Transport of Substances Flashcards
Another name for the cell membrane
plasma membrane
plasma membrane
phospholipid bilayer that encloses the cell’s cytoplasm and separates the cell from its external environment
phospholipid bilayer
hydrophobic fatty acid tails that are placed interiorly, and exteriorly is the hydrophilic head made of glycerol and phosphate groups
semi-permeable
only allows the entry and exit of certain molecules
cell membrane also contains
cholesterols, channel proteins, integral proteins, glycolipids, glycoproteins and peripheral proteins
Functions of the Cell Membrane
- Gives the cell its structure
- Plays a role and regulates the transport of substances
- Communicates with external environment and other cells (cell signaling)
- Aids in identification of cells based on their external projections
Fluid Mosaic Model
describes the cell membrane, it explains the fluidity given to the cell membrane by the structures found within such as phospholipids, cholesterols, proteins, carbohydrates
Substances transported across the cell membrane
passively or actively
Small molecules such as CO2, water and oxygen can pass through the phospholipid bilayer of the cell membrane Larger molecules such as glucose and amino acids cannot readily pass through
Passive transport
does not require energy
Diffusion: net movement of substances from a high concentration to a low concentration, concentration gradient being the difference in concentration between the two areas, diffusion continues until the concentration in both areas is in equilibrium
Facilitated diffusion: the movement of substances across the cell membrane with the use of special transport proteins embedded in the cell membrane. On the cell membranes of liver cells are glucose transporter 2 (GLUT2) which pumps glucose into liver cells for conversion into glycogen. Specific and nonspecific transporter proteins may be used in this type of transport
Osmosis: it is the diffusion of water across a semi permeable membrane into a concentrated solution. Water can diffuse across the phospholipid bilayer or through aquaporins (water channels)
Differences between Diffusion and Osmosis
- Any type of substance passes through
Only water or solvent passes through - Does not require a semi-permeable membrane Requires a semi-permeable membrane
- Not affected by hydrostatic pressure or turgor pressure
Occurs only in a liquid medium and is affected by hydrostatic and turgor pressure - Movement aims to equalize solute concentration
Movement aims to equalize solvent concentration
Active Transport
process by which substances are moved across a cell membrane against the concentration gradient meaning that substances move from an area of low concentration to an area of high concentration. Energy in the form of ATP is required for this type of transport. This transport process is mainly used to acquire high concentrations of ions, amino acids and glucose according to the cell’s needs
2 forms of active transport
Primary active transport: directly uses energy to transport molecules across a cell membrane such as sodium, magnesium, potassium and calcium. Ion channels or pumps are the facilitators of ion movement; Na/K pump is universal to all animals as it helps to maintain the cell potential (moves 3 sodium out of the cell for every 2 potassium pumped into the cell).
Secondary active transport: this is an example of a coupled transport which utilized the electrochemical potential difference established by the movement of ions for transport. For example hydrogen pumps create an electrochemical gradient which can be used via the electron transport chain for cellular respiration in the mitochondria
Other examples of active transport
Endocytosis and Exocytosis
Take place when the material exiting or being brought into the cell is too large to pass through the plasma membrane. Vesicles are structures formed by the plasma membrane which allows substances to move across it.
Endocytosis
process of capturing a substance or particle into the cell (phagosomes and pinosomes are formed).
plasma membrane encapsulates the desired substance, bringing it into the cell.
involves phagocytosis (cellular eating) and pinocytosis (cellular drinking)
Phagocytosis
occurs when a vesicle is formed by the plasma membrane eating a solid particle, whilst pinocytosis occurs when the plasma membrane creates a channel allowing dissolved substances to enter the cell.
This process can be mediated by receptors which are bound on the plasma membrane surface . Phagocytosis is one of the main processes
used by the immune cells (macrophages, neutrophils) to eliminate pathogens.
