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Cell is the most fundamental and basic unit of life. The Majority of organisms around us are multicellular, however, others are unicellular that can perform all activities. There have been numerous attempts to classify organisms based on their organizational levels in relation to their complexity. Distinct creatures have different organizational structures, some basic and some complicated. There are five levels of organization namely cellular organization, tissue, organ, organ-system, and organism. The complexity of organisms and their life forms increases with each stage.
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Key Terms: Levels of Organisation, Cell, Tissue, Connective Tissue, Organs, Organ System, Organism
Levels of Organization
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Multicellular organisms are made of several parts that are divided into levels of the organization. There are basically five levels of organization:
- Cellular Level
- Tissue Level
- Organ Level
- Organ-System Level
- Organisms
Levels of Organization
Read More: Characteristics Of Organisms
Cellular Level
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The cellular level organization is the most basic level of organisation. In this, a single cell carries out each of the essential tasks for existence. There is no clear division of labor. Instead of existing as tissue, cells are present as aggregates. This group included all the solitary cells that belonged to the Phylum Porifera, such as sponges.
Read More: Invertebrates
Tissue Level
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When a collection of cells performs a certain function as a unit to create tissue. These cells, which are specialized to carry out numerous tasks, work together to support the foundation of life. Functions of living things are performed by epithelial, connective tissue, etc. Coelenterata and Ctenophora are two examples.
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Organ Level
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A collection of tissues that cooperate to carry out a certain function is known as an organ. The heart, kidneys, liver, and other organs are necessary for maintaining life in humans. When it comes to plants, the organs are the roots, stems, and leaves. Every organ performs a certain role. This form of organisation can be seen in many animal groups, including Platyhelminthes.
Organ-System Level
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It has to do with how various organs are arranged to make up a certain organ system. In this, a particular function is carried out by a collection of organs. For instance, the digestive system of Platyhelminthes is referred to as being incomplete since it only has one opening to the exterior of the body, which serves as both the mouth and the anus. A complete digestive system includes two openings, the mouth, and anus, as in the human body; it consists of the mouth, esophagus, stomach, bile duct, liver, pancreas, small intestine, large intestine, rectum, and anus. In the same way, under the organ-system level circulatory systems is of two types:-
- Open Type: Since no tissues, organs, or veins that come into direct contact with the blood are present, the blood in this condition flows directly by cavities. It can be found in both Phylum Mollusca, which includes Octopus, Snails, and Oysters, and Phylum Arthropoda, which contains Insects, Vectors, Pests, Lobsters, Crustaceans, and Crabs.
- Closed Type: In this, the heart pumps blood through veins, arteries, and capillaries. Blood does not fill body cavities because it is covered by vessels. It assists in distinguishing between oxygenated and deoxygenated blood and aids in preventing blood mixing. A closed-type circulatory system is present in all vertebrates and some invertebrates.
Open and Closed Circulatory Systems
Read More: Difference Between Small and Large Intestine
Organisms
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It is a living system that performs its own functions. An organism was made up of its organ systems. Unicellular organisms are those that are composed of a single cell that is capable of performing all of the functions of the organism. Others are referred to as multicellular organisms since they are made up of various organs and organ systems and perform their own tasks. There is a Protoplasmic level of organisation which is the lowest level of organisation in which all the necessary life functions are carried out by a single cell in its Cytoplasm and Protozoans come under this category.
Read More: Difference Between Vertebrates and Invertebrates
Things to Remember
- Single-cell carries out all the functions at cellular levels.
- Several cells work together to form tissue.
- A group of tissues works together to form an organ.
- A specific organ system is formed by the organisation of various organs.
- Organ systems that carry out their own functions make up an organism.
Previous Years Questions
- In plants, water supply is due to… [JIPMER 2009]
- The part of the leaf between the upper epidermis and the lower epidermis is called:… [JIPMER 1999]
- A bicollateral vascular bundle has the following arrangement of tissues ..............… [JCECE 2004]
- The apical meristem of the root is present… [NEET 2003]
- The common bottle cork is a product of… [NEET 2012]
- Bamboo and grasses elongate by the activity of......[KCET 2004]
- Specialized epidermal cells surrounding the guard cells are called – [NEET 2016]
- The annular and spirally thickened conducting elements generally develop in the protoxylem when the root or stem is… [NEET 2009]
- Some vascular bundles are described as open because of these… [NEET 2011]
- Somaclonal variation appears in plants… [DUET 2009]
Sample Questions
Ques. Which Phylum shows the organ-system level of organisation? (3 Marks)
Ans. Phylum which shows the organ-system level of organisation are-
- Platyhelminthes- Fasciola (Liver fluke), Taenia (Tapeworm)
- Aschelminthes- Ascaris (Roundworm), Wuchereria (Filaria Worm)
- Annelida- Pheretima (Earthworm), Nereis
- Arthropoda- Insects, Lobsters, and crabs
- Mollusca- Pila (Apple snail)
- Echinodermata- Asterias (Starfish), Echineos (Sea Urchin)
- Hemichordata- Balanoglossus, Saccoglossus
- Chordata- Pisces, Amphibia
Ques. What are organisms? (3 Marks)
Ans. Organisms are the last level of organization. They can carry out their own functions such as taking material in and pushing material out. There are some fully functioning organisms that are made of just one cell. According to the level of organization, organisms are made up of many organ systems working together.
Ques. Explain Organ System. (3 Marks)
Ans. Cells come together to form tissues and a group of tissues in turn form an organ carrying a specific work. When organs work together as a whole, they form organ systems. Organ systems help in keeping the body regulated and in a stable state. Organ systems often work together and rarely work alone. There are a total of 11 organ systems in the human body.
Ques. How significant is an air bladder in Pisces? (3 Marks)
Ans. Air bladder is present in class Osteichthyes, the air bladder controls balance and aids in swimming in the water which stops them from sinking. Animals belonging to the class Chondrichthyes lack an air bladder, hence they must swim continuously to keep from sinking.
Ques. What are the Mantle cavity and its functions? (3 Marks)
Ans. The tiny gap between the visceral hump and the mantle is called the mantle cavity. This has gills that resemble feathers, called ctenidia. They support excretion and respiration. For Example- Pila (Apple snail), Sepia (Cuttlefish), and Octopus (Devil Fish).
Ques. What is the difference between Chordates and Non-Chordates? (3 Marks)
Ans. The difference between Chordates and Non-Chordates is as follows:
| Chordates | Non- Chordates |
|---|---|
| The notochord is present. | The notochord is present. |
| The central nervous system is hollow, dorsal, and single. | The Central Nervous system is solid, ventral, and double. |
| Pharynx perforated by gill slits. | Gill slits are absent. |
| The heart is ventral. | The heart is dorsal (if present). |
| Post-anal tail is present. | Post-anal is absent. |
Ques. Why do cyclostomes migrate to freshwater? (3 Marks)
Ans. Cyclostomes are marine creatures that migrate to freshwater to reproduce and then die shortly thereafter. After undergoing a metamorphosis, their larvae re-enter the ocean to carry out the procedure. For Example- Petromyzon ( Lamprey) and Myxine (Hagfish).
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