Exam Questions Flashcards
explain what is meant by a reflex action
an involuntary response to a stimulus
explain the type of receptor involved in pulling the hand away from a hot surface
thermoreceptor
describe the pathway taken by the nerve impulse from receptor to effector
sensory neurone to intermediate to motor
why is blood leaving the heart through the aorta at a higher pressure than blood leaving the pulmonary artery?
thicker muscle means stronger contraction of left ventricle
which nerve would scientists stimulate to cause a fall in cardiac output?
parasympathetic
why does stimulation of the parasympathetic cause a fall in cardiac output?
sinoatrial node sends fewer impulses, so the heart beats less often ( CO = HR x stroke volume)
what event in the heart causes a pulse?
ventricular systole
why is counting 20 seconds and multiplying by 3 less accurate than counting for 60 seconds?
any error is multiplied by 3
what causes vision in the fovea?
the prescence of cones to detect colour, each receptor connects to a different neurone
group b had the root tip removed and continued to grow horizontally - what conclusion can we draw from this?
IAA is produced in the root tip
group c had the upper half of the root tip removed, and grew downwards but less steeply - what conclusion can we draw from this?
less IAA is produced so there is less inhibition of growth in the lower side
explain the effect of temperature on the rate at which NAA is taken up by the lower surface of the leaf
increasing the temperature increases the kinetic energy, increasing the rate of diffusion
there are differences in the properties of the cuticle on the upper and lower surfaces of the leaves. Suggest how these differances might explain the difference in uptake rate.
upper layer has thicker cuticle - slowing rate of diffusion
explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness?
the rhodopsin has been bleached by the light, time is required for resynthesis of rhodopsin
one reason that the reaction time is slower when body temperature falls is because nerve impulse conduction is slower. Explain how a lower temperature leads to a slower nerve impulse conduction
slows rate of diffusion of K+ amd Na+
other than temperature, give 2 factors that affect the rate of nerve impulse conduction
myelination, diameter of axon
why is the genetic code described as being universal? (1)
in all organisms, the same triplet codes for the same amino acid
The genetic code uses four different bases, what is the maximum number of different DNA triplets that can be made using these four bases?
64
What is epigenetic inheritance? (2)
Changes to inherited gene function without altering the DNA base sequence, caused by an environmental factor.
BMI = mass in kg/ (height in metres)*2 calculate the BMI of a boy weighing 70kg and 170cm tall
24
what is a tumour?
a collection of cells growing out of control
what is cancer?
when cells from a tumour have spread/ metastasis has happened
what is the genome of an organism?
all genes present in a haploid set of chromosomes
Explain how methylation of a tumour suppressor gene can lead to cancer (3)
the methyl group attaches to a cytosine base and stops transcription protein that prevents cell division not produced no control of mitosis —-> cancer
Deletion changes the nature of the protein (in diagram) but substitution does not. Suggest why (3)
deletion causes frame shift code is degenerate so amino acid not altered
Give 2 factors (other than cost) that should be considered when selecting an antibiotic to treat a bacterial disease (2)
side affects, interaction with other drugs, allergies, conditions
A mutation in a tumour suppressor gene can result in the formation of a tumour. explain how (2)
tumour suppressor gene inactivated increasing rate of cell division
some cancer cells have a receptor protein in their cell surface membrane that binds to a hormone called a growth factor, This stimulates cancer cells to divide. this can be prevented using monoclonal antibodies, suggest how (3)
Antibody has a specific tertiary structure complementary to the receptor protein preventing the growth factor from binding
If the DNA of the cell is damaged, a protein called p53 stops the cell cycle. Mutation in the gene for p53 could cause cancer to develop. Explain how (3)
p53 is non functional or not coded for the cell cycle continues in the damaged cell (no apoptosis) resulting in uncontrolled cell division
Name 2 enzymes involved in semi conservative DNA replication (2)
DNA polymerase DNA helicase
When ATR phosphorylates enzymes, they become able to bind to their substrates. Use your knowledge of enzyme structure to suggest why (2)
the addition of the phosphate group alters the tertiary structure, making it complementary to the substrate
1 Closed, open, closed
2 Closed, closed, open
Describe how the resting potential is established in an axon by the movement of ions across the membrane. (2)
Active transport Na+ out, diffusion of K+ out
Why doesn’t every stimulus trigger an action potential? (3)
refractory period
the membrane is hyperpolarised
threshold cannot be reached - greater stimulation required
What is the role of ATP in the contaction of myofibril
hydrolysis of ATP on myosin head causes myosin to bend, pulling actin molecules
allows the actin to detach
Describe how calcium ions are involved in synaptic transmission (2)
Ca2+ enters presynaptic neurone
increase permeability of the presynaptic neurone causing fusion of the vesicles with the membrane
Explain how DNA structure is related to it’s function (6)
Long - so can store a lot of information
Helix - so compact
Base sequences store information code for amino acids/ proteins
Double stranded so semi conservative replication takes place
Hydrogen bonds between base pairs so stable/strong or weak so allow strand seperation
More cancer cells could be destroyed if the grug was administered more frequently
Suggest why the drug was not given more frequently. (2)
Side effects
too many healthy cells killed - more time needed to allow recovery of healthy cell
Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell (2)
Oestrogen-oestrogen receptor complex forms a transcription factor stimulates RNA polymerase
this increases transcription
Describe how genetic fingerprinting may be carried out on a sample of DNA (6)
DNA is cut using a restriction enzyme
carry out gel electrophoresis to seperate strands based off length of VNTRs sequence
do southern blotting method
apply probe - flourescence or radioactivley labelled
Explain how genetic fingerprinting allows scientists to identify father of a cub (2)
The bands in the cub that don’t come from mother must be in father’s DNA fingerprint
(gel electrophoresis) Two bands are usually seen for each person tested. Suggest why only one band was seen for person L?
Homozygous fragments, same mass
Why is a log scale is used to record the number of cells (1)
records rapid/exponential growth
Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis
Heat stress decreases the light dependent reaction of photosynthesis. Explain why this leads to a decrease in the light - independent reaction.
less ATP and NADH ( products of light dependent reaction) which slows down the light independent reaction
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis. Explain why. (2)
less CO2 reacts with RuBP, less GP
Describe how alterations to tumour supressor genes can lead to the development of tumours (3)
hypermethylation
mutation
tumour supressor genes are not transcribed
OR
amino acid sequence/ primary structure altered
uncontrolled cell division
Describe how you would calculate mean percentage cover for beach grass on a sand dune (3)
use random sampling technique - grid, random sampling
large sample
divide total percentage by no. quadrats
The scientists concluded that the results shown in Figure 5 were due to succession
explain why. (4)
the grass is a pioneer species
it alters the conditions
less hostile more suitable for other species
In genetic crosses the observed phenotypic ratios are often not the same as the expected ratio.
suggest two reasons why
Small sample size; Fusion/fertilisation of gametes is random; Linked Genes; Epistasis; Lethal genotypes;
Furosemide and CVT are used to remove excess fluid from the body. Scientists investigated the affects of these drugs on the body, suggest and explain one reason why they were given the same amount of food (2)
affects water potential, and so affects the volume of urine produced
Furosimide inhibits the absorbtion of sodium and chloride ions from the filtrate produced from the filtrate produced in the nephrons
Explain how furosimide causes an increase in the volume of urine produced (3)
water potential of filtrate is decreased
less water is reabsorbed by osmosis
collecting duct is where osmosis occurs
Dopamine is a neurotransmitter released in some synapses of the brain. The transmission of dopamine is similar to that of acetylcholine. Dopamine stimulates the production the nerve impulses in postsynaptic neurones.
Describe how.
dopamine diffuses across the synapses
dopamine attaches to receptors
stimulates the movement of sodium ions triggering an action potential
GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this inhibits postsynaptic neurones. (3)
neurone becomes hyperpolarised
more stimulation required
to trigger action potential
What is precipated DNA? (1)
DNA, the transcription factor, and the antibody
Soybeans are used in a number of processed foods. However, soybeans contain a protein known as P34 that causes an allergic response in some people. Scientists have created transgenic soybeans that produce single-stranded cDNA, which prevents transcription of the P34 gene. They used recombinant plasmids as vectors to transform soybean cells. After they had screened these cells for production of the P34 protein, they cultured the transformed cells to form soybean plants.
Suggest how single-stranded cDNA could prevent transcription of the P34 gene (1)
Binds to P34 gene/DNA/mRNA
OR
Binds to transcription factor gene/DNA
OR
Binds to promoter;
Describe the roles of two named types of enzymes used to insert DNA fragments into box plasmids. (2)
Restriction (endonuclease/enzyme) to cut plasmid/vector; 2. Ligase joins gene/DNA to plasmid/vector;
Red/Green colour blindness affects men more than women
explain why (2)
The gene is on the X chromosome
women can be heterozygous carriers whereas men only require one allele to express the condition
The use of iPS cells could have advantages over gene therapy to treat red green colour blindness, suggest why (3)
iPS cells one time treatment/less chance of rejection / long term
virus could cause side affects
C - Myosin
D- mitochondrion
E - Myofibril
During vigorous exercise the pH of skeletal muscle tissue falls. This fall in muscle pH leads to a reduced ability for calcium ions to stimulate muscle contraction. Suggest how (3)
- Low pH changes shape of calcium ion receptors
- Fewer calcium ions bind to tropomyosin
- Fewer tropomyosin molecules move away;
- Fewer binding sites on actin revealed;
- Fewer cross-bridges can form
OR Fewer myosin heads can bind;
The nerve pathway may be considered a reflex arc suggest why (1)
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain. Explain how this reduces the rate of photosynthesis in weeds. (4)
Reduced transfer of protons across thylakoid membrane OR Reduced chemiosomotic gradient/proton gradient across thylakoid membrane; (So) less ATP produced; (So) less reduced NADP produced; (So) light-independent reaction slows/stops OR Less reduction of GP to triose phosphate;
Explain the loop of the curve in the loop of henle in figure 4 (3)
What is the evidence in figure 4 that ADH was being secreted (2)
1) Concentration rises in descending limb because sodium ions enter and water lost; Concentration falls in ascending limb because sodium ions (and chloride) ions actively removed; But water remains (in ascending limb) because its walls are impermeable (to water);
2) Concentration rises in collecting duct because it loses water by osmosis; ADH increases permeability (of walls of collecting duct) to water;
Define epigenetics (2)
heritable change in gene function without altering the DNA base sequence
Explain how increased Methylation could lead to cancer (4)
Methyl groups (could be) added to (both copies of) a tumour suppressor gene; The transcription of tumour suppressor genes is inhibited; Leading to uncontrolled cell division;
How does Fig.2 show eveidence of succession (5)
- (Overall, data show an) increase in species richness/increase in species diversity/increase in total number of living organisms;
- Baetis quilleri and/or Pentaneurini guttipennis are pioneers;
- (Pioneers cause) named change of environment eg provide food for other species;
- New species/example from data colonise once there is a change;
- Baetis quilleri/Pentaneurini guttipennis/Helicopsyche mexicana decline/outcompeted/eaten as succession continues;
People suffering from pituitary dwarfism do not make enough human growth hormone (HGH). They can be treated using injections of HGH. A geneticist wants to transform the bacterium, Escherichia coli, to make HGH by adding the gene coding for HGH. The geneticist could obtain the HGH gene using any one of three methods.
- Use restriction enzymes to cut out a fragment of DNA containing the HGH gene from a human genome.
- Convert mRNA for HGH into cDNA using reverse transcriptase.
- Create the HGH gene using a ‘gene machine’.
The geneticist decided not to use restriction enzymes to cut out a fragment of DNA containing the HGH gene from a human genome. She made this decision because only methods 2 and 3 would produce DNA that E. coli could use to make HGH.
Explain why only methods 2 and 3 would produce DNA that E. coli could use to make HGH.
- Human DNA/human gene/HGH gene contains introns OR Methods 2 and 3 produce DNA/HGH without introns;
- E. coli cannot remove introns/cannot splice mRNA/cannot splice pre-mRNA;
Describe how the geneticist would attempt to insert copies of the HGH gene into the plasmid (3)
- cut with a restriction enzyme
- leaves complementary sticky ends
- add ligase
Kinesis - the insect is not moving towards a specific region
taxes
The ratio of bar eyed flies to round eyes was not what the student expected.
suggest 2 reasons why (2)
random fertilisation
small population
selective advantage
There were 850 fruit flies in one population. In this population, 510 fruit flies had the genotype WN WN , 255 had the genotype WN WV and 85 had the genotype WV WV . Calculate the actual frequency of the allele WV .
Do not use the Hardy-Weinberg equation in your calculation. [1 mark]
- 25
because. … total no alleles = 850 x 2
total Wv alleles = (2x85)+255 = 425
425/ 1700 = 0.25
Suggest and Explain two reasons why a poor supply of phosphate ions results in poor plant growth (2)
Phosphate for ATP
Phosphate for nucleotides
Explain how the resting potential of -70 is maintained in the sensory neurone (2)
sodium pumped out, potassium pumped in
membrane is more permeable to potassium
explain how pressure to the pacinian corpuscle produces change in the membrane potential (3)
pressure causes lamellae to stretch
ion channels open and sodium moves out
the more pressure there is the more sodium moves out
the membrane potential at q was the same no matter how much pressure was placed on it explain why (2)
threshold is reached
all or nothing principle
MS destroys the myelin sheath, Explain how this results in slower response to the stimuli (2)
less saltutory conduction
more depolarisation along length
suggest two types of stimuli that may cause a blink reflex (1)
light, pressure, touch, temperature, chemical, temperature, noise, smell
some dieseases cause blink rate, doctors do not often use blink rate to diagnose. suggest why? (2)
no normal blink rate for comparison, many factors affect blink rate
Synapses are unidirectional. Explain how acetylcholine contributes to a synapse being unidirectional (2)
acetylcholine released from pre synaptic
binds to receptors on the post synaptic
