Essay

Question 1

Importance of receptors ao1
G protein and enzyme linked receptors

Answer 1

• found in the liver
  Glucagon binds to a transmembrane protein
  complementary receptor. activates adenyl cyclayse. converts ATP to cyclic AMP. activates protein kinases whichactivates enzymes involved in gluconeogenesis and glycogenolysis to produce glucose from alternative sources, e.g. lipids, amino acids, and to hydrolyse glycogen to alpha-glucose
  which can then be phosphorylated to enter glycolysis and produce pyruvate to be fed into the Krebs cycle as part of aerobic respiration.

Question 2

importance of receptors
g protein and enzyme linked receptors
ao2

Answer 2

• allows glucagon to bind to cell surface of liver cells
  without this no homeostatic control of BG as glucagon is released when blood
  glucose concentration is detected to be low.
  It is important to have
  a stable blood glucose concentration to ensure enough glucose is
  available for respiration and to avoid altering the water potential of
  the blood, which would become less negative with reduced blood
  glucose concentration causing cell damage by causing cells to take
  up water due to the water potential gradient that exists.

Question 3

importance of receptors - ach receptors ao1

Answer 3

receptors on the cell-surface membrane on the post synaptic neurone. These receptors are specific to acetylcholine
(ACh) by having a tertiary protein structure that is complementary
in shape to the neurotransmitter.
The neurotransmitter is
important as it is released when a wave of depolarisation reaches
to synaptic knob of the pre-synaptic neurone causing voltagegated calcium ion channels to open which causes an influx of
calcium ions that cause vesicles containing ACh to fuse to the presynaptic membrane and to release ACh by exocytosis. This
neurotransmitter then diffuses down its concentration gradient
across the synaptic cleft and binds to the aforementioned protein
receptors. This binding then causes ligand-gated sodium ion
channels in the post-synaptic membrane to open which allows an
influx of sodium ions into the post-synaptic neurone, and if this is
to a sufficient degree to make the inside of the neurone
sufficiently positive (approximately -55 mV) an action potential is
generated in the post-synaptic membrane.

Question 4

importance of receptors ach ao2

Answer 4

• they ensure the
  unidirectional passage of an action potential and prevent
  hyperstimulation of the pre-synaptic neurone by preventing the
  neurotransmitter stimulating the neurone from which they were
  released due to a lack of the specific acetylcholine receptor on the
  pre-synaptic membrane.
• without ACh receptors no ach can bind
  meaning that synaptic transmission is slowed and maybe even
  halted which in turn prevents the passage of nervous impulses to
  the brain.

Question 5

importance of receptors - chemeoreceptors ao1

Answer 5

• aorta and cartoid arteries
• respond to changes in blood ph
• send impulses to medulla
• more freq impulses to san along Parasym/Sym NS
• cardiac muscles contracrs more/less frequently
• hr increase/decrease

Question 6

importance of receptors ao2
chemoreceptors

Answer 6

• without chemoreceptors nothing to ensure that blood continues to act as a buffer solution to avoid
  damage to its constituent proteins,
• e.g. haemoglobin. blood ph low due to XS H+ disrupt hydrogen and ionic bonds in 3* struc alter the 3D-shape = non func pro.
• long intensive exercise can decrease blood ph more aerobic respiration = additional ATP to allow muscle contraction via actinmyosin cross-bridge formation. more co2 dissolves carbonic acid lowers blood ph
  blood ph wouldnt be brought back to normal without chemoreceptors via neg feedback loop

Question 7

importance of receptors
t-helper cell ao1

Answer 7

• diff shaped receptors on surface of tH complementary to specific shaped antigens.
• binding of antigen to antibody (cell mem of b cell) forming antigen-antibody receptor complex allows t cells to undergo mitosis

Question 8

importance of receptors tH ao2

Answer 8

• without receptors no mitosis of tH so no differentiation into cytoxic t cells to release protein perforin to make bac cell walls freely permeable allowing cell death due to influx of water - increase omotic pressure - lysis
• no b cells so no clonal expansision and differ into plasma b cells so no antibodies secreted to specific antigens
• no aggultination so phagocytes engulf harder
• no mem b cells so cannot remember spec shape of antigen so cannot recognise antigen upon re infection to secrete more antibodies quicker
• slower secondary immune response
• without receptor specifity on th could cause an immune response to be triggered agianst self cells which could cause symptoms of autoimmune disorders

Question 9

ao1 transcription factors

Answer 9

TF is a protein. Oestrogen binds to protein and causes
change in shape of DNA binding site. TF moves into the
nucleus and binds to the promoter region on DNA and
initiates transcription.

Question 10

ao2 transcription factors

Answer 10

• Important protein in controlling the process of gene expression.
  If too much oestrogen, lots bind to the receptor and can result in uncontrolled cell division and breast cancer.
• TF allow for specialised cells and can lead to cancer eg no transcription of tumour suppressor gene due to increased methylation and decreased acetylation

Question 11

ao2 myosin actin

Answer 11

These proteins are important in enabling a response to
a stimulus. e.g. if Pacinian corpuscle receptor detects
pressure (describe process briefly) causes muscle to
contract and move the hand away .

Question 12

ao2 insluin

Answer 12

• too high bg decreases wp
  water moves into blood by osmosis which increases blood pressure, increased risk cardio vascular disease
• no glycogen stores made

Question 13

ao2 reg of blood water potential

Answer 13

Important to response to changes in the water potential
of blood. Too negative will result in cells losing water by osmosis- increasing blood pressure and water is a metabolite and solvent, so very important to cells.

Question 14

importance of haemoglobin bohr shift

Answer 14

This response is important as the increased supply
of oxygen ensures aerobic respiration can continue.
Oxygen as final electron acceptor. Enables
production of ATP for metabolism.

Question 15

ao2 taxes and kinises

Answer 15

Important a woodlouse responds to light, if remains in
higher light intensities it could cause desiccation and
death. Also means more exposed and visible to predators.
reduce biodiversity

Question 16

ao1 water

Answer 16

polar molecule
● Slightly negatively charged oxygen atoms attract slightly positively
charged hydrogen atoms of other water molecules

Question 17

ao2 water

Answer 17

Metabolite Used in condensation / hydrolysis / photosynthesis / respiration
Solvent (can
dissolve solutes)
1. Allows metabolic reactions to occur (faster in solution)
2. Allows transport of substances eg. nitrates in xylem, urea in blood

(Relatively) high
specific heat
capacity
● Buffers changes in temperature
● As can gain / lose a lot of heat / energy without changing temperature
1. Good habitat for aquatic organisms as temperature more stable than land
2. Helps organisms maintain a constant internal body temperature so maintains enzyme activity

(Relatively) large
latent heat of
vaporisation
● Allows effective cooling via evaporation of a small volume (eg. sweat)
● So helps organisms maintain a constant internal body temperature

Strong cohesion
between water
molecules
1. Supports columns of water in tube-like transport cells of plants
eg. transpiration stream through xylem in plants
2. Produces surface tension where water meets air, supporting small
organisms (to walk on water) helps to avoid pred within water as they can survive on surface - more biodiv - more habitats

Question 18

ao1 cohesion tension

Answer 18

transpiration - 4. Creating tension (‘negative pressure’ or ‘pull’) in xylem
5. Hydrogen bonds result in cohesion between water molecules (stick
together) so water is pulled up as a continuous column
6. Water also adheres (sticks to) to walls of xylem

Question 19

ao2 cohesion tension

Answer 19

• water is a solvent and can carried dissolved ions such as nitrates that might’ve been absorbed from cells
• combined with organic substances made in photosynthesis to make proteins eg rubisco enzyme - LIR

Question 20

ao1 photolysis

Answer 20

● Water splits to produce protons, electrons and oxygen
(H2O → 1⁄2 O2 + 2e- + 2H+)

○ Electrons replace those lost from chlorophyll, H+ used to reduce NADP

Question 21

ao2 photolysis

Answer 21

• allows for formation of atp and NADPH
• important for LIR
• no atp means no energy release for regenaration of RuBP and for red of GP to TP which req ox of NADPH
• without water/photolyis.ldr no/less TP into useful organic sub like cellulose (strength) and glucose (respiratory sub in glycolysis release energy)

Question 22

tissue fluid ao1

Answer 22

1. Higher blood / hydrostatic pressure inside
   capillaries (due to contraction of ventricles)
   than tissue fluid (so net outward force)
2. Forcing water (and dissolved substances)
   out of capillaries
3. Large plasma proteins remain in capillary

Question 23

tissue fluid ao2

Answer 23

• tissues or cells are bathed with useful molecules which are forced out eg glucose and o2
• water gets reabsorbed back into capillaries due to plasma proteins red wp so any waste like co2 and urea are transported with water back into blood then trasnported around the body and removed

Question 24

ao2 cooling down due to large latent heat

Answer 24

-maintain constant core body temp needed to max rate of enzyme controlled reactions eg lysozymes high n.o of es complexes
- preventd denaturing as we can prevent very high temps prev change in active site and lower rate

Question 25

ao2 dna (struc and genetic code)

Answer 25

- stable replicable struc allows inheritance - passing on favourable alleles in natural selection - genetic code universal enable gene transfer/transgenic organisms in biotechnology

Question 26

ao2 dna rep

Answer 26

- enables cell divison and genetic continuity between generations - required for pcr (mimics dna rep in vivo) and and clonal expansion in humoural response

Question 27

ao2 protein syn

Answer 27

- dna controls struc and func of cells in protein prod eg 3*/4* struc of haemoglobin - gene mutations changes mrna seq changing struc of protein = non func eg mutation in tumour supressor gene leading to uncontrolled cell div

Question 28

ao2 gene tech

Answer 28

medicine - GM bacteria produce human proteins (eg. insulin for type 1 diabetes) → more ethically acceptable than using animal proteins and less likely to cause allergic reactions agriculture - GM crops resistant to herbicides → only weeds killed when crop sprayed with herbicide ● GM crops with added nutritional value (eg. Golden rice has a precursor of vitamin A)

Question 29

Ao2 pacinian corpuscle

Answer 29

The responses to mechanical stimuli like pressure or pain are important. As it prevents the organism from sustaining damage to cells and tissue. Damage to the skin could result in introduction of foreign antigens that would cause an immune response or be toxic blocking receptor sites on cell membranes or inhibiting enzymes. Blood loss which could result in a fatal reduction in blood pressure or reduce the delivery of oxygen to cells. Oxygen is the final electron acceptor in oxidative phosphorylation and without it aerobic respiration is incomplete. Which would result in a massive reduction in ATP production. ATP is needed for muscle contraction during the power stroke and breaking of the actin -myosin cross bridges.

Question 30

Ao2 phototropism

Answer 30

Phototropism is important because it allows more sunlight to reach photosystem ii in the thylakoid membrane. This increases the amount of photoionisation of the chlorophyll. Releasing more electrons for the formation of ATP and reduced NADP which means more hydrogen, electrons and energy are transferred to the light independent reaction in the stroma and so therefore more GP glycerate-3-phosphate is converted to Triose Phosphate (TP) and more useful organic products are formed such as glucose, lipids, starch, cellulose or amino acids all of which will increase the probability of the plant surviving.