Biology

The diagram shows some animal cells. Some of the cells are dividing by mitosis for growth and repair.

What fraction of the cells in the diagram is dividing by mitosis?

The cells which are not dividing in the diagram each contain 10 chromosomes.

One of these cells divides by mitosis to produce two new cells.

How many chromosomes will each new cell contain after mitosis?

Cells divide in a series of stages called the cell cycle.

Complete the sentences. Choose answers from the box.

contracts, divides, grows, reacts, relaxes, replicates

Before mitosis occurs, the cell ______.
The genetic material in the cell doubles when the DNA ______.
After the chromosomes have been pulled to each end of the cell, the cytoplasm ______.

Figure 2 shows the time taken to complete different stages of the cell cycle.

Which stage of the cell cycle takes the most time?

What percentage of time in the cell cycle is stage A?

Stem cells divide by mitosis.
Scientists can use stem cells from an embryo to create heart cells in a laboratory.

Which organ system contains heart cells?

Name one medical condition that could be treated using heart cells created from an embryo.

Give one reason why a patient may not want to be treated with heart cells created from an embryo.

The diagram shows a simplified microscope.

What is the function of part A?

The diagram shows a simplified microscope.

What is the function of part B?

The diagram shows a simplified microscope.

What is the function of part C?

A student prepared some onion cells and viewed them using a microscope. The method included adding three drops of iodine solution to the layer of cells.

Why was iodine solution added to the layer of onion cells?

Why was a thin layer of onion cells used?

The student was worried about using a sharp knife to cut the onion. The student wrote a risk assessment for using a knife.

Which of the following is the Hazard in this risk assessment?

The student was worried about using a sharp knife to cut the onion. The student wrote a risk assessment for using a knife.

Which of the following is the Plan to minimise risk in this risk assessment?

Figure 4 shows what the student saw using the microscope at a magnification of ×400. Line A–B in Figure 4 shows the length of cell Z.

Calculate the real length of cell Z. Complete the following steps.

1. Measure the length of line A–B in millimetres (mm).
2. Give your measurement of the length of line A–B in micrometres (μm). (1 mm = 1 000 μm)
3. Calculate the real length of cell Z using the equation:
   real length of cell Z (in μm) = length of line A-B (in μm) / magnification

How would onion cells look different if they were seen using an electron microscope?

Tick (✔) two boxes.

This question is about cells and transport.

Complete Table 5.

Cells in potatoes are plant cells. Cells in potatoes do not contain chloroplasts.

What is the function of chloroplasts?

Name one type of cell in a potato plant that does not contain chloroplasts.

A student investigated the effect of salt concentration on pieces of potato. The method involved repeating the experiment with different concentrations of salt solution.

What is the independent variable in the investigation?

Why did the student dry the surface of each potato piece with a paper towel in step 5?

The student calculated the percentage change in mass of each potato piece.
For one potato piece:
• the starting mass was 2.5 g
• the end mass was 2.7 g.

Calculate the percentage increase in mass of the potato piece.
Use the equation:
percentage increase in mass = (increase in mass / starting mass) × 100

Maple syrup urine disease (MSUD) is a rare inherited human condition. The allele for MSUD is recessive.

What is a recessive allele?

Figure 1 shows the inheritance of MSUD in one family. The symbol for a male with MSUD is not in the key. What would this symbol represent?

Persons 1 and 2 in Figure 1 have a child with MSUD and some children without MSUD.
Complete the Punnett square (Figure 2) to show the possible genotypes of the children.
Use the following symbols:
N = allele for not having MSUD
n = allele for MSUD

What is the phenotype of a person with the genotype Nn?

What percentage of the offspring in the Punnett square will have MSUD?

Which scientific term describes the allele N?

Alleles are found in the nucleus of a cell. What chemical substance are alleles made from?