1. Survival and response
Plant growth factors
Organisms increase their chance of survival by responding to
changes in their environment. In flowering plants, specific growth
factors move from growing regions to other tissues, where they
regulate growth in response to directional stimuli. The effect of
different concentrations of indoleacetic acid (IAA) on cell elongation
in the roots and shoots of flowering plants as an explanation of
gravitropism and phototropism in flowering plants.
Plants respond to light, gravity and water
IAA controls cell elongation
Makes the cell wall more elastic by triggering enzymes to move in and break
the hydrogen bonds between the cellulose - response only occurs in young
cell walls
Acid growth hypothesis – active transport of hydrogen ions from the cytoplasm
into spaces in the cell wall causes cell wall to become more plastic
Tropism – the growth of a plant in response to a directional stimulus
Phototropism
Cells in the tip of the shoot produce IAA which is transported down
the shoot
The IAA is initially transported evenly throughout all regions as it moves
down
Light causes the movement of IAA from the light side to the shaded
side
A greater concentration builds up on the shaded side
As IAA causes elongation of the shoots the cells on the shaded side
elongate more
The shaded side elongates faster than the light side causing the
shoot to bend towards the light
Gravitropism
Cells in the tip of the root produce IAA which is transported along the
root
it is initially transported to all sides of the root
Gravity influences the movement of IAA from the upper side to the
lower side
, A greater concentration of IAA builds up on the lower side
IAA inhibits the elongation of the root cells - cells on lower side
elongate less than upper side
Greater elongation on the upper side causes the roots to bend
downwards
A reflex arc
Taxes and kinesis as simple responses that can maintain a mobile
organism in a favourable environment. The protective effect of a
simple reflex, exemplified by a three-neurone simple reflex. Details
of spinal cord and dorsal and ventral roots are not required
Kinesis
A non-directional response to a stimulus
Increased movement and changes in direction until favourable
conditions are found
e.g. woodlice
Taxis
A directional response towards or away from a stimulus
Earthworms - away from the sun (negative taxis) and single celled
photosynthetic algae and light
Central nervous system – brain and spinal cord
Peripheral nervous system – pairs of nerves that originate from the CNS
PNS divided into:
sensory neurones (from receptors to CNS)
Motor neurones (from CNS to effectors)
Motor divided into
Voluntary – to body muscles – conscious
, Autonomic – impulses to glands, smooth muscle, cardiac muscle +
involuntary
A change in the internal or external environment which produces a response - a
stimulus
Stimulus, receptor, co-ordinator, effector, response
Reflex arc
1. Stimulus
2. Receptor
3. Sensory neurone
4. CNS + intermediate neurone
5. Motor neurone
6. Effector
7. Response
Importance of reflex arc
Involuntary – do not require decisions from brain – more complex
responses – response always same
Protect the body from harm – do not have to be learned
Fast – neurone pathway is short – one or two synapses (slowest link in
neural pathways)
Absence of decision making – fast
Required practical 10 – investigating simple animal responses
Receptors
The Pacinian corpuscle should be used as an example of a receptor
to illustrate that:
• receptors respond only to specific stimuli
• stimulation of a receptor leads to the establishment of a generator
potential.
The basic structure of a Pacinian corpuscle. Deformation of stretch-
mediated sodium ion channels in a Pacinian corpuscle leads to the
establishment of a generator potential. The human retina in
sufficient detail to show how differences in sensitivity to light,
sensitivity to colour and visual acuity are explained by differences in
the optical pigments of rods and cones and the connections rods and
cones make in the optic nerve
Sensory reception - receiving a stimulus at a receptor
Sensory perception - making sense of the information from the receptors
Plant growth factors
Organisms increase their chance of survival by responding to
changes in their environment. In flowering plants, specific growth
factors move from growing regions to other tissues, where they
regulate growth in response to directional stimuli. The effect of
different concentrations of indoleacetic acid (IAA) on cell elongation
in the roots and shoots of flowering plants as an explanation of
gravitropism and phototropism in flowering plants.
Plants respond to light, gravity and water
IAA controls cell elongation
Makes the cell wall more elastic by triggering enzymes to move in and break
the hydrogen bonds between the cellulose - response only occurs in young
cell walls
Acid growth hypothesis – active transport of hydrogen ions from the cytoplasm
into spaces in the cell wall causes cell wall to become more plastic
Tropism – the growth of a plant in response to a directional stimulus
Phototropism
Cells in the tip of the shoot produce IAA which is transported down
the shoot
The IAA is initially transported evenly throughout all regions as it moves
down
Light causes the movement of IAA from the light side to the shaded
side
A greater concentration builds up on the shaded side
As IAA causes elongation of the shoots the cells on the shaded side
elongate more
The shaded side elongates faster than the light side causing the
shoot to bend towards the light
Gravitropism
Cells in the tip of the root produce IAA which is transported along the
root
it is initially transported to all sides of the root
Gravity influences the movement of IAA from the upper side to the
lower side
, A greater concentration of IAA builds up on the lower side
IAA inhibits the elongation of the root cells - cells on lower side
elongate less than upper side
Greater elongation on the upper side causes the roots to bend
downwards
A reflex arc
Taxes and kinesis as simple responses that can maintain a mobile
organism in a favourable environment. The protective effect of a
simple reflex, exemplified by a three-neurone simple reflex. Details
of spinal cord and dorsal and ventral roots are not required
Kinesis
A non-directional response to a stimulus
Increased movement and changes in direction until favourable
conditions are found
e.g. woodlice
Taxis
A directional response towards or away from a stimulus
Earthworms - away from the sun (negative taxis) and single celled
photosynthetic algae and light
Central nervous system – brain and spinal cord
Peripheral nervous system – pairs of nerves that originate from the CNS
PNS divided into:
sensory neurones (from receptors to CNS)
Motor neurones (from CNS to effectors)
Motor divided into
Voluntary – to body muscles – conscious
, Autonomic – impulses to glands, smooth muscle, cardiac muscle +
involuntary
A change in the internal or external environment which produces a response - a
stimulus
Stimulus, receptor, co-ordinator, effector, response
Reflex arc
1. Stimulus
2. Receptor
3. Sensory neurone
4. CNS + intermediate neurone
5. Motor neurone
6. Effector
7. Response
Importance of reflex arc
Involuntary – do not require decisions from brain – more complex
responses – response always same
Protect the body from harm – do not have to be learned
Fast – neurone pathway is short – one or two synapses (slowest link in
neural pathways)
Absence of decision making – fast
Required practical 10 – investigating simple animal responses
Receptors
The Pacinian corpuscle should be used as an example of a receptor
to illustrate that:
• receptors respond only to specific stimuli
• stimulation of a receptor leads to the establishment of a generator
potential.
The basic structure of a Pacinian corpuscle. Deformation of stretch-
mediated sodium ion channels in a Pacinian corpuscle leads to the
establishment of a generator potential. The human retina in
sufficient detail to show how differences in sensitivity to light,
sensitivity to colour and visual acuity are explained by differences in
the optical pigments of rods and cones and the connections rods and
cones make in the optic nerve
Sensory reception - receiving a stimulus at a receptor
Sensory perception - making sense of the information from the receptors
