Organism - definition, types and examples | biology dictionary (2023)

organism definition

An organism is a single individual or being. Although it can have many separate parts, since the parts cannot survive without the organism, the organism cannot survive without the parts. Some organisms are simple, containing just one molecule of information that describes how to get energy and reproduce the molecule. Other more complex multicellular organisms go through complex mating rituals to bring together two haploid cells that fuse and become a new organism. Since the diversity of life on Earth is enormous, the definition of an organism is still in flux, and new definitions of what counts as an organism are constantly being introduced.

types of organisms

Scientists classify organisms into 3 domains and 6 kingdoms, although this has changed throughout history. There are 3 recognized domains, or the broader classification of organisms. These are bacteria, archaea and eukaryotes.


In its simplest form, an organism can be a bacterium, a DNA molecule containing genetic information surrounded by a protective plasma membrane. Organisms tend to isolate their information molecules from the external environment, where changes in pH and unknown chemicals can damage the molecule. Bacteria contain their DNA in a single ring and replicate it through a process known as binary fission. DNA replicates so that there are two rings, and the cell divides its contents into two halves, each receiving a ring of DNA.

Although bacteria are among the smallest organisms on Earth, they can have a big impact. It is believed that bacteria in the soil could accelerate the effects of climate change and that bacteria in the intestines of cows could be responsible for much of the greenhouse gases in the atmosphere. Other bacteria help us digest food, and some can make us sick.

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The Archaea domain contains nonbacterial bacteria-like organisms that can perform a variety of functions. For example, many archaea live in some of the most extreme environments on Earth, from hydrothermal vents to lakes so salty that no other life can take hold. However, archaea are also found in most "normal" habitats. Archaeal, bacterial, and eukaryotic organisms are thought to have branched off early in the history of life on Earth. Archaea exhibit high levels of antibiotic resistance and are thought to have evolved in response to a single antibiotic produced around the time the organisms diverged.

One of the newer genetic techniques, the polymerase chain reaction (PCR), relies on an enzyme produced by the archaic organism.aquatic thermos. The polymerase enzyme produced by this organism is very efficient at replicating DNA and can function at high temperatures. This is good because PCR requires DNA to be run at both high and low temperatures in order to replicate faster. HeTaq-polymeraseThe enzyme, as it is also called, allows us to produce a large amount of DNA in a short period of time. With this increased amount of DNA, it is easy to study the genetic code of organisms.


In a eukaryote, or organism that has a nucleus and membrane-enclosed organelles, DNA is contained in the nucleus, and highly specialized organelles complete the various functions of the cell. Some eukaryotes develop into highly complex multicellular organisms. The individual cells are then assembled into tissues that form organs. These organs allow large animals like us to move, eat, and reproduce. Most of the organisms you can imagine are eukaryotes.

All eukaryotic life begins as a single cell. The cell divides through the process of mitosis and becomes many cells. As cells begin to specialize, they receive different signals, chemical or electrical, and grow or change as needed. This allows large organisms to control processes in their bodies through the release of chemicals or through the nervous system.

Organisms in the Eukarya include 5 kingdoms: Animalia, Plantae, Fungi, Protozoa, and Chromista. Protozoa and chromistans are single-celled organisms that have organelles and membrane-bound nuclei. Fungi include mushrooms, molds, and yeasts. Plantae is a large and diverse group that includes everything from single-celled algae to the largest organisms on Earth: trees. Animalia contains most of the typical multicellular organisms that we would see in a zoo.


Some scientists even consider viruses to be organisms because they are self-replicating informational molecules, usually protected by a protein coat. The virus then uses the mechanisms of an infecting cell to replicate. Proponents of classifying the virus as an organism point to this, while other scientists point out that, unlike a living organism, the virus does not generate or store energy or the mechanisms to do so. As the debate progresses, it is important to note that the definition of life is not static. New evidence is found, observational methods are developed, and discoveries are made every day. It may not be long before life is found on another planet that functions very differently from life on Earth.

examples of organisms


Bees are an example of organisms that live socially. Many bees work to collect sugary nectar from flowers, which they store in their hive. They protect the hive and work cooperatively to build and repair it. The hive is usually attached to another organism, a tree. This is an example of a mutual relationship between organisms. The bees are given a place above the ground, away from bears and other animals that want to eat their honey. The tree has a source of pollination for reproduction. Bees are also important pollinators of agricultural crops. In fact, it is estimated that without bees, billions of dollars worth of crops could not be pollinated. That's a scary fact, considering that bees have been in decline around the world for decades.

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Tapeworms are an example of a parasitic organism or an organism that feeds on other organisms to survive. The tapeworm lives in the intestines of mammals and feeds on the dissolved nutrients that the mammal has worked so hard to obtain. Tapeworms reproduce in the intestines, lay eggs in the feces, and new animals are discovered when they come in contact with the eggs, which can lie dormant in the soil for years. Parasitism is a type of relationship between organisms in which one benefits and the other suffers. Individual parasites often do not kill their host because that would mean losing a home. However, a large parasite infestation can lead to malnutrition and even death if left untreated.

great white shark

Considered the top of the oceanic food chain, the great white shark is the quintessential predatory organism. The shark's keen sense of smell allows it to track the scent of blood miles underwater, leading it to injured animals and carcasses to devour. The great white shark is one of the few sharks documented jumping out of the water to attack its prey. Great white sharks often prey on seals, which are very agile and can outrun the shark. However, sharks usually attack from below, sharpening the seal and striking it with great speed. The cells around the shark's mouth are sensitive to tiny electrical impulses given off by the prey, and the shark can literally feel its prey before it touches it. This makes the Great White an ultimate predatory organism.

  • organelle– A membrane-bounded sac specialized for a specific function of a cell.
  • Organo– A collection of tissues or a group of cells in the body that are specialized for a specific function for the body.
  • eukaryote– A cell with organelles enclosed in a membrane and a nucleus.
  • prokaryotic– A cell without organelles or a nucleus enclosed in a membrane.


1. A single blue whale weighs almost 40,000 pounds. A colony of cottonwood trees that share a common root system and grow from the same seed weighs nearly 13 million pounds. The total weight of all bacteria on Earth is about 1.1 x 1014 or 110,000,000,000,000 pounds. What is the largest organism on Earth? eel

Answer to question #1

Bthis right. Although huge, the blue whale can't rival a forest of clonal cottonwoods. Although trees look like individuals to us, they are all connected to a huge underground root system. The oldest known tree, "Pando", is said to be 80,000 years old. Although collectively massive, bacteria represent trillions of individual organisms, all independent of one another. Take out a bacterium, the rest is fine. The roots of Ruina Pando and millions of trees can be lost. This makes the cottonwood the largest living organism.

2. Many plants produce offspring in the form of seeds. To produce seeds, the male gamete must meet the female gamete and fertilization must occur. This can happen with many eggs at once, and many plants are preparing a large number of seeds at the same time. You see a dandelion plant in your garden. The yellow petals of the three different flowers have been replaced by a white ball connected to hundreds of seeds. How many organisms are there?

Answer to question #2

Cthis right. The plant itself represents 1 organism. Each seed also represents an individual organism, as it arose after two haploid cells created a zygote. This zygote can develop into a whole plant. With 3 flowers and over a hundred seeds each, there are over 300 organisms on a single dandelion plant. Cold!

3. Aliens visit our planet. They add us to their categorization of life as a domain of "Eartharia". Could they be wrong?

Answer to question #3

Bthis right. Classification systems are simply a representation of the different relationships between animals. Since all life on Earth is believed to have the same root, scientists focus on the relationships between life on Earth. From an extraterrestrial perspective, it would be perfectly reasonable to classify all terrestrial organisms together.

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