Leaving Certificate Agricultural Science

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Leaving Certificate Agricultural Science
Food Nutrition
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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.

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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.

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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.

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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.

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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.

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Carbohydrates

• 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).

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Monosaccharides

• 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.

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Disaccharides

• Contain two sugar units
• Maltose Glucose Glucose
• Lactose Glucose Galactose
• Sucrose Glucose Fructose

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Polysaccharides

• 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.

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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.

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Testing food for Starch

• Iodine solution is used to test for starch
• A blue / black
• colour is a positive result.

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Proteins

• 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.

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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.

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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.

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Lipids

• 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.

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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.

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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.

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Vitamins

• 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.

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Minerals

• 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)

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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.

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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.

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Enzymes

• 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 pHs. Most at pH 7 but
  pepsin works only at pH 2 3.