The molecule that binds to the operator region of the lac operon to inhibit transcription is:
A. Inducer
B. CAP protein
C. Repressor protein
D. RNA polymerase
Answer: Option C
Solution (By JKSSB Mock Tests)
The lac repressor protein (product of lacI gene) binds to the operator sequence, preventing RNA polymerase from transcribing the structural genes. When lactose is present, allolactose (inducer) binds the repressor, causing it to release the operator, allowing transcription. This is negative regulation.
Consider statements about plant biology: 1. Xylem transports water upwards. 2. Phloem transports food bidirectionally. 3. Cambium is responsible for secondary growth. Which are correct?
Explanation:
Xylem is the vascular tissue responsible for the unidirectional upward transport of water and dissolved minerals from the roots to the aerial parts of the plant. Phloem is the vascular tissue responsible for the translocation of organic nutrients (primarily sucrose) from sources to sinks, which can be bidirectional (up or down depending on the plant's needs). Cambium (vascular and cork) is a lateral meristem responsible for secondary growth, which is the increase in the girth or thickness of stems and roots. All statements are correct.
Explanation:
The medulla oblongata contains the respiratory rhythmicity centre that controls the rate and depth of breathing. The pons also has pneumotaxic and apneustic centres influencing breathing. The cerebrum can exert voluntary control, cerebellum coordinates movement, and hypothalamus regulates homeostasis.
Explanation:
Schwann cells wrap around axons in the PNS to form myelin sheaths. Oligodendrocytes myelinate axons in the CNS. Astrocytes support neurons, microglia are immune cells.
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