biology reproduction

• mitosis


  type of cell division giving rise to genetically identical cells in which the chromosome number is maintained
• asexual reproduction


  process that results in the production of genetically identical offspring from one parent, without the fusion of gametes
• when does mitosis occur?

  asexual reproduction

  new cells produced by mitosis for body growth

  and repair of damaged tissues
• asexual reproduction in plants examples

  stem tuber: swollen end of underground stem with buds, buds grow into new plants. example potato

  
  

  rhizome: underground storage stem that can grow into new plants

  
  

  runner: grows horizontally from parent plant on the surface of the soil. buds grow on it
• Advantages of asexual reproduction

  - only 1 parent needed

  - all beneficial characteristics of parent passed onto offspring

  - no fusion of gametes necessary

  - faster than sexual reproduction
• disadvantages of asexual reproduction

  - no genetic variation in offspring-> not well-adapted to changes in the environment-> whole population vulnerable to the same things, can go extinct easily
• sexual reproduction


  a process involving the fusion of two gametes to form a zygote
• meiosis


  a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halves due to the separation of homologous chromosomes (do we even need to know this)
• advantages of sexual reproduction

  offspring may inherit beneficial qualities from both parents

  
  

  there is genetic variation in the offspring that is better adapted to changes in the environment
• disadvantages of sexual reproduction

  two parents required

  slower than asexual reproduction

  fusion of gametes required
• what is stamen

  male reproductive parts in plant (anther and filament)
• what is pistil/carpel

  female parts of plant (stigma, style, ovary, ovule)
• advantages of self-pollination


  only one plant needed

  higher chance the beneficial characteristics of parent plant passed down to offspring

  does not need to depend on external factors for pollination

  anthers close to stigmas-> higher chance of pollination happening

  less pollen waste
• disadvantages of self-pollination

  less genetic variation in offspring-> species less well-adapted to changes in the environment

  continuous self-pollination can lead to offspring becoming weaker, smaller and less resistant to diseases
• features of self-pollination

  flowers are bisexual (parts mature at same time)

  stigma is close to anthers/directly below

  plants with bisexual flowers have some flowers that never open
• features of cross pollination


  flowers with only either male or female parts on plant

  anther and stigma matures at different times

  stigma and anther located far away

  stigma cannot recognise own pollen

  male part covering female part-> only allows pollination after its own pollen sacs are removed by pollinators
• advantages of cross pollination

  can inherit beneficial qualities from both parents

  greater genetic variation among offspring-> higher chance species survives changes in the environment because lower chance any change in the environment destroys all the varieties in the species

  more viable seeds are produced-> can survive longer before germination
• disadvantages of cross pollination

  two plants needed

  depends on external factors (like wind/insects)

  pollen grains have to be transferred between two plants-> lower chance pollination will occur
• wind pollinated flowers characteristics

  - small and dull-coloured flowers

  - no nectar

  - odourless

  - large feathery stigmas that protrude out of the flower

  - stamens with long, pendulous filaments.

  - light, tiny and abundant pollen

  - no nectar guide
• insect pollinated flowers

  - large flowers, brightly coloured

  - nectar is present

  - flowers are fragrant

  - stamens are not pendulous

  - rough, large pollen grains

  - may have nectar guide
• fertilisation in plants

  1) pollen grain germinates after coming into contact with sugary fluid secreted by mature stigma

  2) pollen tube grows out, male gamete enters pollen tube

  3) pollen tube secretes enzymes that digests tissue of stigma and style

  4) pollen tube enters ovule through micropyle

  5) tip of tube absorbs sap and bursts

  6) nucleus of male gamete fuses with nucleus of ovum
• what is a cotyledon

  seed leaf
• what does the prostate do

  secretes fluid that contains nutrients and enzymes that nourish the sperm and stimulate them to swim actively
• differences between sperm and egg

  shape- spherical vs having a head, tail and body

  movement- passive movement due to cilia in oviduct vs tail enables it to swim

  numbers- one released per month vs millions released during ejaculation
• fertile period

  day 10-15 of menstrual cycle
• when does ovulation take place

  day 13-15
• how long can an egg survive?

  1 day
• how long can a sperm survive

  5 days
• functions of placenta

  - allows oxygen and dissolved food substances to dissolve from maternal blood into fetal blood

  - allows metabolic waste to diffuse from fetal to maternal blood

  -allows protective antibodies to diffuse from maternal blood to fetal blood
• functions of amniotic fluid

  - lubricates birth canal during birth

  - protects fetus against injury

  - promotes muscular development as fetus gets certain degree of movement

  -maintains even temperature for fetus
• why is fetal blood not continuous with mother's blood

  - difference in blood pressure could kill baby

  - different blood types mixing could cause blood cells to agglutinate
• natural selection


  a process in which organisms with desirable traits are selected/favoured to survive and pass on their traits to their offspring
• evolution


  gradual change in inheritable characteristics of a population over time
• steps in describing natural selection

  1. pre-existing variation

  2. selective pressure

  3. differential survival and reproduction

  4.evolutionary change
• factors that drive natural selection


  1. competition

  2. predation

  3.human destruction

  4. environmental factors

  5. habitat loss
• artificial selection steps

  1. natural variation

  2. parents with desired characteristics chosen and made to breed

  3. offspring with desirable characteristics are kept, those without are killed

  4. process is repeated many times-> greater proportion of individuals with that trait in population
• menstruation


  uterine bleeding caused by breakdown of endometrium
• ovulation

  release of matured egg from an ovary into the oviduct
• anterior pituitary gland secretes


  FSH and LH
• ovaries secrete


  oestrogen and progesterone