An introduction to osmosis.

Authors Avatar

Science Coursework

Osmosis

Plan

An introduction to osmosis.

The movement of water molecules from a high concentration of water molecules to a lower concentration of water molecules through a partially permeable membrane is called Osmosis.

Under normal conditions, the concentration of water molecules and salts is the same in both cells and plasma. After sweating, water and salts are lost from the plasma and there is a lower concentration of water in the plasma than inside the cells. Water molecules therefore diffuse out from the cells through the cell membrane. We call a membrane like this partially permeable. Water molecules are small, so they pass through the membrane much more easily than salts.

Diagram:

There are several different types of cells in xylem but the one that transports most water and minerals to the leaves are called xylem vessels. These are formed from dead xylem cells whose end walls have broken down. These form continuous tubes. The xylem vessels act like pipes in transporting water up the plant. Wood is made up of xylem cells; most xylem cells have substances in their walls which strengthen the cells. This is why wood is a strong material.  

Osmosis in plants

The root hairs together increase the surface area of the root. This enables water and mineral ions to be absorbed more quickly. The soil solution is water containing low concentrations of mineral ions. This is a dilute solution. The cytoplasm and the vacuole…

Stacey Owen

Candidate no: 0126

Hampton Community College 

of the root hair cell contain a higher concentration of mineral ions, than the soil solution. Water molecules move from the soil solution to the cytoplasm and vacuole of the cell by osmosis.

Leaves normally contain a lot of water, so water will evaporate from them in exactly the same way that a wet shirt dries on a washing line. Evaporation of water from a leaf surface is called transpiration. If plants lose too much water by transpiration, the leaves droop. This drooping is called wilting. Most of the cells in the leaf are supported by being full of water. If the vacuoles lose water, the plant cells become floppy rather than rigid, severe wilting can kill the plant. To reduce the possibility of wilting most plants have a layer of wax covering the surface of the leaf. This layer of wax is called the cuticle. All the plant cells use osmosis to keep their cells turgid (swollen up with water) to give physical structure to a plant cells body.

This picture shows how water is absorbed by a plant.

Osmosis in humans

The kidney is made up of a very large number of tubules. Each tubule is divided into regions where different processes occur.

  • Filtration is brought about by blood pressure. Because the walls of the kidney tubule are partially permeable only small molecules such as water, glucose, urea and ions are filtered.
  • Reabsorption of the filtered glucose and ions from the filtrate into the blood is by active transport.
  • Most of the urea is not reabsorbed.

This diagram below shows how urea is made and when osmosis is used.

Stacey Owen

Join now!

Candidate no: 0126

Hampton Community College

Osmosis in animals.

Cell membranes behave very like visking tubing. They will let some substances pass through them, but not others. They are selectively permeable membranes.

There is always cytoplasm on one side of any cell membrane. Cytoplasm is a solution of proteins and other substances in water. There is usually a solution on the other side of the membrane too. Inside large animals, cells are surrounded by tissue fluid. In the soil, the roots of plants are often surrounded by a film of water. Single-celled organisms such as amoeba are also surrounded ...

This is a preview of the whole essay