Cell and Nuclear Division

Question 1

List The Functions of Cell Division.

Answer 1

• Growth
• Repair of Tissues and Organs
• Maintenance to Replace Dead or Dying TIssues

The cycle cycle takes 12-24 hours for animal cells.

Question 2

Define Mitosis.

Answer 2

Parent cells divide into two genetically identical daughter cells.

Question 3

Results of Mitosis.

Answer 3

• Two daughter cells are identical to the mother cell.
• Mitosis ensures that all body cells have a complete number and form of chromosomes (all human cells resulting from mitosis will be diploid, 2n = 43).

Note: Mitosis occurs in somatic cells (a plant or animal cell that forms the body of the organism; excludes reproductive cells).

Question 4

Interphase:
G1 Phase (1)

Answer 4

• Growth
• Increase the amount of cytoplasm and organelles.

Question 5

Interphase:
S Phase (2)

Answer 5

• DNA Replication
• Ensures that new cells have equal amounts of DNA.

Question 6

Interphase:
G2 Phase (3)

Answer 6

• Growth
• Organelles for division and mitochondria are formed.
• Centrioles are duplicated.

Question 7

Interphase

Answer 7

• DNA exists as a chromatin.
• Nucleolus is surrounded by a nuclear envelope.
• In G2, centrioles are duplicated.

Question 8

Prophase

Answer 8

• Chromatin supercoils into chromosomes.
• Nuclear membrane breaks down.
• Centrioles move to opposite poles of the cell and sprout microtubules.

Note: Two chromosome arms are called sister chromatids and the chromosomes are joined at the centromeres.

Question 9

Metaphase

Answer 9

• Microtubules (spindle fibres) attach to the centromere (kinetochore proteins) and guide the chromosomes to the metaphase plate.

Note: The metaphase plate is the center of the cell.

Question 10

Anaphase

Answer 10

• Sister chromatids are separated and moved to opposite poles by microtubules.
• Separated sister chromatids are now refered to as chromosomes.
• Each pole has a complete set of chromosomes.

Question 11

Telophase

Answer 11

• Chromosomes reach opposite ends of the cell.
• Chromosomes start to unwind and become chromatin.
• Microtubules break down.
• Nuclear membrane reforms.

Question 12

Cytokinesis

Answer 12

• The cytoplasm of a cell is divided between the two daughter cells.
• Can begin as soon as chromosomes are separated and are far enough apart to ensure none end up in the wrong cell.
• All cytoplasm and the contents of the mother cell are shared between the two daughter cells.

Note: Cytokinesis is different in plant and animal cells.

Question 13

Sometimes there in unequal sharing of the cytoplasm.

Outline One Scenario.

Answer 13

Oogenesis (egg) produces 4 haploid cells (n):
* 3 out of 4 of the cells donate their cytoplasm organelles to the 4th because they are much too small to produce a zygote
* This unequal cytokinesis provides the zygote with the resources that are needed to survive until it is implanted in the walls of the uterus.

Question 14

Cytokinesis in Animal Cells.

Answer 14

• Contractile proteins, actin and myosin pinch the cell along its equator.
• Meaning, it forms a cleavage furrow.

Note: A cleavage furrow “draws the plasma membrane toward the cell center, pinching the cytoplasm into two lobes that are subsequently separated into two cells.”

Question 15

Cytokinesis in Plant Cells.

Answer 15

• Vesicles move to the equator where they fuse to form tubular structures.
• More vesicles fuse and these tubular structures merge to form two layers of membrane across the whole equator which develops into the membranes of the new daughter cells.
• Pectin is brought in vesicles and deposited by exocytosis between the two membranes.
• Cellulose is deposited by exocytosis to form the cell wall.

Note:
* Pectin is “any of a group of water-soluble carbohydrate substances that are found in the cell walls and intercellular tissues of certain plants.”
* Cellulose is “a molecule, consisting of hundreds – and sometimes even thousands – of carbon, hydrogen and oxygen atoms. It is the main substance in the walls of plant cells.”

Question 16

Define Tumors.

Answer 16

An Abnormal Group of Cells.

Question 17

Define Benign Tumors.

Answer 17

Cells ‘stick’ to each other and do not invade nearby tissues or move to other parts.

Question 18

Define Maligant Tumors.

Answer 18

Cells become detached and move elsewhere in the body and develop into secondary tumors.

Question 19

Define Carcinogens.

Answer 19

Cancer causing chemicals, such as viruses, mutagens, and x-rays.

Question 20

Define Mutagens.

Answer 20

Agents that cause gene mutations.

Note: Mutagens can cause cancer.

Question 21

Define Mutations.

Answer 21

Random changes to the DNA sequence (essentially, ‘spelling mistakes’ in the DNA).

Question 22

Define Oncogenes.

Answer 22

• Most genes do not cause cancer when they mutate.
• The few that can become cancer-causing after mutating are known as oncogenes.
• Oncogenes are involved in the control of the cell cycle and cell division.

Question 23

Define Primary Tumors.

Answer 23

• Several mutations must occur in the same cell for it to become a tumor.
• When a tumor cell has been formed, it divides repeatedly.
• This group of cells is called a primary tumor.

Question 24

Define Metastasis.

Answer 24

The movement of cells from a primary tumor to set up secondary tumors in other parts of the body.