Which organelle is the site of the Calvin cycle? MCQ with Answer and Explanation

Which organelle is the site of the Calvin cycle?
A. Thylakoid membrane
B. Mitochondrial matrix
C. Cytoplasm
D. Chloroplast stroma
Answer: Option D
Solution (By JKSSB Mock Tests)
The Calvin cycle (C3 cycle) occurs in the stroma of chloroplasts, where CO₂ is fixed into sugars using ATP and NADPH from light reactions. Thylakoid membrane is the site of light reactions.

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Question #1
The 'Hormone Amylin' (Islet Amyloid Polypeptide) is co-secreted with insulin by the beta cells of the pancreas. Its primary functions include:
A. Slowing gastric emptying, suppressing glucagon secretion, and promoting satiety
B. Increasing gastric acid secretion
C. Stimulating intestinal motility
D. Stimulating insulin release

Correct Answer: Option A


Explanation:
Amylin, also known as Islet Amyloid Polypeptide (IAPP), is a 37-amino acid peptide hormone that is co-secreted with insulin from the pancreatic beta cells in response to meals (in a ratio of about 1:100 to insulin). Its primary functions are to complement the actions of insulin in regulating postprandial (after-meal) glucose levels. It does this by slowing gastric emptying (preventing a rapid spike in blood glucose), suppressing the secretion of glucagon (preventing the liver from releasing glucose), and acting on the brain to promote satiety and reduce food intake.

This question belongs to: Science Biology
Question #2
In the human body, the 'Limbic system' is a complex set of structures in the brain. The 'Amygdala', a key component of the limbic system, is primarily associated with:
A. Controlling voluntary motor movements
B. Forming new declarative memories
C. Regulating body temperature
D. Processing emotions, particularly fear and aggression

Correct Answer: Option D


Explanation:
The limbic system is a group of brain structures located on both sides of the thalamus, supporting emotion, behavior, motivation, long-term memory, and olfaction. The amygdala is an almond-shaped collection of nuclei located deep within the medial temporal lobes. It is a crucial component of the limbic system primarily associated with processing emotions, particularly fear, anxiety, and aggression. It plays a key role in the 'fight or flight' response and in attaching emotional significance to memories. The hippocampus is primarily for forming new declarative memories.

This question belongs to: Science Biology
Question #3
The first stable product of CO₂ fixation in C4 plants is:
A. Ribulose bisphosphate (RuBP)
B. 3-phosphoglyceric acid (PGA)
C. Oxaloacetic acid (OAA)
D. Phosphoenolpyruvate (PEP)

Correct Answer: Option C


Explanation:
In C4 plants like maize and sugarcane, CO₂ is initially fixed in mesophyll cells by PEP carboxylase, producing a four-carbon compound oxaloacetic acid (OAA), which is then converted to malate or aspartate and transported to bundle sheath cells. Here, CO₂ is released and enters the Calvin cycle. This adaptation minimizes photorespiration.

This question belongs to: Science Biology