Biology TA1

• What is diffusion?

  Movement of particles from a high to low concentration
• Three main factors affecting the rate of diffusion

  • Concentration gradient - larger gradient, faster diffusion
  • Temperature - higher temperature, faster diffusion
  • Surface area - larger surface area, faster diffusion
• Examples of substances transported by diffusion in the lungs and the kidney

  • Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient
  • Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine
• How are single-celled organisms adapted for diffusion?

  They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organisms needs
• How is surface area to volume calculated?

  surface area = number of sides x side x length x side width

  volume = length x width x depth

  ratio = surface area:volume
• What four factors increase the effectiveness of a gas exchange surface?

  • Large surface area
  • Thin membrane (short diffusion path)
  • Efficient blood supply
  • Ventilation
• What is osmosis?

  The movement of water particles from a high to low concentration across a semi permeable membrane
• How do plant leaves and stems remain rigid?

  Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall
• What is active transport?

  The movement of molecules from a low to high concentration, using energy from respiration
• How do plant root hair cells use active transport?

  Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth
• What are chromosomes made up of?

  Chromosomes consist of DNA molecules combined with proteins. They contain genes which provide the instructions for protein synthesis
• What is a gene?

  A section of DNA which codes for protein
• How many chromosomes are found in the nucleus of human body cells?

  46
• How many chromosomes are found in the nucleus of gametes?

  23
• How are chromosomes arranged in the nucleus of a body cell?

  Arranged in pairs - 46 chromosomes form 23 pairs
• What are the three main stages of the cell cycle?

  1. replication of DNA and synthesis of organelles
  2. mitosis
  3. division of cell
• Why is mitosis important?

  • produces two identical daughter cells which all have the same genetic information
  • produces additional cells for growth and repair
• First stage of the cell cycle

  Longest stage - cells grow and increase in mass, replicate DNA and synthesise more organelles (e.g. mitochondria and ribosomes)
• Second stage of cell cycles

  Each chromosome in a pair is pulled to opposite poles of the cell, then the nucleus divides
• Third stage of cell cycle

  The cytoplasm and cell membrane divide - two identical daughter cells are produced
• What is a stem cell?

  An unspecialised cell which is capable of differentiating into other cell types and of self-renewal
• Function of stem cells in embryos

  Embryonic stem cells can replicate themselves and differentiate into many other types of cells

  Embryonic stem cells may be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Function of stem cells in adult bone marrow 


  Adult stem cells can differentiate into several cell types to replace dead or damaged tissues. For examples, bone marrow stem cells can form many different types of blood cells
• Function of stem cells in plant meristems

  Meristem stem cells retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant
• What is therapeutic cloning?

  A cloning method where an embryo is produced with the same genetic makeup as the patient.

  The stem cells which originate from the embryo will not be rejected by the patients immune system, so can be used to treat certain medical conditions
• What are advantages of cloning plants using meristem stem cells?

  • Can prevent rare plants from becoming extinct
  • Can produce large numbers of plants with a favourable characteristic
  • Can produce identical plants for research