Studying Cells Flashcards
Cell Theory
All living organisms on earth are composed of cells. Some organisms are single cell, such as bacteria and protozoa. Others, such as ourselves, are collections of cells that have differentiated into tissues and organs.
The cell is the basic unit of life. The components of cells are not alive. Only at the level of the cell do the properties of life emerge.
Cells arise by division of pre-existing cells.
Hypothesis
A tentative answer to a question, usually a rational accounting for a set of observations, based on the available data and guided by inductive reasoning.
Must be testable and falsifiable.
Deductive reasoning
Generally used after a hypothesis has been developed. From general premises, we extrapolate to the specific results we should expect if the premises are true.
If all organisms are made of cells (premise 1), and humans are organisms (premise 2), then humans are composed of cells (deductive prediction about a specific case).
Inductive Reasoning
Collecting and analysing observations lead to important conclusions based on inductive reasoning. Through induction, we derive generalisations from a large number of specific observations. Eg “all organisms are made of cells”
Discovery Science
Involves making careful and repeatable observations and/or measurements with the aim of describing nature.
Uses inductive reasoning.
Hypothesis-based Science
Seeks to explain nature and involves asking questions, making a tentative answer to that question in the form of a hypothesis, the testing that hypothesis by experiment.
Uses deductive reasoning.
Light (brightfield) microscopy
Visible light is passed through the specimen and then through glass lenses. The lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye or into a camera.
Fluorescence microscopy
Differs from brightfield microscopy in that UV light is used as a light source instead of ordinary white light. Fluorescent dyes are used to stain the cells, and these fluorescent dyes emit bright fluorescence when excited by the UV light.
Because UV light has a shorter wavelength than white light the limit of resolution with fluorescence microscopy is better.
Electron Microscope
The electron microscope has a much higher resolving power than a light microscope and is therefore used to probe the internal ultrastructure of cells in more detail.
Uses an electron source instead of a light source, and electromagnets to focus the electron beam instead of glass lenses.
Because the wavelength of an electron beam is much smaller than that of visible light, a very high magnification can be obtained.
Two types:
transmission electron microscope (TEM) and
scanning electron microscope (SEM)
Transmission electron microscope (TEM)
Used to study the internal structure of cells.
The TEM aims an electron beam through a very thin section of the specimen, similar to the way a light microscope transmits light through a slide.
Scanning electron microscope (SEM)
Useful for detailed study of the topography of a specimen. A very fine beam of electrons scans the surface of the specimen. The signal is transferred to a monitor and a 3-dimensional view of the object is obtained. Because we are looking at a 3-dimensional structure with shadows, we get greater depth of field than with the TEM, but less magnification.
Confocal microscopy
Allows you to see cells in 3-dimensions.
1 centimetre (cm)
10-² meter (m)
1 millimetre (mm)
10-3m
1 micrometer (μm)
10-3mm = 10-6m
