Cell Structure (OCR AS Biology)

The image below is a photomicrograph of a mitochondrion.

State the type of microscope used to produce this image.

 [1]

(ii)

Identify the structures labelled M and N in the photomicrograph.

[2]

Describe two ways in which the structure of mitochondrial membranes is related to the function of a mitochondrion.

The endosymbiosis theory suggests that mitochondria may have evolved from bacteria that were taken inside other cells.

These cells then evolved into eukaryotes.

(i)

Give two structural features of mitochondria that support this theory.

[2]

(ii)

Explain why early eukaryotes were able to grow more quickly than cells that did not possess mitochondria.

[3]

Sago pondweed is an underwater plant that grows in many regions of the world.

Fig. 1.1 shows a transmission electron micrograph of a sago pondweed cell.

Fig. 1.1

Identify the cellular components shown at A and B.

[2]

(ii)

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.

[2]

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.

Fig. 1.2

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

 [2]

(iv)

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.

[2]

The onion plant, Allium cepa, is grown as a food crop around the world.

The table below contains statements about the root cells of an onion.

Place ticks (✓) in the boxes in the table to indicate whether the statements are true or false.

Fig. 1 shows a cross section of the root of an onion plant.

Fig. 1

Identify the tissues shown at M and N.

Fig. 1 shows a magnified view of a cell.

Fig. 1

Identify structures L and N in Fig. 1.

Another structure that would be present in the cell in Fig. 1 is the Golgi apparatus.

Describe the function of the Golgi apparatus.

Large numbers of organelle O are found inside neutrophils, a type of white blood cell that carries out phagocytosis.

Suggest why these cells contain large numbers of organelle O.

[1]

(ii)

Explain your answer to part (i).

[2]

Fig. 1 below shows the components of a cell which are responsible for the production of proteins.

Fig. 1

Name the process by which the contents of the vesicle are released in stage 6.

The table below contains descriptions or names of several processes that occur during protein production in cells.

Complete the table by entering the number from Fig. 1 that is associated with the process described.

Numbers can be used once, more than once or not at all.

In prokaryotic cells translation of mRNA can occur while the same piece of mRNA is still being transcribed.

Explain how the features of prokaryote cell structure allow protein synthesis to occur in this way.

Fig. 2 below shows a prokaryotic cell dividing.

Fig. 2

In certain conditions some prokaryotic cells can divide every 25 minutes.

With a starting population of 2.45 × 10³ cells, and assuming that each cell divides every 25 minutes, calculate how many cells there will be after 3.75 hours. Assume that no cells die during this time.

A scientist investigated the lifecycle of the Human Immunodeficiency Virus (HIV). Using a transmission electron microscope, they observed HIV viruses being released from an infected host cell (Figure 1.1). They labelled the image indicating how the replicated particles are released from the cell (“budding”), and the mature form of HIV.

Figure 1.1

In this transmission electron microscope image, the virus indicated with an arrow measures 7mm across. The actual diameter of the virus is 100 nm. 

Calculate the magnification of the image in Figure 1.1. 

Compare the magnification and resolution achieved by a light microscope and a transmission electron microscope.

HIV viruses hijack the machinery of the host cell to replicate themselves. Once the virus proteins are built, immature viruses are assembled and released from the cell in a process called budding.

Suggest and explain which parts of the host cell the virus proteins might use to replicate themselves. 

A student used a light microscope to investigate the presence of white blood cells (WBCs) in a sample of blood. Figure 2.1 shows a micrograph of the sample.

Figure 2.1

Suggest the steps that the student may have taken to visualise the WBCs in their sample. 

White blood cells contain specialised vesicles which carry hydrolytic enzymes.

Explain how white blood cells use these organelles in their cell function. 

Eukaryotic cells contain many membrane-bound cellular components.

Discuss, with examples, the importance of membrane-bound cellular components for cell function. 

Suggest why prokaryotic cells do not have membrane-bound organelles. 

Figure 4.1 shows a diagram of the structure of two centrioles. Centrioles are comprised of microtubules.

Figure 4.1

Compare and contrast the different types of fibres which make up the cytoskeleton. 

Explain the importance of centrioles in animal cells. 

Figure 5.1

A scientist investigated the number of mitochondria in cells taken from barley plant (Hordeum vulgare) leaves. Using a confocal laser scanning microscope, they recorded the number of mitochondria in each cell. They presented their data in a bar chart (Figure 5.1).

Suggest why the number of mitochondria per cell increases as cell size increases. 

The scientist then used flow cytometry to investigate the DNA content of the cells of the barley plant.

Predict how DNA content might change as cell size increases.

It is theorised that mitochondria were once bacteria which were engulfed by other prokaryotic cells. The resulting cells were the first eukaryotic cells. This is called the endosymbiotic theory.

Scientists also theorise that a similar process may have occurred with chloroplasts.

Discuss how the structure of chloroplasts provides evidence in favour of the endosymbiotic theory of chloroplast origin.