Download Animal Behaviour and Plant Responses. - MrHay

Animal Behaviour and
Plant Responses.
Year 13 Biology
Detecting a stimulus
• A stimulus is a change in the environment
(external or internal) that causes a
response in an organism.
• A receptor is any cell or group of cells that
can detect this change
• A effector is a cell or group of cells that
can respond to the change.
Orientation responses
of plants
• Plants respond to light, gravity, water,
chemicals and touch. They do this by a
growth curve towards or away from a
stimulus.
• If the growth is towards the stimulus we
say it is positive; if it is away from the
stimulus we say it is negative.
• The prefixes you learnt before tell us the
type of stimulus e.g. photo = light.
Tropisms
• A tropism is a GROWTH response
towards or away from an environmental
stimulus coming from one direction.
• For example
– If the shoot of a plant grows towards the light,
we say it is positively phototropic
– If the root of a seedling grows down, then we
say it is positively geotropic
Nastic Responses
• The response of plants to diffuse stimuli
that do not come from any particular
direction, such as the temperature,
humidity and light that surround a plant,
are called nastic responses.
• For example
– the opening and closing of flowers in
response to different light intensities.
Nastic Responses
• Nastic movements are classified according
to the nature of the stimulus
• For example
– Photonasty is the response to alterations in
the light intensity
– Thermonasty is the response to changes in
the temperature
Taxis
• This is the movement of the whole animal,
towards or away from a stimulus which is
coming from one side only.
• As with tropisms, movement towards a
stimulus is positive and away from a
stimulus is negative.
• The stimulus is also denoted by the same
prefixes.
Taxis
• Examples
– Flatworms moving towards a pieces of
raw meat are showing positive
chemotaxis
– Moths flying to a light are positively
phototactic
– Trout will line themselves up in an
upstream direction, so they are
positively rheotactic
Taxis
• Taxes often involve moving the head (which
carries the sensory receptors) from side to side.
• If there are two sensory organs then the animal
can move directly towards or away from the
stimulus as it can constantly check the position
of the stimulus.
• If there is only one sensory organ, the animal
must move around to get information about the
stimulus. E.g. a maggot must move its head
from side to side to keep in position. It performs
a zigzag ‘direct’ line.
Kinesis
• This is a non-directional response to a
stimulus.
• It is the change in activity rate in response
to a change in the intensity of the stimulus.
• Example
– If woodlice are placed in a wet/dry choice
chamber, the animals in the dry side
increases their random movements and rate
of turning compared with those on the wet
side.
Kinesis
• Orthokinesis – the speed of the
movement is related to the intensity of the
stimulation
• Klinokinesis – the amount of random
turning is related to the intensity of the
stimulation.
• See diagrams for summary.
Pheromones
• A pheromone is a chemical produced by
an animal and released into the external
environment where it has an effect on the
physiology or behaviour of members of the
same species.