Cell Physiology

Lab- 8- Cell Physiology

The membrane of the cell or of various subcellular organelles (chloroplasts, mitochondria) serves as a regulatory structure by controlling the entry or exit of substances into and out of the cell. The membrane may be permeable, impermeable or partially permeable to a given substance.

1- Diffusion— is the net movement of molecules or ions from an area of higher concentration to an area of lower concentration. Think of it as a rebalancing. Diffusion will continue until a state of equilibrium is reached. Rates of diffusion are affected by temperature and the density of the involved molecules among other things. In the leaves, water diffuses out via the stomata into the atmosphere.

2- Osmosis— in plant cells is basically the diffusion of molecules through a semipermeable, or differentially permeable, membrane from a region of higher solute concentration to a region of lower solute concentration. The application of pressure can prevent osmosis from occurring. Osmotic potential is the minimum pressure required to prevent fluid from moving as a result of osmosis. Fluid will enter the cell via osmosis until the osmotic potential is balanced by the cell wall resistance to expansion. Any water gained by osmosis may help keep a plant cell rigid or turgid. The turgor pressure that develops against the cell walls as a result of water entering the cell’s vacuole. This pressure is also referred to as the pressure potential. If there are two cells next to each other of different water potentials, water will move from the cell with the higher water potential to the cell with the lower water potential. Water enters plant cells from the environment via osmosis. Water moves because the overall water potential in the soil is higher than the water potential in the roots and plant parts. If