Plant Systems

Overview

Plant Systems is a core biology topic in MAHA TET Paper II Science, covering the essential life processes that enable plants to survive, grow and reproduce. This topic tests your understanding of how plants obtain nutrients, transport substances, exchange gases and produce offspring—processes that parallel animal physiology but with unique plant-specific mechanisms.

For the exam, expect questions on photosynthesis equations, differences between transport tissues (xylem vs phloem), types of plant reproduction, and the role of stomata in gas exchange. Diagrams of leaf cross-sections, root hair absorption and flower parts are frequently tested. Mastering this topic also strengthens your ability to teach EVS and Science effectively at the upper-primary level, making it doubly relevant for TET aspirants.

The four sub-systems—nutrition, transport, respiration and reproduction—are interconnected. Photosynthesis produces food, transport moves it around, respiration releases energy from it, and reproduction ensures species continuation. Understanding these links will help you answer application-based questions.

Key Concepts

• **Autotrophic Nutrition**: Plants manufacture their own food through photosynthesis using sunlight, carbon dioxide and water. They are called autotrophs (self-feeders), unlike animals which are heterotrophs.

• **Photosynthesis Equation**: Carbon dioxide + Water → (sunlight + chlorophyll) → Glucose + Oxygen. This occurs primarily in leaves, specifically in chloroplasts containing chlorophyll.

• **Xylem and Phloem**: Two vascular tissues form the plant's transport system. Xylem carries water and minerals upward from roots (unidirectional). Phloem carries food (sucrose) from leaves to all parts (bidirectional).

• **Transpiration Pull**: The primary force driving water movement upward is transpiration—evaporation of water from stomata creates a suction that pulls water through xylem vessels.

• **Stomata Function**: Tiny pores on leaf surfaces (mostly lower epidermis) that allow gas exchange (CO₂ in, O₂ out during photosynthesis) and water vapour release. Guard cells control their opening and closing.

• **Plant Respiration**: Plants respire continuously (day and night), taking in oxygen and releasing carbon dioxide. This occurs in mitochondria of all living cells, not just leaves.

• **Asexual vs Sexual Reproduction**: Asexual reproduction involves a single parent (vegetative propagation, budding, fragmentation). Sexual reproduction involves flowers, pollination, fertilisation and seed formation.

• **Pollination and Fertilisation**: Pollen transfer from anther to stigma is pollination. Fertilisation occurs when male gamete fuses with egg cell in the ovule, forming a zygote that develops into seed.

Formulas / Key Facts

| Process/Structure | Key Fact | |-------------------|----------| | Photosynthesis | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (requires sunlight and chlorophyll) | | Respiration | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP) | | Chlorophyll location | Chloroplasts in mesophyll cells of leaves | | Xylem composition | Tracheids and vessels (dead cells, lignified walls) | | Phloem composition | Sieve tubes and companion cells (living cells) | | Root absorption | Root hairs increase surface area; water enters by osmosis | | Transpiration rate | Increases with temperature, wind, low humidity; decreases in darkness | | Self-pollination | Same flower or same plant (e.g., wheat, rice, pea) | | Cross-pollination | Different plants of same species (e.g., maize, papaya) | | Agents of pollination | Wind (anemophily), insects (entomophily), water (hydrophily), birds |

Worked Examples

**Example 1: Photosynthesis Application**

*Question*: A potted plant is kept in a dark room for 48 hours, then one leaf is partially covered with black paper and placed in sunlight. After 6 hours, the leaf is tested with iodine. What will be observed?

*Solution*:

• Step 1: Dark period destarchs the leaf (removes stored starch)
• Step 2: Covered portion receives no light → no photosynthesis → no starch formed
• Step 3: Uncovered portion receives light → photosynthesis occurs → starch produced
• Step 4: Iodine test—starch turns blue-black; no starch remains brown
• **Answer**: Uncovered portion turns blue-black; covered portion remains brown. This proves light is necessary for photosynthesis.

**Example 2: Transport Tissue Identification**

*Question*: A ring of bark is removed from around a tree trunk. After several weeks, the portion above the ring swells. Explain why.

*Solution*:

• Step 1: Bark contains phloem (outer layer of vascular tissue)
• Step 2: Removing bark removes phloem but xylem (inner) remains intact
• Step 3: Water still moves up through xylem
• Step 4: Food from leaves cannot move down past the ring (phloem blocked)
• Step 5: Food accumulates above the ring causing swelling
• **Answer**: This demonstrates phloem transports food downward; blocking it causes accumulation above the ring.

**Example 3: Flower Part Function**

*Question*: Identify which part of the flower develops into fruit and which into seed after fertilisation.

*Solution*:

• Ovary (contains ovules) → develops into **Fruit**
• Ovule (contains egg cell) → develops into **Seed**
• Zygote inside ovule → develops into **Embryo**
• **Memory aid**: "Ovary = Fruit, Ovule = Seed"

Common Mistakes

• **Confusing photosynthesis with respiration timing** → Wrong: "Plants photosynthesise at night too." Correct: Photosynthesis requires light (daytime only); respiration occurs 24 hours.

• **Mixing up xylem and phloem direction** → Wrong: "Phloem carries water upward." Correct: Xylem carries water/minerals UP; Phloem carries food in BOTH directions (source to sink).

• **Thinking plants don't respire** → Wrong: "Plants only release oxygen." Correct: Plants release oxygen during photosynthesis but consume oxygen during respiration. Net oxygen release occurs only when photosynthesis exceeds respiration.

• **Confusing pollination with fertilisation** → Wrong: "Pollination is when seeds form." Correct: Pollination is pollen transfer to stigma; fertilisation is gamete fusion occurring later inside ovule.

• **Assuming all stomata are on lower surface** → Wrong: "Stomata are always below." Correct: Most plants have more stomata on lower surface, but floating leaves (lotus) have stomata on upper surface only.

Quick Reference

• **Photosynthesis site**: Chloroplast in leaf mesophyll cells
• **Xylem = Water UP (dead cells); Phloem = Food BOTH ways (living cells)**
• **Stomata**: Gas exchange + transpiration; guard cells control opening
• **Day**: Photosynthesis + Respiration; **Night**: Respiration only
• **Pollination → Fertilisation → Seed formation → Fruit development**
• **Vegetative propagation examples**: Potato (tuber), Ginger (rhizome), Bryophyllum (leaf buds), Rose (cutting)