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B1 - cell structure - Coggle Diagram
B1 - cell structure
magnification
light microscopes -
cells range in size
- animal cells - between 0.01mm - 0.05mm
- plant cells - between 0.01mm and 0.10mm
the human eye can see object as small as 0.05mm so a microscope is designed to see a cell in depth
microscopes magnify the image of a biological specimen so that it appears larger
school labs use compound microscopes
calculating magnification of a microscope -
the compound microscope uses two lenses to magnify the specimen -
- the eyepiece
- an objective lens
there is a choice of objective lenses to use
magnification can be varied according to the size of the specimen and the level of detail required
equation -
magnification of the microscope = magnification of eyepiece × magnification of objective
magnification of an eyepiece is ×10 and the objective is ×4, the magnification of the microscope is 10 x 4 = 40
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types of cells
animals cells -
- cytoplasm -jelly-like material that contains dissolved nutrients and salts, where many of the chemical reactions take place
- nucleus - contains genetic material, controls the cell’s activities
- cell membrane -permeable to some substances but not to others so controls what goes in and out of the cell
- mitochondria - contain the enzymes for respiration, where most energy is released in respiration
- ribosomes - where protein sythesis occurs
plants cells -
- cytoplasm -jelly-like material that contains dissolved nutrients and salts, where many of the chemical reactions take place
- nucleus - contains genetic material, controls the cell’s activities
- cell membrane -permeable to some substances but not to others so controls what goes in and out of the cell
- mitochondria - contain the enzymes for respiration, where most energy is released in respiration
- ribosomes - where protein sythesis occurs
- chloroplasts - contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis, enzymes needed for photosynthesis
- cell wall - made form cellulose fibres , strengthens the cell and supports the plant
- permanent vacuole - filled with cell sap to keep the cell turgid
eukaryotes and prokaryotes -
bacteria are among the simplest of organisms - they are made up of single cells
- they are prokaryotic cells
- cells in animals, plants and fungi are eukaryotic cells
comparing eukaryotes and prokaryotes -
size -
- eu - more than 5 μm to 100 μm
- pro - more than 0.2 μm to 2.0 μm
outer layer of cell -
- eu - surrounded by cell wall in plants and fungi
- pro - surrounded by a cell wall
cell contents -
- eu - cytoplasm, cell organelles include mitochondria, chloroplasts in plants and ribosomes
- pro - cytoplasm, ribosomes, no mitochondria or chloroplasts
genetic material -
- eu - DNA in a nucleus- plasmids are found in few simple eukaryotic organisms
- pro - DNA in simple molecule, found in the cytoplasm-additional DNA is found on one or more rings called plasmids
types of cell divisions -
- eu - mitosis
- pro - binary fission
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cell size -
small stuff - some sub-cellular structures, for instance ribosomes, or organisms such as viruses, it’s best to use a smaller unit – the nanometre, symbol nm
average - best unit to measure most cells is the micrometre, symbol μm millimetre (mm) - 1/1000 metre
micrometer (μm) - 1/1000 millimetre
nanometre (nm) - 1/1000 micrometre standard form -
millimetre (mm) - 1 × 10^-3 m
micrometre (μm) - 1 x 10^-6 m
nanometre (nm) - 1 x 10 ^-9 m
preparing biological samples for experimentation -
cheek cell test -
- put a small drop of water in the microscope slide
- gently swab the inside of your cheek with a clean cotton bud
- gently rub the cotton bud in the drop of water and will be able to see the cells with naked eye
onion skin cell -
- put a small drop of water in the microscope slide
- peel some onion skin from inside one of the leaves in an onion bulb
- use forceps to transfer it to the drop of water- make sure the onion skin is flat and there is not trapped air bubbles- stain cells with iodine
square or circle of thin glass called a coverslip is placed over the specimen - protects the microscope and makes sure the slide doesn’t dry out
mounted needle can be used to hold the specimen in place as the coverslip is lowered- important that no air bubbles are trapped underneathrisks -
- illumination may be too bright (hard on the eyes)
- care while using microscope stains
- care when handling coverslips, microscope slides and mounted needles
electron microscope-
use a beam of electrons instead of light rays
there are two types of electron microscope -
- scanning electron microscope (SEM) has a large field of view so can be used to examine the surface structure of specimens- SEMs are often used at lower magnifications
- transmission electron microscope (TEM) is used to examine thin slices or sections of cells or tissues
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