Table of Contents
ToggleElements and atoms
All matter is made up of elements. There are 118 elements defined, although only 92 exist naturally. Elements may exist in solid, liquid and gaseous states and may change state depending on temperature.
Elements are made of atoms. Atoms are made of three types of particles, protons with a positive charge, electrons with a negative charge and neutrons with no charge. Protons and neutrons are clustered in the centre (nucleus) and electrons orbit around the nucleus.
Each element contains a different number of protons giving it its own atomic number. If an atom loses or gains a proton, it becomes a different element. The number of protons is what defines an element. The atom represented above is helium. It has two protons and is said to have an atomic number of 2.
Elements for biology
The elements of most interest to biologists are shown below
Element name | Element symbol | Comments |
---|---|---|
Carbon | C | Found in biomolecules including carbohydrates, lipids, proteins, nucleic acids |
Hydrogen | H | Found in biomolecules including carbohydrates, lipids, proteins, nucleic acids |
Oxygen | O | Found in biomolecules including carbohydrates, lipids, proteins, nucleic acids |
Nitrogen | N | Found in biomolecules including proteins, nucleic acids, lipds |
Phosporus | P | Found in nucleic acids, lipids |
Sulphur | S | Found in proteins, lipids |
Other significant elements found in living organisms
- Sodium (Na)
- Potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Iron (Fe)
- Chlorine (Cl)
- Zinc (Zn)
Combining atoms
Elements can be combined in various ways to make new substances e.g. carbon, oxygen and hydrogen can be combined to make ethanol (alcohol)
Two methods of creating combinations are covalent bonding and iconic bonding.
Covalent bonding
Covalent bonding is achieved through atoms sharing electrons to make molecules which have fixed ratios of constituent atoms.
These are a strong bonds and energy must be expended to break them.
Examples of molecules
Ionic bonding
Ions are formed when an atom loses or gains electrons. Ionic bonding is achieved by the force of attraction between positive and negative charges in ions. As shown in the image gallery below, common table salt is an ionic compound, i.e. it is formed from sodium ions and chlorine ions bonded into a compound held together by electric attraction between the particles. It can be dissolved in water to make a solution.
Materials cycling through ecosystems
The elements/molecules/ions found in ecosystems are present in the soil, the water and the air. These materials are cycled though the ecosystem via food webs and other interactions.
Producers manufacture molecules through the process of photosynthesis (or chemosynthesis in extreme environments). Consumers eat producers to obtain raw materials that they cannot manufacture themselves.
Four major types of biological molecules
Carbohydrates
Carbohydrates are composed of carbon, hydrogen and oxygen. Animals use carbohydrates for energy for building other compounds and for movement.
Simple carbohydrate molecules such as glucose and fructose can be joined together to create larger molecules such as sucrose, starch, cellulose and glycogen.
Lipids
Lipids are primarily composed of carbon and hydrogen. They may also contain minor amounts of oxygen, nitrogen, sulfur, and phosphorous. They are used by organisms for long term energy storage and insulation from low temperatures. Also phosphlipids are a component of cell membranes.
Lipids variants - oils, hormones, steroids, waxes, phospholipids
Proteins
Proteins are composed of carbon, hydrogen, oxygen and nitrogen. They are assembled into chains from sub-units known as amino acids.
Amino acids are made up of a central carbon atom, shown in blue, bonded to 4 groups
- an amino group (-NH2) shown here in green
- a carboxyl group (-COOH) shown here in yellow
- a hydrogen atom
- a variable group of atoms shown here in red as the letter R The composition of the variable group determines the identity of the amino acid
Try to identify the R group in each of the following examples of amino acids
The chains may then be folded into different formations with the addition of bonds some of which are made of sulphur atoms. The shape of the resultant protein is critical to its functioning. If the protein is misshapen in even a minor way, it can lead to disastrous results in an organism's functioning.
Proteins have many important functions in organisms
- enzymes
- transport
- structure
- hormones
- defence
- storage
- motility
Nucleic acids
Nucleic acids are composed of carbon, hydrogen, oxygen, nitrogen and phosphorus. They are made up of subunits called nucleotides, which consist of a 5-carbon sugar, a nitrogenous base, and a phosphate group. The nucleotide chains form DNA and RNA
They are important because
- they carry the information for new cells to be manufactured for an organism's growth and repair
- they forms genes which enable organisms to pass on their characteristics to descendants.