Table of contents
Learning objectives
By the end of this section, you should be able to:
- Describe living things.
- Explain the functions of living things.
Introduction
No matter how simple (e.g, bacteria) or complex (e.g, human) an organism may be, being alive and active means we all share many basic characteristics.
All Living organisms are referred to as living things.
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| Characteristics of Living organisms |
Living things are differentiated from non-living things because living things possess characteristics which non-living things do not, unless you ever saw a table talked or danced.
What makes a living thing?
At the most fundamental level, a living thing is composed of one or more cells. Living things that have just one cell are referred to as UNICELLULAR organisms, while living things with multiple cells (more than one cell or many cells) are referred to as MULTICELLULAR organisms.
A simple unicellular organism performs all its life function within just one cell. Cells are microscopic (very small and cannot be seen with the bare eye), therefore almost all unicellular organisms are microscopic. Unicellular organisms exist as free living, colonies, or filaments.
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| Unicellular organism: Amoeba. Photo_credit: iStock |
However, multicellular organisms do not just contain microscopic cells carrying out life processes, these cells group, specialise and organize themselves.
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| Multicellular organism: Mushroom |
Every multicellular living organism arise from one cell (the egg cell from the female after fertilization; or the cell that chose to divide in the case of asexual reproduction).
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| Fertilised Egg cell |
Afterwards, this cell begins to divide, producing so many cells.
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| Cell Multiplication |
These numerous cells then begin to start grouping themselves, that is, they begin to find others that they are compatible with.
After a number of cells successfully form a group, they start performing a specific function, more like a cooperative work, these grouped cells are referred to as a TISSUE.
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| Tissue: Formed from joining together of several cells |
Just the way cells group together to form a tissue, tissues also group together to perform a specific function. Several tissues that group together form an ORGAN. Organs like the eyes, nose, tongue, are simply a combination of various tissues, which aim to perform functions of sight, smell and taste respectively.
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| Tissues group together to give rise to an Organ |
I know you would be expecting organs to group themselves by now too eh, yeah, several organs work together to perform specific function.
Just one organ can hardly work alone to perform a full task, it needs to connect with others, these form a SYSTEM.
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| The several systems in the human body |
For example, when an organism feeds, its mouth, which has other organs like teeth, tongue and salivary glands, their function is to grind and swallow the food, mouth cannot digest the food so it needs to pass the food to another organ to perform the next work, food passes through the organism's oesophagus by peristalsis (upward and downward movement of the oesophagus) down to its stomach. Stomach is also another organ that temporarily stores the food and releases some chemicals to act on the food, stomach does its own work and then passes the food through an opening called Pyloric sphincter, to another organ which is the small intestine where final digestion and absorption take place. Waste products are then passed down to another organ which is the large intestine, then to the rectum and finally to the anus until the waste product is completely eliminated.
You could see that these are several organs that worked together to perform just one function, (Digestive function), therefore these organs form the digestive system.
However, an organism that can only perform digestive function is incomplete, it needs to respire and perform other characteristics before it can be a fully functional living thing, therefore several other organs form several other systems to make a fully functional multicellular organism.
What are the Characteristics that all Living organisms possess or must possess?
Characteristics of living things
During your basic level, you may have been taught the acronym MRNIGERD,or MRSGREN, pronounced as Mister Naija Dee or Misiss Gren.
MRNIGERD or MRSGREN or MRNIGERCAD are acronyms to remember the characteristics of living things back then,
Where:
M stands for Movement.
R stands for Respiration.
N stands for Nutrition.
I stands for Irritability which is another name for sensitivity or responsiveness.
G stands for Growth.
E stands for Excretion.
R stands for Reproduction.
C stands for Competition.
A stands for Adaptation.
D stands for Death.
However, you're in a higher level now so your level of thinking also needs to grow: characteristics of all Living things are:
If you wish to use an acronym which you can remember, rearranging this, you can use the acronym MRGOHARD, pronounced as Mister Go Hard.
Organization
Living things are highly organized. The smallest part of an organism is a cell. Some single-celled organisms are free-living and they contain structures, called organelles, that allow them to be self-sufficient.
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| Animal Cell |
More complex organisms are multicellular. Cells organise to become tissues, e.g muscle tissue. Tissues organise to become organs, e.g heart. Organs organise to become systems, e.g cardiovascular system. Several systems functioning together make up a living organism.
A population is an organization of more than one individual. This is generally all of only one species in a particular area. We could talk about the population of squirrels in our area or dogs or cats.
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| Fowl Population |
Enlarging our view, comes a Community. An example of a community is the town or place we live. A more accurate biological description would include all the living things in that area, that is, all the plants and animals living in that area.
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| A simple community |
An Ecosystem not only considers the living things in an area, but also the physical environment and the interrelated flow of energy. You may live in a desert ecosystem, a forest ecosystem, or another kind of ecosystem.
Most complex of all is the Biosphere. In our case, this includes all the areas of our planet where living things are found.
Metabolism
Most of us call this eating!
Living things have the ability to exchange chemical materials. In other words, living things are able to convert food, a form of energy, to chemicals which the cells can use through a process which is referred to as metabolism. It is the transformation of energy or matter from one form to another form.
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| Metabolism |
There are 2 types of Metabolism:
Catabolism: which is the breakdown of complex molecules into simpler ones, like the Digestion of complex food molecules (rice and beans) to simpler and absorbable molecules (glucose and amino acids).
Anabolism: which is the build up of complex molecules from several simpler ones, like the growth of bones or the build up of complex glycogen from molecules of glucose.
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| Catabolism and Anabolism |
Metabolism also involves exchange of chemicals with the external environment, and transformations of organic and chemical matter within the cells of a living organism.
Organisms like plants, algae, and a few microorganisms are autotrophs. Autotrophs that we are most familiar with are Green plants that employ photosynthesis to make their own "food."
A number of bacteria use chemosynthesis for food production.
Animals and fungi are heterotrophs, they capture their food in various ways.
The ability to acquire and use energy is extremely important. Without a constant input of usable energy, organisms would quickly become "disorganized" and die.
Homeostasis
Homeostasis is the regulation of a constant internal environment in living organisms.
In order to survive, organisms must be able to achieve homeostasis. Each kinds of organism has specialized ways to stay in balance with external and internal environments. A paramecium has a contractile vacuole that pumps excess water out of its cell in order to survive in a fresh water environment. You and I have an internal "thermostat" that helps us maintain a body temperature of about 98.6 degrees Fahrenheit (37°C). Non-living things do not display homeostasis.
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| Homeostasis |
Responsiveness
All living things are able to respond to stimuli or actions in the external environment. This often results in movement of the individual toward safety. This helps to ensure survival of the organism.
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| Man responds to danger stimuli |
For example, living things respond to changes in light, heat, sound, and chemical or mechanical contact. To detect stimuli, organisms have organs for receiving information, such as eyes, ears, and taste buds.
To respond effectively to changes in the environment, an organism must coordinate its responses. A system of nerves and a number of chemical regulators called hormones, coordinate activities within an organism. The organism responds to the stimuli by means of a number of effectors, such as muscles and glands. Energy is generally used in the process.
Organisms change their behaviour in response to changes in the surrounding environment. For example, an organism may move in response to its environment. Responses such as this occur in definite patterns and make up the behaviour of an organism.
Behaviour is active, not passive; an animal responding to a stimulus is different from a stone rolling down a hill.
Plants have restricted ability to move. Shoots grow up towards the sun, and some have leaves that are able to bend towards the direction of sunlight (phototropism), allowing them to photosynthesize better.
Plant's roots grow downwards to obtain water and minerals. If a plant doesn't acquire enough sunlight, water or minerals it will die.
Living things display responsiveness; non-living things do not.
Growth
Growth is an increase in the total size and mass of a matter.
Growth requires an organism to take in materials from the environment, and transform the materials into its own structures. For example, a poultry fowl grows by the internal transformation of its feed, to its body structures.
Growth is the maintenance of a higher rate of anabolism (build up) than catabolism (break down).
A growing organism increases in size in all of its parts, rather than simply accumulating matter.
During growth, a living organism transforms material that is unlike itself into materials that are like it.
A human, for example, digests a meal of meat and vegetables and transforms the chemical material into more of himself or herself.
A non-living organism does not display this characteristic.
Reproduction
Living things have the ability to produce copies of themselves by a process known as reproduction.
Among plants and simple animals, reproduction is often an extension of the growth process.
For example, bacteria grow and quickly reach maturity, after which they split into two organisms by the process of asexual reproduction. Asexual reproduction involves only one parent, and the resulting cells are generally identical to the parent cell, that is, they look exactly the same.
All living things, even the smallest bacteria, have chromosomes containing DNA.
Prokaryotes like bacteria have circle–shaped chromosomes, called plasmid.
Eukaryotes, e.g multicellular organisms like plants and humans, have a species-specific number of chromosomes. As humans, we have 46 chromosomes, i.e, 23 pairs.
Genes in chromosomes contain instructions for an organism's structure and function.
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| DNA inside a Chromosome |
Many organisms reproduce sexually. Organisms like earthworms and snails are hermaphrodites, that is, only one organism having both male and female sexual organs. Most others have separate sexes, 'male and female' like marijuana plants, fish, birds, cattle and humans.
In order for two organisms to combine their genetic information without doubling the number of chromosomes given to offspring, Nature came up with a way to reduce the number of chromosomes.
Without it, each new generation would have twice the number of parents' chromosomes.
This halving is done by meiosis in sex organs. In females, ovaries produce eggs that are haploid (half number of chromosomes, i.e, 23 chromosomes), and in males, testes produce sperms cells that are haploid (half number of chromosomes, i.e, 23 chromosomes).
During fertilization, sperm and egg unite to form a zygote, a diploid (haploid + haploid, i.e, 23 chromosomes + 23 chromosomes) individual. This new individual is different from either parent, although it contains characteristics from both. This is what gives us the great diversity of life.
In living things, we call this genetic biodiversity Non-living things have no such ability or requirements.
Adaptation
Modifications enable an organism to survive in its environment. Ability to survive a change in environmental conditions allows individuals to survive better and reproduce more.
Thus, their characteristics are passed on to future generations and that makes the species stronger.
It is important to note that individuals can only adapt to their environment, but species don’t adapt, they evolve.
During evolution, changes occur in populations, and the organisms in a population become better able to metabolize, respond, and reproduce. They develop abilities to cope with their environment that their ancestors did not have.
Death
Death is the permanent termination of all vital functions or life processes in an organism or cell.
Death involves a complete change in the status of a living entity—the loss of its essential characteristics.
After death, the remains of an organism become part of the biogeochemical cycle. Organisms may be consumed by a predator or a scavenger and leftover organic material may then be further decomposed by detritivores, organisms which recycle detritus, returning it to the environment for reuse in the food chain.
Summary
📌 Living things are characterized by several features which are not possessed by non-living things, these characteristics are abbreviated as MRGOHARD:
Metabolism, Responsiveness, Growth, Organisation, Homeostasis, Adaptation, Reproduction and Death.
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Test Questions
1.
What characteristics of living things can be viewed using a microscope
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