Problem 7 - Biology Today and Tomorrow with Physiology

Question

Which of the following statements is incorrect? a. Pigments absorb light of certain wavelengths only. b. Many accessory pigments are multipurpose molecules. c. Chlorophyll \(a\) is green because it absorbs green light.

Step-by-Step Solution

Answer

Statement c is incorrect; chlorophyll \(a\) reflects, not absorbs, green light.

Step 1: Understanding Pigment Absorption

Pigments are molecules that absorb specific wavelengths of light. Each pigment absorbs a range of wavelengths and reflects others. This is why different pigments appear as different colors; they reflect the colors they do not absorb.

Step 2: Analyzing Accessory Pigments

Accessory pigments have multiple functions: they broaden the spectrum of light that can drive photosynthesis and protect chlorophyll from damage by excess light. Since they serve various roles, it is correct to say they are multipurpose molecules.

Step 3: Understanding Chlorophyll 'a' and Color Reflection

Chlorophyll \(a\) appears green not because it absorbs green light, but because it reflects green wavelengths and absorbs other colors such as blue and red. Thus, the light that is not absorbed gives chlorophyll \(a\) its green appearance.

Step 4: Identifying the Incorrect Statement

From the analysis of each statement, we observe that chlorophyll \(a\) is not green because it absorbs green light; it's green because it reflects it. Therefore, the statement that chlorophyll \(a\) is green because it absorbs green light is incorrect.

Key Concepts

Pigment Absorption

Pigment absorption plays a crucial role in photosynthesis. Pigments are specialized molecules that capture light energy by absorbing specific wavelengths. Pigments such as chlorophyll absorb light photons and use that energy to facilitate the chemical reactions in photosynthesis. Different pigments absorb different wavelengths, reflecting those they do not absorb.

• This is why leaves can display various colors. Most pigments will appear the color they reflect.
• Examples of pigments include chlorophyll, carotenoids, and phycobilins, each having a unique absorption spectrum.

Understanding which pigments absorb what wavelengths helps in analyzing their role in photosynthesis effectiveness.

Chlorophyll Function

Chlorophyll is the primary pigment involved in photosynthesis, and its main types are chlorophyll \(a\) and chlorophyll \(b\). Chlorophyll \(a\) plays a significant role by capturing light energy and converting it into chemical energy. It absorbs primarily blue and red light, while reflecting green light, which is why chlorophyll \(a\) appears green to our eyes.

• Chlorophyll’s unique ability to absorb specific wavelengths makes it a masterful energy harvester.
• Its structure allows it to stay embedded in the chloroplast membrane, optimizing photosynthesis.

Chlorophyll’s functionality is enhanced by accessory pigments that help capture additional light.

Accessory Pigments

Accessory pigments are important companions in the photosynthesis process. They extend the range of light that plants can use by absorbing different wavelengths that chlorophyll \(a\) cannot. Carotenoids, such as beta-carotene and xanthophylls, are typical examples of accessory pigments.

• These pigments not only capture light but also protect chlorophyll from photodamage.
• They act as antioxidants, preventing cellular damage that could be caused by excess light.

Due to their versatile roles, accessory pigments are indeed multipurpose, ensuring the plant maximizes available light energy.

Light Wavelengths

Light wavelengths are at the heart of photosynthesis as they determine the energy available for capturing by pigments. Sunlight comprises different colors, each with varying wavelengths and energy levels. Blue light, for example, has a shorter wavelength and greater energy compared to red light, which has a longer wavelength and less energy.

• Pigments absorb visible light ranging from approximately 400 nm (violet) to 700 nm (red).
• This range includes all the colors of the rainbow, and each color corresponds to a different wavelength.

Plants have evolved to use a broad spectrum of these wavelengths to drive photosynthesis, ensuring a continuous energy supply for growth and survival.