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AQA A Level Biology > Cells exam qs > Flashcards

Cells exam qs Flashcards

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1
Q

Name the type of bond between adjacent nucleotides in a DNA strand

A

Phosphodiester bond

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1
Q

Give one advantage of a TEM over an SEM

A

Higher resolution OR view internal structures

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2
Q

The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe the function of each of these enzymes.

A
  1. DNA helicase - (unwinding DNA and) breaking/hydrolysing hydrogen bonds / bonds between chains / bases / strands
  2. DNA polymerase - joins (adjacent) nucleotides OR forms phosphodiester bond / sugar phosphate backbone
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3
Q

Adenosine triphosphate (ATP) is a nucleotide derivative.
Contrast the structures of ATP and a nucleotide found in DNA to give two differences.

A
  1. ATP has ribose whereas DNA nucleotide has deoxyribose
  2. ATP has 3 phosphate (groups) whereas DNA nucleotide has 1 phosphate (group)
  3. In ATP, base always adenine whereas in DNA nucleotide base can be different / varies
    (Reject Uracil)
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4
Q

In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules.

A
  1. mRNA fewer nucleotides OR Pre-mRNA more nucleotides OR mRNA has no introns/has (only) exons OR Pre-mRNA has (exons and) introns; 2. (Because of) splicing;
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5
Q

The length of a gene is described as the number of nucleotide base pairs it contains.
Use information in Figure 1 to calculate the length of a gene containing 4.38 ×10^3
base pairs.
(5 base pairs = 1.7nm)

A

Correct answer = 1489 OR 1489.2 (2 marks)
If incorrect:
1 mark for: 876
1 mark for: 1861-1862

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6
Q

Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule.

A
  1. mRNA does not have hydrogen bonds / base pairing, tRNA does;
    OR
    mRNA is linear / straight chain, tRNA is cloverleaf;
  2. mRNA does not have an amino acid binding site, tRNA does;
  3. mRNA has more nucleotides;
  4. (Different) mRNAs have different lengths, all tRNAs are similar / same length;
  5. mRNA has codons, tRNA has an anticodon;
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7
Q

Explain how the structure of xylem vessel cells are adapted to their function

A

Function: transport tissue for water and dissolved ions

Adaptations:
-no top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
-cells are dead, without organelles or cytoplasm, to allow free movement of water
-outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant

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8
Q

Name two structures in a eukaryotic cell that cannot be identified using an optical microscope

A

Two of the following for one mark:
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

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9
Q

Describe viral replication (3 marks)

A
  1. attachment proteins bind/attach to receptors
    (gp41/gp120/glycoprotein can be accepted in place of attachment protein)
    (Ignore receptor protein (on virus)
  2. (viral) nucleic acid enters cell
    (References to engulfment OR injection can be accepted for enters)
    (Ignore references to virus DNA/RNA incorporated into cell genome/nucleus/
    chromosomes)
  3. nucleic acid replicated in cell OR reverse transcriptase makes DNA from RNA
  4. cell produces (viral) protein / capsid / enzymes
    (Accept capsomeres OR reverse transcriptase for protein)
  5. virus is assembled and released (from cell)
    (Accept lysis OR burst OR bud off OR emerge for released)
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10
Q

Give five structure differences between a DNA molecule and an mRNA molecule

A
  1. DNA has deoxyribose whereas mRNA has ribose
  2. DNA has thymine, whereas mRNA has uracil
  3. DNA is long, whereas mRNA is short
  4. DNA is double stranded, whereas mRNA is single stranded
    (Accept double helix / single helix)
  5. DNA has hydrogen bonds, whereas mRNA has no hydrogen bonds
    OR
    DNA has (complementary) base pairing, whereas mRNA does not
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11
Q

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA

A
  1. Weak / easily broken hydrogen bonds between bases allow two strands to separate unzip
  2. Two strands, so both can act as templates
  3. Complementary base pairing allows accurate replication
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12
Q

Name the type of bond between complementary base pairs

A

Hydrogen bonds

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13
Q

Explain the arrangement of phospholipids in a cell-surface membrane (2 marks)

A
  1. Bilayer
    OR
    Water is present inside and outside a cell
  2. Hydrophobic (fatty acid) tails point away / are repelled from water
    OR
    Hydrophilic (phosphate) heads point to / are attracted to water
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14
Q

Describe how a phagocyte destroys a pathogen present in the blood (3 marks)

A
  1. Engulfs
  2. Forming vesicle / phagosome and fuses with lysosome
  3. Enzymes digest/hydrolyse

1. Accept endocytosis or description
3. Accept lysozymes for enzymes

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15
Q

Give TWO types of cell, other than pathogens, that can stimulate an immune response (2 marks)

A
  1. (Cells from) other organisms/transplants
  2. Abnormal/cancer/tumour cells
  3. (Cells) infected by virus
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16
Q

What is the role of the disulfide bridge in forming the quaternary structure of an antibody? (1 mark)

A

Joins two (different) polypeptides

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17
Q

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 marks)

A
  1. DNA in nucleus is code (for protein);
  2. Ribosomes / rough endoplasmic reticulum produce (protein)
  3. Mitochondria produce ATP (for protein synthesis)
  4. Golgi apparatus package/modify
    OR
    Carbohydrate added/glycoprotein produced by Golgi apparatus
  5. Vesicles transport
    OR
    Rough endoplasmic reticulum transports
  6. (Vesicles) fuse with cell surface membrane

2. and 5. Accept rER for ‘rough
endoplasmic reticulum’
4. Accept body for ‘apparatus’
6. Accept exocytosis at cell membrane

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18
Q

Describe binary fission in bacteria (3 marks)

A
  1. Replication of (circular) DNA
  2. Replication of plasmids
  3. Division of cytoplasm (to produce daughter cells)
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19
Q

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue (3 marks)

A
  1. How to break open cells and remove debris;
  2. Solution is cold / isotonic / buffered;
  3. Second pellet is chloroplast.
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20
Q

Describe the structure and function of the nucleus (4 marks)

A

Structure
1. Nuclear envelope and pores OR
Double membrane and pores;
2. Chromosomes/chromatin
OR
DNA with histones;
3. Nucleolus/nucleoli;

Function
4. (Holds/stores) genetic information/material for polypeptides (production)
OR
(Is) code for polypeptides;
5. DNA replication (occurs);
6. Production of mRNA/tRNA
OR
Transcription (occurs);
7. Production of rRNA/ribosomes;

Max 2 for structure or function
1. Ignore porous for pores
2 Ignore genetic material/information
2. Accept nucleoplasm
2. Ignore promoter regions OR genes OR alleles
Accept regulation of gene expression
4. Accept protein OR amino acid sequences OR primary structure for polypeptides
6 Ignore mRNA leaves nucleus

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21
Q

Name the main polymer that forms the following cell walls.
Plant cell wall:
Fungal cell wall:

A

Plant: cellulose
Fungi: chitin

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22
Q

Give two features of all prokaryotic cells that are not features of eukaryotic cells.

A

For 1 mark, accept any two from Prokaryotes have
No membrane-bound organelles/correct example
OR
(Single,) circular/loop DNA (in cytoplasm)
OR
DNA free in cytoplasm
OR
DNA not associated with proteins/histones
OR
Murein/peptidoglycan (in) cell wall;

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23
Q

When HIV infects a human cell, the following events occur.
* A single-stranded length of HIV DNA is made.
* The human cell then makes a complementary strand to the HIV DNA.

The complementary strand is made in the same way as a new complementary strand is made during semi-conservative replication of human DNA.
Describe how the complementary strand of HIV DNA is made. (3 marks)

A
  1. (Complementary) nucleotides/ bases pair
    OR
    A to T and C to G
  2. DNA polymerase
  3. Nucleotides join together (to form new strand)/phosphodiester bonds form
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24
Q

Table 1 shows features of a bacterium and the human immunodeficiency virus (HIV) particle.
Complete Table 1 by putting a tick () where a feature is present (2 marks)
Features: RNA, cell wall, enzyme molecules, capsid

A

RNA: both
Cell wall: bacterium only
Enzyme molecules: both
Capsid: HIV particle only

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25
Q

The letters P, Q, R, S and T represent ways substances can move across membranes.
• P – diffusion through the phospholipid bilayer
• Q – facilitated diffusion
• R – active transport
• S – co-transport
• T – osmosis
For each of the following examples of transport across membranes, select the letter that represents the way in which the substance moves across the membrane.
Write the appropriate letter in each box provided.

Transport through a channel protein?
Transport of small, non-polar molecules?
Transport of glucose with sodium ions?

A

Q
P
S

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26
Q

In the cell wall, bonds hold the cellulose molecules together side by side. Tick one box that describes the type of bond that holds the cellulose molecules together side by side.

A

Hydrogen

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27
Q

The letters A, B, C, D and E represent stages in mitosis.
• A – anaphase
• B – interphase
• C – metaphase
• D – prophase
• E – telophase
Write one of the letters, A to E, in the box to complete the following statement.

Chromosomes line up on the equator of the mitotic spindle in
(1 mark)

A

C

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28
Q

Human papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV.
Describe how giving this vaccine leads to production of antibody against HPV.
[4 marks]

A
  1. Vaccine contains antigen (from HPV)
  2. Displayed on antigen-presenting cells
  3. Specific helper T cell (detects antigen and) stimulates specific B cell
  4. B cell divides / goes through mitosis/ forms clone to give plasma cells
  5. B cell/ plasma cell produces antibody
29
Q

The nucleus and a chloroplast of a plant cell both contain DNA. Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus (3 marks)

A

In chloroplasts
1. DNA shorter;
2. Fewer genes;
3. DNA circular not linear;
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;

Must be comparative statements.
Accept alternatives in context of nuclear DNA
1. Accept smaller
3. Accept DNA in a loop not linear
3. Accept no chromosomes (in chloroplast) unlike nucleus
Ignore references to double and single stranded DNA

30
Q

What is a monoclonal antibody (1 mark)

A

(Antibodies with the) same tertiary structure
OR
(Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes

31
Q

After a disease is diagnosed, monoclonal antibodies are used in some medical treatments. Give one example of using monoclonal antibodies in a medical treatment

A

Accept any one suitable use, eg Targets/binds/carries drug/medicine to specific cells/antigens/receptors
OR
Block antigens/receptors on cells;

32
Q

Name an organelle found in both a chloroplast and a prokaryotic cell

A

(70S) ribosome

33
Q

A scientist determined the volume of a plant cell and the volume of organelles it contained. They found:
-the volume of a plant cell is 17500 µm3
-the volume of all the mitochondria in a plant cell is 262.5 µm3
-the volume of all the mitochondria and all the chloroplasts in a plant cell is 44.1% of the volume of a plant cell.
Use this information to calculate the volume of all the chloroplasts in a plant cell. (2 marks)

A

Correct answer of 7455 = 2 marks;; Accept for 1 mark answers in range: 7717.5 to 7718 (44.1% of 17500)
If incorrect answer, accept for 1 mark working shows an attempt to subtract 262.5

34
Q

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 marks)

A
  1. (Ice) cold to prevent/reduce enzyme activity;
  2. Buffered to prevent denaturing of enzyme/protein;
  3. Same water potential/Ψ to prevent lysis/bursting (of organelle)
  • For 1, 2 and 3 reject context of cell
    2. Accept description of buffer.
    2. Accept: prevent change of tertiary structure.
    3. Accept: isotonic for same water potential.
    3. Reject: references to turgor or plasmolysis or crenation*
35
Q

Following digestion and absorption of food, the undigested remains are processed to form faeces in the parts of the intestine below the ileum.

The faeces of people with constipation are dry and hard. Constipation can be treated by drinking lactulose. Lactulose is soluble, but is not digested or absorbed in the human intestine.

Use your knowledge of water potential to suggest why lactulose can be used to help people suffering from constipation. (2 marks)

A
  1. (Lactulose) lowers the water potential of faeces / intestine / contents of the intestine;
  2. Water retained / enters (due to osmosis) and softens the faeces;
36
Q

Structures A to E are parts of a plant cell.
A Cell wall
B chloroplast
C nucleus
D mitochondrion
E golgi apparatus

Complete Table 1 by putting the correct letter, A,B,C,D,E next to each statement

Has stacked membranes arranged in parallel and contains DNA
is made of polysaccharide
Is an organelle and is not surrounded by two membranes

(3 marks)

A

B
A
E

37
Q

Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein.
Explain the role of these cell adaptations in the production and secretion of breast milk. (2 marks)

A
  1. (Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport;
  2. (Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;

Must include function of organelle and use in context of milk production.
Ignore reference to lipid / triglyceride
1. Reject reference to mitochondria
undergoing anaerobic respiration
1. Reject “produce energy”.
1. Reject “energy for respiration”
2. Accept exocytosis as transport and release
2. Ignore references to protein
synthesis

38
Q

Name two features of HIV particles that are not found in bacteria. Do not include attachment protein in your answer (2 marks)

A

Capsid
Reverse transcriptase
RNA genome
Envelope

39
Q

Name two structures found in all bacteria that are not found in plant cells (2 marks)

A
  1. Circular DNA (molecule in cytoplasm)
  2. Murein/peptidoglycan/glycoprotein cell wall
  3. Smaller/70S ribosomes (in cytoplasm
40
Q

Table 1 shows some parts of cells and two different types of cell (white blood cell and bacterial cell)
Complete Table 1 by putting a tick in a box if the structure is present in the type of cell.

Cell wall
Cell surface membrane
Nucleus

(2 marks)

A

White blood cell has:
-cell surface membrane
-nucleus

Bacterial cell has:
-cell wall
-cell surface membrane

41
Q

Some scientists support the theory that mitochondria are organelles that evolved from prokaryotic cells.

Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells. (1 mark)

A

Circular DNA / smaller/70S ribosomes / no introns / no histones/proteins associated with DNA;

ignore references to plasmids

42
Q

What is the advantage to cells of having mitochondria? (2 marks)

A
  1. Able to respire aerobically;
  2. So make (more) ATP/ release (more) energy;
43
Q

Describe how HIV is replicated (4 marks)

A
  1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
  2. Nucleic acid/RNA enters cell;
  3. Reverse transcriptase converts RNA to DNA;
  4. Viral protein/capsid/enzymes produced;
  5. Virus (particles) assembled and released (from cell);
44
Q

Explain how the doctor could have recognised which cells were in interphase when looking at the tissue samples.

A

No visible chromosomes

45
Q

Cell C is in interphase. Give two processes which occur during interphase that enable cell division to occur. (2 marks)

A

Increased in volume of cell / amount of cytoplasm / increase in mass / cell bigger;
Increase in number of organelles;
Protein synthesis / specific example;
DNA replication / chromosomes become chromatids / chromosomes copy; I references to G1, G2 and S phases)

46
Q

A sample of epithelial tissue from the small intestine of an animal was analysed.
Some of the cells had 8.4 units of DNA, others had only 4.2 units.
Use your knowledge of the cell cycle to explain why some cells had 8.4 units of DNA and others had only 4.2 units. (2 marks)

A
  1. 8.4/cells with twice DNA content = replicated DNA / late interphase / prophase / metaphase / anaphase;
  2. 4.2 = DNA not replicated / (early) interphase / telophase / cell just divided / finished mitosis;
47
Q

Homologous chromosomes carry the same genes but they are not genetically identical.
Explain why. (1 mark)

A

Homologous chromosomes carry different alleles

48
Q

Explain why the biologist chose to examine 200 cells. (1 mark)

A

(Ensures) representative (sample);

49
Q

Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time. (1 mark)

A

Form/replace cells quickly/rapidly / divide/multiply/replicate rapidly

50
Q

The time required for a cell to complete the cell cycle was 4 hours 18 minutes.
Calculate the time required in minutes for this cell to multiply to produce eight cells.
Show your working. (2 marks)

A

Correct answer = 774 minutes/12 hours 54 minutes = 2 marks
Incorrect answer but indicates 3 cell cycles involved = one mark

51
Q

Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer. (2 marks)

A

prevents/slows dna replication/doubling;
prevents/slows mitosis;
new strand not formed/nucleotides (of new strand) not joined together/ sugar-phosphate bonds not formed

52
Q

Mitosis is important in the life of an organism. Give two reasons why. (2 marks)

A

Growth - increase in cell number
Replace cells - repairing tissue/organs
Asexual reproduction

53
Q

The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how. (4 marks)

A

DNA replication takes place during interphase
Involves specific/accurate complementary base pairing OR semi-conservative replication
Sister chromatids move to opposite poles

54
Q

The student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin. (2 marks)

A

To allow (more) light through OR transparent
Single/few layer(s) of cells to be viewed OR thin for better/easier stain penetration

55
Q

In prophase of mitosis, the chromosomes become visible. Describe what happens in
i) metaphase (2 marks)
ii) anaphase (2 marks)

A

i) Spindle formed / chromosome/centromere/chrom atids attaches to spindle;
Chromosomes/chromatids line up/move to middle/equator (of cell);

ii) Chromosome/centromere splits / chromatids/ ‘chromosomes’ separate/pulled apart;
To (opposite) sides/poles/centrioles (of cell);

56
Q

The pieces of leaf tissue examined were very thin. Explain why this was important

A
  1. Single/ few layer(s) of cell
  2. So light can pass through
57
Q

Some cells lining the bronchi of the lungs secrete large amounts of mucus. Mucus
contains protein.
Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus. (2 marks)

A

Organelle named; Function in protein production/secretion;
eg
1. Golgi (apparatus);
2. Package/process proteins;
OR
3. Rough endoplasmic reticulum/ribosomes;
4. Make polypeptide/protein/forming peptide bonds;
OR
5. Mitochondria;
6. Release of energy/make ATP;
OR
7. Vesicles;
8. Secretion/transport of protein;

Function must be for organelle named
Incorrect organelle = 0
1. Accept smooth endoplasmic reticulum
3. Accept alternative correct functions of rough endoplasmic reticulum. ER/RER is insufficient
3. Accept folding polypeptide/protein
6. Reject produce/make energy
6. Accept produce energy in the form of ATP

58
Q

C is a protein with a carbohydrate attached to it. This carbohydrate is formed by joining
monosaccharides together.
Name the type of reaction that joins monosaccharides together. (1 mark)

A

condensation reaction

59
Q

Oxygen and chloride ions can diffuse across cell-surface membranes. The diffusion of chloride ions involves a membrane protein. The diffusion of oxygen does not involve a membrane protein.
Explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not. (5 marks)

A

Chloride ions water soluble/charged/polar;
2. Cannot cross (lipid) bilayer (of membrane);
3. Chloride ions transported by facilitated diffusion OR diffusion involving channel/carrier protein;
4. Oxygen not charged/non-polar;
5. (Oxygen) soluble in/can diffuse across (lipid) bilayer;

60
Q

In the cell wall. bonds hold the cellulose molecules together side by side.
Tick ( one box that describes the type of bond that holds the cellulose molecules together side by side. (1 mark)

A

Hydrogen

61
Q

Oxygen and water move through plasma membranes into cells. Describe two ways in which these movements are similar. (2 marks)

A

Passive OR Do not require energy
Movement down a concentration gradient

62
Q

The letters P, Q, R, S and T represent ways substances can move across membranes.
P- diffusion through the phospholipid bilayer
Q - facilitated diffusion
R - active transport
• S- co-transport
• T - osmosis
For each of the following examples of transport across membranes, select the letter that represents the way in which the substance moves across the
membrane
Write the appropriate letter in each box provided:

  1. Transport through a channel protein
  2. Transport of small, non-polar molecules
  3. Transport of glucose with sodium ions

(3 marks]

A

QPS

63
Q

Name the process that results in the concentration of nitrate ions becoming
greater in the cytoplasm than in the nutrient solution. (1 mark)

A

active transport

64
Q

Some ions can enter the cell faster than others. Use your knowledge of membrane structure to suggest an explanation for this.
(2 marks)

A

1.Ref. to carrier/intrinsic/pore/gate/transport/pump proteins

  1. Ref. to different numbers of carrier proteins;
  2. Ref. to specificity / different types of carrier proteins
  3. Ref. to charge / size of ion
65
Q

Explain why it was necessary to bubble air through the nutrient solution during this investigation. (1 mark)

A
  1. For respiration
  2. Energy for active transport
66
Q

The students were advised that they could improve the reliability of their results by taking additional readings at the same concentrations of sodium chloride.
Explain how (2 marks)

A

Anomalies to be identified/effect of anomalies to be reduced/
effect of variation in data to be minimised;
Reject: idea of not recording anomalies/preventing anomalies from occurring
A mean to be calculated;
Neutral: average

67
Q

The students gave their results as a ratio. What is the advantage of giving the results as a ratio? (2 marks)

A

Allows comparison/shows proportional change;
Neutral: sizes/amounts
Idea that discs had different starting masses/weights;
Neutral: different masses

68
Q

Give three properties of water that are important in biology.
[3 marks]

A
69
Q

Glucose is absorbed from the lumen of the small intestine into epithelial cells.
Explain how the transport of sodium ions is involved in the absorption of glucose by epithelial cells. (5)

A
  1. Na+ ions leave epithelial cell and enter blood;
  2. (Transport out is by) active transport / pump / via carrier protein using ATP;
  3. So, Na+ conc. in cell is lower than in lumen (of gut);
  4. Sodium/Na+ ions enter by facilitated diffusion;
  5. Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;

AQA A Level Biology (12 decks)

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