2.1 – Chemical Elements and Water

2.1 – Chemical Elements and Water

2.1.1 – State that the most frequently occurring chemical elements in living things are carbon, hydrogen, and oxygen

The most common elements in living things are carbon (C), hydrogen (H) and oxygen (O). Carbon is the most important element to life. It is a macronutrient, and basically our entire body is made up of it. It acts as a basic building block, which can be attached to form chains or to other elements. Carbon is essential for the big molecules to be built. They are based around chains of carbon atoms. Without them, we would be a pile of loose atoms with no way of being built into a person.

Hydrogen is also a macronutrient. It forms part of water, which we would die within a few days if we didn’t get any. Water is very important, with around 75% of our bodies (by weight) made up of it. It dissolves other important substances and can transport them. Important reactions also take place in water. Hydrogen bonds are what give water these amazing attributes. Hydrogen is almost always bonded to the carbon our bodies are made of. Also, crucial substances (i.e. Stomach acid – HCl) contain hydrogen. It is essential to life.

Oxygen is another macronutrient. It is needed by plants as well as humans. It forms a part of the water compound, which, of course, is essential to life. This versatile element is the single most important substance to life.

Nitrogen is another important element. It too is a macronutrient, and plays a role in digestion and growth. 80% of the air we breathe is made up of nitrogen, however it is in the wrong form, so we cannot use it. Instead, we get it from our food. It is extracted early to aid
us in growth. Nitrogen is especially useful during pregnancy, as it is necessary for foetus development. Nitrogen is one of the three main elements that make plant life possible.


2.1.2 – State that a variety of other elements are needed by living organisms, including sulfur, calcium, phosphorus, iron and sodium

Many other elements are necessary for the survival of living organisms. These include sulfur, calcium, phosphorus, iron and sodium.

2.1.3 – State one role of each of the elements mentioned above

Sulfur is also needed by living organisms. For example, it is an important element in some amino acids. It protects our cells from environmental hazards like pollution and radiation, as well as helping our liver to function properly. It is important for making blood clots, and keeps our skin supple and elastic.

Calcium is important, and can be found in our bones and teeth. This macronutrient is also important for other things like muscle growth, and electrical impulses in your brain. It maintains proper blood pressure and makes blood clot when you are cut. Calcium deficiency
can lead to muscle spasms, leg cramps and brittle bones.

Iron is found in hemoglobin, the part of our blood that carries oxygen. Hence, an iron deficiency would lead to fatigue and shortened attention span. This may lead to iron deficiency anaemia. It has many functions such as making tendons and ligaments, as well as controlling chemicals in our brains. It is needed for maintaining a healthy immune system.

Sodium is needed for nerve impulses to be sent. It also forms an important part of blood plasma, and without we cannot get the nutrients we need to survive. It maintains the correct amount of water in our blood. Our bodies therefore have various mechanisms to keep our sodium levels right, such as becoming thirsty when we have a lot of salt to dilute it and dispose of the excess.

Phosphorus is found in membrane structures, an integral part of the cell. It the most abundant mineral in our body, second only to calcium. It is needed for the healthy formation of bones and teeth, as well as processing food. It is part of our energy storage system. Contractions of the heart, normal cell growth and repair are all dependent of phosphorus. Deficiency leads to lowered energy levels and decreased attention span. Phosphorus is also one of the three main elements that make plant life possible. High intake from processed foods, etc, may lead to osteoporosis.

2.1.4 – Draw and label a diagram showing the structure of water molecules to show their  polarity and hydrogen bond formation

The hydrogen atoms in a water molecule have a slight positive charge, and the oxygen atoms have a slight negative charge. The give water molecule two poles, which is called polarity.


Hydrogen bonds can form between the positive and negative poles of the molecules. In liquid water, many bonds will form to give the water its properties and making it useful for living organisms.


2.1.5 – Outline the thermal, cohesive and solvent properties of water


  • Water has a large heat capacity, which means that large amounts of energy are required to raise its temperature. This is needed to break the hydrogen bonds.
  • The boiling point of water is high (100oC), as all the hydrogen bonds must be broken between the water molecules.
  • Water is able to evaporate at temperatures below boiling. The heat energy that breaks the hydrogen bonds is taken from the liquid, cooling it down.


Water molecules will stick together because of the hydrogen bonds between them.


The polarity of water means that various substances will dissolve in it. Ions with positive or negative charges dissolve as they are attracted to the poles of water molecules. Many molecules are polar, so they will dissolve. Enzymes will also dissolve in water.


2.1.6 – Explain the relationship between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions and transport medium


Blood (which is mainly composed of water) is able to carry heat from warmer parts of the body to cooler parts of the body. Thus, water can be used as a transport medium for heat. On earth, water is found below boiling point almost everywhere, and usually above freezing
point. Water is a medium for metabolic reactions as a liquid. Evaporation from plant leaves (transpiration) and from human skin (sweat) can have a cooling effect, thus water is useful as a coolant.


Strong pulling forces can be exerted to suck columns of water up to the tops of trees in their transport systems. These columns of water rarely break, so water is used as a transport medium in the xylem of plants. Water surfaces also have surface tension, meaning that it
can have enough structural strength to support the mass of insects.


Most chemical reactions in living organisms with all of the substances dissolved in water. Hence, water is a medium for metabolic reactions. These properties also allow many substances to be carried dissolved in water in the blood of animals and the sap of plants.
Hence, it is a transport medium.