3.2 Cells Flashcards
Explain why organisms with smaller sizes can be seen with a TEM but not with an optical microscope.
TEM has higher resolution as it uses a shorter wavelength of electrons, rather than a long wavelength of light
Why is a TEM microscope used to produce an image of a plant cell, including its mitochondria?
- TEM has a higher resolution
- Electron beam passes through the cell so that the internal structures of the cell can be seen
Describe the principles and limitations of TEM to investigate cell structure.
- Short wavelength of electrons pass through sample, high resolution
- Sample must be extremely thin to allow electrons to pass through
- Sample cannot be living as it is carried out in a vacuum
- Image produced is not in colour or 3D
Describe the structure and function of the nucleus.
- Has nucleolus
- Has nuclear envelope with pores (important for mRNA and ribsome movement)
- Contains chromatin (DNA and histones)
- Site of trancription
What organelle in a eukaryotic cell modifies proteins?
The golgi body
What is the function of the smooth ER?
Synthesises, stores and transports carbohydrates and lipids
What are the main structures of chloroplasts?
Stroma, thylakoid membrane, grana, lipid droplets, starch grain
What are the main structures of mitochondria?
Matrix, inner membrane, outer membrane, cristae, inter membrane space
Why do you use an ice-cold, isotonic buffer solution when preparing a solution for centrifuging?
Ice-cold = slows down the activity of hydrolytic enzymes
Isotonic = stops osmosis, cells are not damaged (burst, shrivel)
Buffer = control pH, slows down enzyme activity which may destroy organelles
Describe how you would use cell fractionation to isolate chloroplasts from leaf tissue.
- Homogenate leaf tissue in cold, isotonic buffer solution.
- Filter off any debris
- Collect 2nd pellet after centrifuging
What organelles require the lowest speed for centrifuge and why?
- Nuclei, mitochondria
- They are the larger and heavier organelles
What organelles require the highest speed for centrifuge and why?
- Lysosomes, ribosomes, endoplasmic reticulum.
- Smallest organelles, have a low density
What are the two components once the mixture is centrifuged?
Pellet and supernatant
What are the cell walls of the following organisms primarily made up of:
a) bacteria
b) fungi
a) Murein
b) Chitin
What is the theory that relates prokaryotic cells to mitochondria and chloroplasts?
Endosymbiotic theory
What are the similarities between prokaryotes and mitochondria/chloroplasts?
Both:
- Contain 70s ribosomes
- Replicate by binary fission
- Have similar sizes
- Have circular DNA
- Have a double membrane
Describe the structure of a bacterial cell.
All:
- No membrane-bound organelles
- 70s ribosomes
- No nucleus, circular DNA instead that is not associated with histones
- Cell wall containing murein
Some have:
- Plasmids
- Capsules
- Flagellum
Describe the structure of a virus.
- Nucleic acid core (RNA/DNA)
- Protein coat/capsid
- Attachment proteins (glycoproteins)
- Phospholipid envelope
Why are viruses classed as acellular and non-living?
- Invade host cell in order to reproduce
- They contain no cellular structures like cytoplasm or cell membranes
What are the phases of the cell cycle?
Interphase, mitosis, cytokinesis
What are the phases of interphase? Describe what happens in each one.
G1 - organelles replicate, protein synthesis, cell grows
S - DNA replicates, sister chromatids created
G2 - DNA checked for errors, energy stores grow
What are the phases of mitosis? Describe what happens in each one.
Prophase:
- chromosomes condense
- centrioles move to form spindle fibres
Metaphase:
- nucleus disappears
- chromosomes line up along spindle fibres
Anaphase:
- centromere splits
- sister chromatids pulled apart to opposite poles
Telophase:
- chromosomes decondense
- nuclear envelope reforms
Where in plants does mitosis occur?
Meristems
Explain how the events in interphase and mitosis leads to the production of genetically identical daughter cells.
- Semi-conservative replication during interphase produces two identical sister chromatids
- Each chromatid seperated during anaphase and pulled to opposite poles
How many cells does mitosis produce and are they haploid or diploid?
Produces 2 genetically identical diploid cells
What two pieces of evidence show that a cell is in the anaphase stage of mitosis?
- V-shape of chromosomes show that they have been pulled apart at the centromere
- Chromosomes are at opposite poles of the spindle fibres
What occurs during cytokinesis in an animal plant? How does this differ in plant cells?
- In animal cells, a cleavage furrow forms and separates the two cells, splitting the cell membrane in two.
- In plant cells, a cell plate forms and new cell walls form once the cell plate reaches the old cell walls