Science Class 11 - Plant Physiology Notes

Plant Physiology

Welcome to the chapter on Plant Physiology for Class 11. In this chapter, you will learn about the vital processes that take place in plants, such as photosynthesis, respiration, transpiration, mineral nutrition, and plant growth. By the end of this chapter, you will understand how plants function, survive, and adapt to their environment.

Introduction

Plant physiology is the study of how plants live, grow, and carry out essential life processes. It explains how plants make food, breathe, absorb water and minerals, and respond to their surroundings.

Key Concepts

• Photosynthesis: The process by which green plants make their own food using sunlight, carbon dioxide, and water.
• Respiration: The process by which plants break down food to release energy.
• Transpiration: The loss of water vapor from the aerial parts of the plant, mainly through stomata.
• Mineral Nutrition: The uptake and use of mineral nutrients by plants for growth and development.
• Plant Growth and Development: The increase in size and changes in form that occur as a plant matures.

Photosynthesis

Photosynthesis takes place in the chloroplasts of plant cells. The main steps are:

• Plants take in carbon dioxide from the air through stomata.
• Roots absorb water from the soil.
• Chlorophyll in leaves captures sunlight.
• Plants make glucose (food) and release oxygen.

Equation: 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂

Respiration in Plants

Plants respire all the time to get energy for their activities. Respiration occurs in mitochondria and involves breaking down glucose to release energy, carbon dioxide, and water.

• Respiration is the opposite of photosynthesis.
• It occurs both in light and dark.

Transpiration

Transpiration is the process by which plants lose water vapor through stomata in their leaves. It helps in cooling the plant, maintaining the flow of water and minerals, and keeping cells turgid.

Mineral Nutrition

Plants need minerals like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur for healthy growth. These minerals are absorbed from the soil through roots.

• Macronutrients: Needed in large amounts (e.g., N, P, K).
• Micronutrients: Needed in small amounts (e.g., Fe, Zn, Mn).

Plant Growth and Development

Plant growth involves cell division, enlargement, and differentiation. Growth is regulated by plant hormones like auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

• Growth can be measured by increase in height, number of leaves, or size of fruits.
• Development includes all changes from seed germination to flowering and fruiting.

Practice Questions

1. Write the equation for photosynthesis.
2. What is transpiration? Name two functions of transpiration.
3. List three macronutrients and three micronutrients needed by plants.
4. How do plant hormones affect growth?
5. Explain the difference between photosynthesis and respiration.

Challenge Yourself

• Design an experiment to show that sunlight is necessary for photosynthesis.
• Observe a plant for a week and record changes in its growth.

Did You Know?

• Some plants can survive in salty water by special adaptations!
• The Venus flytrap is a plant that can catch and digest insects.

Glossary

• Chlorophyll: The green pigment in plants that absorbs sunlight.
• Stomata: Tiny openings on leaves for gas exchange.
• Hormone: A chemical that controls growth and development in plants.
• Macronutrient: A mineral needed in large amounts by plants.
• Micronutrient: A mineral needed in small amounts by plants.

Answers to Practice Questions

1. 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂
2. Transpiration is the loss of water vapor from plant leaves. It helps in cooling the plant and transporting minerals.
3. Macronutrients: Nitrogen, Phosphorus, Potassium. Micronutrients: Iron, Zinc, Manganese.
4. Plant hormones control cell division, elongation, and responses to light and gravity.
5. Photosynthesis makes food using sunlight; respiration breaks down food to release energy.

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Understanding plant physiology helps us grow healthy plants and improve agriculture!