1. Gametes and fertilisation
Human Biology Unit 2
Gametes and fertilisation

2. Gametogenesis
Gametogenesis is the production of sperm and egg cells by meiosis.
ATAR and general

3. Sperm Sperm (spermatozoa) are the male gametes or reproductive cells.
Sperm are formed by the process of spermatogenesis in the testes.
Spermatogenesis involves meiosis – consequently, sperm cells have only 23 chromosomes.
ATAR and general

4. A section through a testis
Epididymis where sperm mature
Lobules of testis consisting of seminiferous tubules where spermato- genesis takes place
Lutz Slomianka, ANHB - UWA

5. Important structures in a spermatozoon
The head - contains the nucleus which carries the 23 chromosomes.
The acrosome - forms a cap over the head. The cap contains enzymes which break down the follicle surrounding the ovum, and permit fertilisation.
The middle piece – contains mitochondria to provide power for the tail.
The tail – is a flagellum; it acts like a propeller.
ATAR and general

6. Structure of a human sperm
Drawing by LadyofHats

7. Spermatogenesis
Lumen of tubule
Spermatids Immature sperm
Germ cells undergoing meiosis
Transverse section through a seminiferous tubule showing development of spermatids
M I Walker, Wellcome Images

8. Sperm developing in the testis
Sperm develop in the seminiferous tubules of the testis with their tails projecting into the lumen of the tubule. These spermatids are in the advanced stages of maturation.
Yorgos Nikas, Wellcome Images

9. Semen
Semen produced during an ejaculation consists of sperm and fluids (seminal fluid) produced by the seminal vesicle, prostate and Cowper’s glands.
Seminal fluid contains a complex mixture of enzymes and nutrients.
ATAR & general

10. Ova Ova (egg cells) are the female gametes or reproductive cells.
Ova are formed by the process of oogenesis in the ovaries.
Oogenesis involves meiosis – consequently, ova have only 23 chromosomes.
Of the four daughter cells, only one develops into an ovum – the remaining three become polar bodies.
ATAR & general

11. Ovary containing follicles in different stages of maturity.
Corpus luteum
Mature ovarian follicle
Primary oocyte (developing ovum)
Medical Art Services, Munich, Wellcome Images

12. Structures in an ovarian follicle
The oocyte – is the immature ovum (nuclear division is suspended at metaphase of meiosis II).
Zona pellucida and corona radiata – the outer protective layers of follicular cells surrounding the ovum.
ATAR only

13. A primary oocyte Zona pellucida Nucleus of primary oocyte
Corona radiata
Nucleus of primary oocyte
Fluid-filled space
Glandular granulosa cells

14. Human egg surrounded by the zona pellucida
Residual coronal cell
Yorgos Nikas , Wellcome Images

15. Fertilisation
Fertilisation typically occurs in the upper region of the Fallopian tube.
It takes many sperm to break down the corona radiata.
Only one sperm enters the oocyte
At this point the nucleus of the oocyte completes meiosis and the two nuclei fuse.
ATAR & general

16. Fertilisation of a human egg - a single sperm entering an ovum
Wellcome Photo Library, Wellcome Images

17. Human egg surrounded by sperm,
Joyce Harper, UCL, Wellcome Images

18. Sperm on the surface of a human egg trying to find their way through the zona pellucida,
Yorgos Nikas, Wellcome Images