Assertion (A): The human heart is myogenic. Reason (R): It beats rhythmically due to signals from the brain. MCQ with Answer and Explanation

Question
Assertion (A): The human heart is myogenic.
Reason (R): It beats rhythmically due to signals from the brain.
A. A is true, but R is false.
B. A is false, but R is true.
C. Both A and R are true, and R is the correct explanation.
D. Both A and R are true, but R is not the correct explanation.
Answer: Option A
Solution (By JKSSB Mock Tests)
The heart is myogenic because the heartbeat originates in the SA node within the heart itself, not from brain signals. The brain can modulate the rate but not initiate. Thus, A is true, but R is false.
This question belongs to: Science Biology
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Question #1
Which of the following is a fungal disease of plants?
A. Citrus canker
B. Late blight of potato
C. Tobacco mosaic
D. Crown gall
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Correct Answer: Option B

Explanation:
Late blight of potato is caused by the oomycete Phytophthora infestans (historically considered a fungus). It caused the Irish Potato Famine. Tobacco mosaic is viral, citrus canker is bacterial (Xanthomonas), crown gall is bacterial (Agrobacterium tumefaciens). Fungal plant diseases also include rust, smut, and powdery mildew. Oomycetes are now classified under Chromista but traditionally studied in mycology.
This question belongs to: Science Biology
Question #2
The enzyme responsible for joining the Okazaki fragments on the lagging strand during DNA replication is:
A. DNA ligase
B. DNA polymerase III
C. DNA helicase
D. DNA primase
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Correct Answer: Option A

Explanation:
During DNA replication, the lagging strand is synthesized discontinuously in short segments called Okazaki fragments. After the RNA primers are removed and replaced with DNA by DNA polymerase I, the fragments remain separated by nicks in the sugar-phosphate backbone. DNA ligase is the enzyme that catalyzes the formation of phosphodiester bonds between these fragments, sealing the nicks and creating a continuous DNA strand.
This question belongs to: Science Biology
Question #3
Consider statements about the human heart: 1. The left ventricle has the thickest wall. 2. The tricuspid valve is between the left atrium and ventricle. 3. The SA node is the natural pacemaker. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 2 only
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Correct Answer: Option A

Explanation:
The left ventricle has the thickest muscular wall to pump blood at high pressure into the systemic circulation. The sinoatrial (SA) node generates impulses spontaneously, acting as the natural pacemaker. The tricuspid valve is located between the right atrium and right ventricle; the bicuspid (mitral) valve is on the left side. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
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