Pack 18 Flashcards
1
Q
What is a stimulus?
A
A detectable change in the internal or external environment of an organism that leads to a response.
2
Q
What does the ability to respond to a stimulus increase for an organism?
A
The chance of survival
3
Q
What is a receptor?
A
Detector of a stimulus - specific to one stimulus.
4
Q
What does a coordinator do? At what levels may the coordination be?
A
- Formulates a suitable response to a stimulus.
* E.g. molecular to brain
5
Q
What is an effector?
A
An effector produces a response to a stimulus. E.g. muscle or gland
6
Q
What are the two means of communication in organisms?
A
- hormones
* nervous system
7
Q
What is a taxis?
A
• A simple response whose direction is determined by the direction of the stimulus.
8
Q
What are negative and positive taxes?
A
- Positive - an organism moves towards a favorable condition/stimulus.
- Negative - an organism moves away from an unfavourable condition/stimulus.
9
Q
Give three specific examples of taxes. Their name, advantage and the specific organism.
A
- Single celled algae move towards light increasing their chance of survival being photosynthetic - positive phototaxis.
- Earthworms move away from light - takes them into the soil where the can conserve water/find food - negative phototaxis.
- Some bacteria move towards a region of high glucose conc. - food source - positive chemotaxis.
10
Q
What is a kinesis?
A
A response in which the organism does not move towards or away from the stimulus. Instead, it changes the speed at which it moves and/or the rate at which it changes direction.
11
Q
Describe how hydrokenesis in woodlice increases their chances of survival. (Turning and movement) (6)
A
- Woodlice lose water in dry conditions.
- When they leave a damp area they move rapidly and change direction more often.
- Increases the chance of returning to the damp area.
- Once back in the damp area they slow down and change direction less often.
- Therefore more likely to remain in the damp area.
- If they are still in a dry area for a long time they move in a straight line rapidly to find a new damp area.
- Therefore more time in damp conditions so increased chance of survival.
12
Q
What is a tropism?
A
The growth of a plant towards a directional stimulus. Positive (towards) or negative (away).
13
Q
Give three stimuli plants respond to.
A
- Light
- Gravity
- Water
14
Q
What is the name for the types of molecules that control the response of plants to stimuli?
A
Plant growth factors.
15
Q
Why is ‘plant growth factors’ better than ‘plant hormones’? (2)
A
- They exert their influence by affecting growth and, they may be made by cells located throughout the plant rather than in particular organs.
- Unlike animal hormones, some plant growth factors affect the tissue from which they are released.
16
Q
Give an example of a plant growth factor and one thing it controls.
A
- IAA
* Cell elongation
17
Q
Describe the response of SHOOTS to light in 6 steps.
A
- Cells in the tip of the shoot produce IAA which is transported down the shoot.
- IAA transported evenly throughout all regions at first.
- Light causes movement of IAA from the light to the shaded side of the shoot.
- Greater conc. of IAA on the shaded side.
- IAA causes elongation of shoot cells - so the cells on the shaded side elongate more.
- The shaded side cells elongate faster than the light sude so the shoot tip bends towards the light.
18
Q
Where is IAA produced?
A
In the tips of shoots and roots.
19
Q
How does IAA affect root cells and shoot cells.
A
- In roots - high concentrations inhibit cell elongation.
* In shoots - high concentrations cause cell elongation.
20
Q
Where is elongation greatest in root cells?
A
on the light side
21
Q
How can you describe the response to light of roots and shoots.
A
- Roots - negatively phototropic
* Shoots - Positively phototropic
22
Q
How can you describe the response to gravity of roots and shoots (specific words) . Why? (for roots)
A
- Roots - Positively geotropic - need to grow into the soil for support and to absorb mineral ions and water
- Shoots - negatively geotropic
23
Q
Describe the response of ROOTS to gravity in 5 steps.
A
- Cells in the tips root produce IAA which is transported along the root initially to all sides.
- Gravity influences the movement of IAA to the lower side of the root.
- Greater concentration of IAA on the lower side inhibits cell elongation.
- Cell on lower side elongate less.
- Therefore the root bends downwards.
24
Q
In shoots describe the response to gravity. (3)
A
- More IAA on lower side.
- Increases cell elongation.
- Grows upwards.
25
Why does IAA only affect young cell walls.
Older cell walls have greater rigidity as they mature.
26
What is the name of the hypothesis that explains how IAA increases plasticity of cells.
Acid growth hypothesis.
27
Describe briefly the acid growth hypothesis.
Active transport of H+ ions from the cytoplasm to spaces in the cells walls causing them to become more plastic.
28
What is the simplest tupe of nervous response in mammals?
A reflect arc.
29
What are the two major divisions of the nervous system? What is each comprised of?
* Central nervous system (CNS) - the brain and spinal cord.
| * Peripheral Nervous System (PNS) - pairs of nerves that originate from either the brain or the spinal cord.
30
What two types of neurones compose the PNS? What does each do?
* Sensory neurones - carry action potentials from receptors towards the CNS.
* Motor neurones - carry action potentials from the CNS to effectors.
31
Into what two subdivision can the motor nervous system be divided? What deco each control?
* Voluntary nerveus system - body muscles (under conscious control).
* Autonomic nervous system - carries nerve impulses to glands, smooth muscle, and cardiac muscle. (subconscious)
32
What is the spinal cord?
A column of nervous tissue the runs along the back and lies inside the vertebral column for protection.
33
How many neurones does a reflex are involve?
3
34
What are the main stages of a spinal reflex arc? With the example of withdrawing hand from heat.
* The stimulus - heat
* Receptor - temp. receptors on skin generates action potential in sensory neurone.
* Sensory neurone. - to spinal cord
* Coordinator - intermediate neurone.
* Motor neurone - action potential to the arm
* Effector - muscle in the arm stimulated to contract.
* Response - pulling away the hand.
35
Where is the intermediate neurone in a spinal reflex reaction?
The spinal cord
36
What is a reflex arc?
The pathway of neurones in a reflex.
37
Give 4 reasons why reflex actions are important.
* Involuntary - no decision making - brain isn't overloaded. (information is still sometimes sent to the brain)
* effective from birth - don't need to be learnt.
* Fast, neurone pathway is short - only one or two synapses.
* Absence of decision making makes it rapid as well.
38
What is a Pacinian corpuscle?
A receptor that responds to the stimulus of mechanical pressure. Specific to one type of stimulus.
39
Why can a Pacinian corpuscle be described as a transducer?
It converts the mechanical energy of the stimulus into a generator potential. A different form of energy. Electrical energy.
40
Where do Pacician corpuscles occur?
* Deep in the skin.
| * Fingers, soles of feet, genitalia, ligaments and tendons.
41
Describe the structure of a Pacician corpuscle. What type of neurone?
* A single sensory neurone
* At the centre of layers of tissue separated by gel.
* Surrounded by a capsule.
42
What type of special channel protein does the Pacician corpuscle CSM contain?
Stretch-mediated sodium ion channel
43
Why are stretch-mediated sodium ion channel called this?
Their permeability to sodium ions changes when they are deformed.
44
Describe how the Pacinian corpuscle functions. (5)
* In normal state, stretch-mediated sodium ion channel of the CSM of the PC neurone are too narrow for sodium ions to pass along them - resting potential.
* When pressure is applied the CSM is stretched/deformed.
* This widens the sodium channels in the membrane and Na+ diffuse into the neurone.
* Influx of Na+ changes the membrane potential - depolarised - generator potential.
* This in turn creates an action potential in the neurone.
45
Where are the light receptors of the eye found?
Retina
46
What are the two types of light receptors.
rods and cones
47
Why can rods and cones be described as transducers?
They convert light energy into the electrical energy of a generator potential.
48
Which light receptors cannot distinguish between different wavelengths? What does this mean about vision using these cells?
* Rods
| * They only allow black and white vision.
49
How many rod cells connect to a single sensory neurone?
Many
50
What is the evolutionary purpose of rod cells?
To detect low light intensities.
51
Which cells do rods and cones directly synapse with?
Bipolar
52
Why does the fact many rod cells connect to one bipolar cell mean they allow vision in low light intensities? What is this called?
* Summation/retinal convergence.
| * Greater chance the threshold value will be exceeded.
53
How is a generator potential created in rod cell and cone cells?
Pigement (rhodopsin or iodopsin) is broken down.
54
Give two ways rod cells allow vision in low light intensity.
* Rhodopsin requires less light energy to be broken down than iodopsin.
* High retinal convergence
55
What are the names of the pigments in rods and cones?
Rods - rhodopsin
| Cones - iodopsin
56
What is visual acuity?
The ability to resolve two distinct points from each other
57
What is a drawback of high retinal convergence in rods?
• low visual acuity - light received by several rod cells will produce only one impulse detectable by the brain.
58
How many types of cone cell are there? What is the difference?
3 - they each respond to a different wavelength of light.
59
How do we perceive full colour when we only have three different colour receptors?
The proportions of each cone cell stimulated.
60
How many bipolar cells does a single cone cell synapse to?
One or very few.
61
Why do cone cells only respond to a high light intensity? (2 reasons)
* They synapse to only one bipolar cells. No/low retinal convergence so threshold value to produce a generator potential has to be reached in a single cone cell.
* Iodopsin breaks down at higher light intensities. So only high light energy will create a generator potential.
62
Why do cone cells have a high visual acuity?
Each cone cell synapses to a single bipolar cell. Therefore stimulation of two adjacent cone cells produces two separate impulses sent to the brain. So they can distinguish between two objects very close together.
63
Describe the distribution of rod and cone cells across the retina.
* At/around the fovea many cones few/no rods.
* At the periphery many rods few/no cones.
* neither at the optic nerve/blind spot
64
What is the fovea?
The point on the retina where
65
Why are cone cells concentrated at the fovea?
• The fovea receives the highest light intensity as the lens focuses light here.
66
Where does much of our sensory information come from?
Receptors inside the body.
67
What does the autonomic nervous system control?
Involuntary activity of internal muscles and glands.
68
What are the 2 divisions of the autonomic nervous system?
* Sympathetic
| * Parasympathetic
69
What does the sympathetic nervous system do in general? (3)
* Stimulates effectors so speeds up any activity.
* It controls effectors when we exercise strenuously or experience powerful emotions.
* Helps us to cope with stressful situations (fight or flight)
70
What does the parasympathetic nervous system do in general? (3)
* Inhibits effectors and so slows down any activity.
* It controls activities under normal resting conditions.
* Conserving energy and replenishing the body's resources.
71
Why can the parasympathetic and the sympathetic nervous system be described as antagonistic?
* Their action normally oppose one another.
* If one system contracts a muscle the other relaxes it.
* Therefore internal muscles and glands are regulated by the balance of the two systems.
72
What is the muscle of the heart known as?
Cardiac muscle.
73
What does myogenic mean?
The contraction of cardiac muscle is initiated from within the muscle itself rather than nervous impulses from outside (neurogenic).
74
Where is the sinoatrial node found?
• In the wall of the right atrium
75
What is the function of the sinoatrial node? What is it often referred to and why?
* Where the initial stimulus for contraction originates.
| * The pacemaker as it has a natural rhythm that determines heart beat.
76
Describe the sequence of events that controls the basic heart rate. (6)
* Wave of electrical excitation spreads out from the SAN actress both atria causing them to contract.
* Atrioventricular septum (non-conductive) prevents the wave crossing to the ventricles.
* Wave of excitation enters the AVN, between the atria.
* After a short delay the AVN conveys the wave between the ventricles along the purkyne tissue which make up the bundle his. To allow the ventricles to fill.
* Bundle of His conducts the wave though the AV septum to the base of the ventricles - branch into small Purkyne tissue fibres.
* Wave of excitation is released upwards causing the ventricles to contract bottom up.
77
Where is the atrioventricular node found?
Between the atria.
78
Why do the ventricles contract from the bottom first.
To force the blood upwards and out of the aorta/pulmonary artery so blood is not forced down to the bottom of the ventricles.
79
Which part of the CNS controls heart rate?
• Medulla oblongata
80
What are the two centres of the medulla and which nervous system are they linked to?
* Centre that increases heart rate linked to SAN by sympathetic nervous system.
* Centre that decreases heart rate, linked to SAN by parasympathetic nervous system.
81
What are the two types of receptors in blood vessels and where are they found?
Chemoreceptors and baroreceptors.
| • Found in the aorta and the carotid arteries.
82
What are chemoreceptors sensitive to? Directly and indirectly.
Blood pH that results from a change of carbon dioxide concentration.
83
What happens to the pH of the blood when carbon dioxide conc. is high? Why?
It lowers the pH as carbon dioxide forms an acid in solution.
84
Describe how chemoreceptors control heart rate. (6) - What key words/ideas do you need to get in
* When blood has higher than normal CO2 concentration, pH lowers.
* Chemoreceptors in the wall of aorta and carted artery detect this and increase the frequency of nervous impulses to the centre of the medulla that increases heart rate.
* This centre increases the frequency of impulses to the via sympathetic nervous system to SAN. Increases the rate of production of electrical waves by the SAN and therefore the heart rate.
* Causes increased blood flow which means more CO2 is removed at the lungs to CO2 conc. returns to normal.
* Therefore, pH of the blood returns to normal and the chemoreceptors reduce the frequency of impulses sent to medulla.
* Medulla reduces frequency of nerve impulses to the SAN. Reduced heart rate.
85
Describe how pressure receptors in the arteries operate when blood pressure is higher than normal.
* Pressure receptors transmit nervous impulses to the centre in the medulla that decreases heart rate more frequently.
* This sends impulses to the SAN node.
* Via parasympathetic nervous system.
* Leads to a decrease in the rate at which the heart beads.
86
Describe how pressure receptors in the arteries operate when blood pressure is lower than normal.
* Pressure receptors transmit nervous impulses to the centre in the medulla that increases heart rate more frequently.
* This sends impulses to the SAN node.
* Via sympathetic nervous system.
* Leads to a increase in the rate at which the heart beads.
