Chloroplast: Definition, Structure, Function & Examples

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  • 0:00 Animal vs. Plant Cells
  • 0:27 What Is a Chloroplast?
  • 0:51 Chloroplast Structure
  • 1:25 Role in Photosynthesis
  • 2:25 Example Variations
  • 3:18 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista
A chloroplast is a basic organelle that in a sense is one of the most important organelles to us, and we don't even have them! In this lesson, we will be looking where chloroplasts are found and what their role and function is in cells.

Animal vs. Plant Cells

When learning about living cells, one should have a basic understanding that all cells contain numerous organelles, which are subunits within cells with different and specific jobs. Both types of cells, plant and animal, have very similar organelles, but there are obviously differences between animal and plant cells. One is that animals lack a cell wall; another is that plants contain something called a chloroplast.

What is a Chloroplast?

A chloroplast is an organelle unique to plant cells that contains chlorophyll (which is what makes plants green) and is responsible for enabling photosynthesis to occur so that plants can convert sunlight into chemical energy. So basically, without chloroplasts, plants could not create energy, and without them, humans would have no food and we would perish, so thank you chloroplasts!

Chloroplasts in the cells of the thyme moss plant

Structure of Chloroplasts

Chloroplasts can be found in the cells of the mesophyll in plant leaves. There are usually 30-40 per mesophyll cell. The chloroplast has an inner and outer membrane with an empty intermediate space in between. Inside the chloroplast are stacks of thylakoids, called grana, as well as stroma, the dense fluid inside of the chloroplast. These thylakoids contain the chlorophyll that is necessary for the plant to go through photosynthesis. The space the chlorophyll fills is called the thylakoid space.

Structure of a chloroplast
Chloroplast structure diagram

Role in Photosynthesis

The role of chloroplasts in photosynthesis is mainly to contain most of the reaction during photosynthesis. The plant will pump water into the leaves, and the leaves will also absorb carbon dioxide. All of the thylakoids, chlorophyll, water, carbon dioxide, etc. are available inside the chloroplast. The entire process of photosynthesis starts and completes inside of the chloroplast. The chloroplast essentially works as the 'powerhouse' for the cell, similar to the mitochondria, except that it creates its own food that then gets used to power the plant.

To use a more realistic human scenario, you can think of the chloroplast as the kitchen in your home or a restaurant. All the materials are brought to the kitchen (chloroplast) to cook with. They are then placed into the oven (thylakoids) to bake, and after awhile, out comes your food. Chloroplasts are similar in a sense to a kitchen; raw materials in, cooked food out.

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