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

IB DP Biology- C3.1 Integration of body systems-IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -All Chapters

Question

Which is the effector in a pain reflex arc?

(A) Skeletal muscle
(B) Sensory nerve ending
(C) Pituitary gland
(D) Grey matter of spinal cord
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{A}} \)

In a pain reflex arc, the effector is the skeletal muscle, which contracts in response to signals from a motor neuron. This rapid contraction withdraws the body part from the harmful stimulus, helping to prevent injury.

Question

The image shows the response of a plant shoot to light exposure.

What facilitates this response?

I. Auxin efflux carriers are located on one side of the cell.
II. Auxin promotes hydrogen ion secretion.
III. Cell walls become acidified and cellulose cross links are loosened.
(A) I and II only
(B) I and III only
(C) II and III only
(D) I, II and III
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{D}} \)

During phototropism, auxin efflux carriers redistribute auxin to the shaded side of the shoot. Auxin stimulates the secretion of hydrogen ions (H⁺), which acidify the cell wall and loosen cellulose cross-links. The cells elongate more on the shaded side, causing the shoot to bend towards the light.

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
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