Cell Structure (Edexcel GCSE Biology: Combined Science)

Cells can be specialised to perform a particular function.

Human gametes are specialised cells adapted to their role in fertilisation.

Describe three adaptations of a human sperm cell that enables it to carry out its role in fertilisation.

Human egg cells are specialised for the function of propagation of life. One adaptation is that they contain a predominantly large cytoplasm.

Explain why the following statement about light microscopes is incorrect.

Figure 1 below shows a cross section of a leaf taken using an optical microscope with a magnification of ×250. 

Figure 1

The image size of a palisade cell is given as 2 cm as marked by the scale bar line A on Figure 1. Use the information provided to calculate the actual length of the palisade cell. Give your answer in μm.

Figure 2 below shows an image of a bacterial cell taken with an electron microscope.

Figure 2

The width of the bacterial cell is estimated at 1 µm. The bacterial cell is 2 cm wide in the image.

Calculate the magnification of the image.

Describe how electron microscopes are different to light microscopes. 

Place the following values in order from smallest to largest size.

Figure 1 shows information about the magnification of a light microscope.

Figure 1

Complete the empty cells in Figure 1. 

A mitochondria has a diameter of 1 µm. What is the diameter in nm?

The diameter of a yeast cell is 10 µm and the diameter of a bacterial flagellum is 10 nm. How many orders of magnitude difference exist between the two diameters...

The potatoes of a potato plant develop underground.

Explain one difference in the sub-cellular structures in a cell in the potato and those in a cell in the leaf of the potato plant.

Figure 1 shows a root tip with cells in different stages of mitosis.

The image was magnified 400 ×.

Figure 1

Explain how a magnification of 400 × can be obtained using the lenses on a light microscope.

A student cut a piece of onion and placed it on a microscope slide.

The student then placed this slide on the stage of a light microscope and looked through the eyepiece.

 No cells could be seen in the piece of onion.

 Explain two ways this method could be improved to see details of the onion cells.

Figure 1 shows mitosis occurring in some plant cells.

Explain one advantage of using an electron microscope to observe plant cells.

Figure 1 shows a cyanobacterium magnified 50000 times.

The line AB shows the diameter of the bacterial cell.

Figure 1

(3)

........................................ μm

(3)

Figure 1 shows two sperm cells.

Figure 1 shows some muscle cells and their sub cellular structures.

Figure 1

Describe the function of the nucleus.

(2)

Suggest why the muscle cell has so many mitochondria.

(2)

Mitochondria are organelles that are too small to be seen using a light microscope.

The electron micrograph shows a mitochondrion that has been magnified.

The actual length of this mitochondrion at the point being measured is 5 μm.

[1 μm = 0.001 mm]

Calculate the magnification of this electron micrograph.

The table gives information about mitochondria in different human cells.

What is the mean number of mitochondria per μm³ in a heart muscle cell?

(1)

Comment on the differences in the data for the sperm and for the egg.

(3)

The image below is an electron microscope photograph of a cell.

Name the group of organisms from which the cell shown in the image has been taken.

(1)

Explain how you identified the group of organisms in part (i).

(1)

Structure Y in part (a) is a starch granule.

Explain why structure Y is present inside structure X in the image in part (a).

Name three structures that are not clearly identifiable in the image in part (a) that you would expect to find inside cells from this group of organisms.

The cell in part (a) has been magnified 7.5 x 10³ times, and the image of the nucleus has a diameter of 6.5 cm.

Use the formula below to calculate the actual diameter of the nucleus. Give your answer in μm.

Note that 1 μm = 0.001 mm 

The image below is a representation of an electron microscope photograph of part of a sperm cell.

Name structures X, Y and Z labelled in the image.

Label two additional features on the image in part (a) with descriptions that explain how the features aid the sperm cell in its function.

The diagram below shows three different cells.

Calculate the size ratio of the bacterial cell compared to the liver cell and mesophyll cell.

The electron microscope image below shows a section from the inside of a liver cell...

Bochimoto H, Matsuno N, Ishihara Y, Shonaka T, Koga D, Hira Y, et al., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons

Name the organelles indicated by X.

(1)

Use the information in the image to suggest the possible cell activities that take place inside a liver cell.

(2)

A group of scientists carried out a study to investigate the starch content of roots in a species of grass at four points throughout the year. 

Their results can be seen in the graph below.

Explain why the grass roots contain starch.

(2)

Explain how the starch found in the roots of grass species helps to support the growth of the grasses.

Calculate the percentage change in stored starch from January to October in the graph in part (b).

(2)

Suggest an explanation for the change calculated in part (i).