The Characteristics of Life – What is Life?
The characteristics of living organisms, or Life on Earth, as we know it, follow.
1. Cells – all living things are made up of the building blocks of cells (apart from Prokaryotes)
2. Organization – cells are specialised or are grouped into tissues, and tissues into organs, organs into systems
3. Metabolism – living things consume and burn up” fuel and turn it into energy for functional use, through chemical reactions
4. Homeostasis – living things self-regulate their internal systems (such as core temperature) through feedback control, in order to adapt to one’s external environment
5. Heredity and Reproduction – lviing things reproduce or replicate and pass on their genetic material to their off-spring
6. Responsiveness – living things respond to stimuli
7. Growth – living things grow
8. Spiritual – a Soul animating a physical matter form (not usually mentioned as a characteristic, but one which I like to add)
There are 7 life processes.
1. Movement – moving parts of the body
2. Reproduction – producing offspring
3. Sensitivity – responding and reacting
4. Nutrition – getting food to stay alive
5. Excretion – getting rid of waste
6. Respiration (or photosynthesis) – turning food into energy
7. Growth – getting to adult size
Bacteria and Archaea (or blue-green algae) are border-line living organisms, classified by some taxonomists into their own Kingdom – the Kingdom Monera. They have very simple cell structures, and some people debate over whether they are in fact living or not. They are also called Prokaryotes and are described as having Prokaryotic cells. Their “cells” do not contain a nucleus, which is a structure that contains or holds the DNA (de-oxy-ribo-nucelic acid).
Click here to listen to how “deoxyribonucleic acid” is pronounced, and for more information about what it is.
Viruses are not classified as living organisms, because they consist of protein material and cannot reproduce or duplicate by themselves.
Fungi, including mushrooms, are curious living organisms; neither plant nor animal, but have some characteristics of each. They cannot move about like an animal, have no chlorophyll as do plants, and cannot manufacture their own energy, but do consume or absorb organic matter. They have a true nucleus in their cells and are able to sexually reproduce by combining like strains of nucleus. They can also reproduce asexually by spores similar to some of the more primitive plants e.g. ferns, liverworts and mosses. Modern molecular studies have shown that fungi are more closely related to animals than to plants.
Fungi have hyphae or long filaments which spread widely through soil, rotten wood, etc., secreting enzymes to dissolve the organic matter, and absorbing the nutrients. The hyphae continue accumulating nutrients until the internal and external conditions are right for the production of the “fruiting body,” which is the stalk and cap of the visible mushroom you can see above the ground, in the case of mushrooms. “Fruiting” body in this case is a term for the part of a fungus that disperses spores, and is akin to the real fruit of a real fruiting tree, such as an apple tree.
The singular for fungi is fungus, and fungi include yeasts and molds, and pathogens, which are microscopic organisms that can cause infections in animals and plants.
More nformation about Fungi at the link below.
Simple multi-cellular and uni-cellular (one celled) organisms that are neither plant nor animal are called Protists, and belong to the Kingdom Protista. Examples of Protists are Amoeba, Slime Moulds, some Algae, and Paramecium. Animal-like Protists are called Protozoa. They eat by phagocytosis, i.e. they engulf their food in their cell membrane, and pinch off a section of membrane to form a hollow space inside the cell.
The other Kingdoms of Life are Kingdom Animalia and Kingdom Plantae, also called the Animal Kingdom and the Plant Kingdom.
These 3 Kingdoms (Protista, Animalia and Plantae) are said to belong to one larger category or group of living organisms called the Eukaryotes. They are said to have Eukaryotic cells.
There are traditionally 5 Kingdoms of Life, as shown in the picture below, although the Kingdom Monera is questionable, and not always included in charts of the Kingdoms of Life.
Organisms are divided into autotrophs and heterotrophs according to their energy pathways. Autotrophs are those organisms that are able to make energy-containing organic molecules from inorganic raw material by using basic energy sources such as sunlight. Plants are the prime example of autotrophs, using photosynthesis. All other organisms must make use of food that comes from other organisms in the form of fats, carbohydrates and proteins. These organisms which feed on others are called heterotrophs.
Click here to read about the differences between Respiration and photosynthesis. You can see from the information that Plants and Animals complement each other. Plants give off Oxygen which Animals need, and some animals help fertilise and otherwise help some Plants, e.g. birds spread plant pollen and help fertilise plants.
Click here to read about how scientists classify living organisms (taxonomy).