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All living beings have several characteristics in common:
- They have a similar chemical composition. The living matter has unit of composition.
- They are made up by structural units called cells. They have unit of organisation.
- They carry out the vital functions: nutrition, interaction and reproduction. They have unit of function.
Composition of living beings
All living beings are made up of the same chemical substances.
The most abundant chemical elements of living matter are: Carbon (C), Oxygen (O), Hydrogen (H), and Nitrogen (N) that make up about 95% of all living matter. But others elements, such as Calcium (Ca), Sodium (Na), Chlorine (Cl), Iron (Fe), Magnesium (Mg), among others, are also important. These elements are called bioelements.
Combinations of these elements form molecules of living matter called biomolecules. These biomolecules can be inorganic and organic.
lnorganic substances do not contain carbon.They are present in living things and 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
- 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.
Organic substances are exclusive of living beings. Carbon is their main element.
There are several types:
- Glucids (sugars or carbohydrates). Their function is provide energy (e.g. glucose) and make structures such as plant cellular wall (e.g. cellulose)
- Lipids. They are insulating and energetic reserve substances (e.g. fatty acids) and they also make structures, such as cell membranes (e.g. cholesterol)
- Proteins. 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 control the cell's activity and contain the inheritance information (e.g. DNA)
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