Survival and response

Question 1

What is a stimulus?

Answer 1

Any change in the internal or external environment

Question 2

What are receptors?

Answer 2

Cells or proteins that detect stimuli

Question 3

What are effectors?

Answer 3

Cells (such as muscle or gland cells) that bring about a response to a stimulus to produce an effect

Question 4

How do receptors and effectors communicate?

Answer 4

Through the nervous system or hormonal system

Question 5

Types of neurones?

Answer 5

Sensory neurone - transmit electric impulses from receptors to the CNS (brain and spinal cord)
Motor neurone - transmit electric impulses from CNS to effectors
Relay neurone - transmit electric impulses between sensory neurones and motor neurones

Question 6

Voluntary response

Answer 6

Stimulus detected by receptor cells
Electrical impulse is sent along a sensory neurone
At synapses neurotransmitters take the information across to the next neurone, which sends an electrical impulse to the CNS
CNS processes the information and sends impulses along the motor neurones to an effector which creates a response

Question 7

2 parts of the nervous system system?

Answer 7

Central Nervous system (CNS) - brain and spinal cord

Peripheral nervous system - connect the CNS to the rest of the body

Question 8

Structure of the peripheral nervous system?

Answer 8

Somatic nervous system - controls concious activities
Autonomic nervous system - unconscious activities - made up of the sympathetic system and parasympathetic system
Sympathetic nervous system - ‘flight or fight’
Parasympathetic nervous system - calms the body - ‘rest and digest’

Question 9

Description of reflex actions?

Answer 9

Body response to stimulus without a conscious decision
Therefore fast - skips the CNS
Called a reflex arc

Question 10

Reflex arc?

Answer 10

Receptor detects stimulus
Sensory neurone carries impulse to relay neurone
Relay neurone connects to the motor neurone
Motor neurone sends impulses to the effector
Response

Question 11

Nervous System Communication description?

Answer 11

Electrical impulses reach the end of neurone, secreting neurotransmitters directly on to target cells - localised
Neurotransmitters are quickly removed once used - short-lived
Electrical impulses are really fast - rapid response

Question 12

What is a tropism?

Answer 12

The response of a plant to a directional stimulus

Question 13

Features of a tropism?

Answer 13

Respond by regulating their growth
Positive tropism - grows towards the stimulus
Negative tropism - grows away from the stimulus

Question 14

Phototropism?

Answer 14

Growth in response to light
Shoots are positively phototropic - grow towards light
Roots are negatively phototropic - grow away from light

Question 15

Gravitropism?

Answer 15

Growth in response to gravity
Shoots are negatively gravitropic - grow upwards
Roots are positively gravitropic - grow downwards

Question 16

Plant growth factors?

Answer 16

Respond to directional stimuli with growth factors that speed up or slow down growth
Produced in the growing regions (shoot tips, leaves) and travel to desired areas
Auxins - stimulate the growth of shoots by cell elongation - cell walls become loose and stretchy so cell becomes longer
High concentrations inhibit growth in roots

Question 17

IAA?

Answer 17

Indoleacetic Acid - type of auxin
Produced in the tips of shoots
Moved around plant to control tropisms - moves by diffusion and active transport for short distances - phloem for longer distances
Results in varied concentrations of IAA around the plant - leads to uneven growth

Question 18

IAA in phototropism?

Answer 18

IAA moves to shaded part of plant shoot and roots - uneven growth
In shoot, growth faster by elongation on shaded side so the plant bends towards the light
In roots, concentration increases on the shaded side - growth is inhibited so the root bends away from the light

Question 19

IAA in gravitropism?

Answer 19

IAA moves to the underside of the shoots and roots - uneven growth
In shoots, IAA concentration increases on lower side, cells elongate and the shoot grows upward
In root, IAA contration increases on the lower side, growth inhibited so the root grows downwards

Question 20

Simple organisms responses?

Answer 20

Have simple responses to keep them in a favourable environment - either tactic or kinetic

Question 21

Tactic responses?

Answer 21

(taxes)
Organisms move towards or away from a directional stimulus
Woodlice show a tactic response to light (phototaxis) - they move away from a light. Helps them keep concealed under stones during the day - safe from predators - keeps them in damp conditions (reduces water loss)

Question 22

Kinetic responses?

Answer 22

(kineses)
Organisms movement is affected by a non-directional stimulus
Woodlice show a kinetic response to humidity - high humidity they move slowly and turn less - stay where they are - when air gets drier they turn more and move faster - leave the area

Question 23

Experiment: Choice Chamber?

Answer 23

Investigates how animals react to changes in environments
1. Construct
2. To investigate light intensity, cover one side with black paper. Put damp filter paper in bot sides of the base.
3. Place 10 woodlice on the mesh in the centre of the chamber and cover with lid.
4. After 10 mins open lid and record how many woodlice are in each section
5. Repeat the experiment by placing the woodlice gently back in the centre
Most should accumulate in the dark region (tactic response to light)
6. To investigate humidity, place some dark filter paper in one side of the base and a desiccating (drying) agent in the other side. Don’t cover the lid with paper.
Can do the same thing with the maze which we did.

Question 24

What are receptors?

Answer 24

specific (only detect one stimulus)

Cells, proteins

Question 25

Nervous system in resting state?

Answer 25

Difference in charge between inside and outside of cell - generated by ion pumps and ion channels
There is a voltage across the membrane - potential difference
Called the resting potential
When 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 the generator potential
A bigger stimulus means there is a bigger movement of ions and a bigger change in potential difference - bigger generator potential created
If the threshold is passed an action potential will be reached - electrical impulse along a neurone
Strength of the stimulus is measured by the frequency of action potentials as they are all one size

Question 26

Pressure receptors?

Answer 26

Pacinian corpuscles
mechanorecptors - detect mechanical stimuli - pressure and vibration
Found in skin
Contain the end of a sensory neurone - sensory nerve ending - wrapped in layers of connective tissue lamellae

Question 27

How do pressure receptors trigger an action potential?

Answer 27

When the pacinian corpuscles are stimulated the lamellae are deformed and press on the sensory nerve ending
Stretches the sensory neurones cell membrane, deforming the stretch-mediated sodium ion channels
They open and sodium ions diffuse into the cell - creating a generator potential
If the generator potential reaches the threshold, it triggers an action potential

Question 28

Light receptors?

Answer 28

Photoreceptors in the eye
Light enters the pupil
Amount of light that enters is controlled by the muscles of the iris
Light rays are focused by the lens onto the retina - lines the inside of the eye
Retina contains photoreceptor cells - detect light
The fovea is an area of the retina where there are lots of photoreceptors
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 photoreceptor cells here - not sensitive to light

Question 29

How do photoreceptors convert light to an electrical impulse?

Answer 29

Light enters the light, hits the photoreceptors and is absorbed by light-sensitive optical pigments
Light bleaches the pigment, causing a chemical change and altering the membrane permeability to sodium ions
A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone
Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain

Question 30

Rods and Cones?

Answer 30

Two types of photoreceptor - rods and cones
Rods are mainly found in the peripheral parts of the retina, cones are packed together in the fovea
Rods and cones contain different optical pigments - sensitive to different wavelengths
Rods only give information in black and white (monochromic vision), but cones give information in colour (trichromatic vision). There are three types of cones, each containing a different optical pigment - red sensitive, green-sensitve and blue-sensitive
Stimulated in different proportions to see different colours

Question 31

Difference in sensitivity and visual acuity (detail) between rods and cones?

Answer 31

SENSITIVITY
Rods are very sensitive to light (fire action potentials in dim light) - because many rods join one neurone - many weak generator potentials reach the threshold
Cones are less sensitive (only fire action potentials in bright light) - because one cone joins one neurone - takes more light to reach the threshold and reach an action potential
VISUAL ACUITY (basically resolution)
Rods give low visual acuity because many rods join the same neurone, light from two points close together can’t be told apart
Cones give high visual acuity - cones are close together and one cone joins one neurone - When light from two points hits two cones, two action potentials are produced

Question 32

Beating of the heart?

Answer 32

Cardiac muscle is myogenic
SAN (sinoatrial node = pacemaker), in the wall of the right atrium sends out waves of electrical activity into the atrial walls
Right and left atria contract
Band of non-conducting collagen tissues prevents the waves of electrical activity from being passed directly from the atria to the ventricles
Transfers to AVN (atrioventricular node)
AVN slight delay - make sure the atria have emptied
Electrical activity travels to bundle of His - group of muscle fibres
Travels to Purkyne tissue
Carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously
Diastole

Question 33

Control of heart rate?

Answer 33

Controlled by part of the brain - medulla oblongata
Alters in response to internal stimuli
Pressure receptors - baroreceptors - aorta and carotid arteries - stimulated by high and low pressure
Chemical receptors - chemoreceptors - aorta and carotid arteries in the medulla - monitor the oxygen level in the blood and also the CO2 and pH (indicators of O2 levels)
Electrical impulses sent along sensory neurones to the medulla
Sends impulses along sympathetic or parasympathetic neurones (autonomic nervous system)

Question 34

Response to high blood pressure?

Answer 34

Baroreceptors detect high blood pressure
Impulses are sent to the medulla
Impulses along parasympathetic neurones
Secrete acetylcholine (neurotransmitter)
Binds to receptors on the SAN
Effects the cardiac muscles
Heart rate slows to reduce blood pressure back to normal

Question 35

Response to low blood pressure?

Answer 35

Baroreceptors detect low blood pressure
Impulses are sent to the medulla
Impulses along sympathetic neurones
Secrete noradrenaline (neurotransmitter)
Binds to receptors on the SAN
Effects the cardiac muscles
Heart rate speeds up to increase blood pressure back to normal

Question 36

Response to high blood O2, low CO2 or high pH

Answer 36

Chemoreceptors detect chemical changes
Impulses are sent to the medulla
Impulses along parasympathetic neurones
Secrete acetylcholine (neurotransmitter)
Binds to receptors on the SAN
Effects the cardiac muscles
Heart rate decreases to return O2, CO2 and pH levels  back to normal

Question 37

Response to low blood O2, high CO2 or low pH levels?

Answer 37

Chemoreceptors detect chemical changes
Impulses are sent to the medulla
Impulses along sympathetic neurones
Secrete noradrenaline (neurotransmitter)
Binds to receptors on the SAN
Effects the cardiac muscles
Heart rate increases to return O2, CO2 and pH levels  back to normal