B1

• Diffusion


  The net movement of particles from an area of higher concentration to an area of lower concentration
• Factors affecting rate of diffusion


  • Concentration gradient - larger gradient, faster diffusion
  • Temperature - higher temperature, faster diffusion
  • Surface area - larger surface area, faster diffusion
• Substances transported by diffusion

  • 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
• Adaptations of single-celled organisms for diffusion

  • They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs
• Calculating surface area to volume ratio

  1. Surface Area = Number of Sides x (Side Length x Side Width)

  2. Volume = Length x Width x Depth

  3. Ratio = Surface Area:Volume
• Factors increasing effectiveness of gas exchange surface


  • Large surface area
  • Thin membrane (short diffusion path)
  • Efficient blood supply (animals)
  • Ventilation (animals)
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Isotonic solution


  The concentrations of the external and internal (inside cell) solutions are the same
• Hypertonic solution


  The concentration of the external solution is higher than that of the internal solution (inside cell)
• Hypotonic solution


  The concentration of the external solution is lower than that of internal solution (inside cell)
• Animal cell in very hypotonic solution


  Water moves into the cell, causing it to burst
• Animal cell in very hypertonic solution


  Water moves out of the cell, causing it to shrivel up
• Chromosomes


  DNA molecules combined with proteins that contain genes which provide the instructions for protein synthesis
• Turgor pressure


  Water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall
• Gene


  A section of DNA which codes for a protein
• Plant cell in very hypertonic solution


  Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed
• Active transport


  The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration
• The nucleus of human body cells contains 46 chromosomes
• The nucleus of gametes contains 23 chromosomes
• Use of active transport by plant root hair cells


  • 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
• Arrangement of chromosomes in body cell nucleus

  Arranged in pairs - 46 chromosomes form 23 pairs
• Use of active transport to absorb products of digestion

  • Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration
• Cell cycle

  1. Replication of DNA and synthesis of organelles

  2. Mitosis

  3. Division of cell
• Mitosis


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


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

  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
• Stem cell

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

  • Can replicate themselves and differentiate into many other types of cells
  • May be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Function of adult stem cells in bone marrow


  • Can differentiate into several cell types to replace dead or damaged tissues
  • Bone marrow stem cells can form many different types of blood cell
• Function of stem cells in plant meristems


  • 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
• 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 patient's immune system, so can be used to treat certain medical conditions
• 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
• Issues associated with the use of stem cells

  • Many embryonic stem cells are sourced from aborted embryos - some people have an ethical/religious objection
  • Development of stem cell therapies is slow, expensive and difficult
  • Adult stem cells infected with viruses could transfer infections to patients
  • If donor stem cells do not have a similar genetic makeup to the patient, an immune response could be triggered
• Eukaryotic cells


  Plant and animal cells
• Differences between eukaryotic and prokaryotic cells


  • Prokaryotic cells are much smaller than eukaryotic cells
  • Eukaryotic cells contain membrane bound-organelles and a nucleus containing genetic material, while prokaryotes do not
• Prokaryotic cell wall

  Composed of peptidoglycan
• Genetic information storage in prokaryotic cells

  Found free within the cytoplasm as: Chromosomal DNA (single large loop of circular DNA), Plasmid DNA
• Plasmids


  Small, circular loops of DNA found free in the cytoplasm and separate from the main DNA, carry genes that provide genetic advantages e.g. antibiotic resistance
• Order of magnitude

  A power to the base 10 used to quantify and compare size