8. Cell division

Question 1

What is the process of binary fission?

Answer 1

1. The bacterial chromosome is attached tp the plasma membrane.
2. The chromosomal DNA replicates and the attachment points separate as the cell grows
3. The cells begin to divide
4. Fission

Question 2

What are the advantages and disadvantages of asexual reproduction?

Answer 2

ADVANTAGE: A large number of individuals can be produced very quickly, ideal for an unchanging environment.
DISADVANTAGE: lacks genetic variation in population (if environment changes for the worst all individuals die)

Question 3

What is sexual reproduction?

Answer 3

A process where new individuals are formed from the fusion of sex cells or gametes, egg and sperm or pollen, and form a zygote. All organisms have the ability to undergo sexual reproduction (even prokaryotes). Genetically unique individuals are produced for, genetically unique gametes

Question 4

What are the advantages and disadvantages of sexual reproduction?

Answer 4

ADVANTAGE: produces genetic variation in offspring, ideal for a changing environment
DISADVANTAGE: need to find a mate, process is slow and signals sent to prospective mate may attract predators

Question 5

What is diploid and haploid?

Answer 5

DIPLOID- refers to organisms or cells that have two copies of each specific chromosomes, pairs
HAPLOID- refers to organisms or cells that only have one copy of each specific chromosome.

Question 6

What is the cell cycle?

Answer 6

The mechanism through which somatic cells of eukaryotes can divide producing two daughter cells which are genetically identical to each other and the parent cell for one parent cell.

Question 7

What are the key events of the cell cycle

Answer 7

Interphase: reproduction of DNA by parent cell
Mitosis: organisation of chromosome followed by their separation into two identical groups at different poles of the parent cell.
Cytokinesis: division of parent cells into two identical daughter cells

Question 8

What are the three stages of interphase?

Answer 8

Gap 1
Synthesis
Gap 2

Question 9

What is the gap 1 stage of interphase?

Answer 9

• Cell undergoes growth increasing the cell cytosol, synthesising proteins that are needed for DNA replication.
• The mitochondria of the cell divide and in the cases of photosynthetic plants, their chloroplasts also divide..
• It is near the end of this stage that the cell will either commit to continuing the cell cycle or will drop out and not divide. If the latter occurs the cell enters a non dividing quiscent g0 stage.

Question 10

What is the genetic material like in the G1 phase?

Answer 10

During G1, each chromosome is a single, unreplicated DNA molecule with associated proteins

Question 11

What happens in the G1 to S transition

Answer 11

The commitment is made to DNA replication and subsequent cell dividion

Question 12

What happens during the S phase of mitosis?

Answer 12

• DNA réplication occurs
• Each chromosome is duplicated and thereafter consists of two sister chromatids which remain joined together until mitosis when they segregate into two daughter cells.

Question 13

What is the gap 2 stage of intephase?

Answer 13

Further growth of the cell occurs in preparation for division. In addition the synthesis of proteins occurs including those that form the microtubules of the spindle. By the end of interphase the cell had doubled its size.

Question 14

What is a chromatin?

Answer 14

The complex of DNA and proteins

Question 15

What are the stages of mitosis?

Answer 15

PROPHASE:
Metaphase
Anaphase
Telophase

Question 16

What are the checkpoints in the cell cycle

Answer 16

G1-check of the DNA to ensure that it is not damaged or incomplete.

G2-replicated DNA of the cell is checked for completeness and lack of damage.

M-ensures that the sister chromatids are attached to the correct microtubules of the spindle

Question 17

What is the centromere?

Answer 17

The region where sister chromatids join

Question 18

What is the centrosome?

Answer 18

The major microtubule organising center of an animal cell

Question 19

What is the nucleosome?

Answer 19

A portion of eukaryotic chromosome consisting of DNA molecule wrapped around histone molecules

Question 20

What happens in prophase?

Answer 20

The chcromatin continues to coil and super coil making the chromatin more and more compact. The chromosomes consist of identical, paired chromatids

Question 21

What happens in Prometaphase?

Answer 21

The nuclear envelope breaks down. Kinetochore microtubules appear and connect the kinetochores with the centrosomes, resulting in movement of the chromosomes

Question 22

What happens in metaphase?

Answer 22

The duplicated centromere regions connecting paired chromatids become aligned in a plane at the cell’s equator

Question 23

What is the process of anaphase?

Answer 23

The centromere pairs separate, and the new chromosomes (each derived from one member of one of the sets of paired chromatids) begin to move towards the poled

Question 24

What happens in telophase?

Answer 24

The separating chromosomes reach the poles. Telophase passes into the next interphase as the nuclear envelopes and nucleoli reform and the chromatin becomes diffuse

Question 25

What is cytokinesis?

Answer 25

The final stage of cell division following mitosis when the cytosol and organelles surround each nucleus and are distributed around the new nuclei.

Question 26

What is the difference between animal and plant cells during cytokinesis?

Answer 26

ANIMAL-the bridge of cytoplasm between the two nuclei narrows as the plasma membrane pinches in to separate the nuclei and cytoplasm into the 2 new cells.

PLANT-A new cell plate forms between two groups of chromosomes and develops into a new cell wall for each of the newly produced cells.

Question 27

What happens at interphase in meiosis?

Answer 27

DNA replicated during which each chromosome replicates. Each chromosome is now two genetically identical up separated sister chromatids.

Question 28

What happens at prophase 1 of meiosis?

Answer 28

The chromosomes condense. The homologues each consisting of two sister chromatids, pair up through synapsids to form bivalents. At this stage segments of chromosomes can be exchanged in a process called crossing over.

Question 29

Metaphase 1 meiosis

Answer 29

The bivalents line up at the equator, metaphase plate in a random way resulting in independent assortment of maternal and paternal chromosomes.

Question 30

Anaphase 1 meiosis

Answer 30

Chromosomes from each pair move to opposite poles of the cell. The centromere of the chromosomes does not divide so each chromosome still consists of two sister chromatids which may not be genetically identical due to crossing over.

Question 31

What is crossing over?

Answer 31

At prophase 1, homologous chromosomes align and pair closely, synapses. Exchanges between a matching segment of one chromosome occur with a strand in its paired homologues. Crossing over produces new combinations of genetic instructions.

Question 32

What is independent assortment?

Answer 32

During meiosis the random separation of genes carried on non-homologous chromosomes into gametes so that inheritance of these genes is random

Question 33

What is chiasma?

Answer 33

The pairing of homologues allows chiasma to form between the chromatids of homologous chromosomes. These are places where the chromatids becomes Criss crossed and the chromosomes exchange segments.

Question 34

What is the first stage where meiosis differs from mitosis?

Answer 34

In prophase I in meiosis the chromosomes attach to the membrane of the nucleus and pair up with their corresponding chromosomes. In mitosis this does not occur as each chromosome is an identical copy.

Question 35

Difference between meiosis and mitosis, metaphase and anaphase I

Answer 35

In metaphase I of mitosis, the chromosomes line up on the metaphase plate as the fibres begin to tug each chromosome toward opposite ends of the cell. In meiosis the chromosomes line up on either side of the metaphase plate. In anaphase I of mitosis the fibres pull the chromatids towards opposite ends of the cell but in meiosis the chromosome pairs separate half.