BIOLOGY Assertion & Reason

(a) Both A and R are true and R is the correct explanation of A.
Explanation: Vocal cords are the folds of mucous membrane stretching across the lumen of larynx. They vibrate when air is blown through the larynx. This produces voice. In human beings, pharynx cavity, mouth cavity and nasal cavity work as resonators. The amplitude of vibrations and the volume and force of air current control the loudness and intensity of the voice, whereas, the length, tightness and frequency of vibration of the vocal cords control the pitch of the voice. The voice in women and children is generally high-pitched because the vocal cords are short. On the contrary, in men the vocal cords are longer (due to male sex hormones) and therefore their voice is lower-pitched and deeper.

(c) A is true but R is false.
Explanation: Cyanide inhibits the activity of cytochrome oxidase by combining it with its metallic ions. It has no structural similarity with the substrate of the enzyme, namely cytochrome C. Cytochrome oxidase is a respiratory enzyme. In its inhibition, the animal is unable to perform respiration properly and gets killed.

(b) Both A and R are true but R is not the correct explanation of A.
Explanation: If a person first inspires with his utmost effort and then expires also with maximum effort the volume of air breathed out is called the vital capacity. An athlete requires more oxygen during exercise on a regular basis. Due to this, amount of oxygen taken in and gases taken out by him is greater than others. This gradual effort of an athlete to meet his oxygen demand ultimately increases the vital capacity.

(c) A is true but R is false.
Explanation: Paramecium shows presence of several noncontractile food vacuoles. They differ in shape and size according to the nature of ingested food particles, but mostly they are rounded in form. The food vacuoles are meant for intracellular digestion.