Question

What accessory pigments are present in phototrophs, and what are their functions? (Section 13.2)

Short answer

Chlorophyll b, carotenoids, and phycobilins capture and transfer light energy while also protecting against damage.

Step-by-step solution

Identify Accessory Pigments

Accessory pigments present in phototrophs include chlorophyll b, carotenoids, and phycobilins.

Chlorophyll b and Its Function

Chlorophyll b assists in photosynthesis by capturing light energy and passing it on to chlorophyll a, enhancing the range of light wavelengths phototrophs can use.

Carotenoids and Their Function

Carotenoids, such as carotenes and xanthophylls, protect the photosynthetic apparatus from excess light and oxidative damage while also broadening the spectrum of light absorption.

Phycobilins and Their Function

Phycobilins, found in cyanobacteria and red algae, absorb light in the green to orange-red spectrum, helping these organisms thrive in deeper or shaded aquatic environments.

Key concepts

Chlorophyll b

Chlorophyll b is one of the essential accessory pigments in phototrophs. While chlorophyll a is the primary pigment involved in photosynthesis, chlorophyll b plays a crucial supportive role. It absorbs light energy primarily in the blue and red regions of the electromagnetic spectrum and transfers this energy to chlorophyll a.
By capturing a broader spectrum of light, chlorophyll b enhances the efficiency of photosynthesis. This means plants can convert more light into chemical energy, especially in low-light conditions.
Chlorophyll b is primarily found in green algae and higher plants, working alongside chlorophyll a to ensure optimal energy absorption.
Without chlorophyll b, plants would struggle to maximize the available light energy, affecting their growth and survival.

Carotenoids

Carotenoids are another crucial group of accessory pigments found in phototrophs. They come in two main types: carotenes (like beta-carotene) and xanthophylls (like lutein and zeaxanthin).
These pigments absorb light in the blue and blue-green regions of the spectrum, thus extending the range of light wavelengths that plants can utilize for photosynthesis.
Besides their role in light absorption, carotenoids serve as protective agents. They help to prevent oxidative damage caused by excess light, thereby protecting the photosynthetic machinery from potential damage.
Carotenoids are responsible for the vibrant colors seen in many fruits and vegetables, such as oranges, carrots, and spinach. These colors reflect the light wavelengths that carotenoids cannot absorb.
In summary, carotenoids not only aid in photosynthesis by capturing additional light but also play a vital role in protecting plants from harmful light-induced stress.

Phycobilins

Phycobilins are specialized accessory pigments found predominantly in cyanobacteria and red algae. They capture light in the green to orange-red region of the spectrum, which chlorophylls cannot absorb efficiently.
Phycobilins are essential for organisms that dwell in deeper or shaded aquatic environments where light penetration is limited. By absorbing different light wavelengths, these pigments enable these organisms to perform photosynthesis efficiently even in low-light conditions.
There are various types of phycobilins, such as phycocyanin and phycoerythrin, each optimized for capturing specific light wavelengths.
In aquatic ecosystems, phycobilins contribute significantly to the energy capture and thus support the survival of cyanobacteria and red algae.
Overall, phycobilins expand the light absorption capabilities of phototrophs, enabling them to thrive in a wider range of environmental conditions.