Biology paper 2 mistakes Flashcards
1
Q
Freshwater marshes have one of the highest rates of gross primary production and net primary production of all ecosystems.
Carbon use efficiency is the ratio of NPP: GPP. Freshwater marshes have high CUE.
Use your knowledge of NPP to explain why freshwater marshes have a high CUE and the advantage of this.
A
Explanation: Less respiration
Advantage: high growth
2
Q
Use your knowledge of the nitrogen cycle to suggest why waterlogged soils contain relatively higher concentrations of ammonium compounds and low concentrations of nitrite and nitrate ions.
A
- more denitrification occurs
- converting nitrate ions into nitrogen gas
3
Q
The student substituted height for biomass. she did not want to destroy the plants to measure their biomass.
A
mp1 - assumed height is proportional to biomass
mp2 - height doesn’t include roots
4
Q
Describe the role of saprobionts in the nitrogen cycle ?
A
saprobionts are used in ammonification to break down organic nitrogen-containing DNA into ammonia
5
Q
One environmental issue arising from the use of fertilisers is eutrophication. Eutrophication can cause water to become cloudy. Describe how you would obtain quantitative measurements of their cloudiness
A
- use of colorimeter
- measure the abundance of light
- sane volume of water
6
Q
Suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them.
A
- place in boiling water
- kill other bacteria that may also break down ammonia
7
Q
Suggest what the scientists should have done during the process to be sure that all of the water has been removed from the plant samples.
A
- weigh samples at intervals
- see if weighing becomes constant
8
Q
Arbuscular mycorrhiza fungi (AMF) grow on, and into, the roots of plants. AMF can increase the uptake of organic ions such as phosphate.
Suggest one way in which AMF may benefit from their association with plants
A
They receive sucrose from plants or carbohydrates
9
Q
Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity.
A
- represents the dry mass of carbon
- represents GPP - R
10
Q
Give two biological molecules that contain phosphorus.
A
- DNA
- ATP
11
Q
Describe the role of microorganisms in producing nitrates from the remains of dead organisms.
A
- sapriobionts break down organic molecules like DNA into ammonium ions. Ammonia ions are broken down into nitrite ions and then nitrate ions by nitrifying bacteria
12
Q
Upwelling often results in high primary productivity in coastal waters. Explain why some of the most productive fishing areas are found in coastal waters.
A
- nitrate ions for the growth of plants
- more producers so more food for consumers
13
Q
Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.
A
- DNA
- Amino Acids
14
Q
Describe another process carried out by microorganisms which adds ammonium ions to soil.
A
sapriobionts breakdown dead matter organic molecules (DNA) into ammonia ions
15
Q
Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil.
A
- Ploughing increases oxygen so less denitrification can take place which means more nitrate ions in the soil.
16
Q
suggest two ways in which crop rotation may lead to high crop yield
A
- grow crops with nitrogen-fixing bacteria so nitrates can be replenished
- different crops require different nutrients
17
Q
It takes longer for the nitrogen-containing substances to get into the lake when an organic fertiliser is used than when an inorganic fertiliser is used. Explain why it takes longer when an organic fertiliser is used.
A
Organic fertilisers are insoluble so they have to be broken down. Take longer to dissolve
18
Q
When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake.
(a) (i) Describe how the nitrogen-containing substances get into the lake.
A
nitrates leach into water, dissolving in the water
19
Q
Suggest one source of the phosphate in the lake?
A
Slurry
20
Q
Describe how the presence of nitrates in a lake may eventually lead to the death of fish?
A
- nitrates cause algae to grow rapidly and cover the surface of the lake, blocking light
- Plants below can’t photosynthesis and die
- Decomposers break down dead matter respiring aerobically, lowering oxygen levels
- fish die due to lower oxygen levels
21
Q
The ecologists dried the samples in an oven at 103c for 24 hours. Describe how the ecologists could have determined whether or not this drying removed all the water from a wood sample.
A
- reheat and record mass
- until a constant mass
22
Q
Start with measuring the diameter of a large number of trees. Assume that the dry biomass of a tree consists of biological molecules that contain carbon.
A
- calculate the mean diameter
- Estimate the mean fresh biomass
- find % water content to find dried biomass
- use dried density to calculate the mass of the tree
- count the number of trees in the area and times by carbon content
23
Q
Describe the part played by the inner membrane of a mitochondrion in producing ATP?
A
- electrons move across ETC, releasing energy for H+ protons to move into intermembral space
- the released energy is used to combine ADP + PI to produce ATP
24
Q
A scientist investigated ATP production in the preparation of isolated mitochondria . He suspended the mitochondria in an isotonic solution and added a suitable respiratory substrate together with ADP and phosphate.
Explain why the scientist did not use glucose as a respiratory substrate.
A
- glucose used in glycolysis
- glucose is too large to pass through mitochondria
25
Describe how NAD is regenerated in anaerobic respiration in yeast cells.
pyruvate is reduced into ethanol and carbon dioxide using H from NADPH regenerating NAD
26
Explain what causes the concentration of blood lactate to fall after the seal's dive.
- seal breathes, bringing in oxygen.
- This allows lactate to be oxides back to pyruvate which can be used for aerobic respiration
27
Give on other way in which blood flow into the diaphragm muscles may be reduced
constriction of the arteriole
28
During a dive, blood flow to the diaphragm muscles of a seal is reduced. Suggest advantage to the seal of maintaining blood supply to the diaphragm muscles during a dive?
supplies oxygen so cells can respire when not contracting
29
Student measured the rate of aerobic respiration of a woodlouse using apparatus. The student closed the tap. After 30 mins the drop of coloured liquid had moved to the left. Explain why?
- oxygen used by woodlice to respire
- carbon dioxide absorbed by potassium
- volume of gas decreases and lower pressure so liquid moves to left
30
What measurement should the student have taken to calculate the rate of aerobic respiration in mm3 of oxygen g-1 h-1?
- unit of mass
- mass of woodlice
- distance drop moces and the time taken
- volume of air mm3 and the radius of the tube.
31
DNP inhibits respiration by preventing proton gradient from being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed: less ATP produced, more heat produced, the uptake of oxygen remained constant
- less ATP produced as less H+ moves through ATP synthase
- oxygen final electron acceptor
- heat released from electron transport
32
Explain the advantages of showing the data using standard deviation rather than ranges.
- can evaluate the significance in the difference in results
- reduce effect of anomalies
33
Suggest two advantages of rotating containers during the process
1. aerate the waste
2. distribute heat
34
Name 2 substances for which there would be net movement into the mitochondrion.
Pyruvate
ADP
35
The mitochondria in muscles contain many cristae. Explain the advantage of this
Larger surface area for electron carrier system
Provide ATP
36
What measurements should the student have taken to determine the rate of photosynthesis?
The volume of gas produced and time
37
Other than temperature and PH, give two factors which should be kept constant during the investigation>
1. distance from light source
2. light intensity
38
The student did not use a budder to maintain the PH of the solution. Explain what would happen to the PH of the solution during this investigation.
- Ph increases
- as more CO2 is produced removed from photosynthesis
39
Suggest and explain why the rate of photosynthesis was low between 525nm and 575n?
- The pigment doesn't absorb this wavelength range
- as light is required for light dependant reaction
40
The plants were left in the dark for 6 hours before the experiment. Explain why?
TP will be lower
41
Explain why it was important to grow the plants under the same conditions up to 10 days before the experiment.
So any difference is due to the independent variable (iron deficiency in this case)
42
Iron deficiency reduces electron transport. Explain the decrease in the production of triose phosphate in the iron-deficient plants.
Less ATP produced meaning less ATP and reduced NADP produced in the light dependent reaction meaning less GP converted into TP.
43
Iron deficiency results in a decrease in the uptake of carbon dioxide. Explain why.
Less TP converted to RuBP meaning less CO2 combines with RuBP
44
In leaves at the top of trees in a forest, carbon dioxide is often a limiting factor for photosynthesis. Use of knowledge of photosynthesis to suggest and explain one reason why.
lots of light (as no shading);
Light-dependent reaction not limiting
45
Each type of chlorophyll is produced by a specific enzyme-controlled pathway. Use this information to suggest how the same beech tree can produce more chlorophyll b in some leaf cells than others.
Greater amount of enzyme
Greater gene expression
46
Energy enters most ecosystems through the light-dependent of photosynthesis. Describe what happens during the light-dependent reaction
1. Chlorophyll absorbs light energy;
2. Excites electrons / electrons removed (from chlorophyll);
3. Electrons move along carriers / electron transport chain releasing energy by redox reactions;
4. Energy used to join ADP and Pi to form ATP;
5. Photolysis of water produces protons, electrons and oxygen;
6. NADP reduced by electrons / electrons and protons / hydrogen;
47
Where exactly in a cell is the enzyme rubisco found?
stroma
48
Use your knowledge of the light-independent reaction to explain why the yield from soya bean plants is decreased at higher concentrations of oxygen. Phosphoglycolate is not used in the light-independent reaction.
Less GP produced
Less TP to form sugars/ protein etc
Less RUBP regenerated
49
In photosynthesis, which chemicals are needed for the light- dependent reaction?
NADP, ADP, Pi and water
50
Describe what happens during photoionisation in the light-dependent reaction
- light hits and is absorbed by photostem, excites electrons raising the energy level
- electrons are lost
51
Explain why the student marked the origin using a pencil rather than using ink.
Ink and pigments would mix
52
Describe the method the student to separate the pigments after the solution of pigments had been applied to the origin.
- level of solvent below origin line
- remove before solvent before it reaches the top
53
The pigments in leaves are different colours, suggest and explain the advantage if having different coloured pigments in leaves.
can absorb a wider range of wavelengths
54
Heat stress decreases the light-independent reaction of photosynthesis. Explain why this leads to a decrease in the light-independent reaction.
Less ATP and LESS NADP
55
Explain why the scientists measured the rate of production of oxygen in this investigation.
- Oxygen produced light-dependent reactions faster
- faster oxygen production
56
The scientists suggested that mutant plants producing more chlorophyll b would grow faster than normal plants in all light intensities.
at all light intensities, chloroplast from mutant plant
- have faster production of ATP and reduced NADP.
- so have a faster light-independent reaction.
- so produce more sugars that can be used in respiration
- they have more energy for growth
57
Name the 2 products of the light-dependent reaction that are required for the light-independent reaction
- NADPH
- FADPH
58
In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how.
1. Carbon dioxide combines with ribulose bisphosphate/RuBP;
2. To produce two molecules of glycerate 3-phosphate/GP;
3. Reduced to triose phosphate/TP;
4. Requires reduced NADP;
5. Energy from ATP;
59
Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars.
1 RuBP combines with CO2;
2 to form 3C compound / TP / GP;
3 using ATP;
4 and reduced NADP / eq;
5 2 molecules of 3C compound/ TP / GP form hexose;
6 all RuBP is regenerated;
7 10 molecules of 3C/TP/GP form 6 molecules of 5C/RuBP;
60
Where do the light-dependent & light-independent reactions occur in plants?
light-dependent: in the thylakoids of chloroplasts
light-independent: stroma of chloroplasts
61
What happens in the electron transfer chain?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reactions, which release energy.
62
The concentration of carbon dioxide in the air at different heights above the ground in a forest changes over a period of 24 hours. Use you knowledge of photosynthesis to describe these changes and explain why the occur.
At night there will be a high concentration of Carbon dioxide
As there is no photosynthesis however the plant is still respiring
In the morning (there will be light) so the rate of photosynthesis greater than the rate of respiration So there will be less CO2
The higher up the plant the less the concentration of CO2
lower down the plant will have less leaves and other animals will be respiring
63
Explain the difference in light sensitivity between rod cells and cone cells.
rod cells are more sensitive to light as rod connect to one bipolar cell and are more likely to produce an action potential
64
Explain the difference in visual acuity between rod cells and cone cells.
cone cells have greater visual actuity, several rods share a single connection to brain and each cone has it's own connection to brain as cones can better discriminate sources of light
65
Explain the difference in sensitivity to colour between rod cells and cone cells.
cone cells are more sensitive as they have 3 tyoes of colour , each sensitive to a different wavelength
66
Suggest and explain how the interaction between the muscles labelled in the diagram above could cause the pupil to constrict (narrow).
- radial muscles relax
- circular muscles contract
67
The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea. Explain how the fovea enables an eagle to see it's prey in detail.
mp1: high visual acuity
mp2: cone are attached to bipolar cells
mp3: so each cone sends a separate impulse to brain
68
Explain how the resting potential of -70mV is maintained in the sensory neurone when no pressure is applied.
- membrane more permeable to potassium ions
- sodium actively out, potassium in
69
Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode P.
- pressure deforms lamellae
- greater pressure causes stretch-mediated sodium channels to open
- Sodium ions enter by diffusion changing charge in neurone
- greater pressure, more sodium channels open creating generator potential
70
The membrane potential at Q was the same whether medium or heavy pressure was applied. Explain why?
- both reached threshold
- threshold causes maximum response
71
MS is a disease in which part of the myelin sheaths surrounding neurones are destroyed. Explain How this results in slower responses to stimuli?
- lower action potetnial
- more depolarisation over length
72
Explain how atrioventricular maintain undirectional flow of blood?
- pressure in the left atrium more than in ventricle causing valve to open
73
Suggest how caffeine could account for increases in mean change in heart rate.
- more impulses along the sympathetic branch
- SAN increases the heart rate
74
Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process.
- chemoreceptors detect a rise
- send impulses to the cardiac centre
- more impulses to SAN
- by sympathetic
75
When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heat after the SAN initiates the heartbeat.
- electrical activity only through a bundle of his
- a wave of electrical activity passes over both ventricles at the same time
76
Myelin sheath damage can cause a range of symptoms, for example, numbness, muscular weakness and muscular paralysis. Damage to the myelin sheath of neurones can cause muscular paralysis. Explain How.
- depolarisation occurs along the axon
- never impulses slowed
77
Use your knowledge of IAA to explain the growth curvature when the tip is removed and then replaced off-centre.
- IAA produced at shoot tip
- IAA diffuses to side, higher concentration of IAA allowing cell elongation
78
What is an example advantage for taxis?
avoid competition
79
Explain why student removed the shoot tip when investigating the effects of IAA on oats.
- Tip produces IAA, which diffuses down and shoots cell elongation
- affectsthe concentration of IAA
- mitosis occurs in shoot so affects shoot length
80
Explain why the student added glucose solution to each petri dish when growing oat seedlings.
- for respiration
- produce ATP for growth
81
Explain why the student kept the lids of the petri dish on when growing oat seedlings.
- to prevent evaporation
- which would alter IAA concentration
82
The nerve pathway shown in the diagram may be regarded as a simple reflex arc.
only 3 neurones
83
Suggest 2 advantages of simple reflexes.
Rapid;
Do not have to be learnt;
84
Suggest how the results might have been different if lengths of root had been used in the IAA experiment.
- increase in iaa concentration the higher the mean change in length
- high iaa stimulates cell elongation
- greater IAA concentration inhibits cells elongation in the root causing root to grow towards the pull of gravity
85
Suggest 2 factors that should be kept constant in the choice chambers so that COTS display normal behaviour.
1. temp
2. oxygen conc
86
Give one similarity and one difference between a taxi and a tropism.
Both directional movement towards or away from stimulus
difference: taxis whole organisms moves whereas tropism is a growth response
87
What do these results show about the responses of the roots of tomato plants to gravity and salt?
- grows towards gravity
- negative chemotropism
- salt increases effect of gravity
88
Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process.
1.Chemoreceptors detect rise in CO2
2. Send impulses to cardiac centre/medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for
chemoreceptors/CO2)
89
What does respiration of fatty acids result in?
Respiration/oxidation of fatty acids provides ATP;
90
to reduce transmission by using the Sterile Insect Technique (SIT). This
involves releasing large numbers of sterile (infertile) male A. aegypti into the
habitat. Explain how using the SIT could reduce transmission of dengue
- intraspecific competition;
- Reduces population (of mosquitoes);
91
How to conduct the mark-capture-release method?
1. Capture, mark and release;
2. Leave time for organisms to disperse
before second sampling/collection;
3. (Population =) number in first sample × number in second sample divided by number of marked in second sample
92
Succinic acid dehydrogenase is an enzyme used in the Krebs cycle.
Suggest one reason for the difference in the staining between the muscle fibres of
the control mice and the trained mice.
Increase in aerobic respiration
93
The scientists then compared the length of time that the control mice and the
trained mice could carry out prolonged exercise. The trained mice were able to
exercise for a longer time period than the control mice.
Explain why.
1. (More aerobic respiration) produces more ATP;
2. Anaerobic respiration delayed;
3. Less or no lactate;
94
explain how chemicals which inhibit the decolourisation of DCPIP could slow the
growth of weeds.
1. Less ATP produced;
2. Less reduced NADP produced;
3. Less GP converted to TP;
95
What is meant by the term phenotype?
1. characteristic due to genotype
2. characteristic due to environment;
96
What is a gene pool?
All the alleles in a population;
97
suggest how these two species of palm tree arose by sympatric speciation.
1. Occurs in the same
habitat
2. Mutation/s cause different flowering times
3. Reproductive isolation
4. Change in frequency of allele/s;
5. Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed to produce fertile offspring;
98
Suggest one reason why it was important that the student left the apparatus for one
hour after the yeast culture reached a constant temperature
(So the) oxygen is used
99
Describe how you would determine the mean percentage cover for beach grass on a sand dune.
1.Beach grass is the pioneer (species);
2. Pioneers named species change the
environment including nitrate ions
3. (So) less hostile for named species
4. Conifer represent climax community;
100
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why.
1. Small sample size;
2. fertilisation of gametes is random;
101
One hypothesis for LP in humans suggests that the selective pressure was related to
some human populations farming cattle as a source of milk.
Describe how farming cattle as a source of milk could have led to an increase in LP.
1. LP due to mutation
2. Milk provides named nutrient;
3. Individuals with LP more likely to survive
4. Directional selection;
5. Frequency of allele increases (in the
offspring/next generation);
102
explain why the number of people showing LP would rapidly increase once selection for this condition had been established.
1. Dominant allele;
2. (Always) expressed
103
It is caused by having only rods and no functional cone cells. People with complete achromatopsia have difficulty in seeing detail (lines 2–3). Explain why.
1. No (functional) cones
2. Cones are connected to a single neurone
3. (Cones) Separate (sets of) impulses to brain
104
One form of red-green colour blindness is caused by a sex-linked recessive
allele which affects more men than women. Red-green colour blindness affects more men than women (lines 7–8).
Explain why.
1. (Gene/allele) is on the X chromosome;
2. Females require two allele
105
Explain how a single base substitution causes a change in the structure of this
polypeptide.
Do not include details of transcription and translation in your answer.
1.Change in primary structure;
2. Change in hydrogen bonds;
3. Alters tertiary
106
In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production of ATP by
anaerobic respiration.
1.Regenerates NAD
2. (So) glycolysis continues;
107
Suggest and explain how digesting insects helps the sundew to grow in soil with very
low concentrations of some nutrients.
1.. Digestion/breakdown of proteins;
2. Provides amino acids
108
In a species of flowering plant, the T allele for tallness is dominant to the t allele for
dwarfness. In the same species, two alleles CR (red) and CW (white) code for the
colour of flowers. When homozygous red-flowered plants were crossed with
homozygous white-flowered plants, all the offspring had pink flowers.
Name the relationship between the two alleles that code for flower colour.
Codominance;
109
During hibernation, the heart rate and the metabolic rate of black bears decrease
(lines 3−5).
Use your knowledge of the nervous control of heart rate to describe how these are
linked.
1. (Lower metabolism so) less/low CO2 (in
blood);
2. (Detected by) chemoreceptors;
3. (Chemoreceptors) located in carotid artery;
4. Fewer impulses to the cardiac centre;
5. (More) impulses along parasympathetic
6. (To) SAN;
110
Malonate inhibits a reaction in the Krebs cycle. Explain why malonate would decrease the uptake of oxygen in a respiring cell.
1. Less reduced NAD
2. Oxygen is the final/terminal (electron) acceptor;
111
Explain how a resting potential is maintained across the axon membrane in a neurone.
1. Higher concentration of potassium ions inside and higher concentration of sodium ions outside (the neurone)
2. (Membrane) more permeable to potassium ions (leaving sodium ions entering)
112
Explain why the speed of transmission of impulses is faster along a myelinated axon
than along a non-myelinated axon.
1. Myelination provides (electrical) insulation;
2. (In myelinated) saltatory (conduction)
3. In non-myelinated depolarisation occurs along the whole/length (of axon);
113
A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.
Explain why.
1.No/less ATP produced;
2. No/less active transport
3. Electrochemical gradient not maintained
114
In fruit flies, males have the sex chromosomes XY and the females have XX.
In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
Male fruit flies are more likely than female fruit flies to have white eyes.
Explain why.
1. The (two) genes are linked
2. No crossing over (occurs)
3. o Gl and no gL (gametes produced)
115
Apart from temperature and pH, give two variables the scientist would have controlled when preparing the liquid medium cultures.
1. Volume of (stock) bacteria (culture);
2. Concentration of (stock) bacteria
(culture);
3. Concentration of glucose
116
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced.
When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit.
Explain how.
1. Less/no ATP used
2. ATP can be used for
growth
117
Suggest how speciation happened to produce two species of lemur.
1.Geographical isolation
2. Reproductive isolation
118
A student used chromatography to separate the different photosynthetic pigments in a chlorophyll solution. She had the following materials.
Describe how she could use these materials to separate the photosynthetic pigments by chromatography.
1. Draw line/origin on (chromatography) paper
2. add chlorophyll
3. Add solvent/A below line/origin;
4. Remove before solvent reaches end (of chromatography paper)
119
The tomato seeds were planted into sterilised soil.
Suggest two reasons why the soil was sterilised.
1. remove mycorrhizae
2. remove nitrogen-fixing bacteria
120
The soil used in this investigation had the recommended concentration of fertiliser.
Suggest two reasons why the soil contained the recommended concentration of fertiliser
1. So mycorrhizae/water is the only variable
2. Affects (crop) production/growth/mass;
121
In cats, males are XY and females are XX. A gene on the X chromosome controls fur
colour in cats. The allele G codes for ginger fur and the allele B codes for black fur. These alleles are codominant. Heterozygous females have ginger and black patches
of fur and their phenotype is described as tortoiseshell female.
The two alleles, F and f of a different gene, which is not sex-linked, interact with the
gene controlling fur colour. The allele F is dominant and stops the formation of
pigment in the fur, resulting in white fur. The allele f is recessive and has no effect on fur colour.
Name the type of interaction between the two genes affecting fur colour.
Epistasis
122
suggest two reasons for conserving rainforests.
1. Miicrovilli provide a large surface area
2. Many channel/carrier proteins for facilitated diffusion;
123
Give three reasons for the low efficiency of energy transfer from secondary
consumers to tertiary consumers in an ecosystem.
1. Heat (loss) from respiration;
2. (Food) not digested
3. Excretion;
124
An increase in muscle activity causes an increase in heart rate (lines 12–14).
Describe and explain how.
1.Increase in CO2 detected by chemoreceptors;
2. Send (more) impulses to the cardiac centre
3. More impulses (from the centre/medulla) along the sympathetic pathway
125
