A mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cell. These organelles range from 0.5–10 mi...

Structure A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes, however, hav...

Cristae The inner mitochondrial membrane is compartmentalized into numerous cristae, which expand the surface area of the inner mitochondria...

Structure of cell membrane The cell membrane (also called the plasma membrane, plasmalemma, or phospholipid bilayer) is the interface betwe...

The phospholipids form a thin, flexible sheet, while the proteins "float" in the phospholipid sheet like icebergs, and the carbohy...

1. Lipid Diffusion (or simple diffusion) A few substances can diffuse directly through the lipid bilayer part of the membrane. The only sub...

2. Osmosis Osmosis is the diffusion of water across a membrane. It is in fact just normal lipid diffusion, but since water is so important ...

Osmotic Pressure (OP). This is an older term used to describe osmosis. The more concentrated a solution, the higher the osmotic pressure. I...

These are problems that living cells face all the time. For example: Simple animal cells (protozoans) in fresh water habitats are surrounded...

3. Passive Transport (or facilitated diffusion) Passive transport is the transport of substances across a membrane by a trans-membrane prot...

4. Active Transport (or Pumping) Active transport is the pumping of substances across a membrane by a trans-membrane protein pump molecule....

The Na+K+ pump is a complex pump, simultaneously pumping three sodium ions out of the cell and two potassium ions into the cell for each mol...

5. Vesicles The processes described so far only apply to small molecules. Large molecules (such as proteins, polysaccharides and nucleotides...

Shape There exist cells which have a variable shape, such as the leukocytes, and some connective tissue cells and cells with a stable shape...

Figure 1: Cell shapes

Volume The volume of the cell is variable and oscillates within broad limits. In plants and in animals, cells are found which are visible to...

Figure 2: Size of cells