Pigments of Photosynthesis: Videos & Practice Problems

Photosynthesis relies on pigments within chloroplasts, primarily chlorophyll a, which absorbs light energy to drive the process. Accessory pigments, like chlorophyll b and carotenoids, absorb different wavelengths, reflecting others, which is why plants appear green. The absorption spectrum illustrates how various pigments absorb light at specific wavelengths, crucial for photosynthesis. Photosystems, complexes of pigments and proteins in thylakoid membranes, play a vital role in capturing light energy, facilitating the light reactions of photosynthesis. Understanding these components is essential for grasping the overall process of photosynthesis.

Pigments of Photosynthesis

Photosynthesis is a vital process for plants, enabling them to convert light energy into chemical energy. Central to this process are pigments, which are molecules that absorb specific wavelengths of visible light. These pigments are crucial for harnessing light energy, allowing plants to power photosynthesis effectively.

The primary pigment involved in photosynthesis is chlorophyll a. It is essential to distinguish chlorophyll a from chloroplasts, which are the organelles where photosynthesis occurs. Chlorophyll a is the main photosynthetic pigment found within chloroplasts, specifically in the mesophyll cells of leaf tissue. While chlorophyll a absorbs various wavelengths of light, it predominantly reflects green light, which is why plants appear green to our eyes. The absorbed light, particularly in the blue and red wavelengths, is utilized to drive the photosynthetic process.

In addition to chlorophyll a, there are accessory pigments that play a supportive role in photosynthesis. One such pigment is chlorophyll b, which is present in smaller amounts compared to chlorophyll a. Chlorophyll b reflects yellow and green light, contributing to the overall light absorption by capturing wavelengths that chlorophyll a does not absorb as efficiently. This allows for a broader spectrum of light to be utilized in photosynthesis.

Another group of accessory pigments is the carotenoids, which include pigments that reflect orange, red, and yellow wavelengths. Carotenoids are responsible for the vibrant colors seen in many fruits and vegetables, and they also absorb light in the blue and green wavelengths, further enhancing the plant's ability to capture light energy.

In summary, the interplay of different pigments, including chlorophyll a, chlorophyll b, and carotenoids, allows plants to maximize light absorption and effectively conduct photosynthesis. Understanding these pigments and their functions is essential for grasping how plants convert light energy into the chemical energy necessary for growth and survival.

Examples of accessory pigments for photosynthesis are:
a) Chlorophyll b and carotenoids.
b) Chlorophyll a and chlorophyll b.
c) Chlorophyll a and carotenoids.
d) Carotenoids, chlorophyll b and chlorophyll a.

• A. Chlorophyll b and carotenoids.
• B. Chlorophyll a and chlorophyll b.
• C. Chlorophyll a and carotenoids.
• D. Carotenoids, chlorophyll b and chlorophyll a.

Answer: (A)

Absorption Spectrum of Photosynthesis

The absorption spectrum is a crucial concept in understanding photosynthesis, as it illustrates how different pigment molecules absorb light. This spectrum is typically represented as a graph, where the y-axis indicates the amount of light absorbed, with lower values signifying minimal absorption and higher values indicating significant absorption. The x-axis represents the wavelength of light in nanometers, focusing on the visible spectrum.

In the absorption spectrum, three primary pigments are highlighted: chlorophyll a (depicted in green), chlorophyll b (shown in yellow), and carotenoids (represented in a dark orange hue). Each pigment has a unique absorption curve, demonstrating the specific wavelengths of light they absorb. Notably, certain wavelengths, particularly in the blue and red regions, are predominantly absorbed by these pigments, while wavelengths in the green and yellow regions are less absorbed and are primarily reflected. This reflection of greenish and yellowish light is why plants appear green to our eyes.

The key takeaway is that the combination of different pigments and their specific absorption characteristics determines the overall color of the plant. Understanding the absorption spectrum not only enhances our knowledge of photosynthesis but also illustrates the relationship between light and plant coloration. This foundational knowledge will be built upon as we explore further topics in the course.

Which of the following pigments does NOT absorb yellow/orange light (650-750nm)?
a) Chlorophyll a.
b) Carotenoids.
c) Chlorophyll b.
d)  Both a & c.

• A. Chlorophyll a.
• B. Carotenoids.
• C. Chlorophyll b.
• D. Both a and c.

Answer: (B)

Introduction to Photosystems

Photosystems are essential complexes found within the thylakoid membranes of chloroplasts, which are the green structures responsible for photosynthesis. These complexes consist of pigments, proteins, and other molecules that work together to capture light energy. The thylakoids, often described as green pancakes, house these photosystems, which play a crucial role in the light reactions of photosynthesis.

Each photosystem is made up of several light-harvesting complexes that surround a central reaction center. The light-harvesting complexes, depicted in purplish colors, contain accessory pigments represented by teal circles. These accessory pigments are vital for absorbing photons of light, enhancing the photosystem's ability to capture energy. At the core of the photosystem is the reaction center, which contains chlorophyll a molecules, the primary pigment in chloroplasts, and a primary electron acceptor, which facilitates the transfer of energy.

In most plants, there are two distinct photosystems that work in tandem during the light reactions of photosynthesis. These systems are integral to converting light energy into chemical energy, which is essential for plant growth and energy production. Understanding the structure and function of photosystems is fundamental to grasping how plants harness sunlight to fuel their metabolic processes.

As we delve deeper into the study of photosystems, we will explore their specific roles in the light reactions and how they contribute to the overall process of photosynthesis.

The figure shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different?



a) Green and yellow wavelengths of light inhibit the absorption of red and blue wavelengths.
b) Oxygen given off during photosynthesis interferes with the absorption of light.
c) Accessory pigments are absorbing light in addition to chlorophyll a which can be used in photosynthesis.
d) Aerobic bacteria take up oxygen, which changes the measurement of the rate of photosynthesis.

• A. Green and yellow wavelengths of light inhibit the absorption of red and blue wavelengths.
• B. Oxygen given off during photosynthesis interferes with the absorption of light.
• C. Accessory pigments are absorbing light in addition to chlorophyll a which can be used in photosynthesis.
• D. Aerobic bacteria take up oxygen, which changes the measurement of the rate of photosynthesis.

Answer: (C)

Here’s what students ask on this topic:

What are the main pigments involved in photosynthesis?

The main pigments involved in photosynthesis are chlorophyll a, chlorophyll b, and carotenoids. Chlorophyll a is the primary photosynthetic pigment, absorbing light most efficiently in the blue-violet and red parts of the electromagnetic spectrum. Chlorophyll b acts as an accessory pigment, extending the range of light wavelengths a plant can use by absorbing blue and red-orange light. Carotenoids, which include carotenes and xanthophylls, absorb light in the blue and green parts of the spectrum and reflect yellow, orange, and red wavelengths. These pigments work together to capture light energy, which is then used to drive the photosynthetic process.

How do different pigments absorb different wavelengths of light?

Different pigments absorb different wavelengths of light due to their unique molecular structures, which determine the specific wavelengths they can absorb. Chlorophyll a absorbs light primarily in the blue-violet and red regions, while chlorophyll b absorbs light in the blue and red-orange regions. Carotenoids absorb light in the blue and green regions. The absorption spectrum of each pigment shows the specific wavelengths of light that are absorbed, with peaks indicating the wavelengths where absorption is highest. This diversity in absorption allows plants to utilize a broader range of the light spectrum for photosynthesis.

Why do plants appear green?

Plants appear green because chlorophyll a, the main photosynthetic pigment, reflects green wavelengths of light. While chlorophyll a absorbs light most efficiently in the blue-violet and red parts of the spectrum, it reflects green light, which is not absorbed. This reflected green light is what we perceive with our eyes, giving plants their characteristic green color. Accessory pigments like chlorophyll b and carotenoids also contribute to the absorption of light but do not significantly alter the green appearance of plants.

What is the role of photosystems in photosynthesis?

Photosystems are complexes of pigments, proteins, and other molecules located in the thylakoid membranes of chloroplasts. They play a crucial role in capturing light energy and converting it into chemical energy during the light reactions of photosynthesis. Each photosystem consists of a reaction center surrounded by light-harvesting complexes. The reaction center contains chlorophyll a molecules and a primary electron acceptor. When light is absorbed by the pigments in the light-harvesting complexes, the energy is transferred to the reaction center, where it excites electrons. These high-energy electrons are then used to drive the synthesis of ATP and NADPH, which are essential for the Calvin cycle.

What is an absorption spectrum and why is it important in photosynthesis?

An absorption spectrum is a graph that shows the absorption of light by pigment molecules at different wavelengths. It is important in photosynthesis because it illustrates which wavelengths of light are absorbed by the various pigments involved in the process. The absorption spectrum helps us understand how different pigments, such as chlorophyll a, chlorophyll b, and carotenoids, contribute to capturing light energy. By absorbing light at different wavelengths, these pigments maximize the efficiency of photosynthesis, allowing plants to utilize a broader range of the light spectrum for energy conversion.