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Past papers - biology > Exampro - ASG 1 > Flashcards

Exampro - ASG 1 Flashcards

1
Q

Give one reason why not all the light energy falling on the producers is used in PHS (1 mark)

A
  • Misses chloroplast
  • Reflected
  • Wrong wavelength
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2
Q

The producers in this ecosystem are seaweeds, which have a large surface area to volume ratio. Give two advantages to seaweeds of having a large surface area to volume ratio. (2 marks)

A
  • Larger area to absorb light
  • Shorter diffusion pathway for gases - O2 and co2
  • Light able to penetrate to all cells
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3
Q

Some species of seaweed are submerged in water for most of the time. Explain how being underwater might affect the rate of PHS. (3 marks)

A
  • Rate of PHS will decrease
  • Light reflected of water’s surface
  • Less light absorbed by the seaweed
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4
Q

Explain what is meant by stabilising selection and describe the circumstances under which it takes place. (5 marks)

A
  1. Occurs in an unchanging environment; 1
  2. (Initial range of values in which) mean is best adapted;
  3. Selection against extremes/selection for the mean;
  4. Mean/median/mode unaltered
  5. Range/S.D is reduced;
  6. Repeated over many generations;
  7. Increasing proportion of populations becomes well adapted to environment;
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5
Q

Explain the proportions of cyanogenic and acyanogenic plants in clover populations growing in the area where the mean minimum winter temperature is below -4 degrees and in the area where it is above 10 degrees. (5 marks)

A
  • All plants are acyanogenic below -4 and most cyanogenic above 10
  • Cyanogenic plant cells freeze below -4
  • Releasing cyanide into their own tissues which killing plants
  • Selective advantage not to produce cyanide at -4
  • Slugs present at higher temperatures
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6
Q

Describe how HIV is replicated after it has entered a human cell. (4 marks)

A
  • Reverse transcriptase
  • Enzyme uses HIV RNA to make DNA copy
  • DNA joined to host cell’s DNA
  • DNA used to make HIV RNA
  • and HIV capsid proteins/ enzymes
  • Made at host ribosomes
  • Assembly of new virus particles
  • Budding off from membrane (of host cell)
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7
Q

The destruction of T-cells by HIV leads to the death of the infected person. Explain how. (2 marks)

A
  • No T-cells to activate B cells which leads to antibody production to activate the immune system
  • Person more prone to infections
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8
Q

Name part F of each nucleotide in DNA ( hexagon shape) - (1 mark)

A
  • Deoxyribose
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9
Q

Scientists determined that a sample of DNA contained 18% adenine. What were the percentages of thymine and guanine in this sample of DNA? (2 marks)

A
  • Thymine = 18%

- Guanine = 32%

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10
Q

Name the enzyme that produces phosphodiester bonds? 1 mark

A
  • DNA polymerase
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11
Q

Use figure 1, figure 2 and your knowledge of enzyme action to explain why the arrows point in opposite directions. (4 marks)

A
  • Figure 1 - DNA has antiparallel strands + shape of the nucleotides is different (flipped) (5-3)
  • Enzymes have active sites with specific shape
  • Only substrates with complementary shape can bind with active site of enzymes/ DNA polymerase
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12
Q

What is the outer layer of a HIV called and the circles in the centre? (2 marks)

A
  • Membrane

- Reverse transcriptase

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13
Q

What is the function of the RNA molecules in this virus? (1 mark)

A
  • Carries genetic information

- To make DNA

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14
Q

Describe how new viruses are produced after HIV has infected a T cell. (3 marks)

A
  • DNA copy made of viral RNA
  • Inserted into host DNA
  • Uses viral DNA to make viral proteins
  • Makes viral RNA
  • Host cell makes new viruses
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15
Q

Eliza test only detects the presence of HIV antibodies. Give two reasons why it cannot be used to find out if a person has AIDS. (2 marks)

A
  • To diagnose AIDS there needs to be AIDS-related symptoms

- Number of helper T cells

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16
Q

The solution will remain yellow if a person is not infected with HIV. Explain why? (2 marks)

A
  • HIV antibody is not present

- SO the enzyme won’t bind to the second antibody as it is not present.

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17
Q

A mother who was infected with HIV gave birth to a baby. The baby tested positive using the test. This does not prove the baby is infected with HIV. Explain why. (2 marks)

A
  • Children receive HIV antibodies from their mothers = maternal antibodies
  • So solution will always turn blue before 18 months
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18
Q

A control well is set up every time this test is used. This is treated in exactly the same way as the test wells, except that blood plasma is replaced by a salt solution.
Use information from the figure above to suggest two purposes of the control well. (2 marks)

A
  • Only the enzyme causes the colour change

- Washing is effective as all unbound antibodies are washed away

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19
Q

What is an antigen? (1 mark)

A
  • Foreign protein

- Stimulates an immune response = production of antibodies

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20
Q

What is an antibody? (1 mark)

A
  • A protein specific to an antigen
  • Produced by B cells
  • Secreted by plasma cells
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21
Q

Calculate the percentage increase in the mean concentration of antibodies in blood between samples 2 and 3. ( 1 mark)

A
  • Work out difference

- New number/ Original number and times by 100

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22
Q

Explain the differences between the mean concentrations of antibodies in blood samples 1,2 and 3. (4 marks)

A
  • Sample 1 - no antibody released because patients not yet encountered vaccine
  • Sample 2 - expansion of B cells into plasma cells
  • Plasma cells release antibodies
  • Sample 3 - memory cells produce more antibodies - quickly
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23
Q

When a person is bitten by a venomous snake, the snake injects a toxin into the person. Antivenom is injected as treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity.
Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity. (2 marks)

A
  • Passive immunity - antibodies bind to the toxin and causes its destruction
  • Active immunity would be too slow
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24
Q

A mixture of venoms from several snakes of the same species is used. Suggest why. (2 marks)

A
  • May be different form of antigen within one species
  • Mutation/allele
  • Different antibodies needed in the antivenom - complementary to several antigens
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25
Q

Horses or rabbits can be used to produce antivenoms. When taking blood to extract antibody, 13cm3 of blood is collected per kg of the animal’s body mass. The mean mass of the horses used is 350 kg and the mean mass of the rabbits used is 2 kg.
Using only this information, suggest which animals would be better for the production of antivenoms.
Use a calculation to support your answer. (2 marks)

A
  • Horses as more antibodies can be taken as more blood is taken
  • 4550 vs 26
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26
Q

During the procedure shown in the chart the animals are under ongoing observation by a vet. Suggest one reason why. (1 mark)

A
  • The animal does not suffer from the venom
  • The animals does not suffer as a result of blood collection
  • The animal does not have a pathogen that could get transferred to humans
27
Q

During vaccination, each animal is initally injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.
Using your knowledge of the humoral immune response to explain this vaccination programme. (3 marks)

A
  • B cells specific to the venom produce by mitosis
  • B cells produce plasma and memory cells
  • Second dose produced antibodies in higher concentration and quickly
28
Q

What is a substitution mutation? (1 mark)

A
  • Replacement of a base by a different base in DNA
29
Q

Suggest how gel electrophoresis separated the proteins obtained from the synapses? (2 marks)

A
  • Depends on the size/ mass of protein

- Depends on charge of protein

30
Q

Each type of labelled antibody binds specifically to one of the proteins. Explain why. (3 marks)

A
  • Each protein has a different tertiary structure
  • Each antibody has a specific antigen
  • Each antibody only binds to complementary proteins and forms different antigen-antibody complex
31
Q

What do these data show about the effects of the mutation of the proteins? (2 marks)

A
  • Less NL3

- More NR2A and NR2B

32
Q

These proteins are part of a receptor found in synapses in the part of the brain called the hippocampus. A high ratio of NR2B to NR2A protein in this receptor has been associated with good memory.
Using all the information, suggest how the mutation affecting the NL3 protein may affect a mouse. (2 marks)

A
  • Higher ratio NR2B to NR2A with mutation

- Perhaps better memory in mice with mutation

33
Q

Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria Meningitidis (Nm) is a leading cause of bacterial meningitis.
In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis.
(6 marks)

A
  • Antigen on the surface of Nm binds to surface receptor on a specific B cell
  • Activated B cell divides by mitosis = clone
  • Division stimulated by T cells
  • B cells/ plasma cells release antibodies
  • Some B cells become memory cells
  • Memory cells produce antibodies faster
34
Q

Penicillin has been the antibiotic of choice for the treatment of bacterial meningitis. Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin, sulfonamides and rifampin have been discovered in the UK.
Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics. (4 marks)

A
  • Mutation
  • Results in Nm cells with allele for resistance to one antibiotic
  • This cell survives and passes the allele for resistance to offspring
  • Process repeated with different genes conferring resistance to each of the other antibiotics
35
Q

Contrast the structure of a bacterial cell and the structure of a human cell. (5 marks)

A
  • Bacterial is much smaller than human
  • Bacterial has a cell wall human doesn’t
  • Bacterial lack a nucleus but humans have a nucleus
  • Bactieral ribosomes are smaller than humans
  • Bacterial DNA is circular but human is linear
36
Q

Describe how phagocytosis of a virus leads to presentation of its antigens. (3 marks)

A
  • Phagosome fuses with lysosome
  • Virus destroyed by lysozymes
  • Antigen from virus are displayed on the cell membrane
37
Q

Describe how presentation of a virus antigen leads to the secretion of an antibody against the virus antigen (3 maks)

A
  • Helper T cells binds to the antigen
  • Stimulates specific B cells
  • B cell clones - divides by mitosis
  • Forms plasma cells that release antibodies
38
Q

Collagen is a protein produced by cells in joints, such as the knee.
Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints.
Scientists have found a virus that produces a protein very similar to human collagen
Suggest how the immune response to this viral protein can result in the development of RA. (2 marks)

A
  • The antibody against virus (antigen) will bind to collagen

- This results in the destruction of collagen

39
Q

DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2 marks)

A
  • Hydrogen bonds between the base pairs holds two strands together
  • Many hydrogen bonds provide strength
40
Q

Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA. (1 mark)

A
  • Ribosomes assemble polypeptides using mRNA code

- DNA has 2 strands each with a different complementary base sequence

41
Q

What name is given to a group of three bases on mRNA that codes for an amino acid? (1 mark)

A
  • Codon
42
Q

Use information from Table 1 to explain why the genetic code is described as degenerate. 2 marks

A
  • Some amino acids have more than one codon

- GAG and GAC both mean ASP

43
Q

Suggest the role of the mRNA base triplets UGA, UAG and UAA. (2 marks)

A
  • Stop translation

- Result in detachment of polypeptide chain from ribosome

44
Q

Why was it necessary to take cells from the root tip? (1 mark)

A
  • Region where mitosis occurs
45
Q

Why was it necessary to firmly squash the root tip? (1 mark)

A
  • Thin - allow light through
46
Q

Explain how the behaviour of chromosomes causes these changes in the amount of DNA per cell between F and G. (3 marks)

A
  • Increase - DNA replication
  • First decrease - Homologous chromosomes separate
  • Second decrease - Sister chromatids separate
47
Q

What would happen to the amount of DNA per cell at fertilisation of cell G. (1 mark)

A
  • DNA would double
48
Q

Give the two types of molecule from which a ribosome is made. (1 mark)

A
  • one Proteins

- one RNA

49
Q

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer. (3 marks)

A
  • mRNA binds to ribosome
  • Idea of two codons/ binding sites
  • Allows tRNA with anticodons to bind
  • Catalyse formation of peptide bond between amino acids held by tRNA molecules
  • Moves along mRNA to the next codon
50
Q

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.
Explain why. (2 marks)

A
  • Introns in the pre-mRNA

- Removal of sections of pre-mRNA/ splicing

51
Q

Name the process by which bacterial cells divide. (1 mark)

A
  • Binary fission
52
Q

A microbiologist investigated the ability of different plant oils to kill the bacterium Listeria monocytogenes. She cultured the bacteria on agar plates. She obtained the bacteria from a broth culture.
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 marks)

A
  • Keep lid on Petri dish
  • Prevent unwanted bacteria contaminating the dish
  • Use sterile pipette
  • Maintain a pure culture of bacteria
53
Q

Plant oils are hydrophobic and can cross the cell-surface membrane of the bacterium. The low temperature of 4 degrees can slow the rate of entry of plant oils into the cells.
Suggest how the low temperature slows the rate of entry (1 mark)

A
  • Less kinetic energy
54
Q

Describe the role of two named enzymes in the process of semi-conservative replication of DNA. (3 marks)

A
  • DNA helicase causes breaking of hydrogen
  • DNA polymerase joins the DNA nucelotides
  • Forming phosphodiester bonds
55
Q

Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis. Explain your answers. (2 marks)

A
  • Individual chromosomes are visible because they have condensed
  • Each chromosome is made up of 2 chromatids because DNA has replicated
  • The chromosomes are not arranged in homologous pairs, which they would e if it was meiosis
56
Q

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher water potential than the cytoplasm. This did not cause the cell to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart. (2 marks)

A
  • Water moves into the cells/cytoplasm by osmosis

- Cell get bigger

57
Q

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped apperance.
Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas. (1 mark)

A
  • Differences in condensation
58
Q

In figure 2 the chromosomes are arranged in homologous pairs. What is a homologous pair of chromosomes?

A
  • 2 chromosomes that carry the same genes
59
Q

Give two ways in which the arrangement of prokaryotic DNA is different from the arrangement of the human DNA in figure 1. (2 marks)

A
  • Pro = circular
  • Not associated with proteins
  • Present as plasmids
60
Q

Meiosis results in cells that have been haploid number of chromosomes and show genetic variatio. Explain how. (6 marks)

A
  • Homologous chromosomes pair up/ bivalents form
  • Crossing over/ chiasmata form
  • = new combination of alleles
  • Chromosome separates
  • At random
  • Produces varying combinations of chromosomes
  • Chromatids separated later
61
Q

Explain how the chromosome number is halved during meiosis. (2 marks)

A
  • Homologous chromosomes pair

- One of each pair goes to each daughter cell

62
Q

Crossing over greatly increases genetic diversity in this species of moss.
Describe the process of crossing over and explain how it increases genetic diversity. (4 marks)

A
  • Homologous pairs of chromosomes associate = form a bivalent
  • Chiasmata form
  • Equal length of non-sister chromatids/ alleles are exchanged
  • Producing new combinations of allele
63
Q

Use your knowledge of directional selection to explain the results shown in the table. (3 marks)

A
  • Scientists selected for breeding plants that produced 2n gametes
  • So these plants passed on their alleles for production of 2n gametes to the next generation
  • The frequency of alleles for production of 2n gametes does change from one breeding cycle to the next.

Past papers - biology (17 decks)

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