organism

We know that everything around us can be either living, such as animals, humans, and plants, or non-living, such as rocks, sand, and water. Living things are capable of reproduction, growth, homeostasis, and reaction to stimuli, they embody properties of life, and in biology are called organisms. Organisms are recognized by having an organized structure. The organism is a synonym for a life form. On Earth, About 8.7 million (give or take 1.3 million) is the new, estimated total number of species.

In this lesson we are going to learn:

• What are organisms?
• Types of living organisms.
• Characteristics of living organisms.

Living things that have organized structures, reproduce, grow, can react to stimuli, and maintain homeostasis are called organisms. Organisms can consist of a single prokaryotic cell, and these are called prokaryotes, or can consist of eukaryotic cells, and these are called eukaryotes. Prokaryotes lack a distinct cell nucleus and their DNA is not organized into chromosomes. Eukaryotic cells are much more complicated than those of prokaryotes and have a nucleus enclosed within a nuclear envelope.

All organisms can be made up either of one cell or more than one cell. From there, organisms can be classified into two different categories, unicellular microorganisms, and multicellular organisms.

 

Multicellular organisms

Multicellular organisms are made up of more than one cell, varying from organisms made up of a few to trillions of cells. Our bodies are composed of trillions of cells. These organisms are animals, plants, and fungi. 

• Animals are multicellular eukaryotic organisms, that eat, breathe, grow, reproduce, move, and have senses. Examples are tigers, elephants, bees, snakes, bears, frogs, and others.
• Plants are mainly multicellular eukaryotic organisms that make their own food, respire, reproduce, grow, and respond to stimuli. Trees, grass, and flowers are examples of plants. 
• Fungi are eukaryotic organisms that include microorganisms such as mold and yeasts and mushrooms.

Multicellular organisms cells are able to perform specific functions. A group of such cells is called a tissue. Several types of tissue work together in a form of an organ.

Unicellular microorganisms

Unicellular microorganisms are made up of only one cell. Such organisms are protists, bacteria, and archaea.

• Protist is any eukaryotic organism that is not an animal, plant, or fungus.
• Bacteria constitute a large domain of prokaryotic microorganisms, which are among the first life forms on Earth. Bacteria are a type of biological cell.
• Archaea are microorganisms that constitute a domain of single-celled organisms, initially classified as bacteria. They lack cell nuclei and are therefore prokaryotes. 

But, both, unicellular microorganisms and multicellular organisms share the same characteristics, which are:

• Nutrition
• Respiration
• Movement
• Excretion
• Growth
• Reproduction
• Sensitivity
• Homeostasis

Characteristics of organisms

Nutrition

The process by which organisms take their food is called nutrition. All living organisms need food to grow, stay alive, and get energy. 

• Plants make their own food through a process called photosynthesis. 
• Animals get their food from other living organisms. Some of them eat plants and are called herbivores. Some of the animals eat other animals, and they are called carnivores. Other animals eat both, plants and other animals, and are called omnivores. And there are some animals that feed on rotting plants and animals. Those are called decomposers. 

Respiration

Respiration is an essential life process carried out by all living organisms to provide the energy that organisms need to function. Cells need and use the energy that is formed through this process to assist with life processes in order for organisms to survive and reproduce. It is also called cellular respiration because it happens in the cells.

Respiration usually involves exchanging two gases—oxygen and carbon dioxide. The cells take in oxygen and release carbon dioxide. This form of respiration is called aerobic respiration. Another form is anaerobic respiration, which is performed without oxygen. 

Movement

 

All living organisms move. While for some is too obvious, like the animals, for some of them it is not, like the plants. All organisms move in different ways, and with help of different organs. Animals move with the help of their muscular and skeletal systems. The movement of an organism from place to place is called locomotion.

Excretion

Excretion is the removal of toxic materials, waste products of metabolism, and substances in excess, from the body of an organism. All living things excrete. As a result of the many chemical reactions occurring in cells, waste products are occurring. Organisms have to get rid of waste products because they might poison the cells.

Growth

Growth is the increase in size and mass of that organism.  For multi-cellular organisms, this is done by making more cells. Unicellular organisms may stay as one cell but they grow too. The transformation of the organism as it goes through the process of growing is called development. 

Reproduction

All living organisms have the ability to produce offspring. Each individual organism exists as the result of reproduction. Reproduction is a fundamental feature of all known life. There are two forms of reproduction:

• sexual reproduction, which requires the sexual interaction of two specialized organisms.
• asexual reproduction, where new offspring is produced by a single organism.

Sensitivity

Organisms are able to sense and respond to stimuli around them. Anything in the environment that causes a change is called a stimulus. Stimuli can be external or internal. Organisms react to many stimuli, including light, temperature, water, odor, pressure, etc. A flower opening in the sunlight is one example of a plant responding to stimuli.

Homeostasis

To function properly, cells require appropriate conditions which are not constant (temperature, pH, etc). But, despite the changes in the environment, organisms are able to maintain internal conditions within a narrow range. This process is called homeostasis. All living organisms, whether unicellular or multicellular, exhibit homeostasis.

What have we learned?

• Organisms are living things that have organized structures, reproduce, grow, can react to stimuli, and maintain homeostasis.
• Organisms can be eukaryotes and prokaryotes.
• Organisms can be unicellular or multicellular.
• All organisms share the same characteristics: nutrition, respiration, movement, excretion, reproduction, growth, sensitivity, and homeostasis.