In this lesson, we'll explore the parts of the chloroplast, such as the thylakoids and stroma, that make a chloroplast the perfect place for conducting photosynthesis in plant cells.
Plant Cells Contain Chloroplasts
Plants love to relax in the sun, and they don't really think about slathering on the sunscreen. That's because sunbathing serves an important purpose to plants beyond getting a tan. You see, plants aren't exactly able to order their favorite food by the poolside. Instead of consuming food, plants make it. And, as any good chef would know, creating food can be hard work. These things require a lot of energy to do. Instead of ordering take-out or putting on their favorite apron to get busy in the kitchen, plant cells go through an efficient process to create food: photosynthesis, a process that converts energy from sunlight into food in plant cells.
Chloroplasts are tiny structures inside of plant cells where photosynthesis occurs
We'll get into the details of how photosynthesis works in future lessons. In this lesson, we'll discuss an important structure essential to this process. Each plant is made of many plant cells performing photosynthesis. Inside of each of these tiny plant cells are one to hundreds of small structures called chloroplasts. Chloroplast comes from the Greek word 'chloros' for 'green' and 'plastis' for 'the one that forms.' That's because chloroplasts are what give plants a green color and help the plant cells form something delicious! Chloroplasts are the structural sites of photosynthesis, where light energy is converted into food. A cell that resides in a plant leaf, for example, might have hundreds of chloroplasts that capture light from its tanning session and use it to make the plant equivalent of a burger and fries.
Chloroplasts exist in the cytoplasm of plant cells. They are flat, Frisbee-shaped structures filled with thylakoids. Thylakoids are small disk-like compartments composed of membranes that are the sites of sunlight-dependent photosynthesis. The thylakoids are surrounded by the stroma, or the inner liquid portion of the chloroplast. Both the stroma and the thylakoids contain important molecules for photosynthesis. Thylakoids are often stacked on top of each other - they look like a stack of flapjacks. Grana, or singular 'granum,' are stacks of thylakoids within chloroplasts.
The stroma surround the thylakoids
The thylakoids contain numerous integral and peripheral membrane proteins as well as chemicals important to photosynthesis. One of these important molecules is called chlorophyll, a pigment or compound that absorbs a specific wavelength of energy from sunlight to use in photosynthesis. This is really like the solar panels of the plant cell, harnessing light energy from the sun. Chlorophyll is also the pigment responsible for making chloroplasts, and therefore all plants on Earth, such lovely shades of green!
Another interesting tidbit about chloroplasts - they contain their own DNA and ribosomes. The DNA is different than the DNA in the nucleus and may code for proteins essential to photosynthesis. Having its own ribosomes also allows the chloroplast to perform translation of these proteins, independent of what goes on outside the chloroplast inside the cytoplasm of the cell.
In summary, the chloroplast is an important plant cell structure and the site of photosynthesis, which converts energy from sunlight into food. The chloroplast contains chlorophyll within its thylakoids, which absorbs light energy and gives chloroplasts its green color. Stacks of thylakoids are known as grana, which exist in the open space of the chloroplast known as the stroma.