movement of substance

• Diffusion


  The net movement of molecules from a region of their higher concentration to a region of their lower concentration, down a concentration gradient
• Diffusion is an essential process to both plants and humans, and is involved in many processes
• Absorption of mineral salts into the root hair cell

  1. Compare concentration

  2. Diffusion

  3. Direction of movement of particles
• Gaseous exchange (of O2 and CO2) between alveolus and blood

  1. Compare concentration

  2. Diffusion

  3. Direction of movement of particles
• Gaseous exchange (of O2 and CO2) between roots/leaves and environment

  1. Describe and explain gaseous exchange through the stoma

  2. Describe and explain gaseous exchange in the roots
• Diffusion refers to the net movement of particles down a concentration gradient
• At equilibrium (i.e. no concentration gradient), there is no net movement, but individual particles will continue to move
• Factors affecting rate of diffusion

  • The higher the temperature, the higher the rate of diffusion
  • The shorter the diffusion distance, the higher the rate of diffusion
  • The steeper the concentration gradient, the higher the rate of diffusion
  • The greater the surface area to volume ratio, the higher the rate of diffusion
• The greater the surface area is to volume ratio, the higher the rate of diffusion
• Ways to increase surface area and exposure to the environment

  • Small size
  • Modified cell surfaces
• Osmosis


  The net movement of water molecules from a region of higher water potential to a region of lower water potential down a water potential gradient, through a partially-permeable membrane
• Investigating osmosis using the visking tubing

  1. Compare water potential

  2. Osmosis

  3. Direction of movement of water molecules

  4. Effect
• Blood cells in different types of solution

  1. Compare water potential

  2. Osmosis

  3. Direction of movement of water molecules

  4. Effect
• Plasmolysis in onion cells

  1. Compare water potential

  2. Osmosis

  3. Direction of movement of water molecules

  4. Effect
• Turgor


  • Maintains the shape of soft tissues in plants
  • Keeps herbaceous (non-woody) plants firm and upright
  • Loss of turgidity causes the plant to wilt
  • Changes in turgor also cause the movements of some plant parts, e.g. opening and closing of stomata
• At 0.23 M, the potato tissue did not show any change in mass. No net movement of water in and out of the cells. Concentration of potato and sucrose solution are the same
• Active transport


  The process in which energy is used to move substances from a region of their lower concentration to a region of their higher concentration, against a concentration gradient
• Ion uptake by root hair cells

  1. Mineral salts are essential for plants to carry out cellular activities like photosynthesis

  2. If there is a lower concentration of mineral salts in the soil compared to the root hair cells, and diffusion cannot occur, the plant will get mineral salts from the soil via active transport
• Glucose uptake by cells in the villi

  1. Many mitochondria to release energy for active transport

  2. Water and ions are actively transported across cell membranes to cause certain plant movements
• Through the processes of diffusion, osmosis and active transport, the internal environments of living organisms are kept constant to provide the optimal conditions for cells to survive
• Gaseous exchange in plants and animals

  • Nutrients uptake in plants and animals
  • Removal of waste substances such as urea and carbon dioxide out of body cells
  • Water absorption by root hair cells
  • Ion uptake by root hairs and uptake of glucose by cells in the villi
• Pinocytosis


  Small molecules move across the cell surface membrane
• Phagocytosis


  Large particles move across the partially permeable cell surface membrane
• Cell membrane is 'fluid' and can break up and re-join easily
• Vesicle-mediated transport


  1. Vesicle inside cell

  2. Fuses with cell membrane

  3. Expels its contents out of the cell
• Vesicle-mediated transport


  • Secretion of insulin out of cell
  • Transport of cholesterol in and out of animal cells
• Guard cells


  Cells that regulate the opening and closing of the stoma on the surface of leaves, allowing for gas exchange between the plant and the environment.
• Turgor pressure


  The water content of a cell, which can change due to changes in the water potential of the cell's surroundings. An increase in turgor pressure can cause the guard cells to swell, opening the stoma, while a decrease in turgor pressure can cause the guard cells to shrink, closing the stoma.