Biology notes that will help you get an A*
Notes have been made to cater to the AQA Biology Mark Scheme
Contains everything on the spec for Response to Changes:
- Nervous Communication
- Survival & Response
- Neurones
- Synapses
- Receptors
- Heart Rate
- Muscle Contraction
- Homeostasis
...
Nervous Communication
Chances of survival are increased by responding to external environment
!
Organisms respond to changes in their internal environment to make sure that the conditions are always optimal for their metabolism
Stimulus: a change in the internal or external environment
Receptor: a cell or protein on cell surface membrane that detects the stimulus
Effectors: cells or cells in glands that bring about a response to stimulus
Response: an action to protect the body from harm or maintain optimal internal conditions
Nervous System
-
Uses electrical impulses to respond to a change in the environment
-
Sensory neurones transmit electrical impulses from receptors to the CNS
Relay neurones transmit electrical impulses between sensory and motor neurones
: Motor neurones transmit electrical impulses from the CNS to effectors.
Sensory Relay Motor
Stimulus Receptors CNS Effectors Response
·
When an electrical impulse reaches the end of a neurone, neurotransmitters take the information across to the next neurone, which
sends an electrical impulse.
Nervous system
Central nervous system Peripheral nervous system
Brain + spinal cord Neurones that connect the CNS to the rest of the body
Autonomic nervous system Somatic nervous system
Controls conscious activities Controls unconscious activities
Sympathetic nervous system Parasympathetic nervous system
Gets the body ready for action Calms the body down
The nervous system is:
i
rapid because electrical impulses are fast
localised - when electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto target cells
short lived - after the response, neurotransmitters are broken down
Reflexes
Reflex is an automatic, involuntary and rapid response to a stimulus to protect the body from harm
The pathway of neurones linking receptors to effectors in a reflex is called a reflex arc
If there is a relay neurone involved in the simple reflex arc then it's possible to override the reflex
The impulse does not go to the brain.
In a reflex action, there will only be 3 neurones
, Survival & Response
Animals
Simple mobile organisms have simple responses to keep them in a favourable environment
Kinesis:
The organisms’ movement is affected by a non-directional stimulus
· Woodlice show a kinetic response to humidity.
·
In high humidity they move slowly and turn less often so that they stay where they are
-
In dry air, they move faster and turn more so that they more into a new area where there is higher humidity.
~
Changes in the speed or number turns of an organism
Taxes:
The organisms’ movement is affected by a directional stimulus (stimulus coming from a particular direction)
~
Woodlice show a tactic response to light (photoaxis) - they more away from light
: This helps them survive as it keeps them concealed under stones during the day where they're safe from predators and keeps them in
damp conditions
Choice chamber:
Plants
i
Plants increase their chances of survival by responding to changes in their environment
Grow towards light to maximise absorption for photosynthesis
Climbing plants have a sense of touch, so they can climb to reach the sunlight
Sense gravity so their roots and shoots grow in the right direction
-
Tropism: the growth response of a plant to a directional stimulus
-
Positive tropism: growth towards stimulus
-
Negative tropism: growth away from stimulus
I
Phototropism: growth of a plant in response to light -
Gravitropism: growth of a plant in response to gravity
Shoots are positively phototropic Shoots are negatively gravitropic
:
Roots are negatively phototropic Roots are positively gravitropic
: Plants respond to directional stimuli using specific growth factors
Growth factors: hormone-like chemicals that speed up or slow down plant growth
↑
Growth factors are produced in the growing regions of the plant (meristems) and diffuse to other parts of the plant or via phloem.
Auxins stimulate growth of shoots by cell elongation (cell walls become loose and stretchy, so the cell gets longer) but high concentrations of
auxins inhibit growth in roots.
Iaa:
Indoleacetic acid is an important auxin produced in the tips of shoots
IAA is moved by diffusion and active transport or via the phloem over long distances
This results in different parts of the plant having different concentrations of IAA. The uneven distribution means there is uneven growth.
, Phototropism
IAA moves to the shady side of the shoot IAA moves to the shady side of the root
:
Cells elongate and shoot bends towards the light Growth is inhibited so the root bends away from the light.
Gravitropism
IAA moves to the lower side side of the shoot IAA moves to the lower side side of the shoot
Cells elongate and shoot bends grows upwards Growth is inhibited so the root bends downwards.
Acid-growth hypothesis:
Increase in IAA concentration means more IAA to bind to a protein pump on cell wall
More hydrogen ions from cytoplasm into cell wall decreases pH
This disrupts the microfibrils causing the cytoplasm to become more stretchy.
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