a level biology

• Organelles found in both plant and animal eukaryotic cells

  • Nucleus
  • Cell surface membrane
  • Mitochondria
  • Ribosomes
  • Golgi apparatus
• Organelles found only in plant eukaryotic cells


  • Chloroplasts
  • Cell wall
  • Vacuole
• Nucleus


  • Where chromosomes are located
  • Enclosed by a nuclear envelope
  • Controls the cell's activity
  • Contains the nucleolus where ribosomes are produced
• Cell surface membrane


  • Made up of lipids and proteins
  • Controls movement of things in and out of the cell
• Mitochondria


  • Have a double membrane
  • Highly folded inner membrane
  • Site of enzymes involved in respiration and ATP production
• Ribosomes


  • Small structures where proteins are made
  • Can be found on the rough endoplasmic reticulum or in the cytoplasm
• Golgi apparatus


  • Fluid-filled membrane
  • Produces and transports new lipids and proteins
• Chloroplasts


  • Site of photosynthesis
  • Have a double membrane
  • Contain thylakoid membranes
• Cell wall


  • Ensures cell structure is maintained
• Vacuole


  • Contains sap
  • Helps maintain cell shape and structure by maintaining pressure
• Rough endoplasmic reticulum


  • Site of protein synthesis and processing
• Smooth endoplasmic reticulum


  • Site of lipid synthesis and processing
• Lysosomes


  • Contain digestive enzymes
• Cytoplasm


  • Where most cell reactions take place
• Eukaryotic cells have physical adaptations to maximise diffusion, such as microvilli and concave shapes
• Cells adapted for storage can have large lipid stores or vacuoles
• Secretory cells are adapted to have large Golgi apparatuses and rough endoplasmic reticulum
• Cells with high energy requirements are adapted to have many mitochondria
• Cells with high active transport requirements are adapted to have many channel and carrier proteins, as well as increased ribosomes
• Structures found in prokaryotic cells


  • Cytoplasm
  • Ribosomes
  • Cell surface membrane
  • Cell wall
  • Flagella
  • DNA (not in nucleus)
  • Plasmid DNA
• Millimeter


  1/1000 of a meter
• Micrometer


  1/1000 of a millimeter
• Nanometer


  1/1000 of a micrometer
• To convert between millimeters, micrometers and nanometers, multiply by 1000 to go up a scale, and divide by 1000 to go down a scale
• Differences between optical and electron microscopes

  • Optical microscopes use light, electron microscopes use electrons
  • Optical microscopes can view living specimens, electron microscopes require fixed specimens
  • Optical microscopes have lower maximum magnification, electron microscopes have higher maximum magnification
  • Optical microscope images are in colour, electron microscope images are black and white
• Optical microscope


  • Has eyepiece, base with light source, course and fine focus, objective lenses, stage to hold slide
• Electron microscope


  • Uses electromagnets to focus electron beam, has screen to view images, requires dedicated room with air conditioning
• Magnification


  Size of image / Actual size of object
• When calculating magnification, convert all measurements to the same scale (e.g. micrometers)
• Biological drawings


  • Use sharp pencil
  • Include scale
  • Use clear continuous lines
  • No shading
  • Include title
  • Accurate and labelled
• Covalent bonding


  Sharing of electrons between two non-metals
• Ionic bonding


  Transfer of electrons from metal to non-metal, forming positive and negative ions
• Hydrogen bonding


  Weak attraction between opposite dipoles
• Water is a polar, bent molecule with hydrogen bonding between the slightly positive hydrogens and slightly negative oxygen
• Hydrogen bonding in water is responsible for its cohesion, surface tension, high specific heat capacity, and suitability as a solvent
• Hydrogen bonds


  Occur between molecules of water, individually weak but collectively very important
• Water


  • Polar
  • Hydrogen bonds involved in a wide range of condensation and hydrolysis reactions
  • Large amount of energy required to break hydrogen bonds, so water is liquid at room temperature
  • Responsible for cohesion and surface tension
  • High specific heat capacity helps regulate temperature
• Water as a solvent

  • Can attract and dissolve ionic compounds
  • Can form hydrogen bonds with polar molecules like glucose
• Important inorganic ions


  • Sodium ions (Na+)
  • Phosphate ions (PO4 3-)
  • Hydrogen ions (H+)
  • Iron ions (Fe2+, Fe3+)
• Monomer


  Single unit that can be joined together to form a polymer