How are sperm and eggs produced, and what happens during fertilisation?
The structure of the male and female reproductive systems, the production of sperm and ova (gametes) and the supporting secretions, and the process of fertilisation.
An SQA Higher Human Biology answer on gamete production and fertilisation, covering the structure of the male and female reproductive systems, sperm production in the seminiferous tubules, the role of supporting glands and seminal fluid, ovum production in the ovaries, and the process of fertilisation.
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What this dot point is asking
The SQA wants you to describe the structure of the male and female reproductive systems, explain where and how sperm and ova are produced, describe the role of the supporting glands and seminal fluid, and describe the process of fertilisation.
The male reproductive system
In the male, sperm are produced in the seminiferous tubules, tightly coiled tubes inside the testes. The cells lining the tubules divide and develop into sperm. Between the tubules lie the interstitial cells, which produce the hormone testosterone; testosterone stimulates sperm production and maintains the male reproductive structures.
After production, sperm are moved along and mixed with secretions from the supporting glands:
The female reproductive system
In the female, the ova develop inside structures called follicles within the ovaries. Each month, hormones cause a follicle to mature and the ovum it contains to be released at ovulation into the oviduct (fallopian tube). The oviduct carries the ovum towards the uterus, and it is in the oviduct that fertilisation usually takes place. The lining of the uterus (the endometrium) builds up ready to receive a fertilised egg.
Fertilisation
During fertilisation, a single sperm penetrates the ovum and the two haploid nuclei fuse. Because each gamete carries 23 chromosomes, fusion restores the diploid number of 46 chromosomes in the zygote. The zygote then divides repeatedly by mitosis to form an embryo. Only one sperm normally fertilises the ovum; changes in the surface of the egg after the first sperm enters prevent others from getting in, which keeps the chromosome number correct.
Examples in context
Example 1. Why semen is alkaline. The female reproductive tract is slightly acidic, which would harm sperm. The alkaline seminal fluid from the prostate and seminal vesicles neutralises this acidity, protecting the sperm and helping them survive long enough to reach the ovum.
Example 2. The fructose in semen. Sperm must swim a long way to reach the ovum, which needs energy. The seminal vesicles add fructose, a sugar the sperm respire to power the movement of their tails, illustrating how seminal fluid maintains the gametes.
Try this
Q1. Name the structure in the testes where sperm are produced. [1 mark]
- Cue. The seminiferous tubules.
Q2. State the chromosome number of a human zygote and explain how it arises. [1 mark]
- Cue. 46, formed when two haploid gametes of 23 chromosomes fuse at fertilisation.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20193 marksDescribe where sperm are produced in the testes and the roles of the supporting glands in the male reproductive system.Show worked answer →
A 3-mark answer needs the site of sperm production and the role of the glands.
Sperm are produced in the seminiferous tubules of the testes. The cells lining the tubules divide and develop into sperm, and the interstitial cells between the tubules produce the hormone testosterone, which stimulates sperm production.
The supporting glands, the prostate gland and the seminal vesicles, add fluid to the sperm to form semen. This seminal fluid maintains the sperm, providing them with fructose for energy and an alkaline medium that protects them and supports their movement.
Award (1) sperm produced in the seminiferous tubules, (2) prostate and seminal vesicles add fluid, and (3) the fluid provides energy (fructose) and protection (alkaline conditions).
SQA Higher 20212 marksState what is meant by fertilisation and the chromosome number that results from the fusion of two human gametes.Show worked answer →
This is a 2-mark recall question.
Fertilisation is the fusion of the nucleus of a sperm with the nucleus of an ovum (egg) to form a zygote.
Each gamete is haploid and carries 23 chromosomes. When they fuse, the diploid chromosome number is restored, so the zygote has 46 chromosomes.
Markers reward (1) fusion of sperm and ovum nuclei to form a zygote, and (2) the diploid number of 46 chromosomes restored from two haploid gametes of 23.
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