18 sexual reproduction

Why sex?• Sexual reproduction results in a

greater diversity of individuals

Diversity• This means that we, as a species, can adapt to an unfavourable environment

• Some will die, but the strong ones will go on and produce strong babies

Diversity• We will also be able to adapt and

change with a changing environment

Plant sex

• Most plants are true hermaphrodites, which means that they have both male and female working sex organs

Reproduction in flowering plants

• Most flowering plants have flowers containing both male and female sexual organs.

• A small number are monoecious (flowers only carry male or female sexual organs)

• Some are dioecious (plant has single sex flowers of both genders)

Hermaphrodites

• Could this really be possible in animals?

Fertilization is not always internal!

• In many fish females will lay their eggs and the male will come and spray them with sperm

Reproduction in humans

• …um, when two people love each other very much …

• …then a stork comes and drops off the baby

• The End

Reproduction in humans

The male reproductive organs

The female reproductive organs

PubertyMales Females

• Development of sexual organs

• Growth spurt• Increased muscle

and bone mass• Hair growth• Voice breaks• Acne / odours

• Development of sexual organs

• Growth spurt• Breasts &

buttocks grow, hips widen

• Hair growth• Menstruation

begins

Menstruation

• The shedding of the uterine lining (blood, mucous, cell debris) in preparation for the potential arrival of a fertilised egg

Sexual intercourse

• When aroused the male’s penis becomes erect and the females vagina becomes lubricated.

• When the male ejaculates, the sperm swim up the fallopian tubes until they encounter an egg.

Why is sex pleasurable?• Evolutionarily speaking, sex is

essential for the continuation of the species, but there is also a biological advantage:

• The male orgasm is tied to the ejaculation of sperm.

• The female orgasm causes the cervix to contract, thereby drawing in the sperm.

Fertilisation

• Once an egg is encountered the few hundred sperm that have made the distance surround it.

Fertilisation

• Once one sperm penetrates the egg, the surface changes and no more can enter

Development• The egg travels a further 5 days

down the fallopian tubes before embedding in the uterus wall.