Carbohydrates, lipids and proteins
3.2.1 Distinguish between organic and inorganic compounds.
Organic compounds are compounds that are found in living organisms and contain carbon. Inorganic compounds are the ones that don’t contain carbon. Although, there are a few compounds found in living organisms which also contain carbon but are considered as inorganic compounds. These include carbon dioxide, carbonates and hydrogen carbonates.
3.2.2 Identify amino acids, glucose, ribose and fatty acids from diagrams showing their structure.
3.2.3 List three examples each of monosaccharides, disaccharides and polysaccharides.
- Glucose, galactose and fructose are all monosaccharides.
- Maltose, lactose and sucrose are all disaccharides.
- Starch, glycogen and cellulose are all polysaccharides.
3.2.4 State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants.
In animals, glucose is used as an energy source for the body and lactose is the sugar found in milk which provides energy to new borns until they are weaned. Finally, glycogen is used as an energy source (short term only) and is stored in muscles and the liver.
In plants, fructose is what makes fruits taste sweet which attracts animals and these then eat the fruits and disperse the seeds found in the fruits. Sucrose is used as an energy source for the plant whereas cellulose fibers is what makes the plant cell wall strong.
3.2.5 Outline the role of condensation and hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol and triglycerides; and between amino acids and polypeptides.
3.2.6 State three functions of lipids.
- Lipids can be used for energy storage in the form of fat in humans and oil in plants.
- Lipids can be used as heat insulation as fat under the skin reduces heat loss.
- Lipids allow buoyancy as they are less dense than water and so animals can float in water.
3.2.7 Compare the use of carbohydrates and lipids in energy storage.
Carbohydrates and lipids can both be used as energy storage however carbohydrates are usually used for short term storage whereas lipids are used for long term storage. Carbohydrates are soluble in water unlike lipids. This makes carbohydrates easy to transport around the body (from and to the store). Also, carbohydrates are a lot easier and more rapidly digested so their energy is useful if the body requires energy fast. As for lipids, they are insoluble which makes them more difficult to transport however because they are insoluble, lipids do not have an effect on osmosis which prevents problems within the cells in the body. They also contain more energy per gram than carbohydrates which makes lipids a lighter store compared to a store of carbohydrates equivalent in energy.