Cell division

Question 1

What are the three stages of cell cycle?

Answer 1

Interphase - This occupies the majority of the cycle as cells prepare for division.
Mitosis - This is when the nucleus of the cell divides in two.
Cytokinesis - This is when the whole cell and cytoplasm divides in two to produce two identical cells.

Question 2

What happens during interphase, to include the G1 G2 and S phase.

Answer 2

During interphase, preparing for cell division occurs. This involves replicating the DNA and organelles.
1. G1 phase - This is when the cell grows and makes new proteins to replicate organelles.
2. S phase - This is when DNA is replicated.
3. G2 phase - This is when the cell continues to grow and replicated DNA is checked for errors.

Question 3

How is cell cycle regulated?

Answer 3

1. G1 checkpoint - This checks that the cell has the chemicals needed for replication and checks all needed organelles have been replicated
2. G2 checkpoint - This checks that DNA has been replicated without any errors (if errors are found, the cell tries to repair them).
3. Metaphase checkpoint - Each chromosome is checked to ensure it is attached to the spindle.

Question 4

What is mitosis?

Answer 4

Mitosis is a type of cell division in which a parent cell divides to produce two genetically identical daughter cells. Each of these daughter cell contains the same DNA as the original parent cell.

Question 5

Stages of mitosis (prophase).

Answer 5

1. The chromosomes condense (become shorter and thicker) and are now visible.
2. Centrioles (bundles of protein) migrate to opposite poles (sides) of the cell. Each centriole starts forming spindle fibres.
3. The nucleolus disappears and the nuclear envelope starts to break down, leaving the chromosomes free in the cytoplasm.

Question 6

Stages of mitosis (Metaphase)

Answer 6

1. The chromosomes line up at the equator (middle) of the cell.
2. Each chromosome attaches to the spindle by their centromere.
3. At the metaphase checkpoint, each chromosome is checked to ensure it is attached to the spindle.

Question 7

Stages of mitosis (Anaphase)

Answer 7

1. The centromeres divide to separate each pair of sister chromatids.
2. The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell.

Question 8

Stages of mitosis (Telophase)

Answer 8

1. The chromatids reach the opposite poles of the cell where they uncoil to become long and thin chromosomes again.
2. A nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform.

Question 9

What is the importance of mitosis in life?

Answer 9

Mitosis is used by multicellular organisms for many processes, including:
1. Growth - Unicellular zygotes can divide by mitosis to form multicellular organisms.
2. Replacement of damaged or dead tissues - Cells are constantly dying and being replaced using mitosis.
3. Asexual reproduction - Some organisms reproduce using mitosis to form genetically identical offspring.
4. Development of body plans - Mitosis is used to form the different parts of an organism.
5. Production of stem cells - Stem cells divide by mitosis.

Question 10

What is the importance of meiosis?

Answer 10

This type of cell division serves two important roles:
1. Production of haploid gametes - This allows sexual reproduction to take place.
2. Creates genetic variation - This increases diversity, allowing natural sel

Question 11

What are the two events that take place to allow genetic variation in meiosis?

Answer 11

Crossing over (or recombination)
Independent segregation (or random assortment)

Question 12

How does crossing over cause genetic variation?

Answer 12

Occurs during prophase I of meiosis:
Steps of crossing over:
1. During prophase I, the homologous chromosomes condense and pair up.
2. The chromatids of each chromosome then twist around one another, forming a chiasmata.
3. When the chromosomes are separated during anaphase I, the chromatids break at the chiasmata and then reconnect to the chromatid from the homologous chromosome.

This swaps alleles between the homologous chromosomes to produce different combinations on each chromosome. Each cell has a different chromatid (and a different set of alleles), increasing the genetic variation of the offspring.

Question 13

How does independent segregation ( random assortment) cause genetic variation?

Answer 13

During metaphase I, pairs of homologous chromosomes line up along the cell’s equator. However, whether the paternal or maternal chromosomes appears on the left or right is completely random. As a result, which chromosomes end up in each daughter cell is also random. This principle is known as independent segregation or random assortment.

Question 14

Stages of meiosis ( Prophase I)

Answer 14

The chromosomes condense and homologous chromosomes pair up.
Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres. The nucleolus disappears and the nuclear envelope starts to break down, leaving the chromosomes free in the cytoplasm.

Question 15

Stages of meiosis (Metaphase I)

Answer 15

Each chromosome attaches to the spindle by their centromere.

Question 16

Stage of meiosis (Anaphase I)

Answer 16

Homologous chromosome pairs are separated and pulled to opposite poles of the cell (chromatids stay joined together).

Question 17

Stages of meiosis (Telophase I)

Answer 17

The chromosomes reach the opposite poles of the cell where they uncoil. A nuclear envelope forms around each set of chromosomes and the nucleolus starts to reform. The cytoplasm divides to form two cells (cytokinesis).

Question 18

Stages of meiosis (Prophase II)

Answer 18

The chromosomes condense and are now visible. Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres. The nucleolus disappears and the nuclear envelope starts to break down.

Question 19

Stages of meiosis (Metaphase II)

Answer 19

Each chromosome attaches to the spindle by their centromere.

Question 20

Stages of meiosis (Anaphase II)

Answer 20

The centromeres divide and separate each pair of chromatids.
The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell.

Question 21

Stages of meiosis (Telophase II)

Answer 21

The chromatids reach the opposite poles of the cell where they uncoil to become long and thin again. A nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform. The cytoplasm divides (cytokinesis) and 4 cells are produced.

Question 22

Squamous epithelium cells?

Answer 22

Squamous epithelium tissue provides a thin lining for many organs such as the lungs. This tissue is made up of a single layer of squamous epithelial cells. Due to being only one cell thick, gases can quickly diffuse through the tissue.

Question 23

Ciliated epithelium cells?

Answer 23

Ciliated epithelium tissue lines organs such as the trachea where it can sweep mucus away from the lungs. This tissue is made up of ciliated epithelial cells and goblet cells. The goblet cells release mucus to trap pathogens, whilst the ciliated epithelial cells use cilia to sweep the mucus away.

Question 24

Cartilage?

Answer 24

Cartilage is a type of connective tissue that acts as a cushion between bones and also provides support to organs such as the ears and nose.

Question 25

Muscle?

Answer 25

Muscle tissue is made up of muscle fibres (bundles of elongated cells). These fibres contract (shorten) and relax to move different parts of the body. There are three types of muscle tissue: 1. Smooth - Found in the walls of organs. 2. Cardiac - Found in the heart. 3. Skeletal - Found attached to bones.

Question 26

The function and structure of Erythrocytes?

Answer 26

Erythrocytes or red blood cells are responsible for transporting oxygen around the body. 1. Flattened biconcave shape - This increases the surface area to volume ratio to allow diffusion of oxygen. 2. No nucleus or organelles - This provides more room for haemoglobin (the molecule that binds to oxygen). 3. Flexible - This is so they can fit through narrow capillaries.

Question 27

The function and structure of Neutrophils?

Answer 27

Neutrophils are types of white blood cell that help to defend the body against pathogens. 1. Flexible cell membrane - This allows the cell to engulf pathogens. 2. Contain many lysosomes - These contain digestive enzymes to break down engulfed particles. 3. Multi-lobed nucleus - This allows cells to deform so they can squeeze through small gaps to reach sites of infection.

Question 28

The function and structure of Sperm cell?

Answer 28

Sperm cells (male gametes) carry genetic information to the female gamete. 1. Flagellum (tail) - This allows the cell to swim to the egg cell. 2. Many mitochondria - These supply the energy needed for movement 3. Acrosome containing digestive enzymes - These digest the protective layers around the egg cell to allow the sperm cell to enter it.

Question 29

What are the types of stem cell?

Answer 29

1. Totipotent stem cells - These can differentiate into any cell type and go on to form whole organisms. 2. Pluripotent stem cells - These can differentiate into most cell types, but cannot form whole organisms. 3. Multipotent stem cells - These can only differentiate into a few different cell types. 4. Unipotent stem cells - These can only differentiate into one type of cell.