Who classified living organisms?
R.H. Whittaker gave the Five Kingdom classification for living organisms. He categorized living organisms based on multiple characteristics such as cellular structure, mode of nutrition, body organization, reproduction, phylogenetic relationship, etc. These five kingdoms were Monera, Protista, Fungi, Plantae and Animalia.
Plant Kingdom: Plantae
Kingdom Plantae includes all the plants. They are eukaryotic, multicellular and autotrophic organisms. The plant cell contains a rigid cell wall. Plants have chloroplast and chlorophyll pigment, which is required for photosynthesis.
Characteristics of Kingdom Plantae
The plant kingdom has the following characteristic features:
- They are non-motile.
- They make their own food hence are called autotrophs.
- They reproduce asexually by vegetative propagation or sexually.
- These are multicellular eukaryotes. The plant cell contains the outer cell wall and a large central vacuole.
- Plants contain photosynthetic pigments called chlorophyll present in the plastids.
- They have different organelles for anchorage, reproduction, support and photosynthesis.
Classification of Kingdom Plantae
A plant kingdom is further classified into subgroups. Classification is based on the following criteria:
- Plant body: Presence or absence of a well-differentiated plant body. E.g. Root, Stem and Leaves.
- Vascular system: Presence or absence of a vascular system for the transportation of water and other substances. E.g. Phloem and Xylem.
- Seed formation: Presence or absence of flowers and seeds and if the seeds are naked or enclosed in a fruit.
The plant kingdom has been classified into five subgroups according to the above-mentioned criteria:
Thallophytes lack a well-differentiated body structure and the plant body is thallus like.
- Primitive plants where the body is not differentiated into stem, roots and leaves
- Thallophyta includes plants with primitive and simple body structure. The plant body is thallus, they may be filamentous, colonial, branched or unbranched. Examples include green algae, red algae and brown algae.
Common Examples: Volvox, Fucus, Spirogyra, Chara, Polysiphonia, Ulothrix, etc.
- Bryophytes do not have vascular tissues. The plant body has root-like, stem-like and leaf-like structures. Bryophytes are terrestrial plants but known as “amphibians of the plant kingdom” as they require water for sexual reproduction. They are present in moist and shady places. Bryophyta includes mosses, hornworts and liverworts. Some of the common examples are Marchantia, Funaria, Sphagnum, Antheoceros, etc.
Pteridophytes have a well-differentiated plant body into root, stem and leaves. They have a vascular system for conduction of water and other substances. Some of the common examples are Selaginella, Equisetum, Pteris, etc.
- Gymnosperms have a well-differentiated plant body and vascular tissues. They bear naked seeds, i.e. seeds are not enclosed within a fruit. Some of the common examples of gymnosperms are Cycas, Pinus, Ephedra, etc.
- Angiosperms are seed-bearing vascular plants with a well-differentiated plant body. The seeds of angiosperms are enclosed within the fruits. Angiosperms are widely distributed and vary greatly in size, e.g. Wolffia is small measuring about 0.1 cm and Eucalyptus trees are around 100 m tall. Angiosperms are further divided into monocotyledons and dicotyledons according to the number of cotyledons present in the seeds.
Some of the common examples are mango, rose, tomato, onion, wheat, maize, etc.
Cryptogams and Phanerogams
The plant kingdom is also classified into two groups:
- Cryptogams: Non-flowering and non-seed bearing plants.
Example: Thallophyta, Bryophyta, Pteridophyta.
- Phanerogams: Flowering and seed-bearing plants.
Example: Gymnosperms, Angiosperms
Frequently Asked Questions
1. Name the pigment responsible for photosynthesis in plants.
Ans. Chlorophyll is the pigment responsible for photosynthesis in plants.
2. Describe the criteria for levels of classification in plants.
Ans. The plant kingdom is further classified based on the following three criteria:
- Plant body
- Vascular system
- Seed formation
3. Explain the characteristic of Thallophytes.
Ans. Members of this class lack a well-differentiated body structure, or in other words, the body is not clearly divided into stem, leaves and roots.
4. Explain the significant features of Gymnosperms.
Ans. Gymnosperms include plants that possess a vascular system and a well-differentiated body structure. Furthermore, they bear seeds like the angiosperms, but they are not encased within a fruit. Hence, the term “Gymnosperm”, which is derived from Greek word, gymno = naked and Sperma = seed.
5. List the characteristics of Angiosperms.
- Seed-bearing plants
- Seeds are enclosed within fruits
- Presence of well-differentiated plant body
- Produce flowers during their lifespan
- Presence of two subtypes – monocots and dicots