B1 - Cell Biology

• Different parts of a cell are known as organelles.
• Cell membrane controls what enters and leaves a cell.
• The nucleus controls the cell activities, and contains the genetic information.
• The cytoplasm is where many of the cell's reactions occur.
• The ribosomes are where proteins are made.
• The mitochondria is where respiration takes place.
• Chloroplasts are a plant specific organelle, which is where photosynthesis occurs.
• The cell wall is a plant specific organelle made out of cellulose, which provides structure and support to the cell.
• The vacuole is a plant specific organelle that stores sap, an energy store, and helps with water movement.
• Cells are either eukaryotic or prokaryotic.
• Both plant and animal cells are eukaryotic.
• Eukaryotic cells:

  • Contain a nucleus surrounded by cell membrane
  • Contain specialised organelles (mitochondria)
• Prokaryotic cells:

  • are smaller than eukaryotic cells
  • don't have DNA in a nucleus
  • contain less organelles
• Both eukaryotic and prokaryotic cells:

  • have DNA
  • have cytoplasm
  • have cell membranes
• • 1000µm (micrometres) = 1mm (millimetre)
  • 1000nm (nanometres) = 1µm (micrometre)
• One order of magnitude = 10^1
• The single loop of DNA found in prokaryotic cells is called a plasmid.
• There are two types of microscopes:

  • Electron microscopes
  • Light microscopes
• Electron microscopes use beams of electrons instead of light, which increases the magnification and resolution to nano-dimensions.
• Magnification is how much bigger a sample appears to be under the microscope than it is in real life
• Resolution is the ability to distinguish between two points on an image (the amount of detail)
• Light microscopes:

  • Are affordable
  • Are portable
  • Are easy to use
  • Can't see past where light reaches (therefore have a lower maximum magnification than electron microscopes)
• Electron microscopes:

  • Have a high resolution
  • Have a high magnification
  • Are hard to use
  • Are expensive
  • Are large and not portable
• Magnification = image size / actual size
• Preparing an onion slide:

  1. Take a small piece of onion and using forceps (tweezers), peel off the membrane from the underside (the rough side).​
  2. Lay the membrane flat on the surface of the slide​
  3. Add a drop of Iodine solution to the onion epidermis.​
  4. Using a pin, lower the thin glass cover slip or cover glass onto the slide. Make sure there are no air bubbles.
• Preparing a cheek cell slide:

  1. Take a clean cotton swab and rub around the inside of your mouth and along the gum for about 30-60 seconds​
  2. Roll the cotton swab on the centre of the microscope slide for a few seconds.​
  3. Add a drop of methylene blue solution and place a coverslip on top. ​
  4. Remove any excess solution by allowing a paper towel to touch one side of the coverslip.​
  5. Use the lowest power to find the cells. ​
  6. Once you have found them, increase the magnification by using a higher power objective lens and use the focussing knob get a clear image.
• In animals, cell differentiation begins in the early embryo from stem cells.
• In adults, cell division and specialisation is mostly restricted to repair and replacement of cells. 
• As an embryo develops, the stem cells become specialised and turn into different types of cell.
• • Cells group to form tissues
  • Tissues group to form organs
  • A group of organs working together forms an organ system
• Plants contain a constant source of stem cells.
• Ciliated epithelial cells in the airways have:

  • Lots of mitochondria and ribosomes
  • Hair-like projections from the surface
  • Cells that are tightly packed
• In ciliated epithelial cells:

  • The ribosomes make mucus that is secreted onto the surface of the cells that dirt and bacteria will stick to.
  • The mitochondria release energy to move the cilia to keep the mucus moving
• Palisade cells have many chloroplasts to absorb as much energy as possible for photosynthesis.
• Root hair cells have an elongated cell membrane which gives a large surface area to maximise water and mineral uptake.
• Nerve cells have:

  • A highly folded cell membrane
  • Lots of mitochondria
  • Lots of ribosomes
• In nerve cells:

  • The highly folded cell membrane allows contact with lots of other cells
  • The mitochondria release energy
  • The ribosomes make and release proteins (neurotransmitters)
• A white blood cell has:

  • Lots of ribosomes
  • A changeable shape of cell membrane
• In white blood cells:

  • The ribosomes make lots of proteins (such as antibodies and enzymes)
  • The membrane can wrap around pathogens to ingest them
• A red blood cell has:

  • No nucleus
  • A biconcave shape