Cell Biology

• Cells can be eukaryotic and prokaryotic
• Eukaryotes contain a nucleus.
• Prokaryotes are single-celled organisms.
• Prokaryotes have a single circular strand of DNA that floats freely in the cytoplasm.
• Prokaryotes may contain small DNA rings called plasmids.
• Mitochondria are the site for aerobic respiration. Respiration transfers energy that the cell needs to function.
• Nuclei contain genetic material and control cell activity.
• Cytoplasm is a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions.
• The cell membrane holds the cell together and controls what goes in and out.
• Ribosomes are the site of protein synthesis.
• Plants have a rigid cell wall made of cellulose. It supports the cell and strengthens it.
• Chloroplasts are the site of photosynthesis. They contain a green substance called chlorphyll, which absorbs the light needed for photosynthesis.
• Magnification = image size/real size (I/AM)
• Electron microscopes use electrons to form an image. They have a higher resolution than light microscopes.
• Advantages of Electron Microsopes- High magnification, high resolution, allow us to see small organelles such as ribosomes and plasmids.
• Electron microscopes are more expensive than light microscopes.
• • Add a drop of water to the middle of a clean slide
• Observing plant cells under a microscope

  1. Add a drop of water in the middle of a clean slide

  2. Cut up an onion and separate it into layers

  3. Use tweezers to peel off some of the epidermal tissue from the bottom of one of the layers

  4. Using the tweezers, place the epidermal tissue into the water on the slide

  5. Add a drop of iodine solution as a stain

  6. Place a cover slip on top
• The iodine solution highlights aspects of the cell by adding colour to them
• Try not to get any air bubbles as it will obstruct your view of the specimen
• Clip the slide you have prepared onto the stage.
• Select the lowest-powered objective lens (that produces the lowest magnification.)
• Use the coarse adjustment knob to move up the stage to just below the objective lens.
• Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
• Adjust the focus with the fine adjustment knob until you get a clear image of what's on the slide.
• If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
• Cells differentiate to become specialised.
• As cells change, they develop different subcellular structures and turn into different types of cells. This allows them to carry out specific functions.
• Plant cells never lose the ability to differentiate.
• Differentiation in mature animals is used for repairing and replacing cells, such as skin and blood cells.
• Stem cells are undifferentiated cells.
• Sperm cells are used in reproduction.
• Sperm have a long tail and streamlined head to help swim to the egg.
• There are lots of mitochondria in sperm cells to provide the energy needed to reach the egg.
• Sperm carry enzymes in their head to digest through the egg cell membrane.
• Nerve cells carry electrical signals from one part of the body to another.
• Nerve cells are long to cover more distance.
• The fuction of a muscle cell is to contract quickly.
• Muscle cells are long so they have space to contract.
• Mucsle cells contain lots of mitochondria to generate the energy needed for contraction.