8 min readPathway sheetPart III (4 marks) on differences; Part IV (7 marks) with flow charts

Gametogenesis: spermatogenesis and oogenesis

Gametogenesis is the making of gametes by meiosis. In spermatogenesis, one cell gives four sperms; in oogenesis, one cell gives one ovum and polar bodies.

SpermatogenesisIn the seminiferous tubules of the testes; 1 primary spermatocyte → 4 sperms

OogenesisIn the ovary; 1 primary oocyte → 1 ovum + 3 polar bodies

Chromosome numberBody cells 46 (2n); sperm and ovum 23 (n)

Parts of a spermHead (nucleus and acrosome), neck, middle piece (mitochondria), tail

Spermatogenesis

Happens in the seminiferous tubules from puberty onwards. Sertoli cells nourish the developing cells.

Oogenesis

The first polar body may divide again, giving three polar bodies in all. Polar bodies are tiny and soon die.

Spermatogenesis vs oogenesis

Point	Spermatogenesis	Oogenesis
Where	Testes (seminiferous tubules)	Ovaries
When	Starts at puberty and goes on through life	Starts before birth; one ovum is released each month from puberty to menopause
From one primary cell	4 sperms	1 ovum (and 3 polar bodies)
Division of cytoplasm	Equal	Unequal: the ovum keeps most of the cytoplasm
Gamete	Small and moves with a tail	Large and does not move

Sperm vs ovum

SpermTiny and motile (it swims). The head has the nucleus and a cap, the acrosome, with enzymes to break into the ovum. The middle piece has mitochondria for energy. The tail helps it swim.

OvumLarge, round and non-motile. Has a nucleus and cytoplasm with very little yolk. Covered by an inner zona pellucida and an outer corona radiata.

How to draw a human sperm

1
Draw an oval head. Shade a nucleus inside. Label head and nucleus.
2
Draw a small cap on the front of the head. Label acrosome.
3
Below the head, draw a short narrow part. Label neck.
4
Then draw a thicker part with a spiral line. Label middle piece and mitochondria.
5
End with a long, thin, wavy tail. Label tail.

In real life

Healthy gametes in adult life need a balanced diet with protein, zinc and folic acid (pulses, nuts, greens, eggs). Staying away from tobacco and alcohol also protects them.

Exam angle

2 marks: “What is the role of the acrosome in a sperm?” It has enzymes that help the sperm break through the coverings of the ovum.

4 marks: “Differentiate between spermatogenesis and oogenesis.” Place; when it starts; one primary cell gives 4 sperms vs 1 ovum; equal vs unequal division; motile vs non-motile gamete.

7 marks: “Explain spermatogenesis with a flow chart and draw a labelled diagram of a sperm.” Spermatogonium → primary spermatocyte (2n) → meiosis I → 2 secondary spermatocytes (n) → meiosis II → 4 spermatids → spermiogenesis → 4 sperms; sperm diagram with head, acrosome, neck, middle piece and tail.

Remember it

Sperm: one cell gives four, all swimmers. Egg: one cell gives one, and it keeps all the food.