Biology

• Magnification on a photo


  The number of times the object is enlarged compared to its actual size
• Calculating magnification of a microscope

  Multiply the magnifications of the eyepiece lens and objective lens
• Microscope magnifications


  • 5x eyepiece lens and 10x objective lens = 50x total magnification
  • 5x eyepiece lens with 5x, 15x and 20x objective lenses = 25x, 75x and 100x total magnifications
• Electron microscopes can magnify up to x2000000, with resolutions down to 0.0000002 mm
• Electron microscope images


  Show more detail than light microscopes
• SI units


  Prefixes that divide or multiply units by powers of 1000
• Eukaryotic cell


  A cell that contains a nucleus
• Robert Brown discovered the nucleus in plant cells
• Matthias Schleiden and Theodor Schwann developed the idea of cells as the basic building blocks of life
• Sub-cellular structures in eukaryotic cells

  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Nucleus


  Controls the cell and contains chromosomes with DNA
• Cytoplasm


  Watery jelly where most of the cell's activities occur
• Mitochondria


  Structures that carry out aerobic respiration to produce energy
• Ribosomes


  Tiny structures that make new proteins for the cell
• Cell wall


  Made of cellulose and supports and protects the plant cell
• Chloroplasts


  Contain chlorophyll and trap energy from sunlight for photosynthesis
• Vacuole


  Large permanent structure that stores cell sap and helps keep the plant cell firm and rigid
• Cells on leaf surfaces contain vacuoles and carry out aerobic respiration but are not green
• Cells on leaf surfaces

  Lack chloroplasts
• Hooke realised the importance of making accurate drawings to help explain his work
• Stains can be used to make cell features show up more clearly under a microscope
• A coverslip is used to keep the specimen flat, hold it in place and stop it drying out
• Nerve cells can be extremely long, up to about 1 m
• Cells with microvilli absorb substances more quickly than those without
• Hepatocytes contain many ribosomes and make a lot of serum albumin, which is a protein
• Nerve cells require a lot of energy and are adapted by having many mitochondria
• Sperm cells are haploid, containing only one copy of each chromosome
• Gametes need to be haploid so that when they fuse, the resulting cell has the correct diploid number of chromosomes
• Specialised human cells


  • Cells for digestion
  • Cells for reproduction
• Cells that line the small intestine

  • Absorb small food molecules produced by folds (called microvilli)
  • Adaptations increase the surface area of the cell
• Cells in the pancreas

  • Make enzymes needed to digest certain foods in the small intestine
  • Adapted by having a lot of ribosomes
• Muscle cells in the small intestine wall

  • Require a lot of energy and are adapted by having many mitochondria
• Gametes


  Specialised cells that fuse during sexual reproduction
• Egg cell


  • Cytoplasm packed with nutrients to supply the fertilised egg cell with energy and raw materials
  • Cell membrane fuses with the sperm
  • Nucleus contains one copy of each chromosome (haploid)
• Sperm cell


  • Acrosome contains enzymes to break down the egg cell's jelly coat
  • Many mitochondria arranged in a spiral around the tail to release lots of energy
  • Tail waves from side to side to swim
• Cells lining the oviduct


  • Adapted with hair-like cilia that wave to sweep substances along
• An egg cell does not need a tail but a sperm cell does
• Bacteria are difficult to see with light microscopes because they are very small and mostly colourless
• Stains are often used to make bacteria show up
• Estimating the size of a bacterium

  1. Measure the size on the image

  2. Use the scale bar to calculate the real size