Biology, 10: Reproduction

• In asexual reproduction, cells from organisms divide to produce offspring

  Offspring is genetically identical to the parent
• Asexual reproduction is used by bacteria for binary fission

  When large enough, genetic material copies itself and splits in half

  This allows for rapid production of identical cells
• What is the asexual reproduction of spores?

  As hypha grows up vertically, tip swells with cytoplasms containing many nuclei

  Tip releases spore into the atmosphere
• What is the asexual reproduction in tubers?

  Potatoes produce tubers, formed from end of the stem growing underneath the soil surface

  Stem swell into storage organs, filled with starch

  Tubers stay dormant until next growing season, the leaves and stems die

  Each produces several potato plants from buds on side of tubers

  Each potato plants result in more tubers

  New plants are formed
• What are the advantages of asexual reproduction?

  Only one parent needed, no need to find mate or pollination

  Allows for large numbers of organisms to be produced in a short period of time

  All offsprings produced are identical, so should survive in conditions that parents grow in
• What are the disadvantages of asexual reproduction?

  Lack of variation, adverse changes in conditions will affect all equally

  No variation, is not suited to moving away and exploiting environments with different conditions
• Sexual reproduction is a common method of reproduction for larger organisms
• How does sexual reproduction occur?

  Fertilisation of male gamete and female gamete fusing their nucleus

  A zygote is formed- contains genetic information of each parent

  Offspring is genetically different from parent
• Haploid cells contain one set of genetic information
• Diploid cells contain two sets of genetic information
• Gametes are haploid cells

  When fused and forming zygotes, it becomes a diploid cell
• Cells of zygote will divide repeatedly to produce all cells of new organisms

  All cells created will be diploid
• What are the advantages of sexual reproduction?

  Fusion brings variety, making individual better adapted to conditions- increasing chances of survival
• What are the disadvantages of sexual reproduction?

  Takes time and energy to find mate

  Need to find mate takes longer to produce offspring
• Flowering plants has true flowers

  Seeds are produced with a tough protective coat
• How does sexual reproduction occur in plants?

  Male and female gametes are produced

  Some produce in same colour, some in different

  Male pollen is transferred to the carpel where pollination can take place

  Male gamete and female gamete fuse during fertilisation, forming zygote

  Zygote develops and forms embryo within seeds

  Embryo is protected and provided food during seed germination

  Seeds are then dispersed, germinated, and grows away from the parent
• Structure of flower:

  
• What is the stamen?

  Male part of the flower

  Contains anther and filament

  Pollen grains develop in anther

  Pollen develops a thick outer wall to protect male gamete inside

  When pollen grains in anther are mature, it splits open and releases the gamete
• What is the carpel?


  Female part of the flower

  Contains style, stigma, and ovary

  Pollen lands at the stigma during pollination

  Ovary at the base of carpel protects female gamete from dry outside air

  Ovary contains one or more ovule

  Ovule contains egg sac, surrounding the egg cell
• The structure of the carpel:

  
• What are the characteristics of wind-pollinated plants?

  Small petals, do not obstruct pollen dispersal

  Green and inconspicuous petals

  No scent

  No nectaries

  Large anthers, hanging outside the flower so it is easily dispersed

  Large and feathery stigma, hanging outside to trap pollen

  Produces large amounts of pollen

  Pollen is lightweight

  Smooth pollen
• What are the characteristics of insect-pollinated plants?

  Large petals for insects to land on

  Brightly coloured petals attracts insects

  Often scented to attract insects

  Nectaries at base of flowers produces sugary liquid to attract insects

  Few small anthers, held inside the flower

  Small stigma, held inside the flower

  Produces small amounts of pollen

  Pollen is heavy

  Spiky pollen sticks on insect's body
• Germination is when the seed breaks open, and embryo starts to grow and develop into a new plant
• What does germination depend upon?

  Temperature

  Moisture

  Oxygen
• Light is not needed in germination, as it occurs below ground and cannot get food from photosynthesis.
• Seeds are dormant during cold periods

  Seeds grow when it is warmer

  If too hot, seed may be killed

  Therefore must be stored in the correct conditions
• Water swells seed, bursting the seed coat

  Germination metabolic reactions are carried out rapidly

  Water is needed for:

  • Activation of hormones and enzymes
  • Hydrolysis of storage compounds
  • Transport of materials to be used for respiration and growth
  • Metabolic reactions and enzyme actions occurring in solution
• Oxygen is needed as the seeds have living cells that aerobically respires

  Seeds can use anaerobic respiration for a short while, but it releases too little energy and releases toxic byproducts
• Male reproductive system:

  
• Testes is contained in the scrotum

  It is where the sperm and testosterone is produced

  It is outside the body so it stays cool
• The scrotum is a sac holding the testes outside the body
• The sperm duct transfers sperm to the urethra
• The prostate gland secretes fluids for sperm to swim in

  This forms semen
• The urethra carries sperm and urine out of the body
• The penis transfers sperm to the vagina during sexual intercourse
• Female reproductive system:

  
• The ovaries releases eggs
• The oviduct transfers egg to uterus

  It is the site of fertilisation
• The uterus is where the fetus develops
• The cervix is a ring of muscle at the opening of the uterus