What Is Life? A Guide to the Common Features of all Living Things
What is Life?
Take a moment and reflect on the huge diversity of the natural living world. Life has taken on a huge variety and complexity of form: bacteria and archaea dominate the microscopic world; plants form the basis of most ecosystems; animals interact with and around each other. Everywhere you look (almost) you see traces of life. Indeed, even locations that have been previously thought to be completely inhospitable to life are starting to reveal their secret ecosystems. Weird and wonderful organisms are being discovered in the depths of the oceans and at the centre of deserts (both hot and cold).
But have you ever stopped to think what links all of these different types of living organisms together? What separates a moss or a plant from a rock? All living things share seven key traits that identifies them as 'living.' We shall explore each trait individually until we have covered the seven characteristics of living things
The most obvious difference between a living and a non-living thing is their ability to move under their own power. Different living things move at different speeds - animals move very quickly whilst plants (with some notable exceptions) generally move slowly.
- The fastest moving animal on Earth is the Peregrine Falcon, which can move at 155mph (250kph).
- The fastest accelerating organism on Earth is the Hat Thrower Fungus which can go from 0-20mph in 2 millionths of a second.
Respiration is not simply 'breathing.' Respiration is a series of metabolic processes that releases energy stored in food. All living things need to release the energy from their food to fuel their other activities. There are two types of respiration commonly used in the living world:
- aerobic respiration releases energy using oxygen
- anaerobic respiration releases energy in the absence of oxygen
Metabolism is a constant process that begins at the conception of the organism; once metabolism ceases, the organism dies.
Kick a stone down a path and it doesn't know it has been kicked. Living things are capable of sensing, and responding to, environmental stimuli. It is a myth that humans have 5 senses - a sense is the ability to gather information about the world; humans have more than a dozen senses including pain, pressure, proprioception, hunger and thirst.
- Butterflys taste with their feet, catfish taste with their entire body.
- Some bizarre senses found in the living world include: sensing electricity (sharks and rays); sensing the Earth's magnetic field (migrating birds); sense polarisation of light (birds and insects); and heat vision (pit vipers)
Boulders do not spontaneously get bigger, houses do not suddenly grow another storey. On the other hand, all living things grow - they increase their size by assimilating biomolecules from their environment.
- The largest organism on Earth is not the Blue Whale. It is a fungus (Armillaria ostoyae) that measures nearly 10 square kilometers in size. This organism occupies 2384 acres of forest in Oregon's Blue Mountains (this could be one of the oldest organisms on Earth too!)
- The fastest growing organism on Earth is Giant Kelp (Macrocystis pyrifera) which can grow up to 2 feet per day
It is probable, as you sit there reading this hub, that you have parents. The chances are that your parents themselves have parents. You may even have children of your own. All living things reproduce - they create fertile offspring that can carry on their genes. There are many different reproductive strategies favoured across the natural world from parthenogenesis in lizards, to asexual reproduction in tapeworms and bacteria, to sexual reproduction favoured by most plants and animals.
- A baby blue whale is born after an entire year inside the womb. They are born weighing in at a hefty 3 tons and 25 feet long
- Aphids are one of the most versatile reproducers in the natural world. They can lay eggs, or go viviparous and give birth to live young (which can already be pregnant!) They can mate with males or undergo parthenogenesis and skip the need for a man completely. It has been suggested that, in perfect conditions with no predators, a single aphid could produce as many as 600 billion offspring in a single year.
Living things take in various chemicals for a series of reactions collectively known as 'metabolism.' The problem with this is that metabolism produces waste products that must be removed. Products that need removal include:
- Carbon Dioxide
- Undigestable food
- The human organ with the highest blood flow are the kidneys - these filter out waste products from our blood for excretion. Up to 2 litres of urine can be made per day
- The largest human organ of excretion is the skin
Living things release energy from their food through respiration, but first they must either make or consume this food. Autotrophs create their own food using energy from the sun or from hydrothermal vents. Heterotrophs get their food by consuming other living things.
- The Atlas moth spends its entire life searching for a mate - this time is limited to a few weeks as the adult does not eat...unlike its pupae stage which has a voracious appetite
- The largest mouth in the animal world belongs to the Bowhead Whale at 16 feet long, 8 feet wide and 12 feet high.
Can't remember all that? The Mneumonic 'Mrs. Gren' can be used to remember the common characteristics of living things
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Where Next? Life
- BBC Nature - Home
BBC Nature - telling Life’s amazing story Where wildlife goes, we follow, telling Life’s story via breaking news, features, opinions, amazing films and photographs of animals and plants.
- ARKive - Discover the world's most endangered species
ARKive - the ultimate multimedia guide to the world's endangered species. Includes endangered species videos, photos, facts & education resources.