Diffusion AS Level. Flashcards
Movement into and out of cells.
Define diffusion.
Diffusion is the net movement of molecules from a region of its higher concentration to a region of its lower concentration down a concentration gradient as a result of their random movement.
Where does the energy for diffusion come from?
The energy for diffusion comes from the kinetic energy of the random movement of molecules and ions.
Four factors that affect the rate of diffusion and therefore the movement of molecules through membranes:
- Distance.
- Temperature.
- Surface area.
- Concentration gradients.
How does surface area affect the rate of diffusion?
As the surface increases, the rate of diffusion increases. This is because there is more space available for the substances to diffuse through.
How does distance affect diffusion?
A greater diffusion distance slows the rate of diffusion as molecules must travel further.
How does temperature affect diffusion?
As temperature increases, the rate of diffusion increases. This is because the molecules gain kinetic energy and thus move faster.
How does the concentration gradient affect the rate of diffusion?
As the concentration gradient increases, rate of diffusion increases.
Describe the importance of diffusion of gases and solutes in living organisms.
- obtain many of their requirements.
- get rid of many of their waste products.
- carry out gas exchange for respiration.
SUMMARY - Basically metabolic reactions.
For how long will diffusing particles spread?
The particles spread out until they are evenly spread and have reached an equilibrium.
What is a cell membrane?
The cell membrane is a partially permeable membrane therefore it controls the movement of substances in and out of a cell.
What is simple diffusion with reference to:
- The definition.
- Energy requirements.
- Molecules involved.
- Rate of diffusion.
- Mechanism.
Definition: Movement of molecules from an area of higher concentration to an area of lower concentration directly through the phospholipid bilayer.
Energy Requirement: Does not require energy (passive process).
**Molecules Involved: ** Typically small, nonpolar molecules such as oxygen (O₂), carbon dioxide (CO₂), and lipids.
Rate of Diffusion: Depends on the concentration gradient, membrane permeability, and temperature.
Mechanism: Molecules diffuse freely through the cell membrane without the need for transport proteins.
Simple diffusion does not saturate.
What is facilitated diffusion with reference to:
- The definition.
- Energy requirements.
- Molecules involved.
- Rate of diffusion.
- Mechanism.
Definition: Movement of molecules from an area of higher concentration to an area of lower concentration through a membrane protein.
Energy Requirement: Does not require energy.
Molecules Involved: Typically larger, polar molecules or ions such as glucose, amino acids, and ions (e.g., Na⁺, K⁺, Cl⁻).
Rate of Diffusion: Depends on the concentration gradient, the number of available transport proteins, and the specific binding affinity between the molecule and the transport protein.
Mechanism: Involves specific transport proteins (carrier proteins or channel proteins) that facilitate the movement of molecules across the cell membrane.
Facilitated diffusion can become saturated if all transport proteins are occupied.
Explain surface area to volume ratio.
The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface.
