Cell structure

• Key areas


  • Cell Structure
  • Transport across cell membranes
  • DNA and the production of proteins
  • Proteins
  • Genetic engineering
  • Respiration
• Living things (organisms) are made of cells. Different kingdoms of living things are made from different types of cells. There are 4 cell types you need to remember.
• Cell ultrastructure


  All the parts that make up a cell
• Cell wall


  Structure surrounding a cell that protects and helps the cell to keep its shape
• Cell membrane


  Controls what enters and leaves the cell (it is selectively permeable)
• Selectively permeable


  Only certain molecules can pass through
• Chloroplast


  Small green discs in plant cells where photosynthesis takes place
• Cytoplasm


  The jelly inside a cell where the organelles are found
• Nucleus


  Contains genetic information (DNA)
• Ribosome


  Site of protein synthesis
• Mitochondria


  Site of aerobic respiration
• Organelle


  Any part of the cell found in the cytoplasm

  
• Fungal cell


  The cell type found in fungi
• Cellulose


  The chemical that makes up plant cell walls
• Vacuole


  A structure found in the cytoplasm that contains cell sap in plants
• Plant cell walls are made from cellulose. The cell walls in fungal cells and bacterial cells are made from different chemicals.
• Yeast cells


  An example of a fungus. They are similar to plant and animal cells but they have a different cell wall structure.
• Bacterial cells


  Do not have a nucleus. Their DNA floats around in the cytoplasm as a large circular DNA molecule. They also lack a number of other organelles found in the other cell types. Their cell walls are also different to plant and yeast cells.

  
• Both cells have cell walls, genetic material and ribosomes. Plant cells have mitochondria and chloroplasts, whereas bacterial cells have neither of these.

  
• Cell membrane


  The structure that controls movement of molecules into and out of a cell
• Phospholipids


  Molecules that make up the cell membrane with proteins
• Selectively permeable


  Allows some molecules through but not others
• Passive transport


  Movement of molecules that does not require energy
• Concentration gradient


  When there is a difference in concentration on each side of a cell membrane
• Diffusion


  The movement of molecules from higher concentration to lower concentration, down a concentration gradient
• Osmosis


  The movement of water from higher water concentration to lower water concentration, through a selectively permeable membrane
• Turgid


  A plant cell that has filled up with water
• Plasmolysed


  A plant cell that has shrunk as water moved out of it
• Active transport


  The movement of molecules and ions against the concentration gradient that requires energy
• The cell membrane consists of phospholipids and proteins and is selectively permeable.
• Osmosis is the movement of water molecules from a higher water concentration to a lower water concentration, through a selectively permeable membrane.
• Osmosis in animal cells


  Too much water in = burst, Too much water out = shrink
• Osmosis in plant cells

  Too much water in = turgid, Too much water out = plasmolysed
• Active transport is the movement of molecules against the concentration gradient. This requires energy.
• Proteins in the cell membrane help to pump the molecules to where they are needed.
• Differences between active and passive transport


  • Requires energy / No energy required
  • Against the concentration gradient / Molecules move down the concentration gradient
• Types of passive transport


  • Diffusion
  • Osmosis
• Structure present in a plant cell that prevents it from bursting when full of water

  Cell wall
• Osmosis


  A passive process
• What will happen to the model cell during the experiment


  1. Cell will gain mass

  2. Due to osmosis

  3. Water will move from higher water concentration outside to lower water concentration inside

  4. Water molecules small enough to pass across selectively permeable membrane