Exam questions 2

Question 1

How does a tetraploid form

Answer 1

Cross between two species. The offspring are sterile, the chromosomes double due to nondisjunction. This forms a tetraploid.

Question 2

How can a MAB be used to identify something

Answer 2

The fluorescent antibody binds to the protein, when you view sections with a microscope fluorescent areas indicate the location of the antibody

Question 3

How would an organism differentiate between a large and small stimulus

Answer 3

The larger the intensity of stimulus, the greater the frequency of action potential. The all or nothing law, if there is a small stimulus an action potential may not be generated. A bigger stimulus may involve more receptors.
neurone

Question 4

Physical factors of leaf which affect rate of photosynthesis

Answer 4

Number of stomata, number of chloroplasts. Surface area of leaf, rubisco concentration, age.

Question 5

Outline the stage in which hybridoma cells are formed in Mabs (3)

Answer 5

The plasma cell and cancer cell have their cell membranes fused after an electric current is used

Question 6

Outline the uses of mAbs in the treatment of diseases (3)

Answer 6

Some mAbs act directly on target cells by binding to complimentary antigens. A radioactive isotope can be attached to mAbs. Enzymes can be attached to mAbs so that drugs can be activated at the site of action. MAbs can interrupt cell signalling. They can be used for passive immunity

Question 7

Why is is important that stem cells form more stem cells (1)

Answer 7

To provide cells that can differentiate for continued growth of the tissue

Question 8

How is the structure of a sieve tube related to its function (4)

Answer 8

Elongated cells form long tubes. Small amount of cytoplasm so there is little resistance to the flow of phloem sap. Sieve plates have pores so there is little barrier to the movement of phloem sap. Sieve plate supports sieve tube element. Plasmodesmata between sieve tube and companion cell for ease of loading.

Question 9

What is the function of companion cells for transport in the phloem (2)

Answer 9

Movement of sucrose from source cells, the sucrose is moved into sieve tubes through pladmodesmata. They pump hydrogen ions into the cell. They provide ATP for sieve tubes

Question 10

Why is the left ventricle thicker then the right (3)

Answer 10

The left ventricle pumps blood into the systemic circulation. More muscle is needed to overcome the greater resistance to flow in systemic circulation. Higher blood pressure is required in systemic circulation and high pressure requires more muscular force

Question 11

Function of anticodon (2)

Answer 11

Anticodon binds to codon on mRNA, specificity ensures correct primary structure of polypeptide

Question 12

What happens in the Phagocytic vesicle (3)

Answer 12

Bacteria are killed by the use of hydrolytic enzymes, for example carbohydrase, which kill the bacteria by the use of hydrogen peroxide.

Question 13

Why do very few T-lymphocytes respond to a specific bacteria (2)

Answer 13

Few T-lymphocytes have the correct specificity, as different T-lymphocytes are specific to different antigens. The T-cell receptor is complimentory to the shape of the antigen

Question 14

Advantage of smooth muscle during periods of exercise (2)

Answer 14

The bronchioles widen so more air reaches the alveoli so greater rate of gas exchange. Satisfies increased demand for oxygen

Question 15

Why might bigger tree have a higher rate of transpiration then smaller trees (4)

Answer 15

For bigger trees they have access to higher light intensity which will cause their stomata to open. Lower humidity for taller trees so steeper water potential gradient. Higher temperature for taller trees so higher rate of evaporation. Higher wind speed for taller trees so steeper water potential gradient. Taller trees have longer roots so take up more water. Taller trees have more leaves so greater surface area.

Question 16

Describe the role of the spindle fibres during mitosis (2)

Answer 16

The spindle fibres attach to centromeres at prophase, on the centrioles. They arrange the chromosomes on the equator and pull the chromosomes apart, they pull the chromatids torwards the poles of the spindle.

Question 17

What happens when someone enters low altitudes

Answer 17

Lower partial pressure of oxygen, less oxygen in alveoli so the haemoglobin is not fully saturated. Less oxygen is transported in the blood so less aerobic respiration which can lead to altitude sickness. More red blood cells are produced to increase the concentration of haemoglobin to allow a similar volume of oxygen to be transported as at sea level

Question 18

State one structural difference between a guard cell and a epidermis cell

Answer 18

Epidermis cell has chloroplasts

Question 19

State how monoclonal antibodies can be used to collect a substance from the blood (3)

Answer 19

1) Produces many antibodies which are specific to the substance
2) They can be immobilised
3) The substance is allowed to pass over the antibodies
4) So the substance will bind to the monoclonal antibodies
5) Treatment is needed to release the substance from the antibodies

Question 20

Why do human cells need to be used for mAbs and not bacterial cells (1)

Answer 20

Sugars need to be added, Bacteria do not have a Golgi body

Question 21

How do offspring produced by self-pollination and cross-pollination differ in their genetic diversity (3)

Answer 21

In self-pollination the genes come from one parent this gives less genetic variation and results in inbreeding, thus increasing homozygosity

Question 22

How can natural selection produce smaller flowers (5)

Answer 22

1) Range of flower sizes in original population
2) There is genetic variation in flower size in original population
3) Change in environment
4) Plants with smaller flowers are at a selective advantage
5) Alleles for smaller size are passed to offspring as they are more likely to reproduce
6) Frequency of advantageous alleles increase
7) Directional selection

Question 23

How does Gibberelin lead to sedd germination (4)

Answer 23

1) Gibberellin moves from embryo to aleurone layer
2) A gene is used to make mRNA
3) This produces amylase
4) Amylase hydrolyses starch to maltose
5) For respiration.
6) Which is used for growth

Question 24

How might a toxin which binds to cholingeric synapses cause paralyses (3)

Answer 24

1) Toxin may bind to receptors on post synaptic membrane.
2) This stops ACh from binding
3) So stimulated ACh receptors cause continuous depolarisation.
4) Stops recycling of ACh
5) Inhibits acetyl cholinsterase

Question 25

What’s the role of calcium ions in synaptic transmission (3)

Answer 25

The calcium ions enter the presynaptic neurone and cause vesicles containing ACh to fuse with the presynaptic membrane, so ACh is released into the synaptic cleft.

Question 26

Outline the hybridoma method for the production of a monoclonal antibody (7)

Answer 26

A mouse is injected with an antigen, you wait for an immune response to occur. The B lymphocytes will go through a clonal selection and clonal expansion stage. The plasma cells are them extracted from the mouse’s spleen and fused with cancer cells to form a hybridoma. The hybridoma cells producing antibodies are identified and cultured on a large scale

Question 27

What’s the effect of hydrogen ions moving into the cell wall of a plant (3)

Answer 27

The pH decreases, expansins break between cellulose microfibrils. The cell wall is now able to stretch when turgor pressure increases

Question 28

How do genes and the environment affect continuous variation (3)

Answer 28

There many genes which effect the characteristic, the genes have an additive effect. The environment has a big effect ie diet

Question 29

How does a gene affect the expression of other genes (3)

Answer 29

This is a regulatory gene. The gene codes for transcription factors. The transcription factor binds to DNA at the promoter. This helps RNA polymerase to bind

Question 30

How can one gene provide a large structural difference in different organisms (3)

Answer 30

The one gene causes a big phenotypic effect, because the gene controls lots of other genes. There is a different intensity of gene expression in different species

Question 31

How can a base substitution lead to the production of a non-functioning enzyme (5)

Answer 31

There is a missense mutation, this means mRNA is formed with a different codon. A different tRNA will bind then normal, the amino acid will be different. The tertiary structure of the enzyme will change, this will distort the shape of the binding site. Alternatively a stop codon could be formed or no amino acid added resulting in a shortened polypeptide

Question 32

Outline the role of NAD in aerobic respiration (4)

Answer 32

Acts as coenzyme, it dehydrogenases substance. It takes away hydrogen atoms and carries them to the electron transport chain. It is used for redox. 3 ATP molecules are released per reduced NAD

Question 33

How can speciation result from founders effect (3)

Answer 33

1) Allopatric speciation
2 Populations are geographically isolated and have different selection pressures
3) Different mutations occur
4) Ginetic drift
5)The populations are reproductively isolated

Question 34

Why are founder populations at a higher risk of extinction (3)

Answer 34

1) Small population
2) With low genetic diversity
3) Interbreeding depression results in low heterozygosity
4) Environmental changes may make the whole population extinct

Question 35

What is needed for high levels of biodiversity

Answer 35

Genetic diversity, species richness and a large number of habitats

Question 36

Describe how you would use DCPIP to investigate how wavelength of light effects rate of photosynthesis

Answer 36

1) Hill reaction
2) Oxidised DCPIP is blue
3) DCPIP goes colourless when reduced
4) To make the chloroplast extract you crush the leaf in an extract before filtering off the sediment
5) Add a buffer soloution
6) Add the DCPIP to the chloroplast and expose them to 5 different wavelengths of light
7) Measure the time it takes for the blue colour to disappear
8) Measure rate using 1/t
9) Do three repeats and after excluding anomalies calculate the mean