Movement of Substances across Membranes
- Created by: Jacqui2
- Created on: 18-05-17 14:14
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- Movement of Substances across Membranes
- Diffusion
- Diffusion is the free passage of molecules (and atoms and ions) from a region of high to low concentration
- The energy comes from the kinetic energy of molecules
- Diffusion in Cells occurs where:
- The plasma membrane is fully permeable to the solute
- Water diffuses across the plasma membrane via membrane proteins called aquaprions, and tiny spaces
- Facilitated Diffusion
- Allows faster movement with the use of proteins to assist or facilitate diffusion
- Channel Protein
- Open spaces and pores across the membrane
- Usually specific for one ion
- Carrier Protein
- Allow larger polar molecules such as sugars and amino acids to diffuse across
- Molecule attaches to the carrier protein at its particular binding site
- Changes shape
- Osmosis
- Diffusion of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane
- Water Potential = Solute Potential + Pressure Potential
- Water Potential
- A weak solution will have a high conc of water molecules - lots of free water molecules
- Free water molecules with lots of kinetic energy
- Pure water has the highest water potential at 0 (water pot at all solutions will be negative)
- A weak solution will have a high conc of water molecules - lots of free water molecules
- Solute Potential
- Conc of dissolved substances
- Value is always negative - solute molecules reduce the no. of free water molecules
- A measure of the reduction in water potential due to the presence of solute molecules
- Pressure Potential
- The pressure of the cell wall develops as water goes into it
- Cell is said to be turgid when no more water can enter the cell - hypotonic solution
- Value is positive
- The pressure exerted on the cell contents by the cell wall and cell membrane
- Only present in plant cells due to the presence of a cell wall
- The pressure of the cell wall develops as water goes into it
- Water Potential
- Plasmolysis
- When the water potential is higher in the plant cell than an external solution - hypertonic solution
- The cell surface membrane starts to shrink away from the cell wall as water leaves the cell
- When pressure pot. is zero the cell is flaccid (point of incipient plasmolysis
- When 50% of cells are plasmolysed it is said to be at incipient plasmolysis
- When pressure pot. is zero the cell is flaccid (point of incipient plasmolysis
- As more water leaves the cell the membrane becomes completely detached and the cell is plasmolysed
- Active Transport
- The uptake of molecules or ions against a concentration gradient using energy from respiration
- Respiration rate can be affected by:(controlled by enzymes)
- Temperature
- Oxygen conc
- Presence of poisons
- Respiration rate can be affected by:(controlled by enzymes)
- Relies upon specific carrier proteins - needs an input of energy, provided by ATP
- Molecule or ion binds with a specific carrier protein (binding site)
- Undergoes a change in shape which carries molecule to the other side of the membrane
- Molecules or ion is released and protein reverts to its original shape
- Undergoes a change in shape which carries molecule to the other side of the membrane
- Molecule or ion binds with a specific carrier protein (binding site)
- Processes that involve active transport
- Nerve impulse transmission
- Muscle contraction
- Absorption of mineral salts by plat roots (transpiration)
- Excretion of urea by the kidney
- The uptake of molecules or ions against a concentration gradient using energy from respiration
- Endocytosis and Exocytosis
- The cell can transport large quantities of material into or out of the cell
- Endocytosis
- Passage of material into the cell
- Phagocytosis
- Solid material
- Lysosomes fuse with vesicle
- Enzymes digest the material and the products are absorbed into the cytoplasm
- Phagocytes remove bacteria and cell debris by phagocytosis
- Pinocytosis
- Liquid material
- Vesicles formed during, can be extremely small
- Phagocytosis
- Passage of material into the cell
- Exocytosis
- Passage of material out of the cell
- Useful secretion, as in the case of digestive enzymes, hormones or mucus
- Passage of material out of the cell
- Diffusion
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