All Free Biology MCQs with Answers

731. The testes hang in the scrotum outside the body cavity because

• A. sperm production needs a temperature slightly below body temperature
• B. the testes are too large to fit inside the abdomen
• C. testosterone breaks down at body temperature
• D. sperm must be released directly to the outside

Explanation: Spermatogenesis fails at the normal 37 degrees of the abdomen, so the scrotum keeps the testes about two degrees cooler. This is why undescended testes in childhood need correction to preserve fertility.

732. The umbilical cord of a human fetus normally contains

• A. one artery and one vein
• B. two arteries and one vein
• C. two arteries and two veins
• D. one artery and two veins

Explanation: Two umbilical arteries carry deoxygenated blood and wastes from fetus to placenta, while the single umbilical vein returns oxygenated blood and nutrients. Veins here carry waste and arteries carry it away, the reverse of the adult pattern, which catches many students.

733. After fertilisation, the zygote undergoes a series of rapid mitotic divisions without overall growth, called

• A. meiosis
• B. gastrulation
• C. cleavage
• D. implantation

Explanation: Cleavage divides the zygote into a ball of smaller cells as it travels down the oviduct, forming the morula and then the blastocyst. Meiosis makes gametes, and implantation happens later, once the blastocyst reaches the uterus.

734. Which of the following is NOT a part of the male reproductive system?

• A. Prostate gland
• B. Vas deferens
• C. Seminal vesicle
• D. Uterus

Explanation: The uterus belongs to the female system, where it nourishes the developing fetus. The prostate and seminal vesicles add fluids to semen, and the vas deferens transports sperm, so all three are male structures.

735. The changes of puberty in boys, such as a deeper voice and facial hair, are driven mainly by

• A. testosterone
• B. oestrogen
• C. progesterone
• D. insulin

Explanation: Testosterone from the Leydig cells stimulates the development of male secondary sexual characteristics and continues to support sperm production. Oestrogen and progesterone are the principal female sex hormones, though small amounts occur in both sexes.

736. The narrow lower end of the uterus that opens into the vagina is called the

• A. oviduct
• B. cervix
• C. ovary
• D. urethra

Explanation: The cervix produces mucus that changes through the cycle, guides sperm and protects the uterus during pregnancy. The urethra is part of the urinary system, a common confusion since both open near each other in the female.

737. At the start of the menstrual cycle, rising levels of FSH stimulate

• A. ovulation
• B. the shedding of the endometrium
• C. the development of follicles in the ovary
• D. the formation of the placenta

Explanation: FSH, follicle stimulating hormone, recruits a batch of follicles at the beginning of the cycle, and the growing follicle then secretes oestrogen. Ovulation comes later, triggered by LH, and the placenta only forms after pregnancy begins.

738. During the first half of the menstrual cycle, the hormone that rebuilds the lining of the uterus is

• A. progesterone
• B. LH
• C. FSH
• D. oestrogen

Explanation: Oestrogen from the developing follicle drives the endometrium to proliferate after menstruation. Progesterone takes over after ovulation to maintain the rebuilt lining, so the two hormones divide the cycle between them.

739. After ovulation, progesterone from the corpus luteum

• A. maintains the thickened endometrium ready for implantation
• B. immediately triggers menstruation
• C. stimulates a second ovulation
• D. dissolves the zona pellucida of the egg

Explanation: Progesterone makes the endometrium glandular and rich in blood supply, the state needed for an embryo to implant. Menstruation follows only when the corpus luteum fails and progesterone levels drop.

740. As a follicle matures, its rising oestrogen output suppresses the secretion of FSH by the

• A. ovary itself
• B. anterior pituitary through negative feedback
• C. posterior pituitary
• D. hypothalamus releasing oxytocin

Explanation: Oestrogen feeds back on the anterior pituitary to reduce FSH, which prevents several follicles from maturing at once. This negative feedback keeps the cycle to a single dominant follicle in humans.