Cell Biology

• Sugar molecules are used for cell respiration
• An example of active transport in humans is when there is a lower concentration in the gut and a higher concentration of nutrients in the blood
• In humans, active transport allows nutrients to be taken into the blood
• Plants need ions for healthy growth
• In plants, active transport allows mineral ions to be absorbed into plant root hair cells
• Active transport requires energy from respiration
• Active transport is the movement of substances from a lower concentration to a higher concentration
• Water can move across a cell membrane via osmosis
• Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of high water concentration to an area of low water concentration
• To be more effective, exchange surfaces have:

  - thin membrane = shorter diffusion distance

  - large surface area = lots of substances can diffuse at once

  - efficient blood supply = quick transport to the blood

  - ventilated gas exchange surfaces = air moves in and out efficiently
• Roots and leaves are adapted to exchange materials by having:

  - thin leaves = shorter diffusion distance

  - flat leaves = large surface area to volume ratio

  - many stomata = allows movement of gases in and out of the air spaces which maintains a deep concentration gradient
• Mammal lungs are adapted to exchange materials by having:

  - alveoli = increases surface area

  - thin walls = shorter diffusion distance

  - moist walls = helps gases move through exchange surface
• The small intestine is adapted to exchange materials by having:

  - villi = increases surface area so digested food can be efficiently absorbed into the bloodstream and to the rest of the body
• Fish gills are adapted to exchange materials by having:

  - large surface area of gills

  - large surface area of the blood capillaries in each gill

  - short distance required for diffusion as capillary walls have a thin membrane
• Multi cellular organisms have a smaller surface area to volume ratio so they can have a exchange surface for efficient diffusion
• Single cellular organisms have a larger surface area to volume ratio so molecules can transport sufficiently
• Cells use diffusion to take in substances they need and get rid of waste products
• Surface area affects the rate of diffusion because a larger surface area means faster diffusion as more particles can pass through at once
• Temperature affects the rate of diffusion because a higher temperature means faster diffusion as particles have more energy to move around faster
• A difference in concentration affects the rate of diffusion because the bigger the difference in concentration, the faster the rate of diffusion
• 3 factors that affect the rate of diffusion:

  - difference in concentration

  - temperature

  - surface area
• Some substances transported by diffusion

  oxygen, carbon dioxide, and urea
• Diffusion happens in liquids and gases because particles are free to move around
• Diffusion is the movement of particles from an area of high concentration to an area of low concentration.
• Why are some people against stem cell research?

  - religious and ethical reasons

  - human embryos are potential human lives

  - other sources of stem cells should be found

  - stem cell research is banned in some countries
• What is the risk of therapeutic cloning?

  - can transfer viral infection
• What happens during therapeutic cloning?

  - the embryo can be made to have the same genetic information as the patient

  - the stem cells will not be rejected by patients body
• What health conditions can stem cells help treat?

  - diabetes

  - paralysis
• What is the function of stem cells in meristem tissues?

  - can differentiate into any type of plant cell throughout the plant's life

  - produces clones quickly and cheaply

  - rare species can be cloned to prevent extinction

  - plants with desired characteristics can be cloned
• Embryonic stem cells can differentiate into any type of cell and be cloned to make different types of human cells
• What is the function of stem cells in adult animals?

  - found in bone marrow

  - turns into specific cells such as blood cells

  - specialised to make functioning tissues and organs
• Where are stem cells found?

  - in early human embryos

  - bone marrow of adults
• What is a stem cell?

  an undifferentiated cell that can divide to produce more undifferentiated cells
• Why is cell division by mitosis important?

  for the growth and development of multicellular organisms
• What are the 3 stages of mitosis?

  STAGE 1:

  - cell grows and increases the number of sub-cellular structures

  - the DNA replicates to form two copies of each chromosome

  STAGE 2:

  - genetic material separates to different ends of the cell

  - nucleus divides

  STAGE 3:

  - the cytoplasm and cell membrane split

  - two new daughter cells are made
• What does mitosis result in?

  two identical daughter cells with the same number of chromosomes
• What is mitosis?

  - a type of cell division where cells divide

  - these cells are used to grow or replace damaged cells
• What is a cell cycle?


  a series of stages in which cells divide
• How are chromosomes found in body cells?

  in pairs, humans have 23 pairs of chromosomes
• What do chromosomes carry?

  lots of genes