Diffusion Flashcards
What is the definition of diffusion?
the net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
Describe simple diffusion through the phospholipid gaps
Small non-polar and lipid-soluble molecules can pass between the phospholipid molecules in the cell membrane
the fluid movements f the phospholipids create gaps in the membrane and the molecules can slip between
this happens without any energy being available from the cell, by simple diffusion
What can and what cannot pass through the bilayer by simple diffusion (name the examples)
CAN: non-polar and small molecules (such as oxygen, CO2 water, urea and steroid hormones)
CAN’T: ions, glucose and amino acids
What is facilitated diffusion?
Facilitated diffusion describes the process of passive transport (doesn’t require energy expenditure) of molecules across a membrane, with the help of carrier proteins.
Each substance has one specific carrier protein.
Facilitated diffusion usually occurs when a molecule cannot pass through the plasma membrane because of their polarity or charge.
Why is facilitated diffusion a passive process?
because it relies only on the inbuilt motion of the diffusing molecules.
there is no external input of ATP from respiration
What does it mean to say that a channel is gated and why might some channels be gated?
it opens and closes = regulates when molecules can enter and leave
How do Carrier proteins help in facilitated diffusion?
Moves large molecules down the concentration gradient
Proteins that aid in facilitated diffusion shield these molecules from the hydrophobic core of the membrane, allowing molecules to cross the membrane through a pore or channel.
What is the definition of osmosis?
the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane, down a concentration gradient
Describe how you could use your graph to find out the water potential of the leaf cells
Draw a graph with percentage change on the y-axis and concentration on the x-axis, then a curve of best fit.
Where the line meets the x-axis is the water potential of the cell because that is where the leaf cells have not yet gained or lost length = when the solution is isotonic
What is a hypotonic solution
when the solution has a higher water potential (lower conc) than the cell
What is a hypertonic solution
When the solution has a lower water potential (higher conc) than the cell
Describe what happens to cells when they are placed in a hypotonic solution
Water potential is lower in the cell than the solution
so water moves from the solution, from a low concentration to a high concentration,
down a concentration gradient through a selectively permeable membrane and into the cell via osmosis,
causing the cell to burst.
Describe what happens to cells when they are placed in a hypertonic solution
Water potential is higher in the cell than in the solution
so water moves from the cell, from a low concentration to a high concentration
, down the concentration gradient,
through a selectively permeable membrane,
into the solution by osmosis and the cell shrinks
Describe what happens to PLANT cells when they are placed in a hypertonic solution
because the cell has a higher water potential than the solution,
the water molecules move down the concentration gradient from the cell to the solution,
through a selectively permeable membrane
causing the cells to become flaccid and then, if it loses so much water, plasmolysed
What does plasmolysed mean
The cytoplasm of the plant cell removes from the cell wall
What does flaccid mean
when the volume of the vacuole decreases
Describe what happens to PLANT cells when they are placed in a hypotonic solution
it takes up water by osmosis and starts to swell, but the cell wall prevents it from bursting = turgid
Young carrots store sugars in their tissues but, in older carrots, some of this is converted to starch. How would using cylinders of tissue from older carrots affect the results obtained for a sucrose solution of 0.6moldm–3? Give a reason for your answer.
Greater decrease/length smaller;
More water removed;
Greater difference in water potential/cell with higher/less negative water potential;
Starch is insoluble/has no effect on osmosis
What is the definition of active transport?
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
Describe the process of active transport
- Molecules/ions bind to receptors on the carrier protein
- On the inside of the cell: ATP binds to carrier protein = causing it to split into ADP and phosphate molecule
Causes carrier protein molecule to change shape, releasing molecules/ions to the other side of the membrane
Phosphate molecule is released from carrier protein & recombines with ADP to form ATP during respiration
Causes carrier protein to revert to its original shape
When is active transport used?
- when substances need to move into a cell against the concentration gradient
- when a cell needs to move substances in quantities that diffusion would not allow
What are adaptations for the small intestine/ ileum for the absorption for glucose
folded to form Villi (large surface area)
cells lining SI have Microvilli (large surface area)
wall of SI is thin (short diffusion distance)
rich blood supply (maintains concentration gradient)
cells lining SI have transport proteins, enzymes (maltase, lactase, sucrase, didpeptidase) and many mitochondri
Describe the co-transport of sodium ions and glucose
sodium ions are actively transported from the epithelial cells of the SI into the blood via a sodium-potassium pump
lowers the sodium ion concentration in the cell than in the lumen
therefore sodium ions move from the lumen of the SI into the cell, down the concentration gradient trough a co-transport protein
this pulls in glucose and amino acids
therefore glucose and amino acids builds up in the cell and moves into the blood by facilitated diffusion using a carrier protein
Why does glucose need to be co-transported in the small intestine
because there is already a high conc of glucose in the epithelial cell
