KA 2: Transport across Cell Membranes

• What are solids, liquids, and gases made up of?

  Atoms or molecules
• How are molecules arranged in solids?

  Molecules are close together and ordered
• How do molecules behave in liquids compared to solids?

  Molecules are close but not ordered and can move freely
• What is the arrangement of molecules in gases?

  Molecules are far apart and move freely
• What is diffusion?

  Movement of molecules down a concentration gradient
• Is diffusion an active or passive process?

  Diffusion is a passive process
• What happens to molecules during diffusion over time?

  Molecules spread evenly in a given area
• Why do living organisms depend on diffusion?

  For movement of molecules into and out of cells
• How does oxygen enter animal cells?

  By diffusion
• What diffuses out of animal cells?

  Carbon dioxide
• What soluble food passes into cells by diffusion?

  Glucose
• What controls the movement of molecules into and out of cells?

  The cell membrane
• What determines the passage of molecules through the cell membrane?

  The size of the molecule
• Can glucose pass through the cell membrane?

  Yes, glucose can pass through
• Can starch pass through the cell membrane?

  No, starch cannot pass through
• What is osmosis?

  Movement of water through a selectively permeable membrane
• How does osmosis occur in terms of water concentration?

  From higher water concentration to lower concentration
• Is osmosis an active or passive process?

  Osmosis is a passive process
• What are selectively permeable membranes?

  Membranes allowing small but not large molecules
• What are examples of selectively permeable membranes in cells?

  Cell membrane and vacuole membrane
• What is Visking tubing?

  An artificial selectively permeable membrane
• What happens to plant cells in distilled water?

  Water enters cells by osmosis, causing turgidity
• What is a turgid plant cell?

  A cell that swells due to water intake
• How do turgid cells support plants?

  They provide structural support
• What occurs during plasmolysis in plant cells?

  Cells lose water and shrink
• What happens to the cell membrane during plasmolysis?

  It gets pulled towards the inside of the cell
• How can plasmolysed cells return to a turgid state?

  By placing them in distilled water
• What happens to red blood cells in distilled water?

  They swell and may burst
• What occurs when red blood cells are placed in strong sucrose solution?

  They lose water and shrink
• What is the composition of the cell membrane?

  Phospholipids and proteins
• What is active transport?

  Movement of molecules against the concentration gradient
• What does active transport require?

  Energy to move molecules
• What factors affect active transport?

  Oxygen concentration, glucose concentration, temperature
• What role do proteins in the cell membrane play in active transport?

  They form channels for ions and molecules