Home / IB DP Biology- C3.1 Integration of body systems – IB Style Questions For SL Paper 1A

IB DP Biology- C3.1 Integration of body systems - IB Style Questions For SL Paper 1A -FA 2025

IBDP Biology Paper 1 - All Chapters

Question

Which of the following structures functions as the effector in a pain reflex arc?

A. Grey matter
B. Skeletal muscle
C. Motor neuron
D. Pineal gland

▶️ Answer/Explanation
In a pain reflex arc, sensory neurons detect the stimulus and send signals to the spinal cord, where they connect with motor neurons. The motor neurons then stimulate skeletal muscles, which act as the effectors to produce a rapid response (e.g., withdrawing the hand from a hot surface).
✅ Answer: (B) Skeletal muscle

Question

What is a function of the pancreas?

A. To control the rate of metabolism by releasing thyroxine when metabolic rate is low
B. To release glucagon when blood glucose levels are low
C. To release insulin when blood glucose levels are low
D. To secrete an endopeptidase which lowers the blood glucose levels

▶️ Answer/Explanation

Pancreas function diagram Answer: (B) To release glucagon when blood glucose levels are low

Explanation:
The pancreas helps regulate blood glucose levels by releasing two main hormones:

• When blood glucose is low, the pancreas releases glucagon. Glucagon signals the liver to break down glycogen into glucose and release it into the bloodstream.

• When blood glucose is high, the pancreas releases insulin, which helps cells absorb glucose and reduces blood glucose levels.

Option Evaluation:
A. Incorrect — Thyroxine is produced by the thyroid gland, not the pancreas.
B. Correct — Glucagon is released when blood glucose is low.
C. Incorrect — Insulin is released when blood glucose is high, not low.
D. Incorrect — Endopeptidases digest proteins and do not regulate blood glucose.

✅ Answer: (B)

 

Question

The diagram shows how heart sounds align with changes in blood pressure during the cardiac cycle.

Heart sounds aligned with pressures

What can be deduced about the cause of the heart sounds?

A. The \(1^{\text{st}}\) heart sound is caused by the closing of the atrio-ventricular valves

B. The \(2^{\text{nd}}\) heart sound is caused by the opening of the atrio-ventricular valves

C. The \(1^{\text{st}}\) heart sound is caused by the closing of the semi-lunar valves

D. The \(2^{\text{nd}}\) heart sound is caused by the closing of the atrio-ventricular valves

▶️ Answer/Explanation

Answer: (A)

Explanation:

The heart sounds correspond to valve closures in the cardiac cycle:

\(S_1\) (“lub”): occurs at the start of ventricular systole when ventricular pressure exceeds atrial pressure, causing closure of the atrio-ventricular (AV) valves (mitral and tricuspid). This prevents backflow into the atria.

\(S_2\) (“dub”): occurs at the end of ventricular systole when ventricular pressure falls below arterial pressure, causing closure of the semi-lunar valves (aortic and pulmonary).

Option checks:
(B) Incorrect — valve openings are not heard; \(S_2\) is due to semi-lunar closure.
(C) Incorrect — \(S_1\) is AV valve closure, not semi-lunar.
(D) Incorrect — \(S_2\) is semi-lunar valve closure, not AV.

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