cell elongation on shaded side
- Shoot bends towards light
How do auxins result in gravitropism in the roots? [5]
- Cells in tip of root produce IAA
- Which initially is evenly transported through the root
- IAA concentration increases on the lower side of the root
- Inhibiting cell elongation on the lower side
- Root curves downwards towards gravity
