Cell biology

• Cells


  The building blocks of every organism on the planet
• Types of organisms

  • Prokaryotes
  • Eukaryotes
• All living things are made of cells
• Eukaryotic cells


  Complex cells that include all animal and plant cells
• Prokaryotic cells


  Smaller and simpler cells, e.g. bacteria
• Eukaryotes are organisms made up of eukaryotic cells
• A prokaryote is a prokaryotic cell (a single-celled organism)
• Subcellular structures in most animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional subcellular structures in plant cells

  • Rigid cell wall
  • Permanent vacuole
  • Chloroplasts
• Bacterial cells are much smaller than plant and animal cells
• Bacterial cells


  Don't have chloroplasts or mitochondria, have a single circular strand of DNA in the cytoplasm, may also contain plasmids
• Microscopes


  Allow us to see things we can't see with the naked eye
• Types of microscopes


  • Light microscopes
  • Electron microscopes
• Light microscopes


  Use light and lenses to form an image and magnify it
• Electron microscopes


  Use electrons instead of light, have higher magnification and resolution than light microscopes
• Magnification


  The ratio of the image size to the real size
• Calculating magnification


  Image size / Real size
• Microscopes can see very small objects, so numbers are sometimes written in standard form
• Standard form


  A way of writing very big or small numbers with lots of zeros in a more manageable way, using powers of 10
• Preparing a slide to view onion cells

  1. Add drop of water

  2. Peel off epidermal tissue

  3. Add iodine solution

  4. Place coverslip
• Using a light microscope

  1. Clip slide onto stage

  2. Select lowest-powered objective lens

  3. Use coarse adjustment to focus

  4. Use fine adjustment to refine focus

  5. Switch to higher magnification if needed
• Drawing observations from a microscope

  Use a pencil, take up at least half the space, use clear unbroken lines, don't colour or shade, draw subcellular structures in proportion, include title and magnification
• Cell differentiation


  The process by which a cell changes to become specialised for its job
• Most differentiation occurs as an organism develops, and the ability to differentiate is then lost at an early stage in most cells</b>
• Plant cells often retain the ability to differentiate even in mature organisms
• Examples of specialised cells

  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Chromosomes


  Coiled up lengths of DNA that contain genes
• Body cells normally have two copies of each chromosome, one from each parent
• The cell cycle


  1. Growth and DNA replication

  2. Mitosis
• Mitosis


  The stage of the cell cycle when the cell divides
• Stages of mitosis


  1. Chromosomes line up at the centre

  2. Chromosome arms are pulled to opposite ends

  3. Nuclei form around the chromosome sets

  4. Cytoplasm and cell membrane divide
• Binary fission


  A type of simple cell division in prokaryotic cells
• Stages of binary fission

  1. DNA and plasmids replicate

  2. Cell gets bigger, DNA moves to opposite ends

  3. Cytoplasm begins to divide, new cell walls form

  4. Cytoplasm divides, two daughter cells produced
• Binary Fission


  1. The circular DNA and plasmid(s) replicate

  2. The cell gets bigger and the circular DNA strands move to opposite 'poles' (ends) of the cell

  3. The cytoplasm begins to divide and new cell walls begin to form

  4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of plasmids
• Prokaryotic cells can reproduce using a type of simple cell division called binary fission
• Bacteria can divide very quickly if given the right conditions (e.g. a warm environment and lots of nutrients)
• Some bacteria, such as E. coli, can take as little as 20 minutes to replicate in the right environment
• If conditions become unfavourable, the cells will stop dividing and eventually begin to die
• Mean division time


  The average amount of time it takes for one bacterial cell to divide into two
• Using mean division time to find the number of bacteria in a population

  1. Make sure both times are in the same units

  2. Divide the total time that the bacteria are producing cells by the mean division time to get the number of divisions

  3. Multiply 2 by itself for the number of divisions to find the number of cells