Plant Kingdom — Class 8 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 8 Science, Biology — Chapter 17. Classifying the green world — from algae to flowering plants.
1. About this chapter
This chapter covers the classification of the plant kingdom into cryptogams and phanerogams, the groups within each, and the difference between monocots and dicots.
2. Cryptogams — non-flowering, seedless plants
The plant kingdom is first divided into cryptogams (no flowers, no seeds) and phanerogams (seed-bearing). Cryptogams have three groups:
- Thallophyta — simple plants with a thallus (no true root, stem or leaf), e.g. algae (Spirogyra, Chlamydomonas).
- Bryophyta — mosses and liverworts; they need water to complete their life cycle, so they are called the "amphibians of the plant kingdom."
- Pteridophyta — ferns; the first plants with vascular tissue (xylem and phloem) for transport.
3. Phanerogams — seed-bearing plants
Phanerogams (seed plants) have two groups:
- Gymnosperms — bear naked seeds (not enclosed in a fruit), e.g. pines, cycas.
- Angiosperms — flowering plants whose seeds are enclosed inside the ovary/fruit.
4. Angiosperms — monocots and dicots
| Feature | Monocots | Dicots |
|---|---|---|
| Seed leaves (cotyledons) | one | two |
| Leaf venation | parallel | reticulate (net) |
| Roots | fibrous | tap root |
| Example | grass, maize | bean, mango |
5. Worked examples
Example 1. Why are bryophytes called amphibians of the plant kingdom? Because they live on land but need water to complete their life cycle (reproduction).
Example 2. What are naked-seeded plants called? Gymnosperms.
Example 3. How many cotyledons does a monocot seed have? One.
6. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- Plants that produce seeds enclosed in a fruit are — (a) gymnosperms / (b) angiosperms. Ans: (b) angiosperms.
- The "amphibians of the plant kingdom" are — (a) bryophytes / (b) pteridophytes. Ans: (a) bryophytes.
- The first plants to have vascular tissue are — (a) thallophytes / (b) pteridophytes. Ans: (b) pteridophytes.
- A plant with naked seeds is a — (a) gymnosperm / (b) angiosperm. Ans: (a) gymnosperm.
- A monocot seed has ____ cotyledon(s) — (a) one / (b) two. Ans: (a) one.
II. Fill in the blanks 6. Plants without flowers and seeds are called cryptogams. 7. Algae belong to the group thallophyta. 8. Dicot leaves show reticulate (net) venation.
III. Match / Answer briefly 9. Differentiate gymnosperms and angiosperms. 10. Give one example each of a monocot and a dicot.
7. Common mistakes
- Mistake: Calling pteridophytes the amphibians of the plant kingdom. Fix: Bryophytes are the amphibians; pteridophytes are the first vascular plants.
- Mistake: Saying gymnosperms have seeds inside fruit. Fix: Gymnosperm seeds are naked; only angiosperm seeds are enclosed in the ovary/fruit.
- Mistake: Swapping monocot and dicot features. Fix: Monocot = one cotyledon, parallel veins, fibrous roots; dicot = two cotyledons, net veins, tap root.
8. Quick revision
- Biology Ch 17 · plant classification.
- Cryptogams (no seeds): thallophyta (algae), bryophyta (mosses = amphibians), pteridophyta (ferns = first vascular).
- Phanerogams (seeds): gymnosperms (naked seeds) and angiosperms (seeds in fruit).
- Angiosperms split into monocots (1 cotyledon) and dicots (2 cotyledons).
