NCERT Class 11 Biology Biology: Chapter 3 — Plant Kingdom
This chapter, 'Plant Kingdom,' delves into the detailed classification within Kingdom Plantae, building upon Whittaker's Five Kingdom classification. It clarifies that organisms like cyanobacteria, fungi, Monera, and Protista with cell walls are no longer classified under Plantae. The chapter outlines the historical evolution of classification systems, from early artificial systems based on superficial morphological characters to natural systems considering internal features and embryology, and finally to current phylogenetic systems based on evolutionary relationships. It also introduces modern approaches like Numerical Taxonomy, Cytotaxonomy, and Chemotaxonomy. The section on Algae describes them as chlorophyll-bearing, simple, thalloid, autotrophic organisms found in diverse aquatic and terrestrial habitats. Their reproduction methods—vegetative (fragmentation), asexual (zoospores), and sexual (isogamy, anisogamy, oogamy)—are explained, highlighting their varied forms from colonial to filamentous and massive structures.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biology |
| Book | Biology |
| Chapter | Chapter 3 — Plant Kingdom |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 640 |
Learning outcomes
- Understand the historical development of plant classification systems.
- Differentiate between artificial, natural, and phylogenetic classification.
- Identify the characteristics of algae and their habitats.
- Describe the different modes of reproduction in algae (vegetative, asexual, sexual).
- Recognize the diversity in form and size among algae.
Vocabulary
| Word | Meaning |
|---|---|
| Thalloid | A plant body not differentiated into stem, root, and leaves. |
| Autotrophic | Organisms that can produce their own food using light, water, carbon dioxide, or other chemicals. |
| Zoospores | Motile spores, typically flagellated, produced asexually. |
| Isogamous | Fusion of two gametes that are similar in size and morphology. |
| Anisogamous | Fusion of two gametes that are dissimilar in size. |
| Oogamous | Fusion between one large, nonmotile female gamete and a smaller, motile male gamete. |
| Phytochemistry | The study of chemicals derived from plants. |
| Cytotaxonomy | Classification based on cytological information, such as chromosome number and structure. |
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Practice questions
- What are the main characteristics of algae? Answer: Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic organisms.
- Name the three types of reproduction found in algae. Answer: Algae reproduce by vegetative, asexual, and sexual methods.
- What is vegetative reproduction in algae by fragmentation? Answer: Each fragment of the alga develops into a new thallus.
- Define isogamy, anisogamy, and oogamy. Answer: Isogamy is the fusion of similar gametes; anisogamy is the fusion of dissimilar gametes; oogamy involves the fusion of a large female gamete with a smaller male gamete.
Frequently asked questions
What is the 'Plant Kingdom' in biological classification?
The 'Plant Kingdom' refers to the classification group Plantae, which includes multicellular eukaryotic organisms that are generally photosynthetic.
Why are cyanobacteria no longer considered algae?
Cyanobacteria, also known as blue-green algae, are prokaryotic and have been reclassified, now being excluded from the Plantae kingdom.
What is the main difference between artificial and natural classification systems?
Artificial systems are based on superficial characters (like habit, colour), while natural systems consider a wider range of features, including internal anatomy and embryology.
What is phylogenetic classification?
Phylogenetic classification is based on the evolutionary relationships between organisms, assuming they share a common ancestor.
Where are algae typically found?
Algae are predominantly aquatic (freshwater and marine) but can also be found in moist stones, soils, and wood, or in association with fungi (lichens) and animals.
What are zoospores in algae?
Zoospores are flagellated, motile spores produced during asexual reproduction in algae, which germinate to form new plants.
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NCERT Class 11 Biology — Biology — Chapter 3 — Plant Kingdom. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.