Cells: Exchange Of Materials Across A Membrane Flashcards
Diffusion definition
The movement of particles from a region of high concentration to an area of low concentration down a concentration gradient until evenly spread. The particles that pass through the membrane must be lipid soluble, small and uncharged: it is a passive process
Concentration gradient definition
The path from an area of higher concentration to an area of lower concentration - therefore particles can diffuse down (in this case) or up a concentration gradient
Factors that affect the rate of diffusion
- The concentration gradient
- Surface area (large S.A, increased diffusion)
- Length of diffusion distance
Facilitated diffusion definition
The movement of particles down a concentration gradient, using the kinetic energy of the molecules themselves, passing through a protein channels or carrier proteins. It is still passed down a concentration gradient: it is a passive process
Carrier protein function
- Move large molecules into or out of cells down their concentration gradient
- Specific proteins move specific molecules
- When a molecule is present it will attach to the carrier protein, changing the proteins shape and causing the molecule to be released from the protein to the opposite side of the membrane
Protein channel function
- Form pores for water soluble ions and molecules i.e glucose, amino acids, Na+, K+
- Each channel is selective and remains closed until the specific molecule is present
Osmosis definition
The movement of water molecules from a solution with a higher water potential to a solution with a lower water potential through a partially permeable membrane
Active Transport definition
- The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins: ATP is produced during respiration (metabolic energy)
ATP function in active transport
The molecule used for energy: produced in the mitochondria during respiration, which is when energy is released from glucose. ATP is comprised of a molecule of sugar and 3 phosphate groups bound to it
In primary active transport ADP and Pi combine when energy is released
Carrier proteins change shape using energy from…
…ATP
Co-transporters are…
… A type of carrier proteins change shape, but they bind to two molecules at the same time. A concentration gradient of one molecule is used to move the other molecule against its concentration gradient
Uniport
1 molecule moved in 1 direction
Symport
2 molecules moved in 1 direction
Antiport
2 molecules moved in opposite directions
Chyme
The soup-like mixture made by the digested food when it reaches the small intestine
Facilitated diffusion in the absorption of glucose in the ileum: What happens?
- This occurs by transporting glucose from the lumen of the intestine, into an epithelial cell and then into the blood
- This occurs via different channel and carrier proteins
- When the carbohydrate molecules are first broken down there is a higher concentration of them in the intestinal lumen, so glucose moves down its concentration gradient from the intestinal lumen into the cell, and then into the blood stream
- When equilibrium is reached then indirect active transport takes over
What is the difference between direct and indirect active transport?
Primary (direct) active transport – Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport. Secondary (indirect) active transport – Involves coupling the molecule with another moving along an electrochemical gradient. This uses the downhill flow of an ion to pump some other molecule or ion against the gradient
What is the role of the sodium-potassium pump?
It helps to maintain osmotic equilibrium and membrane potential in cells. The sodium and potassium move against the concentration gradients
Different factors that can affect the rate of glucose absorption
- The concentration of glucose
- temperature
- Amount of protein channels / carrier proteins
- Amount of co-transporter proteins
