p2 photosytn

Question 1

light dependent reaction

Answer 1

• light absorbed by photosystem
• photoionisation + leave
• photolysis (H+, O2,e-) replaces lost e-
• e- move along transport chain releasing energy
• energy used to A.T H+ across thy. membrane
• hi H+ conc created in thy. vs stoma.
• facilitated diffusion via atp synthase (ADP + Pi)
• NADP + H+ = NADPH

Question 2

light independent

Answer 2

• Carbon dioxide combines with ribulose bisphosphate (RuBP) + rubisco catalyses this reaction
• The resulting six-carbon (6C) compound is unstable + splits
• This gives two molecules of (GP)

Question 3

how does exercise affect heart rate

Answer 3

• Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall in pH
• Send impulses to cardiac centre / medulla;
• More impulses to SAN;
• By sympathetic (parasympathetic for baroreceptors)

Question 4

how does heart cintract

Answer 4

• wave of depolarisation from SAN
• atria contract
• delayed at AVN
• then sent thru bundles of His
• Ventricles contract

Question 5

how does pacician corpsule work

Answer 5

• pressure = distorts connective tissue
• strech med. Na channels open = Na into axon
• depolarisation of membrane
• depolarisation = gemeratro potential = action potential

Question 6

how blood pressure lowers

Answer 6

• baro detect hi bp
• increase in impulses to medulla (autonomic)
• increased impulses to SAN (parasympathetic)
• heart rate decreases + b.p is lowered

Question 7

WHAT HAPPENS AT A SYNAPSE

Answer 7

• Action potential arrives + the presynaptic membrane is depolarised
• Calcium ion channels open and calcium ions diffuse in
• Causing presynaptic vesicles to fuse with presynaptic membrane;
• Neurotransmitter/Acetylcholine is released into synaptic cleft;
• Acetylcholine binds to receptor proteins on sodium channels on postsynaptic membrane;
• Receptor proteins open and sodium ions diffuse in, causing depolarisation of the postsynaptic membrane;
• Neurotransmitter/Acetylcholine is broken down (by acetylcholinesterase) and recycled.

Question 8

how to muscles contract

Answer 8

• action potential arrives
• Calcium ions are released from the sarcoplasmic reticulum
• Ca ions bind to troponin molecules, stimulating them to change shape.
• causes troponin and tropomyosin proteins to change position on the actin filaments
• Myosin binding sites are exposed on the actin molecules
  The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
  The formation of the cross-bridges causes the myosin heads to spontaneously bend (releasing ADP and inorganic phosphate), pulling the actin filaments towards the centre of the sarcomere and causing the muscle to contract a very small distance
  ATP binds to the myosin heads producing a change in shape that causes the myosin heads to release from the actin filaments
  The enzyme ATP hydrolase hydrolyses ATP into ADP and inorganic phosphate which causes the myosin heads to move back to their original positions (this is known as the recovery stroke)
  The myosin heads are then able to bind to new binding sites on the actin filaments, closer to the Z disc
  The myosin heads move again, pulling the actin filaments even closer the centre of the sarcomere, causing the sarcomere to shorten once more and pulling the Z discs closer together
  ATP binds to the myosin heads once more in order for them to detach again
  As long as troponin and tropomyosin are not blocking the myosin-binding sites and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted

Question 9

why is long loop of henle good for camels

Answer 9

• longer a limb –> more ions reabsorbed
• longer d limb –> more water reabsorbed
• less water lost in urine

Question 10

why less water = less water lost

Answer 10

• lowblood pressure detected by hypotgalamus
• more adh secreted by hypothalamus
• membrane of collecting duct/ dct more permeable
• more reasborbed into blood
• by osmosis