B3 - Cell structure

Question 1

The figure below shows transmission electron microscope micrographs of two cells, one animal cell and one prokaryotic cell. Contrast the structure of the two cells visible in the electron micrograph shown in figures above.

Answer 1

1. magnification shows A is larger than B
2. A has a nucleus, whereas B has free DNA
3. A has mitochondria, whereas B does not
4. A has a Golgi body/ endoplasmic reticulum, whereas B does not
5. A has no cell wall, whereas B has a murrain/ glycoprotein cell wall
6. A has no capsule, whereas B has a capsule
7. A has DNA bound to histones/proteins, whereas B has DNA not associated with histones/proteins OR A has a linear DNA, whereas B has circular DNA
8. A has larger ribosomes

Question 2

Contrast the structure of a bacterial cell and the structure of a human cell.

Answer 2

1. Bacterial cell is smaller than human cell
2. Bacterial cell has a cell wall, human cell does not
3. Bacterial cell does not have a nucleus, human cell has a nucleus
4. Bacterial cell does not have membrane bound organelles, human cell organelles are membrane bound
5. Bacterial ribosomes are smaller than human ribosomes
6. Bacterial DNA is circular, human DNA is bound to histones

Question 3

Compare and contrast the DNA in eukaryotic cells with that in prokaryotic cells.

Answer 3

Comparisons:
1. Nucleotide structure is identical
2. Nucleotides joined by phosphodiester bonds OR deoxyribose joined to phosphate
3. DNA in mitochondria/ chloroplasts are same

Contrasts:
4. Eukaryotic DNA is longer
5. Eukaryotic DNa contains introns, prokaryotic DNA does not
6. Eukaryotic DNA is linear, prokaryotic DNA is circular
7. Eukaryotic DNA is associated with histones, prokaryotic DNA is not

Question 4

Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.

Answer 4

1. Chromosomes shorten/ thicken
2. Chromosomes two identical chromatids (due to replication)
3. Chromosomes/ chromatids move to equator/ middle of spindle
4. Chromatids attach to individual spindle fibres
5. Spindle fibres contract/ centromeres divide
6. Chromatids move to opposite poles of the spindle
7. Each pole receives all genetic information/ identical copies of each chromosome
8. Nuclear envelope forms around each group of chromosome (chromatids) at each pole

Question 5

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 5

Prophase:
1. Chromosomes
2. Condense/ shorten/ thicken/ become visible

Metaphase:
13. Chromosome line up on the equator/ centre of cell
4. Chromosomes attached to spindle fibres
5. By their centromere

Anaphase:
6. Centromere splits/ divides
7. Sister chromatids/ chromosomes are pulled to opposite poles/ ends of the cell

Telophase:
8. Chromatids/ chromsomes uncoil/ unwind/ become longer/ thinner