Nutrition is the way living things obtain and use food. Nutrients are the chemical substances present in food that are use by living things. Food is material that is a good source of one or more of the following:
Living organisms need food for energy, growth, repair, defence and reproduction and for metabolism.
There are six common elements found in food. There are five common elements found as dissolved salts.
They are: They are:
1. carbon (C) 1. sodium (Na)
2. hydrogen (H) 2. magnesium (Mg)
3. oxygen (O) 3. chlorine (Cl)
4. nitrogen (N) 4. potassium (K)
5. phosphorus (P) 5. calcium (Ca)
6. sulfur (S)
There are three trace elements. They are found in tiny amounts in organisms. They are:
1. iron (Fe)
2. copper (Cu)
3. zinc (Zn)
All of these elements except carbon, hydrogen and oxygen are called minerals.
The elements listed above combine in different ratios to form most of the molecules found in living things. These molecules are called biomolecules or biochemicals. The four main types of biomolecules are:
2. lipids (fats and oils)
Carbohydrates are formed by different ratios of the elements carbon, hydrogen and oxygen. The general formula is C x (H2O) y and x and y are the same number. In other words, there is twice as much hydrogen as there is oxygen in a carbohydrate.
There are 3 categories of carbohydrates. They are monosaccharides, disaccharides, and polysaccharides.
These are the smallest unit of carbohydrates. They consist of a single sugar unit. The most common one is glucose which is C6 H12 O6. They are sweet to taste and soluble in water. Glucose is the main molecule from which animals get energy. They get this energy from eating fruits, sweets, etc. Plants make glucose by photosynthesis.
1 glucose molecule
Disaccharides are made of two monosaccharides that are joined together. Common disaccharides are:
Polysaccharides are the carbohydrate type that is insoluble in water. (Some are slightly soluble.) They are made of many monosaccharides that are linked together. They have thousands of repeating units. Examples of polysaccharides are:
Dietary Sources of Carbohydrates
Monosaccharides: fruit, honey and jam.
Disaccharides: Sucrose - fruit, table sugar. Lactose - milk. Maltose - germinating seeds.
Polysaccharides: Starch: bread, rice, pasta, potatoes, seeds.
Cellulose: fruit, vegetables, wholegrain cereals, nuts.
Structural Role of Carbohydrates
Metabolic Role of Carbohydrate
Lipids, like carbohydrates, contain carbon, hydrogen and oxygen. However, unlike carbohydrates, they have no simple ratios. Also, they have very little oxygen.
Fats are lipids that are solid at room temperature while oils are liquid at room temperature.
The smallest lipids are composed of one glycerol molecule linked to 3 fatty acid molecules. Because it has 3 fatty acids it is called a triglyceride.
Good dietary sources of lipids are meat, milk, butter, cheese, plant oils, and margarine.
If one of the fatty acids is replaced by a phosphate molecule or a phosphate molecule is added top it then it is called a phospholipid.
Structural Role of Lipid
All proteins contain the elements C, H, O and N. Some proteins also contain P and/or S. There is no set ratio of atoms in proteins. They contain many atoms and are very large and complex. They contain many combinations of smaller units called amino acids. There are 20 common amino acids. Two Amino Acids bond to form a DIPEPTIDE. Two Amino Acids form a Covalent Bond, called a PEPTIDE BOND. All 20 amino acids can bond to each other one at a time, forming a long chain called a POLLYPEPTIDE. Proteins are composed of one or more polypeptides. Some proteins are very large molecules, containing hundreds of amino acids.
All proteins contain the following:
a -COOH, which is a carboxyl group (acidic).
a -NH2, which is an amine group (basic).
an -H hydrogen.
a residue R which varies depending on the amino acid.
All 20 different amino acids have this same structure, but their side chain groups (the R group) may vary in size, shape, charge, and reactivity. The amino acids could be considered as the alphabet in which the proteins are written. The different combinations of the alphabet determine the type of protein which is made.
Along with the R group variation, proteins also differ by their shape. Fibrous proteins form long fibres and have little folding to make large 3 dimensional shapes. Globular proteins have many foldings and are, therefore, rounded. Pritons are proteins that are folded incorrectly. They cause various nervous system diseases in animals and humans.
Protein synthesis takes place at the ribosomes of the cell. Meat, fish, eggs, milk, beans, peas and nuts are good sources of dietary protein.
Excess amino acids are taken to the liver and form urea. This process is called deamination. The urea is carried by the blood to the kidneys where it is excreted as part of the urine.
Structural Role of Protein
Metabolic Role of Protein
A vitamin is an organic compound needed in small quantities in the diet for health. They are not made by the body but are ingested in nutrition. There are 2 general types of vitamins:
Water-soluble vitamins: These are vitamins that are soluble in water. Vitamin C (ascorbic acid) is the most common water-soluble vitamin. It is obtained in fresh fruit and vegetables. It is needed to make and maintain connective tissue and the absorption of iron by the gut. Long term deficiency of vitamin C causes a disease called scurvy. Scurvy symptoms include internal bleeding, bruising, bleeding gums, poor healing.
Fat-soluble vitamins: These vitamins are soluble in fat. The most common fat soluble vitamin is Vitamin D and the most common Vitamin D is D2 (calciferol). Vitamin D is obtained from milk, eggs, liver, fish liver oils and produced in skin exposed to UV light. It is needed for bone and tooth formation, bone maintenance and the absorption of calcium from the gut. Long term deficiency cause diseases known as rickets and osteomalacia. Major deficiency symptoms include late teething and walking, deformed legs and arms, weak bones.
Metabolism is the full set of chemical processes carried out by a living organism. Metabolism may be:
Anabolism: the formation of large complex organic molecules by linking smaller simpler organic molecules. Anabolic reactions require energy input. Examples of anabolic reactions are the formation of muscle tissue from amino acids and the formation of cellulose from glucose.
One of the most important anabolic reactions found in nature is photosynthesis. In photosynthesis the plant converts carbon dioxide and water into glucose:
Carbon Dioxide + Water + Light Energy Glucose + Oxygen
Catabolism: the breakdown of large complex molecules into smaller simpler biomolecules. Catabolic reactions release energy and require enzymes. These reactions include digestion of food ant the decay of dead matter.
One of the most important anabolic reactions found in nature is respiration. In respiration the organism breaks down a large, complex molecule such as glucose, into smaller molecules of water and oxygen. This process releases energy from the glucose.
Glucose + Oxygen Carbon Dioxide + Water + Energy
Minerals or mineral nutrients are soluble inorganic salts that contain elements essential for metabolism. Minerals are only needed in small quantities in comparison to proteins, carbohydrates and lipids. Plants obtain their minerals by absorbing them from external ‘water’ — soil water, freshwater and seawater. Animals receive most of their minerals in the food they eat; some from the ‘water’ they drink.
General Role of Minerals in Living Organisms
You are responsible to know 2 plant and 2 animal minerals:
Water is the most abundant compound in living things. It composes 99% of all molecules in the body as well as 60% of the mass of the human body and 90% of the mass of plants.
The main purposes of water are:
More specifically, water is needed for: