topic 6 stimuli/nerves/homeostasis

Question 1

Suggest two advantages of simple reflexes. {2}

Answer 1

. help escape from predators

. rapid

. protect against harm to tissue

Question 2

Explain how resting potential is maintained across axon membrane in neurone. {3}

Answer 2

. K+ diffuse out / Na+ diff in

. Membrane more permeable to K+ (leaving than Na+ entering)

. Na+ (actively) transported out and K+ in

Question 3

Explain why speed of transmission of impulses is faster along myelinated axon than along nonmyelinated axon. {3}

Answer 3

.Myelination provides (electrical) insulation

. mylented: saltatory conduction

.non mylenated: depolarisation happens over entire length of axon

Question 4

Give 2 safety precautions that should be followed when dissecting a heart {2}

Answer 4

. use a sharp scalpel/scissors
. wash hands/wear gloves
. disinfect bench/equipment
. cover any cuts
. cut away from self/on a hard surface
. safe disposal

Question 5

Explain how the atrioventricular valve maintains a unidirectional flow of blood {2}

Answer 5

. when press above valve (in atrium) is higher than below valve (in ventricle) it opens
. when press below valve (in ventricle) in greater than press above valve (in atrium) it closes

Question 6

Exercise causes an increase in heart rate.

Desc the role of receptors and of the nervous system in this process. {4}

Answer 6

. chemoreceptors detect rise in CO2 / acidity / fall in pH
OR
pressure receptors detect rise in blood pressure

. send impulses to medulla

. more impulses to SAN;

. by sympathetic nervous system (for chemoreceptors)
OR

. by parasympathetic nervous system (for baroreceptors)

Question 7

Explain how both ventricles contract at the same time in the heart after initiation of the heartbeat
by the SAN {2]

Answer 7

. electrical activity only through Bundle of His / AVN;

. wave of electrical activity passes over / through both ventricles at the
same time

Question 8

Eagle focuses the image of its prey onto the fovea.

Explain how the fovea enables an eagle to see its prey in detail {3}

Answer 8

. high (visual) acuity

. (Each) cone is connected to 1 single neurone
Accept ‘bipolar/nerve cell’ for neurone.

. (Cones send) separate (sets of) impulses to brain

Question 9

Retina of owl has high density of rod cells.

Explain how this enables an owl to hunt its prey at night. {3}

Do not refer to rhodopsin in your answer.

Answer 9

. high (visual) sensitivity

. several rods connected to a single neurone/bipolar cell

.spatial summation to reach/overcome threshold

Question 10

Explain how applying pressure to the Pacinian corpuscle produces the
changes in membrane potential {3}

Answer 10

. press causes membrane/lamellae to become deformed /stretched

. Na+ channels in membrane open and Na+ move in

. greater pressure more channels open / more sodium ions enter

Question 12

Scientists investigated the relationship between the thickness of the kidney medulla of
different species of mammals and the concentration of their urine

The thicker the medulla= more conc urine

Explain this relationship {3}

Answer 12

. Thicker medulla means a longer loop of Henle

.The longer the loop of Henle means increase in sodium ion concentration (in medulla)
OR
The longer the loop of Henle means sodium ion gradient maintained for
longer (in medulla)
OR
(The longer the loop of Henle means) more sodium ions are moved out (intomedulla);

. water potential gradient maintained (for longer), so more water
(re)absorbed (from loop and collecting duct);
OR
More water is (re)absorbed from the loop (of Henle) / collecting duct by
osmosis;

Question 13

When a person is dehydrated, the cell volume of an osmoreceptor decreases.
Explain why {2}

Answer 13

. water potential of blood will decrease
. water moves from osmoreceptor into blood by osmosis.

Question 14

Stimulation of osmoreceptors can lead to secretion of the hormone ADH.
Describe & explain how secretion of ADH affects urine produced by the kidneys. {3}

Answer 14

. permeability of membrane to water is increased

. more water absorbed from / leaves distal tubule / collecting duct;

. smaller volume of urine

. urine becomes more concentrated

Question 15

Describe how urea is removed from the blood. {2}

Answer 15

. hydrostatic pressure / description of pressure / description of how pressure generated;

. causes ultrafiltration at Bowman’s capsule /glomeruli / renal capsule;

. through basement membrane;

. enabled by small size urea molecule

Question 16

Explain how urea is concentrated in the filtrate {3}

Answer 16

. reabsorption of water / by osmosis;

. at the PCT / descending LoH;

. at the DCT / CD;

. active transport of ions / glucose creates gradient (in context);

Question 17

Describe how ultrafiltration produces glomerular filtrate {5}

Answer 17

. high lood pressure / hydrostatic pressure

. smol named molec e.g glucose, ions, water

. pass through basement membrane / basement membrane acts as filter;

. Protein too large to go through / large so stays behind;

. Presence of pores in (capillaries) epithilium / presence of podocytes;

Question 18

Some people who have diabetes do not secrete insulin.

Explain how a lack of insulin
affects reabsorption of glucose in the kidneys of a person who does not secrete insulin. {4}

Answer 18

. high concentration of glucose in blood;

. high concentration in tubule / in filtrate;

. reabsorbed by facilitated diffusion / active transport;

. requires proteins / carriers;

. these are working at maximum rate / are saturated;

. not all glucose is reabsorbed / some is lost in urine;

Question 19

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction.

Suggest how {3}

Answer 19

. low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move

. 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

Question 19

ATP is an energy source used in many cell processes.
Give 2 ways in which ATP is a
suitable energy source for cells to use. {2}

Answer 19

. releases relatively small amount of energy / little energy lost as heat;

. releases energy instantaneously /rapidly

. phosphorylates other compounds, making them more reactive;
.
Can be rapidly re-synthesised;

. Is not lost from / does not leave cells.

Question 20

What is the role of ATP in myofibril contraction? (2)

Answer 20

.Breaks/allows binding of myosin to actin/actinomyosin bridge

.Provides energy to move myosin head

Question 21

Use your knowledge of fast muscle fibres to explain why time for phosphocreatine to be reformed after muscle contraction increases with age. (4)

Answer 21

.Fast muscle fibres used for rapid/brief/powerful/strong contractions

.Phosphocreatine used up rapidly during contraction/to make ATP

.As people get older, slower metabolic rate/slower ATP production/slower respiration

.ATP used to reform phosphocreatine