B2.1 Diffusion, Osmosis, Active Transport Flashcards
(30 cards)
Define diffusion.
Diffusion is the net movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient.
Why is diffusion a passive process?
Diffusion occurs because of the ordinary motion of the particles, so energy is not transferred.
How do particles in a gas or solution move?
Particles move constantly, and randomly.
When does diffusion stop?
When the concentration of the particles is equal everywhere, the concentration gradient is zero.
Give a example of diffusion in the body.
Oxygen and glucose diffuse into your cells, and carbon dioxide diffuses out.
Which factors affect the rate of diffusion?
- Distance
(Blood capillaries - one cell thick) - Concentration Gradient
- Surface area
(Highly folded small intestine) - (Temperature)
(Higher kinetic energy of particles)
What is osmosis?
Osmosis is the movement of water molecules across a selectively permeable membrane from an area of high water potential to an area of low water potential (down the water potential gradient).
How do water molecules behave around solute molecules?
Water molecules cluster around solute molecules, leaving few free water molecules to diffuse.
What is water potential?
Water potential is the concentration of free water molecules.
What meant by a hypertonic solution?
When a solution has a higher osmotic pull and higher solute concentration (lower water potential) than another solution.
What meant by a hypotonic solution?
When a solution has a lower osmotic pull and lower solute concentration (higher water potential) than another solution.
What meant by an isotonic solution?
As isotonic solution has the same osmolarity, or solute concentration, as another solution.
What happens when a plant cell is placed in a hypotonic solution?
Water moves into the vacuole via osmosis.
Turgor pressure in the cell increases.
The cell becomes turgid/firm.
The cell wall stops cell from bursting.
What is does it mean when a plant cell becomes turgid?
When a plant cell is placed in a hypotonic solution, water enters the vacuole which pushes against the cell wall. The cell becomes firm and swollen.
What happens when a plant cell is placed in an isotonic solution?
There is no net movement of water.
What happens when a plant cell is placed in a hypertonic solution?
Water moves out of the vacuole via osmosis.
Turgor pressure in the cell falls.
The cell becomes flaccid (soft).
The cell contents collapse away from the cell wall.
The cell becomes plasmolysed.
What is plasmolysis?
Plasmolysis is the process of a cell losing water when placed in a hypertonic solution, which causes the shrinking of the plasma membrane away from the cell wall. It is reversible.
What happens when an animal cell is placed in a hypotonic solution?
Water moves into the cell via osmosis.
The cells takes up water and swells.
The cell could also burst (lysis).
What is lysis?
Lysis is the rupture/disintegration of the cell membrane, resulting in the release of cell contents or the subsequent death of the cell.
What happens when an animal cell is placed in an isotonic solution?
There is no net movement of water.
What happens when an animal cell is placed in an hypertonic solution?
Water moves out of the cell via osmosis.
The cells shrinks and crinkles (crenation).
Crenation is mainly observed in RBCs.
What is crenation?
When an animal cell is placed in a hypertonic solution causing too much water to leave the cell by osmosis and the cell to shrink and shrivel.
How are the small intestines adapted to maximise diffusion?
Small intestines
Villi & Microvilli - increases surface area, therefore volume that can be absorbed.
Good blood supply – substances diffuse straight into the bloodstream, maintains concentration gradient.
How are the lungs adapted to maximise diffusion?
Alveoli
- They are very thin - small distance to diffuse over
- They are covered by a network of fine capillaries so diffusion happens straight into the bloodstream, maintains concentration gradient.
- They are moist.
- They have a large combined surface area.
