Leaving certificate agricultural science
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Leaving Certificate Agricultural Science. Food & Nutrition. The Functions of Food. Food supplies the animal with energy for all animal activities. To provide the materials for growth and repair of cells To provide materials for production of hormones and enzymes.

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Leaving Certificate Agricultural Science

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Leaving certificate agricultural science

Leaving Certificate Agricultural Science

Food & Nutrition

The functions of food

The Functions of Food

  • Food supplies the animal with energy for all animal activities.

  • To provide the materials for growth and repair of cells

  • To provide materials for production of hormones and enzymes.

  • To provide raw materials for milk, egg and wool production etc.

Food elements

Food Elements

  • The six most common elements found in food are Carbon (C), Hydrogen (H), Nitrogen (N) Oxygen (O), Phosphorous (P) and Sulphur (S).

  • The elements found in dissolved salts include Sodium (Na), Magnesium (Mg), Chlorine (Cl), Potassium (K) and Calcium (Ca).

  • Trace elements are required in our body in very small amounts and include Iron (Fe), Copper (Cu) and Zinc (Zn).

  • These elements, when combined in different ratios form larger units called biomolecules.

The major food groups bio molecules

The Major Food Groups (Bio-molecules)

  • There are five main food groups:

    • Carbohydrates

    • Lipids (Fats and Oils)

    • Protein

    • Vitamins

    • Minerals

  • Water is often considered the sixth food group, due to the huge importance it plays in our bodies.

Autotrophic and heterotrophic

Autotrophic and Heterotrophic

  • Green plants can make their own food in a process known as PHOTOSYNTHESIS.

  • Therefore plants are known as autotrophs or autotrophic.

  • Animals have to ingest their food and cannot make all their food needs.

  • Animals are known as heterotrophs or heterotrophic.

The food pyramid

The Food Pyramid

  • The food pyramid is a diagram illustrating which proportions of food types are required in our everyday diet.

  • Complex Carbohydrates (Starch and Fibre) are the most important.

  • While fats and sugars are to be taken in the least amount.

  • The diagram is shown on the next slide.



  • The main sources of carbohydrates in our diet are starches and sugars.

  • Carbohydrates are made up of Carbon, Hydrogen and Oxygen molecules with the common formula Cx (H2O)x

  • Carbohydrates are classified by their number of sugar units, called saccharides.

  • Monosaccharides (1 sugar unit), Disaccharides (2) or Polysaccharides (many).



  • Are glucose, fructose and galactose.

  • All have the formula C6H12O6 but arranged differently.

  • Sources of monosaccharides are energy drinks, but indirectly through all other sugars.



  • Contain two sugar units:

  • Maltose = Glucose + Glucose

  • Lactose = Glucose + Galactose

  • Sucrose = Glucose + Fructose



  • Starches, Cellulose, Chitin and glycogen etc.

  • Humans cannot digest cellulose.

  • However cattle and horses (and other ruminants) can, by a symbiotic relationship with bacteria in their stomachs.

  • While monosaccharides and di-saccharides provide energy for our bodies, polysaccharides are mainly structural.

Testing food for a reducing sugar

Testing Food for a Reducing Sugar

Benedicts or Fehlings solution is added to the food sample (dissolved if necessary) and placed in a water bath.

A brick red colour is a positive result.

Testing food for starch

Testing food for Starch

Iodine solution is used to test for starch

A blue / black

colour is a positive result.



  • The main sources are lean meat, egg white, fish, milk, pulse and nuts.

  • Contain the elements Carbon, Hydrogen, Oxygen and Nitrogen (sometimes Sulphur)

  • Proteins are made up of units called amino acids.

  • There are over 80 known amino acids, but only 26 occur in proteins.

Proteins 2

Proteins (2)

  • These amino acids form long chains which come together as a protein molecule.

  • A typical Protein molecule has 500+ amino acids

  • Some amino acids can be made by our body and these are called non – essential amino acids.

  • Other amino acids can only be brought into our bodies by ingestion.

  • These are known as essential amino acids.

Proteins 3

Proteins (3)

  • There are no essential amino acids for ruminants.

  • Proteins are used in the body for growth and repair of cells.

  • The Biuret Reagent is used to test for the presence of protein in a food sample.

  • A lilac colour indicates a positive result.



  • Sources of fats are obvious – butter, oils, nuts, milk and general fatty foods.

  • Contain the elements Carbon, Hydrogen and Oxygen but not in any given ratio unlike Carbohydrates.

  • A unit of fat (called a triglyceride) is made up of one molecule of Glycerol with three fatty acids chemically attached.

Role of fats

Role of Fats

  • Fats provide energy to the body (twice as much as carbohydrates), insulation and contain vitamins (known as Fat Soluble).

  • Phospholipids are oil like substances but contain a phosphate group instead of one fatty acid.

  • Phospholipids are important as they form cell membranes.

Saturated vs unsaturated

Saturated vs. Unsaturated

  • Fats can be known as saturated or unsaturated.

  • Saturated means that as many Hydrogen atoms as possible are attached to the Carbon atoms.

  • Saturated fats are usually solid at room temperature and are related to heart disease.

  • Unsaturated fats contain fewer Hydrogen atoms, and contain what are known as double or triple bonds.

  • They are usually oil at room temperature.



  • Vitamins have many functions in the body.

  • Vitamins mainly act as co-enzymes, which means they trigger enzymes to work.

  • Vitamins can be water soluble or fat soluble.

  • Vitamin C (A water soluble vitamin)

    • Found in Citrus Fruits

    • Involved in the absorption of Iron & Respiration

    • Lack of Vit. C causes Scurvy!!

  • Vitamin A (A fat soluble vitamin)

    • Found in the carotene pigment (found in carrots).

    • Involved in formation of the visual pigments.

    • Lack of Vit. A causes night blindness.



  • Minerals have no energy value but are used in the body for many different reasons

    • Osmo-regulation (control of water levels)

    • Acid – Base balance (pH balance)

    • Formation of enzymes, pigments and hormones.

    • Triggers or activators in different reactions.

  • Iron for Haemoglobin in Blood (Anaemia)

  • Role of water

    Role of Water

    • Water has no energy value but again is essential for all bodily functions

    • Our bodies are made up of 75% water.

    • Waters main function is as a medium where other food items are stored and moved.

    • Of course our blood is made of nearly all water so it is vital that the human body gets 3 – 4 pints of water a day.

    Structural role of biomolecules

    Structural Role of Biomolecules

    • Carbohydrates:

      • Cellulose as a component of Cell Walls

    • Protein:

      • Fibrous proteins like Keratin are found in hair and nails.

      • Myosin is found in muscles.

    • Lipids:

      • Phospholipids are a major component of cell membranes.



    • Enzymes are biological catalysts.

    • They are natural substances, which speed up the breakdown of food substances and other materials.

    • They work by combining with the substrate forming the enzymes – substrate complex.

    • The enzymes – substrate complex breaks down and forms the product and releases the enzyme.

    • The enzyme can then be used again.

    • Enzymes are very specific and will only work on one substrate.

    • Enzymes are very important in the breakdown of food in our digestive system.

    • Enzymes work at specific pH’s. Most at pH 7 but pepsin works only at pH 2 & 3.

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