Movement of substances (Unit-2)

• Diffusion and Osmosis are passive transport because there is no expenditure of energy.
• Active transport is a process of moving substances from one place to another which require energy to take place.
• Diffusion is net movement of a substance from a region where it is in higher concentration to a region where it is in lower concentration.
• The rate of diffusion is fastest in gases and slowest in solids.
• The diffusion of one type of substances is not affected by the concentration of the other types.

  e.g. oxygen and carbon dioxide diffuse according to their own differences in concentrations between two regions.
• Diffusion in humans

  • Diffusion takes place during gaseous exchange in lungs.

  1. Carbon dioxide diffuses out of blood into lungs.
  2. Oxygen diffuses into blood from the lungs.

  • The digested food nutrients enter the bloodstream from the lumen of the small intestine by diffusion.
  • When a person's suffers certain diseases, such as stroke or cancer, there will be some changes in diffusion patterns of water in body tissues. Therefore, modern technology is used to generate images to detect these changes. So that appropriate actions can be done to tackle these diseases.
• Osmosis is a net movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane.
• A semi-permeable membrane is a membrane that only allows certain substances to pass through it.
• A semi-permeable membrane restricts the movement of substances across it by their size. Only substances with particle size smaller than the pores of the membrane can pass through it.
• Cell membrane in plant and animal cells are the natural semi-permeable membrane. In laboratory, Viking Tubing and cellophane bag act as the artificial semi-permeable membrane.
• Osmosis causes the living cells to change its size and mass.
• Active transport is the process in which energy is used to move a substance from a region of lower concentration to a region of higher concentration.
• Root hair cells absorb mineral salts from soil using active transport when the mineral salt becomes scare in soil.
• In humans, absorption of glucose into the bloodstream involves diffusion as well as active transport.
• The smaller the size of an object, the greater the surface area to volume ratio, hence the faster the movement of substances in and out of the object. The smaller the size of the cell, larger the ratio of surface area to volume.