Unit 1: The basis of life                                              1   2   3   4   5   6

2. Composition of living matter

All living beings are made up of chemical elements.

The most abundant ones in them are: Carbon (C), Oxygen (O), Hydrogen (H), and Nitrogen (N) that make up about 95% of all living matter. But others elements, much less abundant, are also important, such as Calcium (Ca), Sodium (Na), Chlorine (Cl), Iron (Fe), Magnesium (Mg), etc.

These chemical elements that form part of living matter are called bioelements.

Combinations of these elements form molecules called biomolecules.

These biomolecules can be inorganic and organic.

a) Inorganic biomolecules

   They do not contain carbon. They are not exclusive of living beings, because

   they also form part  of non-living things. The main inorganic substances are

   mineral salts and water.

- Mineral salts have various functions:

- Solid: They make up different structures, like shells, bones and teeth.

- Dissolved: They are present in internal fluids, like tears, sweat and blood.

- Water is the most abundant substance in living things. Water is necessary for chemical reactions and to transport all other substances.

b) Organic biomolecules

     They are exclusive of living beings. They are not present in non-living matter.

     Carbon is their main element.
     There are four types:

    - Glucids (sugars or carbohydrates).

They can be simple (monosaccharides) or complex (polysaccharides).

Polysaccharides are long chains of monosaccharides.

        Their function is provide energy (e.g. glucose)

        and make structures such as plant cellular wall (e.g. cellulose)

    - Lipids

       They are a group of compounds of varied composition but all of them

       are insoluble in water.

       They are insulating and energetic reserve substances (e.g. fats)

       and they also make structures, such as cell membranes

       (e.g. phospholipids, cholesterol) or protective covers (e.g. waxes)

    - Proteins
        They are long chains of little molecules called amino acids.

        They have several functions:

        transport substances (e.g. haemoglobin transport oxygen),

        defense against microorganisms (e.g. antibodies),

        help in chemical reactions (e.g. enzymes),

        make structures (e.g. queratine forms nails and hair), etc

    - Nucleic acids

       They are also long molecules of smaller molecules called nucleotides.

       They control the cell’s activity and contain the inheritance information

       (e.g. DNA, RNA)

    2.1. About the following bioelements:

           a. Which of them are typical of the living matter?

           b. Which are the most abundant ones in the organic matter?

           c. Which percentage of it do they represent?

           d. Which is the most representative one of the living beings?

    2.2. How can we classify the biomolecules?

            What criteria do we have to follow?

     2.3. Indicate which biomoleculeperform each function:

            a. Contains the inheritance information

            b. Give energy to the organism

            c. Transport other substances through the body

            d. Build structures, transport substances, etc

            e. Be reserve and insulating substances

            f. Regulate chemical reactions and build skeletal structures

    2.4. Explain what the relationship between these couples of terms is:

            a. Biomolecule - Biolement

            b. Monosaccharide- Polysaccharide

            c. Amino acid – Protein

            d. Nucleic acid - Nucleotide