Stimuli and Responses Flashcards
1
Q
How do organisms respond to the environment?
A
- Organisms increase their chances of survival by responding to changes in their external environment (animals and plants respond in different ways)
- Organisms also respond to changes in their internal environment to make sure that the conditions are optimal for their metabolism
2
Q
What is a stimulus?
A
- Any change in the internal or external environment e.g. change in pressure, temperature, light intensity
- Response can be tactic or kinetic
- By detecting harmful stimulus, can move away from predators and extreme temperatures
- This increases chance of survival and the alleles being passed on
- Selection pressure that favours organisms with more appropriate responses to keep them in their favourable environment
3
Q
Tactic response (taxis)
A
- Directional movement in response to a stimulus
- The direction of stimulus affects response (woodlice move away from light so they don’t lose water- negative taxis)
4
Q
Kinetic response (kinesis)
A
- Non-directional (random) movement in response to a stimulus
- Intensity of stimulus affects response
- Woodlice example= show a kinetic response to humidity
- In high humidity, turn less often and move slowly, so that they stay where they are
- As air gets drier, they move faster and turn often, so that they move into a new area
- Response helps move woodlice to humid air to increase their chances of survival-reduces water loss and keeps them concealed
5
Q
Responses of earthworms, bacteria, single-called algae
A
- Algae (positive phototaxis) survival increased as they use light to make food
- Earthworms (negative phototaxis) survival increased as they are taken into the soil to conserve water, find food and avoid predators
- Some bacteria (positive chemotaxis) move towards glucose as they use it to make food
6
Q
Receptors
A
- Detect stimuli- can be cells or proteins on cell surface membranes
- Loads of different receptors that detect different stimuli
- Receptors are specific to one type of stimulus
7
Q
Effectors
A
- Cells that bring about a response to a stimulus, to produce an effect
- Examples include muscle cells or cells found in glands
- Receptors communicate with effectors via the nervous system or hormonal system (or both)
8
Q
The nervous system
A
Made up of a complex network of cells called neurones
9
Q
Sensory Neurones
A
- Transmit electrical impulses from receptors to CNS- the brain and spinal cord
- Have 1 dendron that is often long
10
Q
Motor Neurones
A
- Transmit electrical impulses from CNS to effectors
- Long axon, many short dendrites
11
Q
Relay Neurones
A
(intermediate) Transmit electrical impulses between sensory neurones and motor neurones
12
Q
Nervous Communication
A
- Stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neurone
- When an electrical impulse reaches the end of a neurone chemicals called neurotransmitters take the information across the gap (synapse) to the next neurone, where another electrical impulse is generated
- CNS (coordinator) processes information and sends impulses along motor neurones to an effector
13
Q
Nervous response
A
- When an electrical impulse reaches the end of a neurone, chemical messengers called neurotransmitters are secreted directly onto cells- so nervous response is localised
- Neurotransmitters are quickly removed once they have done their job, so response is short-lived
- Electrical impulses are really fast, so response is rapid- allows animals to react quickly to stimuli
14
Q
Simple reflex
A
- Rapid, involuntary response to a stimulus
- Pathway of communication goes through spinal cord but not through conscious parts of the brain-so response is automatic
- Protective as they help organisms to avoid damage to the body because the response happens so quick
- Fast due to absence of decision making (brain can’t get overloaded) and short neurone pathway
15
Q
Reflex arc
A
- Pathway of neurones linking receptor to effectors in a simple reflex
- If relay neurone involved, then possible to override refelx
16
Q
Spinal cord
A
- Column of nervous tissue that runs along the back and lies inside the vertebral column for protection
- By the time the brain has recieved nerve impulses from receptors, the muscles have already moved
20
Q
Auxins
A
- Plants respond to directional stimuli using specific growth factors- these are hormone like chemicals that speed up or slow down plant growth
- Plant growth factors are produced in the growing regions of the plant (shoot and root tips) and they move to where they’re needed in the other parts of the plant
- Some plant growth factors affect tissues that release them
- Growth factors called auxins are produced in the tips of shoots and diffuse backwards to stimulate the cell just behind the tips to elongate
- This is where cell walls become loose and stretchy, so cells get longer
- If the tip of a shoot is removed, no auxin will be available and the shoot stops growing
- Auxins stimulate growth in shoots but high concentrations inhibit growth in roots
22
Q
IAA phototropism and gravitropism
A
24
Q
Resting Potential
A
- When nervous sytem is in it’s resting state, there’s a difference between inside and outside of cell (inside is more negatively charged)
- Means their is a voltage across the membrane (potential difference)
- Potential difference at resting state is resting potential
- It is generated by ion pumps and ion channels
25
Q
Generator Potential
A
- When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell-altering the potential difference
- Change in potential difference due to a stimulus is called the generator potential
- A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference-so a bigger generator potential is produced
27
Q
Pacinian Corpuscles
A
- Mechanoreceptors (detect mechanical stimuli like pressure and vibrations, found in skin)
- They contain a sensory nerve ending wrapped in loads of layers of connective tissue called lamellae
- When stimulated (tap on the arm), lamellae are deformed and press on sensory nerve ending
- This causes sensory neurone’s cell membrane to stretch, deforming the stretch-mediated sodium ion channels
- Channels open and sodium ions diffuse into the cell, creating a generator potential
- If generator potential reaches threshold, it triggers an action potential
28
Q
Cone cells
A
- Made of iodopsin pigment which is only broken down at high light intensity
- One cone cell connects to one bipolar neurone which connects to one sensory neurone (therefore no summation of light can take place so only detects high light intensity as threshold isn’t that easy to reach)
- But because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli can be distinguished as two separate action potentials go to the brain= high visual acuity
- Mainly found in fovea
- Contain different optical pigments- red, green and blue sensitive (colour vision)
29
Q
Rod cells
A
- made of rhodopsin pigment which can be broken down at low light intensity
- a few rod cells connect to one bipolar neurone which connects to one sensory neurone (therefore summation of light can take place so can detect low light intensity)
- This is due to combining weak generator potentials to trigger an action potential
- but because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, the stimuli will be merged together = low visual acuity
- Found in peripheral parts of the retina
- Can’t distinguish between different wavelengths of light so monochromatic vision
30
Q
Photoreceptors
A
- Receptors in the eye that detect light
- Amont of light entering pupil is controlled by the muscles of the iris
- Light rays are focused by the lens onto the retina
- Retina contains photoreceptor cells (most in fovea)
- Nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones
- Where the optic nerve leaves the eye is called the blind spot- no photorecptor cells
33
Q
Control of heart beat
A
- Cardiac muscle is myogenic (contract and relax without recieving nerve signals)
- Sinoatrial node (SAN) which is a small mass of tissue in the wall of the right atrium is a pacemaker
- Sets out rhythm of heartbeat by sending out regular waves of electrical activity to the atrial walls
- Causes left and right atria to contract at the same time
- A band of non-conducting collagen tissue prevents waves of electrical activity from being passed directly from the atria to the ventricles
- Waves of electrical activity are transferred from SAN to atrioventricular node (AVN)
- AVN responsible for passing waves of electrical activity to bundle of His
- Slight delay before AVN reacts, to make sure atria have emptied before ventricles contract
- bundle of His is a group of muscle fibres responsible for conducting waves of electrical activity between ventricles to the bottom of the heart
- bundle of His splits into finer muscle tissues in the right and left ventricle walls, called purkyne tissue
- Purkyne tissue carries waves of electrical activity into the walls of the ventricles, causing them to contract simultaneously, from the bottom up
- Involves autonomic nervous system
