bio

• Cell


  The basic unit of life
• Eukaryotic cell


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Plant cell


  • Chloroplasts
  • Permanent vacuole
• Bacterial cell


  • Cytoplasm
  • Membrane
  • Cell wall
  • Genes not in distinct nucleus
  • Circular structures called plasmids
• Cells may be specialised to carry out a particular function
• Tissue


  A group of cells with similar structure and function
• Organ


  Made of tissues, may contain several tissues
• Organ system


  Groups of organs that perform a particular function
• Animal tissues


  • Muscular
  • Glandular
  • Epithelial
• Plant tissues


  • Epidermal
  • Palisade mesophyll
  • Spongy mesophyll
  • Xylem
  • Phloem
• Plant organs include stems, roots and leaves
• Diffusion


  The spreading of particles of a substance in solution or gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Dissolved substances can move into and out of cells by diffusion
• Oxygen required for respiration passes through cell membranes by diffusion
• 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
• Differences in the concentrations of the solutions inside and outside a cell cause water to diffuse into or out of the cell by osmosis
• Active transport


  The absorption of substances against a concentration gradient, requiring energy from respiration
• Active transport enables plants to absorb ions from very dilute solutions and animals to absorb sugar from low concentrations
• A single-celled organism has a relatively large surface area to volume ratio, allowing necessary exchanges to occur across its surface membrane
• The increased size and complexity of an organism increases the difficulty of exchanging materials
• Effectiveness of an exchange surface

  • Large surface area that is thin, to provide a short diffusion path
  • Efficient blood supply (in animals)
  • Ventilation (in animals, for gaseous exchange)
• Gas and solute exchange surfaces in humans and other organisms are adapted to maximise effectiveness
• Photosynthesis


  The process where light energy is used to convert carbon dioxide and water into glucose and oxygen
• Photosynthesis


  1. Light absorbed by chlorophyll

  2. Carbon dioxide and water converted into glucose

  3. Oxygen released as by-product
• Factors limiting photosynthesis rate

  • Low temperature
  • Shortage of carbon dioxide
  • Shortage of light
• The glucose produced in photosynthesis may be used as a source of chemical energy or converted to larger molecules for storage and use later
• To produce proteins, plants also use nitrate ions that are absorbed from the soil
• Gas exchange in flowering plants

  • Carbon dioxide enters leaves through stomata
  • Most water and mineral ions absorbed by roots
• Adaptations of plant surfaces for exchange

  • Root hairs increase surface area of roots
  • Flattened shape and internal air spaces increase surface area to volume ratio of leaves
• Stomata


  Pores in leaves that allow carbon dioxide uptake and oxygen release, and control water loss
• Water transport in plants

  1. Absorbed by roots

  2. Transported through xylem

  3. Evaporates from leaves
• Transpiration stream


  The movement of water from the roots through the xylem and out of the leaves
• Translocation


  The transport of dissolved sugars from the leaves to the rest of the plant in the phloem
• Circulatory system


  The heart, blood vessels and blood that transport substances around the body
• Heart structure


  • Four main chambers (right and left atria, right and left ventricles)
  • Wall made of muscle tissue
• Pacemaker


  Group of cells in the right atrium that control the natural resting heart rate
• Coronary heart disease


  Buildup of fatty material in the coronary arteries, reducing blood flow and oxygen supply to the heart muscle
• Faulty heart valves


  Can stiffen, preventing full opening, or develop leaks
• Faulty heart valves can be replaced with biological or mechanical valves
• Artificial hearts are occasionally used to keep patients alive whilst waiting for a transplant or to allow the heart to rest