Module 2.1.1 Cell Structure King Flashcards
Describe the passage of light through a light microscope
-condenser lens refracts light
-this increases the intensity of the light beam through the specimen
Define magnification
-the degree to which an image is larger than the object itself
Define resolution
-the clarity of the image giving us the ability to distinguish between 2 objects that are close together
Advantages of a light microscope
-cheap
-easy to use
-portable
-living specimens
Disadvantages of a light microscope
-low magnification and resolution
-objects can only be seen if a light wave passes through them
What type of cells can be observed during light microscopy?
-multicellular organisms
-single cells
- small and thin enough to let light through
- easily obtained cells eg cheek/ blood cells
What are single cells called?
Euglena
What are multicellular organisms called?
Daphnia
How do we perform sectioning ?
(For light microscope)
-dehydrate the specimen
-embed the specimen in the wax
-cut the wax block into very thin sections
(Good for soft tissue that can be deformed eg brain)
Why do we use staining ?
(For light microscopes)
-increases contrast between the objects in the cell.
-overcomes problems with lack of visible detail.
What is a stain?
Chemicals which bind to specific molecules/ structures
What is differential staining?
Using lots of stains on the same specimen allowing us to see different bits
What is acetic orcein used to stain?
DNA -> dark red
What is gentian violet used to stain?
Bacteria wall
What is Sudan red used to stain ?
Lipids
What is haematoxylin used to stain?
Nuclei
What is eosin used to stain ?
Protein -> pink
How do electron microscopes work ?
-generate beams of electrons to generate and image
-lenses are magnets that focus the beam of electrons on the specimen
How is a scanning electron microscope used ?
-electron doesn’t pass through specimen it’s reflected
-3D image of surface specimen is created
How is a transmission electron microscope used ?
-thin specimen
- electron beam passes through specimen
-2D image
-some electrons are transmitted, some absorbed
First step of preparing samples for TEM?
1) fix sample in glutaraldehyde
Second step of preparing samples for TEM?
2) dehydrate with ethanol to remove water
Fourth step of preparing samples for TEM?
4) stain with leaf salts -> electrons can have contrast
Fifth step of preparing samples for TEM?
5) mount on a copper grid and place grid in the vacuum specimen chamber
What is an artefact?
A specimen that is caused by human interaction- non natural
Advantages of electron microscopes
-really high resolution
-highest magnification (TEM)
-detailed images of organelles
-3D image of how tissues are arranged (SEM)
Disadvantaged of electron microscopes
-very expensive
-hard to learn to use
Description of plasma membrane
(Both)
-membrane bound
-made of lipids and proteins
Function of plasma membrane
-regulates movement of substances in and out the cell
-receptor molecules -> allow it to respond chemicals eg hormones
Description of cell wall
(Plant)
-non membrane bound
-rigid
-carbohydrate cellulose
Function of cell wall
Supports cell
Description of Nucleus
(Both)
-nuclear envelope ->membrane bound
-chromatin -> DNA and proteins