Topic 1: Cell Biology

• Eukaryotes

  Plant and Animal Cells
• Prokaryotes

  Smaller, Bacterial Cells (Unicellular)
• Animal Cells - Subcellular Structures

  Nucleus, Mitochondria, Cytoplasm, Cell membrane and Ribosomes
• Nucleus

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

  Where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work
• Cytoplasm

  Gel-like substance where most of the chemical reactions happen, containing enzymes to control these chemical reactions
• Cell membrane

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

  Site of protein synthesis (where proteins are made in the cell)
• Plant Cells - Subcellular Structures

  Nucleus, Mitochondria, Cytoplasm, Cell membrane, Ribosomes, Cell wall, Permanent Vacuole, and Chloroplasts
• Cell Wall

  Supports the cell and strengthens it (made of cellulose)
• Permanent Vacuole

  Contains cell sap, a weak solution of sugar and salts
• Chloroplasts

  Where photosynthesis occurs. Contains Chlorophyll, which absorbs the light needed for photosynthesis
• Bacterial Cells - Subcellular Structures

  Cytoplasm, Cell membrane, Cell wall, Circular strand of DNA and Plasmids
• Circular strand of DNA

  Contains the genetic material of the cell, with the genes required to survive and reproduce
• Light Microscopes

  Use light and lenses to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures
• Electron Microscopes

  Use electrons to form an image. Have a much higher magnification and resolution than light microscopes.
• Resolution

  The ability to distinguish between two points
• Magnification Formula

  magnification = image size / real size
• RP 01 - Microscopy

  Use a light microscope to investigate a selection of plant and animal cells
• Equipment

  Light microscope, Microscope slide, Cover slip, Onion, Forceps, Iodine solution, White tile and Scalpel
• Method

  1. Peel off an epidermal layer on the onion using forceps

  2. Mount onto the microscope slide with a drop of water using a pipette, making sure the tissue lies flat

  3. Add 2 drops of iodine solution to stain the cells

  4. Place the cover slip on by first placing one edge down on the slide and slowly lowering the other side of the cover slip using forceps. Make sure no air bubbles are trapped

  5. Remove any excess stain by soaking it with paper towels

  6. Place the slide on the stage of the microscope

  7. Turn the nosepiece to select a lower power objective

  8. Set up the microscope. Use the coarse adjustment knob to raise the stage until the cover slip just touches the objective

  9. Look into the eyepiece and turn the coarse adjustment knob to move the stage away until the image comes into focus to avoid breaking the slide

  10. Turn the nosepiece to select a higher power objective

  11. Repeat the same process as above and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus

  12. Make a labelled drawing of a few of the cells you can see, including any features e.g. cell wall, nucleus. Write down the magnification

  13. Repeat these steps using a prepared slide
• Describe how you would prepare a microscope slide using onion tissue

  Peel off epidermal layer using forceps. Place sample on drop of water on microscope slide. Add drops of iodine solution to sample. Lower cover slip onto sample using mounting needle.
• Why is a thin sample of tissue required?

  Allows light to pass through so internal structures can be observed.
• Why is water added to the slide before the sample is mounted?

  Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place.
• Why is iodine solution added to stain the cells?

  Iodine solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus) to become more visible.
• Why is the cover slip lowered using a mounting needle?

  Ensures that no air bubbles are trapped.
• How would you measure the length of a cell viewed under the microscope?

  Measure using eyepiece graticule and calibrate with stage micrometer.
• What safety precautions should be taken during this experiment?

  Wear safety goggles when handling iodine solution.
• Drawing Your Observations

  Draw what can be seen under the microscope using a pencil with a sharp point. Ensure the drawing takes up at least half of the space available and that it is drawn with clear, unbroken lines. Do not include colouring or shading in the drawing. Draw the subcellular structures in proportion to one another. Include a title of what was being observed and write down the magnification that it was observed under. Label the important features of the drawing (e.g. nucleus, chloroplasts), using straight, uncrossed lines.
• Light Microscope structure

  Shown below:

  
• Cell Differentiation


  The process by which a cell changes to become specialised for a specific function.
• As cells change…


  They develop different subcellular structures and turn into different types of cells to carry out specific functions
• Most differentiation occurs as an organism develops
• In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised
• Lots of plant cells don't ever lose this ability to differentiate
• Differentiated cells in mature animals


  Used for repairing and replacing cells such as skin or blood cells
• Undifferentiated cells


  Stem cells
• Sperm Cells are Specialised for…

  Reproduction
• The function of a sperm is to…

  Get the male DNA to the female DNA
• Adaptations of a sperm cell

  Has a long tail and a streamlined head to help it swim to the egg. Many mitochondria in the cell to provide the energy needed and also carries enzymes in its head to digest through the egg cell membrane.