Biology

• Eukaryotic cells


  Have genetic material (DNA) that forms a nucleus
• Plant cell


  • Have chloroplasts
  • Have a cell wall
• Comparing sub-cellular structures


  • Animal cell
  • Plant cell
  • Prokaryotic cell
• Prokaryotic cells (Bacteria)


  • Single-celled
  • Have a single loop of DNA
  • Have plasmids
  • Smaller than eukaryotic cells
• Structures in cells


  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Cell wall
  • DNA
  • Plasmid
  • Chloroplasts
  • Permanent vacuole
• Light microscope


  • Uses light to form images
  • Relatively cheap
  • Low magnification
  • Low resolution
• Electron microscope


  • Uses a beam of electrons to form images
  • Expensive
  • High magnification
  • High resolution
• To calculate the magnification of an image

  Image size / Actual size
• Electron microscopes allow you to see sub-cellular structures that cannot be seen with a light microscope
• Cells in animals and plants have specialised functions at different stages of development
• Specialized cells


  Cells in animals and plants that differentiate to form different types of cells. Most animal cells differentiate by stage of development, whereas a plant's cells differentiate throughout
• Functions of specialized cells

  • Transport oxygen around the body
  • Contract and relax to allow movement
  • Carry electrical impulses around the body
  • Absorb mineral ions and water from the soil
  • Enable photosynthesis in the leaf
• Nerve cell


  • Adaptations: contain many mitochondria to release energy from respiration, have a large surface area-to-volume ratio, contain haemoglobin that binds to oxygen molecules, have a flat bi-concave disc shape, contain proteins that can contract to make the cells shorter, contain a lot of endoplasmic reticulum to release energy from respiration, have branched endings called dendrites to make connections with other neurones or effectors, have a myelin sheath to increase the transmission speed of electrical impulses
• Root hair cell


  • Adaptations: have a long projection to speed up the absorption of water and mineral ions by increasing the surface area of the cell, contain lots of mitochondria to release energy for the active transport of mineral ions from the cell
• Leaf cell


  • Adaptations: contain lots of chloroplasts containing chlorophyll to absorb light energy, located at the top surface of the leaf where it can absorb the most light energy
• Cell membrane


  Surrounds the cell and controls what goes in and out
• Eukaryotic


  Cells that have a true nucleus and membrane-bound organelles
• Cell wall


  Provides structural support and protection for plant cells
• Magnification


  The number of times an image is enlarged
• Chloroplast


  Organelle in plant cells that contains chlorophyll and is the site of photosynthesis
• Chromosome


  Structures in the nucleus that contain DNA
• Cytoplasm


  Jelly-like substance inside the cell where chemical reactions take place
• Mitochondria


  Organelles that release energy from food in the process of respiration
• Nucleus


  Controls the activities of the cell and contains the cell's genetic material
• Plasmid


  Small, circular DNA molecules found in some bacteria and used in genetic engineering
• Prokaryotic


  Cells that do not have a true nucleus or membrane-bound organelles
• Resolution


  The ability of a microscope to distinguish between two closely spaced objects
• DNA


  The genetic material that carries the instructions for the development and functioning of living organisms
• Permanent vacuole


  Large sacs in plant cells that store water, waste products, and other substances
• Ribosome


  Organelles in the cell where protein synthesis takes place
• B1 Knowledge
• Examples


  • Diffusion, osmosis, active transport
• Diffusion


  The movement of particles from an area of higher concentration to an area of lower concentration
• Osmosis


  The movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane
• Active transport


  The movement of particles against a concentration gradient, using energy from respiration
• Factors that affect the rate of diffusion
• Adaptations for exchanging substances
• Examples of exchange surfaces

  • Villi in the small intestine, alveoli in the lungs, fish gills, root hair cells
• Concentration gradient

  The difference in concentration of a substance between two areas
• Partially permeable membrane

  A membrane that allows some substances to pass through but not others