1.4 Membrane Transport Flashcards
Essential idea
Membranes control the composition of cells by passive and active transport
Diffusion
The net movement of particles from an area of high to low concentration facilitated by kinetic energy of particles
Concentration gradient
The difference in concentration between two locations
Factors that influence diffusion rates
- temperature (high = fast)
- length of diffusion path (short = fast)
- surface area (more = fast)
- particle size (small = fast)
- concentration gradient (bigger = fast)
Active transport
Movement of substances across selectively permeable membrane that involves the use of energy (ATP)
Passive transport
The movement of particles through a semi-permeable membrane that does not require energy (e.g diffusion or facilitated diffusion)
Osmosis
The movement of water through a semi-permeable membrane from low solute concentration to high solute concentration
Process of cellular osmosis
Water cannot diffuse through the cell membrane due to it’s size and the presence of the hydrophobic lipid center, instead water travels through the membrane via the integral protein channel aquaporin
Hyper-tonic
A state of osmolarity wherein a cell is plasmalysed due to a high solute concentration and a low water concentration. When cells are hyper-tonic water flows into them
Hypotonic
State of osmolarity wherein the concentration of a solute is lower inside the cell than outside the cell, leading the cell to become turgid
Isotonic
State of osmolarity wherein the cell is in equilibrium and its solute concentration is balanced in and out of the cell, in this state cells are flaccid
Osmolarity
Referring to the concentration of a solution and the number of solute particles per liter of solvent
Facilitated diffusion
The movement of large or polar models that can’t pass through the cell membrane via protein channels. The direction of facilitated diffusion depends on the concentration gradient
Primary active transport
The movement of large and polar molecules against a concentration gradient that requires the use of carrier proteins and energy
Secondary active transport
Transport of molecules using energy derived from primary active transport against concentration gradient
Endocytosis
The process by which a cell taken in an external substances by an inward pouching of the membrane to form a vesicle
Vesicles
Small spherical packages often found near the RER and Golgi apparatus that carry substances in, out and around the cell
Exocytosis
The secretion of a substance from a cell when a vesicle joins with the plasma membrane
Consecutive secretion
Secretion that occurs continually to maintain homeostasis
Regulated secretion
Secretion of substances that occurs in response to a specific trigger
Phagocytosis
Variation of endocytosis where cell takes in solid particles (cell eating)
Pinocytosis
Variation of endocytosis wherein a cell takes in extra cellular fluid (cell drinking)
Process of endocytosis
- vesicle approaches membrane, the membranes of both are phospholipid bilayers meaning they share the same proteins
- membrane fluidity facilitates the fusion of the cell and vesicle membranes
- a temporary intermediate structure is formed when there is a point of contact consisting of a single phospholipid bilayer
- membrane pores opens, allowing the contents of the vesicle to pass through
- vesicle membrane then joins cell membrane
- at no point is either membrane broken
Reasons for membrane transport
- take in molecules like glucose
- expel waste
- cell defense
- cellular homeostasis
Tissue and organ storage
Tissue needs to be kept in saline solution for storage. The osmolarity of the saline solution must be identical to the cytoplasm of the tissue so that no water can be absorbed into or out of the tissue, disrupting the homeostasis
Process of active transport
- molecule or ion enters open part of carrier protein
- carrier protein is activated by ATP
- protein changes shape to allow molecule to travels through protein
- ADP and molecule/ion is expelled from the protein
- protein changes back to original state and process repeats
Process of sodium-potassium ion pump
- pump opens on inside, three sodium ions attach
- ATP triggers protein to reconfigure and expel sodium
- 2 potassium ions attach, triggering the release of the phosphate molecule
- release of phosphate reconfigures protein back to original protein, releasing potassium
- process repeats
- used to maintain resting potential in the cell
