Cells Exam Qs Flashcards
Give two ways in which pathogens can cause disease. (2 marks)
(Start if cell recognition)
- (Releases) toxins;
- Kills cells / tissues.
- Accept any reference to cell / tissue damage
Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria. (3 marks)
- Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells);
- Water leaves bacteria / cells by osmosis;
- (Loss of water) stops (metabolic) reactions.
A mutation of a tumour suppressor gene can result in the formation of a tumour.
Explain how. (2 marks)
- (Tumour suppressor) gene inactivated / not able to control / slow down
cell division; - Rate of cell division too fast / out of control.
Not all mutations result in a change to the amino acid sequence of the
encoded polypeptide.
Explain why. (1 mark)
- (Genetic) code degenerate;
2. Mutation in intron.
Some cancer cells have a receptor protein in their cell-surface membrane that binds
to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops
the growth of a tumour. (3 marks)
- Antibody has specific tertiary structure / binding site / variable region;
- Complementary (shape / fit) to receptor protein / GF / binds to receptor
protein / to GF; - Prevents GF binding (to receptor)
Herpes simplex virus (HSV) infects nerve cells in the face, including some near the
lips. Like many other viruses, HSV can remain inactive inside the body for years.
When HSV becomes active, it causes cold sores around the mouth.
HSV infects nerve cells in the face (line 1). Explain why it infects only nerve cells. (3 marks)
- Outside of virus has antigens / proteins;
- With complementary shape to receptor / protein in membrane of cells;
- (Receptor / protein) found only on membrane of nerve cells.
HSV can remain inactive inside the body for years. Explain why this
virus can be described as inactive (2 marks)
- No more (nerve) cells infected / no more cold sores form;
2. (Because) virus is not replicating.
Suggest one advantage of programmed cell death (1 mark)
Prevents replication of virus.
What organelle is responsible for protein synthesis?
Ribosomes
What organelle is responsible for modifying protein?
Golgi apparatus
What organelle is responsible for aerobic respiration?
Mitochondria
Describe and explain how centrifuging the culture allowed the scientists to obtain a
cell-free liquid. (3 marks)
- Large / dense / heavy cells;
- Form pellet / move to bottom of tube (when centrifuged);
- Liquid / supernatant can be removed.
Give one function of lysosomes.
Break down cells / cell parts / toxins
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. (3 marks)
- How to break open cells and remove debris;
- Solution is cold / isotonic / buffered;
- Second pellet is chloroplast.
Name two structures in a eukaryotic cell that cannot be identified using an optical
microscope. (2 marks)
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface
membrane.
Explain the difference in the structure of the starch molecule and the cellulose
molecule (2 marks)
- Starch formed from α-glucose but cellulose formed from β-glucose;
- 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. (2 marks)
- Insoluble;
- Don’t affect water potential;
OR - Helical;
- Compact;
OR - Large molecule;
- Cannot leave cell.
Explain how cellulose molecules are adapted for their function in plant cells. (2 marks)
- Long and straight chains;
- Become linked together by many hydrogen bonds to form fibrils;
- Provide strength (to cell wall).
What is the purpose of a nucleus?
To store genetic material/dna
What is the purpose of a chloroplast?
Photosynthesis
Describe how phospholipids are arranged in a plasma membrane. (2 marks)
- Bilayer;
Accept double layer - Hydrophobic / fatty acid / lipid (tails) to inside;
- Polar / phosphate group / hydrophilic (head) to outside;
Cells that secrete enzymes contain a lot of rough endoplasmic reticulum (RER) and
a large Golgi apparatus.
(i) Describe how the RER is involved in the production of enzymes. (2 marks)
- (Rough endoplasmic reticulum has) ribosomes;
accept “contains / stores” - To make protein (which an enzyme is);
Describe how the Golgi apparatus is involved in the secretion of enzymes. (1 mark)
(Golgi apparatus) modifies (protein) OR packages / put into (Golgi) vesicles OR transport to cell surface / vacuole
Describe and explain how cell fractionation and ultracentrifugation can be used to
isolate mitochondria from a suspension of animal cells (5 marks)
- Cell homogenisation to break open cells;
- Filter to remove (large) debris / whole cells;
- Use isotonic solution to prevent damage to mitochondria / organelles;
- Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
- Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments /
heavy organelles; - Re-spin (supernatant / after nuclei / pellet removed) at higher speed to
get mitochondria in pellet / at bottom.
Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure. (5 marks)
Principles:
- Electrons pass through / enter (thin) specimen;
- Denser parts absorb more electrons;
- (So) denser parts appear darker;
- Electrons have short wavelength so give high resolution;
Limitations:
- Cannot look at living material / Must be in a vacuum;
- Specimen must be (very) thin;
- Artefacts present;
- Complex staining method / complex / long preparation time;
- Image not in 3D / only 2D images produced.
The events that take place during interphase and mitosis lead to the production of two
genetically identical cells. Explain how. (4 marks)
- DNA replicated;
- (Involving) specific / accurate / complementary base-pairing;
- (Ref to) two identical / sister chromatids;
- Each chromatid / moves / is separated to (opposite) poles / ends of cell.
A student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin. (2 marks)
- To allow (more) light through;
Accept: transparent - A single / few layer(s) of cells to be viewed.
Accept: (thin) for better / easier stain penetration
Describe and explain how centrifuging the culture allowed the scientists to obtain a
cell-free liquid. (3 marks)
- Large / dense / heavy cells;
- Form pellet / move to bottom of tube (when centrifuged);
- Liquid / supernatant can be removed.
Give one function of lysosomes.
Break down cells / cell parts / toxins.
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. (3 marks)
- How to break open cells and remove debris;
- Solution is cold / isotonic / buffered;
- Second pellet is chloroplast.
Name two structures in a eukaryotic cell that cannot be identified using an optical
microscope.
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface
membrane.
The student prepared a temporary mount of the onion tissue on a glass slide. She
covered the tissue with a cover slip. She was then given the following instruction.
“Push down hard on the cover slip, but do not push the cover slip sideways.”
Explain why she was given this instruction. (2 marks)
- Push hard – spread / squash tissue;
- Not push sideways – avoid rolling cells together / breaking chromosomes.
Neutral – to see cells clearly
List the stages of mitosis?
Prophase - Prometaphase - metaphase - anaphase telophase
While looking at an onion root tip you must firmly squash the root tip. Explain why
To allow light
through
Why are the root tips examined while observing the cell cycle in a onion?
Region where mitosis / cell division occurs;
Give two ways in which pathogens can cause disease. (2 marks)
- (Releases) toxins;
2. Kills cells / tissues.
Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria. (3 marks)
- Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells);
- Water leaves bacteria / cells by osmosis;
- (Loss of water) stops (metabolic) reactions.
Explain how tissue fluid is formed. (2 marks)
- High outward pressure
2. Forces small molecules out of capillary.
The hydrostatic pressure falls from the arteriole end of the capillary to the venule
end of the capillary. Explain why (1 marks)
Loss of water / loss of fluid / friction (against capillary lining).
High blood pressure leads to an accumulation of tissue fluid. Explain how (3 marks)
- High blood pressure = high hydrostatic pressure;
- Increases outward pressure from (arterial) end of capillary / reduces
inward pressure at (venule) end of capillary; - (So) more tissue fluid formed / less tissue fluid is reabsorbed
The water potential of the blood plasma is more negative at the venule end of the
capillary than at the arteriole end of the capillary. Explain why. (3 marks)
- Water has left the capillary;
- Proteins (in blood) too large to leave capillary;
- Increasing / giving higher concentration of blood proteins (and thus wp).
Describe how you would test a piece of food for the presence of lipid. (1 mark)
- Dissolve in alcohol, then add water;
2. White emulsion shows presence of lipid.
E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why. (2 marks)
- Cell unable to change shape;
- (Because) cell has a cell wall;
- (Wall is) rigid / made of peptidoglycan / murein.
