Home / IB DP Biology- C2.1 Chemical signaling-IB Style Questions For HL Paper 1A

IB DP Biology- C2.1 Chemical signaling-IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -FA 2025- All Chapters

Question

What is an example of quorum sensing?

(A) Expression of incomplete dominance by Mirabilis jalapa flowers
(B) Spring growth of the Arctic mouse-ear chickweed Cerastium arcticum
(C) Bioluminescence in the marine bacterium Vibrio fischeri
(D) Biochemical control of lactase synthesis in Escherichia coli bacteria
▶️ Answer/Explanation

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

Quorum sensing is a communication process in which bacteria release and detect signalling molecules to monitor their population density. When enough bacteria are present, genes controlling specific activities, such as bioluminescence in Vibrio fischeri, are switched on simultaneously.

Question

Which plant hormone promotes a positive feedback loop that accelerates the ripening of fruit?

A. Auxin
B. Cytokinin
C. Epinephrine
D. Ethylene

▶️ Answer/Explanation
Ethylene is a gaseous plant hormone that stimulates fruit ripening. As fruits ripen, they release more ethylene, which in turn increases the production of ethylene further — a positive feedback mechanism that ensures rapid and uniform ripening.
✅ Answer: (D) Ethylene

Question

The hormone leptin has been tested on patients with clinical obesity to try to treat the disease.

From where is leptin secreted, where does it act and what is its function?

Leptin function diagram

A) Secreted from adipose tissue, Acts on hypothalamus, Inhibits appetite

B) Secreted from hypothalamus, Acts on adipose tissue, Stimulates appetite

C) Secreted from pancreas, Acts on hypothalamus, Stimulates appetite

D) Secreted from intestine, Acts on adipose tissue, Inhibits absorption

▶️ Answer/Explanation
Answer: A
Leptin is produced by adipose (fat) tissue and signals fat storage levels to the brain. It acts on the hypothalamus to suppress appetite and regulate energy balance. The other options incorrectly describe either the source, target, or function of leptin.
More DP Biology HL Paper 1- FA 2025- Questions..
Scroll to Top