Unit 2

•  Nearly all plants and animals are made up of thousands or millions of microscopic cells. 
•  All cells contain cytoplasm enclosed in a cell membrane.
• Most cells have a nucleus.
• Many chemical reactions take place in the cytoplasm to keep the cell alive.
• The nucleus directs the chemical reactions in the cell and also controls cell division.
• Plant cells have a cellulose cell wall and a large central vacuole.
• Cells are often specialised in their shape and activity to carry out particular jobs.
• Large numbers of similar cells packed together form a tissue.
• Different tissues arranged together form organs.
• A group of related organs makes up a system. 
• The magnification of a specimen can be calculated if the actual size and the size of the image are known. 
• Cytoplasm contains organelles such as mitochondria, chloroplasts and ribosomes.
• The magnification and size of biological specimens can be calculated using millimetres or micrometres.
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