Class 9 Biology Chapter 9 – Plant Physiology (2026 New Syllabus)

Plant Physiology is a fascinating branch of biology that explores the vital life processes in plants. From how plants obtain and use nutrients to how they transport water, food, and gases, this chapter gives students a deep understanding of the mechanisms that keep plants alive and thriving.

In this chapter, we will study:

• Nutrition in Plants – How plants make their own food through photosynthesis and absorb essential nutrients.

• Transport in Plants – The movement of water, minerals, and organic substances throughout the plant body.

• Transpiration – How water is lost from plants and its role in cooling and nutrient movement.

• Transport of Water in Plants – Mechanisms like xylem transport, root pressure, and cohesion-tension theory.

• Translocation of Food in Plants – How sugars and other organic compounds move through phloem to different parts of the plant.

• Gaseous Exchange in Plants – How plants exchange oxygen and carbon dioxide for respiration and photosynthesis.

• Mechanisms for Excretion in Plants – How plants remove metabolic wastes efficiently.

• Osmotic Adjustment in Plants – How plants maintain water balance and survive under stress conditions like drought or salinity.

This chapter builds a foundation for understanding how plants live, grow, and respond to their environment, making it essential for Class 9 students to master.

Class 9 Biology Chapter 9 Plant Physiology MCQs

Which of the following plant nutrients is required in large amount?

(a) Iron
(b) Zinc
(c) Potassium ✅
(d) Boron

Which ion plays a role in the opening of stomata?

(a) Sodium (Na⁺)
(b) Potassium (K⁺) ✅
(c) Calcium (Ca²⁺)
(d) Magnesium (Mg²⁺)

Which process allows plants to make their own food?

(a) Respiration
(b) Osmosis
(c) Photosynthesis ✅
(d) Fermentation

Which factor decreases the rate of transpiration?
(a) Wind
(b) High temperature
(c) High humidity
✅
(d) Large surface area of leaves

Which cells provide energy for active transport of food into phloem?

(a) Mesophyll cells
(b) Guard cells
(c) Companion cells ✅
(d) Epidermal cells

Class 9 Biology Chapter 9 – Short Questions

Q1: Define mineral nutrition in plants.

Answer: ✅
Mineral nutrition is the process by which plants absorb inorganic nutrients (minerals) from the soil for their growth and development.

Explanation / Extra Info:

• Minerals like Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Iron (Fe), Zinc (Zn) are essential for various plant functions.

• Proper mineral nutrition ensures healthy growth, photosynthesis, enzyme activation, and reproduction in plants.

Q2: Define macronutrients and micronutrients and give examples.

Answer: ✅

• Macronutrients are nutrients required by plants in large amounts for proper growth and development.
  Examples: Nitrogen (N), Potassium (K), Calcium (Ca), Phosphorus (P), Magnesium (Mg), Sulfur (S).

• Micronutrients are nutrients required by plants in small or trace amounts, but they are still essential for various physiological functions.
  Examples: Iron (Fe), Zinc (Zn), Boron (B), Manganese (Mn), Copper (Cu), Molybdenum (Mo).

Q3: What is transpiration?

Answer: ✅
Transpiration is the loss of water in the form of vapour from plant surfaces, mainly from the leaves.

Explanation / Extra Info:

• Transpiration occurs mainly through stomata, but a small amount also occurs through cuticle and lenticels.

• It helps in:

  1. Cooling the plant

  2. Creating transpiration pull for water transport

  3. Maintaining water and mineral balance

  4. Facilitating gaseous exchange

Q4: Name any three factors that affect the rate of transpiration.

Answer: ✅
Three factors that affect the rate of transpiration are:

1. Temperature – Higher temperature increases the rate of transpiration.

2. Wind – Windy conditions remove water vapour from leaf surfaces, increasing transpiration.

3. Humidity – Higher humidity reduces the rate of transpiration because the air is already saturated with water vapour.

Q5: What are mesophytes? Give one example.

Answer: ✅
Mesophytes are terrestrial plants adapted to moderate environments, neither too dry nor too wet.

Example: Rose

Extra Info:

• Mesophytes have well-developed leaves and roots, and normal stomatal distribution.

• They require moderate water supply for growth.

• Unlike xerophytes (adapted to dry conditions) or hydrophytes (adapted to aquatic conditions), mesophytes thrive in average conditions.

📥 Download Chapter 9 Notes – Plant Physiology

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Get Class 9 Biology Chapter 9 complete notes for the 2026 syllabus, including:

• Nutrition in Plants

• Transport in Plants

• Transpiration & Water Transport

• Translocation of Food

• Gaseous Exchange

• Excretion Mechanisms

• Osmotic Adjustment

• Important MCQs, Short & Long Questions

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