Chloroplasts are vital photosynthetic organelles in plants and algae, varying in shape from biconvex to elaborate forms. They contain complex membrane systems, including the thylakoid membranes where light-dependent reactions occur. The stroma, filled with enzymes and DNA, is crucial for the Calvin cycle and energy storage. Chloroplasts' double-membrane structure and DNA support the endosymbiotic theory of their evolution from cyanobacteria.
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Chloroplasts in terrestrial plants are generally biconvex or lens-shaped and range from 3 to 10 micrometers in diameter
Unique Algal Chloroplast Shapes
Algal chloroplasts exhibit a diverse range of shapes, including reticulate, cup-shaped, helical, and band-shaped forms
Unique Algal Chloroplast Sizes
Algal chloroplasts can vary in size, with some filling most of the cell's interior in unicellular algae like Chlorella
Desmidiales, a group of unicellular algae, have elaborate chloroplasts that mirror the cell's shape
The outer chloroplast membrane is permeable to small molecules and ions and transports larger proteins through specific complexes
The inner chloroplast membrane is selectively permeable and involved in the synthesis of fatty acids, lipids, and carotenoids
Thylakoid membranes form a network of flattened sacs and are the site of light-dependent reactions in photosynthesis
The stroma contains the chloroplast's DNA, ribosomes, and enzymes such as RuBisCO, as well as starch granules for energy storage
The stroma is similar to the cytoplasm of ancestral cyanobacteria, from which chloroplasts are derived
Chloroplasts have smaller ribosomes than those in the cytoplasm and synthesize proteins specific to the chloroplast
Plastoglobuli are lipid-containing particles involved in the storage and metabolism of lipids
Some chloroplasts have a peripheral reticulum, a membranous network that may assist in the transport of molecules across membranes
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Function of chloroplasts in plant and algal cells
Conduct photosynthesis, converting light energy into chemical energy.
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Unique chloroplast shapes in specific algae species
Star-shaped in Zygnema, mirror cell shape in Desmidiales, fills cell interior in Chlorella.
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Specialized regions in unicellular algae chloroplasts
Chlorella chloroplasts reserve space for nucleus and other organelles within the cell.
