Concept: This question tests your understanding of the fundamental principles of neural coordination, including neuronal excitability, synaptic transmission, brain functions, and the definition of coordination.

Why (B) is correct:

Let's analyze each statement:

A. Neurons are excitable cells because their membranes are in a polarised state. This statement is correct. The resting membrane potential, maintained by the sodium-potassium pump, creates a polarized state (negative inside, positive outside) across the neuronal membrane, which is crucial for generating and transmitting nerve impulses.

B. Impulse transmission across a chemical synapse is always faster than that across an electrical synapse. This statement is incorrect. Electrical synapses allow direct and very rapid transmission of impulses via gap junctions, making them generally faster than chemical synapses, which involve neurotransmitter release and receptor binding.

C. The hypothalamus contains centers that control respiration and gastric secretions. This statement is incorrect. The hypothalamus primarily controls body temperature, hunger, thirst, and endocrine functions. Centers for respiration are mainly in the medulla oblongata and pons, while gastric secretions are regulated by the medulla oblongata and local enteric nervous system.

D. Coordination is the process through which two or more organs interact and complement the functions of one another. This statement is correct. This is the precise definition of coordination in a biological context, ensuring that different organ systems work together efficiently.

Therefore, two statements (A and D) are correct.

Why other options are wrong:

• Option A is wrong because it states only one correct statement.
• Option C is wrong because it states three correct statements.
• Option D is wrong because it states four correct statements.

Common Mistake: Students often confuse the speed of electrical vs. chemical synapses. Remember that direct ion flow in electrical synapses is faster than the multi-step process of chemical synapses.

NEET Tip: For brain functions, associate specific regions with their primary roles (e.g., Medulla for vital reflexes, Hypothalamus for homeostasis, Cerebrum for higher functions).

Correct Answer: (B)