A-level paper 1 mistakes

Question 1

Why might a patient have an unusually high proportion of eosinophils?

Answer 1

The patient will produce more of these cells due to an allergy

Question 2

Explain why heart cells are damaged as a result of heart disease.

Answer 2

Plaque can lead to arteries becoming blocked
This deprives heart cells of oxygen
So cells cannot respire

Question 3

Compare and contrast the properties and uses of embryonic stem cells and pluripotent stem cells (IPS cells)

Answer 3

Similarities:
Both are able to divide indefinitely
Both are able to differentiate into a number of different cells
Differences:
IPS cells were adult cells, embryonic cells taken from inner cell mass
IPS have a gene, embryonic stem cells don’t.
Less ethical issues surrounding IPS cells
IPS cells form adult cells whereas embryonic stem cells form younger cells

Question 4

Explain how a mutation can result in a shortened protein being produced.

Answer 4

The mutation may produce a stop codon
Therefore translation will stop sooner

Question 5

Some people have mutations that affect proteins involved in the electron transport chain.
Explain why these mutations lead to a build up of lactate.

Answer 5

Electron carriers can’t transport electrons
Reduced NAD will not be oxidised
So pyruvate will produce lactate

Question 6

State the role of platelets in the blood clotting process.

Answer 6

They form a scab to seal the blood vessel.

Question 7

What happens to oxygen availability in water as temperature increases?

Answer 7

It decreases

Question 8

Describe the structure of a globular protein.

Answer 8

They have a 3 dimensional structure/ quaternary structure.
Held together by peptide bonds

Question 9

Explain the role of the Krebs cycle.

Answer 9

Completely oxidises acetyl coA
To release energy
And generates ATP
Reduced NAD formed
Which can be used in the ETC

Question 10

What substances are transported by xylem and phloem tissues?

Answer 10

xylem = water and mineral ions
Sucrose = water and sucrose

Question 11

Describe the differences between the structure of the xylem and that of the phloem.

Answer 11

xylem cell walls contain lignin but phloem cell walls contain only cellulose.
Xylem is hollow but phloem has cell contents
Xylem doesn’t have companion cells but phloem does.

Question 12

Do salmonella produce endo or exotoxins?

Answer 12

Endotoxins

Question 13

A scientist wanted to grow some salmonella.
Explain why the use of streak plating on a selective media is a good method for isolating salmonella.

Answer 13

Media allows only salmonella to grow
Colonies will be spread out on agar
Separates individual bacteria
So colonies are individual and can be picked up.

Question 14

Explain how stem rust fungus causes a reduction in a grain plant’s yield.

Answer 14

Stem rust fungus uses up nutrients.
Less glucose to form starch and for plant respiration.
Stem rust fungus also interferes with vascular tissue.
This can cause weakened stems.

Question 15

State the meaning of DNA methylation.

Answer 15

The addition of a methyl group to a cytosine base.

Question 16

Why is DNA methylation involved in the development of an embryo.

Answer 16

genes can be activated/ switched off
Causing cells to become specialised.

Question 17

Compare and contrast the structure of amylose and amylopectin.

Answer 17

Both contain alpha glucose
Both contain glycosidic bonds.
Amylose is helical but amylopectin is branched.

Question 18

Why do viruses have to be cultured with appropriate cells.

Answer 18

Viruses can only bind to one type of cell.
Due to receptors on their surface.
They cannot replicate without host cells.

Question 19

Most ATP is produced by mitochondrial respiration.
Describe how the remaining ATP is produced.

Answer 19

During glycolysis, glucose is converted to pyruvate by substrate level phosphorylation.

Question 20

Do archaea have ribosomes?

Answer 20

No

Question 21

How many sets of chromosomes does a tube nucleus have?

Answer 21

1

Question 22

Why does blood plasma have a higher protein content?

Answer 22

proteins are too large to diffuse through the capillary wall.

Question 23

Why does tissue fluid have less dissolved oxygen than blood plasma?

Answer 23

Oxygen has diffused into the cells.

Question 24

what happens to the tissue fluid that is not reabsorbed into the blood capillary?

Answer 24

Tissue fluid enters the lymphatic system.
Lymph returns to the blood.

Question 25

Bone marrow stem cells can differentaite into 2 different cells. Explain why.

Answer 25

Epigenetic modification. For example DNA methylation. Genes needed in both cell types remain switched on. Then genes needed for one cell may become switched off. Causing proteins to be made that are specific to one cell type.

Question 26

Explain the importance of vaccinating as many people as possible against rubella.

Answer 26

Results in herd immunity. Fewer infected people to pass virus onto unaffected people.

Question 27

Is there hydrogen bonding in carbohydrates and lipids?

Answer 27

Carbohydrates = yes Lipids = no

Question 28

Explain why lipids can be respired in only aerobic conditions?

Answer 28

In anaerobic conditions, pyruvate is used to reoxidise NADH so no krebs cycle. No oxygen available to act as terminal electron acceptor. NADH and FADH2 cannot be oxidised. So no coenzyme can bind to H+

Question 29

Explain how the types of bacteria found in the female genital tract could be identified.

Answer 29

Take a sample from the female genital tract. Grow bacteria on an agar plate. Add different antibiotics to the agar. Use of antibodies. Use the shape of colonies to distinguish.

Question 30

Compare and contrast the structure of fructose with the structure of glucose.

Answer 30

Both are hexose sugars. Both have covalent bonds. Glucose has a hexagon shape, fructose has a pentagon shape. Glucose has one CH2OH whereas fructose has 2.

Question 31

Explain the advantages of the presence of fructose in seminal fluid.

Answer 31

Acts as an energy source for the sperm. Movement through the female genital tract requires ATP. In order to reduce competition for carbohydrates with the bacterial cells in the female genital tract.

Question 32

Name the molecule that contains calcium ions in plant cell walls.

Answer 32

Calcium pectate

Question 33

Give the meaning of the term tissue.

Answer 33

A group of similar cells that perform similar functions.

Question 34

Describe how sugars are transported through the phloem.

Answer 34

By mass flow. Sucrose actively transported into the phloem at the source. Sucrose diffuses out of the phloem to the sink.

Question 35

Give 2 RNA viruses which have an envelope.

Answer 35

Ebola HIV

Question 36

Explain why antibiotics should not be taken by people with viral infections.

Answer 36

Antibiotics won't work as viruses are non-living. Unnecessary usage will act as a selection pressure which will increase antibiotic resistance.

Question 37

Explain the importance of the thylakoid membrane in light-dependent stage of photosynthesis.

Answer 37

Contains photosystems so light photons can be absorbed. contain carrier proteins so Hydrogen ions can be pumped into thylakoid space. Contains ATP synthase which hydrogen ions can pass through. Membranes are the site of photolysis.

Question 38

Compare and contrast the humoral response with the cell-mediated immune response.

Answer 38

both are active forms of immunity (1) both involve T helper cells (1) both involve cytokines (1) both result in the production of memory cells (1) {B cells / plasma cells} involved in the HIR but not in the C-MIR antibodies involved in HIR AND {not in the C-MIR

Question 39

vaccines can stimulate humoral immune response and the cell-mediated immune response. Explain how the products of these responses result in the destruction of cancer cells.

Answer 39

Perforins are released from T killer cells which kill cancer cells. Antibodies from humoral immune response will bind to antigens on cancer cells. Macrophages will engulf cancer cells as a result of Humoral immune response. Cancer cells are then digested.

Question 40

Are T killer cells humoral or cell-mediated response?

Answer 40

Cell-mediated immune response

Question 41

What is the meaning of epigenetic modification?

Answer 41

Change in the phenotype of an organism without changing the DNA.

Question 42

Describe the differences between the structure of xylem and that of phloem.

Answer 42

xylem cell walls contain lignin and cellulose, phloem cell walls contain only cellulose. xylem is hollow whereas phloem contains sieve plates. Phloem contains companion cells, xylem does not.

Question 43

Explain why a patient had an unusually high proportion of eosinophils in their blood smear.

Answer 43

Patient releases more cells into the blood due to an allergy.

Question 44

Describe the techniques that should be used to confirm food poisoning was caused by staphylococcus.

Answer 44

Isolate bacteria from vomit. Use of gram staining to show gram positive. Grow on selective agar. Use antibodies against staphylococcus.

Question 45

Describe how carbon fixation takes place in chloroplasts.

Answer 45

Carbon dioxide diffuses into the stroma. Carbon dioxide binds to RuBP. Using RUBISCO. Resulting in the formation of GP.

Question 46

Explain why mutations in nuclear DNA can be inherited fro mother or father but mitochondrial DNA can be inherited from only the mother.

Answer 46

Nuclear DNA is present in both male and female gametes. Mitochondria present in the egg cell but not the sperm head.

Question 47

People with Leigh syndrome have mutations that affect the proteins involved in the electron transport chain. Explain why these mutations lead to a build-up of lactate.

Answer 47

Mutation may prevent electrons being passes down the ETC. NADH cannot be oxidised. Therefore pyruvate and NADH will produce lactate. Lactate produced at a faster rate than it can be removed.

Question 48

Describe epigenetic modification.

Answer 48

Changes that effect gene expression. e.g DNA methylation. This can change the proteins synthesised.

Question 49

How many GALP molecules go on to form one glucose molecule?

Answer 49

2

Question 50

Describe the differences between the apoplastic and the symplastic pathways.

Answer 50

Apoplastic non-living, symplastic living. Apoplectic uses cell walls, symplastic uses cytoplasm. Apoplectic faster as there is less resistance.

Question 51

Explain how red blood cells are adapted for their function.

Answer 51

No nucleus to carry more haemoglobin. Biconcave shape increases surface area to absorb more oxygen. Contain haemoglobin which transport oxygen.

Question 52

Why is hydrochloric acid added to a root tip to observe the stages of mitosis?

Answer 52

To break down the middle lamella.

Question 53

The cell membranes of archeae are made from bipolar lipids. Explain why this is a suitable molecule to form the cell membrane.

Answer 53

Two polar groups will interact with aqueous environment. Rest of the molecule will be a hydrophobic layer inside.

Question 54

Explain why it is important that the lipid composition of the membrane of organisms changes if the temperature changes.

Answer 54

Membranes control permeability. Control the uptake of nutrients. Membranes need to be fluid for cell division.

Question 55

In high levels of carbon dioxide, will the spiracles of insects be open or closed? Explain why

Answer 55

Open because ventilation rate is faster.

Question 56

Describe the structure of a ribosome.

Answer 56

Composed of protein and mRNA. Arranged in 2 subunits.

Question 57

How is DNA packaged into chromosomes?

Answer 57

DNA is wrapped around histone proteins to form nucleosomes. These nucleosomes coil and fold to form chromatin. The chromatin condenses further to form chromosomes.

Question 58

What type of viruses are the following (include genetic information and envelope) 1) Ebola 2) Lambda phage 3) Tobacco mosaic

Answer 58

1) RNA enveloped 2) DNA non-enveloped 3) RNA non-enveloped.