bio p2 Flashcards
(140 cards)
1
Q
Why is DNA described as a polymer?
A
it is made of many repeating units
2
Q
Sickle-cell anaemia is an inherited disease caused by a mutation in the haemoglobin gene.
Genes are small pieces of DNA. The DNA in a gene consists of a sequence of bases. The figure below shows part of the base sequence in the DNA of a normal haemoglobin gene and the same section in the sickle-cell gene. A, C, G and T represent the different bases.
Normal gene: GGACTCCTC
Sickle-cell gene: GGACACCTC
Describe how the mutation causes a change in the shape of the haemoglobin protein molecule. (5)
A
- three bases code for one amino acid
- the middle code of CTC has changed to CAC
- so there will be a different amino acid in the (protein) chain
- therefore the protein / chain will have a different shape
- because there is a different sequence of amino acids
3
Q
A cat breeder noticed that four kittens from one Siamese cat mother had a new blue colour at the tip of their tails.
What has caused the new colour to appear?
A
mutation
4
Q
In 2006, Blue-moon butterflies almost became extinct.
Wolbachia bacteria killed males before they could hatch from eggs. Only females were resistant to the bacteria.
In 2006, the number of Blue-moon butterflies had decreased to only 1 percent of the population. Two years later, the number of males was equal to the number of females.
The number of Blue-moon butterflies in the population increased quickly after the new form of the gene had appeared.
Suggest why. (4)
A
- the mutated gene allows male to hatch
- the organisms with this allele are more likely to survive
- and reproduce
- to pass on the useful gene to the next generation / offspring
5
Q
Describe how a human gene could be used to genetically modify a pig embryo. (2)
A
- (human) gene is attached / inserted into pig DNA using enzymes
- transfer (DNA) into (pig) embryo using a vector / plasmid / virus
6
Q
The allele in bollworms for being able to eat GM cotton and survive is recessive.
A bollworm may evolve that has a new dominant allele that allows the bollworm to eat GM cotton and survive.
Explain how a new dominant allele emerging would cause a greater problem than the recessive allele that already exists. (4)
A
- more offspring will be able to eat (GM) cotton and survive
- (because) only one copy of the dominant allele is needed
- (and so) dominant allele is passed on
- (therefore) the population will evolve (to eat GM cotton and survive) faster
7
Q
Name five harmful substances that could cause water pollution.
A
herbicide
fungicide
insecticide
oil
nuclear waster
fertiliser
sewage
8
Q
Give two reasons why it is more energy-efficient to rear cows indoors that to rear cows outdoors. (2)
A
- less energy lost as heat (for maintaining body temperature / keeping warm)
- less energy lost in / for movement
9
Q
Explain how you could tell if a condition is recessive.
A
parents without conditions produce a child with the coondition
10
Q
Give three advantages of asexual reproduction. (3)
A
- only one parent is needed
- faster / takes less time
- (more) energy efficient
- successful traits / propagated / maintained / - passed on
- no transfer of gametes or seed dispersal
- colonisation of local area
- not wasteful of flowers / pollen / seeds
- genetically identical offspring
11
Q
Person K runs a 10km race.
The volume lost from the body through the skin and by breathing increased.
Explain why more water was lost through the skin during the race. (2)
A
- more sweating
- to maintain body temperature / to cool down the body / exercise releases heat
12
Q
Person K runs a 10km race.
The volume lost from the body through the skin and by breathing increased.
Explain why more water was lost by breathing during the race. (3)
A
more energy is needed
(for) more respiration
so breathing rate increases or to remove carbon dioxide
13
Q
Bluebell plants grow in woodlands in the UK and can sexually reproduce by producing seeds.
Explain why sexual reproduction is an advantage for bluebells. (4)
A
- (there is) genetic variation (in offspring)
- (so they are) better adapted to survive
- (and) colonise new areas by seed dispersal or escape adverse event in original area
- many offspring (are produced) so higher probability some will survive
14
Q
A large amount of untreated sewage entered a river. Many fish died.
Untreated sewage contains organic matter and bacteria.
Explain why many fish died. (5)
A
- bacteria decay organic matter / sewage
- (by) digestion
- (and) bacteria respire aerobically / using oxygen
- (which) lowers oxygen concentration in water or fish have less oxygen
- (so) reduced energy supply from respiration causes fish to die
15
Q
Give three biotic factors that could affect the size of a population.
A
pathogens / disease / bacteria / fungi
predators / carnivores / consumers
food
16
Q
Give two ways that a person can reduce the chance of developing Type 2 diabetes.
A
- more exercise
- eat less carbohydrate / sugar / fat
17
Q
Amino acids are broken down by enzyme A to make ammonia and Toxic substance P. Ammonia is broken down by other enzymes to make urea. Toxic substance P is broken down by enzyme B to make harmless products.
A person with MSUD cannot make enzyme B.
Explain why the blood of a person with MSUD will have a high concentration of toxic substance P. (3)
A
- (enzyme B is not made so) P cannot be broken down
- (but / however) toxic substance / P is still made
- (and) toxic substance / P diffuses into the blood
18
Q
Amino acids are broken down by enzyme A to make ammonia and Toxic substance P. Ammonia is broken down by other enzymes to make urea. Toxic substance P is broken down by enzyme B to make harmless products.
A person with MSUD cannot make enzyme B.
Explain why the urine of a person with MSUD will have a high concentration of toxic substance P. (2)
A
toxic substance / P passes through filter in kidney
(and is) not reabsorbed
19
Q
Amino acids are broken down by enzyme A to make ammonia and Toxic substance P. Ammonia is broken down by other enzymes to make urea. Toxic substance P is broken down by enzyme B to make harmless products.
A person with MSUD cannot make enzyme B.
Explain why a person with MSUD must have a low-protein diet. (3)
A
- proteins are broken down into amino acids
- so amino acids should be kept in low amounts
- so (that) toxic substance / P does not build up in the body and cause damage to cells / tissues / organs
20
Q
How would you change an investigation to make it repeatable? (1)
A
repeat the investigation and see if the results are the same / different
21
Q
What structure in the eye changes the size of the pupil?
A
iris
22
Q
Describe how the iris causes a change in the size of the pupil.
A
muscle contraction
23
Q
Describe how receptors, effectors, neurones and the spinal chord help to coordinate reflex actions. (6)
A
Indicative content
- receptor detects stimulus
- eg receptor detects pressure
- receptor generates impulses / electrical signals
/ - neurones conduct impulses / electrical signals
- sensory neurone conducts impulses to spinal cord
- synapse between neurones
- chemical (/ neurotransmitter) crosses synapse
- chemical stimulates impulse(s) in relay neurone
- motor neurone
/ - effector carries out response
- eg muscles of the arm / leg contract
- muscles contract or gland secretes chemicals
/
to access level 2, candidates need to consider, in terms of the indicative content, the receptor, the neurones and the effector in the correct sequence
24
Q
Students investigated geotropism in the roots of bean seedlings.
Why was damp blotting paper used to surround the seedlings? (1)
- to prevent light affecting the direction of root growth
- to prevent photosynthesis taking place
- to prevent the growth of mould on the roots
- to prevent water affecting the direction of root growth
A
to prevent water affecting the direction of root growth
25
Some students investigated geotropism in the roots of bean seedlings.
This is the method used.
1. Measure the length of the root of each of 10 bean seedlings.
2. Pin 5 seedlings to the cork mat in one experiment where seedlings are placed in a cork mat, surrounded by damp blotting paper and is stationary.
3. Pin 5 seedlings to the cork mat in another experiment where it is the same set-up as the prior but a motor rotates the bean seedlings.
4. Leave both experiments in a dark cupboard for 2 days.
How did the second experiment that rotated act as a control? (1)
gravity acts evenly on all sides
26
Explain how a change in one amino acid in an enzyme molecule could stop the enzyme working. (3)
- different protein made
- active site changed
- substrate doesn't bind / fit
27
Scientists want to produce a type of cattle that makes large volumes of low-fat milk by selectively breeding some animals.
Explain how the scientists would do this. (4)
- find female with lowest fat in milk **and** highest milk yield
- find male whose female offspring have highest milk yield **and** lowest fat in milk
- cross the best male with the best female
- select best offspring for both features from each generation and repeat for several generations
28
Name the 8 parts of the classification system.
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
29
50-60 million years ago, one species of lemur arrived in Madagascar on masses of vegetation via strong water currents.
Today, there are three species of lemur living in three different parts of Madagascar.
Describe how ancestors of the modern lemur may have evolved into the three different species in Madagascar today. (5)
- isolation of different populations
- habitat variation between lemur populations
- genetic variation or mutation
- better adapted to survive and reproduce **and** pass on favourable alleles to offspring
- cannot interbreed to produce fertile offspring
30
Explain the effect a high concentration of insulin has on blood glucose concentration. (3)
- lowers
- glucose converted to glycogen
- by cells / liver / muscles
31
Person K is obese and a doctor thinks that person K hast Type 2 diabetes.
The doctor tests a sample of blood from person K.
These are the results for person K:
- cholesterol in mmol/dm^3 - 6.21
- glucose in mmol/dm^3 - 9.56
- insulin in arbitrary units - 24.32
These results show the mean for people who do not have diabetes:
- cholesterol in mmol/dm^3 - 5.20
- glucose in mmol/dm^3 - 4.51
- insulin in arbitrary units - 14.83
Give two ways the results of the blood test show that person K might have Type 2 diabetes.
higher glucose **and** higher insulin
32
Describe how substances that pollute air and water could be harmful to humans and other living organisms. (6)
**Indicative content**
**air pollution:**
(carbon dioxide / methane / greenhouse gases)
- global warming / climate change / traps heat
* floods / fire / drought **or** ice caps melt **or** rise in sea level **or** extreme weather
* loss of habitat / food
* migration
/
(acidic gas / named – eg SO2 / NOx)
- damage to leaves so less photosynthesis
- damage to roots or alters ions in soil (/ e.g. phosphates / iron)
* (so) less protein manufacture
- damage to lungs
* breathing difficulties / bronchitis / asthma
/
(carbon monoxide)
- combines with haemoglobin
* less oxygen carried (by haemoglobin / blood)
/
(particulates / ‘soot’)
- cover leaves or block light
* less photosynthesis so less glucose made
- damage to lungs
* breathing difficulties / bronchitis / asthma
**water pollution:**
(sewage)
- bacteria multiply
* use oxygen in respiration
* water animals cannot respire
* pathogens in water
/
(fertiliser)
- algae multiply
* (algae) block light so plants cannot photosynthesise
* lack of oxygen for respiration – fish die
/
(toxic substances)
- damages / harms cells **or** bioaccumulation
* interferes with metabolism – e.g. respiration / protein synthesis
/
(plastics)
- entrap animals **or** causing internal damage if swallowed
/
(particles)
- block light
* plants / algae cannot photosynthesise so less glucose made
/
(oil)
- damages birds’ feathers
* cannot fly so cannot find food or escape predators
/
(acid rain / acids)
- lowers pH of water
* damages fish gill
33
Suggest three possible disadvantages of rearing cows indoors.
- increased spread of disease
- extra cost of food / heating / lighting / drugs
- more antibiotics in food / milk
- aggressive behaviour
34
Explain why it is an advantage for a hedgehog to decrease its body temperature during hibernation. (2)
- less energy transferred for maintaining body temperature / keeping warm
- so more energy available for processes vital for life
**OR**
- loses less energy
- body energy store lasts longer
**OR**
- lower temperature gradient
- loses less energy
35
During hibernation, a bear may wake up and become active.
Explain why the bear has a higher body temperature when it is active. (2)
- activity / movement requires energy from respiration
- respiration releases **heat**
36
Name the type of reponse displayed by seedlings when their growth is influenced by light.
phototropism
37
Who came up with the theory that changes in an organism's life could be inherited?
Lamarck
38
Who published joint studies with Darwin?
Wallace
39
Who developed the theory of speciation?
Wallace
40
What book did Darwin publish?
'On the Origin of Species'
41
Who came up with 'hereditary units'?
Mendel
42
Who put forward the theory of evolution?
Darwin
43
Why was there controversy surrounding Darwin's ideas?
- contradicted God being creator of everything
- limited evidence on how organisms changed over time
- mechanism of inheritance and variation not known at the time
44
What is Wallace best known for?
warning colouration in animals and theory of speciation
45
Who worked worldwide gathering evidence for evolutionary theory?
Wallace
46
Explain how the fossil in [**Figure 1**](https://docs.google.com/document/d/18lq2SPSXQEDyn0QrcvmyXEFHTqs_To6KnDwB_WyvfQw/edit?tab=t.0) may have formed. (4)
- (snake is) covered in sediment / mud **or** sinks into the mud
- soft parts decay
- bones / hard parts do not decay
- bones are replaced by minerals **or** minerals enter bones
47
Give five reasons why a species might become extinct. (5)
- new predator
- new disease
- new competitor
- catastrophic event
- changes to the environment
48
A gardener wants to makes his own compost to add to the soil to increase his yield of strawberries.
An airtight compost heap causes anaerobic decay.
Explain why the gardener might be against producing compost using this method. (2)
- methane is produced
- which is a greenhouse gas **or** causes global warming
49
What is the product of anaerobic decay?
methane
50
Dead leaves fall off a rasberry plant onto the ground.
The carbon in the dead leaves is recycled through the cabron cycle.
Explain how the carbon is recycled into the growth of new leaves. (6)
**Indicative content**
**statements:**
- (carbon compounds in) dead leaves are broken down by microorganisms / decomposers / bacteria / fungi
- photosynthesis uses carbon dioxide
**explanations:**
- (microorganisms) respire
- (and) release the carbon from the leaves as carbon dioxide
- plants take in the carbon dioxide released to use in photosynthesis to produce glucose
**use of carbon in growth:**
- glucose produced in photosynthesis is used to make amino acids / proteins / cellulose
- (which are) required for the growth of new leaves
51
Give four possible reasons that may have caused [strawberry A](https://docs.google.com/document/d/1ePGW-SocKCcDMhHKOz5Hi0Si5-6r76S4g3Evn8tbKFU/edit?tab=t.0) to decay.
- high**er** temperature
- **more** oxygen
- **more** water / moisture
- **more** microorganisms / bacteria / fungi (that cause decay)
52
Suggest three reasons why people might selectively breed cats.
- so they don't causes allergies
- for aesthetic reasons
- so they don't have specific genetic defects
- to produce docile cats **or** so they aren't aggressive
53
Describe two reasons inbreeding causes.
- more likely to pass on (recessive) disorders
- more likely to be susceptible to diseases
54
Explain why inbred organisms may be more likely to be susceptible to diseases. (1)
less genetic variation
55
Many people have breathing problems because they are allergic to cats.
The allergy is caused by a chemical called Fel D1; different cats produce different amount of Fel D1.
A cat has been bred so that it does not produce Fel D1.
Explain how the cat has been produced using selective breeding. (6)
**Indicative content**
**process:**
- parents with the desired characteristic are selected
- the parents are bred together to produce offspring
- offspring with the desired characteristics are selected and bred
- this is repeated over many generations
**explanations:**
- parents who produce the least Fel D1 are initially selected
- in their offspring there will be individuals with differing amounts of Fel D1 produced
- of these, in each generation, the lowest Fel D1 producing individuals are chosen
- care is taken to ensure cats are healthy and avoid possible problems associated with selective breeding
- over time the population of (selectively bred) cats will produce less Fel D1
56
Mould spores are hazardous.
Give one safety precaution a student should take when carrying out an investigation using mould.
wear gloves / face mask
57
Describe the changes in the pupil and iris going from **A** to **B** in [Figure 4](https://docs.google.com/document/d/1W5y4XHo_O93CKzXn0s2ICdiBhcDuiIN8iR9wdzEsLsE/edit?tab=t.0).
Explain how these changes occur.
Refer to the changes in light level in your answer. (4)
- pupils dilated (in **B**)
- in low light levels
- because circular muscles (in iris) relax
- (and) radial muscles contract
58
**Figure 5** shows light entering the eye in a person with blurred vision.
**Figure 6** shows how this condition is corrected with glasses.
Compare [**Figure 5** and **Figure 6**](https://docs.google.com/document/d/1Xz4Hp4QvPaHNHUF8xcmXQnISaqjIs6FCx6TFhY6cTRE/edit?tab=t.0).
Explain how the blurred vision is corrected.
- figure 5 shows myopia where light does not focus on the retina
- in figure 6 the lens bends the light so that light focuses on the retina
59
What is the medical term for 'short-sightedness'?
myopia
60
What lens is used to correct hyperopia?
convex
61
Two students investigated reflex action times.
This is the method used:
1. Student A sits with her elbow resting on the edge of a table.
2. Student B holds a ruler with the bottom of the ruler level with the thumb
of Student A.
3. Student B drops the ruler.
4. Student A catches the ruler and records the distance.
5. Steps 1 to 4 were then repeated.
Suggest three ways the students could improve the method to make sure the test would give valid results.
- drop the ruler from the same height each time
- let the ruler drop without using any force
- use the same hand to catch the ruler each time
- same type / weight of ruler
- thumb should be the same distance from the ruler each time at the start
- carry out the experiment with the lower army resting in the same way on the table
62
What are the three parts of the brain?
- medulla
- cerebellum
- cerebral cortex
63
What lens is used to correct myopia?
concave
64
What is the medical term for 'long-sightedness'?
hyperopia
65
Which part of the brain is associated with balance?
cerebellum
66
How many millimetres are in a centimetre?
10
67
How many nucleotides are there?
4
68
What does a nucleotide consist of?
- a common sugar
- phosphate group
- a base
69
What are the four different bases?
A, C, G and T
70
Which bases pair up together?
- C and G
- A and T
71
Syndrome H is an inherited condition.
People with syndrome K do **not** produce the enzyme IDUA.
Strand **A** from person **without** H: CTCATTCAGCTC
Strand **B** from person **with** H: CTCATTTAGCTC
Strand **B** shows a mutation which has caused syndrome H.
The enzyme IDUA produced from Strand **B** will not work.
Explain how the mutation could cause the enzyme **not** to work. (5)
- (mutation) changes the code of CAG to TAG
- changes the amino acid
- changes the protein
- forms a different shape / changed active site
- the enzyme no longer fits the substrate
72
Explain how the intensive farming of pigs increases the efficiency of food production. (4)
**statements:**
- kept inside or in a temperature controlled environment
- kept enclosed or in a restricted environment
**explanations:**
- less energy / heat is lost in controlling body temperature
- less energy required for movement
- so more energy is available for growth
- less energy / heat is transferred to the environment
73
Other than ethical issues, suggest two other possible disadvantages of intensive farming methods.
- diseases spread more rapidly
- over use of antibiotics
- increased use of fossil fuels (for heating)
74
Which two hormones control blood glucose concentration?
insulin and glucagon
75
Where are the hormones that control blood glucose concentration released from?
pancreas
76
Which organ converts glucose into glycogen for storage?
liver
77
What is **Type 1** diabetes caused by?
no / not enough insulin produced
78
What is **Type 2** diabetes caused by?
body not responding to insulin
79
What does thyroxine control?
basal metabolic rate
80
Where is adrenaline produced?
adrenal glands
81
Where is thyroxine produced?
thyroid gland
82
What are thyroxine levels controlled by?
negative feedback
83
A glucose tolerance test checks how well the body processes glucose.
Concentrations of glucose in the blood are measured before and after drinking a glucose drink.
Suggest why patients are **not** alloweed to eat for 8 hours before the test.
8 hours is sufficient time for insulin to have acted on any glucose from food eaten **or** results not affected by glucose from food **or** so that there's a low starting point to show the effect
84
Hyperthyroidism is caused by an overactive thyroid gland.
Suggest what could happen in the body of a person with hyperthyroidism. (3)
- too much thyroxine is released into the blood
- which raises BMR
- increase in rate of respiration
85
Describe the role of FSH in the menstrual cycle.
causes eggs to mature and stimulates ovaries to produce oestrogen
86
Describe the role of LH in the menstrual cycle.
LH stimulates the egg to be released
87
The combined pill is a contraceptive that contains progesterone and oestrogen.
The ‘mini-pill’:
- is a contraceptive that only contains the progesterone hormone
- has to be taken at the same time each day to prevent pregnancy.
-
The success rate of the mini-pill in preventing pregnancy is lower than that of the combined pill.
Explain why missing a dose of the mini-pill would reduce the success rate of the mini-pill. (4)
- (missing a dose causes a) drop in progesterone levels
- (therefore) FSH is not inhibited anymore
- (therefore) LH is not inhibited anymore
- (thus) an egg is matured and released
88
Which four hormones are involved in the menstrual cycle?
FSH, LH, oestrogen and progesterone
89
FSH
- produced in the pituitary gland
- causes maturation of the egg
- stimulates ovaries to produce oestrogen
90
Oestrogen
- produced in the ovaries
- causes lining of uterus to build up
- stimulates LH
- inhibits FSH
91
LH
- produced in the pituitary gland
- causes ovulation
92
Progesterone
- produced in the ovaries
- seccreted from egg follicle
- maintains lining of the uterus
- inhibits FSH
- inhibits LH
93
What are the three plant hormones?
- ethene
- auxin
- gibberellins
94
Name the type of reponse displayed by seedlings when their growth is influenced by gravity.
gravitropism
95
How are auxins used?
- as weed killers
- as rooting powders
- for promoting growth in tissue culture
96
What is ethene used for in the food industry?
to control the ripening of fruit during storage and transport
97
What can gibberellins be used for?
- end seed dormancy
- promote flowering
- increased fruit size
98
What is the genome of an organism?
the entire genetic material of that organism
99
Why is it important to understand the human genome? (3)
- trace human migration patterns from the past
- understand and treat inherited disorders
- search for genes linked to different types of disease
100
What happens when a protein shape is complete?
it folds up
101
Proteins are synthesised on ribosomes, according to a --------.
tenplate
102
What is used to bring specific amino acids to a growing protein chain in the correct order?
carrier molecules
103
What do non-coding parts of DNA do?
switch genes on and off
104
genotype
the genetic makeup of an individual for a particular characteristic
105
phenotype
the physical appearance / biochemistry of an individual for a particular characteristic
106
homozygous
when the two alleles present are the same
107
heterozygous
when the two alleles present are different
108
What are the sex chromosomes in females?
XX
109
What are the sex chromosomes in males?
XY
110
fossils
**remains** of organisms from millions of years ago
111
extinction
when there are no remaining individuals of a species still alive
112
Who classified organisms into the DKPCOFGS system?
Linnaeus
113
Explain how phototropism in a plant shoot helps the plant to survive. (3)
- plant absorbs **more** light
- **more** photosynthesis
- produces **more** glucose
114
Who developed the 'three domain system'?
Woese
115
What are the three domains?
- archaea
- bacteria
- eukaryota
116
biodiversity
the variety of all the different species of organisms on earth or within an ecosystem
117
Give two reasons for large-scale deforestation in tropical areas.
- to provide land for cattle and rice fields
- to grow crops for biofuels
118
Give 5 programmes that have been put in place to reduce the negative effects of gumans on ecosystems and biodiversity.
- breeding programmes for endangered species
- protection and regeneration of rare habitats
- reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop
- reduction of deforestation and carbon dioxide emissions by some governments
- recycling resources rather than dumping waste in landfill
119
What percentage of incident energy from light do most plants and algae transfer for photosynthesis?
1%
120
food security
the ability to hae enough food to feed a population
121
Give the six factors threatening food security.
- increasing birth rate
- new pests and pathogens
- changing diets in developed countries
- cost of agricultural inputs
- conflicts
- environmental changes
122
Describe two measures that have been taken to try and make fishing sustainable.
control of net size and fishing quotas
123
Give the name of the fungus used for producing mycoprotein?
*Fusarium*
124
Give an example of a GM crop.
golden rice
125
Plan an investigation to show the effect of light from one direction on the growth of plant seedlings.
Include deatails of any controls needed. (6)
You may use the equimpment as follows as well as any other laboratory apparatus:
- lamps
- several pots of seedlings
- scissors
- ruler
- cardboard boxes with lids
**Indicative content**
- several seedlings in each batch **or** one pot of seedlings in each batch
- measure heights of shoots
- leave some in dark with light from one side / direction in box with hole
- control(s) with all-round light **or** in dark
- control variable(s) eg same temperature / water / soil type
- after suitable time (at least several hours)
- record appearance of seedlings re. light direction
- re-measure heights of shoots
- detail of how bent shoots were measured – eg straighten them out
- calculate mean height increase for each group
- use ruler / protractor to estimate angle of bending
126
Explain how a person's eye could adjust to form a clear image of a **nearer** object. (6)
- ciliary muscles contract
- smaller diameter
- suspensory ligaments loosen
- lens becomes thicker / rounder / fatter
- light is refracted more **or** lens is more convergent
- image focused on retina
127
Explain why a long-sighted person has difficulty seeing near objects clearly. (2)
- eye is too short **or** lens cannot be thickened enough
- so light 'focuses' behind retina
128
Describe how spectacle lenses can correct long-sightedness. (3)
- convex lens
- light rays refracted more
- light rays focused on retina
129
Explain why several groups of cells are scraped off a leaf when using the tissue culture technique to produce plants. (1)
so many plants can be produced
130
Explain why **nutrients** are added to the agar jelly when using the tissue culture technique to produce plants. (1)
for making proteins / amino acids / chlorophyll **or** for respiration **or** for providing energy
131
Explain why **hormones** are added to the agar jelly when using the tissue culture technique to produce plants. (1)
so differentiation occurs **or** so roots / shoots develop
132
Explain why plants cells may be kept at 20°C when using the tissue culture technique to produce plants. (1)
optimum temperature
133
Explain why plants cells are kept in sterile conditions when using the tissue culture technique to produce plants. (1)
to prevent growth of pathogens / microorganisms
134
Which hormone controls water loss from the body?
ADH
135
Which gland release the hormone that controls water loss from the body?
pituitary gland
136
Explain how the hormone ADH and the kidneys reduce water loss. (3)
- high(er) concentration of blood **causes** (more) ADH release
- (ADH causes) increased permeability of kidney tubules (to water)
- (so) increased water **re**absorption
137
Other than cost or convenience, explain three biological reasons why most doctors think that a kidney transplant is a better method of treatment than dialysis. (6)
**Reason 1:**
- skin is not repeatedly punctured
- so less / no risk of infection
**Reason 2:**
- blood not in contact with machine **or** blood does not leave the body
- so less / no chance of blood clots **or** no need to take anti-clotting drugs
**Reason 3:**
- no / minimised changes in the concentrations of substances / urea
- so less / no chance of causing damage to body cells / tissues
138
The rate of bacterial reproduction in a solution of nutrients at 25°C was greatest between 2 hours and 7 hours.
After 12 hours, the rate of reproduction started to plateau.
Suggest three ways a high rate of reproduction could be maintained.
- add (more oxygen)
- remove toxins / waste **or** maintain pH
- sitr the culture
- add (more) sugar
- add (more) amino acids / protein
- increase temperature
*range between 26°C and 40°C*
139
Scientists transferred a gene for resistance to the herbicide glyphosate into the bacteria.
The genetically-modified (GM) bacteria can then transfer the glyphosate-resistance gene to a crop plant.
Explain the advantage of making crop plants resistancce to glyphosate. (3)
- glyphosate kills weed **but** doesn't kill crop plants
- less competition for light / minerals / ions
- (so) crops have higher yield **or** crops grow better
140
Explain why a person with Type 2 diabetes often has a higher blood insulin concentration that a non-diabetic person. (4)
- the body does not respond to insulin
- cells / liver / muscles convert **less** glucose into glycogen
- (so) blood glucose concentration remains high
- (which stimulates) **pancreas** to release more insulin
