Structures of Carbohydrates , protein and lipids

• The major nutrients required for a healthy diet are carbohydrates, proteins and lipids.
• The digestive system breaks down large molecules of food, which are then absorbed into the bloodstream.
• Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess.
• In plants, carbohydrates are important for photosynthesis.
• Foods in our diet include sugars and starches.
• A simple carbohydrate that is sweet to the taste is a sugar.
• A type of carbohydrate is starch.
• Plants can turn the glucose produced in photosynthesis into starch for storage, and turn it back into glucose when it is needed for respiration.
• The glucose molecule is small enough to be absorbed directly through the walls of the digestive system.
• Starch is a polymer, a large molecule formed from many identical smaller molecules known as monomers.
• Glucose is a simple sugar used by cells for respiration.
• Starch cannot be broken down by the digestive system, so is egested.
• Once absorbed by the body, glucose molecules are transported to cells and used for respiration or reassembled into the storage form of carbohydrate in animals - glycogen.
• Animals store glucose as glycogen in their liver and muscle tissues.
• Lipids are fat or oils, composed of fatty acids and glycerol, and are esters or fats found in nature as fats and oils.
• Lipid molecules are too large to pass through the gut wall and must be digested first.
• Glucose is converted into starch for storage, and cellulose, for cell wall synthesis, in plants and animals.
• In a lipid, there may be 1, 2 or 3 fatty acids combined with glycerol.
• Amino acids are the building blocks that make up a protein molecule.
• Proteins are organic compounds made up of amino acid molecules, one of the three main food groups, and are needed by the body for cell growth and repair.
• Fatty acids 1, 2 and 3 may be the same, or different.
• In plant metabolism, close metabolism refers to all the chemical reactions in the cells of an organism, including respiration, the glucose produced by photosynthesis, and the conversion of glucose into starch for storage.
• In humans and animals, glucose is stored in glycogen.
• Algae subsumed within plants and some bacteria are also photosynthetic.
• In the body's cells, lipids are reassembled into the lipids the cell needs, for instance, for the cell membranes.
• Proteins are big molecules that are too large to pass through the gut wall and must be broken down into amino acids before they can be absorbed by the body.
• Excess amino acids are broken down in the liver.