Changes In Environments Exam Qs

Question 1

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from
glucose. This lowers the concentration of glucose in liver cells.
Explain how the formation of glycogen in liver cells leads to a lowering of blood
glucose concentration. (3 marks)

Answer 1

1. Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein);

Question 2

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain
how this causes the blood glucose concentration to increase.

Answer 2

1. Adenylate cyclase activated / cAMP produced / second messenger produced;
2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited;

Question 3

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain
how this causes the blood glucose concentration to increase. (2 marks)

Answer 3

1. Adenylate cyclase activated / cAMP produced / second messenger produced;
2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited;

Question 4

.Multiple sclerosis (MS) is a disease that involves damage to the myelin sheaths of neurones.
Movement in MS sufferers may be jerky or slow.
(a) Damage to the myelin sheaths of neurones can lead to problems controlling the contraction of muscles.
Suggest one reason why.

Answer 4

1. Action potentials travel more slowly / don’t travel;
2. So delay in muscle contraction / muscles don’t contract / muscles
   contract slow(er);

Question 5

Cannabinoids are hydrophobic molecules. In the body, they easily pass into neurones.
Explain why.

Answer 5

Lipid-soluble / pass through phospholipid bilayer.

Question 6

Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular
junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction.

Answer 6

1. Prevents influx of calcium ions (into pre-synaptic membrane);
2. (Synaptic) vesicles don’t fuse with membrane / vesicles don’t release neurotransmitter;
3. Neurotransmitter does not diffuse across synapse / does not bind to
   receptors (on post-synaptic membrane);
4. No action potential / depolarisation (of post-synaptic membrane) /
   sodium (ion) channels do not open / prevents influx of sodium ions.

Question 7

A myelinated axon conducts impulses faster than a non-myelinated axon.
Explain this difference. (3 marks)

Answer 7

1. (In myelinated) action potential / depolarisation only at node(s);
2. (In myelinated, nerve impulse) jumps from node to node / saltatory;
3. (In myelinated) action potential / impulse does not travel along whole length;

Question 8

Serotonin is a neurotransmitter released in some synapses in the brain. It is transported
back out of the synaptic gap by a transport protein in the pre-synaptic membrane.
(a) Serotonin diffuses across the synaptic gap and binds to a receptor on the post-synaptic membrane.
Describe how this causes depolarisation of the post-synaptic membrane. (2 marks)

Answer 8

1. Causes sodium ion channels to open;

2. Sodium ions enter (cell and cause depolarisation);

Question 9

It is important that a neurotransmitter such as serotonin is transported back out of
synapses. Explain why. (2 marks)

Answer 9

1. (If not removed) keeps binding (to receptors);
   Accept answers based on what happens if it
2. Keeps causing action potentials / depolarisation (in post-synaptic membrane);

Question 10

.Osmoreceptors are specialised cells that respond to changes in the water potential of the
blood.
(a) Give the location of osmoreceptors in the body of a mammal. (1 mark)

Answer 10

Hypothalamus.

Question 11

When a person is dehydrated, the cell volume of an osmoreceptor decreases.
Explain why. (2 marks)

Answer 11

1. Water potential of blood will decrease;

2. Water moves from osmoreceptor into blood by osmosis.

Question 12

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe
and explain how the secretion of ADH affects urine produced by the kidneys. (4 marks)

Answer 12

1. Permeability of membrane / cells (to water) is increased;
2. More water absorbed from / leaves distal tubule / collecting duct;
3. Smaller volume of urine;
4. Urine becomes more concentrated.

Question 13

Creatinine is a breakdown product of creatine found in muscle tissues. Apart from
age and gender, give two factors that could affect the concentration of creatinine in
the blood. (2 marks)

Answer 13

Muscle / body mass
Ethnicity
Exercise
Kidney disease

Question 14

2. In a mammal, urea is removed from the blood by the kidneys and concentrated in the filtrate.
   (a) Describe how urea is removed from the blood (2 marks)

Answer 14

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 15

Explain how urea is concentrated in the filtrate. (3 marks)

Answer 15

Reabsorption of water / by osmosis;
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions / glucose creates gradient

Question 16

Describe how ultrafiltration produces glomerular filtrate. (5 marks)

Answer 16

1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;

Question 17

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 marks)

Answer 17

1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed / some is lost in urine;

Question 18

Some desert mammals have long loops of Henle and secrete large amounts of
antidiuretic hormone (ADH). Explain how these two features are adaptations to living
in desert conditions. (6 marks)

Answer 18

1. More water (from filtrate) reabsorbed / returned to blood / less lost in
   urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
   For loop of Henle, maximum 2 marks:
5. Sodium / chloride ions absorbed from filtrate in ascending limb;
6. Gradient established in medulla / concentration of ions increases down
   medulla; For ADH, maximum 2 marks:
7. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
8. Makes cells more permeable / inserts aquaporins in plasma membranes;

Question 19

A diabetic person and a non-diabetic person each ate the same amount of glucose.
One hour later, the glucose concentration in the blood of the diabetic person was
higher than that of the non-diabetic person. Explain why. (3 marks)

Answer 19

1. Lack of insulin / reduced sensitivity of cells to insulin;
2. Reduced uptake of glucose by cells / liver / muscles;
3. Reduced conversion of glucose to glycogen;

Question 20

The urine of a non-diabetic person does not contain glucose. Explain why. (2 marks)

Answer 20

Leaves the blood at kidney;

Taken back into blood / reabsorbed (from kidney tubule);

Question 21

A high blood glucose concentration could cause glucose to be present in the
urine of a diabetic person. Suggest how. (2 marks)

Answer 21

Large amount / high concentration of glucose in filtrate;
Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb
all of glucose / saturation of carriers;

Question 22

A test for glucose in urine uses immobilised enzymes on a plastic test strip. One of these enzymes is glucose oxidase. Explain why the test strip detects glucose and no other substance. (2 marks)

Answer 22

Enzyme has specific shape to active site / active site has specific tertiary
structure;
Only glucose fits / has complementary structure / can form ES complex;

Question 23

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why. (3 marks)

Answer 23

Glucose in filtrate lowers water potential;
Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma;
Less water reabsorbed by osmosis;

Question 24

In some forms of kidney disease, proteins from the blood plasma are found in the
urine. Which part of the nephron would have been damaged by the disease to cause
proteins from blood plasma to be present in the urine? Explain your answer. (3 marks)

Answer 24

1. Glomerulus / Bowman’s capsule / renal capsule;
2. Basement membrane;
3. Proteins are large (molecules) / proteins cannot normally pass through filter / proteins can only pass through if filter damaged;

Question 25

The kangaroo rat is a small desert mammal. It takes in very little water in its food and it
rarely drinks. Its core body temperature is 38 °C.
The kangaroo rat takes in some water by feeding and drinking. Describe another method
by which the kangaroo rat could obtain water. (2 marks)

Answer 25

metabolic water / from respiration;

aerobic / use of oxygen;

Question 26

Scientists investigated the control of blood glucose concentration in mice. They kept a group
of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations
of the mice were the same as at the start of the experiment.
(a) Explain how the normal mice prevented their blood glucose concentration falling
when they had not eaten for 48 hours.

Answer 26

1. Release of glucagon;
2. Leads to formation of glucose in liver (cells);
3. From non-carbohydrates / amino acids / fatty acids.

Question 27

In humans, when the stomach starts to become full of food, receptors in the wall of
the stomach are stimulated. This leads to negative feedback on the desire to eat.
Suggest why this negative feedback is important.
(3 marks)

Answer 27

1. (Negative feedback) stops desire / wish to eat / appetite;
2. (This) limits amount eaten / stops eating;
3. Prevents / reduces risk of obesity / too much energy intake;

Question 28

Different substances are involved in coordinating responses in animals.
(a) Synapses are unidirectional. Explain how acetylcholine contributes to a synapse
being unidirectional. (2 marks)

Answer 28

1. (Acetylcholine) released from / in presynaptic side;

2. Receptors in postsynaptic (side) / binds on postsynaptic (side);

Question 29

Diabetic people who do not control their blood glucose concentration may become
unconscious and go into a coma. A doctor may inject a diabetic person who is in a
coma with glucagon. Explain how the glucagon would affect the person’s blood
glucose concentration. (2 marks)

Answer 29

Glycogen to glucose / glycogenolysis by activating enzymes;

Gluconeogenesis;

Question 30

The control of water balance in the body involves negative feedback.
(i) Describe what is meant by negative feedback.

Answer 30

Where a change triggers a response which reduces the effect of a change;

Question 31

Water is removed from the body via the kidneys. Give two other ways in which
water is removed from the body.

Answer 31

e.g. sweating, breathing, defaecating,

Question 32

Name the part of the brain which acts as the coordinator in the control of water
balance

Answer 32

hypothalamus;

Question 33

A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how (3 marks)

Answer 33

recessive alleles can be carried by individuals without showing effects / dominant allele always expressed;
organism that are carriers more likely to reproduce / affected organism
less likely to reproduce;
therefore recessive alleles are more likely to be passed on / dominant
alleles less likely to be passed on;

Question 34

What is meant by homeostasis? (1 mark)

Answer 34

maintaining a constant internal environment;

Question 35

Giving one example, explain why homeostasis is important in mammals. (2 marks)

Answer 35

temperature / pH; optimum for enzymes / effect of pH /
temperature on enzyme activity;

water potential / blood glucose;
effect of osmotic / blood glucose imbalance on cells;

Question 36

Cross-channel swimmers may suffer from muscle fatigue during which the
contraction mechanism is disrupted. One factor thought to contribute to muscle
fatigue is a decrease in the availability of calcium ions within muscle fibres. Explain
how a decrease in the availability of calcium ions could disrupt the contraction
mechanism in muscles. (3 marks)

Answer 36

cannot interact with / move tropomyosin from binding sites on actin;
(reject active sites)
myosin(heads) do not bind / actinomyosin not formed;
does not activate ATPase / energy not released from ATP;

Question 37

Both slow and fast muscle fibres contain ATPase.

Explain why. (2 marks)

Answer 37

1. Splitting / breakdown / hydrolysis of ATP;
2. (Muscle) contraction requires energy / ATP;
3. Use of ATP by myosin.

Question 38

Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5 marks)

Answer 38

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin
   heads to detach (from actin sites).

Question 39

ATP is an energy source used in many cell processes. Give two ways in which ATP
is a suitable energy source for cells to use. (2 marks)

Answer 39

1. Releases relatively small amount of energy / little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cells.

Question 40

What is the role of phosphocreatine (PC) in providing energy during muscle contraction? (2 marks)

Answer 40

1. (Phosphocreatine) provides phosphate / phosphorylates;

2. To make ATP;

Question 41

Give one similarity and one difference between a taxis and a tropism. (2 marks)

Answer 41

1. Similarity − directional response (to a stimulus) / movement towards / away from a stimulus;
2. Difference − taxis (whole) organism moves and tropism a growth
   (response) .

Question 42

Explain how this distribution of IAA causes the root to bend.

Answer 42

1. (IAA) at bottom of root / where IAA concentration high inhibits expansion / elongation (of cells);
2. (IAA) at top of root / where IAA concentration low leads to expansion / elongation (of cells

Question 43

.Multiple sclerosis (MS) is a disease that involves damage to the myelin sheaths of neurones.
Movement in MS sufferers may be jerky or slow.
(a) Damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles.
Suggest one reason why (2 marks)

Answer 43

1. Action potentials travel more slowly / don’t travel;
2. So delay in muscle contraction / muscles don’t contract / muscles
   contract slow(er);

Question 44

Cannabinoids are hydrophobic molecules. In the body, they easily pass into
neurones.
Explain why. (1 mark)

Answer 44

Lipid-soluble / pass through phospholipid bilayer.

Question 45

Cannabinoids include substances found in cannabis that can enter brain tissue.
Scientists are developing artificial cannabinoids that can enter neuromuscular
junctions but cannot enter brain tissue.
Suggest why these artificial cannabinoids would be better to use than cannabis
when treating someone with MS. (2 marks)

Answer 45

1. They won’t affect synapses in brain;
2. They won’t cause problems with the brain’s function / won’t damage brain;
3. (So only the) muscle / neuromuscular junctions treated / affected

Question 46

Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5 marks)

Answer 46

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin
   heads to detach (from actin sites).

Question 47

ATP is an energy source used in many cell processes. Give two ways in which ATP
is a suitable energy source for cells to use. (2 marks)

Answer 47

1. Releases relatively small amount of energy / little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cells.