Movement of Substances into and out of cells Flashcards
How can substances move in and out of cells?
All cells are surrounded by a cell membrane which is partially permeable
Molecules can move in and out of cells by diffusion or active transport
Water can move in and out of cells by osmosis.
What is diffusion?
The movement of particles from a high concentration to a lower concentration.
What is osmosis?
Movement of water molecules down a concentration gradient, through a partially permeable membrane.
What is active transport?
Movement of molecules and substances against a concentration gradient (From lower concentration to higher concentration)
Which requires energy from respiration as molecules will not naturally move like this.
Active Transport works by using carrier proteins which are embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against the concentration gradient.
How does surface areas affect the movement across membranes?
The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface
Many cells which are adapted for diffusion have increased surface area in some way – eg root hair cells in plants (which absorb water and mineral ions) and cells lining the ileum in animals (which absorb the products of digestion).
How does distance effect the movement across membranes?
The smaller the distance molecules have to travel the faster transport will occur
This is why blood capillaries and alveoli have walls which are only one cell thick, ensuring the rate of diffusion across them is as fast as possible.
How does temperature affect the movement across membranes?
The higher the temperature, the faster molecules move as they have more energy
This results in more collisions against the cell membrane and therefore a faster rate of movement across them.
How does the concentration gradient effect the movement across membranes?
The greater the difference in concentration either side of the membrane, the faster movement across it will occur
This is because on the side with the higher concentration, more random collisions against the membrane will occur.
How to test for diffusions in a Non-living system?
A crystal (Potassium permanganate) is added to water (solvent)
The potassium permanganate particles will diffuse with solvent particles (move from areas of higher concentration to lower concentration), diffusing throughout the solvent
The potassium permanganate particles will be less concentrated in one place in the end, so the color will not be as deep.
How to test diffusion in a Living system?
During inhalation, oxygen rich air enters alveoli
There is a higher concentration of oxygen in the alveoli than in the blood running past the alveoli
Oxygen will diffuse out of alveoli down the concentration gradient into blood
At the same time, there is a higher concentration of carbon dioxide in the blood (from respiration) than in the alveoli
Carbon dioxide will diffuse out of blood down the concentration gradient into the alveoli
This is how gas exchange takes place in mammals.
How to test for osmosis in a non-living system?
A visking tubing bag (partially permeable) filled with sucrose solution is placed into a beaker of water
A capillary tube (a very thin diameter tube) is placed in the bag and the level of liquid in the tube is observed
The concentration of water particles is higher outside (in the beaker of water) than inside the visking tubing bag
Water molecules will move through the partially permeable membrane of the visking tubing down the water concentration gradient
Over time, the level of liquid in the capillary tube will rise as more water molecules move into the bag due to osmosis
How to test for osmosis in a living system?
The most common osmosis practical involves cutting cylinders of potato and placing them into distilled water and sucrose solutions of increasing concentration
The potato cylinders are weighed before placing into the solutions
They are left in the solutions for 20 – 30 minutes and then removed, dried to remove excess liquid and reweighed
The potato cylinder in the distilled water will have increased its mass the most as there is a greater concentration gradient in this tube between the distilled water (high water concentration) and the potato cells (lower water concentration)
This means more water molecules will move into the potato cells by osmosis, making them turgid and increasing the mass of the cylinder
The potato cylinder in the strongest sucrose concentration will have decreased its mass the most as there is a greater concentration gradient in this tube between the potato cells (higher water concentration) and the sucrose solution (lower water concentration)
This means more water molecules will move out of the potato cells by osmosis, making them flaccid and decreasing the mass of the cylinder
If there is a potato cylinder that has not increased or decreased in mass, it means there was no overall movement of water into or out of the potato cells
This is because the solution that cylinder was in was the same concentration as the solution found in the cytoplasm of the potato cells, so there was no concentration gradient.
What are hypertonic cells?
Greater concentration of water inside the cell than outside the cell.
What is an isotonic cell?
The same concentration of water + solute outside the cell as there is inside the cell.
What are hypotonic cells?
Greater concentration of water outside the cell than inside. Shriveled
