Bio CBA1

• What are the 4 steps of natural selection?

  1. Variation
  2. Selection pressure
  3. Higher chance of survival + reproduction
  4. After many generations, pop increase
• Examples of environmental factors that act as forces of natural selection

  • climate
  • predators
  • food sources
• Variation and competition lead to…


  …differential survival of, and reproduction by, those organisms best fitted to the environment
• Examples of artificial selection include…

  • Belgian blue cows
  • Dog breeding
  • Breeding of teosinte into modern corn
• Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent.
• Sexual reproduction is the process involving the fusion of nuclei of male and female gametes to form a zygote and the production of genetically dissimilar offspring.
• The function of the sepal is to enclose and protect the flower bud.
• The function of the petal is to attract pollinators to the flower.
• The anther is a sac where meiosis occurs. Its function is to produce pollen grains which house the cells that develop into sperm.
• The carpel consists of a long slender neck (style) with a sticky stigma at its tip. At its base is the ovary.
• Self-pollinated flowers have…


  filaments longer than the style, so pollen grains will be deposited onto the style and pollinate its own stigma.
• Cross-pollinated flowers have…


  style longer than the filaments, so the pollen grains from the flowers’ own anthers will not be deposited onto its own stigma.
• Cross-pollination includes:

  Pollen grains from flowers on a plant being deposited onto the stigma of flowers from another plant.
• Self-pollination includes:

  • pollen grains from a flower’s anthers being deposited onto the same flower’s own stigma
  • pollen grains from a flower’s anthers being deposited onto a flower’s stigma from the same plant
• Advantages of self-pollination:

  • only one parent needed
  • higher chance of pollination
  • does not depend on agents of pollination
• Disadvantages of self-pollination:

  • less genetic variation in offspring
  • weaker offspring
• Advantages of cross-pollination:

  • may inherit beneficial qualities from both parents
  • greater genetic variation
  • seeds are more viable
• Disadvantages of cross-pollination:

  • two parents needed
  • depends on external agents
  • lower probability of successful pollination
• How to describe insect-pollination:

  1. insect lands on petal
  2. it follows nectar guide
  3. it forces its way in to collect nectar
  4. its back/head brushes against anthers
  5. pollen grains are deposited on insect’s back/head
  6. when it travels to another flower, it deposits pollen grains from its neck onto the stigma
  7. OR it deposits pollen grains from its neck onto the same flower’s stigma
• Animal-pollinated flowers have:

  • brightly-coloured petals
  • presence of nectar guides on petals
  • nectar found at the bottom of the stamen trough
  • stamen is inside the flower, so animals have to brush past them to get nectar
  • small and compact stigma
  • long, curved and hairy style
• Wind-pollinated flowers have:

  • long and feathery stigmas to provide a large SA to trap pollen floating in the ar
  • stigmas protrude out of the bracts
  • long filaments
  • anthers hanging outside the bracts. when the wind blows, they sway and release pollen.
• Describe the route taken by a growing pollen tube in a plant and explain its importance in plant reproduction.

  • Pollen tube grows out from the germinated pollen grain on the stigma
  • As pollen tube grows down the style, it secretes enzymes to digest the tissue of the stigma and style
  • Pollen tube enters the ovule through the micropyle in the ovule wall
  • within ovule, the tip of the pollen tube absorbs sap and bursts, releasing the two male gametes
• The function of the testes is to produce sperm and testosterone.
• The scrotum is a loose pouch-like sac of skin that hangs behind the penis. Its function is to keep the sperm-forming cells in the testis about 2 degrees cooler than body temperature, allowing them to function normally.
• The function of the sperm duct is to deliver sperm to the urethra during ejaculation.
• The function of the prostate gland is to produce a fluid that nourishes the sperm and provides protection from the natural acidity of the vagina.
• The function of the urethra is to convey, at different times, both sperm and urine out of the body, through the penis.
• The function of the penis is to deliver sperms to the vagina during sexual intercourse.
• The function of the ovaries is to produce egg cells and oestrogen and progesterone (produced by corpus luteum).
• The function of the oviduct is to act as the site of fertilisation, and contains cilia to sweep the released egg into the uterus.
• The function of the uterus is to act as the site of pregnancy, and has a thick muscular wall lined with the endometrium (blood-rich layer of tissue).
• The function of the cervix is to allow the flow of menstrual blood out of the vagina and direct the sperms into the uterus.
• The function of the vagina is to serve as a repository for sperm.