Molecules of life
Food belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis., Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair. and Fat or oils, composed of fatty acids and glycerol. (or fats) are major nutrients that we need in large quantities.
We get these by eating them. They are broken down first and then reassembled into our own carbohydrates, proteins and lipids.
This is because:
- most of the molecules in food are too large to pass through the absorbing surface of the The digestive system. It is involved in breaking down complex food molecules and the absorption of simple food molecules into the bloodstream. wall
- the carbohydrates, proteins and lipids are reassembled in the form required, rather than other animal or plant versions
| Nutrient | Major function | Major sources |
| Carbohydrates | Source of energy, glucose is the main respiratory substrate | Starch - potatoes, rice and wheat products, bread, cereals and pasta; sugars - fruit, smoothies, fizzy drinks, chocolate and sweets |
| Proteins | Growth and repair | Meat, eggs, cheese, beans, nuts and seeds |
| Lipids | Energy, make up part of cell membranes so essential for normal growth | Butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds |
| Nutrient | Carbohydrates |
|---|---|
| Major function | Source of energy, glucose is the main respiratory substrate |
| Major sources | Starch - potatoes, rice and wheat products, bread, cereals and pasta; sugars - fruit, smoothies, fizzy drinks, chocolate and sweets |
| Nutrient | Proteins |
|---|---|
| Major function | Growth and repair |
| Major sources | Meat, eggs, cheese, beans, nuts and seeds |
| Nutrient | Lipids |
|---|---|
| Major function | Energy, make up part of cell membranes so essential for normal growth |
| Major sources | Butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds |
Carbohydrates
Carbohydrates in our diet include A simple carbohydrate that is sweet to the taste. and A type of carbohydrate. 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 A simple sugar used by cells for respiration. molecule is small enough to be absorbed directly through the walls of the Organ system involved in breaking food down so that it can be absorbed into the bloodstream.. It is essential for The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration..
Starch is a carbohydrate made from a long chain of glucose molecules. So, starch is a A large molecule formed from many identical smaller molecules known as monomers. of glucose. It must be broken down into glucose molecules – it is too large to pass through the gut wall.
A carbohydrate. It forms the cell wall in plant cells. is also made up of glucose molecules. It makes up plant cell walls so it is a fundamental part of our diet. It cannot be broken down by the digestive system, so it is The process of passing out the remains of food that has not been digested, as faeces, through the anus. from the gut.
Once absorbed by the body, glucose molecules are transported to cells and:
- used for respiration
- reassembled into the storage form of carbohydrate in animals - Animals store glucose as glycogen in their liver and muscle tissues.
In plant All the chemical reactions in the cells of an organism, including respiration., the glucose produced by A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. is converted into starch for storage, and cellulose for cell wall synthesis.
Proteins
Proteins are made up of The building blocks that make up a protein molecule. folded into the correct shape.
Proteins are big molecules that are too large to pass through the gut wall. They must first be broken down into amino acids.
Once inside the body, the amino acids are reassembled into the proteins the individual requires – the process of The production of proteins from amino acids, which happens in the ribosomes of the cell..
Excess amino acids are broken down in the The large organ, beside the stomach, which has many functions, including processing substances absorbed by the digestive system and a role in the storage of the body's carbohydrate..
Lipids
Lipids are A type of organic compound formed in the reaction between an alcohol and a carboxylic acid. of Carboxylic acids with a long chain of carbon atoms. Fatty acids react with glycerol to produce lipids (fats and oils). and Propane-1,2,3-triol. It reacts with fatty acids to form esters, found in nature as fats and oils..
Lipid molecules are too large to pass through the gut wall and must be digested first.
In the body's cells, they are reassembled into the lipids the cell needs, for instance, for the A selectively permeable membrane surrounding the cell and controlling the entry and exit of materials..
Lipids are a store of energy because cells can break them down and use them in respiration.