4. Transport in Cells Flashcards
Simple Diffusion
Definition + Energy requirement
Simple diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration, down a concentration gradient, until equilibrium is reached, caused by the constant random motion of particles
Passive process - no ATP is required
6 Factors Affecting Rate of Diffusion
- Concentration gradient: Greater difference in concentration (steeper concentration gradient) => Faster rate of diffusion
- Distance over which diffusion occurs: Shorter distance => Faster rate of diffusion
- Surface area to volume ratio: Larger surface area to volume ratio => Faster rate of diffusion
- Size/mass of particle: Smaller size/mass of particle => Faster rate of diffusion
- Temperature: Higher temperature => Faster rate of diffusion
- Medium: Rate of diffusion fastest in gas, slowest in solids
Facilitated Diffusion
Definition + Energy requirement
Facilitated diffusion is the diffusion of ions and water-soluble/hydrophilic molecules across the cell membrane using two types of transport proteins, channel proteins or carrier proteins, down a concentration gradient.
Passive process - no ATP required
Rate of facilitated diffusion is affected by the number of channel proteins or carrier proteins available.
Channel Proteins
How does it facilitate diffusion?
Channel proteins provide a hydrophilic channel across the cell membrane for ions and hydrophillic molecules to enter or leave the cell.
Carrier Proteins
How does it facilitate diffusion?
Diffusing substances bind temporarily to the carrier protein, causing it to change shape to transport the substances across the membrane.
Osmosis
Definition + Energy requirement
Osmosis is the net movement of water molecules from a solution of higher water potential to a solution of lower water potential, down a water potential gradient, through a partially permeable membrane.
Passive process - no ATP required
How does the surrounding solution affect the state of an animal cell?
Placed in a dilute solution + Placed in a concentrated solution
Placed in a dilute solution:
1. Dilute solution has a higher water potential than cell sap
2. Water enters animal cell by osmosis
3. Cell swells and may burst (cell lysis)
Placed in a concentrated solution:
1. Concentrated solution has a lower water potential than cell sap
2. Water leaves animal cell by osmosis
3. Cell shrinks and crenates
How does the surrounding solution affect the state of a plant cell?
Placed in a dilute solution + Placed in a concentrated solution
Placed in dilute solution:
- Dilute solutution has a higher water potential than cell sap
- Water enters plant cell by osmosis
- Vacuole swells, pushes cytoplasm and cell membrane against the cell wall
- Cell becomes turgid (does not lyse because of the rigid cell wall)
- Pressure exerted by the vacuole on the cell wall is known as turgor pressure
- Keeps plant firm and upright, leaves spread out more, opens stomata => increases rate of photosynthesis
Placed in concentrated solution:
- Concentrated solution has a lower water potential than cell sap
- Water leaves the plant cell by osmosis
- Vacuole decreases in volume and size, and the cytoplasm and cell membrane pull away from the cell wall
- Cell becomes plasmolysed (reversible if full plasmolysis is not reached)
- The space between the cell wall and cell membrane will be filled with the surrounding solution
- Plant starts to wilt as turgor pressure in the plant cell decreases => decreases rate of photosynthesis
Full plasmolysis is reached when the cell membrane has completely withdrawn from the cell wall. This process is irreversible.
Active Transport
Definition + Energy requirement
Active transport is the movement of ions or molecules across the cell membrane from a region of lower concentration to a region of higher concentration, against a concentration gradient, with the expenditure of energy from ATP by the cell.
It requires the use of specific carrier proteins which require energy.
Active process - ATP is required
Importance of Active Transport
Importance of active transport:
- It allows cells to take up nutrients/ions even when the concentrations outside the cells are lower than inside of the cells.
- It allows cells to get rid of waste products even when the concentrations outside the cells are higher than inside the cells.
Sodium-Potassium Pump
What it is + Function
The sodium–potassium pump is a carrier protein found in the cell membrane of all animal cells.
Function:
An animal cell needs to maintain a much higher concentration of K+ and a much lower concentration of Na+ ions as compared to its surroundings.
The cell maintains this using active transport.
The sodium-potassium pump is used, to pump sodium ions out of the cell and potassium ions into the cell.
ATP is required for the carrier protein to change its shape.
3 sodium ions are pumped out in exchange for 2 potassium ions pumped in.
Bulk Transport
Definition + Types + Energy requirement
Bulk transport is the transport of materials into or out of the cell by enclosing them within a vesicle.
- It allows large molecules or large quantities of molecules to enter or leave a cell without passing through the membrane
2 types: endocytosis & exocytosis
Active process - ATP is required to provide energy
Endocytosis
What it is + When it occurs + Energy requirement + Example
Endocytosis is a form of bulk transport
- Occurs when substances are taken into the cells by the inward folding of the cell membrane to form vesicles that separate from the membrane
Active process - ATP is required to provide energy
Example: Phagocytosis where there is formation of pseudopodia
Exocytosis
What it is + When it occurs + Energy requirement + Examples
Exocytosis is a form of bulk transport
- Occurs when substances in secretory vesicles move towards and fuse with the cell membrane, releasing the contents of the vesicle out of the cell into the surroundings
Active process - ATP is required to provide energy
Examples: Secretion of insulin by pancreatic cells & release of neurotransmitters by neurones
