Paper 1

• Light Microscope

  • Low resolution
  • Uses light waves
  • Magnification x1500
  • Able to observe cells and larger organelles
  • 2D images only
• Magnification

  How many times bigger an object is through a microscope
• Magnification

  Image size = real size x magnification
• Micrometer (μm)


  1 x 10^-6 m
• Plant cell

  • cell wall cellulose
  • cell membrane -controls What enters and leaves
  • chloroplasts Contains chlorophyll where photosynthesis occurs
  • permanent vacuole where sap is stored
• Mitochondria


  • where respiration takes place
• Cells are usually a few micrometers long
• Eukaryotic cells are found in plants, animals, fungi and single cell organisms
• Eukaryotic cells are 10-100 micrometers in size
• Eukaryotic cells contain cell membrane, cytoplasm and nucleus
• Prokaryotic cells are found in bacteria
• Prokaryotic cells are 0.1-0.5 microbus
• Prokaryotic cells are unicellular
• Prokaryotic genetic material is stored in a single loop of DNA in the cytoplasm
• Prokaryotic cells may have one or more loops of small rings of DNA called plasmids which can be replicated between cells so genetic information can be shared
• To convert μm to mm

  Divide by 1000
• Resolution

  The ability to distinguish between 2 or more objects close together
• Mitosis

  The process of cell division that results in two genetically identical daughter cells
• Electron Microscope

  • Uses electrons
  • High resolution
  • Magnification up to x500,000
  • Able to observe small organelles
  • 2D and 3D images
• Stages of the cell cycle

  1. Initial growth stage where extra subcellular structures are produced (mitochondria, ribosomes)

  2. Chromosome replication resulting in 2 sets

  3. Mitosis process
• Cell specialisation

  Animal cells are specialised and have adaptations which help them carry out a certain function
• Human cells have 23 pairs of Chromosomes
• Differentiation

  When cells become specialised
• Gametes (eggs/sperms) have only 23 chromosomes
• Mitosis

  • New cells are made
  • For growth and repair
• Sperm cells

  • Have an engine
  • Job is to join with an egg cell during fertilisation
  • Contain half the genetic information of a normal adult cell
  • Have a long tail to help them swim
  • Have lots of mitochondria in the middle section to generate energy for swimming
  • Contain an acrosome with digestive enzymes to help penetrate the egg cell
  • Have a streamlined head to help them manoeuvre faster
• Sperm cells contain their genetic information in the nucleus
• During fertilisation, the genetic information from the egg and sperm combine
• Dendrites

  Increase the surface area so that other nerve cell's can connect more easily
• Synapses


  Junctions which allow the impulses to pass from one nerve cell to another
• Mitosis

  1. Nucleus dissolves and genetic material is duplicated

  2. The two sets of chromosomes move to different sides of the cell

  3. Mitochondria and ribosomes & other organelles are duplicated

  4. The cell divides producing two genetically identical diploid cells

  5. New nuclei are formed
• Nerve Cells

  Their job is to send electrical impulses around the body
• Myelin

  Insulates the axon and speeds up the transmission of nerve impulses
• Mitochondria

  Organelles in cells that provide energy
• Muscle cells

  • Can contract (get shorter)
  • Contain protein fibers which can change their length
• Transmission of nerve impulses

  1. Axon carries electrical impulses from one part of the body to another

  2. Myelin insulates the axon and speeds up the transmission of nerve impulses

  3. Synapses allow the impulses to pass from one nerve cell to another
• Muscle cell contraction

  1. Protein filores shorten

  2. Decreasing the length of the cell
• Muscle cells

  • Have lots of mitochondria to provide energy for muscle contraction
• Phloem cells

  • Tubes that transport dissolved sugars up and down the plant
  • Lack a nucleus and have only limited cytoplasm
• Sieve plates

  Pores at the ends of the phloem vessel cell walls that allow dissolved sugars to move through the cell interior