The World of Chloroplasts in Biology (Grade A)

Summary:

The essay “I am a Chloroplast” by Sharon Sookhai-Mahadeo describes the chloroplast’s structure, functions, and interactions within the cell. The chloroplast is a unique, self-replicating organelle in green algae and plant cells. It contains green pigments like chlorophyll a and b, responsible for photosynthesis. The chloroplast has a double-membrane envelope enclosing thylakoids, where light-dependent reactions occur. During photophosphorylation, chlorophyll pigments absorb light energy to split water, release oxygen, and create ATP and NADPH. In the light-independent Calvin Cycle, carbon dioxide is converted into simple organic molecules using ATP and NADPH. The chloroplast interacts with other organelles like the nucleus, ER, Golgi, and plasma membrane, and its photosynthesis is essential for all living beings as it produces oxygen and food for plants and other organisms.

Excerpt:

The World of Chloroplasts in Biology

ILLUSTRATIVE ESSAY – I AM A CHLOROPLAST – by Sharon Sookhai-Mahadeo

INTRODUCTIONS -WHO AM I?
Hello, my name is Chloroplast, and I am a unique, self-replicating, round or oval-shaped structure found in
green algae, and within the parenchyma cells of the mesophyll of plants. I am green because I contain green
pigments, chlorophyll a and chlorophyll b. I also have small amounts of orange/red/purple carotenoid and
yellow xanthophyll pigments. All these pigments absorb light energy to help me to synthesize food for my host.
I come from a family known as the Plasmids. I believe that I am the most important organelle on Earth. Can
you guess why?

The World of Chloroplasts in Biology

MY STRUCTURE:

I am small, 5–7 μm in diameter and 1–2 μm thick. I am enclosed in a double-membrane envelope, a gap called the intermembrane space. I also have stacks of internal disks or thylakoids. Each stack is called a granum. The membranes of many thylakoids extend as stromal lamellae, and these interconnect the grana. The chlorophylls, different protein complexes called Photosystems l & ll and ATP synthase are embedded in my Thylakoid membrane. Inside the thylakoid membrane is an aqueous lumen or watery space. Outside of the grana is an aqueous stroma containing dissolved enzymes, starch granules, and copies of my circular DNA.