Cell Division (Finished)

Question 1

What is a diploid cell

Answer 1

A cell containing two complete sets of chromosomes, one from each parent.

Question 2

What is a haploid cell

Answer 2

A cell containing a single set of chromosomes

Question 3

What type of cells tend to be diploids

Answer 3

Body cells

Question 4

What type of cell tend to be haploid cells

Answer 4

Gametes

Question 5

Define loci

Answer 5

The position of a gene found within the chromosome. Both copies of a gene are found at the same loci of a chromosome

Question 6

Define chromosome number

Answer 6

The number of chromosomes found in each cell of a particular species

Question 7

What are homogeneous chromosomes

Answer 7

Chromosomes which are the same size and carry the same gene at the same loci. (However,they may have different variations of these genes). These pair up.

Question 8

What are homogeneous chromosomes

Answer 8

Chromosomes which are the same size and carry the same gene at the same loci. However,they may have different versions (alleles) of these genes, as one copy is from the mother and one from the father. These pair up.

Question 9

Give the steps for the cell cycle in a eukaryotic cell

Answer 9

Interphase:
-G1
-S
-G2

Mitosis:
-Prophase
-Metaphase
-Anaphase
-Telophase (containing cytokinesis)

Question 10

What happens during G1 in interphase

Answer 10

The cell begins to grow and normal metabolism occurs

Question 11

What happens during S in the interphase

Answer 11

DNA replication

Question 12

What happens during G2 in interphase

Answer 12

More growth and prep for mitosis

Question 13

What happens during prophase

Answer 13

1) chromosomes coil and condense, becoming visible. They appear as two sister chromatids joined at the centromere.

2) Centrioles migrate to the poles of the cell.

3) The nuclear membrane begins to degrades

Question 14

What happens during metaphase

Answer 14

Chromosomes line up on the equator and attach to the spindle fibres by their centromere

Question 15

What happens during anaphase

Answer 15

The spindle fibres shorten (contract), the centromere splits, the sister chromatids are separated and are pulled to opposite poles of the cell (often described as v shaped)

Question 16

What happens during telophase

Answer 16

The chromosomes uncoil and become thinner

The nucleus membrane re-forms

Cytokinesis (division of the cytoplasm) takes place, producing two new cells.

Question 17

Name all the different stages of meiosis

Answer 17

Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

Question 18

Outline what happens during prophase 1 in meiosis

Answer 18

1) DNA condenses and becomes visible as chromosomes.
2) Each chromosome consists of two sister chromatids joined by a centromere.
3) Chromosomes are arranged in homologous pairs. Their non-sister chromatids then ‘cross over’. This leads to exchange of genetic information, creating new combinations of alleles.
4) The centrioles migrate to opposite poles and the spindle fibre is formed.
5) The nuclear membrane begins to break down and the nucleolus disintegrates.

Question 19

Outline what happens during Metaphase 1 in meiosis

Answer 19

The homologous chromosomes pairs align randomly at the equator. This causes independent segregation to occur, as each daughter cell consists of only one of each homologous chromosome pair- which combination they have depends on how they align

Question 20

Outline what happens during anaphase 1 in meiosis

Answer 20

The homologous chromosomes are pulled to opposite poles of the cell by the spindle fibres. This halves the chromosome number of each daughter cell.

Question 21

Outline what happens during telophase 1 in meiosis

Answer 21

The cell divides, and two daughter cells are produced, both haploid, but containing 2 copies of each chromosome (sister chromatids)

Question 22

What happens during metaphase 2 in meiosis

Answer 22

The chromosomes align single file at the equator.

Question 23

What happens during anaphase 2 in meiosis

Answer 23

The sister chromatids are pulled apart to opposite poles of the cell

Question 24

How does cancer happen

Answer 24

Mitosis is a controlled process. If a mutation ( a change in the base sequence of the DNA ) occurs in one of these control genes, the cell cycle is completed quickly and uncontrolled cell division occurs. A tumor develops, and if these cells start to spread into other parts of the body, the tumor is regarded as cancer

Question 25

Explain one way cancer treatments can work

Answer 25

Many cancer treatments are directed at controlling the rate of cell division. These drugs may stop DNA synthesis, spindle formation, cytokinesis or other processes linked to mitosis

Question 26

How do bacteria cells replicate

Answer 26

Binary fission

Question 27

Give 3 cell structures to do with mitosis that prokaryotic cells have but bacteria cells do have

Answer 27

Centrioles Spindle fibres Chromosomes

Question 28

Outline the steps of binary fission

Answer 28

1) Replication of the circular DNA and of plasmids. 2) The cell elongates from the middle, moving the DNA loops to the poles of the cell, 3) The cytoplasm divides and a new cell wall forms. 4) This produces 2 daughter cells, each with a singular copy of the circular DNA and a variable number of copies of plasmids.

Question 29

How does cell division further show us that mitochondria and chloroplasts were once prokaryotes

Answer 29

They replicate by binary fission during interphase

Question 30

Outline how viruses generally replicate

Answer 30

1) Attachment proteins attach to the complimentary receptors in the target cell. 2) They inject their nucleic acid (genetic material) into the host cell. This combines with the host cell DNA and is transcribed. 3) Using the host cell's organelles, the viral proteins are produced. The virus is assembled using these proteins and is released from the cell.

Question 31

Outline how HIV replicates

Answer 31

1) Attachment proteins attach to the receptors on the helper T cells (Helper T cell is the name of the specific type of cell it targets) 2) RNA enters the cell and reverse transcriptase converts the RNA to DNA 3) Viral proteins, such as those involved in the capsid, are produced. 4) Virus particles are assembled and they are released from the cell.

Question 32

What is a retro virus? Give one example.

Answer 32

A virus that contains RNA not DNA. E.g. HIV.

Question 33

Why is reverse transcriptase needed for retro virus replication

Answer 33

Reverse transcriptase turns RNA into DNA so it can alter the cells genetic material with it's own, as cells can only contain DNA

Question 34

Outline how you can find the mitotic index of a plant

Answer 34

1) Add a dye that changes the colour of chromosomal 2) View the plant through a microscope. 3) Count all the cells in mitosis ( all cells with visible chromosomes) in the field of view 4) divide this number by the total number of cells in the field of view 5) repeat this at least 5 times on fields of view selected at random

Question 35

Give 2 ways you can ensure you have an accurate mitotic index

Answer 35

1) examine a large number of fields of view to ensure a representative sample 2) repeat the count on multiple random fields of view to ensure the figures are correct

Question 36

How can you recognise when meiosis occurs in an unfamiliar life cycle

Answer 36

Its when the chromosome number is halved

Question 37

Give the formula to calculate the number of combinations of chromosomes after the random fertilisation of 2 gametes

Answer 37

N is the haploid number (e.g. 23 in humans)

Question 38

What is non disjunction and what does it cause

Answer 38

This occurs during meiosis, as the homologous chromosomes do not seperate (in division one) or sister chromatids do not seperate (In division 2). This causes mutations in the number of chromosomes. This mutation will be found in all cells of any offspring that arise from that gamete after fertilisation, as all cells are derived from the diploid zygote by mitosis, and mitosis produces genetically identical cells

Question 39

Give 2 disorders caused by non disjunction and what positions chromosome do they occur in

Answer 39

Patau Syndrome - Trisomy 13 Downs syndrome - Trisomy 21

Question 40

Outline the differences in mitosis and meiosis (7)

Answer 40

Mitosis produces genetically identical clones but meiosis produces genetic variation between the daughter cells Mitosis involves one nuclear division but meiosis involves 2 nuclear divisions Mitosis produces 2 daughter cells but Meiosis produces 4 daughter cells Mitosis is used in asexual reproduction but Meiosis is used in sexual production Mitosis doesn't involve crossing over but Meiosis does Mitosis doesn't involve independent segregation but meiosis does In mitosis, the chromosome number is maintained , but in Meiosis, the chromosome number is halved