Topic 3 - Water, Carbs, Lipids and Proteins
3.1 Chemical elements and water
3.1.1 State that the most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen.
3.1.2 State that a variety of other elements are needed by living organisms, including sulphur, calcium, phosphorus, iron and sodium.
3.1.3 State one role for each of the elements mentioned before
Nitrogen:
Required by proteins. (Remember, nitrogen is included in the amino acid structure) Contains enzymes essential for plant function.
Calcium:
The mineral that strengthens bone and teeth uses calcium. Also important in nerve synaptic transmission of nerve impulses and muscle contraction. Regulates the cell wall construction in plants.
Phosphorus:
Part of the phosphate groups in ATP and DNA molecules. In plants it is needed for cell reproduction and division. It is part of the cell membrane.
Iron:
Found in the structure of haemoglobin and essential for the production of red blood cells. It is involved in the light energy transferring compounds involved in photosynthesis in plants.
Sodium:
Major ion associated with the propagation of a nerve impulse. Can replace potassium in some plants.
Sulphur:
It is a component of amino acids
3.1.4 Draw and label a diagram showing the structure of water molecules to show their polarity and hydrogen body formation.

3.1.5 Outline the properties of water that are significant to living organisms, including transparency, cohesion, solvent properties and thermal properties. Refer to the polarity of water molecules and hydrogen bonding when relevant.
Water is transparent which allows light to filter into the oceans. This allows for aquatic plants to absorb light and perform photosynthesis. Since the ancestor of all plants originated in the ocean, the transparency of water has had an immeasurable influence on life as we know it.
Water is also cohesive, that is it binds to itself, due to the polarity of the water molecule. The positive, hydrogen side of the molecule binds to the negative, oxygen side of another water molecule. This bond is called a hydrogen bond. This property allows for transport of water against gravity in plants.
Water is a very versatile solvent. All the reactions in cells must take place in aqueous solution.
Water's polarity also inhibits movement of its molecules. Since all the molecules are connected, they cannot freely move about as other, non-polar molecules do. Heat, the kinetic energy of molecules, is thus restricted and so water has a high specific heat (it must absorb large amounts of energy in order to change states). This means that water can serve as a temperature insulator, and does so in organisms of all kinds.
3.1.6 Explain the significance to organisms of water as a coolant, transport medium and habitat in terms of its properties
Coolant:
Allows us to perform homeostasis. (We sweat to cool ourselves down). Additionally, water's high heat of vaporization allows water molecules to absorb large amounts of energy from the body before evaporating - thus, the sweating individual loses heat.
Transport medium:
Digestion, also important to help transport blood. Phloem in plants transport nutrients dissolved in water using the cohesive and adhesive properties.
Habitat:
Organisms need water; the ready availability of it is essential in the choosing of a habitat. Water's high heat capacity (the amount of energy needed to increase the temperature of 1gm of water by 1 Degrees Celsius) and high heat of vaporization (amount of energy absorbed by 1gm of liquid to be converted to the gaseous form) prevents from plants and animals from overheating and dying.
3.2 Carbohydrates, lipids, and proteins
3.2.1 Distinguish between organic and inorganic compounds
Organic compounds are defined as compounds containing carbon that are found in living organisms.
Compounds are considered inorganic when they contain carbon but are widely found in the