Biology topic 1

• that they'd seen the building blocks of every organism on the planet...
• Organisms can be Prokaryotes or Eukaryotes
• All living things are made of cells


  Cells can be either prokaryotic or eukaryotic
• Eukaryotic cells

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


  • Smaller and simpler, e.g. bacteria
• Eukaryotes


  Organisms that are made up of eukaryotic cells
• Prokaryote


  A prokaryotic cell (it's a single-celled organism)
• Subcellular structures in animal cells

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

  • Rigid cell wall
  • Permanent vacuole
  • Chloroplasts
• Bacterial cells don't have a 'true' nucleus - instead they have a single circular strand of DNA that floats freely in the cytoplasm
• Bacteria may also contain one or more small rings of DNA called plasmids
• Bacteria don't have chloroplasts or mitochondria
• Microscopes


  Allow us to see things that we can't see with the naked eye
• Light microscopes


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

  • Use electrons instead of light to form an image, have a much higher magnification and resolution than light microscopes
• Magnification


  The ratio of the image size to the real size
• Preparing a slide

  1. Add a drop of water

  2. Cut up an onion and separate it out into layers

  3. Use tweezers to place epidermal tissue into the water

  4. Add a drop of iodine solution

  5. Place a cover slip on top
• Parts of a light microscope

  • Eyepiece
  • Coarse adjustment knob
  • Fine adjustment knob
  • High and low power objective lenses
  • Stage
  • Light
• Using a light microscope

  1. Clip the slide onto the stage

  2. Select the lowest-powered objective lens

  3. Use the coarse adjustment knob to move the stage up

  4. Look down the eyepiece and use the coarse adjustment knob to focus

  5. Adjust the focus with the fine adjustment knob

  6. Swap to a higher-powered objective lens if needed
• Drawing observations

  Use a pencil, take up at least half the space, clear unbroken lines, no colouring or shading, draw subcellular structures in proportion, include title and magnification
• Cells differentiate to become specialised for their function
• Examples of specialised cells

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

  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different cell types
• Stem cells are found in early human embryos and also in adults, but adult stem cells can only differentiate into certain cell types
• Stem cells from embryos and bone marrow can be grown in a lab to produce clones and made to differentiate into specialised cells
• Stem cells may be able to cure many diseases by replacing faulty cells
• Arguments against stem cell research

  • Embryos should not be used as they are potential human lives
  • Curing existing patients is more important than the rights of embryos
• Stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient and so make them sick
• Some people are against stem cell research because they feel that human embryos should not be used for experiments since each one is a potential human life
• Others think that curing patients who already exist and who are suffering is more important than the rights of embryos
• The embryos used in the research are usually unwanted ones from fertility clinics which, if they weren't used for research, would probably just be destroyed
• Campaigners for the rights of embryos usually want this banned too
• In some countries stem cell research is banned, but it's allowed in the UK as long as it follows strict guidelines
• Stem cells in plants

  • Found in the meristems (parts of the plant where growth occurs)
  • Throughout the plant's entire life, cells in the meristem tissues can differentiate into any type of plant cell
• Clones

  Identical copies of whole plants
• Stem cells can be used to grow crops of identical plants that have desired features for farmers, for example, disease resistance
• Some species of orchid are endangered in the UK. Many can be successfully reproduced by cloning using stem cells
• Research has been done into getting human stem cells from other sources-eg. it may be possible to programme differentiated adult cells back to an undifferentiated stage
• Nucleus


  Contains the genetic material in the form of chromosomes
• Chromosomes


  Coiled up lengths of DNA molecules that carry a large number of genes