All Free Biology MCQs with Answers

741. The luteal phase of the menstrual cycle is the period

• A. of menstruation itself
• B. before the follicle begins to grow
• C. between ovulation and the start of the next menstruation
• D. during which the egg is fertilised

Explanation: After ovulation the corpus luteum secretes progesterone for about fourteen days, the luteal phase. If no embryo implants, the corpus luteum degenerates, hormone levels fall and menstruation begins.

742. Oral contraceptive pills prevent pregnancy mainly by

• A. killing sperm in the vagina
• B. blocking the oviducts mechanically
• C. thickening the cervical mucus only
• D. suppressing ovulation through their oestrogen and progesterone content

Explanation: The steady hormones of the pill inhibit FSH and LH, so no follicle matures and no egg is released. Thickened cervical mucus adds a secondary barrier, but the suppression of ovulation is the principal mechanism.

743. If fertilisation does not occur, the corpus luteum

• A. degenerates into a scar called the corpus albicans
• B. continues to grow throughout the cycle
• C. develops into the placenta
• D. starts secreting hCG

Explanation: Without hCG from an embryo, the corpus luteum survives only about ten days and then degenerates, its progesterone falling to trigger menstruation. Only in pregnancy does it persist, sustained by embryonic hCG.

744. The hormones FSH and LH that regulate the menstrual cycle are secreted by the

• A. ovary
• B. anterior pituitary gland
• C. uterus
• D. thyroid gland

Explanation: The anterior pituitary releases both gonadotropins under direction from hypothalamic GnRH. The ovary responds to them by producing oestrogen and progesterone, so the control runs from the brain to the ovary, not the reverse.

745. The average length of a complete menstrual cycle in human females is about

• A. 14 days
• B. 21 days
• C. 28 days
• D. 35 days

Explanation: Counting from the first day of one menstruation to the day before the next gives roughly 28 days, though normal cycles vary between about 21 and 35. Fourteen days is only the average time from menstruation to ovulation.

746. The causative agent of syphilis is

• A. a virus
• B. a fungus
• C. a protozoan
• D. the bacterium Treponema pallidum

Explanation: Treponema pallidum is a spirochaete bacterium, which is why syphilis responds to penicillin. Viral STDs such as HIV and herpes cannot be cured with antibiotics, an important clinical distinction.

747. Genital warts are caused by the

• A. human papillomavirus
• B. human immunodeficiency virus
• C. herpes simplex virus
• D. bacterium Neisseria gonorrhoeae

Explanation: Certain strains of HPV produce warts, and other high risk strains can transform cervical cells. Being viral, warts cannot be treated with antibiotics, which is why vaccination against HPV is the best protection.

748. The HPV vaccine offered to adolescent girls protects mainly against

• A. gonorrhoea
• B. cervical cancer
• C. syphilis
• D. hepatitis A

Explanation: By immunising against the cancer causing strains of human papillomavirus, the vaccine prevents most cases of cervical cancer decades later. It does not protect against bacterial STDs such as gonorrhoea and syphilis.

749. The bacterial STD that frequently causes no symptoms, especially in women, yet can silently lead to infertility is

• A. syphilis
• B. gonorrhoea
• C. chlamydia
• D. genital herpes

Explanation: Chlamydia is the commonest bacterial STD and often passes unnoticed until it damages the oviducts, causing pelvic inflammatory disease and infertility. Its quiet course is why screening programmes target young people.

750. Which of the following sexually transmitted diseases is caused by a protozoan?

• A. Gonorrhoea
• B. Syphilis
• C. AIDS
• D. Trichomoniasis

Explanation: Trichomonas vaginalis is a flagellated protozoan causing discharge and irritation, and it is treated with antiprotozoal drugs. Gonorrhoea and syphilis are bacterial and AIDS is viral, so only trichomoniasis fits the protozoan description.