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A Level H2 Biology Human Physiology Quiz

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A-Level Biology H2 Quiz - Human Physiology

Name: __________________________
Class: __________________________
Date: __________________________
Score: ______ / 45

Duration: 45 Minutes
Total Marks: 45

Instructions:

Answer all questions.
Write your answers in the spaces provided.
The number of marks is indicated in brackets [ ] at the end of each question or part question.
This quiz focuses on Homeostasis, Nervous Coordination, and Muscle Physiology.

Section A: Homeostasis and Control (Questions 1–5)

1. Define the term homeostasis. [2]

2. Fig 1.1 shows the changes in blood glucose concentration in a human subject after consuming a glucose-rich meal.

(Imagine a graph showing a rise in glucose at t=0, peaking at t=30 mins, and returning to baseline by t=120 mins.)

(a) Explain the mechanism by which insulin lowers blood glucose concentration in liver cells. [3]

(b) Suggest why blood glucose concentration does not fall below the normal resting level during the period shown in Fig 1.1, despite the action of insulin. [2]

3. Describe the role of the hypothalamus in thermoregulation when body temperature rises above the set point. [3]

4. Explain how the kidney contributes to the regulation of blood water potential via the production of ADH. [4]

5. Distinguish between negative feedback and positive feedback, giving one biological example of each. [2]

Section B: Nervous Coordination (Questions 6–10)

6. Fig 2.1 shows the structure of a myelinated motor neurone.

(a) State the function of the Schwann cells. [1]

(b) Explain how myelination increases the speed of nerve impulse transmission. [2]

7. Describe the events that occur at a cholinergic synapse from the arrival of an action potential at the presynaptic knob to the generation of a new action potential in the postsynaptic neurone. [4]

8. Explain why the transmission of impulses across a synapse is unidirectional. [2]

9. Fig 3.1 shows the changes in membrane potential of an axon during an action potential.

(Imagine a graph showing Resting Potential (-70mV), Depolarization to +40mV, Repolarization, and Hyperpolarization.)

(a) Explain the cause of the depolarization phase. [2]

(b) Explain the importance of the refractory period. [2]

10. Compare the roles of the sympathetic and parasympathetic nervous systems in the control of heart rate. [3]

Section C: Muscle Physiology and Integration (Questions 11–15)

11. Describe the structure of a sarcomere, identifying the A-band, I-band, H-zone, and Z-line. [3]

12. Explain the role of calcium ions in the contraction of a skeletal muscle fiber. [3]

13. Describe the sliding filament theory of muscle contraction. [3]

14. Explain the role of ATP in muscle contraction and relaxation. [3]

15. Differentiate between slow-twitch (Type I) and fast-twitch (Type II) muscle fibers in terms of their metabolic characteristics and suitability for different types of exercise. [4]

Section D: Data Interpretation and Application (Questions 16–20)

16. A student investigated the effect of temperature on the rate of reaction of an enzyme involved in cellular respiration. The results are shown in Table 1.

Temperature (°C)	Rate of Reaction (arbitrary units)
10	2.1
20	4.5
30	8.2
40	12.5
50	6.0
60	1.2

(a) Explain the increase in reaction rate between 10°C and 40°C. [2]

(b) Explain the decrease in reaction rate between 40°C and 60°C. [2]

17. In Type 1 diabetes, the beta cells of the pancreas are destroyed by an autoimmune response.

(a) Explain why individuals with Type 1 diabetes must inject insulin rather than take it as a tablet. [2]

(b) Suggest one long-term consequence of poorly controlled blood glucose levels in diabetic patients. [1]

18. Botulinum toxin prevents the release of acetylcholine from presynaptic neurones at neuromuscular junctions.

Explain how this toxin leads to muscle paralysis. [3]

19. During intense exercise, lactic acid accumulates in muscle tissues.

(a) Explain how lactic acid is produced in muscle cells. [2]

(b) Describe how the body removes lactic acid after exercise has ceased. [2]

20. The baroreceptor reflex helps regulate blood pressure.

Describe the sequence of events that occurs when blood pressure rises significantly. [4]

*** End of Quiz ***

Answers

A-Level Biology H2 Quiz - Human Physiology (Answer Key)

1. Define the term homeostasis. [2]

The maintenance of a constant/stable internal environment [1]
Within narrow limits / despite changes in the external environment [1]

2. (a) Explain the mechanism by which insulin lowers blood glucose concentration in liver cells. [3]

Insulin binds to specific complementary receptors on the cell surface membrane of liver cells [1]
This triggers the translocation of GLUT4 transporter proteins to the membrane / increases permeability to glucose [1]
Glucose enters the cell via facilitated diffusion and is converted to glycogen (glycogenesis) / oxidized in respiration [1]

(b) Suggest why blood glucose concentration does not fall below the normal resting level... [2]

As blood glucose falls, insulin secretion decreases / stops [1]
Glucagon is secreted (by alpha cells), stimulating glycogenolysis / gluconeogenesis to raise blood glucose back to normal [1]

3. Describe the role of the hypothalamus in thermoregulation when body temperature rises above the set point. [3]

Thermoreceptors in the hypothalamus detect an increase in blood temperature [1]
The heat loss center in the hypothalamus is activated [1]
It sends impulses via the sympathetic nervous system to effectors (e.g., skin arterioles vasodilate, sweat glands secrete sweat) [1]

4. Explain how the kidney contributes to the regulation of blood water potential via the production of ADH. [4]

Osmoreceptors in the hypothalamus detect low blood water potential (high osmolarity) [1]
This stimulates the posterior pituitary gland to release ADH (Antidiuretic Hormone) [1]
ADH increases the permeability of the collecting duct walls to water by inserting aquaporins [1]
More water is reabsorbed from the filtrate into the blood by osmosis, producing a smaller volume of concentrated urine [1]

5. Distinguish between negative feedback and positive feedback... [2]

Negative feedback: The response counteracts the change, returning the system to the set point (e.g., thermoregulation) [1]
Positive feedback: The response amplifies the change, moving the system further away from the set point (e.g., blood clotting / childbirth) [1]

6. (a) State the function of the Schwann cells. [1]

They produce the myelin sheath / insulate the axon [1]

(b) Explain how myelination increases the speed of nerve impulse transmission. [2]

Myelin acts as an electrical insulator, preventing ion exchange across the membrane except at the Nodes of Ranvier [1]
The impulse "jumps" from node to node (saltatory conduction), which is faster than continuous conduction [1]

7. Describe the events that occur at a cholinergic synapse... [4]

Arrival of action potential causes voltage-gated Ca²⁺ channels to open; Ca²⁺ enters the presynaptic knob [1]
Vesicles containing acetylcholine (ACh) fuse with the presynaptic membrane and release ACh by exocytosis [1]
ACh diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane [1]
This opens Na⁺ channels, causing depolarization; if threshold is reached, a new action potential is generated [1]

8. Explain why the transmission of impulses across a synapse is unidirectional. [2]

Neurotransmitter receptors are only present on the postsynaptic membrane [1]
Neurotransmitter vesicles are only present in the presynaptic knob [1]

9. (a) Explain the cause of the depolarization phase. [2]

Voltage-gated Na⁺ channels open [1]
Na⁺ ions rush into the axon down their electrochemical gradient, making the inside positive relative to the outside [1]

(b) Explain the importance of the refractory period. [2]

It ensures that action potentials are discrete / separate events [1]
It limits the frequency of impulse transmission / ensures unidirectional travel [1]

10. Compare the roles of the sympathetic and parasympathetic nervous systems in the control of heart rate. [3]

Sympathetic nervous system releases noradrenaline, which binds to receptors in the SAN, increasing heart rate (during stress/exercise) [1.5]
Parasympathetic nervous system releases acetylcholine, which binds to receptors in the SAN, decreasing heart rate (during rest) [1.5]

11. Describe the structure of a sarcomere... [3]

A-band: Contains myosin filaments (and overlapping actin); does not change length during contraction [1]
I-band: Contains only actin filaments; shortens during contraction [1]
H-zone: Central region of A-band with only myosin; shortens/disappears during contraction [1]
(Note: Z-line marks the boundary of the sarcomere)

12. Explain the role of calcium ions in the contraction of a skeletal muscle fiber. [3]

Ca²⁺ binds to troponin on the actin filament [1]
This causes tropomyosin to move away from the myosin-binding sites on actin [1]
This exposes the binding sites, allowing myosin heads to attach to actin [1]

13. Describe the sliding filament theory of muscle contraction. [3]

Myosin heads bind to actin forming cross-bridges [1]
Myosin heads pivot (power stroke), pulling actin filaments toward the center of the sarcomere [1]
ATP binds to myosin, causing it to detach from actin and reset for the next cycle [1]

14. Explain the role of ATP in muscle contraction and relaxation. [3]

Hydrolysis of ATP provides energy for the power stroke of the myosin head [1]
Binding of ATP to the myosin head causes it to detach from actin [1]
ATP is required for the active transport of Ca²⁺ back into the sarcoplasmic reticulum (for relaxation) [1]

15. Differentiate between slow-twitch (Type I) and fast-twitch (Type II) muscle fibers... [4]

Slow-twitch: High myoglobin content, many mitochondria, rich blood supply, relies on aerobic respiration, resistant to fatigue, suited for endurance (e.g., marathon running) [2]
Fast-twitch: Low myoglobin, fewer mitochondria, relies on anaerobic respiration/glycolysis, fatigues quickly, generates rapid powerful contractions, suited for sprinting/weightlifting [2]

16. (a) Explain the increase in reaction rate between 10°C and 40°C. [2]

Kinetic energy of enzyme and substrate molecules increases [1]
Frequency of successful collisions between enzyme and substrate increases, forming more enzyme-substrate complexes [1]

(b) Explain the decrease in reaction rate between 40°C and 60°C. [2]

High temperature breaks hydrogen/ionic bonds maintaining the tertiary structure of the enzyme [1]
The active site changes shape (denaturation), so the substrate no longer fits/complementary shape is lost [1]

17. (a) Explain why individuals with Type 1 diabetes must inject insulin rather than take it as a tablet. [2]

Insulin is a protein/polypeptide [1]
It would be digested/hydrolyzed by protease enzymes in the stomach/small intestine if taken orally [1]

(b) Suggest one long-term consequence of poorly controlled blood glucose levels... [1]

Damage to blood vessels (atherosclerosis) / Kidney failure / Retinopathy (blindness) / Neuropathy [1]

18. Explain how this toxin leads to muscle paralysis. [3]

Acetylcholine is not released into the synaptic cleft [1]
ACh cannot bind to receptors on the muscle fiber membrane [1]
Na⁺ channels do not open, so no depolarization/action potential is generated in the muscle, preventing contraction [1]

19. (a) Explain how lactic acid is produced in muscle cells. [2]

During intense exercise, oxygen supply is insufficient for aerobic respiration [1]
Pyruvate is converted to lactate (lactic acid) via anaerobic glycolysis to regenerate NAD+ [1]

(b) Describe how the body removes lactic acid after exercise has ceased. [2]

Lactic acid is transported to the liver via the blood [1]
It is converted back to pyruvate/glucose (Cori cycle) using oxygen (oxygen debt) [1]

20. Describe the sequence of events that occurs when blood pressure rises significantly. [4]

Baroreceptors in the carotid sinus/aortic arch detect increased stretch/pressure [1]
They send increased frequency of impulses to the cardiovascular center in the medulla oblongata [1]
The center sends more impulses via the parasympathetic nervous system (vagus nerve) to the SAN [1]
Acetylcholine is released, decreasing the heart rate, which lowers blood pressure [1]