Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Structures found in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Structures found only in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures found in bacterial cells


  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA and plasmids
• Sperm cells


  • Streamlined head and long tail to aid swimming
  • Many mitochondria to supply energy
  • Acrosome with digestive enzymes to break down egg cell membrane
• Nerve cells

  • Long axon to transmit signals
  • Many dendrites to form branched connections
  • Mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Special proteins (myosin and actin) to cause contraction
  • Many mitochondria to provide energy for contraction
  • Can store glycogen for respiration
• Root hair cells

  • Large surface area for water and mineral uptake
  • Large vacuole to affect water movement speed
  • Mitochondria to provide energy for active transport of minerals
• Xylem cells

  • Hollow structure with lignin deposits to withstand water pressure
  • Joined end-to-end to form continuous tubes
• Phloem cells

  • Sieve plates allow movement of substances between cells
  • Rely on mitochondria in companion cells for energy
• In animals, most cells differentiate early and lose ability to differentiate further
• In plants, many cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece) to magnify and view tissues, cells and large subcellular structures
• Electron microscope


  Uses electrons instead of light to form images, allowing viewing of subcellular structures in high detail
• Components of culture medium

  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• Autoclave


  An oven used to sterilise Petri dishes and culture media
• Bacteria have a supply of nutrients and suitable temperature


  They can multiply by binary fission as fast as every 20 minutes
• Inhibition zone


  The clear area around antibiotic discs where bacteria have died
• Chromosomes


  Contain coils of DNA and carry genes
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each gamete cell
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up and are pulled to opposite sides

  3. Cytokinesis: cytoplasm and cell membranes divide to form two daughter cells
• Stem cells

  Undifferentiated cells that can divide to produce more similar cells, some of which will differentiate
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning

  Producing an embryo with the same genes as the patient, to obtain stem cells that won't be rejected
• Benefits and problems of stem cell research

  • Benefits: Can replace damaged/diseased body parts, use unwanted embryos, research differentiation
  • Problems: Don't fully understand differentiation, destroying embryos, ethical objections, risk of contamination, money could be better spent
• Diffusion


  The spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Substances can move across cell membranes via diffusion, but only small molecules like oxygen, glucose, amino acids and water can do this</b>
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in gas exchange
  • Urea from liver to kidneys for excretion
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area
  • Thickness of membrane
• Water can move across cell membranes by osmosis, but starch and proteins cannot
• Where this takes place in the body

  • Oxygen moves through the membranes of structures in the lung called alveoli into the red blood cells, and is carried to cells across the body for respiration. Carbon dioxide (the waste product of respiration) moves from the red blood cells into the lungs to be exhaled. These movements of gases is called gas exchange.
  • Urea (a waste product) moves from the liver cells into the blood plasma to be transported to the kidney for excretion
• Surface area to volume ratio

  The size of the surface area of the organism compared to its volume
• Single-celled organisms can use diffusion to transport molecules into their body from the air because they have a relatively large surface area to volume ratio
• In multicellular organisms the surface area to volume ratio is small so they cannot rely on diffusion alone
• Osmosis


  The movement of water from a dilute solution to more concentrated solution
• Water potential


  The concentration of water in a solution
• Isotonic

  When the concentration of sugar in the external solution is the same as the internal, there will be no movement of water