Section 2 - Unit 3: Cell Structure Flashcards
Process of TEM
1) electron gun produces a beam of electrons that is focused on specimen by a condenser electromagnet
2) the specimen absorbs some electrons to appear dark and in other areas, the electrons pass straight through, looking bright
3) an image known as a photomicrograph is produced
Process of SEM
1) a beam of electrons is focused on the specimen from below
2) the electrons are scattered by the specimen and the pattern of scattering depends on the contours of the specimen
3) from this, a 3D image is built
Advantages of using a SEM
- specimens do not have to be extremely thin
- 3D images are created automatically
Why is the resolution not necessarily achieved in electron microscopes? (1)
- High resolution requires a higher energy electron beam and this can sometimes destroy the actual specimen
Eye Piece Graticule
A glass disc placed in the eyepiece of a microscope which has a printed scale from 0 to 100 on it
Differences between eukaryotic and prokaryotic cells
- membrane bound organelles vs non-membrane bound organelles
- mitosis/meiosis vs binary fission
- multicellular vs unicellular
Explain the advantages and the limitations of using a TEM to investigate cell structure (5 marks)
- Higher resolution due to shorter wavelength of electrons
- so structure of organelles can be seen
- In a vacuum so living specimens cannot be viewed
- Cells must be extremely thin so that the beam of electrons pass through
- Doesn’t produce a colour image even though there’s an extremely complex staining process
Explain why it’s important for the cell specimen to be thin in microscopes (2 marks)
- Only a single layer of cells is needed
- So that light can pass through
Explain why the solution should be ice cold in centrifugation (1 mark)
- To slow the enzymes and prevent them from denaturing the organelles
Describe how the length of the cell could be estimated in an optical microscope (2 marks)
- The length of the cell could be measured with an eyepiece graticule
- And then calibrated against a stage micrometer
Explain the function of stroma in a chloroplast (1 mark)
- It contains enzymes for a light independent reaction
Explain the function of granum in a chloroplast (1 mark)
- Contains chlorophyll molecules to trap light for a light dependent reaction
Explain the advantage of the width of mitochondria being no more than 1μm (1 mark)
- There’s a shorter diffusion pathway
Explain why large numbers of Golgi apparatus and mitochondria are found in mucus-secreting cells (2 marks)
- Golgi Apparatus adds sugars to proteins
- Mitochondria provides ATP for this process
Explain why viruses are not considered living (3 marks)
- Cannot reproduce independently
- They have no nucleus, plasma membranes, cytoplasm or ribosomes
- They are not made of cells
Describe the position of the protein components in a eukaryotic cell membrane (2 marks)
- Either integral (across the entire bilayer)
- Or extrinsic (only on one side of the bilayer)
Describe cholesterol and its role in a phospholipid bilayer (2 marks)
- Acts as a buffer for membrane fluidity
- At high temperatures, it prevents fluidity from rising too high, and at low temperatures, it prevents the membrane from becoming solid
Describe the structure and function of the cell-surface membrane (3 marks)
- Phospholipid bilayer
- With hydrophilic head and hydrophobic tail
- Regulates the transport of substances
Describe the structure and function of the nucleus (6 marks)
- Surrounded by a nuclear envelope
- Which acts as a semi-permeable double membrane
- Nuclear pores
- Which allows substances to enter/exit
- A dense nucleolus made of RNA and proteins
- Which assemble ribosomes
Describe the function of the Golgi Apparatus
- Processes and packages proteins and lipids
- Produces lysosomes
(classrooms that package and store materials)