Diffusion, Osmosis And Active Transport Flashcards
What is diffusion?
• spreading out of particles in a gas or any substance in a solution
• net movement is from an area of higher concentration to lower concentration
• takes place because of random movement, particles bump into each other which moves them all around
What happens if there is a big difference in concentration between two areas?
• particles will diffuse quickly
Larger the surface area of the membrane…
… the faster the diffusion rate, because more particles can pass through at once
What molecules can/can’t diffuse through a cell membrane?
Small molecules like oxygen, glucose, amino acids and water
Large molecules like starch and proteins
What is a partially permeable membrane?
A membrane with very small holes in it - only molecules like water can pass through, and bigger molecules (like sucrose) can’t
Key facts about osmosis
• water molecules pass both ways through the membrane during osmosis because the molecules are always moving randomly
• but when then are more water molecules on one side than on the other, there’s a steady net flow of water into the region with less water molecules
• means it will be more dilute
• passive movement
Define osmosis
Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
What is active transport?
When substances need to be absorbed against a concentration gradient, i.e. from a lower to a higher concentration
Root hairs and active transport
• concentration of minerals is usually higher in the root hair cells than in the soil around them, so root hair cells can’t use diffusion
• AT allows the plant to absorb minerals from a very dilute solution against the gradient
What does active transport need?
Energy from respiration
What does hypotonic mean?
If the concentration of solutes in the solution is lower than the internal concentration
What does hypertonic mean?
• if the concentration of solutes in the solution outside the cell is higher than the internal concentration, the solution is hypertonic to the cell
What does isotonic mean?
• if the concentration of solutes in the solution outside the cell is the same as the internal concentration, the solution is isotonic
How does osmosis help the cytoplasm?
• if cell uses up water in its chemical reactions, the cytoplasm becomes more concentrated
• surrounding fluid becomes hypotonic and immediately moves in by osmosis
• if too dilute because more water is made in a reaction, fluid becomes hypertonic and leaves the cell by osmosis
• restores balance
Osmosis in animals - problems
• if solution outside the cell becomes much more dilute, water will move in by osmosis
• cell will swell and burst - therefore some fresh water animals have a special vacuole
• if solution outside the cell becomes much more concentrated (hypertonic), water will move out the cell and cytoplasm becomes too concentrated. Therefore will shrivel up and die
