Mutations are responsible for

MCQ

✓

Answer

Correct option: B.

Variations in organisms

b
(b)Mutation produce variations. Some of these variations are useful in struggle for existence and formation of new species.

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Assertion: A special neural centre in the medula oblongata can moderate the cardiac function through autonomic nervous system (ANS).
Reason: Neural signals through the sympathetic nerves can decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.

$T$-cells are lymphocytes which produce the cellular immunity. These are developed from

$I.$ $A$ might be before $B$ and $C$

$II.$ $B$ might be between $A$ and $C$

$III.$ $C$ might be between $A$ and $B$

$IV.$ More crosses has occurred between $A$ and $C$ than $A$ and $B$

Assertion: Smoking causes oxygen deficiency in the body.
Reason: Smoking increases carbon monoxide (CO) content in blood and reduces the concentration of haem bound oxygen.

$(1)$ On and average a healthy human breaths ...$X$....times/minutes

$(2)$ Every $100\, ml$ of oxygenated blood can deliver around ....$Y$.... of $O_2$ of the tissues under normal physiological conditions.

$X-Y$