Cell structure

This is an electron micrograph of an intestine cell.

Use the image to answer questions 14 and 15.

Identify the structure labelled X.

A Centriole

B Lysosome

C Mitochondrion

D Nucleolus

This is an electron micrograph of an intestine cell.

Use the image to answer questions 14 and 15.

Identify the structure labelled Y.

A Cell wall

B Cilium

C Plasma membrane

D Smooth ER

The electron micrograph shows the junction between two neurones.

State the name given to the region labelled B.

Identify whether structure A or structure C is the first neurone in the pathway.

Use one piece of evidence visible in the electron micrograph to explain your choice.

Complete the sentences about the action potential.

The action potential involves rapid opening of voltage-gated sodium ion channels.

This is an example of........ feedback. During the action potential,

the inside of the neurone becomes more positive than the outside. This is known as

Mutations in genes coding for proteins in the cytoskeleton have been associated with several diseases of the nervous system, including neurodegenerative disorders.

Give three functions of the cytoskeleton.

Suggest how a mutation in cytoskeleton genes could cause a disease of the nervous system.

Fig. 2.1 shows a light micrograph of a blood smear.

The cells labelled X and Y in Fig. 2.1 are two different types of white blood cell.

Identify the types of white blood cell labelled X and Y.

The blood cell labelled Z in Fig. 2.1 contains a high concentration of haemoglobin.

Outline two other ways in which the blood cell labelled Z is adapted for its function.

The diameter of another blood cell is represented by the line W in Fig. 2.1.

The magnification used to produce Fig. 2.1 was × 800.

Calculate the actual diameter, W, of the blood cell.

Give your answer in m.

Diameter =........ m

Some white blood cells have a high concentration of lysosomes.

State the role of lysosomes in white blood cells.

A scientist calculated two values for the lysosomes in a white blood cell:

• mean volume of a lysosome = 6.5 × 10^–14 cm³

• mean number of H⁺ ions per lysosome = 1.3 × 10^–21 mol

Use these values to calculate the mean H + ion concentration per lysosome in this white blood cell.

Give your answer in mol dm^–3.

Mean H⁺ ion concentration =........ mol dm^–3

The formula used to calculate pH is

pH = -log [H + ] where [H⁺] is H⁺ ion concentration in mol dm^–3.

Use your answer from part (ii) to calculate the mean pH of the lysosomes in this white blood cell.

Give your answer to 2 significant figures.

The scientist stained the lysosomes in a sample of living white blood cells.

The table shows the properties of five stains, A to E.

Select the most appropriate stain for the scientist to use, based on your answer from part (iii).

Differential staining can be used to distinguish between bacteria with thick cell walls and bacteria with thin cell walls.

Four substances are used when differentially staining bacteria:

• Crystal violet, which stains bacteria purple.

• Safranin, which stains bacteria pink but is not visible in the presence of crystal violet.

• Alcohol, which removes fixed stains from bacteria with thin cell walls.

• Iodide solution, which fixes crystal violet to bacterial cells.

Suggest a practical procedure for staining a slide that would allow thin-walled bacteria to be differentiated from thick-walled bacteria.

Fig. 2.2 shows stained tissue that includes two different blood vessels, labelled L and M, and a substance labelled N.

State whether L is an artery or a vein and give two pieces of evidence from Fig. 2.2 that allow you to reach your decision.

State the substance labelled N.

Which of the options describes the path taken by proteins, such as digestive enzymes, that are exported from a cell?

Prokaryotic cells have cytoskeletons. The molecules in prokaryotic cytoskeletons are different from the molecules in eukaryotic cytoskeletons.

Table 4.1 lists three molecules present in a prokaryotic cytoskeleton.

Suggest the function of Protein A.

Suggest the function of Protein C.

An antibiotic called A22 binds irreversibly to Protein B. Despite its antibiotic properties, A22 is not used in humans.

Suggest why scientists have advised that A22 should not be used in humans.

Vancomycin is an antibiotic that has been used to treat bacterial infections for many decades. Several strains of bacteria have evolved resistance to vancomycin.

Oritavancin is an antibiotic with a similar structure to vancomycin.

Table 4.2 shows data obtained from treatments with the two antibiotics.

Use the data in Table 4.2 to evaluate the advantages and disadvantages of using oritavancin rather than vancomycin as an antibiotic.

Complete the diagram above by writing the missing words or phrases in the boxes labelled X, Y and Z.

........ Answer on the diagram........

Suggest why the scientists used a plasmid that contained an antibiotic resistance gene.

The scientists observed the following:

• 1 in 400 bacteria took up the plasmid

• 1 in 1000 of the plasmids taken up by bacteria contained the ‑galactosidase gene.

Calculate the percentage of bacteria that contained the ‑galactosidase gene.

A technique called quantitative PCR is used to check that the E. coli population is growing on the mice liver tumours rather than on healthy tissue.

Suggest how the scientists could use PCR to compare E. coli growth rates on cancerous liver tissue and healthy tissue.

Some people think that the genetic engineering of certain organisms is unethical.

However, there are very few ethical concerns about the genetic engineering of bacteria such as E. coli.

Suggest why there are very few ethical concerns about the genetic engineering of E. coli

Fig. 16 shows pressure changes during the cardiac cycle.

Using Fig. 16, compare the changes in pressure in the left ventricle with the changes in pressure in the left atrium.

Using Fig. 16, calculate the heart rate of this individual.

Give your answer to 2 significant figures.

Using Fig. 16, calculate the percentage change between minimum and maximum pressure in the aorta.

Give your answer to 2 significant figures.

Name the valve which closes at point X on Fig. 16.

The heart supplies oxygenated blood to the tissues.

VO₂^max is a measurement of the maximum volume of oxygen that an individual can use during intense exercise in a given time.

Smart watches can estimate the VO₂^max of an individual by measuring heart rate while exercising.

Having a higher VO₂^max is associated with improved aerobic fitness.

Two male students exercised for 30 min and used smart watches to record their VO₂^max. Table 16 shows their masses and the VO₂^max values they recorded.

Student 1 drew the following conclusion from this result:

Student 2 said that this conclusion is invalid because several variables have not been controlled.

State three variables necessary for a valid comparison that have not been controlled in the above experiment.

Brown fat is a type of tissue.

Brown fat has a higher need for oxygen because fat cells in this tissue carry out aerobic respiration at a higher rate than fat cells in other tissues.

Suggest which organelle is present in higher numbers in brown fat cells than in other fat cells.

Identify the cellular components shown at A and B.

The real size of the line between C and D on Fig. 1.1 is 1.4 × 10⁻⁶ m.

Calculate the magnification that was used to produce the image in Fig. 1.1.

Give your answer to 2 significant figures.

Fig. 1.2 shows a student’s drawing of another sago pondweed cell, which was observed under a light microscope. The student used a sharp pencil but did not label the drawing.

Describe two other ways in which the drawing could be improved.

The student stained a sago pondweed sample to improve the contrast between cellular components when viewed under a microscope.

The student used the following procedure to stain the sample:

• Use forceps to place the sample on a glass slide.

• Use a pipette to place two drops of the stain in the centre of the sample.

• Carefully lower a cover slip onto the sample, ensuring that the cover slip is parallel with the slide as it is lowered.

Describe two improvements the student should make to their staining procedure.

Sago pondweed has evolved many adaptations to its aquatic environment. Three such adaptations are described below.

Explain the advantage of each adaptation.

Adaptation 1: No waxy cuticle

Adaptation 2: Stem tissue that contains air spaces

Adaptation 3: A thin, flexible stem