Photosynthesis Notes

Photosynthesis

Introduction

Living organisms require energy to perform metabolic functions and are interdependent. The primary energy source is the sun.

Ultimate Energy Source

Energy originates from nuclear fusion within the sun's core and radiates into the solar system. The intensity of this energy diminishes as it passes through the atmosphere.

Light Spectrum and Seasons

The sun emits energy in various forms including:

• Ultraviolet (UVC, UVB, UVA)
• Visible light
• Infrared

The intensity and type of light vary depending on the season and hemisphere:

• Summer in Northern Hemisphere (NH): NH leans into the sun.
• Winter in Northern Hemisphere (NH): NH leans away from the sun.
• Winter in Southern Hemisphere (SH): SH leans away from the sun.
• Summer in Southern Hemisphere (SH): SH leans into the sun.

Relevant wavelengths are:

• UVC: 100-280 nm
• UVB: 280-315 nm
• UVA: 315-400 nm
• Visible: 400-700 nm

Radiant Energy and Photosynthesis

Radiant energy, comprising light and heat from the sun, needs conversion into another form for use. Photosynthesis converts radiant energy into chemical potential energy.

Transfer of Energy

Plants act as natural solar panels by absorbing and transforming solar energy into chemical energy. This stored chemical energy transfers through the food chain:

Plant → Grasshopper → Frog → Bird

Each organism utilizes the transferred chemical energy for its functions.

Photosynthesis: How Plants Do It

Green plants use chloroplasts to absorb sunlight. Chloroplasts, found within plant cells, contain chlorophyll, a green pigment. Chlorophyll absorbs radiant energy and converts it into chemical potential energy.

Energy Conversions in Photosynthesis

Photosynthesis involves two primary energy conversions:

1. Radiant energy (sun) → Chemical potential energy (organic food).
2. Inorganic substances (carbon dioxide and water) → Organic substances (glucose).

Requirements for Photosynthesis

Photosynthesis requires:

1. Sunlight and chlorophyll: Chlorophyll absorbs sunlight.
2. Water: Absorbed by roots.
3. Carbon dioxide: Absorbed from the atmosphere through stomata (tiny holes).

Stomata

Stomata are tiny pores in the plant that facilitate the absorption of carbon dioxide from the atmosphere.

Products of Photosynthesis

The main products of photosynthesis are:

• Glucose (organic substance)
• Oxygen (by-product)

Process of Photosynthesis

Photosynthesis uses solar energy to convert carbon dioxide and water into glucose and oxygen. The overall reaction is:

6CO2 + 6H2O \xrightarrow{\text{chlorophyll}} C6H{12}O6 + 6O2

• Carbon dioxide (absorbed from air).
• Water (absorbed through soil).
• Energy (from sunlight).
• Glucose (used by plant).
• Oxygen (released into air).

The process converts solar energy into potential energy (fuel).

What Plants Do with the Sugars They Produce

Plants convert sugars into other chemical compounds and store energy as sugar or starch in various parts:

• Leaves
• Fruit (apples)
• Tubers (potato)
• Specialized roots (carrots)

Cellulose, a structural material, is also derived from glucose.

Activity 2 Summary

1. Radiant energy is used in photosynthesis.
2. Key gases involved are oxygen and carbon dioxide; carbon dioxide is sourced from the atmosphere.
3. Water is essential for photosynthesis.
4. The process is photosynthesis.
5. The equation for photosynthesis (simplified) is: Water + Carbon Dioxide → Glucose + Oxygen
6. Starch is stored energy in plants, while cellulose makes up the cell wall, providing support.
7. In the dark, plants do not perform photosynthesis; they respire and use stored energy.
8. Plants serve as a food source for other organisms and convert solar energy into usable forms.

Scientific Method

The scientific method involves:

1. Observation
2. Asking a question
3. Background research
4. Constructing a hypothesis
5. Testing the hypothesis through experiment
6. Analyzing data and drawing conclusions
7. Reporting results

Example:

• Question: Which type of fertilizer works the best?
• Hypothesis: Plants grown with Fertilizer A will grow the fastest.
• Conclusion: The hypothesis was proven correct.

Iodine Test for Starch

The iodine test determines if photosynthesis has occurred by testing for starch:

• No change = no starch present.
• Blue/black color = starch present.

Practical Investigation: Do Green Leaves Produce Starch?

The practical investigation includes the following steps:

1. Define the aim.
2. Write a hypothesis.
3. Plan the investigation (methodology).
4. Conduct the investigation and record findings.
5. Analyze results and draw conclusions.
6. Evaluate the investigation.