Which of the following is a correct statement about mitochondria?
A. They are single-membrane organelles.
B. They contain 80S ribosomes.
C. They have their own circular DNA.
D. They are found in both prokaryotes and eukaryotes.
Answer: Option C
Solution (By JKExamLibrary)
Mitochondria are double-membrane organelles with circular DNA (like prokaryotes) and 70S ribosomes, supporting the endosymbiotic origin. They are absent in prokaryotes. They are the site of aerobic respiration. The matrix contains enzymes for Krebs cycle. The inner membrane forms cristae, housing electron transport chain and ATP synthase.
Explanation:
The blood-brain barrier (BBB) is formed by tight junctions between endothelial cells of brain capillaries, restricting the passage of pathogens and large molecules. Meninges cover the brain, choroid plexus makes CSF, corpus callosum connects hemispheres.
Explanation:
Sericulture is the process of rearing silkworms (primarily Bombyx mori) for the production of silk. The silkworm feeds on mulberry leaves (Morus alba) and spins a continuous filament of silk protein (fibroin) to form a cocoon around itself during its pupal stage. The cocoons are then boiled to kill the pupa and unwind the silk filament for textile production.
Explanation:
Chiasmata become clearly visible during the diplotene stage of Prophase I. While the actual exchange of genetic material (crossing over) occurs during the pachytene stage, the homologous chromosomes begin to repel each other and move apart in diplotene, remaining connected only at the sites of crossing over, which appear as X-shaped chiasmata. Exam tip: Pachytene = crossing over; Diplotene = chiasmata visible.
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