Sexual Reproduction in Humans

Section 1 of 9Male reproductive system

Structure	Function
Testis	Produces sperm and testosterone
Scrotum	Holds the testes outside the body so sperm are slightly cooler than body temperature
Sperm duct	Carries sperm to the urethra
Prostate gland	Produces fluid that mixes with sperm to form semen
Urethra	Carries urine or semen; a ring of muscle prevents mixing
Penis	Passes urine out and places semen in the vagina

Section 2 of 9Female reproductive system

Structure	Function
Ovary	Contains ova which mature when hormones are released
Oviduct	Carries the ovum to the uterus; ciliated; fertilisation occurs here
Uterus	Muscular bag with a soft lining where the zygote implants
Cervix	Ring of muscle at the lower end of the uterus holding the foetus in place
Vagina	Muscular tube that receives the penis and sperm

Section 3 of 9Gametes and fertilisation

Fertilisation

Fertilisation the fusion of the nuclei of a sperm and an egg cell, usually in the oviduct.

Sperm flagellum

• Sperm flagellum a tail that lets the sperm swim to the egg.

Sperm acrosome

• Sperm acrosome enzymes in the head digest a route into the egg.

Sperm mitochondria

• Sperm mitochondria supply energy for movement of the flagellum.

Egg cytoplasm

• Egg cytoplasm an energy store for cell division after fertilisation.

Egg jelly coat

• Egg jelly coat changes after fertilisation to stop more sperm entering.

Section 4 of 9Sperm and egg compared

Feature	Sperm	Egg
Size	Very small (about 45 µm)	Large (about 0.15 mm)
Structure	Head, flagellum, many adaptations	Round, covered in a jelly coating
Movement	Capable of locomotion	Not capable of locomotion
Numbers	Around 100 million made each day	Thousands of immature eggs but one released each month

Section 5 of 9Development in pregnancy

1

The zygote travels along the oviduct, dividing repeatedly to form a ball of cells, the embryo.

2

The embryo embeds in the thick uterus lining (implantation).

3

Over the first 12 weeks the organs develop, with nutrients reaching the embryo by diffusion.

4

After this the placenta has formed and the embryo is called a foetus.

5

The rest of the 9 months is growth in size.

1Amniotic sac

• Amniotic sac contains amniotic fluid, made from the mother's blood plasma, which cushions the foetus.

2Umbilical cord

• Umbilical cord joins the foetal blood supply to the placenta.

Section 6 of 9The placenta

Exchange

• Exchange glucose, amino acids, fats, water and oxygen pass from mother to foetus.

Waste

• Waste carbon dioxide and urea pass from foetus to mother.

Diffusion

• Diffusion all movement is by diffusion down concentration gradients.

Adaptations

• Adaptations a large surface area and a thin wall.

Blood

• Blood maternal and foetal blood flow close together but never mix.

Barrier

• Barrier it blocks many toxins and pathogens, but some, such as nicotine and the rubella virus, cross.

Section 7 of 9More from the specification

1

Human Male Reproductive Anatomy

• Testes suspended within the scrotum produce flagellated spermatozoa and testosterone,
• which travel along the vas deferens and mix with alkaline seminal fluid before ejaculation.

2

Human Female Reproductive Anatomy

• Paired ovaries release secondary oocytes into fallopian tubes (oviducts);
  • upon fertilisation, the resulting zygote cleaves as it travels to implant into the vascularised endometrium of the uterus.

3

Role of the Placenta and Umbilical Cord

• The placenta acts as an exchange organ where maternal and fetal bloodstreams come into close proximity, enabling diffusion of nutrients, oxygen,
  • and antibodies into fetal blood while expelling urea and carbon dioxide.

4

Oestrogen

• The main female sex hormone, made in the ovaries.

5

Progesterone

• A hormone that maintains the uterus lining.

6

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

7

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

8

Genetically identical

• Having the same alleles

9

Pituitary gland

• The master gland whose hormones control other glands.

10

Genetic variation

• Differences in alleles within a population.

11

Pollen

• Grains made by plants, each type with a different shape.

12

Pollination

• Transfer of pollen from an anther to a stigma.

13

Variation

• Differences between individuals of the same species.

14

Germination

• The start of growth of a seed.

Section 8 of 9Key terms

Term	Meaning
Fertilisation	The fusion of the nuclei of a sperm and an egg cell.
Zygote	The fertilised egg cell.
Implantation	Embedding of the embryo in the uterus lining.
Placenta	The organ where substances are exchanged between mother and foetus.
Umbilical cord	Links the foetus to the placenta.
Amniotic fluid	Fluid that cushions the foetus.
Acrosome	The enzyme-containing head region of a sperm.

Section 9 of 9Exam technique

1

Saying the mother's blood flows into the baby — substances diffuse across the placenta and the bloods never mix.

2

Giving vague answers like waste products or nutrients — name specific substances such as urea and glucose.

3

Saying fertilisation occurs in the uterus — it usually occurs in the oviduct.

4

Saying the foetus forms immediately — the embryo becomes a foetus after about 12 weeks.