The gland X which is located just below the brain in the human head secretes a chemical substance Y which controls the development of bones and muscles in the body of a person. Secretion of too little of substance Y as well as the secretion of too much of substance Y by the gland X leads to abnormal development of the body of a person.

(a) Name the gland X.

(b) What is the chemical substance Y?

(c) What happens if too little of substance Y is secreted?

(d) What happens if too much of substance Y is secreted?

(e) Name the system of glands in the human body of which gland X is a part.

The human body contains a large number of cells A which are very long and branched, and look like electric wires. The longest branch of this cell is B whereas there are many small branches C. Any two A cells do not join to one another completely in the human body. There is a microscopic gap D between every pair of adjacent A cells through which electric impulses can pass by the release of a chemical substance.

(a) What are cells A?

(b) What is the name of (i) branch B, and (ii) branches C?

(c) What is the microscopic gap D known as?

(d) What is the function of cells like A in the human body?

(e) The cells A are of three types. Name the three types.

When we touch a hot plate unknowingly, then this heat is sensed by a receptor P present in our fingers. The receptor triggers an impulse in neuron Q which transmits the message to an organ R which is a part of the central nervous system. Here the impulse is passed on to a neuron S which in turn passes it to a yet another neuron T. The neuron T passes the impulse to a tissue U in our arm. The tissue U then contracts and pulls our hand away from the hot plate.

'(a) What is the name of (i) receptor P (ii) neuron Q, and (iii) organ R?

(b) What is (i) neuron S, and (ii) neuron T?

(c) Name the tissue U.

(d) What name is given to the phenomenon in which hand is pulled away quickly from the hot plate?

(e) Name the effector in this whole process.

A and B are the two systems of control and coordination in the human body. The messages in system A are transmitted in the form of chemical substances C which travel comparatively slowly through the blood stream. The substances C are made in tissues D present in the head and trunk of human body. The messages in system B are transmitted very quickly in the form of electrical impulses through fibres E. The effect of messages transmitted by system B usually lasts for a much shorter time as compared to those transmitted by system A.

(a) Name the system A. What does system A consist of?

(b) Name the chemical substance C.

(c) What is tissue D? Name any five such tissues in the human body.

(d) Name the system B. What does system B consist of?

(e) Name the fibres E.

(f) State whether system A controls the working of system B or system B controls the working of system A.

A cylindrical structure P in our body begins in continuation with medulla and extends downwards. It is enclosed in a bony cage Q and surrounded by membranes R. As many as x pairs of nerves arise from the structure P. The structure P is involved in the reflex actions of our body and conduction of nerve impulses to and from another organ S of our body with which it forms CNS.

(a) Name the structure P.

(b) Name (i) bony cage Q, and (ii) membranes R.

(c) How much is x?

(d) Name the organ S.

(e) What are the reflexes involving structure P only known as?