I. Choose the right answer:
1. Bacteria divides to produce daughter cells by the process of _________
a. Mitosis c. Binary fission
b. Meiosis d. None of them
2. During meiosis gametes produced have _________number of chromosome.
a. Diploid c. both of them
b. Haploid d. None of them
3. Sister chromatids are aligned in the centre of the cell during _________stage
a. Prophase c. Telophase
b. Metaphase d. Anaphase
4. Chromosomes attach to fibers at structures called __________________.
a. Telomeres c. Centromeres
b. Genes d. neither of them
5. Which of the following is not a function of mitosis in humans?
a. Repair of wounds c. Production of gametes
b. growth d. Replacement of lost cells
6. A biochemist measures the amount of DNA in cells growing in the lab. The quantity of DNA in a cell would be found double
a. Between prophase and anaphase c. Between metaphase and telophase
b. between G1 and G2 of cell cycle d. during M phase of cell cycle
7. In comparing somatic cells and gametes, somatic cells are
a. diploid with half the number of chromosomes
b. haploid with half the number of chromosomes
c. diploid with twice the number of chromosomes
d. haploid with twice the number of chromosomes
8. What are homologous chromosomes?
a. two halves of a replicated chromosomes
b, two identical chromosomes from one parent
c. two identical chromosomes, one from each parent
d. Two similar chromosomes, one from each parent.
9. Duplicated chromosomes consist of two identical DNA double helices, called __________.
a. Homologous c. Sister Chromatids
b. Chromatin strands d. neither of them
II. Answer whether true or false: (0.25 points each)
1. Diploid means n chromosomes and haploid means 2n chromosomes.
2. If an intestinal cell in a dog contains 78 chromosomes, a dog sperm cell would contain ______chromosomes
3. A micrograph of a dividing mouse cell shows 19 chromosomes each consisting of two sister chromatids. During which stage of meiosis could this picture be taken,
4. Meiosis is a cell division that occurs only in sex cells
5. Prophase is the last stage in mitosis where the two daughter cells separate
6. Cell cycle involves the G1, S and G2 phase only.
7. Cytokinesis in plant cells takes place by the formation of cell plate
8. Movement of sister chromatids to the same pole occurs in meiosis.
9. During meiosis there is only one round of replication for two divisions
10. Gametes are diploid with double the number of chromosomes
III. Answer any four of the following ( each carries 1.5 mark)
1. Diagram and describe the eukaryotic cell cycle. Name the various phases, and briefly describe the events that occur during each.
LABEL THE PARTS FROM PRESENTATION OR TEXT
1. Eukaryotic cell cycle is divided into two major phases: interphase and cell division
2. Interphase is the stage where the cell acquires nutrients from its environment, grows and duplicates its chromosomes it contains three sub phases
G1_ a newly formed daughter cell enters this stage, and carries out activities like: it grows in size, specializes to perform specific function and it decides whether to divide or not, and enters the next phase
S-phase: DNA synthesis takes place via semiconservative replication
G2: cell grows some more and then synthesize the proteins needed for cell division.
Cell division: cell carries out either mitosis or meiosis’ in order to form new daughter cells
2. Explain the process of Mitosis.
Mitosis consists of nuclear division followed by cytoplasmic division.
Mitosis occurs in the following phases
1: Prophase is the first phase, duplicated chromosome condense, spindle microtubules form , chromosomes are captured by microtubules
2 : Metaphase – duplicated chromosome are connected to spindle fibers leading to opposite poles of the cell. Microtubules shorted and lengthen until each chromosome lines up along the equator of the cell
3: Anaphase- sister chromatids formed during S-phase separates becoming independent daughter chromosomes, one of the 2 daughter chromosomes from each original parental chromosomes move to each pole of the cell
4: telophase- spindle fibers disintegrate nuclear envelope forms around each group of chromosome. The DNA revert to its original extended state, nucleoli begin to form
5: cytokinesis- microfilaments attached to membrane form a ring around the equator of the cell, constricts dividing the cell, in plants cell plate is formed forming 2 daughter cells
3. Compare the process of cytokinesis in plant cell and animal cell.
Cytokinesis in animal cells
a. Microfilaments attached to the plasma membrane form a ring around the equator of a cell . The ring contracts and constricts the cell’s equator
b. Eventually, contraction of the ring pinches off the membrane, forming two daughter cells, each with a nucleus identical with the other
c. Following cytokinesis, animal cells enter G1 of interphase, thus completing the cell cycle
Cytokinesis in plant cells
a. Stiff plant cell walls prevent the “pinching off” of cytokinesis seen in animal cells, which only have a plasma membrane
b. Instead, carbohydrate-filled vesicles assemble along the cell’s equator, between the daughter nuclei
c.The vesicles fuse into a continuous flattened sac, surrounded by plasma membrane and filled with sticky carbohydrates .This is called a cell plate
d. The plasma membranes of the plate fuse with the plasma membrane of the cell, forming two cells, with the carbohydrate in between becoming part of the cell wall
e. As in animals, plant cells enter G1 of interphase following cytokinesis, thus completing the cell cycle
4. Describe in humans the three categories of cells, based on their ability to divide and differentiate
1.Stem cells :
– have two important characteristics: self-renewal, and the ability to differentiate into a variety of cell types
-Stem cells self-renew because they retain the ability to divide, perhaps for the entire life of the organism
-Some stem cells in early embryos can produce any of the specialized cell types of the entire body
2.Other cells capable of dividing
-Some cells other than stem cells are capable of continuing to divide, but typically differentiate into only one or two different cell types
· Dividing liver cells, for example, can only become more liver cells
3. Permanently differentiated cells
· Permanently differentiated cells differentiate and never divide again
· For example, most heart and brain cells cannot divide
5. Complete the following table to compare mitosis and meiosis
|a. Number of chromosomal duplications|
|b. Number of cell divisions|
|c. Number of daughter cells produced|
|d. Number of chromosomes in daughter cells|
|e. How chromosomes line up during metaphase|
|f. Genetic relationship of daughter cells to parent cells|
|g. functions performed in the human body|