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B2 Topic 1 - Genes and Enzymes

• Cells
• Animal cells contain a nucleus which contains DNA that controls what the cell does; cytoplasm, which is a gel-like substance where most of the chemical reactions occur; a cell membrane, which holds the cell together and controls what goes in and out of the cell; and mitochondria, which are where most of the reactions for respiration take place - respiration releases energy that the cell needs to work.
• Plant cells contain all of these, along with a cell wall which is made of cellulose and gives support for the cell; a vacuole which contains sap, a weak solution of sugars and salts; and chloroplasts, where photosynthesis occurs - they contain a green substance called chlorophyll.
• Bacterial cells are smaller than plant and animal cells and don't contain a nucleus. They contain a cell wall; chromosomal DNA, which controls the cell's activities and replication and floats free in the nucleus; plasmids, which are small loops of extra DNA that aren't part of the chromosome - they contain genes for things like drug resistance and can be passed between bacterium; and flagella, long hair-like structures that rotate to make the bacterium move.

B2 Topic 1 - Genes and Enzymes

• Microscopy
• Microscopes let us see things that we can't see with the naked eye. Light microscopes were invented in the 1590s. They let us see things like nuclei, chloroplasts and mitochondria. Electron microscopes were invented in the 1930s. They let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts, and even tinier things like plasmids. You need to be able to calculate magnification. Magnification is how much bigger the image is than the specimen. It's calculated using the formula: magnification = length of image / length of specimen.

B2 Topic 1 - Genes and Enzymes

• DNA
• A DNA molecule