year 2- tricky AO1

Explain how foetuses developed two different genes for haemoglobin when humans originated with a single gene?

1. Duplication mutation occurred

2. Copy of gene developed mutations

3. Both genes are expressed

4. Natural selection- genes passed on

Explain how mutation in ion channel protein in cell membrane leads to symptoms of cystic fibrosis (thick mucus)

1. Channels non functioning

2. Fewer ions transported out of cells lining airways

3. Water gradient not established so less movement of water by osmosis

4. Mucus is thicker

Explain how mutation in gene encoding an enzyme/ protein may be damaging?

1. Amino acid sequence/ Primary structure altered

2. Changes in bonding

3. Tertiary structure altered

4. No longer complementary/ cant form complexes

Explain how a mutation in calcium ion channel genes could stimulate muscles to contract in response to anaesthetic?

1. Mutation alters shape of calcium ion channel receptor

2. Anaesthetic complementary to receptor

3. Channels stimulated by anaesthetic to open

4. Calcium ions diffuse out of SR

5. Ions bind to tropomyosin, exposing myosin binding sites

6. Actin-myosin cross bridges form causing muscle to contract

Explain how T tubules help initiation of muscle contraction?

1. Form connection between sarcolemma and sarcoplasmic reticulum

2. Depolarisation carried to centre of muscle cell quicker, calcium ions released quicker

Define a stem cell?

1. Can divide an unlimited number of times

2. Undifferentiated cell

3. Can differentiate into a specialised cell

Suggest why its advantageous for scientists to use island populations for investigations into inheritance?

1. All individuals in population can be sampled

2. Less sampling error

3. Little gene flow- more chance of genetic drift

Explain what epigenetic modifications are?

1. Factors affecting gene expression

2. Without altering DNA base sequence

Define ‘induced pluripotent stem cell’?

1. An adult somatic cell with the properties of pluripotent stem cell

2. Treated by transcription factors turning on genes allowing differentiation

Define epigenetic modifications?

1. Heritable changes to DNA

2. Without changes to base sequence of DNA

Explain how stem cells develop into specialised cells?

1. Stimulus e.g. chemical/ hormone

2. Some genes activated

3. Activated genes transcribed- producing mRNA

4. mRNA translated into proteins

5. Proteins modify cell, determining structure and function

6. Cell becomes specialised

Explain how siRNA silence genes?

1. bind to complementary mRNA strand

2. mRNA cut into fragments

3. by protein complex

4. preventing translation into polypeptide

Describe siRNA?

1. small double stranded RNA molecules

2. which breakdown mRNA preventing transcription

Describe methylation and explain how it makes genes inactive?

1. The addition of methyl groups

2. To the cytosine bases on DNA

3. DNA less accessible to transcriptional factors

4. RNA polymerase does not bind and transcribe section of DNA

5. Gene not expressed

Explain the different types of stem cells?

1. Pluripotent- differentiate into almost any cell type, found in zygote

2. Totipotent- differentiate into any body cell type, found in embryo

3. Multipotent- differentiate into limited number of cell types, found umbilical cord/ some tissues

4. Unipotent- differentiate into a single type of cell,

Define a Mutation?

1. Change in base sequence

2. Results in formation of a new allele

Why has lactose tolerance only increased in frequency recently despite cattle farming originating centuries ago?

1. Selection pressure is weak to availability of alternative food sources

2. Mutations are infrequent

3. Human lifespan is long therefore genes passed on slower

Explain how mutagenic substances in red meat could lead to cancer?

1. Change base sequence of DNA

2. By addition/ substitution mutation

3. Primary and tertiary structure altered, protein shape changed

4. Loss of function of tumour suppressor genes

5. Cell division dysregulated

Explain why speciation may occur is small populations?

1. Genetic drift

2. Reduced gene pool

3. Alleles do not have equal chance of being passed on due to small population

4. Alleles passed on increase in frequency faster

Explain what discontinuous variation is?

1. Where the allele phenotype has a discrete value e.g. colour.

2. Mutations happen within gene at different locations resulting in new allele variants

Explain how the structure of myofibril changes during muscle contraction?

1. Sarcomere shortens

2. A band remains same length

Define term silent mutation

1. Change in nucleotide base sequence that does not alter amino acid sequence

2. No effect on protein synthesized

Explain how mutation x leads to formation of new protein?

1. Change in nucleotide base sequence

2. Primary structure altered

3. Different bond formations so secondary structure altered

4. Different tertiary structure leads to new protein w dif shape

Explain why stores of glycogen are found in fast muscle fibres?

1. Hydrolysed into glucose for anaerobic respiration

2. Large amounts of glucose required to produce sufficient ATP for muscle contraction

Compare the structure of actin and myosin?

1. Actin is thin fibre

2. Made up of two filaments twisted around each other

3. Myosin is a thick fibre

4. Consisting of long tails and globular heads

Suggest why slow muscle fibres contain large amounts of myoglobin?

1. Stores O2 in muscle

2. More O2 available for aerobic respiration

3. To produce ATP for contraction

Describe what a tendon is and its function?

1. Lengths of connective tissue

2. Joining skeletal bone to muscle

What defines Positive feedback?

A deviation away from the norm leads to further deviation away from the norm.

What is the difference between spatial and temporal summation at synapses?

1. Temporal: impulses reach the same synaptic knob quickly,

2. Spatial: impulses reach different knobs simultaneously.

How is blood filtered in the kidney?

1. Blood enters through afferent arteriole,

2. High hydrostatic pressure in glomerular capillaries,

3. Filtrate is formed from water and small molecules,

4. Large proteins cannot pass through.

Explain selective reabsorption in the kidney.

1. Sodium transported into blood,

2. Low sodium in epithelial cells lining the PCT,

3. Sodium diffuses out of PCT into epithelial cells,

4. Glucose/ Amino Acids cotransported with sodium,

5. All glucose reabsorbed.

How is water reabsorbed in the loop of Henle?

1. Sodium ions leave ascending limb creating a gradient,

2. Water exits descending limb,

3. Ascending limb is impermeable to water.

What happens in the DCT and collecting ducts?

1. Filtrate is dilute,

2. Water moves out via osmosis,

3. Remaining filtrate forms urine.

How is low water potential of blood corrected?

1. Osmoreceptors detect changes in water potential,

2. Hypothalamus produces ADH.

How does ADH increase permeability in the DCT and collecting duct?

1. ADH binds to receptors,

2. Activates phosphorylase,

3. Vesicles with aquaporins fuse to membrane.

Describe the structure of the glomerular capillary endothelium?

1. One cell thick,

2. Basement membrane,

3. Podocytes with gaps.

How is the PCT adapted for reabsorption?

1. Microvilli increase surface area,

2. Many mitochondria for active transport.

Explain how the endocrine system brings about change in body?

1. Releases Hormones

2. Hormones transported in blood to target organs

3. Hormones bind to complementary receptors on target organs

Explain how negative feedback mechanism work

1. Receptors detect changes in conditions

2. Corrective mechanisms return conditions to within normal range

Explain how insulin lowers blood glucose concentration

1. binds to complementary receptors on cell membranes of target cells

2. stimulates glucose transporter channel proteins to fuse with cell membrane

3. this increases permeability of tissues to glucose

4. activates enzymes involved in glycogenesis

Explain why its advantageous for adrenaline to be amplified through secondary messenger model

1. Many cAMP produced,

2. Large numbers of enzymes activated,

3. Glucose conc raised rapidly

Explain how glucagon causes an increase in blood glucose?

1. Binds to complementary receptors on target cells

2. Activates adenylate cyclase

3. ATP converted to cAMP which is the second messenger model

4. Protein kinase enzymes activated,

5. Activates cascade for breakdown of glycogen into glucose

Explain how IAA causes cell elongation

1. Binds to receptor on cell membrane

2. Stimulates proton pump, protons pumped into cell wall

3. Cell wall acidified, cellulose myofibrils weakened

4. K+ channels open and K+ enters cytoplasm

5. Water enters cytoplasm down gradient

Compare visual acuity of rod and cone cells

Multiple rod cells synapse with a single bipolar cell (which multiple bipolar synapse with ganglion etc)

Single cone cell synapse with single bipolar cell so brain recieves specific impulse

Explain how summation occurs in rod cells?

1. Multiple rod cells stimulated,

2. Combined generator potentials is enough to meet threshold and stimulate action potential in bipolar neurone

3. Greater visual sensitivity compared to cones

Explain how heart beats

1. SAN is group of cells in right atrium,

2. initiates wave of depolarisation causing atria to contract.

3. Non conductive tissue prevents depolarisation reaching ventricles, passed to AVN

4. AVN sends impulse down bundle of His after delay,

5. Purkyne tissue carries impulse to base of ventricles.

6. Ventricles contract from base

Explain effect of exercise on heart rate

1. Increased conc of CO2 and decrease in blood pressure

2. Detected by chemoreceptors in carotid,

3. Send impulse to medulla (acceleratory centre)

4. Impulses via sympathetic neurones to SAN,

5. Noradrenaline secreted at synapse,

6. SAN stimulated increasing frequency of depolarisation waves

Explain process of lactate fermentation

1. Pyruvate is reduced to lactate by NADH

2. NAD is regenerated

3. Enzyme is lactate dehydrogenase

4. Pyruvate is final hydrogen acceptor

5. Lactate can be oxidised back to pyruvate or converted into glycogen for storage

Explain process of ethanol fermentation?

1. Pyruvate is decarboxylated to ethanal,

2. Ethanal reduced to ethanol by NADH

3. NAD regenerated

4. Ethanal is final hydrogen acceptor

5. Enzyme is alcohol dehydrogenase

Explain how alternative respiratory substrates are used in respiration

1. Proteins hydrolysed into amino acids

2. Undergo deamination

3. Converted to either pyruvate or intermediates in Krebs cycle

4. Lipids hydrolysed into glycerol and fatty acids

5. Glycerol phosphorylated into triose phosphate (enters in glycolysis)

6. Fatty acids converted into acetyl CoA (enter Krebs cycle)

Explain why damage to proteins in electron transport chain inhibits growth

1. Fewer electrons passed down chain

2. Fewer protons transported across thylakoid membrane

3. Reduced chemiosmotic gradient

4. Less ATP and NADPH synthesised

5. Light independent reaction slows

6. Rate of photosynthesis reduced

Explain nitrogen nutrient cycle?

1. Nitrogen fixing bacteria convert N2 gas into ammonia

2. Ammonium ions oxidised into nitrite then nitrate ions (nitrification)

3. Nitrate ions absorbed by plants

4. Saprobionts feed on dead organic matter and release ammonium ions

5. Denitrifying bacteria convert nitrates to N2 gas in anaerobic conditions

Define a saprobiont?

1. Bacteria or fungi

2. feed on dead organic matter

3. Carry out extracellular digestion- secrete enzymes onto food

Explain how saprobionts obtain nutrients from animal waste?

1. Carry out extracellular digestion

2. Secrete enzymes onto food

3. Absorb nutrients

Explain how a mutation in a transcription factor which activates tumour suppressor genes can lead to cancer?

1. Tertiary structure of transcription factor is altered

2. Transcription factor no longer complementary to promotor region

3. RNA polymerase doesn’t bind and transcription is inhibited

4. Cell cycle and cell division becomes dysregulated leading to uncontrolled cell division - tumours.

Explain how including leguminous plants in crop rotations improves yields?

1. Contain nitrogen fixing bacteria in roots/nodules

2. when crops die/harvested additional nitrogen compounds are released into soil

Explain how an impulse is transmitted across a neuromuscular junction leading to muscle contraction?

1. Presynaptic membrane depolarised

2. Calcium ions diffuse into neurone

3. Vesicles (containing A choline) fuse w membrane

4. A choline released and diffuses across junction

5. A choline binds to receptor proteins on sarcolemma

6. Sodium ions diffuse in, depolarising sarcolemma

7. Action potential passes down Ttubules to muscle fibre

8. Calcium ions diffuse out of sarcoplasmic reticulum into sarcoplasm

Explain process of natural selection?

1. Genetic variation due to mutations

2. Change in environment leads to selection pressure

3. Individuals with advantageous alleles survive

4. Reproduce and advantageous alleles passed on through generations

5. Frequency of allele in gene pool increases

Explain the oestrogen stimulation pathway?

1. Oestrogen diffuses into cytoplasm through cell surface membrane

2. Oestrogen enters nucleus through nuclear pore

3. Oestrogen binds to oestrogen receptor attached to protein complex

4. Receptor undergoes conformational change, detaching from protein complex

5. Receptor diffuses towards gene to be expressed

6. Receptor binds to cofactor, allowing it to bind to promoter region of gene

7. RNA polymerase stimulated to bind and transcribe

Explain how allopatric speciation occurs

1. Geographical isolation due to physical barrier

2. Gene pools become separated, no interbreeding between populations

3. Variation exists within each population due to mutations

4. Different selection pressures- abiotic/biotic factors in environment

5. Advantageous alleles passed on

6. Alelle frequencies change due and gene pools different

7. Reproductive isolation- no longer breed to produce fertile offspring

Explain how Sympatric speciation occurs

1. No geographical isolation

2. Mutation occurs

3. Populations become reproductively isolated

4. Different selection pressures

5. Advantageous alleles passed on

6. Change in allele frequencies

7. No longer produce fertile offspring

Explain why two species cannot occupy the same niche?

1. Interspecific competition

2. One species will out compete the other

Describe how a gene can be isolated from human DNA?

1. Using restriction enzyme/ endonuclease

2. To cut DNA in a specific place

Describe how an isolated gene can be replicated by the polymerase chain reaction (PCR)?

1. Heat DNA to 90-95

2. Strands separate

3. Add primers and nucleotides

4. Temperature lowered (55) so that primers bind to DNA

5. (temp increased to 72) DNA polymerase joins complementary nucleotides

6. Cycle repeated 20-40 times

Explain how modified plasmids are made by genetic engineering and how use of markers enables detection of plasmid containing bacteria?

1. Desired gene isolated from another organism

2. Using restriction enzymes to cut DNA

3. Producing sticky ends

4. Ligase used to join wanted gene to plasmid

5. Marker gene included

6. Plasmid inserted into bacteria to grow

7. On medium that selects for marker

8. Bacteria not killed have inserted plasmid

Describe one way Embryonic Stem Cells may lead to more harm to patient?

1. Might divide out of control

2. Leading to tumour/ Cancer

Suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues?

1. Greater blood supply

2. Bringing more O2/ glucose for respiration

3. Brings more amino acids for protein synthesis

4. For cell repair/ mitosis

Explain how transcription factors result in expression of gene?

1. Transcription factors move from cytoplasm into nucleus

2. Bind to complementary promoter region on DNA

3. Initiates transcription of gene/ RNA polymerase bind

4. mRNA is translated to produce polypeptide

Suggest how the binding of interferon gamma to its receptor protein leads to the production of phosphorylated STAT1?

1. Binds to complementary receptor, altering its tertiary structure

2. Enzyme stimulated

3. Phosphorylates STAT1 using ATP

Explain how an activated oestrogen receptor affects the target cell?

1. Binds to promoter, stimulating RNA polymerase

2. Initiates transcription

Explain shape of curve?

1. Number of fragments doubles each cycle- exponential increase

2. Few fragments initially

3. Plateaus when no more nucleotides/ primers

Explain how scientists used a radioactively labelled DNA probe to show that the cells of tobacco plant leaves contained the SUT1 gene?

1. Extract DNA and add restriction enzymes

2. Separate fragments using gel electrophoresis

3. Treat DNA to form single strands

4. Probe binds to complementary gene

5. Use autoradiography to identify bound probe

Suggest how the production of ‘antisense’ SUT1 mRNA in plants would reduce the expression of the SUT1 gene?

1. Antisense mRNA is complementary to (sense)mRNA

2. Antisense binds to mRNA

3. Ribosomes cannot bind

4. Preventing translation into polypeptide

Define a DNA probe?

1. Short, single strand of DNA

2. Complementary bases to specific target gene

Describe how DNA is broken down into smaller fragments?

1. Restriction endonucleases

2. Cut DNA at specific base sequences/ restriction sites

3. Break phosphodiester bonds

What would the scientists have inserted into the plasmid along with the spider gene to ensure that the spider gene was only expressed in the silk glands of the silkworms?

1. Promoter region

Explain how plants containing gene from insect can synthesise insect protein?

1. Genetic code is universal

2. Insect gene can be transcribes

3. Translated into polypeptide using same amino acids

Suggest why DNA replication stops during PCR?

1. Limited number of nucleotides

2. DNA polymerase eventually denatured

Explain how the drop in pH during exercise reduces the ability of calcium ions to stimulate muscle contraction?

1. Low pH alters the tertiary structure of calcium ion receptors

2. Fewer calcium ions bind to tropomyosin causing it to change shape

3. Fewer myosin binding sites exposed

4. Fewer cross bridges from

Describe the roles of calcium ions and ATP in muscle contraction?

1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum

2. Causing tropomyosin to move

3. Exposing binding sites on actin

4. Myosin heads attach to binding sites

5. Hydrolysis of ATP on myosin heads causes them to bend

6. Pulling actin molecules

7. Attachment of new ATP molecule onto myosin head causes detachment from actin

Explain why if myosin molecules cant bind to each other muscles cannot contract?

1. Cant form thick myosin filament

2. Actin not pulled/ filaments don’t slide past each other

3. Myosin heads not attached/ fixed therefore move

4. Sarcomere not shortened

Describe the role of saprobionts in the nitrogen cycle?

1. Secrete enzymes to digest proteins/ urea in organic matter

2. Release ammonia/ ammonium compounds into soil

Explain why some of the most productive fishing areas are found in coastal waters?

1. Leaching of nitrates into water

2. Nitrates absorbed by producers/ algae

3. Lots of producers/ food so more fish

Explain why freshwater marshes have a high NPP?

1. Low rates of respiration

2. More biomass/ growth

Describe and explain how succession works?

1. Colonisation by pioneer species

2. Change environment/ named factor

3. Environment becomes less hostile/ more suitable for other species

4. Biodiversity increases

5. Until climax community reached

Suggest why petroleum is used as a comparison when evaluating biofuels?

1. Widely used

2. Benchmark/ reference- produces known amount of CO2

3. Produces large amount of CO2

4. Is a decreasing resource- could be replaced by biofuel

Why did scientists use animals of same breed for investigation?

1. Same breed so similar alleles

2. Factor controlled so only independent variable affects results

Explain when scatter graph is suitable for data?

1. Relationship between two discrete/ independent variables

Describe the process of glycolysis?

1. Glucose phosphorylated using 2 ATP

2. (Lysis) into triose phosphate

3. Triose phosphate oxidised then decarboxylated

4. Into pyruvate

5. NAD reduced

6. Net gain of 2 ATP (4 produced through substrate level phosphorylation)

Suggest why apparatus in respiration (air bubble) practical is left for 10 mins?

1. Reach equilibrium

2. Allow for pressure changes in apparatus

3. Allow rate of respiration of seeds to stabilise

Describe how acetyl coenzyme A is formed in the link reaction?

1. Oxidation of pyruvate

2. Decarboxylation releasing CO2

3. Addition of coA

Explain how a high density of cones in fovea allows predator to see prey in detail?

1. High visual acuity

2. Each cone synapsed to a single neurone

3. Brain receives separate impulses

Explain how high density of rod cells allows predator to hunt at night?

1. High visual sensitivity

2. Multiple rod cells synapsed to a single neurone

3. Threshold to generate action potential reached by spatial summation

4. Enough neurotransmitter to overcome threshold

Explain how resting potential of -70mV is maintained in sensory neurone?

1. Membrane more permeable to K+ ions, less permeable to Na+ ions

2. Sodium potassium pump actively transports Na+ out of axon and K+ in

3. Higher conc of K+ inside axon, higher conc of Na+ out of axon

Explain how applying pressure to Pacinian Corpuscle results in changes to membrane potential?

1. Layers of membrane deformed

2. Sodium ion channels open, Na+ diffused into axon

3. More channels open, more Na+ diffuses in

Explain how damaged myelin sheaths results in slower responses to stimuli?

1. No saltatory conduction

2. Depolarisation occurs along entire length of axon

Explain when a t test would be selected?

1. When determine significant differences between means

Explain how damage to myelin sheaths of neurones can cause muscle paralysis?

1. Depolarisation occurs along entire length of neurone

2. Slower transmission of impulses

3. Neuromuscular junction affected

Suggest advantages of simple reflexes?

1. Rapid

2. Protect against damage to body tissues

3. Do not have to be learnt

4. Escape from predators

5. Enable homeostatic control

Explain how IAA results in curvature of shoot?

1. IAA produced in shoot tip

2. Diffuses into shoot

3. Accumulates on shaded side

4. Stimulates cell elongation