past paper 1 failed questions

a student wanted to extract the DNA from fresh peas.

the student crushed the peas and added washing up liquid and water.

the enzyme protease was then added to this mixture.

explain why the enzyme protease was added to the mixture

• to break down proteins in the cell membrane

• it destroys enzymes that may break down the DNA

state why ice cold ethanol is poured into the filtrate in DNA extraction

too see the DNA because DNA is insoluble in ethanol

explain how HIV can lead to the onset of AIDS

HIV destroys white blood cells, weakening the immune system so the person is more susceptible to other pathogens

state how the use of antibiotics could contribute to bacteria developing resistance to antibiotics

people not completing their course of antibiotics

5cm³ of milk A and 1cm³ of lipase were added to a test tube

the pH of the mixture was 7.

there was no change in the pH after 10 minutes

explain why there was no change in the pH of the mixture containing milk A

there are no lipids in the milk to break down, so fatty acids were not produced

a student was investigating mitosis in the roots of a garlic plant

describe how to student could prepare a microscope slide to show mitosis in the growing roots of a garlic plant

• use the root tip of the garlic, soften the root with heat.

• crush the root onto the slide

• stain the root with iodine

• add a drop of water to the slide

• add a cover slip