This is the third attempt at finding a suitable method for a project focussed on independent study.
Previously, a Q&A format was used. Despite the upsides there was often a need for prerequisite knowledge, proving the approach to be too narrow.
This latest method shifts the focus from essential questions to essential areas of study.
Beginning with biology and ecology, ChatGPT provided the essential topics that a beginner should know—starting with the characteristics of life.
What defines life?
There are various theories as to what constitutes life, which can be defined by what it does or what it is, depending on the scientific perspective.
For example, NASA defines it as a self-sustaining chemical system capable of Darwinian evolution.
Victor and George V. Tetz coined the term genetic information metabolism with the aim of categorizing living and non-living carriers of genetic information.
Simplifying it, they argue that living organisms have their own genetic material and perform biological processes independently.
The Encyclopedia Britannica has a solid article that looks at numerous definitions of life from different scientific perspectives and in some depth.
However, some of the refutations seem to rely semantics, such as that of a car being able to “metabolise”, to possibly rule out a definition.
But does imperfection mean incorrect?
So what are the characteristics of life?
Characteristics of Living Organisms
If you search for the characteristics of living organisms, the results typically list between seven and fifteen characteristics.
From 15 different sources, you will be shown 13 different characteristics.
- Complex chemistry
- Excretion
- Genetic inheritance
- Growth and change
- Homeostasis
- Highly ordered and structured
- Locomotion or movement
- Made of a cell or cells
- Metabolism
- Relies on a source of energy to survive
- Reproduction
- Responsive to stimuli
- Respiration
Complex chemistry
Complex chemistry refers to the chemical reactions that occur within cells that enable a living being to maintain life and carry out essential functions.
These reactions include processes such as energy production and waste management.
Excretion
Excretion is the process by which an organism removes waste, excess water or potentially toxic substances to maintain homeostasis.
This can be accomplished through various mechanisms such as exhalation, perspiration or urination.
Genetic inheritance
Genetic inheritance refers to the transfer of genes from parents to offspring via reproduction.
Genes are carried by reproductive cells and contain the instructions— DNA —for building and regulating the organism.
The genetic information passed on to offspring determines various traits, characteristics or even predisposition to certain diseases.
Growth & change
Living organisms have the capacity to grow and change in a variety of ways; whether it’s a plant growing larger and producing more leaves or a caterpillar transforming into a butterfly.
Single-celled (unicellular) organisms don’t grow nearly as large as multicellular organisms. However, they still consume nutrients or materials for energy, which are used for building or replacing structures within (see page 3), resulting in growth and change.
Homeostasis
Homeostasis refers to self-regulating processes that help a biological entity maintain stability; essentially, that which allows a living organism to survive and function correctly.
Highly ordered & structured
Christian Mayer suggests that a combination of structural order and functional complexity may mark the boundary between living and non-living matter
A highly ordered structure refers to the way molecules, cells, and systems within an organism are organised. This structured arrangement is what enables cells to carry out life processes.
“Only a combination of the two requirements, complexity and structural order, can mark the difference between living and dead matter,”
Locomotion or movement
While locomotion and movement sound similar, there are subtle differences between the two.
Locomotion typically refers to movement that changes an organism’s physical location, such as walking, swimming, or flying.
Movement, however, does not require locomotion. For example, breathing involves internal movement, such as the expansion and contraction of lungs, or the beating of a heart.
Made of a cell or cells
A cell is considered the most basic structural and functional unit of life.
As such, any living organism must be made of at least one cell to be considered alive.
Examples of unicellular organisms include bacteria and yeast, while animals and plants are multicellular.
There are, however, exceptions. For example, some bacteria can form multicellular structures.
Metabolism
Metabolism refers to the sum of all biochemical reactions that take place within an organism. It is sometimes described as the reliance on an energy source to survive.
There are two main types of metabolic processes— the ways in which an organism converts molecules into energy or uses them to build and repair structures:
- Anabolism – the building of complex molecules from simpler ones (e.g., forming proteins from amino acids)
- Catabolism – the breakdown of complex molecules into simpler ones (e.g., digestion or cellular respiration)
Reproduction
Living organisms can reproduce via sexual or asexual processes.
Sexual reproduction involves two parent cells and produces genetically unique offspring, with DNA that is a combination of both parents.
Asexual reproduction requires only one parent and results in genetically identical offspring. There are several types of asexual reproduction, including:
- Fission
- Budding
- Vegetative propagation
- Spore formation
- Fragmentation
- Parthenogenesis
- Apomixis
Responsive to stimuli
Living organisms respond to their environment and the stimuli within it. This typically involves moving towards or away from a stimulus, such as a plant growing towards light.
Some sources list responsiveness to stimuli and environmental adaptation as separate characteristics, while others group them together.
Respiration
Respiration is a chemical process that occurs in all living organisms to release energy from glucose.
There are two types of respiration:
- Aerobic respiration uses oxygen to break down glucose and produce energy efficiently.
- Anaerobic respiration breaks down glucose without oxygen, but produces less energy as a result.
This energy is used for essential functions such as growth, repair, and maintaining homeostasis.
Conclusion
Together, these characteristics offer a practical framework for identifying what we consider to be alive.
Even if different scientific fields have differences of opinion.