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These are complete NCERT Solutions for CBSE Class 11 Biology Chapter 6 — Anatomy of Flowering Plants. Attempt each question before checking. For anatomy questions, use precise tissue names — marks are given for terms like 'conjunctive', 'pericycle', 'vascular cambium', 'cork cambium', etc.
Key Concepts (Quick Recap)
- Meristems: Apical (tips — primary growth), Lateral (vascular cambium, cork cambium — secondary growth), Intercalary (at nodes — regrowth).
- Epidermal tissue system: Epidermis, cuticle, stomata (guard cells + subsidiary cells), trichomes, root hairs.
- Ground tissue system: Cortex (parenchyma, collenchyma, sclerenchyma), pericycle, pith, medullary rays.
- Vascular tissue system: Xylem (tracheids, vessels, xylem parenchyma, xylem fibres) + Phloem (sieve tubes, companion cells, phloem parenchyma, phloem fibres).
- Dicot stem: Vascular bundles in a ring, conjoint collateral open, endarch xylem, cambium present.
- Monocot stem: Vascular bundles scattered, conjoint collateral closed, no cambium, no secondary growth.
- Dicot root: Radial vascular bundles (xylem and phloem alternate), exarch xylem, tetrarch.
- Monocot root: Similar to dicot root but polyarch (many xylem bundles), large pith.
- Secondary growth: Vascular cambium → secondary xylem + secondary phloem; cork cambium → phellem + phelloderm; annual rings, heartwood, sapwood.
Intext Questions
Page 83
Q1. State the location and function of different types of meristems.
Answer
| Meristem | Location | Function |
|---|
| Apical meristem | Tips of roots and shoots | Primary growth — increases length |
| Lateral meristem | Along the sides of roots and stems (vascular cambium, cork cambium) | Secondary growth — increases girth/diameter |
| Intercalary meristem | At the base of internodes or leaf blades (nodes) | Regrowth of parts removed by herbivores; internode elongation |
Q2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Answer
Yes, this statement is correct. The cork cambium (phellogen) is a secondary lateral meristem that develops from the cortical cells of the stem. It divides and produces:
- Phellem (cork) on the outer side — dead cells with suberin in walls, impervious to water and gases.
- Phelloderm (secondary cortex) on the inner side — living parenchymatous cells.
Together, phellem + phellogen + phelloderm constitute the periderm, which replaces the epidermis as the protective layer in older stems and roots.
Page 87
Q1. Explain the process of secondary growth in the stems of woody angiosperms with the help of diagrams.
Answer
Secondary growth in dicot stems involves:
1. Formation of vascular cambium: The cambium present between xylem and phloem in vascular bundles (intrafascicular cambium) and the cells of the medullary rays (interfascicular cambium) join to form a continuous vascular cambium ring.
2. Activity of vascular cambium: The cambium divides periclinally, producing:
- Secondary xylem (wood) towards the inside — more production on the inner side pushes the cambium outward.
- Secondary phloem towards the outside — less in amount.
3. Annual rings: In temperate regions, cambium activity varies seasonally:
- Spring wood (early wood): Large, thin-walled, light-coloured xylem vessels produced in spring.
- Autumn wood (late wood): Small, thick-walled, dark-coloured xylem vessels produced in autumn.
- One spring wood ring + one autumn wood ring = one annual ring (used to estimate tree age).
4. Heartwood and sapwood: Inner older xylem becomes heartwood (hard, dark, non-functional in conduction, stores tannins/resins). Outer younger xylem is sapwood (lighter, functional in water conduction).
5. Cork cambium: Develops from cortical cells; produces cork (phellem) outside and secondary cortex (phelloderm) inside. The bark includes all tissues outside the vascular cambium.
Chapter-End Exercise
Q1. State the location and function of different types of meristems.
Answer
(See Intext Page 83 Q1 — answered above.)
Q2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Answer
(See Intext Page 83 Q2 — answered above.)
Q3. Explain the process of secondary growth in the stems of woody angiosperms with the help of diagrams.
Answer
(See Intext Page 87 Q1 — answered above.)
Q4. Draw illustrations to bring out the anatomical difference between: (a) Monocot root and Dicot root (b) Monocot stem and Dicot stem
Answer
(a) Monocot Root vs Dicot Root:
| Feature | Dicot Root | Monocot Root |
|---|
| Epidermis (epiblema) | Present, with root hairs | Present, with root hairs |
| Cortex | Wide, parenchymatous | Wide, parenchymatous |
| Endodermis | Present (Casparian strips) | Present (Casparian strips) |
| Pericycle | Present, gives rise to lateral roots | Present, gives rise to lateral roots |
| Vascular bundles | Radial — 2 to 4 xylem patches (diarch to tetrarch) | Radial — many xylem patches (polyarch) |
| Xylem arrangement | Exarch (protoxylem towards periphery) | Exarch (protoxylem towards periphery) |
| Pith | Absent or very small | Large, well-developed |
| Cambium | Present (during secondary growth) | Absent (no secondary growth) |
| Examples | Gram, pea, bean | Maize, wheat, rice |
(b) Monocot Stem vs Dicot Stem:
| Feature | Dicot Stem | Monocot Stem |
|---|
| Epidermis | Present, with trichomes | Present, with cuticle |
| Hypodermis | Collenchymatous | Sclerenchymatous |
| Cortex | Well-defined (collenchyma + parenchyma) | Not differentiated |
| Endodermis | Present (starch sheath) | Absent |
| Pericycle | Present (sclerenchymatous or parenchymatous) | Absent |
| Vascular bundles | In a ring, fewer, conjoint collateral open | Scattered, many, conjoint collateral closed |
| Cambium | Present (between xylem and phloem) | Absent |
| Pith | Present, well-developed | Not distinct (ground tissue) |
| Secondary growth | Present | Absent |
| Examples | Sunflower, Gram | Maize, Wheat |
Q5. Cut a transverse section of young stem of a plant from your garden and observe it under the microscope. How would you ascertain whether it is a monocot or dicot stem? Give reasons.
Answer
To determine whether the stem is monocot or dicot, look for these key differences under the microscope:
1. Arrangement of vascular bundles: If they are arranged in a ring → dicot. If they are scattered throughout the ground tissue → monocot. 2. Cambium: If cambium is present between xylem and phloem (open vascular bundle) → dicot. If absent (closed vascular bundle) → monocot. 3. Hypodermis: If it is collenchymatous → dicot. If sclerenchymatous → monocot. 4. Ground tissue differentiation: If cortex and pith are distinct → dicot. If ground tissue is undifferentiated → monocot.
Q6. The transverse section of a plant material shows the following anatomical features: (a) Vascular bundles are conjoint, scattered, and surrounded by sclerenchymatous bundle sheath (b) Phloem parenchyma is absent. Identify the tissue system.
Answer
This is a monocot stem. The features confirm this:
- Conjoint, scattered vascular bundles are characteristic of monocot stems.
- Sclerenchymatous bundle sheath around each vascular bundle is typical of monocots (e.g., maize stem).
- Phloem parenchyma is absent in monocot stems (it is present in dicot stems).
Q7. What are stomata? Give the functions of stomata.
Answer
Stomata are minute pore structures found on the epidermis of leaves and young stems. Each stoma consists of:
- Two guard cells (kidney-shaped in dicots, dumbbell-shaped in monocots) that control the opening and closing of the stomatal pore.
- Surrounding subsidiary cells that assist guard cells.
Functions of stomata: 1. Gas exchange: Allow CO₂ to enter for photosynthesis and O₂ to exit. 2. Transpiration: Release water vapour, creating a transpiration pull for water and mineral transport. 3. Cooling effect: Transpiration cools the leaf surface. 4. Stomatal conductance: Regulate the rate of photosynthesis by controlling CO₂ intake.
Q8. Does the arrangement of vascular bundles in monocot stem differ from that of dicot stem? If so, how?
Answer
Yes, the arrangement differs significantly:
- Dicot stem: Vascular bundles are arranged in a ring around the pith. They are fewer in number, larger in size, and are conjoint, collateral, and open (cambium present between xylem and phloem). This allows secondary growth.
- Monocot stem: Vascular bundles are scattered throughout the ground tissue. They are more numerous, smaller in size, and are conjoint, collateral, and closed (no cambium). No secondary growth occurs.
Q9. Why is the arrangement of xylem described as endarch in stem and exarch in root?
Answer
- Endarch (stem): In the stem, the protoxylem (first-formed xylem) is towards the centre (pith side) and the metaxylem (later-formed xylem) is towards the periphery. Development is centripetal (from centre outward). This is called endarch arrangement.
- Exarch (root): In the root, the protoxylem is towards the periphery and the metaxylem is towards the centre. Development is centrifugal (from periphery inward). This is called exarch arrangement.
The difference arises because xylem develops differently in stems (towards centre first) and roots (towards periphery first).
Q10. What is the difference between spring wood and autumn wood?
Answer
| Feature | Spring Wood (Early Wood) | Autumn Wood (Late Wood) |
|---|
| Season | Spring (favourable) | Autumn (unfavourable) |
| Cambium activity | Very active | Less active |
| Xylem vessels | Large, thin-walled | Small, thick-walled |
| Colour | Lighter | Darker |
| Density | Less dense | More dense |
| Amount | More abundant | Less abundant |
Together, one ring of spring wood + one ring of autumn wood = one annual ring, which can be used to estimate the age of the tree.
Internal Links
- [Chapter 6 Guide — Anatomy of Flowering Plants](/school/cbse/class/11/biology/cbse-anatomy-of-flowering-plants)
- [All Class 11 Biology Solutions](/school/cbse/class/11/biology/solutions)
- [Class 11 Biology Subject Guide](/school/cbse/class/11/biology)
