OCR GCSE Combined Science A (Gateway) Biology Paper 8 Higher November 2020 question paper J250/08

A scientist crossed a white flower with a purple flower. The white flower is homozygous recessive. The purple flower is heterozygous.

The scientist uses this Punnett square to predict the expected ratio of offspring.

What is the expected ratio of phenotypes in the offspring?

A 1 purple: 1 white

B 1 purple: 2 white

C 2 purple: 1 white

D 4 purple: 0 white

Which of these is a biotic factor that can affect an ecosystem?

A Acidity of soil

B Bacterial levels in a river

C Carbon dioxide levels in the atmosphere

D Oxygen levels in a river

Lichens are made up of a fungus and algae living together. The fungus gets nutrients from the algae and algae is sheltered by the fungus.

Which term describes this type of relationship?

A Competition

B Mutualism

C Parasitism

D Predation

The genetic cross shows how genes are passed from parents to offspring.

Which part of the genetic cross shows the gametes?

Carbon is recycled in the ecosystem.

Which process helps reduce the level of carbon in the atmosphere?

A Photosynthesis

B Respiration

C Translocation

D Transpiration

The phenotype of rabbits can be black or white fur. The allele for black fur is dominant.

Which genetic cross identifies the genotype of a rabbit with black fur (rabbit X) as Bb?

A Cross rabbit X with a black rabbit. All offspring have black fur.

B Cross rabbit X with a black rabbit. 50% of offspring have black fur and 50% have white fur.

C Cross rabbit X with a white rabbit. All offspring have white fur.

D Cross rabbit X with a white rabbit. 50% of offspring have black fur and 50% have white fur.

Chalara ash dieback is a fatal disease affecting ash trees. It is caused by a fungus growing on the leaves.

When the leaves fall to the ground the fungus releases spores spreading the disease.

Which of these would help prevent the spread of Chalara ash dieback?

A Collecting the fallen leaves to make compost that is then added to the soil.

B Cutting off infected leaves and branches, and leaving them on the ground to decay.

C Stopping the import of ash seeds, plants and trees from countries with infected trees.

D Replanting young ash trees to replace those that have died.

Which statement about alleles and genes is correct?

A Alleles are found in the cytoplasm, while genes are only found in the nucleus on the DNA.

B Allele is just another name for gene, they are both the same codes for a characteristic.

C Genes are sections of DNA that code for a characteristic, alleles are different forms of a gene.

D It is possible to have two different genes for a characteristic but only one allele.

Phylogenetics is used in the process of classification of organisms.

Which of these is not part of Phylogenetics?

A All species existing today descended from a single common ancestor.

B Organisms are grouped using characteristics visible to the human eye.

C Phylogenetics is used to identify common ancestors.

D Sequencing of DNA can reveal the evolutionary history of an organism.

Scientists studied a population of men. They grouped the men by their blood cholesterol levels.

The chart shows the percentage of the population in each blood cholesterol level group. It also shows the men in each group that died from heart disease as a percentage of the whole population that died from heart disease.

What conclusions can be made from the data in the chart?

Calculate the ratio for percentage of total heart disease deaths for blood cholesterol <5.0 mmol / dm³ compared to those 5.0 mmol / dm³ or greater.

Hormone replacement therapy (HRT) involves giving oestrogen to women.

A group of scientists did a double-blind study of 643 women given either HRT or a placebo.

The study followed-up these women after five years. It showed reduced build-up of cholesterol in the arteries of women given HRT.

The scientists made this conclusion:

Women on HRT may be at less risk from heart disease.

Explain why HRT could reduce the risk of heart disease.

The reduced build-up of cholesterol observed during the study might not be large enough to have an impact on a person’s risk from heart disease.

What change could be made to the study to gain enough evidence to support the conclusion?

Oestrogen is known to interfere with the cell cycle, increasing the rate of mitosis.

Suggest why HRT might increase the risk of breast cancer.

Name one lifestyle change someone could make that could also reduce the risk of heart disease.

A patient has a urinary tract infection caused by bacteria. The doctor needs to know the best antibiotic to use to treat the infection.

They send a sample of the patient’s urine for testing. The bacteria in the urine are grown on agar jelly plates. On the plates are four different antibiotic discs.

Aseptic techniques are used to prepare the agar jelly plates.

Fig. 12.1 shows the neck of a glass bottle containing the agar jelly being heated in a flame for 2 seconds. This is done before the agar jelly is poured into the Petri dish.

Suggest why the scientist uses a glass bottle and not a plastic bottle.

The neck of the glass bottle is heated before transferring the agar jelly to the Petri dish.

Explain why.

Fig. 12.2 shows the results of the four different antibiotics A, B, C and D.

The line XY is the diameter of clear agar jelly for Antibiotic A.

Use the line XY to calculate the cross-sectional area of clear agar jelly for Antibiotic A

The area of a circle = r²

= 3.14

Give your answer to 3 significant figures.

Some bacteria are resistant to antibiotics.

Explain why antibiotic resistant bacteria show evidence of evolution.

Algae can photosynthesise and grow rapidly in lakes during the summer.

The growth of algae is affected by abiotic factors.

An experiment measured the dry mass of algae at different temperatures for 25 days. Light intensity was kept constant.

Table 13.1 shows the results for 25 °C and 35 °C.

Describe the trends shown in the graph.

Table 13.2 shows the dry mass of algae on day 25 for all the temperatures measured in the experiment.

In some lakes, algae are the main producers.

One year, water temperatures in a lake did not rise above 20 °C.

Use data from Table 13.2 to explain how this might affect the community of organisms living in the lake.

The algae produce a toxin. High levels of toxins can kill fish in the water.

Suggest why scientists are concerned about the effects of global warming on algae growth.

Scientists have used genetically engineered bacteria to produce the human hormone insulin.

Describe the main steps in the process of genetic engineering.

Insulin may be used to treat type 2 diabetes.

Describe the interaction between type 2 diabetes and nutrition.

The human genome has been mapped.

Discuss how this could help with the future treatment of type 2 diabetes.

Complete the sentence about cancer.

Cancer is the result of changes in cells that lead to uncontrolled........ and

........

*(b) Treatment of lung cancer can involve surgery and painful chemotherapy. Survival rates for lung cancer are low.

Replication of damaged DNA can lead to cancer. A gene called p53 prevents the replication of damaged DNA. Lung cancer and faults in the p53 gene are linked.

Gene therapy involves replacing faulty genes.

Explain why gene therapy could be used to treat lung cancer and discuss the issues involved in using this type of treatment.