Transport in cells Flashcards
Define simple diffusion
Simple diffusion is the net movement of a substance from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is reached
What is simple diffusion caused by
Constant random motion of all particles
What are the factors affecting diffusion and how do they affect diffusion
- Concentration gradient =
- Distance /
- Sa:V =
- Particle size /
- Temperature =
- Medium (Fastest in gas, slowest in solid)
What does simple diffusion result in
Equilibrium
Define facilitated diffusion
Facilitated diffusion is the diffusion of ions and water-soluble molecules across the cell membrane using transport proteins, down a concentration gradient
What are the characteristics of facilitated diffusion
- Passive process –> no energy required
- Quantity of transport proteins is a limiting factor
How are channel proteins used in facilitated diffusion
- Provides a hydrophilic channel across the membrane for ions or hydrophilic molecules to enter/leave the cell
- Specific for molecules that can move across membrane
What are the transport proteins used in facilitated diffusion
- Channel proteins
- Carrier proteins
Define water potential
Water potential is the tendency of water to move from one region to another
Define osmosis
Osmosis is the net movement of water molecules across a partially permeable membrane, from a region of higher water potential to a region of lower water potential, down a water potential gradient
How are carrier proteins used in facilitated diffusion
- Diffusing substances bind temporarily to carrier protein
- Causes carrier protein to change shape
- Changes in shape are triggered by the binding and release of substances
What happens when too much water leaves an animal cell
Cell shrinks and crenates
What happens when too much water enters an animal cell
Cell swells and may lyse
What happens when too much water enters a plant cell
Cell swells and become turgid
What happens when too much water leaves a plant cell
Cell shrinks and becomes plasmolysed
Describe what happens when a plant cell is placed in a diluted solution
- Diluted solution has higher water potential than plant cell
- Water moves into plant by osmosis
- Vacuole swells, pushing cytoplasm and cell membrane against cell wall
- Cell become turgid
- Cell does not lyse because of cell wall
Define turgor pressure
Turgor pressure is pressure exerted by the vacuole on the cell wall
Define full plasmolysis
Full plasmolysis is when cell membrane has completely withdrawn from cell wall and this is irreversible
Describe what happens when a plant cell is placed in a concentrated solution
- Concentrated solution has lower water potential than plant cell
- Water moves out of cell by osmosis
- Vacuole decreases in size, pulling cytoplasm and cell membrane away from cell wall
- Cell becomes plasmolysed
- Space between cell wall and cell membrane will be filled with surrounding solution
- Plant starts to wilt
Define active transport
Active transport is the movement of ions or molecules across a 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 molecule in cell
What are the characteristics of active transport
- Allows a cell to maintain internal concentration of solutes regardless of surrounding concentration
- Requires use of specific carrier proteins
Explain how the sodium-potassium pump works
- Animal cell needs to maintain a high concentration of potassium ions and a low concentration of sodium ions
- Cell maintains this by pumping potassium ions in and sodium ions out
- Carrier protein used is the sodium-potassium pump
- ATP required for carrier protein to change shape
- 3 sodium ions are exchanged for 2 potassium ions
Define bulk transport
Bulk transport is the transport of materials into or out of a cell by enclosing it within a vesicle
What are the characteristics of bulk transport
- Allows large molecules or large quantities of molecules to enter/leave a cell without passing through membrane
- Active process as it requires expenditure of energy by ATP molecule in cell
Define endocytosis
Endocytosis is when substances are taken into a cell when ATP provides energy for the inward folding of cell membrane to form vesicles that separate from the membrane
What is one example of endocytosis
Phagocytosis
Define phagocytosis
Phagocytosis is the process of engulfing foreign particles
Define exocytosis
Exocytosis is when ATP provides energy for substances in secretory vesicles to move towards and fuse with cell membrane, releasing vesicle contents outside the cell
Is a membrane required for exocytosis
Yes
What substances move by active transport
Ions and water soluble molecules
What substances move by simple diffusion
Small and uncharged substances
What substances move by facilitated diffusion
Ions and water soluble molecules
Is a membrane required for endocytosis
Yes
Is a membrane required for osmosis
Yes
