Cell structure and transport -B1

• Define active transport: The movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient across a partially permeable membrane
• Define diffusion: The movement of particles from an area of high concentration to an area of low concentration. down a concentration gradient
• Define osmosis: The movement of water molecules from a region of high water potential to a region of low water potential down a water potential gradient across a partially permeable membrane
• Why would a cell have a folded cell membrane ?

  Increased surface area - to increase rate of diffusion
• What is the purpose of lots of mitochondria in a cell ?

  aerobic respiration - to release energy for active transport
• What does a hypertonic solution cause?


  Causes osmosis out of the cell Shrinking (plasmolysis) - in a plant cell

  shrivelling (flaccid ) - in an animal cell
• What is a hypotonic solution?

  A solution with a lower water potential than the cell
• What is a hypertonic solution?

  A solution with a higher concentration of solutes than the cell
• What does a hypotonic solution cause ?


  causes osmosis into the cell

  swelling (turgid) - in a plant cell due to cell wall

  bursting (lysis) - in an animal cell
• Electron microscope advantages:

  • has greater magnification
  • can see details much more clearly
  • can see much smaller objects
  • has a greater resolution
• Light microscope advantages:

  • its portable
  • it’s cheaper
  • live samples can be viewed
• Why is iodine used on microscope slides?


  as a stain to make organelles visable
• What does the lowest magnification allow for on a light microscope?


  largest field of vision

  the most of the sample to be visible
• Ways cells can specialise:

  • change number of a particular organelle
  • change cell shape - to increase surface area
  • change some of the contents of the cell
• How do you convert from millimetres to micrometers ?


  Multiply by 1000.
• How do you convert from micro meters to millimetres?


  divide by 1000
• How do you avoid air bubbles when preparing microscope slides?


  use a mounted needle
• What can be seen with a normal light microscope?


  Cells and possibly the nucleus
• What advantage does an electron microscope have over a light microscope?

  It allows us to see finer details of organelles
• How can you calculate the actual size of a cell using a microscope?

  By dividing the image size by the magnification
• What are the two main groups of cells?

  Eukaryotic cells and prokaryotic cells
• What is a characteristic of eukaryotic cells?

  They have a nucleus containing DNA
• Where is DNA found in prokaryotic cells?

  In a ring called a plasmid
• What is the function of the cell membrane?

  It keeps everything inside the cell and is semi-permeable
• What do plant cells and most bacteria have that provides a rigid structure?

  A cell wall made of cellulose
• What is the cytoplasm?

  The liquid that makes up the cell where most chemical reactions occur
• Where does respiration take place in a cell?

  In the mitochondria
• What is the role of ribosomes in a cell?

  They are where proteins are assembled or synthesized
• What do chloroplasts contain and what is their function?

  They contain chlorophyll and are where photosynthesis takes place
• What is a permanent vacuole in plant cells used for?

  To store sap
• How do bacteria multiply?

  By binary fission
• What is the purpose of using aseptic technique in culturing bacteria?

  To prevent contamination of the culture
• What is the role of the flame when lifting the lid of the agar dish?

  It causes microbes in the air to move away and destroys them
• At what temperature do we incubate bacterial cultures?

  25°C
• Where are stem cells found in humans and animals?

  In embryos and bone marrow
• How can stem cells be used in medicine?

  To combat conditions like diabetes and paralysis
• What is diffusion?

  The movement of molecules from an area of high concentration to low concentration
• What is osmosis specifically?

  The diffusion of water across a semi-permeable membrane
• What happens to a cell in a hypertonic solution?

  Water moves out of the cell, decreasing its mass
• What factors can increase the rate of diffusion and osmosis?

  Increasing concentration difference, temperature, or surface area