Topic 3: Cell Structure, Reproduction and Development

Question 1

Explain why J can be seen using the electron microscope but not the light microscope

Answer 1

• because electron microscope has a high magnification
• because this structure is small

Question 2

Explain why the nuclear envelope cannot be seen as two membranes using this electron microscope

Answer 2

• two membranes are close together
• resolution of this microscope is not high enough.

Question 3

The student describe one organelle that was seen as “several curved membrane-bound sacs decreasing in size (1)

Answer 3

B- golgi apparatus

Question 4

(ii) Explain why this organelle cannot be seen using a light microscope.
(2)

Answer 4

because the magnification of the light microscope is not high enough
because it is very small.

Question 5

Give two differences between an organ and a tissue

Answer 5

1- Organ has many functions whereas a tissue has fewer
2- Organ has several groups of cell types whereas a tissue has one cell type.

Question 6

(b) Plant cells can also be studied using an electron microscope.
Name two structures present in animal cells that are not present in a plant cell.
(2)

Answer 6

• flagellum
• cilia

Question 7

State the function of these cells:
Slimy capsule
Pili

Answer 7

Slimy capsule prevents dehydration of the cell.
Pili allows bacteria to adhere to surfaces.

Question 8

Name three structures found in a prokaryotic cell but not in a eukaryotic cell.
(3)

Answer 8

1. plasmid
2. pili
3. slimy capsule

Question 9

Describe what occurs during prophase (4 marks)

Answer 9

• chromatin condenses
• chromosome becomes visible
• nuclear envelope breaking down.
• centrioles moving to poles.
• nucleolus disappears.

Question 10

Describe the process of crossing over. (3 marks)

Answer 10

• homologous chromosomes pair up.
• chromatids from a pair of chromosomes overlap.
• chiasmata break in chromatid.
• recombination of chromatids.

Question 11

Explain what is meant by the term chromatid

Answer 11

one of two DNA molecules that make up a chromosome.
DNA replicates in S phase.

Question 12

Explain why several divisions of mitosis are involved in the production of sperm cells.

Answer 12

• to increase the number of primary spermatocytes.
• there is are many sperm cells produced.

Question 13

1.Heat the root tip of the acid
2. warm gently to intensify the stain.
3. press down gently on the cells.
4. cover with a glass coverslip
5. add the stain to the root tip
6. tease the cell apart.

What is the correct order for these steps.
A. 1,5,6,4,3,2
B. 1,6,3,4,5,2
C. 5,2,6,1,4,3,
D.6,1,5,4,3,2

Answer 13

A - 1,5,6,4,3,2

Question 14

Describe the role of the rough endoplasmic reticulum

Answer 14

for protein synthesis
to fold the protein
for protein transport
to package the protein into vesicles.

Question 15

Explain the importance of mitosis in budding

Answer 15

• mitosis result in two cells that each have a nucleus.
• each bud contains a full set of chromosome.
• so each bud are genetically identical to the parent yeast cell.

Question 16

Explain the role of meiosis in the production of genetically varied sperm cells. (5 marks)

Answer 16

• to produce haploid cells
• chiasmata break in chromatid which leads to the formation of chromatids.
• homologous chromosomes maternal and paternal chromosomes line up in different combinations.
• New combinations of alleles in the gametes.

Question 17

Describe the structure of plasmodesmata.

Answer 17

• pores in the cell wall between adjacent cells.
• there is cytoplasm running through the plasmodesmata.

Question 18

Describe the role of structure S

Answer 18

• structure S is flagellum enabling the sperm to swim.
• to transfer the male genetic material from the cervix to the ovum.

Question 19

Give two difference other than size between the structure of a sperm cell and the structure of a female gamete (2)

Answer 19

Sperm cell has flagellum whilst female gamete does not have.
Sperm cell has an acrosome but a female gamete does not have.

Question 20

Compare mitosis with meiosis (3)

Answer 20

• mitosis produces two cells but meiosis produces four cells.
• mitosis produces diploid cells but meiosis produces haploid cells.
• no crossing over in mitosis but there is in meiosis.

Question 21

Describe the process of fertilisation in mammals.

Answer 21

release of enzymes from sperm.
sperm digests the zona pellucida
fusion of sperm cell and female gamete membrane.
cortical reaction occurs allowing the zona pellucida to harden.