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Methods of Sexual Reproduction. BC Science Probe 9 Section 3.3 Pages 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.
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Methods of Sexual Reproduction BC Science Probe 9 Section 3.3 Pages 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 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.
