Topic 2 - cells EXAM QUESTIONS Flashcards
Suggest one explanation for the faster rate of plasmid replication in cells
growing in a culture with a high amino acid concentration. (2)
- (Amino acids used in) protein synthesis;
Accept for ‘protein synthesis’, translation - (So) more enzymes (for DNA/plasmid replication)
Describe how a sample of chloroplasts could be isolated from leaves. (4)
- Break open cells/tissue and filter
Accept homogenise and filter - In cold, same water potential/concentration, pH controlled solution;
Accept for ‘same water potential/ concentration’,
isotonic
Accept for ‘pH controlled’, buffered - Centrifuge/spin and remove nuclei/cell debris;
- (Centrifuge/spin) at high(er) speed, chloroplasts settle out;
Give one feature of the chloroplast that allows protein to be synthesised
inside the chloroplast and describe one difference between this feature in
the chloroplast and similar features in the rest of the cell. (2)
Ribosomes;
4. Are smaller than cytoplasmic ribosomes;
) Eukaryotic cells produce and release proteins.
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.
(4)
DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
Accept rER for ‘rough endoplasmic reticulum’
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus;
Accept body for ‘apparatus’
5. Vesicles transport
(Vesicles) fuse with cell(-surface) membrane;
) A biologist separated cell components to investigate organelle activity. She
prepared a suspension of the organelles in a solution that prevented
damage to the organelles.
Describe three properties of this solution and explain how each property
prevented damage to the organelles. (3)
- (Ice) cold to prevent/reduce enzyme activity;
For 1, 2 and 3 reject context of cell - Buffered to prevent denaturing of enzyme/protein;
Accept description of buffer.
Accept: prevent change of tertiary structure. - Same water potential/ Ψ to prevent lysis/bursting (of organelle);
Accept: isotonic for same water potential.
Contrast how an optical microscope and a transmission electron
microscope work and contrast the limitations of their use when studying
cells. (6)
TEM use electrons and optical use light;
2. TEM allows a greater resolution;
3. (So with TEM) smaller organelles / named cell structure can be
observed
OR
greater detail in organelles / named cell structure can be
observed;
4. TEM view only dead / dehydrated specimens and optical (can)
view live specimens;
5. TEM does not show colour and optical (can);
6. TEM requires thinner specimens;
7. TEM requires a more complex/time consuming preparation;
8. TEM focuses using magnets and optical uses (glass) lenses;
Explain why the solution the biologist used was ice-cold, buffered and the
same water potential as the liver tissue (3)
- Ice-cold – Slows / stops enzyme activity to prevent digestion of
organelles / mitochondria; - Buffered – Maintains pH so that enzymes / proteins are not
denatured;
Reject reference to cells - Same water potential – Prevents osmosis so no lysis / shrinkage of
organelles / mitochondria / C;
No organelles are visible in the cytoplasm of this red blood cell.
Suggest why (1)
Cytoplasm of red blood cell filled with haemoglobin.
Before the cell was examined using the electron microscope, it was
stained. This stain caused parts of the structure of the cell-surface
membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane
as two dark lines. (3)
- Membrane has phospholipid bilayer;
- Stain binds to phosphate / glycerol;
- On inside and outside of membrane.
Describe how you could make a temporary mount of a piece of plant tissue
to observe the position of starch grains in the cells when using an optical
(light) microscope. (4)
- Add drop of water to (glass) slide;
- Obtain thin section (of plant tissue) and place on slide / float on
drop of water; - Stain with / add iodine in potassium iodide
- Lower cover slip using mounted needle
Describe binary fission in bacteria (3)
- Replication of (circular) DNA;
Accept nucleoid
Reject chromosome
Reject mitosis - Replication of plasmids;
- Division of cytoplasm (to produce daughter cells);
Name the fixed position occupied by a gene on a DNA molecule. (1)
Locus
Explain why the student:
1. used only the first 5 mm from the tip of an onion root.
2. pressed down firmly on the cover slip.
- Where dividing cells are found / mitosis occurs;
- Single / thin layer of cells / spread out cells so light passes through
(making cells / nuclei visible);
Accept thin layer of tissue
A scientist treated growing tips of onion roots with a chemical that stops
roots growing. After 24 hours, he prepared a stained squash of these root
tips.
Figure 2 is a drawing showing the chromosomes in a single cell observed
in the squash of one of these root tips in anaphase. This cell was typical of
other cells in anaphase in these root tips.
Use all of this information to suggest how the chemical stops the growth of
roots. (3)
- Stops anaphase / cell division / mitosis;
Accept prevents telophase / cytokinesis - (By) stopping / disrupting / spindle fibres forming / attaching / pulling;
Ignore affects anaphase - Preventing separation of (sister) chromatids;
Ignore chromosomes separate / split
Accept chromatids split - (So) no new cells added (to root tip);
The dark stain used on the chromosomes binds more to some areas of the
chromosomes than others, giving the chromosomes a striped appearance.
Suggest one way the structure of the chromosome could differ along its
length to result in the stain binding more in some areas. (1)
Differences in base sequences
OR
Differences in histones/interaction with histones
OR
Differences in condensation/(super)coiling;
Describe two aseptic techniques she would have used when transferring a
sample of broth culture on to an agar plate.
Explain why each was important. (4)
- Keep lid on Petri dish
OR
Open lid of Petri dish as little as possible. - To prevent unwanted bacteria contaminating the dish.
OR
L. monocytogenes may be dangerous / may get out. - Wear gloves
OR
Wear mask
OR
Wash hands; - To prevent contamination from bacteria on hands / mouth
OR
Prevent spread of bacteria outside the lab;
OR - Use sterile pipette
OR
Flame the loop
OR
Flame the neck of the container of the culture; - To maintain a pure culture of bacteria
Describe the appearance and behaviour of chromosomes during mitosis. (5)
(During prophase)
1. Chromosomes
coil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the
centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles /
ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes
uncoil / unwind / become longer / thinner.
Name and describe five ways substances can move across the
cell-surface membrane into a cell. (5)
- (Simple) diffusion of small/non-polar molecules down a
concentration gradient; - Facilitated diffusion down a concentration gradient via
protein carrier/channel; - Osmosis of water down a water potential gradient;
- Active transport against a concentration gradient via
protein carrier using ATP; - Co-transport of 2 different substances using a carrier protein;
Describe and explain two features you would expect to find in a cell
specialised for absorption.
(2)
- Folded membrane/microvilli so large surface area (for absorption);
- Large number of co-transport/carrier/channel proteins so
fast rate (of absorption)
OR
Large number of co-transport/carrier proteins for active transport
OR
Large number of co-transport/carrier/channel proteins for facilitated
diffusion; - Large number of mitochondria so make (more) ATP (by respiration)
OR
Large number of mitochondria for aerobic respiration
OR
Large number of mitochondria to release energy for active transport; - Membrane-bound (digestive) enzymes so maintains
concentration gradient (for fast absorption);
The movement of substances across cell membranes is affected by
membrane structure. Describe how (4)
- Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
- Phospholipid (bilayer) prevents movement/diffusion of polar/
charged/lipid-insoluble substances - Carrier proteins allow active transport;
- Channel/carrier proteins allow facilitated diffusion/co-transport;
- Shape/charge of channel / carrier determines which
substances move; - Number of channels/carriers determines how much movement;
- Membrane surface area determines how much
diffusion/movement; - Cholesterol affects fluidity/rigidity/permeability;
Give two similarities in the movement of substances by diffusion and by
osmosis. (2)
- (Movement) down a gradient / from high concentration to low
concentration;
Ignore along / across gradient
Reject movement from gradient to gradient - Passive / not active processes;
OR
Do not use energy from respiration / from ATP / from metabolism;
Sodium ions from salt (sodium chloride) are absorbed by cells lining the
gut. Some of these cells have membranes with a carrier protein called
NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one
proton (hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how
NHE3 does this.
(3)
- Co-transport;
- Uses (hydrolysis of) ATP;
- Sodium ion and proton bind to the protein;
- Protein changes shape (to move sodium ion and / or proton
across the membrane);
High absorption of salt from the diet can result in a higher than normal
concentration of salt in the blood plasma entering capillaries. This can lead
to a build-up of tissue fluid.
Explain how. (2)
- (Higher salt) results in lower water potential of tissue fluid;
- (So) less water returns to capillary by osmosis (at venule end);
OR - (Higher salt) results in higher blood pressure / volume;
- (So) more fluid pushed / forced out (at arteriole end) of
capillary;/ forced out (at arteriole end) of
capillary;
Compare and contrast the processes by which water and inorganic ions
enter cells. (3)
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
Accept aquaporins (for water) and ion channels - Contrast: ions can move against a concentration gradient by active
transport
Contrast the processes of facilitated diffusion and active transport. (3)
- Facilitated diffusion involves channel or carrier proteins whereas
active transport only involves carrier proteins; - Facilitated diffusion does not use ATP / is passive whereas
active transport uses ATP; - Facilitated diffusion takes place down a concentration gradient
whereas active transport can occur against a concentration
gradient.
