Definition

Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.

The definition contains three important statements:

1. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
   
2. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
   
3. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.

It does not matter too much which order you put these statements in. Nor does it matter if you write the definition as one sentence or three sentences. All that matters in your exam is that you make all three points when you explain what osmosis is.

Diffusion

Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. Consider two containers of gas A and B separated by a partition. The molecules of both gases are in constant motion and make numerous collisions with the partition. If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules. In time a uniform mixture of A and B molecules will be produced in the container.

The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.

Cell Membrane: A thin layer that surrounds the cell. Cell Wall: A rigid layer that surrounds the cell membrane of a plant cell. Chloroplast: (KLOR-o-plast) A cell structure in which photosynthesis takes place, and it contains the chloropyll. Chlorophyll: (KLOR-a-fil) A green substance in plant cells that helps to make food. Cytoplasm: (SIGH-ta-plaz-em) The jellylike liquid in cells where activities take place. Nucleus: (NEW-kle-us) The dark structure inside the cell that controls the cell's activities and contains material such as DNA. Photosynthesis: (foto-SIN-thi-sis) The process when plants use lights energy to make food.

Cell Membrane: A cell membrane works like a screen. It lets the good things in like nutrients and lets the bad things out like waste. It is liNucleus: The nucleus is the brain of the cell. It controls the cell, and tells it what to do. The nucleus also contains the DNA which is like a blueprint. A blueprint is a plan that people use when they build. A cell's blueprint is the plan the cell uses when it reproduceske a sieve. Cytoplasm: Cytoplasm is the jelly-like part of the cell where the action takes place. It is where the nutrients are used.

Root Hair cell

These cells are found near to the tip of the roots.

Most water enters the root through them.

The thin hair-like extension of each cell gives a large surface for water to enter across.