Introduction to Cells

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Review- Cell Theory All organisms are composed of one or

more cells. Cells are the smallest living units of all

living organisms. Cells arise only by division of a

previously existing cell.

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Generalized Eukaryotic Cell

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Visualizing Cells Compound microscopes - magnify in

stages using multiple lenses Transmission electron microscope -

electrons transmitted through specimen Scanning electron microscope - electrons

beamed onto surface of the specimen

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Electron microscope

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Transmission Electron Microscope

Beam of electrons passed through the specimen before being viewed

Only electrons that are transmitted (pass through the specimen) are seen

Allows to see thin sections of specimens (inside the cell)

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Bacterium (TEM)(Image provided by: ceiba.cc.ntu.edu.tw)

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Scanning Electron Microscope

Electron beam is used to scan the surfaces of structures and only the reflected beam is observed

Surface structures can be seen Cannot achieve same resolution as a

transmission electron microscope

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Electron microscope image of a fly foot

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Scanning Electron Microscope (SEM) photograph of tobacco seed

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Light microscope

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Cheek cells 100X

Cheek cells 400X

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Measurements

1 millimeter (mm)- 1 thousandth of a meter

1 micrometer(um)- 1 thousandth of a millimeter

1 nanometer (nm)- 1 thousandth of a micrometer

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scale of the universe - from atom to living things

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Visualizing Cells

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Cell sizes-Seatwork

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Magnification and ResolutionMagnification

- the number of times larger an image is compared with the real size of the object

- magnification = size of image actual size of

specimen

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Surface Area and Volume of cells Surface area Volume As the cell size increases the surface

area to volume ratio decreases. Simple calculation

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Cell Size Most cells are relatively small because as size

increases, volume increases much more rapidly. longer diffusion time Larger volume and more demands for the cell

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Respiration- cells need to be small

A cell requires oxygen for the process.

Oxygen is obtained form the surrounding environment

Oxygen diffuses across the cell membrane.

More membrane more diffusion (Surface area= increases by the 2).

Bigger cell (Volume = increases by the 3).

Cells must not get too big because they cannot obtain sufficient oxygen to satisfy the demands of the cell

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Emergent properties The whole is more than the sum of its

parts

choir brain

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Emergent properties of the body

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Differentiation of cells Cells in the body

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Embryology

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Stem Cells Capacity to divide and differentiate into

different pathways Genes are not yet expressed so the cells

are not yet specialized Stem cells can be obtained from

Blastocyst Adult organs placenta

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