y9 biology

• Cells


  The basic unit of all forms of life
• Structural differences between various types of cells

  • Enable them to perform specific functions within the organism
  • Controlled by genes in the nucleus
• Cell division by mitosis

  1. Cells divide producing two new identical cells

  2. Allows organism to grow
• Stem cell technology


  Allows doctors to repair damaged organs by growing new tissue from stem cells
• Parts of eukaryotic cells

  • Cell membrane
  • Cytoplasm
  • Nucleus
• Parts of prokaryotic cells


  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single DNA loop
  • Plasmids
• Parts of animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional parts of plant cells

  • Chloroplasts
  • Permanent vacuole filled with cell sap
  • Cell wall made of cellulose
• Specialised cells


  • Sperm cells, nerve cells, muscle cells in animals
  • Root hair cells, xylem and phloem cells in plants
• Electron microscope


  • Has much higher magnification and resolving power than a light microscope
  • Enables study of subcellular structures in finer detail
• Chromosomes


  Coiled DNA molecules in the nucleus containing genetic information
• Mitosis and the cell cycle

  1. Genetic material is doubled and then divided into two identical cells

  2. Cell grows and increases subcellular structures

  3. DNA replicates

  4. Chromosomes are pulled to each end of the cell

  5. Cytoplasm and cell membranes divide
• Stem cells


  Undifferentiated cells capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Stem cells have an important role to play in embryos, in adult animals and in the meristems in plants
• Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
• Stem cells from adult bone marrow can form many types of cells including blood cells
• Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
• Treatment with stem cells may be able to help conditions such as diabetes and paralysis
• In therapeutic cloning an embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment
• The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
• Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
• Rare species can be cloned to protect from extinction
• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers
• Diffusion

  The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Substances transported by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area of membrane
• A single-celled organism has a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell to meet its needs
• Exchange surfaces


  Surfaces with a large surface area to volume ratio, adapted for exchanging materials
• Examples of exchange surfaces

  • Small intestine
  • Lungs
  • Gills
  • Roots
  • Leaves
• Effectiveness of an exchange surface

  • Large surface area
  • Thin, to provide a short diffusion path
  • (in animals) Efficient blood supply
  • (in animals, for gaseous exchange) Ventilated
• Osmosis


  The diffusion of water from a dilute to a more concentrated solution, through a partially permeable membrane that allows the passage of water molecules
• Active transport


  Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
• Active transport


  • Absorption of mineral ions into plant root hairs from dilute solutions in the soil
  • Absorption of sugar molecules from lower concentrations in the gut into the blood which has a higher sugar concentration
• The human digestive system provides the body with nutrients and the respiratory system provides it with oxygen and removes carbon dioxide, which are then moved around the body in the blood by the circulatory system
• Damage to any of these systems can be debilitating if not fatal, and many interventions would not be necessary if individuals reduced their risks through improved diet and lifestyle
• The plant's transport system is dependent on environmental conditions to ensure that leaf cells are provided with the water and carbon dioxide that they need for photosynthesis
• Tissue


  A group of cells with a similar structure and function
• Sugar molecules move


  1. From lower concentrations in the gut into the blood which has a higher sugar concentration

  2. Sugar molecules are used for cell respiration
• Human digestive system


  • Provides the body with nutrients
  • Respiratory system provides it with oxygen and removes carbon dioxide
  • Dissolved materials need to be moved quickly around the body in the blood by the circulatory system
• Damage to any of these systems can be debilitating if not fatal