Diffusion

• What happens to molecules when they are left alone?

  They move about randomly and spread out
• What is the definition of net movement in diffusion?

  the overall movement of the particles
• How does perfume demonstrate diffusion?

  It spreads quickly across the room
• What happens when food coloring is added to water?

  It diffuses until the water is uniform in color
• What is a partially permeable membrane?

  A membrane allowing only some molecules to diffuse
• Which molecules can generally diffuse through cell membranes?

  Small molecules like water and glucose
• Why can't larger molecules diffuse through cell membranes?

  They are too big to fit through
• What type of process is diffusion?

  Passive process that requires no energy
• What is the concentration gradient?

  Difference in concentration between two places
• How does a larger concentration gradient affect diffusion?

  It increases the rate of diffusion
• How does temperature affect the rate of diffusion?

  Higher temperatures increase particle movement
• What is the effect of surface area on diffusion rate?

  Larger surface area increases the rate of diffusion
• What are the three factors that affect the rate of diffusion?

  • Concentration gradient
  • Temperature
  • Surface area
• Why does a larger surface area lead to a higher rate of diffusion?

  More particles can diffuse in and out simultaneously
• What is diffusion?

  The net movement of particles down its concentration gradient (from an area of higher concentration to an area of lower concentration) .
• In which states of matter will diffusion occur and why?

  Liquids and gases because the particles in these substances are free to move about randomly
• What is the function of the cell membrane?

  Holds the cell together and controls which substances move in and out by providing a selective barrier. They also contain receptor molecules that are used for cell communication
• Only small molecules can diffuse through cell membranes. Name 4

  glucose, amino acids, water and oxygen
• Big molecules such as starch and proteins can't diffuse through the cell membrane
• Which three molecules move in and out the cell by diffusion?

  Carbon dioxide, oxygen and urea
• Cells are surrounded by a high concentration of oxygen. Oxygen is transported in the bloodstream from the lungs
• When the oxygen has diffused into the cell, it is used to generate energy in respiration and this produces the waste gas, carbon dioxide which will then diffuse out of the cell
• What is urea?

  A waste product produced inside cells. It diffuses out of the cells, into the blood plasma and then excreted by the kidneys.
• What three factors affect the rate of diffusion?

  Concentration gradients, temperature and surface area to volume ratio
• How does the concentration gradient of a cell affect diffusion?

  A steeper concentration gradient leads to a faster rate of diffusion as there are more molecules in the area of high concentration that can move into the area of lower concentration, whereas a shallow concentration gradient results in a slower rate as there are fewer molecules available to move from the higher concentration area to a lower concentration area
• How does temperature affect the rate of diffusion?

  The higher the temperature, the greater the rate of diffusion because the particles have more kinetic energy, therefore moving much faster + causing more frequent collisions with any barriers they encounter. As the speed of the molecules increases, the particles are more likely to spread out and move from an area of high conc. to an area of low conc.

  If the temp decreases, the kinetic energy of the molecules decreases as well, resulting in slower movement of the molecules and a reduced rate of diffusion.
• How does the surface area to volume ratio affect diffusion?

  When the surface area to volume ratio is high, there is more surface area available for molecules to diffuse across meaning that more molecules can enter/exit a space at the same time, leading to a faster rate of diffusion. When the surface area to volume ratio is low, there is less surface area available compared to the volume. This limits the number of molecules that can diffuse at any given time, resulting in a slower rate of diffusion.
• Define the term 'partially permeable' ?

  Only some molecules can diffuse through such as water, glucose and amino acids
• Diffusion is a passive process - doesn't require any energy from the cell
• Define the term 'concentration gradient' ?

  The difference in concentration between two places
• A larger surface area just means that more particles can fit around the cell's surface
• What is the process called when molecules move across the cell membrane without special proteins?

  Diffusion
• Which types of molecules can pass directly through the lipid bilayer?

  Small, nonpolar molecules
• Can oxygen and carbon dioxide pass through the cell membrane without assistance?

  Yes
• What occurs for larger or polar molecules during diffusion?

  Facilitated diffusion
• What are the specific proteins involved in facilitated diffusion called?

  Channel proteins or carrier proteins
• What do channel proteins and carrier proteins help transport substances down?

  Their concentration gradient