Cell Biology/Organelles/Chloroplasts

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Chloroplasts[edit | edit source]

Chloroplasts are major organelles. They contain green pigments that make plants green. They are often called plastids, though plastids and chloroplasts are not exactly the same thing—a chloroplast is a special kind of plastid that photosynthesizes. Chloroplasts do lots of things, but their main function is photosynthesis.

Plant cells, and some protists have chloroplasts, though animal and fungal cells lack them. Prokaryotes do not have chloroplasts (or any other organelles), though some can carry out photosynthesis, its cell acting like one big chloroplast. Chloroplasts are mainly green in colour since it absorbs red and blue light via their green pigment chlorophyll that is present in the thylakoid membranes.(Refer to wikibooks.org for more information)

Chloroplasts are cellular generators. They take in carbon dioxide and water, and release sugar and oxygen. This process is called photosynthesis. Mitochondria then use the sugar and oxygen to carry out cellular respiration, producing energy.

Mitochondria are essential parts of many eukaryotes, but they are useless without oxygen. Therefore, chloroplasts are extremely important. They produce breathable air for life.

Root hairs are seen to not have chloroplasts as their job is to collect water and nutrients. They do NOT carry out photosynthesis.

Like mitochondria, chloroplasts have their own DNA. Scientists also think chloroplasts are descended from a kind of bacteria, called cyanobacteria. Cyanobacteria are the photosynthetic bacteria we mentioned earlier. In early stages of Earth, cyanobacteria produced oxygen for their friends, the ærobic bacteria (ærobic means they use oxygen). Some of these ærobic bacteria later migrated into a eukaryotic cell, becoming mitochondria. The cyanobacteria followed, becoming chloroplasts. All eukaryotic cells contain mitochondria, but only plants and algæ contain chloroplasts, so scientists think mitochondria came first.

Chloroplasts visible in the cells of Plagiomnium affine — Many-fruited Thyme-moss. Small green dots are chloroplasts, hexagons are plant cells. Chlorophylls contained in chloroplasts are so small to be distinguished in this picture.