In green plants, the main green pigment responsible for capturing light energy for photosynthesis is called what?

Introduction / Context:
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in sugars. To do this, they need pigments that can absorb light efficiently. The most important of these pigments in higher plants is a green coloured compound found in chloroplasts. This question asks you to identify the name of this primary green pigment.

Given Data / Assumptions:

• The focus is on the main green pigment of higher plants.
• Options list chlorophyll, xanthophyll, carotene, phycobilin, and anthocyanin.
• We assume typical leaf pigments found in chloroplasts.
• We are concerned with the pigment directly involved in light capture for photosynthesis.

Concept / Approach:
Chlorophyll is the key photosynthetic pigment in green plants, giving leaves their characteristic colour. There are different forms, such as chlorophyll a and chlorophyll b, but together they absorb light mainly in the blue and red regions of the spectrum and reflect green light, which is why plants appear green. Xanthophylls and carotenes are accessory pigments that absorb light in other wavelengths and pass the energy to chlorophyll. Phycobilins are pigments found in some algae and cyanobacteria, and anthocyanins are water soluble pigments responsible for red, purple, and blue colours in some flowers and leaves. Thus, the main green pigment that drives photosynthesis in higher plants is chlorophyll.

Step-by-Step Solution:
Step 1: Recall that leaves appear green due to a specific pigment present in chloroplasts. Step 2: Identify chlorophyll as the primary green pigment involved in the light reactions of photosynthesis. Step 3: Recognise that chlorophyll absorbs light and initiates the conversion of light energy into chemical energy. Step 4: Note that xanthophylls and carotenes are yellow and orange accessory pigments that protect chlorophyll and broaden the absorption spectrum. Step 5: Understand that phycobilins are mainly found in red algae and cyanobacteria, not in higher plant chloroplasts. Step 6: Anthocyanins create red and purple colours and are not the primary photosynthetic pigments. Step 7: Therefore, chlorophyll is the main green pigment responsible for trapping light energy.

Verification / Alternative check:
Plant physiology texts describe chlorophyll a as the primary pigment in photosystems, with chlorophyll b and accessory pigments assisting. Diagrams of chloroplast structure highlight chlorophyll molecules embedded in thylakoid membranes. Experiments where pigments are separated by chromatography show the dominant green band corresponding to chlorophyll. All of this confirms chlorophyll as the correct answer.

Why Other Options Are Wrong:
Xanthophyll: A yellow accessory pigment that participates in photoprotection and light harvesting but is not the main green pigment. Carotene: An orange pigment that also helps in light absorption and protection but is not the primary green photosynthetic pigment. Phycobilin: Pigment groups found mainly in cyanobacteria and red algae, not the central pigment in higher plants. Anthocyanin: Pigments responsible for red and purple colours, more related to flower and fruit coloration than to core photosynthesis.

Common Pitfalls:
Some learners may see multiple pigment names and get confused, or think that accessory pigments are more important because they are less familiar. A simple way to remember is that “chloro” means green and chlorophyll is the green leaf pigment that directly drives photosynthesis in plants.

Final Answer:
The correct answer is Chlorophyll.