Biology cells and microscopy exam questions Flashcards
Why can a light microscope not view ribosomes ?
- The resolution of the microscope is too low
- because wavelength of light is too long
Describe the role of a named organelle in digesting bacteria
- lysosomes
- fuse with phagosome ( vesicle that forms around a substance that has been engulfed by phagocytes)
- and release lysozymes ( hydrolytic enzymes)
How does DNA differ in chloroplasts compared to in a nucleus ? How do ribosomes in chloroplasts differ to ribosomes in a nucleus ?
- DNA in chloroplasts is circular, shorter and not associated with proteins
- ribosomes in chloroplasts are smaller than cytoplasmic ribosomes
Outline the role of organelles in the production, transport and release of
proteins from eukaryotic cells.
Do not include details of transcription and translation in your answer.
- DNA in nucleus contains the code for protein
- ribosomes/ RER produces proteins
- mitochondria produce ATP ( energy carrying molecule) for protein synthesis
- golgi apparatus packages proteins into vesicles which transport them to cell surface membrane and release
Describe how a sample of chloroplasts could be isolated from leaves.
- homogenise cells ( break them into smaller pieces) and filter cell debris
- release into a cold, same water potential pH controlled solution
- spin in a centrifuge at a low speed to separate out nuclei
- increase speed and eventually chloroplasts will be separated out from the mixture of organelles
Describe and explain how centrifuging the culture allowed the scientists to obtain a
cell-free liquid from a bacterial culture
- heaviest/ densest cells
- form a pellet ( forced to bottom of tube) if they are spun in a centrifuge
- supernatant (liquid) can be removed
H. pylori cells produce an enzyme that neutralises acid.
Suggest one advantage to the H. pylori of producing this enzyme, considering they attack the stomach
To stop them being destroyed
by the stomach acid ( HCL)
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue.
- homogenise tissue in a homogeniser and filter cell debris
- place in a solution which is cold , has same water potential as tissue and is pH controlled
- spin in centrifuge, chloroplasts will be the second organelle to form pellet
What is a structural difference between starch and cellulose ?
Starch formed from α-glucose but cellulose formed from β-glucose;
2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
Explain one way in which starch molecules are adapted for their function in plant
cells
Insoluble ( don’t dissolve in water) so they don’t affect water potential and thus no effect on net osmosis
OR
large molecules so they cannot leave plant cell
Explain one way in which cellulose molecules are adapted for their function in cell walls
Long and straight chains;
Become linked together by many hydrogen bonds to form fibrils;
Provide strength (to cell wall)
Describe the chemical reactions involved in the conversion of polymers to
monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to
illustrate your answer
-condensation reaction joins monomers together and forms a chemical bond between monomers and releases water
- hydrolysis reaction breaks a chemical bond between monomers and uses water
- alpha glucose are polymers of starch
- beta glucose are polymers of cellulose
What is a monomer
A single (repeating) unit of a polymer
A biochemical test for reducing sugar produces a negative result with
raffinose solution.
Describe a biochemical test to show that raffinose solution contains a
non-reducing sugar.
- Heat with acid and neutralise;
- Heat with Benedict’s (solution);
- Red precipitate/colour or other coloured precipitates such as yellow/orange depending on conc of sugar
Raffinose is a molecule made from glucose sucrose and galactose. State the number of carbons, hydrogens and oxygen in a molecule of raffinose
C - 18
H - 32
O - 16
This is because two molecules of water will be removed due ti three monomers being joined together in a condensation reaction. 2 bonds formed so 2 water molecules removed
