Chloroplasts are considered organelles in plant cells. Organelles are special structures in cells that perform specific functions. The main function of the chloroplast is photosynthesis.
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Most chloroplast are oval-shaped blobs, but they can come in all sorts of shapes such as stars, cups, and ribbons. Some chloroplasts are relatively small compared to the cell, while others may take up the majority of the space inside the cell.
- Outer membrane – The outside of the chloroplast is protected by a smooth outer membrane.
- Inner membrane – Just inside the outer membrane is the inner membrane which controls which molecules can pass in and out of the chloroplast. The outer membrane, the inner membrane, and the fluid between them make up the chloroplast envelope.
- Stroma – The stroma is the liquid inside the chloroplast where other structures such as the thylakoids float.
- Thylakoids – Floating in the stroma is a collection of sacks containing chlorophyll called the thylakoids. The thylakoids are often arranged into stacks called granum as shown in the picture below. The granum is connected by disc-like structures called lamella.
- Pigments – Pigments give the chloroplast and the plant its color. The most common pigment is chlorophyll which gives plants their green color. Chlorophyll helps to absorb energy from sunlight.
- Other – Chloroplasts have their own DNA and ribosomes for making proteins from RNA.
Chloroplasts use photosynthesis to turn sunlight into food. The chlorophyll captures energy from light and stores it in a special molecule called ATP (which stands for adenosine triphosphate). Later, the ATP is combined with carbon dioxide and water to make sugars such as glucose that the plant can use as food.
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Other functions of chloroplast include fighting off diseases as part of the cell’s immune system, storing energy for the cell, and making amino acids for the cell.
Interesting Facts about Chloroplasts
- Simple cells, like those found in algae, may only have one or two chloroplasts. More complex plant cells, however, may contain hundreds.
- Chloroplasts will sometimes move around within the cell in order to position themselves to where they can best absorb sunlight.
- The “chloro” in chloroplast comes from the Greek word chloros (meaning green).
- The most abundant protein in chloroplasts is the protein Rubisco. Rubisco is likely the most abundant protein in the world.
- Human and animal cells do not need chloroplasts because we get our energy from eating and digesting food rather than through photosynthesis.
- Scientists estimate that there are around 500,000 chloroplasts in a single square millimeter of a leaf.
- There are actually different colors of chlorophyll. Chlorophyll A is the most common type and is green. Chlorophyll C is a golden or brownish color.