Plastids Flashcards
What are plastids?
Organelles found in plant cells that vary in form and function (e.g., chloroplasts, amyloplasts, chromoplasts). They originated from a cyanobacterial ancestor through endosymbiosis.
Example sentence: Chloroplasts are a type of plastid responsible for photosynthesis.
What is the endosymbiotic theory in relation to plastids?
The theory that plastids originated from cyanobacteria that were engulfed by a proto-eukaryotic cell. This led to a permanent symbiotic relationship, where the cyanobacterium became the plastid.
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Name the different types of plastids.
Proplastid, Leucoplast, Etioplast, Amyloplast, Chromoplast, Elaioplast, Proteinoplast, Chloroplast.
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What is the function of proplastids?
Proplastids are undifferentiated plastids found in young meristem cells (plant equivalent of stem cells). They differentiate into other plastid types depending on the tissue’s needs.
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Where are leucoplasts typically found, and what is their function?
Leucoplasts are non-pigmented plastids found in roots, petals, and young seedlings. They synthesize fatty acids, amino acids, and tetrapyrroles like heme.
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What are etioplasts, and how do they form?
Etioplasts are plastids found in plants grown in darkness or very low light. They contain protochlorophyllide, a precursor to chlorophyll, and transform into chloroplasts upon light exposure.
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What is the role of amyloplasts?
Amyloplasts are unpigmented plastids that store starch and act as gravity sensors (statoliths) in certain root cells.
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What is the main function of elaioplasts?
Elaioplasts synthesize and store lipids, particularly in oilseeds (e.g., sunflower, citrus fruit). They also produce terpenes, which are important in food and pharmaceuticals.
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What are proteinoplasts, and where are they found?
Proteinoplasts are plastids found in seeds and nuts (e.g., brazil nuts, peanuts). They contain crystalline protein bodies and enzymes, but their exact function is unclear.
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What is the function of chromoplasts, and where are they found?
Chromoplasts store carotenoids (yellow, orange, red pigments) and give fruits, flowers, and roots their color, attracting pollinators and aiding in seed dispersal.
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Describe the structure of chloroplasts.
Chloroplasts have a double membrane and an internal membrane system called thylakoids, which form grana stacks. The stroma contains enzymes for carbon fixation and biosynthesis pathways.
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What processes occur in chloroplasts?
Photosynthesis (light-dependent reactions and carbon fixation), pigment biosynthesis (chlorophyll, carotenoids), starch storage, fatty acid biosynthesis, amino acid biosynthesis, and nitrogen assimilation.
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How does nitrogen assimilation occur in chloroplasts?
Chloroplasts convert nitrate from the soil into ammonium and glutamine, which are essential for amino acid synthesis and nitrogen-containing molecules.
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What happens to etioplasts when exposed to light?
Etioplasts rapidly convert protochlorophyllide into chlorophyllide, leading to the formation of chlorophyll. The process also involves the appearance of thylakoid membranes and the disappearance of prolamellar bodies.
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What is the plastid genome (plastome), and why is it significant?
The plastome is the plastid’s own DNA, similar to bacterial DNA, which encodes genes necessary for photosynthesis, transcription, and translation. Plastids are polyploid, containing many copies of the plastome.
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