Ch 11 Cell cycle and division

Question 1

Interphase

Answer 1

The cell prepares for cell division
1. It synthesizes proteins and produces new organelles
2. It grows to its maximum size

Question 2

Mitotic cell division

Answer 2

Interphase
- DNA is replicated
- Chromosomes are not visible

Prophase
- Chromosomes shorten and thicken. They become visible.
- The nuclear membrane breaks down

Metaphase
- The chromosomes line up in the equator
- Spindle fibres attach to the chromosomes

Anaphase
- The spindle fibres contract. The sister chromatids separate and move the opposite poles of the cell.
- They cytoplasm starts to divide

Telophase
- A new nuclear membrane forms around each group of chromosomes
- The chromosomes uncoil to become chromatin again

Cytokinesis
Animal cells: cell membrane constricts inwards until the cell splits into two
Plant cells: cell plate mae up of new cell membranes and cell walls is formed between two daughter nuclei. Cell plate grows outwards, dividing the cell into two

Question 3

Importance of mitotic cell division

Answer 3

1. Growth: it provides new cells for the growth of multicellular organsims
2. It provides new cells for replacing worn-out cells or repairing damaged tissues
3. Asexual reproduction: the offspring produced are genetically identical to their parent

Question 4

Meiotic cell division

Answer 4

Interphase
- DNA is replicated
- Chromosomes are not visible

Prophase I
- Chromosomes shorten and thicken. They become visble
- Homologous chromosomes pair up
- Crossing over may occur
- The nuclear membrane breaks down

Metaphase I
- Homologous pair line up along the equator
- Spindle fibres attach to the chromosomes

Anaphase I
- The spindle fibres contract. The two membres of each homologous pair separate and move to opposite poles of the cell
- The cytoplasm starts to divide

Telophase I
- A new nuclear membrane forms around each group of chromosomes

Cytokinesis
- Two haploid daughter cells with duplicated chromosomes are formed

Prophase II
- The nuclear membranes break down again

Metaphase II
- The chromosomes line up along the equator
- New spindle fibres attach to the chromosomes

Anaphase II
- The spindle fibres contract. The sister chromatids separate and move to the opposite poles of the cells
- The cytoplasm starts to divide

Telophase II
- A new nuclear membrane forms around each group of chromosomes
- The chromosomes uncoil to become chromatin again

Cytokinesis
- Four haploid daughter cells are formed

Question 5

Importance of meiotic cell division

Answer 5

1. Producing haploid gametes for sexual reproduction. When the male gamete and the female gamete fuse during fertilization to form a zygote, the diploid number of chromosomes is restored. This allows a species to preserve a constant number of chromosomes from generation to generation
2. Producing genetic variations in gametes by independent assortment of chromosomes and crossing over. Fusion of male and female gametes during fertilization produces individuals with different genetic combinations. Genetic variations among individuals of the same species increase the chance for the species to survive when environmental conditions change

Question 6

Interpreting a graph of DNA content in a cell against time

Question 7

Importance of homologous chromosomes pair lining up along the equator

Answer 7

• Homologous chromosomes pair up when they arrange themselves on the equator of the cell, after separation, the gametes formed would have only one member of each homologous pair
• Crossing over occurs between homologous chromosomes / Homologous chromosomes assort themselves independently, resulting in variation in gametes