Characteristics and classification of living organisms

Characteristics of living organisms

7 Characteristics of living things (MRS GREN):

• Movement — an action by an organism or part of an organism causing a change of position or place.
• Respiration — the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
• Sensitivity — the ability to detect and respond to changes in the intel or extel environment.
• Growth — a permanent increase in size and dry mass.
• Reproduction — the processes that make more of the same kind of organism.
• Excretion — the removal of the waste products of metabolism and substances in excess of requirements.
• Nutrition — the taking in of materials for energy, growth and development.

Concept and uses of classification systems

Organisms can be classified into groups by the features that they share.

Classification - systems aim to reflect evolutionary relationships

• Sequences of bases in DNA are used for classification.
• They classify organisms by using their genetics to trace their evolutionary relationships.
• Many species have similar features that allow us to put them into groups.
• Organisms who share a more recent ancestor (i.e. more closely related) have DNA base sequences that are more similar than those who only share a distant ancestor.

• Species — A group of organisms that can reproduce to produce fertile offspring (with organisms sharing similar characteristics and living space.)
• Binomial Naming — an intetionally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species. E.g. homo (genus) sapiens (species)
• Dichotomous key — used to classify animals based on their visible characteristics

Features of Organism

Kingdom -> phylum -> class -> order -> family -> genus -> species

All living things are classified into five kingdoms:

• Plants — multicellular, contains nucleus, chloroplasts & cell walls.
• Animals — multicellular, contains nucleus, no chloroplasts/cell wall.
• Fungi — multicellular, contains nucleus & cell walls.
• Protoctists — unicellular, contains nucleus.
• Prokaryotes — unicellular, contain cell walls, no nucleus.

Animal kingdom

Main groups of vertebrates (animals with a backbone): mammals birds, reptiles, amphibians, fish

Main groups of arthropods (invertebrates — animals with no backbone): myriapods, insects, arachnids, crustaceans

Traits:

• Most have a firm/hard extel skeleton made up of chitin.
• Jointed limbs
• Arachnid: 8 legs
• Crustaceans: 10 legs
• Insects: 6 legs
• Myriapods: uncountable
• Body segmentation (2 or 3).
• Arachnid and Crustaceans: cephalothorax, abdomen.
• Insects: head, thorax and abdomen.
• Myriapods: not obviously divided.
• Eyes
• Arachnids & Myriapods: simple eyes.
• Insects & Crustaceans: compound eyes.

Plant kingdom

• Ferns — the first plants to adapt to living on land. They have evolved to have roots, stems, complex leaves and vascular tissues.
• Angiosperms — plants with flowers and seeds. They have evolved most recently.

Viruses

• Viruses are not considered as living things.
• They DO NOT display the 7 characteristics of living things.
• They need a living host cell in order to make copies of themselves.