3.1.2 Cells and Cell Structure Flashcards
÷ Divide to make ____
bigger
× Multiply to make _____
smaller
Describe how you convert cm → mm → μm → nm & vice versa
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Define Magnification
How many times bigger the image is than the specimen (object)
Define Resolution
Minimum distance apart that two objects can be in order for them to appear as separate items
State the formula used to work out magnification
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Describe how optical (light) microscopes work
Light from bulb travels through condenser lens, then specimen, up through objective lens and through eyepiece lens into your eye
State the maximum magnification for an optical microscope
x 1500
State the maximum resolution for an optical microscope
0.2 µm
Name 2 pros of optical (light) microscopes
- Easy and cheap to operate
- Can have living specimens
Name 2 cons of optical (light) microscopes
- Low resolution & magnification
- Can’t see organelles smaller than 0.2 µm (e.g. ribosomes, endoplasmic reticulum and lysosomes)
- Specimens often need staining to show specific organelles
Why does optical microscopes have a maximum resolution of 0.2 µm?
∵ of the long wavelength of light rays
Name 2 Electron Microscopes
- Transmission Electron Microscopes
- Scanning Electron Microscopes
Describe how transmission electron microscopes work
- Use electromagnets to focus a beam of electrons which is then transmitted through the specimen
- Denser parts of specimen absorb more electrons = makes them look darker on image you end up with
State the maximum resolution for a transmission electron microscope
0.1 nm
State the maximum magnification for a transmission electron microscope
x 10 000 000
Name a pro of transmission electron microscopes
- Has highest resolutions & magnification
- See internal structure of organelles e.g. chloroplasts
Name 4 cons of transmission electron microscopes
- Non-living matter only
- Image in black and white and 2D
- Preparation may distort structure/give artefacts
- Vacuum required
- Elaborate preparation - staining is complex
Describe how scanning electron microscopes work
- They scan a beam of electrons across specimen = knocks off electrons from specimens
- Electrons gathered in cathode ray tube to form image
State the maximum magnification of SEMs
x 30,000
State the maximum resolution of SEMs
20 nm
Name 3 pros of SEMs
- Can form complex 3D images of sample
- Can be used on thick specimens
- Magnifications & resolutions are higher than light microscopes
Name 3 cons of SEMs
- Large and expensive & difficult to operate
- Specimens has to be mounted in vacuum
- Specimen has to be dead
What type of cells are like algal cells?
Plant cells = have same organelles
(Can be single-celled or multicellular)
What type of cells are like fungal cells?
Plant cells
What are 2 differences between fungal and plant cells?
In fungal cells:
Cell walls are made from of chitin & they don’t have chloroplasts
What is the function of the cell-surface (plasma) membrane?
Regulates movement of substances into and out of cells
(has receptor molecules on it = respond to chemicals)
What is the function of the nucleus?
Holds genetic information of cell
What is the function of the nucleolus?
Makes RNA and ribosomes
What are chromosomes made of?
DNA and proteins
What is the function of chromosomes?
Provides instructions for the cell
What is the function of nuclear pores?
Allow passages of large molecules (e.g. RNA)
What is the nucleoplasm?
Jelly-like material that makes up bulk of nucleus
What is the nuclear envelope?
Double membrane that surrounds nucleus
What is the function of the nuclear envelope?
Controls entry/exit of materials in and out of nucleus & reactions taking place within it
Where is chloroplast found?
Plant cells and some protoctists