Plant Kingdom
NCERT Biology | Class 11 CBSE | NEET-UG Preparation
Chapter overview:
Learn the classification of the plant kingdom, major characteristics of algae, bryophytes, pteridophytes, gymnosperms and angiosperms, plant life cycles, and alternation of generations. This summary highlights important concepts for CBSE examinations and NEET-UG revision.
Algae: Characteristics and Classification
Algae are simple, chlorophyll-bearing, autotrophic organisms found mainly in aquatic environments. They may be unicellular, colonial or filamentous. Their body is generally not differentiated into true roots, stems and leaves.
General characteristics
- Most algae are aquatic, occurring in freshwater or marine habitats.
- They contain photosynthetic pigments and produce organic food.
- Vegetative reproduction commonly occurs through fragmentation.
- Asexual reproduction often involves spores, including zoospores in many forms.
- Sexual reproduction may be isogamous, anisogamous or oogamous.
Chlorophyceae: Green algae
- Chlorophyll a and chlorophyll b are the principal photosynthetic pigments.
- Chloroplasts may contain pyrenoids associated with storage and carbon fixation.
- Stored food is mainly starch, commonly associated with pyrenoids.
- Cell walls commonly contain an inner cellulose layer and an outer pectose layer.
- Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.
Phaeophyceae: Brown algae
- Mostly marine organisms, especially common in colder seas.
- Contain chlorophyll a, chlorophyll c and fucoxanthin, which gives them a brown appearance.
- The body may be differentiated into holdfast, stipe and frond.
- Stored food includes laminarin and mannitol.
- Cell walls commonly contain cellulose and algin.
- Examples: Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
Rhodophyceae: Red algae
- Mostly marine, with many species found in warmer waters.
- Contain chlorophyll a, chlorophyll d and phycobilin pigments, especially phycoerythrin.
- Phycoerythrin contributes to their red colour.
- Stored food is floridean starch.
- Motile or flagellated stages are absent.
- Examples: Polysiphonia, Porphyra, Gracilaria and Gelidium.
Comparison of the major algal classes
| Feature | Green algae | Brown algae | Red algae |
|---|---|---|---|
| Class | Chlorophyceae | Phaeophyceae | Rhodophyceae |
| Important pigments | Chlorophyll a, b | Chlorophyll a, c; fucoxanthin | Chlorophyll a, d; phycoerythrin |
| Reserve food | Starch | Laminarin and mannitol | Floridean starch |
| Common habitat | Freshwater and marine | Mostly marine | Mostly marine |
| Examples | Spirogyra, Chara | Sargassum, Laminaria | Porphyra, Gelidium |
Economic importance of algae
- Algae are important primary producers in aquatic ecosystems.
- Some are used as food, including species of Porphyra and Laminaria.
- Agar obtained from certain red algae, including Gelidium and Gracilaria, is used in laboratories and food products.
- Algin is obtained from brown algae and has industrial applications.
- Carrageenan is obtained from certain red algae and is used as a thickening agent.
NEET focus: Match algal class with pigments, reserve food and examples. These comparisons are especially useful for multiple-choice questions.