Biological Classification: NCERT Class XI (Part 1)

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Biological Classification

Biological classification, also known as taxonomy, is the science of organizing living organisms into groups based on their similarities and differences. The main important points of biological classification include:

  1. Hierarchical organization: Organisms are classified into a hierarchical system of categories, starting with the broadest group (kingdom) and narrowing down to the most specific (species).
  2. Use of a standardized system: The most widely used system of classification is the Linnaean system, developed by Carl Linnaeus in the 18th century, which uses a binomial naming system (genus and species) for organisms.
  3. Use of physical and genetic characteristics: Organisms are classified based on their physical and genetic characteristics, such as morphology, physiology, biochemistry, and molecular biology.
  4. Evolutionary relationships: Classification reflects the evolutionary relationships between organisms, with closely related species placed in the same genus and broader groups containing more distantly related organisms.
  5. Constantly evolving: Classification is a constantly evolving field, as new information and technology become available, and as our understanding of evolutionary relationships changes.

Characteristics of the five kingdoms

The five kingdom classification system, proposed by Robert Whittaker in 1969, groups organisms into five major categories based on their characteristics:

  1. Monera: This kingdom includes prokaryotic organisms, such as bacteria, that lack a defined nucleus and other membrane-bound organelles. They are typically unicellular and can be found in a wide variety of environments.
  2. Protista: This kingdom includes eukaryotic organisms that are primarily unicellular, such as algae and protozoa. They can be photosynthetic or heterotrophic, and can exhibit diverse forms and lifestyles.
  3. Fungi: This kingdom includes eukaryotic organisms that are typically multicellular and absorb their food from other organisms. They can be found in many different forms, from mushrooms and yeasts to molds and lichens.
  4. Plantae: This kingdom includes eukaryotic organisms that are multicellular, typically photosynthetic, and have a cell wall. They include a wide variety of organisms such as mosses, ferns, and flowering plants.
  5. Animalia: This kingdom includes eukaryotic organisms that are multicellular, heterotrophic, and lack cell walls. They can be found in a wide variety of forms, from sponges and jellyfish to birds and mammals.

It’s worth mentioning that the classification of organisms is a constantly evolving field and some classification system like “Six kingdom” and “Three domain” system have been proposed as well.

Examples of five kingdoms

Here are some examples of organisms that belong to each of the five kingdoms in the classification system proposed by Robert Whittaker:

  1. Monera: Escherichia coli (bacteria)
  2. Protista: Amoeba (protozoa), Chlamydomonas (green algae)
  3. Fungi: Penicillium (mold), Agaricus (mushroom)
  4. Plantae: Pinus (pine tree), Rosa (rose)
  5. Animalia: Homo sapiens (human), Canis lupus (gray wolf)

It’s worth mentioning that these are just a few examples of the vast diversity of organisms that exist in each kingdom and there are many more examples in each kingdom that can be found in different habitats, environments and also with different characteristics.

What is three domain system?

The three-domain system is a classification system proposed by Carl Woese and George E. Fox in 1977 that divides organisms into three domains: Bacteria, Archaea, and Eukarya. This system is based on differences in the genetic makeup of organisms rather than on morphological or other traditional characteristics.

  1. Bacteria: This domain includes prokaryotic organisms that are unicellular and have a wide range of metabolic capabilities. They can be found in a wide variety of environments, including soil, water, and living organisms.
  2. Archaea: This domain includes prokaryotic organisms that are structurally similar to bacteria but have a unique genetic makeup and are often found in extreme environments, such as high temperatures, high salinities, and low oxygen levels.
  3. Eukarya: This domain includes eukaryotic organisms that have a defined nucleus and other membrane-bound organelles. They can be found in many different forms, from single-celled organisms such as protozoa to multicellular organisms such as plants and animals.

The three-domain system is now widely accepted by the scientific community and has replaced the traditional five-kingdom system in many fields of biology such as genetics, molecular biology and evolutionary biology.

Chlaymydomonas

Chlamydomonas is a genus of green algae that belongs to the kingdom Protista in the classification system proposed by Robert Whittaker. They are unicellular, photosynthetic organisms that can be found in a wide variety of environments, such as freshwater, soil, and even on surfaces such as mosses and lichens.

Chlamydomonas cells are typically spherical or elliptical in shape, and have two flagella that allow them to move through water. They have a simple cell structure, with a single chloroplast, mitochondria, and a small nucleoid region where the DNA is located. Some species of Chlamydomonas are able to survive in extreme conditions such as high salt or high temperature.

Chlamydomonas has been extensively studied as a model organism in the field of photosynthesis and micro algae biotechnology, due to its simple cell structure, easy cultivation and genetic manipulation.
Chlorella

Chlorella is a genus of green algae that belongs to the kingdom Protista in the classification system proposed by Robert Whittaker. They are single-celled, photosynthetic organisms that are commonly found in fresh and saltwater environments.

Chlorella cells are typically spherical or oval in shape, and are enclosed by a rigid cell wall made of cellulose. They have a simple cell structure, with a single chloroplast, mitochondria, and a small nucleoid region where the DNA is located. They are able to carry out photosynthesis efficiently and are known for their high rates of growth.

Chlorella reproduces asexually through binary fission, where the cell divides into two daughter cells. Some species of Chlorella can also reproduce sexually by forming a thick-walled zygote. Chlorella is an important primary producer in aquatic environments and is often used as a model organism in the study of photosynthesis and microalgae biotechnology. It is also used as a dietary supplement and in animal feed.

Paramoecium and Amoeba

Paramoecium and Amoeba are both genera of protozoa that belong to the kingdom Protista in the classification system proposed by Robert Whittaker. They are single-celled, eukaryotic organisms that can be found in a wide variety of environments, such as freshwater, soil, and even within other organisms.

  1. Paramoecium: This genus of protozoa is characterized by its cilia, which are short, hairlike structures that are used for movement. They are typically found in freshwater environments and are known for their ability to move in a coordinated manner, often forming chains or clusters. They have a simple cell structure, with a single chloroplast, mitochondria, and a small nucleoid region where the DNA is located.
  2. Amoeba: This genus of protozoa is characterized by its ability to change shape, which is achieved through the movement of pseudopodia, or false feet, that extend out from the cell. They are also found in freshwater environments and are known for their ability to engulf other organisms by using their pseudopodia. They have a simple cell structure, with a single chloroplast, mitochondria, and a small nucleoid region where the DNA is located.

Both genera are important model organisms in the study of cell biology and evolution, and are also used in research on parasitology, biotechnology and environmental science.