Plant Life — Photosynthesis, Transpiration and Plant Nutrition

Overview

Plant Life is a core biology topic for Bihar TET Paper II, testing your understanding of how plants manufacture food, transport water, and obtain essential nutrients. Questions typically appear in the Science section and assess both factual recall (processes, definitions, factors) and conceptual understanding (why plants wilt, how minerals reach leaves).

This topic connects directly to ecosystem concepts—plants as producers form the base of all food chains. For the exam, you must master the three interconnected processes: photosynthesis (food making), transpiration (water loss and movement), and plant nutrition (nutrient uptake). Expect 2–4 questions ranging from identifying raw materials of photosynthesis to explaining why plants need nitrogen.

Pedagogy-linked questions may ask how to teach photosynthesis through simple experiments (testing starch in leaves) or how to correct student misconceptions about plants "breathing" carbon dioxide.

---

Key Concepts

• **Autotrophic nutrition**: Plants are autotrophs—they synthesise their own food using sunlight, carbon dioxide and water. This distinguishes them from heterotrophs (animals, fungi) that depend on other organisms.

• **Photosynthesis equation**: Carbon dioxide + Water → (sunlight, chlorophyll) → Glucose + Oxygen. This occurs in chloroplasts, specifically in the green pigment chlorophyll.

• **Role of stomata**: Tiny pores on leaf surfaces (mainly underside) allow CO₂ entry for photosynthesis and water vapour exit during transpiration. Guard cells control stomatal opening.

• **Transpiration pull**: Water evaporating from leaves creates a suction force that pulls water upward through xylem vessels from roots to leaves—this is the main mechanism for water transport in tall plants.

• **Xylem and Phloem**: Xylem transports water and minerals upward (unidirectional); phloem transports food (sucrose) from leaves to all plant parts (bidirectional).

• **Essential nutrients**: Plants need 17 essential elements. Macronutrients (N, P, K, Ca, Mg, S) are needed in large amounts; micronutrients (Fe, Zn, Mn, Cu, B, Mo, Cl, Ni) in trace amounts.

• **Nitrogen fixation**: Atmospheric nitrogen (N₂) cannot be directly used by plants. Rhizobium bacteria in root nodules of legumes convert N₂ to usable ammonia/nitrates.

---

Formulas / Key Facts

| Fact | Detail | |------|--------| | Photosynthesis equation | 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂ | | Site of photosynthesis | Chloroplasts (in mesophyll cells of leaves) | | Chlorophyll function | Absorbs sunlight (mainly red and blue light); reflects green | | Stomata location | More on lower epidermis of dorsiventral leaves | | Transpiration rate factors | Light, temperature, humidity, wind speed | | Water absorption organ | Root hairs (increase surface area) | | Xylem components | Vessels and tracheids (dead cells, lignified walls) | | Phloem components | Sieve tubes and companion cells (living cells) | | NPK fertilisers | Nitrogen (leaf growth), Phosphorus (root/flower), Potassium (disease resistance) | | Deficiency symptoms | N deficiency → yellow older leaves; Fe deficiency → yellow young leaves |