A level Bio 2.1 Cell Structure and Microscopy

 Explain why it is not possible to determine the identity of the structures labelled X using an optical microscope. (2) 

Resolution (too) low (1)

Because wavelength of light is (too) long; (1)

Suggest one explanation for the faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration.(2)

(Amino acids used in) protein synthesis (1)

(So) more DNA polymerase (1)

A scientist prepared a culture of a bacterial species.

• She extracted the plasmids and the circular DNA molecules from a sample of cells taken from this culture (A).

• She then added antibiotic X to the culture and let the cells divide for 4 hours.

• She then extracted the plasmids and the circular DNA molecules from a sample of these cells (B).

• The scientist separated the plasmids from the circular DNA molecules in A and in B using ultracentrifugation

What can you conclude from the figure above about a structural difference between the plasmids and the circular DNA? Explain your answer. (2)

Circular DNA is bigger/heavier/denser (1) 

(Because band) moved further/is lower (in tube)/closer to bottom (of tube) (1) 

Describe how a sample of chloroplasts could be isolated from leaves(4) 

Grind the leaves in a cold, isotonic, buffered solution to break open the cells while preventing osmotic damage, and pH changes. (1)
Filter the mixture to remove large pieces of tissue and cell debris. (1)
Centrifuge the filtrate at a low speed to separate out the heavier cell debris. (1)
Collect the supernatant and centrifuge again at a higher speed so the chloroplasts form a pellet at the bottom.(1)

Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell. (2)

Ribosomes (1) 

Are smaller than cytoplasmic ribosomes (1)

The figure below shows transmission electron micrographs of two cells, one animal cell and one prokaryotic cell.

Contrast the structure of the two cells visible in the electron micrographs shown in the figure above. (5)

A has a nucleus whereas B has free DNA (1)

A has mitochondria whereas B does not (1)

A has Golgi body whereas B does not (1)

A has no cell wall whereas B has a murein cell wall (1)

A has linear DNA whereas B has circular DNA (1)

Eukaryotic cells produce and release proteins.

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.

Do not include details of transcription and translation in your answer(4) 

DNA in nucleus is code (for protein) (1) 

Ribosomes/rough endoplasmic reticulum produce (protein) (1) 

Mitochondria produce ATP (for protein synthesis) (1) 

Golgi apparatus package/modify (1) 

Suggest why a nucleus may not be visible in a microscopic image (1)

the nucleus is not stained(1)

Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope.(1)

Higher resolution (1)

The detail shown in the diagram above would not be seen using an optical microscope. Explain why. (2) 

Light has long(er) wavelength (1) 

so lower resolution (1) 

Name the structures labelled W to Z in the diagram.(2) 

W – (cell surface) membrane

X – cell wall

Y – capsule

Z – flagellum

Name the main biological molecule in W and X (2) 

W - Phospholipids

X - Murein

What type of microscope was used to obtain the image shown in the diagram above?

Give one piece of evidence to support your answer.

Scanning electron (microscope) (1)

3D (image) (1)

DNA and RNA can be found in bacteria.

Give two ways in which the nucleotides in DNA are different from the nucleotides in RNA. (2)

DNA contains thymine and RNA contains uracil(1)

DNA contains deoxyribose and RNA contains ribose (1)

Name the parts of the chloroplast labelled A and B. (2)

A-stroma

B-granum

Name two structures in a eukaryotic cell that cannot be identified using an optical microscope. (2) 

Ribosome (1)

Lysosome (1)