Characteristics of living organisms
Every living organism have certain traits that it needs to be demonstrating in order for it to classify as “living”. There are 7 characteristics that we need to go through. If even a single one of these characteristics are not present in an organism, then it not alive.
- 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 or sense stimuli in the internal or external environment and to make appropriate responses
- Growth – Permanent increase in size and dry mass by an increase in cell number or cell size or both
- Reproduction – The processes that make more of the same kind of organism
- Excretion – Removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements
- Nutrition -Taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds and ions and usually need water
Concept and use of classification system
Organisms can be classified into groups by features that they share. Classification systems aim to therefore classify groups of organisms in a systemic way, in order to reflect their evolutionary relationships.
Before the advance of technology and science, classification was traditionally based on morphology and anatomy. Basically this means that if certain organisms “looked” similar and shared similar features, then they would be classified under the same umbrella. But it is important to understand that now, we can more accurately classify organisms by analyzing their DNA (rather than look at appearance alone). Organisms which share similar DNA base sequences and protein amino acid sequences are more likely to be closely related.
Every organism has a scientific name. The binomial system is an internationally agreed system in which the scientific name of an organisms is made up of two parts (Genus & Species). The Genus is a generic term used in the classification of living organisms or binomial nomenclature and species is a group of organisms that can reproduce to produce fertile offspring.
For example: Homo sapiens
It is important to understand here that Homo represents the genus and is always starts in capital letters. Sapiens is the species and is all lower case and in italics.
Features of organisms
All organisms are made of cells. Although the cellular structure may be different depending on the type of organism, there are certain things that are universally shared across every single organism:
- Cytoplasm
- Cell membrane
- DNA
- Ribosomes
- Enzymes
Now, we can actually organize every single organism into 5 main categories called “kingdoms”. Here are the 5 kingdoms that you need to know:
- Animal (i.e. Lion)
- Plant (i.e. Tree)
- Fungus (i.e. Yeast)
- Prokaryote (i.e. Bacteria)
- Protoctist (i.e. Marimo)
You need to know the features of these 5 kingdoms so that for a given example of an organism, you can determine the kingdom it belongs in. Here is a simple table to help you.
Now that we understand the features of the 5 kingdoms, we can actually branch further. The syllabus wants you to understand how to classify different “types” of animals and plants. In the animal kingdom, animals they can further be classed as vertebrates (with backbone) or invertebrates (no backbone).
In the plant kingdom, plants can be classed into either flowering plants or ferns. The table below (Oxford Revision Guide 2018) demonstrates the further classification of both the animal and the plant kingdom.
Dichotomous keys
A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item.
For example, use the key to answer the question
- Wings present ……………………………………… Go to 2
Wings absent ……………………………………….. Go to 3 - One pair of wings visible ………………………………. A
Two pairs of wings visible …………………………….. B - Three pairs of legs …………………………………………. C
Two pairs of legs …………………………………………… D
Since this insect has wins, and has two pairs visible, the answer is B!