How does responding to the environment help organisms survive?
Animals increase their chances of survival by responding to changes in their external environment i.e. avoiding places too hot or cold
They also respond to changes in their internal environment to ensure conditions are always optimal for their metabolism
Plants also increase their chances of survival by responding to changes in their environment
What is a stimulus?
Any change in the internal or external environment
What are Receptors?
Receptors detect stimuli - they can be cells or proteins on cell surface membranes
What are Effectors?
Effectors are cells that brings about a response to a stimulus, to produce an effect. Effectors include muscle cells and cells found in glands e.g. the pancreas
What are the 3 types of neurones?
Sensory Neurones -> transmit electrical impulses from receptors to the central nervous system (CNS = Brain & Spinal Cord)
Motor Neurones -> transmit electrical impulses from the CNS to effectors
Relay Neurones -> transmit electrical impulses between sensory neurones & motor neurones
How does the Nervous System respond to stimuli?
A stimulus is detected by receptor cells, causing an electrical impulse to be sent along a sensory neurone
When an electrical impulse reaches a synapse, a neurotransmitter takes the information to the next neurone, carrying on the electrical impulse
The CNS (the coordinator) processes the information & sends impulses along motor neurones to an effector
2 systems of the Nervous System:
Central NS (brain & spinal cord)
Peripheral NS (connects CNS to rest of body)
PNS has 2 sub-divisions:
Somatic NS (controls conscious activities)
Autonomic NS (controls unconscious activities)
ANS has 2 further sub-divisions:
Sympathetic NS (gets body ready for action, 'fight or flight')
Parasympathetic NS (calms body down, 'rest and digest')
How do reflexes work?
A reflex is where your body responds to a stimulus without making a conscious decision to respond
Info travels fast from receptors to effectors, it protects organisms due to how rapid it is
The pathway of neurones is called a reflexarc - it goes from sensory neurone -> relay -> motor
If there is a relay neurone involved in a simple reflex arc, you can override the reflex e.g. your brain telling you to withstand the heat
Reflex Arc Example- the hand-withdrawal response to heat
Thermoreceptors in the skin detect the heat stimulus
The sensory neurone carries impulses to the relay neurone
The relay neurone connects to the motor neurone
The motor neurone sends impulses to the effector (your bicep muscle)
Your muscle contracts to withdraw your hand, stopping it being damaged
What are 3 attributes of Nervous System Communication?
Localised - At the neurone end, neurotransmitters are secreted directly onto target cells
Short-Lived - Neurotransmitters are quickly removed after secretion
Rapid - Electrical impulses are really fast, allowing animals to react quickly to stimuli
What ways to plants respond to environmental change?
They sense the direction of light to maximise light absorption for photosynthesis
They can sense gravity, so roots & shoots grow in the right direction
Climbing plants have a sense of touch, so they can find things to climb up & reach sunlight
Phototropism is the growth of a plant in response to light
Shoots are positively phototropic & grow towards light
Roots are negatively phototropic & grow away from the light
Gravitropism is the growth of a plant in response to gravity
Shoots are negatively gravitropic & grow upwards
Roots are positively gravitropic & grow downwards
Describe how a plant shoot responds to directional light:
IndoleaceticAcid (IAA) is an auxin produced in the tip of shoots
IAA moves via diffusion/activetransport to the shaded part of the shoot
This stimulates growth of the shaded side by elongating the cells
The shoot bends towards the light stimulus, maximising light absorption for photosynthesis
Describe how a plant root responds to directional light:
IndoleaceticAcid (IAA) is an auxin produced in the tip of roots
IAA moves via diffusion/active transport to the shaded part of the root
IAA has a inhibiting effect in roots so the root bends downwards, away from the light & anchoring the plant
Describe how a plant shoot responds to gravity:
IndoleaceticAcid (IAA) is an auxin produced in the tip of shoots
IAA moves via diffusion/active transport to the underside of the shoot
IAA stimulates growth on the underside of the shoot by elongating cells
Shoot bends upwards and grows up
Describe how a plant root responds to gravity:
IndoleaceticAcid (IAA) is an auxin produced in the tip of roots
IAA moves via diffusion/active transport to the underside of the root
IAA inhibits growth in roots, so the roots grows downward
What is Taxis + an example:
Taxis is when organisms move towards or away from a directional stimulus
Example: Woodlice show a tactic response to light (phototaxis) - they move away from light, helping them stay concealed away from predators in the day & keeps them in damp conditions
What is Kineses + an example:
Kineses is the organisms' movement is affected by a non-directional stimulus.
Example: Woodlice show a kinetic response to humidity. In high humidity, they move slowly and turn less often so they stay where they are. In dry conditions, they become faster and turn more often so they move into a new area, potentially with higher humidity.
This improves the organisms chance of survival as higher humidity is advantageous to conserve water & remain concealed
How would you use a Choice Chamber to investigate Animal Response?
Make a choicechamber using given equipment
Cover 1 half with black paper to create dark condition
Place dampfilter paper over 1 light & dark condition
Place a dryingagent (i.e. anhydrous calciumchloride) on the remaining quarters
Place 10 maggots in the centre of the chamber & cover with a lid
After 10 minutes, take off the lid and record the number of maggots in each condition
Repeat. You should find maggots move towards the dark, damp condition
What do receptors being specific mean?
They only detect one particular stimulus, e.g. light, pressure or glucose concentration.
What are the different types of receptors:
Cells - e.g. photoreceptors in the eye
Proteins on Surface CellMembranes - e.g. glucose receptors in the pancreas
What does the potential difference in a receptor mean?
When a nervous system receptor is in its resting state, there is a difference in charge inside & outside of the cell.
This is generated by ion pumps or ion channels.
The voltage across the membrane is the potentialdifference
What occurs in a receptor when a stimulus is detected?
Cell membrane become more permeable, allowing more ions to move in and out of the cell
This alters the potentialdifference
The change in potential difference is called the generatorpotential
How is an action potential produced?
If the generator potential is big enough, it triggers the electrical impulse along the neurone
This will only occur if the size of the generator potential exceeds the threshold level
Action potentials are all one size, so the strength of the stimulus is measured by the amount of action potentials.
Pacinian Corpuscles:
They are mechanoreceptors, responding to pressure in your skin
They contain the end of a sensory neurone wrapped in layers of lamellae
When the Pacinian corpuscle is stimulated, the lamellae is deformed & press on the sensory neurone
This deforms stretch-mediated sodium channels, causing them to open and Na+ ions diffuse into the cell
Creating the generator potential
Photoreceptors:
Light enters through the pupil, the amount of light being controlled by muscles around the iris
Light rays are focused onto the retina by the lens. The retina contains rod & cone cells.
The fovea is an area with lots of photoreceptor cells
Nerve impulses from the photoreceptors cells are carried to the brain by the opticnerve, which is a bundle of neurones.
Where the optic nerve leaves the eye is the blindspot, as there's no photoreceptor cells.
How do photoreceptors convert light into electrical impulses?
Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive opticalpigments
Light bleaches the pigments, causing a chemical change & altering the membrane permeability to Na+ ions
Creates the generator potential and sends the nerveimpulse along a bipolar neurone, which connect photoreceptors to the optic nerve
Rod Cells:
Mainly concentrated in the peripheral parts of the retina
Monochromatic vision
Very sensitive to light/Works well in dim light (Many rods join one neurone so weak generator potentials combine to reach threshold for action potential)
Low visualacuity (Many rods join one neurone so light from two points can't be told apart)
Cone Cells:
Packed together in the fovea
Trichromatic vision (There are 3 types of cone: red-sensitive, green & blue. When they're stimulated in different proportions you see different colours)
Less sensitive to light/Works well in bright light (One cone per neurone so it takes more light to trigger action potential)
High visualacuity (One cone per neurone means brain can distinguish two points close together as 2 separate points)
What qualities does cardiac muscle have?
Myogenic - It can contract & relax without receiving contractions from nerves
Non-tiring - Lots of mitochondria to maintain regularbeating
Part 1 - Heartbeat:
Sinoatrial Node (in the wall of right atrium) sends out regular waves of electrical activity to the atrial walls.
Causes the right & left atria to contract at the same time
A band of non-conductingcollagentissue prevents the waves of electrical activity from passing from the atria to the ventricles
The waves instead are transferred from SAN to the atrioventricularnode (AVN)
Part 2 - Heartbeat:
The AVN passes on the electrical activity onto the bundle of His. However, there is a slight delay before the AVN reacts to ensure the atria is empty before the ventricles contract
The bundle of His is a group of musclefibres responsible for conducting waves between the ventricles to the apex (bottom) of the heart.
The bundle splits into finer muscle fibres in the left & rightventricles walls, called the Purkynetissue
The Purkyne tissue carries the waves into ventricle walls causing them to contract simultaneously, from the bottom up.
How is Heart Rate controlled?
The SAN generates electrical impulses that cause the cardiac muscles to contract
Heart rate is unconsciously controlled by the medullaoblongata
Animals need to alter their heart rate to respond to internal stimuli
Stimuli are detected by pressure & chemical receptors
Electrical impulses from receptors are sent to the medulla along sensory neurones. The medulla processes the info + sends impulses to the SAN along sympathetic or parasympathetic neurones
What receptors respond to pressure?
Baroreceptors are found in the aorta & the carotid arteries. They're stimulated by high or low bloodpressure
What receptors respond to chemicals?
Chemoreceptors are found in the aorta, the carotid arteries & the medulla. They monitor the oxygen levels in the blood and also CO2 and pH levels (which are indicators of O2 levels)
How does the body respond to High Blood Pressure?
Baroreceptors in the aorta /carotid artery detect high blood pressure
Impulses are sent to the medullaoblongata
This sends impulses along the parasympathetic nervous system
These secretes acetylcholine which binds to receptors on the SAN
The heart rate slows and this reduces blood pressure
How does the body respond to Low Blood Pressure?
Baroreceptors in the aorta /carotid artery detect low blood pressure
Impulses are sent to the medulla oblongata
This sends impulses along the sympathetic nervous system
These secretes noradrenaline which binds to receptors on the SAN
The heart rate speeds up and this increases blood pressure
How does the body respond to High Blood O2, low CO2 or high pH levels?
Chemoreceptors in the aorta /carotid artery detect chemical changes in the blood
Impulses are sent to the medullaoblongata
This sends impulses along the parasympathetic nervous system
These secretes acetylcholine which binds to receptors on the SAN
The heart rate slows and O2, CO2 and pH levels return to normal
How does the body respond to Low Blood O2, high CO2 or low pH levels?
Chemoreceptors in the aorta /carotid artery detect chemical changes in the blood
Impulses are sent to the medullaoblongata
This sends impulses along the sympathetic nervous system
These secretes noradrenaline which binds to receptors on the SAN
The heart rate increases and O2, CO2 and pH levels return to normal