Free Reproduction MCQs with Answers

11. The acrosome of a spermatozoon contains

• A. the mitochondria that power the tail
• B. hydrolytic enzymes that digest the coverings of the egg
• C. the haploid nucleus
• D. contractile proteins of the flagellum

Explanation: The acrosome is a lysosome like cap over the front of the head, and its enzymes, including hyaluronidase, break down the corona radiata and zona pellucida so that one sperm can reach the egg membrane. The nucleus lies behind it in the head, and the mitochondria are packed into the middle piece. A sperm whose acrosome reaction fails cannot fertilise even a normal egg.

12. The mitochondria of a spermatozoon are concentrated in the

• A. head
• B. acrosome
• C. middle piece
• D. tip of the tail

Explanation: A spiral sheath of mitochondria wraps the middle piece and supplies the ATP that the flagellum needs for the long journey to the oviduct. Placing them immediately behind the head puts the energy source next to the machinery that uses it. Almost none of these mitochondria enter the egg at fertilisation, which is why human mitochondrial DNA is inherited from the mother alone.

13. The number of chromosomes in a human secondary oocyte is

• A. 23
• B. 46
• C. 44
• D. 92

Explanation: The first meiotic division is completed before ovulation and halves the chromosome number, so the secondary oocyte is haploid with 23 chromosomes, each still made of two chromatids. Forty six is the diploid number of the primary oocyte and of every body cell, which is why it is the common error. The second division is completed only if a sperm actually penetrates the egg.

14. Meiosis of one human primary oocyte finally produces

• A. four functional ova
• B. two ova and two polar bodies
• C. one ovum and three polar bodies
• D. four polar bodies and no ovum

Explanation: Cytoplasmic division in oogenesis is deliberately unequal, so almost all the cytoplasm and stored food goes to one cell while the other products are tiny polar bodies that soon degenerate. This gives the single ovum the reserves an early embryo needs before implantation. Spermatogenesis, by contrast, divides the cytoplasm evenly and yields four functional sperm from each primary spermatocyte.

15. Gonorrhoea is caused by

• A. a bacterium
• B. a virus
• C. a fungus
• D. a protozoan

Explanation: Neisseria gonorrhoeae is a diplococcus bacterium that infects the mucous membranes of the urinary and reproductive tracts, and because it is bacterial the infection can be cured with the right antibiotic. Untreated it can spread to the fallopian tubes and cause sterility, and it can infect the eyes of a baby during birth. Antibiotic resistant strains are now common, so self medication is dangerous.

16. Which sexually transmitted disease is caused by a spirochaete and passes through primary, secondary and tertiary stages?

• A. Gonorrhoea
• B. Syphilis
• C. Genital herpes
• D. Candidiasis

Explanation: Syphilis is caused by the spiral bacterium Treponema pallidum, beginning as a painless ulcer, then a body wide rash, then a long latent period, and finally damage to the heart, blood vessels and nervous system years later. This staged course is unique among the common sexually transmitted infections. Gonorrhoea is also bacterial but does not follow this pattern, and herpes and candidiasis are viral and fungal respectively.

17. Which sexually transmitted disease cannot be cured by antibiotics?

• A. Gonorrhoea
• B. Syphilis
• C. Chlamydia
• D. Genital herpes

Explanation: Genital herpes is caused by herpes simplex virus, and antibiotics act only on bacterial structures and pathways, so they are useless against it. Antiviral drugs can shorten and space out the attacks but the virus stays latent in nerve ganglia for life. The other three are bacterial infections and are curable if treatment is started early and completed.

18. The most effective way to prevent sexually transmitted infections is

• A. taking an antibiotic after every possible exposure
• B. vaccination, since a vaccine exists for every such infection
• C. washing thoroughly after exposure
• D. avoiding contact with infected persons and using barrier protection

Explanation: Prevention works by stopping the exchange of infected body fluids, so avoiding contact with an infected person and using a barrier are what actually reduce risk, together with screened blood and sterile needles. Taking antibiotics after exposure treats nothing viral and encourages resistance. Vaccines exist for hepatitis B and human papillomavirus but not for gonorrhoea, syphilis, herpes or HIV.

19. The fluid filled membrane that cushions the developing fetus and protects it from mechanical shock is the

• A. chorion
• B. allantois
• C. amnion
• D. yolk sac

Explanation: The amnion encloses the amniotic fluid in which the fetus floats, spreading any pressure evenly, keeping the temperature steady and allowing free movement of the limbs. The chorion is the outer membrane that contributes the fetal part of the placenta, so it has a nutritive rather than a protective role. In humans the yolk sac and allantois are much reduced compared with birds and reptiles.

20. The umbilical vein carries

• A. deoxygenated blood from the fetus to the placenta
• B. oxygenated blood from the placenta to the fetus
• C. fetal urine to the placenta for disposal
• D. maternal blood directly into the fetal circulation

Explanation: The cord contains two arteries and one vein, and as always the vein is named for the direction of flow towards the heart, so it brings oxygen and nutrients from the placenta to the fetus. The umbilical arteries do the reverse, carrying deoxygenated blood loaded with waste to the placenta. Maternal and fetal blood remain in separate vessels throughout, exchanging only by diffusion across the placental barrier.