Photosynthesis in Higher Plants
1. Introduction
Photosynthesis is a vital biological process where green plants, algae, and some bacteria convert light energy, typically from the sun, into chemical energy stored in glucose. This process is fundamental to the survival of most life forms on Earth as it produces oxygen and organic compounds, which are essential energy sources for organisms.
2. Chloroplasts: The Photosynthesis Hub
Chloroplasts are specialized organelles found in plant cells where photosynthesis occurs. They contain chlorophyll pigments that capture the light energy necessary for photosynthesis.
Key Points about Chloroplasts:
- Found in the mesophyll cells of leaves.
- Comprise thylakoid membranes where light reactions occur.
- The stroma is the site for the Calvin cycle.
3. Photosynthetic Pigments
The main pigments involved in photosynthesis are chlorophyll a, chlorophyll b, carotenoids, and xanthophylls. Each pigment plays a unique role in capturing light energy.
Detailed Insights on Photosynthetic Pigments:
Chlorophyll a: The primary pigment that directly participates in the light reactions.
Chlorophyll b: Helps in capturing light energy and passes it on to chlorophyll a.
Carotenoids and Xanthophylls: Accessory pigments that absorb additional light wavelengths and protect the plant from excessive sunlight.
4. Photosynthesis Process
Photosynthesis is divided into two main stages: the light-dependent reactions (light reactions) and the light-independent reactions (dark reactions or Calvin cycle).
Stages of Photosynthesis in Higher Plants:
Light Reactions:
-Occur in the thylakoid membranes of chloroplasts.
-Light energy splits water molecules, releasing oxygen, and producing ATP and NADPH.
-The equation for light reactions:
2H2O+ 2NADP++3ADP+3Pi → O2+2NADPH+3ATP
Calvin Cycle:
- Occurs in the stroma of chloroplasts.
- Uses ATP and NADPH from the light reactions to fix carbon dioxide from the atmosphere into glucose.
- The equation for the Calvin cycle:
3CO2+9ATP+6NADPH+5H2O→G3P+9ADP+8Pi+6NADP++2H+
5. Factors Affecting Photosynthesis
Several factors influence the rate of photosynthesis, including light intensity, carbon dioxide concentration, and temperature.
Key Factors in Detail:
Light Intensity:
- Higher light intensity increases the rate of photosynthesis until a saturation point is reached.
- Beyond this point, no further increase in the rate occurs.
Carbon Dioxide Concentration:
- Increased CO2 levels boost the rate of photosynthesis up to a saturation point.
Temperature:
- Optimal temperatures enhance photosynthesis.
- Extreme temperatures can denature the enzymes involved in the process.
6. Significance of Photosynthesis
Photosynthesis has far-reaching impacts on life on Earth and the environment.
Also Read: Biotechnology and Its Applications
Production of Oxygen:
- Photosynthesis is the primary source of atmospheric oxygen, which is essential for aerobic respiration in organisms.
Food Production:
- Provides carbohydrates and other organic compounds that serve as food for plants and other organisms.
Carbon Cycle:
- Helps regulate the Earth's carbon cycle by removing CO2 from the atmosphere and converting it into organic compounds.
Examples of Photosynthesis Process in Higher Plants
Photosynthesis is a fundamental process for higher plants, enabling them to produce energy and sustain life. Here are some examples that illustrate how this process works in various types of higher plants:
1. Oak Trees (Quercus spp.):
Description: Oak trees are large, deciduous trees found in temperate regions.
Photosynthesis: In oak trees, photosynthesis takes place in the broad, flat leaves. The chloroplasts in the leaf cells capture sunlight, and the stomata allow for gas exchange. The produced glucose supports the tree's growth and development, including the production of acorns.
2. Wheat (Triticum spp.):
Description: Wheat is a staple cereal crop grown worldwide for its grain.
Photosynthesis: In wheat plants, photosynthesis occurs in the narrow, elongated leaves. The efficient light capture and gas exchange through stomata enable the plant to produce glucose, which is crucial for grain development. The energy stored in the grains is used for human and animal consumption.
3. Sunflowers (Helianthus annuus):
Description: Sunflowers are annual plants known for their large, bright yellow flowers.
Photosynthesis: Sunflowers have large leaves with a high surface area, maximizing light absorption. During photosynthesis, the leaves produce glucose, which is used for the growth of the stem, leaves, and flowers. The seeds produced in the flower heads are rich in oil and nutrients.
4. Maple Trees (Acer spp.):
Description: Maple trees are known for their vibrant fall foliage and sweet sap.
Photosynthesis: In maple trees, photosynthesis occurs in the broad, lobed leaves. The process produces glucose, which is stored in the sap. In early spring, this sap can be harvested and processed into maple syrup. The energy produced also supports the tree's overall growth and seasonal changes.
5. Rice (Oryza sativa):
Description: Rice is a key food crop grown in flooded fields known as paddies.
Photosynthesis: Rice plants have narrow leaves that perform photosynthesis efficiently under submerged conditions. The glucose produced is used for the development of grains, which are a primary food source for billions of people globally. The submerged leaves also help in efficient CO₂ absorption.
6. Cacti (Cactaceae family):
Description: Cacti are succulent plants adapted to arid environments.
Photosynthesis: Unlike typical plants, many cacti perform CAM (Crassulacean Acid Metabolism) photosynthesis. They open their stomata at night to reduce water loss and store CO₂ as malic acid. During the day, the stored CO₂ is used for photosynthesis. This adaptation allows them to survive in extreme drought conditions.
7. Tomato Plants (Solanum lycopersicum):
Description: Tomato plants are widely cultivated for their edible fruits.
Photosynthesis: Tomato plants have compound leaves with multiple leaflets that capture sunlight effectively. Photosynthesis in these leaves produces glucose, which is essential for fruit development. The sugars and acids in the fruits provide their characteristic flavour.
7. Summary
Photosynthesis is a complex process that sustains life on Earth by converting light energy into chemical energy stored in glucose. Understanding the mechanisms and factors influencing photosynthesis is crucial for studying plant biology and ecology.
These notes provide a basic overview of photosynthesis in higher plants, covering key concepts and processes relevant to Class 11 biology. For a deeper understanding, further study and exploration are recommended.