Biology

• Animal cells range in size from 0.01 to 0.05 mm
• Plant cells range in size from 0.01 to 0.10 mm
• The human eye can see objects as small as around 0.05 mm
• The type of microscope most used in schools is a compound microscope
• A compound microscope uses two lenses to magnify the specimen - the eyepiece and an objective lens
• Magnification can be varied according to the size of the specimen to be viewed and the level of detail required.
• Magnification of the microscope = magnification of eyepiece × magnification of objective
• Magnification = size of image / real size of object
• The maximum magnification with a light microscope is around ×1500
• The ability to see greater detail in an image depends on the resolution
• Resolution is the ability to see two points as two points, rather than merged into one
• The resolution of a light microscope is around 0.2 μm which can also be written as 200 nm.
• Electron microscopes use a beam of electrons instead of light rays
• The scanning electron microscope (SEM) has a large depth of field so it can be used to examine the surface structure of specimens
• SEMs are often used at lower magnifications
• The transmission electron microscope (TEM) is used to examine thin slices or sections of cells or tissues
• TEMs have a maximum magnification of around x1,000,000
• The limit of resolution of the transmission electron microscope is now less than 1 nm
• The TEM has revealed structures in cells that are not visible with the light microscope
• Cytoplasm is a jelly-like material
• Cytoplasm contains dissolved nutrients and salts and structures called organelles
• Cytoplasm is where many of the chemical reactions happen
• The Nucleus contains genetic material, including DNA, which controls the cell's activities.
• Cell membrane is semi-permeable and controls the movement of substances in and out of the cell
• Mitochondria are organelles that contain the enzymes for respiration
• Mitochondria are organelles where most energy is released in respiration
• Ribosomes are tiny structures where protein synthesis occurs.
• Only plant cells have Chloroplasts, Cell walls, and Permanent vacuoles
• Chloroplast are organelles that contain the green pigment, chlorophyll, which absorbs light energy for photosynthesis
• Chloroplast contains the enzymes needed for photosynthesis
• Cell wall is made from cellulose fibres and strengthens the cell and supports the plant
• Permanent vacuole is filled with cell sap to help keep the cell turgid
• Animal cells may also have vacuoles, but these are small and temporary
• In animals, vacuoles are commonly used to store or transport substances
• Bacteria are made of single cells
• The cell structure of bacteria is simpler than the cells of animals, plants and fungi
• Cells of animals, plants and fungi are called eukaryotic cells
• Cells of bacteria are called prokaryotic cells
• Most Eukaryotic cells are 5–100 μm
• Most Prokaryotic cells are 0.2–2.0 μm