Saturday, October 11, 2008


Cells are the basic unit of structure and function in living things.

The cell theory states: All living things are composed of cells; cells are the basic unit of structure and function in livings things, all cells are produced from other cells.

Many of the compounds found in living things contain the element carbon. Most compounds that contain carbon are called organic compounds. Carbohydrates, proteins, lipids, and nucleic acids are important groups of organic compounds in living things. Compounds that do not contain the element carbon are called inorganic compounds.

Diffusion is the main method by which small molecules move across the cell membrane. Many cellular processes depend on osmosis. The main difference between passive transport and active transport is that active transport requires the cell to use its own energy while passive transport does not.

All living things obtain energy either directly or indirectly from the energy of sunlight. Photosynthesis is a process in which plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and glucose. During respiration, cells break down simple food molecules such as sugar and release the energy they contain. Fermentation provides energy for cells without using oxygen.

During interphase, the cell grows, makes a copy of its DNA, and prepares to divide into two cells. During mitosis, one copy of the DNA is distributed into each of the two daughter cells. During cytokinesis, the cytoplasm divides, distributing the organelles into each of the two new cells.