Explanation:
Rhodopsin (visual purple) is a photopigment in rod cells consisting of opsin and retinal (from vitamin A). It bleaches upon absorbing light, initiating signal transduction for vision in low light. Cone cells contain iodopsin for color vision. Melanin is skin pigment, hemoglobin carries oxygen.
Explanation:
Natural killer (NK) cells were discovered in the 1970s by Rolf Kiessling and others. They are part of innate immunity, killing virus-infected and tumor cells.
Explanation:
The primary cell wall of plants consists of cellulose microfibrils embedded in a matrix of hemicellulose, pectin, and proteins. Secondary walls contain lignin. Chitin is in fungi and arthropods, peptidoglycan in bacteria. Cellulose is a polymer of β-glucose units and provides structural support.
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