Transport in Cells

• What is diffusion?

  Diffusion is the movement of particles from an area of high concentration to an area of low concentration.
• Where does diffusion happen in?

  Happens in substances where the particles are free to move about such as:

  • Cells
  • Solutions
  • Gases
• The bigger the concentration gradient....

  The faster the diffusion rate
• The higher the temperature....

  The faster the diffusion rate due to particles gaining more kinetic energy, so move around faster.
• What is diffusion in gas?

  When the smell of perfume diffuses (spreading of particles) through the air in the room.
• What are the 3 types of molecules that diffusion takes place?

  • Oxygen - O
  • Carbon dioxide - CO2
  • Urea
• What is diffusion in oxygen?

  • Cells need oxygen for respiration which is carried out by mitochondria.
  • Cells are surrounded by a high concentration of oxygen.
  • Oxygen is then transported in the bloodstream from the lungs
  • Outside the cell = higher concentration of oxygen
  • Inside the cell = lower concentration of oxygen
• What is diffusion in carbon dioxide?


  • The oxygen is used to generate energy in respiration and this produces the waste gas known as carbon dioxide CO2.
  • Inside cell = higher concentration of carbon dioxide.
  • The carbon dioxide moves out of the cell by diffusion.
• What is diffusion by urea?

  • Urea is a waste product produced inside cells.
  • It diffuses out of the cells into the blood plasma and is excreted by the kidneys.
• What are the 3 factors that rate of diffusion is affected?

  • Concentration gradient (difference in concentration)
  • Temperature
  • Surface area of cell membrane
• Ex. Concentration gradient (faster & slower)


  • The greater concentration gradient = the faster the diffusion takes place.
  • The smaller concentration gradient = the slower the diffusion takes place

  
• Ex. Temperature (higher & lower)

  • The higher the temperature = the greater the rate of diffusion (particles have more kinetic energy, so move around faster)
  • The lower the temperature = the slower the rate of diffusion (particles have less kinetic energy, so move around slower)
• Ex. Surface area of the cell membrane (larger & smaller)


  • The larger the surface area of the cell membrane = the greater the rate of diffusion.
  • The smaller the surface area of the cell membrane = the slower the rate of diffusion.
• What is osmosis?

  • Osmosis is the movement of water molecules from an area of higher solute concentration to an area of lower solute concentration across a selectively permeable membrane.
  • Selectively permeable membrane allows some molecules to pass through but not all molecules (allows water, but not sugar).
  • Higher concentration water on the left and lower on the right.
  • The water now diffuses from the left to right. (high to low)

  
• Ex. Osmosis in animal and plant cell

  1. Equal concentration of water inside and outside the cell
  2. More concentration of water outside the cell
  3. More concentration of water inside the cell

  
• What is active transport?


  Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. This requires energy from respiration.