Biology Paper 2 Mistakes

Describe sympatric speciation (6)

1. mutation occurs randomly which causes variation

2. members of the same population become reproductively isolated from eachother, without a geographical barrier

3. preventing gene flow between the two populations

4. different selection pressures act on the two populations

5. different allele varieties are favoured in the population, resulting in change in allele frequencies

6. eventually two populations cannot breed to produce fertile offspring

Describe allopatric speciation (6)

1. mutation occurs randomly which causes variation

2. members of the same population become reproductively isolated from eachother by geographical barrier

3. preventing gene flow between the two populations

4. different selection pressures act on the two populations

5. different allele varieties are favoured in the population, resulting in change in allele frequencies

6. eventually two populations cannot breed to produce fertile offspring

A precaution when marking to make sure estimate is valid, using capture recapture

Marking does not affect survival

How many degrees of freedom to use in Chi squared

phenotypes - 1

Statistical test to see if observed frequencies of phenotypes is different to frequencies expected by Hardy Weinberg

Chi squared

5 Hardy Weinberg Assumptions

1. no genetic mutations

2. all genotypes are equally fertile

3. mating is random

4. large population

5. no immigration / emmigration

Hardy Weinberg equillibrium states…

genetic variation in a population iwll remain constant from one generation to the next

Temporal summation

Singular nerve stimulated repeatedly causes enough Na+ to diffuse into axon to reach threshold, causing an action potential

How can the inibition of acetylcholinesterase manage the weakening of muscles (3)

1. less Ach broken down

2. Ach can repeatedly rebind to/ stimulate receptors on post-synaptic membrane

3. Enough Na+ enter to reach threshold

4. Action potential is produced

3 signs / symptoms that result from a derease in ADH

1. feeling thirsty

2. less concentrated urine

3. frequent urination

What part of the body releases ADH into the blood

Posterior pituitary

Describe the effect of ADH on the collecting duct on the kidneys (3)

1. Stimulates the addition of channel proteins on membrane

2. increases premeability to water / more water reabsorbeed

3. by osmosis

What happens to sacromere when muscle contracts

Decreases in length

Desribe how fast muscle fibres having a higher concentration of glycogen is related to the different properties of these muscle fibres (4)

1. Fast muscle fibres contract quickly, slow muscle fibres contract slowly

2. fast fibres mainly use anaerobic respiration, slow muscles use aerobic respiration

3. fast fibres produce ATP quickly, slow fibres produce ATP slowly

4. Glycogen is a store of glucose

Describe the myogenic stimulation of the heart and how the regular contraction of the atria and ventricles in coordinated

1. SAN releases a wave of excitation across atria

2. causing the atria to contract (atria systole)

3. after a short delay, the AVN relays the wave of excitation down the

4. purkyne fibres that form bundles of His

5. so ventricles contract at the same time from the bottom upwards

Give two reasons why a weightloss programme could be used to treat type 2 diabets but not type 1.

1. obesirt is a risk factor for type 2 diabetes, not type 1

2. type 1 diabetes do not produce insulin

describe and explain two precautions required to ensure that the estimate is valid in capture recapture

• time delay after release so geckoes spread into population

• marking does not effect chances of survival eg is non-toxic. not visible to predators

Describe how to seperate photosynthetic pigments by chromatography (4)

1. draw line / origin on chromatohraphy paper using pencil and ruler

2. add chlorophyll solution to origin with tubing / pipette

3. add solvent below ling / origin

4. remove stopper before solvent reaches end of chromatography paper

Solvent A seperates 5 pigments. solvent B seperates 6. Explain (2)

two pigments have the same solubility in solvent A

but have different solubiility in solvent B

Ziconotide is a polypeptide that acts on synapses in the spinal cord. why is it injected into the patient’s cerebrospinal fluid? (2)

1. drug is broken down by enzymes / acid

2. so drug reaches spinal cord quickly / directly

Z was injected at 3 ng kg-1 h-1 for 8 days into a patient. calculate the total mass in grams of z injected after 8 days into a patient with body mass 82 kg.

1ng = 1×10-9

4.7×10^-5 g

In an experiment, why do we sterilise soil? (2)

1. to remove any pathogens or pest

2. to ensure no nitrifying / denitrifying bacteria are affecting results

if a gene is sex linked, does sex appear in the phenotype?

Yes

How is orange colour seen when both red-sensitive an green-sensitive photoreceptors are stimulated? (3)

1. colour vision involves cones

2. each type of photoreceptor has its own pigment

3. greater absorbance by red-sensitive cones than green-sensitive cones, therefore more impuulses sent across optic nerve

Why is there a high sensitivity to light in the retina (1)

several photoreceptors connecting to one neurone and spatial summation

V receptors only bind with ADH. Explain why (2)

• has specific tertiary structure / 3d shape

• structures are complimentary

how does the release of ADH affect blood pressure when blood pressure is decreased

• ADH increases reabsorption of water into blood

• higher water volume means blood volume increases, increasing blood pressure to normal

Populations of different species form a… (1)

community

how does an increase in glucose and fatty acid transport proteins benefit you when you exercise (4)

1. more glucose enters muscle cells

2. glucose / fatty acids enter by facilitated diffusion

3. fatty acids used in krebs cycle

4. respiration provides more ATP

how does an incerase in muscle activity increase the heart rate (4)

1. increased CO2 concentration in blood is detected by chemoreceptors

2. more impulses are sent to cardiac center by chemoreceptors

3. more implues are sent along sympathetic pathway / neurones

4. to SAN

Dengue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation. 0 2 .

1 Explain how using the SIT could reduce transmission of dengue. [2]

1. infertile males compete with fetile males for food and resources

2. decreaing population

The release of radiation-sterilised A. aegypti has not been very successful in controlling the transmission of dengue. Suggest one reason why. [1]

radiation effects courtship behaviours

OR lifespan / survival

name the advantages of aerobic respiration over anaerobic respiration (3)

1. aerobic respiration happens for longer

2. aerobic respiration produces more energy

3. aerobic respiration does not produce lactate / lactic acid

if there are numerical values in the graph you need to…

refer to them in your points

why do you set up a tube of no chloroplasts, but DCPIP, in the light, in the photosynthesis practical (2)

1. prove that chlorophyll is needed

2. to prove that DCPIP is not affected by light

The student evaluated the effectiveness of different chemicals as weed-killers by assessing their ability to prevent the decolourisation of DCPIP in chloroplast suspensions.

He added different concentrations of each chemical to illuminated chloroplast suspensions containing DCPIP.

He then determined the IC50 for each chemical. The IC50 is the concentration of chemical which inhibits the decolourisation of DCPIP by 50%.

Explain the advantage of the student using the IC50 in this investigation. (2)

roviudes standard / reference point

Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity.

1. Represents dry mass / mass of carbon;

2. Represents gross production minus respiratory losses;

Give 3 reasons why pancreas transplants are not used for the treatment of type II diabetes.

1. usually type II produce insulin

2. receptors less sensitive / responsive to insulin

3. type 2 treated with diet and exercise

Suggest how transcription factors can reprogramme cells to form iPS cells. [2 marks]

1. transciption factor binds to promotor region of DNA

2. stimulating RNA polymerase / transcription

What is meant by the term phenotype? (2)

1. (Expression / appearance / characteristic due to) genetic constitution/genotype/allele(s);

2. (Expression / appearance / characteristic due to) environment;

Any dna in the sample is hydrolysed before mRNA is converted to DNA, before PCR. why? (2)

1. to remove any DNA present

2. as this DNA would be amplified

Scientists have used the RT-PCR method to detect the presence of different RNA viruses in patients suffering from respiratory diseases.

The scientists produced a variety of primers for this procedure. Explain why. (2)

1. base sequence differs

2. so different complementary primers required

gene pool definition

all alleles in a population

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.

Using this information, suggest how these two species of palm tree arose by sympatric speciation. (6)

1. populations in same habitat / area

2. random mutation produces different flowering times

3. reproductive isolation, no gene flow

4. different alleles passed down / change in frequency of alleles

5. disruptive selection

6. eventually species cannot interbreed to produce fertile offspring

Yaramul is a town in a historically isolated region of the Andes Mountains. The population of this town has the highest frequency of the E280A mutation in the world.

The origin of the E280A mutation in this population has been traced back to a common ancestor in the 17th century. Natural selection has not reduced the frequency of the E280A mutation in the population. Explain why (2)

1. small, isolated population so interbreeding

2. allele inherited from a common ancestor

The age at which the E280A mutation is expressed to cause AD can vary (lines 11–12). Suggest and explain one reason for this. (2)

1. epigentics / named enviromental factor

2. methylation

One scientific study which analysed chromosome 14 involved 102 individuals. The scientists recorded a sample size of 204. In this sample they detected 75 E280A mutations but only 74 potential AD cases

WHY (2)

one person had homozygous dominant alleles