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Leaving Cert Biology Revision: Food and Food Tests

Food and Food tests

Why Do We Need Food?

1. Energy Source: Provides the energy necessary to sustain our cells and keep us alive.

2. Chemical Production: Supplies the chemicals required for metabolic reactions.

3. Growth and Repair: Offers the raw materials needed for the growth and repair of cells and the body.

What's in Our Food?

- Common Elements:

  - Carbon (C)

  - Hydrogen (H)

  - Oxygen (O)

  - Nitrogen (N)

  - Phosphorus (P)

  - Sulfur (S)

- Elements Found as Salts:

  - Sodium (Na)

  - Magnesium (Mg)

  - Chlorine (Cl)

  - Potassium (K)

  - Calcium (Ca)

- Trace Elements:

  - Iron (Fe)

  - Copper (Cu)

  - Zinc (Zn)


are substances produced by living organisms.

Food contains four main types of biomolecules: proteins, lipids (fats and oils), carbohydrates, and vitamins.


Carbon, hydrogen, and oxygen make up carbohydrates. (C, H, O). They have a 1:2:1 ratio. Hydrogen is twice as abundant as Carbon/Oxygen. A common notation for the ratio is Cx(H2O)y. The formula for glucose is C6H12O6.

Three categories of carbohydrates exist:


These are sweet single sugars, such as glucose and fructose.


These are sweetened double sugars, such as sucrose.


These are chains made up of many sugars that don't taste sweet. For instance, starch.


There are three that you must be aware of.

Plants use it as a storage polysaccharide—for example, potatoes. Maltose, a disaccharide, is produced when the salivary enzyme amylase breaks down starch.

Long, cross-linked chains of glucose make up cellulose. Cellulose is more difficult to stomach and break down.

In the diet, it serves as roughage or fiber. This structural polysaccharide is found in the cell walls of plants. Long glucose chains are also a component of glycogen. In animals, it serves as a storage polysaccharide. It is broken down to liberate glucose, which muscles use as fuel.

The liver, brain, and muscles all store it.

  • They cannot be located in any ratio. They don't have much oxygen. Lipids that are solid at room temperature (20°C) are called fats, and liquid lipids are called oils.

  • Lipids are structured as triglycerides. They contain three fatty acids and one glycerol.

  • One of the fatty acids in phospholipids is swapped out for a phosphate. Since they are a component of cell membranes, they are crucial. Life could not have started in the absence of a cell membrane.

  • Protease is a word that ends in N. The atoms are big and extremely complicated, but there is no ratio for them.


  • Amino acids, of which there are 20 common types, make up proteins.

  • Peptide bonds are what keep amino acids bound together.

  • Twenty amino acids or fewer make up a peptide.

  • Over 20 amino acids are present in a polypeptide.

  • A protein is a polypeptide long chain with more than 200 amino acids.

  • After a protein is created, it must be folded for it to function.

Mad cow disease is caused by a protein called aprion that has misfolded.

Types of Proteins

Fibrous proteins, such as keratin in hair, nails, and feathers, are long, non-folding threads.

The many folds that globular proteins have let them take on round forms, such as albumin in egg white.

Protein Sources

  • Rich in protein are foods like meat, fish, eggs, almonds, milk, peas, and beans.

  • The body must metabolize amino acids since they cannot be kept there.

  • 'Deamination' is the process by which the liver breaks down amino acids.

  • After the amine component is transformed to urea, the blood carries it to the kidneys where it is transformed into urine.

  • After that, the pee is expelled.


The body cannot produce the complex molecules known as vitamins.

  • Vitamins are soluble in water.

  • Ascorbic acid, or vitamin C, dissolves in water.

  • Citrus fruits, like oranges and lemons, contain it.

  • Vitamin C deficiency causes scurvy or bleeding gums.

Energy Transfer Reactions

Anabolic and catabolic metabolic processes are the two categories into which they fall.

Small molecules are transformed into larger ones by anabolic processes. For instance. The process of photosynthesis. Energy is required for anabolic processes to add the components.

Roles of Biomolecules

Structural Role

  1. Plant cell walls contain polysaccharides or cellulose.

  2. The protein keratin is found in nails, hair, and feathers.

  3. An energy source is lipids. They are twice as energy dense as carbs.

  4. In animals, lipids shield internal organs and function as insulators.

  5. In cell membranes, lipids and phosphates combine to generate phospholipids.

Metabolic Role

During respiration, lipids and carbohydrates are broken down to release energy.

Enzymes contain proteins, which regulate the majority of chemical reactions in the body.

Certain proteins function as infection-fighting antibodies, while other proteins function as hormones.


Animals and plants require trace amounts of minerals.

  1. Animal bones and cell walls are formed by calcium.

  2. To build muscle tissue, need nitrogen and sulfur.

  3. Sodium is needed to generate bodily fluids like saliva and tears.

  4. Iron is needed to make hemoglobin, the pigment that gives red blood cells their oxygen.

  5. Chlorophyll, the pigment that absorbs solar energy, is made of magnesium.


makes up 90% of plants and about 60% of people.

Water is the source of life, and it continues to be essential to all living beings.

1. It is the liquid where all metabolic processes occur.

2. It serves as the foundation for an organism's transport systems.

3. It is the habitat for a variety of living things.

  • Tissue fluid, blood plasma, and cell cytoplasm all contain water.

  • It transports several molecules and is an excellent solvent.

  • The water utilized in photosynthesis is divided, producing electrons and hydrogen.

  • The final product we exhale is water from our respiration.

  • For plant cells to maintain their form, it is crucial.

  • It regulates body temperature and is an effective heat absorber.

Food Experiments

  1. Cut Down on Sugar (Glucose) Required Heat for Benedict's Solution, Blue becomes brick red.

  1. Lipids (Fats/Oils): Heat is unnecessary, Butter or oil and brown paper, Translucent turns brown.

  1. Milk proteins No need for heat, Solution for Biuret Cu(Sulfuric acid) + Sodium Hydrogen, Blue becomes purple (lilac) in color.

  1. Starch Iodine Solution No heat needed, Blue/Black replaces clear.

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