Chloroplast
Say it: KLOR-uh-plast
A chloroplast is the green organelle in plant and algal cells that captures light energy and uses it to make sugars by photosynthesis.
Also: chloroplasts
Definition
What is a chloroplast?
A chloroplast is a type of plastid, an organelle of plants and algae, and it is where photosynthesis takes place. In land plants, chloroplasts are most plentiful in the mesophyll, the middle tissue layer of the leaf. Each one is wrapped in an outer and an inner membrane. Inside lies a third set of membranes forming flattened sacs called thylakoids, which are often stacked into piles known as grana. The fluid surrounding the thylakoids is the stroma.
The thylakoid membranes hold chlorophyll, the green pigment that absorbs light, and carry out the light-dependent reactions, which split water, release oxygen and produce the energy carriers ATP and NADPH. In the stroma, the Calvin cycle spends that ATP and NADPH to turn carbon dioxide into sugar.
Like mitochondria, chloroplasts contain their own circular DNA and bacteria-like ribosomes. These features point to their origin from cyanobacteria, photosynthetic bacteria that were engulfed by an early eukaryotic cell and kept as permanent partners. Chloroplasts are why leaves are green and why plants can make their own food.
Word parts
Where does the word “chloroplast” come from?
- chloro-
- pale greenGreek khloros
- -plast
- formed or molded thing; a cell bodyGreek plastos
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Related
Terms that go with it
- PhotosynthesisPhotosynthesis is the process in which plants, algae and cyanobacteria capture light energy and store it in sugar built from carbon dioxide and water.
- ChlorophyllChlorophyll is the green pigment in plants, algae and cyanobacteria that absorbs light energy to drive photosynthesis.
- OrganelleAn organelle is a specialized structure inside a cell, usually wrapped in its own membrane, that carries out a particular job for the cell.
- MitochondrionA mitochondrion is a double-membraned organelle that makes most of a eukaryotic cell's ATP by breaking down fuel molecules with oxygen.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 4.3 Eukaryotic Cells
- OpenStax Biology 2e, 8.1 Overview of Photosynthesis
- MeSH (NLM): Chloroplasts
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