Haeckel’s Three kingdom classification system

Ernst Haeckel introduced Haeckel’s Three kingdom classification system; the three kingdoms were Animalia, Plantae, and Protista.

Introduction

Ernst Haeckel was born on February 16, 1834. Haeckel was a zoologist, an accomplished artist and illustrator, and later a professor of comparative anatomy.

Although Haeckel’s ideas are important to the history of evolutionary theory, and although he was a competent invertebrate anatomist most famous for his work on radiolaria, many speculative concepts that he supported are now considered incorrect.

For example, Haeckel described and named hypothetical ancestral microorganisms that have never been found.

Features of Haeckel’s Three kingdom classification system

Ernest Hackle introduced the Three Kingdoms classification system in 1866, solved the first objection, and produced the 3rd kingdom Protista for that organism with characters, plants, and animals.

In the kingdom Protista, all the organisms that create problems in the two-kingdom classification are included in the kingdom Protista. So he classifies all living organisms into three kingdoms. Animalia, Plantae, and Protista were the three kingdoms that Haeckel recognized.

Kingdom Plantae

Kingdom Plantae comprises autotrophic organisms that can produce their own food through photosynthesis. Autotrophs can synthesize their food from inorganic substances like carbon dioxide, water,kingdom, and sunlight. The word ‘auto’ means self, and ‘troph’ means nourishment.

Through the process of photosynthesis, autotrophs can convert light energy into chemical energy that the organism can use. The chemical reaction for photosynthesis is:

6CO2 + 6H2O + Light energy ——–> C6H12O6 + 6O2

So autotrophs take carbon dioxide and water as raw materials and, using sunlight, can produce glucose and oxygen as end products. The glucose produced gives them the energy they need to grow and survive.

Using sunlight, autotrophs can manufacture complex organic molecules like sugars, proteins, fats, etc. from simple inorganic molecules. Nearly all plants are autotrophs, as well as algae and some bacteria. These autotrophic organisms are classified under the kingdom Plantae.

The kingdom Plantae is characterized by organisms that are non-mobile, have cell walls made of cellulose, and carry out photosynthesis. The kingdom consists of various organisms such as flowering plants, conifers, ferns, mosses, liverworts, green algae, red algae, brown algae, and more.

These organisms play a vital role in most ecosystems, as they form the base of the food chain and provide food for heterotrophs. Threcosystems,ough the process of photosynthesis, they also provide much of the oxygen in Earth’s atmosphere.

In summary, Kingdom Plantae consists of diverse autotrophic organisms that can synthesize their own food through photosynthesis and form the primary producers in most ecosystems.

Kingdom Animalia 

Kingdom Animalia is characterized by heterotrophic organisms, like plants, that cannot produce their own food. Heterotrophs are organisms that obtain nutrition by consuming other organisms.

The word ‘hetero’ means ‘other’, and ‘troph’ means ‘nourishment.’ So, heterotrophs rely on autotrophs or other heterotrophs as sources of energy and carbon. Kingdom Animalia comprises multicellular eukaryotic organisms that ingest their food.

They have to consume and digest organic molecules like carbohydrates, proteins, and fats to get their energy, carbon, and nutrients. Unlike plants, they lack chloroplasts and cell walls. Animal cells also have centrioles, which play a role in cell division.

The kingdom Animalia contains a vast diversity of organisms divided into two broad categories – invertebrates and vertebrates. Sponge, worm, mollusk, arthropod, and echinoderm species account for approximately 95% of all animal species.

Fish, amphibians, reptiles, birds, and mammals are vertebrates. Although nutrition is heterotrophic, the precise mode of feeding is highly variable; many animals are predatory and seek for food, whereas others are parasites, detritivores, or filter feeders.

In summary, Kingdom Animalia contains complex heterotrophic organisms that require organic molecules for growth rather than synthesizing their own food, like plants. They exhibit mobility and depend on plants or other animals for their energy needs.

Kingdom Protista

Kingdom Protista comprises eukaryotic organisms that cannot be classified as plants, animals, or fungi. It is a highly diverse grouping containing protists with varied nutritional modes and features that are sometimes plant-like, animal-like, or fungus-like.

The protists in this kingdom are united by their relatively simple organization – they are unicellular, colonial, or multicellular, without highly specialized tissues. The kingdom includes an array of organisms, some of which show characteristics of both plant and animal kingdoms.

For example – Euglena has chlorophyll to produce its own food by photosynthesis like plants, but it is also motile and heterotrophic in the absence of light like animals.

Other examples of protists include algae, amoebas, paramecia, and slime molds. Kingdom Protista consists of the following major groups:

• Algae – include kelp, diatoms, and phytoplankton. Have chlorophyll and make food with photosynthesis.
• Protozoa – unicellular heterotrophs that ingest food. Include amoeba and paramecium.
• Slime molds – feed as individual amoebas but aggregate to form multicellular reproductive structures.
• Water molds – fungus-like protists that reproduce with spores.

In summary, Kingdom Protista is a diverse collection of eukaryotic organisms that lack the complex organization seen in plants, animals, and fungi. It includes unicellular and simple multicellular organisms with varied nutrition modes – autotrophic, heterotrophic, or both. They display a combination of plant, animal, and fungal characteristics.

Objections and Limitations

• However, Haeckel’s system was not widely accepted, and microorganisms continued to be classified as plants (for example, bacteria and fungi) or animals (for example, protozoa).
• Nucleated and anucleated organisms were kept together in protists.
• Heterotrophic bacteria and fungi are placed along with autotrophic algae.

Key Points:

• 📚 Ernst Haeckel introduced Haeckel’s Three kingdom classification system, and the three kingdoms recognised were Animalia, Plantae, and Protista.
• 🦠 The Three kingdom classification system aimed to address the classification of organisms that posed challenges in the two-kingdom system.
• 🌱 Kingdom Plantae comprises autotrophs that can make their food through photosynthesis or nitrogen fixation.
• 🐾 Kingdom Animalia includes heterotrophs that get their food from autotrophs or other sources, and it encompasses various types of animals, bacteria, and fungi.
• 🦠 Kingdom Protista comprises organisms that possess characteristics of both animals and plants, and they can produce food through photosynthesis.
• ⚠️ Haeckel’s system faced objections and limitations, such as the lack of clear division between prokaryotes and eukaryotes and classifying microorganisms as plants or animals.

Questions about the Three Kingdom classification system

References and Sources

1. Engelkirk, P. G., Duben-Engelkirk, J. L., & Burton, G. R. W. (2011). Burton’s microbiology for the health sciences. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.
2. Trivedi P.C., Pandey S, and Bhadauria S. (2010). Textbook of Microbiology. Pointer Publishers; First edition.
3. Tortora, Gerard J., Funke, Berdell R.Case, Christine L.. (2013) Microbiology: an introduction Boston: Pearson,
4. https://en.wikipedia.org/wiki/Comparative_anatomy

Also Read:

• The Five Kingdom Classification – Features and Limitations
• Two Kingdom System of Classification – History, Classification & Limitations