Current Affairs updated daily
KalviGavaniKalviGavani

Samacheer Kalvi 10th Science Chapter 12 Long Answer Questions — Plant Anatomy and Plant Physiology with Answers

Long answer questions (5 marks) from Samacheer Kalvi Class 10 Science Chapter 12 Plant Anatomy with detailed answers covering plant tissues, photosynthesis, and transpiration.

Updated 25 May 20268 min read

Chapter 12 — Plant Anatomy and Plant Physiology: Long Answer Questions

1. Classify plant tissues and explain the structure and function of meristematic tissues.

Classification of Plant Tissues

Plants have two main categories of tissues:

A. Meristematic Tissue (Dividing tissue) B. Permanent Tissue (Non-dividing tissue)

  • Simple permanent tissue: Parenchyma, Collenchyma, Sclerenchyma
  • Complex permanent tissue: Xylem, Phloem

Meristematic Tissue

Meristematic tissue consists of actively dividing cells that are responsible for the growth of plants.

Characteristics of meristematic cells:

  • Small, densely packed cells with no intercellular spaces
  • Large nucleus; dense cytoplasm
  • Thin cell walls (primary walls only)
  • No vacuoles (or very small)
  • Capable of continuous cell division

Types based on location:

1. Apical meristem:
Answer
  • Present at the tips (apices) of roots and shoots
  • Responsible for primary growth — increase in length
  • Types: Root apical meristem, Shoot apical meristem
2. Lateral meristem (Cambium):
Answer
  • Present along the sides of roots and stems
  • Responsible for secondary growth — increase in thickness (girth)
  • Types: Vascular cambium (produces xylem and phloem), Cork cambium (produces cork/bark)
3. Intercalary meristem:
Answer
  • Present at the base of nodes and leaves (e.g., grasses, bamboo)
  • Responsible for re-growth after grazing/mowing
  • Why cut grass keeps growing — intercalary meristem at the base is not removed
2. Describe the structure and functions of xylem and phloem.
Answer

Xylem and phloem are complex permanent tissues that form the vascular system of plants — responsible for transport.

Xylem

Function: Transport of water and dissolved minerals from roots to aerial parts (upward transport = ascent of sap).

Components of xylem:

ComponentStructureFunction
TracheidsLong, narrow dead cells with tapering ends; pits in wallsTransport water; provide structural support
Xylem vessels (tracheae)Wide, hollow, dead cells joined end to end (walls dissolved) — continuous tubesMain water-conducting elements; more efficient than tracheids
Xylem fibres (sclerenchyma)Dead cells with thick wallsMechanical support
Xylem parenchymaLiving cellsStorage of food; lateral transport of water

Key features: Xylem cells are dead at maturity; their hollow, thick-walled structure forms a pipe-like system for efficient water transport.

Direction of transport: Roots → Stem → Leaves (unidirectional, upward)

Phloem

Function: Transport of organic food (mainly sucrose) produced by photosynthesis from leaves to all other parts of the plant — including roots, growing shoots, fruits, and seeds (translocation).

Components of phloem:

ComponentStructureFunction
Sieve tubesLong cells with sieve plates (perforated end walls); living but no nucleusMain food-conducting elements
Companion cellsSmall cells with nucleus, adjacent to sieve tube cellsControl and support sieve tube function (provide ATP and proteins)
Phloem fibresDead cells with thick wallsMechanical support
Phloem parenchymaLiving cellsStorage and lateral transport

Direction of transport: Bidirectional — from leaves to other parts (downward and upward). Food goes where needed — growing regions, storage organs, seeds.

Comparison:

FeatureXylemPhloem
Material transportedWater + mineralsOrganic food (sucrose)
DirectionUpward (unidirectional)Both directions
Cell conditionDeadLiving (sieve tubes)
Driving forceTranspiration pullActive loading/unloading (ATP energy)
3. Explain photosynthesis in detail — the raw materials, products, site, and the two stages.

What is Photosynthesis?

Photosynthesis is the process by which green plants, algae, and some bacteria manufacture their own food using sunlight, carbon dioxide, and water.

Overall equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ Light energy Chlorophyll

Raw Materials

MaterialSourceEntry point
Carbon dioxide (CO₂)AtmosphereEnters through stomata
Water (H₂O)SoilAbsorbed by roots, transported by xylem
Light energySunAbsorbed by chlorophyll
ChlorophyllPresent in chloroplastsTraps light energy

Products

  • Glucose (C₆H₁₂O₆) — stored as starch or used for energy
  • Oxygen (O₂) — released as a by-product (comes from water molecules, not CO₂)

Site of Photosynthesis

Chloroplasts in mesophyll cells of leaves.

  • Thylakoids (membrane sacs stacked as grana) — site of light reactions
  • Stroma (fluid-filled space around thylakoids) — site of dark reactions (Calvin cycle)

Stage 1: Light Reactions (Light-dependent reactions)

Location: Thylakoid membranes

What happens: 1. Light absorption: Chlorophyll molecules absorb light energy (mainly red and blue wavelengths; green light is reflected — that's why leaves look green) 2. Photolysis of water: Light energy splits water molecules:

3. Production of ATP and NADPH: The energy from light is used to:

4. ATP and NADPH are the products that power the next stage

  • 2H₂O → 4H⁺ + 4e⁻ + O₂↑ (oxygen released — source of all atmospheric O₂)
  • Phosphorylate ADP to ATP (photophosphorylation)
  • Reduce NADP⁺ to NADPH

Stage 2: Dark Reactions (Calvin Cycle / Light-independent reactions)

Location: Stroma of chloroplast Does NOT directly require light — but requires ATP and NADPH from light reactions

What happens (simplified): 1. CO₂ from air combines with RuBP (5-carbon compound, ribulose bisphosphate) — catalysed by enzyme RuBisCO 2. This produces two 3-carbon molecules (3-PGA, 3-phosphoglyceric acid) 3. 3-PGA is reduced using ATP and NADPH (from light reactions) → G3P (glyceraldehyde-3-phosphate) 4. G3P molecules combine to form glucose 5. Some G3P is used to regenerate RuBP (cycle continues)

To make 1 glucose: 6 CO₂ + 18 ATP + 12 NADPH are needed

4. Explain the movement of water in plants from roots to leaves (ascent of sap).
Answer

The movement of water from roots through stems to leaves is called ascent of sap. Water moves upward against gravity through the xylem.

Forces Involved

1. Root pressure:
Answer
  • Mineral ions are actively transported into root cells using ATP
  • This lowers the water potential inside root cells
  • Water from soil enters root cells by osmosis → creates root pressure (pushing force)
  • Evidence: Guttation — water droplets appear at leaf tips in the morning when transpiration is low and root pressure is high
2. Capillary action:
Answer
  • Water molecules are attracted to xylem walls (adhesion) and to each other (cohesion)
  • In the narrow xylem tubes, capillary action causes water to rise
  • Alone, it can raise water only a few cm — insufficient for tall trees
3. Transpiration pull (Cohesion-Tension Theory — main mechanism):
Answer
  • Water evaporates from mesophyll cells into air spaces in leaves → exits through stomata (transpiration)
  • This creates a deficit of water in leaf cells
  • Water is drawn from adjacent cells → eventually from xylem vessels in leaves
  • This creates a tension (negative pressure) in the continuous water column in xylem
  • Due to cohesion (water molecules stick together) and adhesion (water sticks to xylem walls), the water column does not break
  • The tension pulls the entire water column upward from roots
  • This force is sufficient to lift water up the tallest trees (over 100 m in Giant Sequoias)

Summary:

  • Root pressure: Push from below (minor)
  • Capillary action: Minor contribution
  • Transpiration pull: Main driving force (pull from above)
5. Describe the internal structure of a leaf. How is it adapted for photosynthesis and transpiration?
Answer

The leaf is the primary organ of photosynthesis. Its structure is beautifully adapted for its functions.

Internal Structure of a Dicot Leaf (Vertical section):

1. Upper epidermis:
Answer
  • Single layer of cells, no chloroplasts, covered by cuticle (waxy layer)
  • Cuticle reduces water loss and prevents pathogen entry
  • Few or no stomata on upper surface (prevents excessive water loss from direct sunlight)
2. Palisade mesophyll:
Answer
  • Elongated cells, densely packed, below the upper epidermis
  • Contain large numbers of chloroplasts (main site of photosynthesis)
  • Arranged perpendicular to leaf surface to maximise light absorption
3. Spongy mesophyll:
Answer
  • Loosely arranged cells with large air spaces between them
  • Fewer chloroplasts than palisade cells
  • Air spaces allow CO₂ to diffuse from stomata to all mesophyll cells
  • Also allow water vapour to diffuse out during transpiration
4. Vascular bundles (veins):
Answer
  • Xylem on the upper side — brings water and minerals
  • Phloem on the lower side — takes away sugars produced by photosynthesis
  • Bundle sheath cells surround the vascular bundle
5. Lower epidermis:
Answer
  • Contains stomata (singular: stoma) — pores for gas exchange
  • Each stoma is flanked by two guard cells containing chloroplasts
  • Guard cells control the opening and closing of stomata:
  • In light: guard cells absorb water → become turgid → bulge outward → stoma opens
  • In darkness (or drought): guard cells lose water → become flaccid → stoma closes

Adaptations for photosynthesis:

  • Broad, flat blade — maximum surface area for light absorption
  • Transparent epidermis — allows light through
  • Dense palisade layer — maximum chloroplasts near light source
  • Air spaces — CO₂ distribution

Adaptations for transpiration control:

  • Waxy cuticle — reduces evaporation from surface
  • Stomata (mostly on lower surface) — controlled opening/closing
  • Stomatal closure in drought, darkness, and CO₂ abundance

📚 Samacheer Kalvi 10th Science Guide — Buy Online

Frequently Asked Questions

Overall equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Two stages: (1) Light reactions (in thylakoid membranes of chloroplast): Light energy absorbed by chlorophyll; water is split (photolysis of water) releasing O₂, H⁺ ions and electrons; ATP and NADPH are produced. (2) Dark reactions / Calvin cycle (in stroma of chloroplast): CO₂ is fixed using ATP and NADPH to form glucose (C₆H₁₂O₆). CO₂ + C₅ compound (RuBP) → 2 molecules of 3-carbon compound (3-PGA) → glucose.