Methods of Sexual Reproduction

BC Science Probe 9Section 3.3Pages 83-87

Methods of Sexual Reproduction

• In chapter 2, we learned that there are a variety of methods of asexual reproduction.

• There are also several different methods of sexual reproduction.

Conjugation

• Conjugation is a way for single-celled organisms to exchange genetic information.– These organisms can also reproduce asexually by

binary fission.• It happens in some bacteria and some

protists.

Conjugation

• This is how it happens in the bacteria E. coli.– One cell copies an extra piece of its DNA called a

plasmid.– It then donates the plasmid copy to another cell.– Both of the daughter cells then reproduce

asexually by binary fission.– The offspring they produce have the same amount

of genetic information as the parent cell.

Conjugation

Conjugation

• Conjugation is important because it increases the diversity of the individuals in the unicellular species.– This may also be a factor that helps some bacteria

become resistant to antibiotics.– They survive and pass their resistance to their

offspring.

Hermaphrodites

• There are some species who rarely come into contact with other members of their species throughout their lifetime.– Think plants and animals that don’t move and

animals like earthworms• This would make it inconvenient if the

individual they encounter is not of the opposite sex.– Reproduction wouldn’t be able to take place!

Hermaphrodites

• To solve this problem, some species are hermaphrodites.

• A hermaphrodite is an organism that produces both male and female sex cells in the same individual.– This means that a hermaphrodite can mate with

ANY other member of the species to produce offspring!

Hermaphrodites

• Earthworms are a good example:– All earthworms produce both eggs and sperm.– To reproduce, two earthworms attach, exchange

sperm, then separate.– The worms store the sperm in special sacs until

the eggs are ready for fertilization.

Hermaphrodites

– Once fertilization takes place, the clitellum makes a mucus ring/coccoon for the fertilized eggs and slips off the worm into the soil.

Hermaphrodites

• There are some aquatic hermaphrodites that are stuck in one place.– Sponges– Barnacles

• The produce their sperm and eggs at different times so they do not fertilize their own eggs.

Hermaphrodites

• Sponges– Sponges release their sperm

into the water to be carried to other sponges.

– Fertilization occurs inside the sponge.

– Then the baby sponges (larvae) swim away and settle somewhere else.

Hermaphrodites

• Barnacles– Barnacles actually have a penis that extends to the

neighboring barnacle to deposit sperm.– The barnacle larvae are then released into the

water to be carried away to other locations.

Flowering Plants

• Most flowers are hermaphrodites.

Flowering Plants

• The male reproductive structure is the stamen.– The stamen is made of the filament and the

anther.– The filament

supports the anther.

– The anther produces pollen.

Flowering Plants

• The female reproductive structure is the pistil.– The top of the pistil is the stigma. It is sticky so

that it can receive the pollen grain.– The pollen will travel down the tube called a style.– At the bottom of

the style is the ovary where the eggs are contained.

Flowering Plants

• The most noticeable part of the flower is the petals and they serve a purpose in reproduction too.– The colour or the

scent of the flower is what attracts the birds and the bees to it, then they fly away with pollen stuck to them to pollinate/fertilize another flower.

Flowering Plants

• The sperm of the flowering plants is contained in the pollen grains.

• Pollination is when the pollen gets moved from the stamen of one flower to the pistil of another in a variety of ways:– Wind– Insects– Birds– Mammals

Flowering Plants

• Some plants can pollinate themselves.– This is called self-pollination

• Plants can also pollinate other individuals (of the same species).– This is called cross-pollination

• Fertilization follows, then the fertilized egg, or zygote, develops into a seed.

Separate Sexes

• More complex animals and some plants have separate females and males.– The females produce eggs.– The males produce sperm.

Separate Sexes

• Some plants like conifers have separate male and female cones on the same plant.

• Some others have separate male and female flowers on the same plant.

• And others have separate male and female flowers on separate plants.

Separate Sexes

• And now we finally get to animals!• In animals with separate sexes, there are two

possible methods of fertilization:– External fertilization– Internal fertilization

Separate Sexes

• External fertilization:– Eggs and sperm are released and fertilized outside

of the body.– Salmon are a good example:• The female lays the eggs• The male releases

sperm over top of the eggs

Separate Sexes• Internal fertilization:– Some aquatic animals and most land animals

require the sperm from the male to be deposited inside the body of the female.

– These animals have specialized structures to accomplish this.

Separate Sexes

Separate Sexes