Structure of the plant cell
The cell is the smallest structural unit of a living organism; it was discovered in 1665 by the English scientist Robert Hooke. A plant cell has a wall, cytoplasm and a nucleus. The wall is made of cellulose (kletchatka), is strong and transparent, protects the cell and keeps its shape. The cytoplasm is a colourless, thicker, constantly moving substance where most of the cell’s work happens. The nucleus holds the hereditary information and controls cell division. There are three kinds of plastids: green chloroplasts carry out photosynthesis, chromoplasts give flowers and fruit yellow-red colours, and colourless leucoplasts store reserve substances. The vacuole is a space filled with cell sap, which is 70–95% water with sugars, salts and other substances dissolved in it. Bacteria and blue-green algae (cyanobacteria) have no formed nucleus.
Practical “Onion-skin slide”: (1) peel a thin transparent skin from the fleshy layer of an onion; (2) lay it in a drop of water on a slide; (3) cover with a cover slip; (4) look under the microscope at 10×–40× and draw the wall, cytoplasm, nucleus and vacuole. Safety: use knives and glass only under teacher supervision, never pick up broken glass by hand, carry the microscope with both hands, and never aim sunlight directly into it with the mirror.