Topic 6 - Organisms respond to changes Flashcards
1
Q
What is a stimulus?
A
Any change in the internal or external environment
2
Q
How do organisms increase their chances of survival?
A
Responding it changes in their external environment
Responding to changes in their internal environment - to make sure that the conditions are always optimal for their metabolism
3
Q
What is a tactic response (taxis)?
A
Directional movement in response to a stimulus
The direction of the stimulus affects the response
4
Q
Give an example of how woodlice show a tactic response?
A
Light
Move away from a light source
Helps them survive as it keeps them concealed under stones during the day where they can be safe from predators
and keeps them in damp conditions (reducing water loss)
5
Q
What is a kinetic response (kinesis)?
A
Non-directional (random) movement in response to a stimulus
The intensity of the stimulus affects the response
6
Q
Give an example of how woodlice show a kinetic response?
A
Humidity
In high humidity they move slowly and turn less often, so that they stay where they are
As the air gets drier, they move faster and turn more often, so that they move into a new area
This response helps woodlice move from drier air to more humid air, and then stay put
This improves their chances of survival - reduces their water loss and it helps to keep them concealed
7
Q
What is a choice chamber?
A
A container with different compartments, in which you can create different environmental conditions.
8
Q
Describe the method of using a choice chamber? Required Practical 10
A
- Construct a choice chamber using the equipment (petri dish base, divider, fine mesh)
- To investigate the effect of light intensity on woodlouse movement, cover one half of the lid (including the sides) with black paper. This will make one side of the chamber dark. Put damp filter paper in both sides of the base to make the humidity constant throughout the chamber
- Place 10 woodlice on the mesh in the centre of the chamber and position the lid on the mesh so it’s lined up with the base below
- After 10 minutes, take off the lid and record the number of woodlice on each side of the chamber. Try to minimise the amount of time the lid is off, so that the environmental conditions created aren’t disturbed
- Repeat the experiment after gently moving the woodlice back to the centre. You can use a small, soft paintbrush to help with moving them. Most woodlice should end up on the dark side of the choice chamber (tactic response to light)
- To investigate humidity, place some damp filter paper in one side of the base and a desiccating (drying) agent (e.g. anhydrous calcium chloride) in the other side. Don’t cover the lid with paper. Put the lid on and leave the chamber for 10 minutes for the environmental conditions to stabilise before carrying out 3-5
9
Q
What do receptors detect?
A
Stimuli
10
Q
What are effectors?
A
Cells that bring about a response to a stimulus, to produce and effect
11
Q
How do receptors communicate with effectors?
A
Via nervous system and/or hormonal system
12
Q
What are the three types of neurones?
A
Sensory
Motor
Relay
13
Q
What is a sensory neurone?
A
Transmit electrical impulses from receptors to the CNS - the brain and spinal cord
14
Q
What is a motor neurone?
A
Transmit electrical impulses from the CNS to effectors
15
Q
What is a relay neurone?
A
Transmit electrical impulses between sensory neurones and motor neurones
16
Q
Describe nervous communication?
A
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 next to the neurone, where another electrical impulse is generated
The CNS processes the information and sends impulses along motor neurones to an effector
17
Q
Describe the nervous response
A
When an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto cells - so the nervous response is localised
Neurotransmitters are secreted directly onto cells - so the nervous response is localised
Neurotransmitters are quickly removed once they’ve done their job, so the response is short-lived
Electrical impulses are really fast, so the response is usually rapid - this allows animals to react quickly to stimuli
18
Q
What is a simple reflex?
A
Rapid, involuntary, automcatic response to a stimulus
19
Q
Where does the pathway of communication travel in a simple reflex?
A
Through the spinal cord but not through conscious parts of the brain, so the response happens automatically
20
Q
Why are simple reflexes important?
A
Protective
Help organisms to avoid damage to the body because the response happens so quickly
21
Q
What is the reflex arc?
A
The pathway of neurones linking receptors to effectors in a simple reflex
stimulus -> receptors -> sensory neurone -> CNS with relay neurone in spinal cord -> motor neurone -> effectors -> response
22
Q
What is a tropism?
A
Response of a plant to a directional stimulus
23
Q
What is a positive tropism?
A
Growth towards the stimulus
24
Q
What is a negative tropism?
A
Growth away from the stimulus
25
What is phototropism?
Growth of a plant in response to light
26
What type of phototropism do shoots show?
Positive and grow towards light
27
What type of phototropism do roots show?
Negative and grow away from light
28
What is gravitropism?
Growth of plant in response to gravity
29
What type of gravitropism do shoots show?
Negative and grow upwards
30
What type of gravitropism do roots show?
Positive and grow down
31
What are specific growth factors?
Hormone-like chemicals that speed up or slow down plant growth
32
Where are plant growth factors 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
33
What is the name of growth factors?
Auxins
34
Where are auxins produced and what do they do?
Produced in 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 the cells get longer
If the tip of a shoot is removed, no auxin will be available and the shoot stops growing
35
What do auxins do in shoots and what do auxins do in roots?
Auxins stimulate growth in shoots but high concentration inhibit growth in roots
36
What is IAA?
An important auxin that's produced in the tips of shoots and roots in flowering plants
37
How does IAA move around the plant?
Diffusion and active transport over short distances, and via the phloem over long distances
38
What does an uneven distribution of IAA mean?
Uneven growth in the plant
39
Where does IAA move to with phototropism?
Shaded parts of the shoots and roots, so there's uneven growth.
In shoots, IAA concentration increases on the shaded side - cells elongate and the shoot bends towards the light
In roots, IAA concentration increases on the shaded side - growth inhibited so root bends away from the light
40
Where does IAA move in gravitropism?
IAA moves to the underside of shoots and roots, so there's uneven growth
In shoots, IAA concentration increases on the lower side - cells elongate so the shoot grows upwards
In roots, IAA concentration increases on the lower side - growth is inhibited so the root grows downwards
41
How do receptors work?
Receptors are specific - they only detect one particular stimuli
42
What is the resting potential?
When a nervous system receptor is in its resting state, there's a difference in charge between the inside and outside of the cell - the inside is negatively charged relative to the outside
This means there's a voltage across the membrane
Voltage is also known as potential difference
The potential difference when a cell is at rest is called its resting potential
The resting potential is generated by ion pumps and ion channels
43
What is the generator potential?
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
The 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
44
What is the action potential?
If the generator potential is big enough it'll trigger an action potential - an electrical impulse along a neurone
An action potential is only triggered if the generator potential reaches a certain level called the threshold level
Action potentials are all one size, so the strength of the stimulus is measured by the frequency of action potentials (the number of action potentials triggered during a certain time period)
If the stimulus is too weak the generator won't reach the threshold, so there's no action potential
45
What are Pacinian corpuscles?
Mechanoreceptors
Contain the end of a sensory neurone - called a sensory nerve ending
Sensory nerve ending is wrapped in loads of layers of connective tissue called lamellae
46
What is a mechanoreceptor?
Detect mechanical stimuli
e.g. pressure and vibrations
47
What happens when a Pacinian corpuscle is stimulated?
The lamellae are deformed and press on the sensory nerve ending
This causes the sensory neurone's cell membrane to stretch, deforming the stretch-mediated sodium ion channels
The channels open and sodium ions diffuse into the cell, creating a generator potential
If the generator potential reaches the threshold, it triggers an action potential
48
What are photoreceptors?
Receptors in your eye that detect light
49
How do photoreceptors detect light in the eye?
Light enter the eye through pupil
Amount of light that enter controlled by muscles in the iris
Light rays are focused by the lens onto the retina, which lines the inside of the eye
Retina contains the photoreceptor cells
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 - there aren't any photoreceptor cells, so it's not sensitive to light
50
How do photoreceptors work?
Light enter eye
Hits photoreceptors
Absorbed by light-sensitive optical pigments
Light bleaches the pigments, 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
51
What are the two types of photoreceptor?
Rods
Cones
52
Where are rods mainly found?
Peripheral parts of the retina
53
Where are cones usually found?
Packed together in the fovea
54
What do rods give information in?
Black and white (monochromatic)
55
What do cones give their information in?
Colour
(trichromatic)
56
What are the three types of cones?
Red-sensitive
Green-sensitive
Blue-sensitive
57
What does it mean if rods very sensitive to light?
They fire action potentials in dim light
58
Why are rods very sensitive to light?
Many rods join one bipolar neurone, so many weak generator potentials combine to reach a threshold and trigger an action potential
59
What does it mean if cones are less sensitive to light?
They only fire action potentials in bright light
60
Why do cones less sensitive to light?
One cone joins to one bipolar neurone, so it takes more light to reach threshold and trigger action potential
61
What is visual acuity?
The ability to tell apart points that are close together
62
What visual acuity do rods have?
Rods have low visual acuity
63
Why do rods have low visual acuity?
Because many rods join the same bipolar neurone, which means light from two points close together can't be told apart
64
What visual acuity do cones have?
High visual acuity
65
Why do cones have high visual acuity?
Cones are close together and one cone joins to one bipolar neurone
When light from two points hits two cones, two action potentials (one from each cone) go to the brain - so you can distinguish between two points that are close together as two separate points
66
What is the nervous split into?
CNS
Peripheral nervous system
67
What is the CNS made up of?
Brain
Spinal cord
68
What is the peripheral system?
Made up of neurones that connect the CNS to the rest of the body
69
What are the two systems of the peripheral nervous system?
Somatic
Autonomic
70
What does the somatic nervous system do?
Controls conscious activities
e.g. running and playing video games
71
What does the autonomic nervous system control?
Unconscious activities
e.g. digestion
Involved in controlling heart rate
72
What are the branches of the autonomic nervous system?
Sympathetic
Parasympathetic
73
What does the SNS do?
'Fight or flight; system that gets body ready for action
74
What does the PsNS do?
'Rest and digest' system
Calms body down
75
What is the cardiac muscle? HINT: begins with M
Myogenic
76
What does myogenic mean?
Can contract and relax without receiving signals from nerves
This pattern of contractions controls the regular heartbeat
77
Describe the control of heartbeat
Sinoatrial node sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls
Causes right and left atria to contract at same time
Band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles
Instead, waves of electrical activity are transferred from SAN to atrioventricular node
But, there's a delay before the AVN reacts, to make sure the atria have emptied before the ventricles contract
Bundle splits into finer muscle fibres in the right and left ventricle walls, called the Purkyne tissue
Purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from bottom up
78
What is the SAN?
Small mass of tissue in the wall of the right atrium
It is like a pacemaker - sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls
79
What does a band of non-conducting collagen tissue do?
Prevents the waves of electrical activity from being passed directly from the atria to the ventricles
80
What does the AVN do?
Passes waves of electrical activity on the bundle of His
81
What is the bundle of His?
Group of muscle fibres responsible for conducting waves of electrical activity between the ventricles to the bottom of the heart
82
What part of the brain controls the rate at which the SAN fires?
Medulla
83
What are internal stimuli detected by for blood pressure?
Pressure receptors
Chemical receptors
84
Where are the pressure receptors to do with blood pressure found? What are they called? What are they stimulated by?
Aorta and carotid arteries
Baroreceptors
Stimulated by high and low blood pressure
85
Where are the chemical receptors to do with blood pressure found? What are they called? What do they do?
Aorta, carotid arteries, medulla
Chemoreceptors
Monitor the oxygen level in the blood and also carbon dioxide and pH
86
Describe the control of heart rate in high blood pressure
Baroreceptors detect high blood pressure and send impulses along sensory neurones to the medulla, which sends impulses along parasympathetic neurones. These secrete acetylcholine, which binds to receptors on the SAN
This causes the heart rate to slow down in order to reduce blood pressure back to normal
87
Describe the control of heart rate in low blood pressure?
Baroreceptors detect low blood pressure and send impulses along sensory neurones to the medulla, which sends impulses along sympathetic neurones
These secrete noradrenaline, which binds to receptors on the SAN
This causes the heart rate to speed up in order to increase blood pressure back to normal
88
How do sodium and potassium ions move across a neurone's membrane?
Sodium-potassium pumps and potassium ion channels
-Sodium-potassium pumps use active transport to move three sodium ions out of the neurone for every two potassium ions moved in. ATP is needed to do this
-Potassium ion channels allow facilitated diffusion of potassium ion out of the neurone, down their concentration gradient
89
Describe the process of the movement of sodium and potassium ions across a resting cell membrane
1. The sodium-potassium pumps move sodium ions out of the neurone, but the membrane isn't permeable to sodium ions, so they can't diffuse back in. This creates a sodium ion electrochemical gradient (a concentration gradient of ions) because there are more positive sodium ions outside the cell than inside
2. The sodium-potassium pumps also move potassium ions in to the neurone
3. When the cell's at rest, most potassium ion cannels are open. This means that the membrane is permeable to potassium ions, so some diffuse back out through potassium ion channels
90
What is the refractory period?
After an action potential, the neurone cell membrane can't be excited again straight away. This is because the ion channels are recovering and they can't be made to open - sodium ion channels are closed during repolarisation and potassium ion channels are closed during hyperpolarisation
91
Describe what causes an action potential
When a neurone is stimulated, other ion channels in the cell membrane, called sodium ion channels open.
If the stimulus is big enough, it'll trigger a rapid change in potential difference.
This causes the cell membrane to become depolarised
92
What does the refractory period act as?
Time delay between one action potential and the next
Ensures action potentials don't overlap but pass along as discrete impulses
The refractory period also means that there's a limit to the frequency at which the nerve impulses can be transmitted, and that action potentials are unidirectional
93
What causes a wave of polarisation?
When an action potential happens, some of the sodium ions that enter the neurone diffuse sideways
This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part
94
Why does the wave move away from the parts of the membrane in the refractory period?
These parts can't fire and action potential
95
What is the all-or-nothing principle?
Once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is
If the threshold isn't reached, an action potential won't fire
96
What does a bigger stimulus do?
Won't cause a bigger action potential but it will cause them to fire more frequently
97
What three factors affect the speed of conduction?
Myelination
Axon diameter
Temperature
98
What is myelination?
Some neurones, including many motor neurones, are myelinated - they have a myelin sheath
The myelin sheath which is an electrical insulator
In the peripheral nervous system, the sheath is made of a Schwann
Between the Schwann cells are tiny patches of bare membrane called nodes of Ranvier
Sodium ion channels are concentrated at the nodes of Ranvier
99
What is saltatory conduction?
In a myelinated neurone, depolarisation only happens at the nodes of Ranvier (where sodium ions can get through the membrane)
The neurone's cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse 'jumps' from node to node
100
Describe how impulses travel in a non-myelinated neurones?
Impulse travels as a wave along the whole length of the axon membrane - so you get depolarisation along the whole length of the membrane
This is slower than saltatory conduction
101
How does axon diameter affects speed of conduction?
Action potentials are conducted quicker along axons with bigger diameters because there's less resistance to the flow of ions than in the cytoplasm of a smaller axon
With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker
102
How does temperature affect speed of conduction?
The speed of conduction increases as the temperature increases too, because ions diffuse faster
The speed only increases up to around 40 degrees C though - after that the proteins begin to denature and the speed decreases
103
What is a synapse?
Junction between a neurone and another neurone, or between a neurone and an effector cell, e.g. a muscle or gland cell
104
What is the tiny gap between the cells at the synapse called?
Synaptic cleft
105
What is the swelling of the presynaptic neurone called?
Presynaptic knob
106
What is the synaptic knob filled with?
Synaptic vesicles filled with chemicals called neurotransmitters
107
What happens when an action potential reaches the end of a neurone?
Neurotransmitters released into synaptic cleft
108
What happens when neurotransmitters bind to receptors?
Might trigger an action potential in a neurone, cause muscle contraction in a muscle cell, or cause a hormone to be secreted from a gland cell
109
What does unidirectional mean?
Impulse can only travel in one direction
110
What makes the impulses unidirectional?
Neurotransmitters are removed from the cleft so the response doesn't keep happening
e.g. they're taken back into the presynaptic neurone or they're broken down by enzymes and the products are taken into the neurone
111
What is acetylcholine?
Binds to cholinergic receptors
112
What are the synapses called that use acetylcholine?
Cholinergic synapses
113
Describe the first stage of a nerve impulse being transmitted across a cholinergic synapse
1. Arrival of an action potential
An action potential arrives at the synaptic knob of the presynaptic neurone
The action potential stimulates voltage-gated calcium ion channels in the presynaptic neurone to open
Calcium ions diffuse into the synaptic knob
114
Describe the second stage of a nerve impulse being transmitted across a cholinergic synapse
2. Fusion of vesicles
The influx of calcium ions into the synaptic knob causes the synaptic vesicles to fuse with the presynaptic membrane
The vesicles release the neurotransmitter acetylcholine into the synaptic cleft of exocytosis
115
Describe the third stage of a nerve impulse being transmitted across a cholinergic synapse
ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane
This causes sodium ion channels in the postsynaptic neurone to open
The influx of sodium ions into the postsynaptic membrane is generated if the threshold is reached
ACh is removed from the synaptic cleft so the response doesn't keep happening
It's broken down by the enzyme acetylcholinesterase and the products are re-absorbed by the presynaptic neurone and used to make more ACH
116
What does excitatory neurotransmitter do?
Depolarises the postsynaptic membrane, making it fire and action potential if the threshold is reached
117
What does an inhibitory neurotransmitter do?
Hyperpolarises the postsynaptic membrane (making the potential difference more negative), preventing it from firing an action potential
118
What is summation?
Where the effect of neurotransmitters released from many neurones (or one neurone that's stimulated a lot in a short period of time) is added together
It means synapses accurately process information, finely tuning the response
There are two types
119
Describe the sequence of events involved in transmission across a cholinergic synapse
Do not include details on the breakdown of acetylcholine in yur answer
-Depolarisation of presynaptic membrane
-Calcium channels open and calcium ions enter synaptic knob
-Calcium ions cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine
-Acetylcholine diffuses across synaptic cleft
-Acetylcholine attaches to receptors on the postsynaptic membrane
-Sodium ions enter postsynaptic neurone leading to depolarisation
120
What are the three types of muscle?
Smooth
Cardiac
Skeletal
121
What is smooth muscle?
Contracts without conscious control
Found in walls of internal organs
e.g. stomach, intestine, blood vessels
122
What is cardiac muscle?
Contracts without conscious control like smooth muscle, but is only found in the heart
123
What is skeletal muscle?
Type of muscle you use to move
124
What are antagonistic pairs?
Muscles that work together to move a bone
The contracting muscle is the agonist and the contracting muscle is the antagonist
125
What is skeletal muscle made up of?
Large bundles of long cells, called muscle fibres
126
What is the cell membrane of muscle fibres called?
Sarcolemma which fold inwards across the muscle fibre and stick into the sarcoplasm
127
What is a muscle fibre's cytoplasm called?
Sarcoplasm
128
What do the folds of the sarcolemma and what are they called?
Folds are called transverse tubules and they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
129
What network of internal membranes run through the sarcoplasm?
Sarcoplasmic reticulum
130
What does the sarcoplasmic reticulum store and release?
Calcium ions that are needed for muscle contraction
131
What organelle do muscle fibres have lots of?
Mitochondria
132
Why are lots of mitochondria useful in muscles?
Provide ATP needed for muscle contraction
133
What other organelle do muscle fibres have lots of and what is the name for this?
Nuclei
Multinucleate
134
What are the cylindrical organelles that muscle fibres have lots of?
Myofibrils
135
What are myofibrils made up of and what are they highly specialised for?
Proteins myosin and actin
Contraction
136
What are the dark bands of a myofibril under a microscope?
Contain the thick myosin filaments and some overlapping thin filaments - called A-bands
137
What are light bands of myofibril under an electron microscope?
Contain thin actin filaments only - called I-bands
138
What are the short units called that make up a myofibril?
Sarcomere
139
What line marks the end of the sarcomere?
Z-line
140
What line is in the middle of each sarcomere?
M-line
141
What is the M-line?
The middle of the myosin filaments
142
What is the H-zone?
Only contains myosin filaments
Around the M-line is the H-zone
143
What is the sliding filament theory?
Where myosin and actin filaments slide over one another to make the sarcomeres contract - the myofilaments themselves don't contract
The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
Sarcomeres return to their original length as the muscle relaxes
144
What are myosin filaments?
Have globular heads that are hinged, so they can move back and forth
Each myosin head has a binding site for actin and a binding site for ATP
145
What are actin filaments?
Have binding sites for myosin heads, called actin-myosin binding sites
Another protein called tropomyosin is found between actin filaments which helped myofilaments move past each other
146
What happens in resting muscles?
The actin-myosin binding site is blocked by tropomyosin
This means myofilaments can't slide past each other as the myosin heads can't bind to the actin filaments
(The myosin heads need to bind to the actin-myosin binding site on the actin filament so that myosin and actin filaments can move past each other)
147
Describe the arrival of an action potential in the process of muscle contraction
When an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma
Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum
This causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm
This influx of calcium ions into the sarcoplasm triggers muscle contraction
Calcium ions bind to a protein attached to tropomyosin, causing the protein to change shape
This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
This exposes the binding site, which allows the myosin head to bind
The bond formed when a myosin head binds to an actin filament is called an actin-myosin cross bridge
148
Describe the movement of the actin filament in the process of muscle contraction
Calcium ions also activate the enzyme ATP hydrolase, which hydrolyses ATP to provide the energy needed for muscle contraction
The energy released from ATP causes the myosin head to bend, which pulls the actin filament in along in a kind of rowing action
149
Describe the breaking of the cross bridge in the process of muscle contraction
Another ATP molecule provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after it's moved
The myosin head then returns to its starting position, and reattaches to a different binding site further along the actin filament
A new actin-myosin cross bridge is formed and the cycle is repeated
Many actin-myosin cross bridges form and break very rapidly, pulling the actin filament along - which shortens the sarcomere, causing the muscle to contract
The cycle will continue as long as calcium ions are present
150
Describe the return to resting state in the process of muscle contraction
When muscle stops being stimulated, calcium ions leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum using ATP
Causes tropomyosin molecules to move back, so they block the actin-myosin binding sites
Muscles aren't contracted because no myosin heads are attached to the actin filaments
The actin filaments slide back to their relaxed position, which lengthens the sarcomere
151
What are the three ways in which ATP is generated for muscle contraction?
Aerobic respiration
Anaerobic respiration
ATP-phosphocreatine (PCr) system
152
Describe aerobic respiration for muscle contraction
Most ATP is generated via oxidative phosphorylation in the cell's mitochondria
Aerobic respiration only works when there's enough oxygen so it's good for long periods of low-intensity exercise e.g. a long walk
153
Describe anaerobic respiration for muscle contraction
ATP is made rapidly by glycolysis
The end product of glycolysis is pyruvate, which is converted to lactate by lactate fermentation
Lactate can quickly build p in the muscles and cause muscle fatigue
Anaerobic respiration is good for short periods of hard exercise e.g. 400m sprint
154
Describe ATP-phosphocreatine system for muscle contraction
ATP is made by phosphorylating ADP - adding phosphate group taken from PCr
The equation for this is ADP + PCr --> ATP + Cr
PCr is stored outside of cells
ATP-PCr system generates ATP very quickly
PCr runs out after a few seconds so it is used during short bursts of vigorous exercise e.g. tennis serve
ATP-PCr system is anaerobic and it's alactic
Some of the creatine gets broken down into creatinine, which is removed from the body via the kidneys
Creatine levels can be higher in people who exercise regularly and those with a high muscle mass
155
What do high creatinine levels indicate?
Kidney damage
156
What are the two types of muscle fibres?
Slow twitch
Fast twitch
157
What are slow twitch muscle fibres?
Contract slowly
Work for a long time without getting tired
Good for endurance activities
High proportions are found in the muscles used for posture e.g. in back and calves
Energy is released slowly through respiration
Have lots of mitochondria and blood vessels to supply muscles with oxygen
The mitochondria are mainly found near to the edge of muscle fibres, so that there's a short diffusion pathway for oxygen from the blood vessels to the mitochondria
Rich in myoglobin
158
What are fast twitch muscle fibres?
Contract very quickly but also get tired quickly
Makes them good for short bursts of speed and power
e.g. sprinting and eye movement
High proportions of fast twitch muscle fibres are found in muscles you use for fast movement such as the legs, arms and eyes
Energy is released through anaerobic respiration using glycogen in fast twitch muscle fibres
Also have stores of PCr so that energy can be generated very quickly when needed
Fast twitch muscle fibre have few mitochondria or blood vessels
They don't have much myoglobin so can't store much oxygen
159
What is homeostasis?
The maintenance of a stable internal environment, involving physiological control systems that keep your internal environment roughly constant. Means your internal environment is in a state of dynamic equilibrium
160
Why is keeping your internal environment stable vital?
Vital for cells to function normally and stop them being damaged
161
What is the importance of homeostasis?
It's particularly important to maintain the right core body temperature and blood pH
This is because they both affect enzyme activity which control the rate of metabolic reactions
Also important to maintain the right blood glucose concentration because cells need glucose for energy and blood glucose concentration affects the water potential of blood
162
Describe temperature in the role of homeostasis
The rate of metabolic reactions increases when the temperature's increased
More heat means more kinetic energy, so the molecules move faster
This makes the substrate molecules more likely to collide with the enzymes' active sites
The energy of these collisions
