Osmosis

• How do oxygen and glucose molecules enter a cell?

  By diffusing down their concentration gradient
• What is osmosis?

  The net movement of water molecules across a partially permeable membrane down a water potential gradient ( i.e. from a region of high water concentration to a region of lower concentration )
• Define the term 'water concentration' .

  The amount of water, as compared to other molecules like sugar and salts ( solutes ) that are dissolved in the water
• What are solutes?

  Dissolved molecules like sugars or salts
• How does water concentration affect osmosis?

  • Higher water concentration means more water molecules
  • Lower water concentration means fewer water molecules
  • Water moves from high to low concentration
• What happens when two beakers have different solute concentrations?

  The beaker with more solute has lower water concentration
• What determines the concentration of water in a solution?

  The proportion of water compared to solutes
• How does the concentration of water inside and outside a cell affect osmosis?

  Water moves from high to low concentration across the membrane
• What is the role of the cell's partially permeable membrane in osmosis?

  It allows water to diffuse while blocking solutes
• What happens to water particles when the outside of a cell has a higher water concentration?

  Water particles diffuse into the cell
• What is the process of osmosis in cells?

  • Water moves from outside to inside the cell
  • Occurs when outside has higher water concentration
  • Driven by concentration gradient of water
• Water molecules will pass through the membrane in both directions during osmosis since the water molecules are consistently moving about randomly
• When there is more water molecules on one side than on the other, there's a steady net flow of water into the region with fewer water molecules
• When there is a solution mixed with water molecules, there is a steady net flow of water into this region and the solution becomes more dilute; the water acts like it's trying to even up the concentration either side of the membrane
• A higher concentration of solutes means there will be a low water concentration and vice versa
• What determines the concentration?

  The proportion of water : solutes
• What does water potential tell you?

  How concentrated a solution is
• What is water potential?

  The potential (likelihood) of water molecules to diffuse out of / into a solution
• If a solution has a high water potential, then it has a high concentration of water molecules and vice versa
• Pure water has the highest water potential
• Dilute solutions contain a high concentration of water
• Osmosis is simply the diffusion of water
• Osmosis is simply the diffusion of what?

  Water
• The cytoplasm of cells is a relatively concentrated solution as it contains a relatively low concentration of water
• If we place a cell in water, the water will move by osmosis from outside the cell to inside the cell.
• In the case of an animal cell, what will happen when water enters the cell?

  The water moving in will cause the cell to expand and it could even burst
• What happens when you place an animal cell in a very concentrated solution?

  The water will move out the cell by osmosis and the cell will shrink
• What will happen if you place a plant cell in water?

  Water will move into the cell by osmosis and the cell will expand however the cell wall prevents the plant from bursting. Instead the cell becomes turgid ( swollen )
• What will happen when you place a plant cell in a very conce solution?

  Water moves out the cell by osmosis, causing the cell to become flaccid ( shrink )
• Plants are supported by turgid cells
• Watering a plant increases the water potential of the soil around it. What does this mean?

  All the plant cells will draw water in by osmosis until they become turgid
• Define the term ' turgor pressure '

  When the plants become turgid, the contents of the cell push against the cell wall. Turgor pressure helps support the plant tissues
• What will happen to a plant if there's no water in the soil and why?

  The plant will begin to wilt because the cells become flaccid however the plant won't completely lose it's shape due to the inelastic cell wall which keeps things in position
• Animal cells don't have cell walls so they're more fragile to their surroundings - e.g. cells can burst if they're surrounded by a solution with a higher water potential than them
• There is usually a higher conc. of water in the soil than inside the plant, so water is drawn in by osmosis