All Free Biology MCQs with Answers

751. Untreated gonorrhoea in women may spread upwards and cause

• A. kidney stones
• B. diabetes mellitus
• C. anaemia
• D. pelvic inflammatory disease and infertility

Explanation: The gonococcus can climb from the cervix into the uterus and oviducts, inflaming and scarring them, which blocks the passage of eggs. Early antibiotic treatment prevents this chain, which is why prompt diagnosis matters.

752. Which of the following infections can be transmitted sexually but is preventable by vaccination?

• A. Hepatitis B
• B. Gonorrhoea
• C. Syphilis
• D. HIV

Explanation: Hepatitis B virus spreads in blood and sexual fluids and can damage the liver, but a highly effective recombinant vaccine exists. No vaccine yet protects against HIV, gonorrhoea or syphilis.

753. When one partner is diagnosed with a curable bacterial STD, treatment should be given to

• A. only the partner showing symptoms
• B. both partners, to prevent reinfection
• C. only the male partner
• D. only the female partner

Explanation: An untreated partner harbours the organism and passes it straight back, so both must be treated even if one feels well. This partner notification principle applies to gonorrhoea, syphilis and chlamydia alike.

754. The painless sore called a chancre appears in which stage of syphilis?

• A. Secondary stage
• B. Tertiary stage
• C. Primary stage
• D. Congenital stage

Explanation: About three weeks after infection a chancre forms at the entry point, marking primary syphilis, and heals on its own, which lets the disease go unnoticed. The rash belongs to the secondary stage and gummas to the tertiary.

755. In humans, the exchange of gases between air and blood takes place in the

• A. alveoli
• B. bronchi
• C. trachea
• D. larynx

Explanation: The millions of thin walled alveoli provide the enormous surface where oxygen enters the blood and carbon dioxide leaves. The bronchi and trachea are only conducting tubes, with no gas exchange through their walls.

756. The voice box of the human body is the

• A. pharynx
• B. larynx
• C. trachea
• D. nasal cavity

Explanation: The larynx houses the vocal cords, which vibrate as air passes to produce sound. The pharynx is the shared passage above it, and the trachea carries air below, so location identifies each structure.

757. The passage common to both food and air is the

• A. trachea
• B. larynx
• C. pharynx
• D. bronchus

Explanation: The pharynx receives air from the nose and food from the mouth and directs them onwards, which is why swallowing must temporarily close the airway. The trachea and bronchi carry air only.

758. The trachea divides at its lower end into

• A. alveoli
• B. alveolar ducts
• C. pleural sacs
• D. two bronchi

Explanation: Each primary bronchus enters a lung and branches into ever finer bronchioles ending in alveoli. The division mirrors the need to serve both lungs from a single windpipe.

759. The double membrane covering each lung is the

• A. pleura
• B. pericardium
• C. peritoneum
• D. meninges

Explanation: The pleura secretes fluid that lets the lungs slide smoothly against the chest wall during breathing. The pericardium wraps the heart and the peritoneum the gut, so each serous membrane is named for its organ.

760. The normal breathing rate of a resting adult is about

• A. 6 per minute
• B. 16 per minute
• C. 40 per minute
• D. 75 per minute

Explanation: Quiet breathing runs at roughly 12 to 20 cycles per minute, around 16. The figure 75 per minute belongs to the heart rate, and examiners often offer it as the trap.