Robert Hooke, in 1665, observed thin slices of cork under a compound microscope and saw box-like structures he named 'cells'. Leeuwenhoek observed live cells, Brown discovered the nucleus, Virchow proposed cells arise from cells.
Explanation:
Cortisol (a glucocorticoid) from the adrenal cortex is a steroid hormone derived from cholesterol. Insulin and growth hormone are peptides, adrenaline is a catecholamine (amino acid derivative).
Explanation:
Simple permanent tissues (parenchyma, collenchyma, sclerenchyma) consist of a single cell type. Meristematic tissues are dividing and have thin walls; xylem/phloem are complex; epidermis is dermal.
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