06Class 11 Biology
Anatomy of Flowering Plants short notes
Short notes on plant tissues and the differences between dicot and monocot anatomy, which is where most questions come from.
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Tissues
- Meristems are apical, intercalary or lateral. Lateral meristems cause secondary growth.
- Parenchyma: living, thin-walled, for storage. Collenchyma: living, with corner thickening, for flexible support. Sclerenchyma: dead, with lignified walls.
- Xylem has tracheids, vessels, fibres and parenchyma. Vessels are typical of angiosperms.
- Phloem has sieve tubes, companion cells, parenchyma and fibres. Gymnosperms have albuminous cells and sieve cells.
Dicot and monocot
- Dicot stem: a conjoint, open vascular bundle, with ring arrangement and cambium.
- Monocot stem: scattered, closed vascular bundles with no cambium, and a sclerenchymatous bundle sheath.
- Dicot root: 2 to 6 xylem bundles. Monocot root: more than 6, and a large pith.
- Dicot leaves are dorsiventral, with palisade and spongy mesophyll. Monocot leaves are isobilateral.
- Stomata have guard cells, bean-shaped in dicots and dumb-bell shaped in grasses.
- Bulliform cells in grasses help the leaf curl to reduce water loss.
Secondary growth
- Vascular cambium forms secondary xylem inside and secondary phloem outside.
- Spring wood is lighter and less dense than autumn wood. Together they make annual rings.
- Heartwood is dark and no longer conducts water, and sapwood still does.
- Cork cambium (phellogen) forms cork outside and secondary cortex inside.
- Lenticels allow gas exchange through the bark.
Where students slip up
- Saying sclerenchyma is living. Mature cells are dead.
- Giving monocot stems a cambium. Their bundles are closed.
- Reversing the direction of secondary tissues from cambium.
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