Photosynthesis in Higher Plants Class 11 NCERT Notes PDF for Quick Revision

Overview of Photosynthesis in Higher Plants

Photosynthesis is the process by which green plants synthesize food using sunlight, carbon dioxide, and water. In higher plants, this process mainly occurs in the leaves within specialized organelles called chloroplasts. The overall chemical equation for photosynthesis is:

$$6CO_2 + 6H_2O + light \ energy \rightarrow C_6H_{12}O_6 + 6O_2$$

This equation shows that carbon dioxide and water are converted into glucose and oxygen using light energy. Class 11 NCERT notes emphasize understanding this process as the foundation for biology studies.

Structure of Chloroplast and Its Role

Chloroplasts are double-membrane organelles found in the mesophyll cells of leaves. Key parts include:

• Thylakoids: Flattened sacs stacked into grana where light reactions occur.
• Stroma: Fluid surrounding thylakoids, site of dark reactions (Calvin cycle).
• Chlorophyll: The green pigment embedded in thylakoid membranes that absorbs sunlight.

Understanding chloroplast structure helps explain how photosynthesis is divided into two stages: light-dependent and light-independent reactions.

Light Reactions: Capturing Energy from Sunlight

Light reactions take place in the thylakoid membranes and require light. Key points:

• Chlorophyll absorbs light, exciting electrons.
• Water molecules split (photolysis) releasing oxygen.
• ATP and NADPH are produced as energy carriers.

The simplified reaction:

$$2H_2O + light \rightarrow 4H^+ + 4e^- + O_2$$

ATP and NADPH generated here are used in the Calvin cycle to synthesize glucose.

Dark Reactions: The Calvin Cycle Explained

Dark reactions occur in the stroma and do not require light directly. They use ATP and NADPH from light reactions to fix carbon dioxide into glucose. The Calvin cycle has three phases:

1. Carbon fixation: CO$_2$ attaches to ribulose bisphosphate (RuBP). 2. Reduction: ATP and NADPH convert the fixed carbon into G3P. 3. Regeneration: RuBP is regenerated to continue the cycle.

The overall reaction for one CO$_2$ fixed is:

$$CO_2 + ATP + NADPH \rightarrow G3P$$

This cycle is crucial for producing carbohydrates in plants.

Factors Affecting Photosynthesis in Higher Plants

Several environmental and internal factors influence the rate of photosynthesis:

• Light intensity: Higher light increases photosynthesis up to a point.
• Carbon dioxide concentration: More CO$_2$ enhances the process.
• Temperature: Optimal temperature range is necessary; extremes reduce efficiency.
• Water availability: Water stress limits photosynthesis.

Solved Example: Calculating Photosynthesis Rate

Example: If a plant fixes 12 molecules of CO$_2$ in 6 minutes, what is the rate of photosynthesis in molecules per minute?

Solution:

Rate = Total CO$_2$ fixed / Time

$$= \frac{12}{6} = 2 \text{ molecules per minute}$$

This simple calculation helps students quantify photosynthesis rates during experiments.

Summary and Exam Tips for Class 11 NCERT Photosynthesis Chapter

• Focus on understanding the two stages: light and dark reactions.
• Memorize the overall photosynthesis equation.
• Practice diagram labeling of chloroplast and Calvin cycle.
• Solve numerical problems on photosynthesis rates.
• Review factors affecting photosynthesis for application-based questions.

Using the photosynthesis in higher plants class 11 NCERT notes PDF will help you revise efficiently and perform well in exams.