Key concepts

• Organisms


  Can be Eukaryotes or Prokaryotes
• Eukaryotic cells


  Complex and include all animal and plant cells
• Prokaryotic cells


  Smaller and simpler, e.g. bacteria
• Plant and Animal Cells Have Similarities and Differences
• Subcellular structures


  The different parts of a cell
• Subcellular structures found in most animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Nucleus


  Contains genetic material that controls the activities of the cell
• Cytoplasm


  Gel-like substance where most of the chemical reactions happen
• Cell membrane


  Holds the cell together and controls what goes in and out
• Mitochondria


  Where most of the reactions for respiration take place
• Ribosomes


  Involved in translation of genetic material in the synthesis of proteins
• Additional subcellular structures found in plant cells

  • Rigid cell wall
  • Large vacuole
  • Chloroplasts
• Rigid cell wall


  Made of cellulose, supports and strengthens the cell
• Large vacuole


  Contains cell sap, maintains internal pressure to support the cell
• Chloroplasts


  Where photosynthesis occurs, contain chlorophyll
• Subcellular structures found in bacterial cells

  • Chromosomal DNA
  • Ribosomes
  • Cell membrane
  • Plasmid DNA
  • Flagellum
• Chromosomal DNA


  One long circular chromosome that controls the cell's activities and replication
• Plasmid DNA


  Small loops of extra DNA that aren't part of the chromosome, contain genes for things like drug resistance
• Flagellum


  Long, hair-like structure that rotates to make the bacterium move
• Cells aren't all the same-they have specialised structures and functions
• Specialised cells


  Cells that have a structure which makes them adapted to their function
• Multicellular organisms contain lots of different types of cells with different structures
• Egg Cells and Sperm Cells Are Specialised for Reproduction
• Haploid


  Having half the normal number of chromosomes
• Egg cell


  • Contains nutrients in the cytoplasm to feed the embryo
  • Has a haploid nucleus
  • Membrane changes structure after fertilisation to stop more sperm getting in
• Sperm cell


  • Has a long tail to swim to the egg
  • Has lots of mitochondria to provide energy for swimming
  • Has an acrosome to digest the egg membrane
  • Contains a haploid nucleus
• Ciliated epithelial cells


  Epithelial cells with hair-like cilia that beat to move substances in one direction along the surface
• Cells are Studied Using Microscopes
• Resolution


  How well a microscope distinguishes between two points that are close together
• Light microscopes


  Work by passing light through the specimen
• Electron microscopes


  Use electrons rather than light, have higher magnification and resolution
• Using a light microscope

  1. Take a thin slice of the specimen

  2. Place it on a slide with a drop of water

  3. Add a stain if needed

  4. Cover with a coverslip

  5. Use the lowest power objective lens

  6. Adjust the focus

  7. Swap to higher power lens if needed
• Creating a scientific drawing of a specimen

  1. Draw outlines of main features with clear, unbroken lines

  2. Make drawing take up at least half the space

  3. Keep parts in proportion

  4. Label important features with straight lines

  5. Include magnification and scale
• Magnification


  How many times bigger the image is compared to the real object
• Magnification


  Ratio of image size to real size
• Calculating magnification


  1. Measure image size

  2. Measure real size

  3. Divide image size by real size
• You don't know which lenses were used, but you can still work out the magnification of an image
• Both measurements (image size and real size) should have the same units. If they don't, you'll need to convert them first
• Estimating magnification


  1. Round numbers to 1-2 significant figures

  2. Do calculation with rounded numbers
• Standard form


  Writing very big or very small numbers in a more manageable way