Cell organic matter: lipids.

Lipids are an extensive group of fat-like substances (esters of fatty acids and trihydric alcohol of glycerol), insoluble in water. Lipids include fats, waxes, phospholipids, and steroids (lipids that do not contain fatty acids).

Lipids are made up of hydrogen, oxygen and carbon atoms.

Lipids are present in all cells without exception, but their content in different cells varies greatly (from 2–3 to 50–90%).

Lipids can form complex compounds with substances of other classes, such as proteins (lipoproteins) and carbohydrates (glycolipids).

Lipid functions:

• storing – fats are the main form of lipid storage in the cell.
• Energy – half of the energy consumed by the cells of vertebrates at rest is formed as a result of the oxidation of fats (when oxidized, they provide more than twice as much energy as carbohydrates).
• Fats are also used as a source of water (when 1 g of fat is oxidized, more than 1 g of water is formed).
• Protective – the subcutaneous fat layer protects the body from mechanical damage.
• Structural – phospholipids are part of cell membranes.
• Heat insulating – subcutaneous fat helps to keep warm.
• Electrical insulating – myelin secreted by Schwann cells (they form the sheaths of nerve fibers) isolates some neurons, which speeds up the transmission of nerve impulses many times over.
• Hormonal (regulatory) – adrenal hormone (cortisone) and sex hormones (progesterone and testosterone) are steroids.
• Lubricating – waxes cover the skin, wool, feathers and protect them from water. The leaves of many plants are coated with a wax coating; wax is used in the construction of honeycombs.