Cell Division

Question 1

What are the four different phases of the cell cycle?

Answer 1

G1, S, G2 and M

Question 2

What is the collective term for G1, S phase and G2 phase?

Answer 2

Interphase

Question 3

What is M phase?

Answer 3

Mitosis

Question 4

What is the purpose of the G1/S and G2/M checkpoints?

Answer 4

• Prevent uncontrolled cell division which could lead to cancerous tumours
• Detect and repair damaged DNA

Question 5

What can happen to cells if the p53 protein itself is mutated?

Answer 5

Cells will pass through the checkpoints without being checked and therefore could quickly become cancerous

Question 6

What is G0 phase?

Answer 6

A phase that cell can enter from the G1 phase when triggered by a checkpoint chemical at the G1 checkpoint. In G0 the cell can undergo apoptosis (programmed cell death) or differentiation or senescence (meaning the cell can no longer divide). Some cells stay in this phase for a very long time or indefinitely

Question 7

What happens in G1 phase?

Answer 7

• Cells grow and increase in size
• RNA is produced from transcription of genes
• Organelles duplicate
• Biosynthesis occurs including protein synthesis and making enzymes that are needed for DNA replication in S phase
• p53 (tumour suppressor) gene helps control this phase

Question 8

What happens in S phase?

Answer 8

• DNA is replicated (all 46 chromosomes are replicated)
• If a cell enters this phase, it’s committed to completing the cell cycle
• Each chromosome consists of a pair of identical sister chromatids after the DNA has been replicated. There are still 46 chromosomes but double the amount of genetic material
• This phase is rapid to reduce the chance of spontaneous mutations as the exposed DNA base pairs are more susceptible to mutagenic agents

Question 9

What happens in G2 phase?

Answer 9

• Special chemicals ensure the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in formation of the spindle
• Cells also grow in this phase

Question 10

What happens during prophase?

Answer 10

• Chromosomes supercoil and become visible
• Nuclear envelope also breaks down
• Centrioles divide and move to opposite poles of the cell where tubulin threads start forming a spindle between these centrioles

Question 11

What happens in metaphase?

Answer 11

• Pairs of chromatids attach to the spindle threads at the equator region
• They attach by their centromeres

Question 12

What happens during anaphase?

Answer 12

• Centromere of each pair of spindle fibres breaks down
• Motor proteins walk along tubulin threads and pull each sister chromatid of a pair to opposite poles of the cell
• Because the centromere has been removed, the chromatids (now called chromosomes) are V shaped

Question 13

What happens in telophase?

Answer 13

• Separated chromosomes reach the poles
• New nuclear envelope forms around each new set of chromosomes
• Cell now contains two nuclei each genetically identical to each other and the parent cell from which they arose

Question 14

What happens in cytokinesis?

Answer 14

• The cell divides to form two genetically identical daughter cells
• Each new cell has a full set of chromosomes (each with one chromatid)

Question 15

What is the significance of mitosis in life?

Answer 15

• Asexual reproduction
• Tissue repair
• Growth

Question 16

What happens in prophase 1?

Answer 16

• Chromatin condenses and each chromosome supercoils
• Nuclear envelope breaks down and tubulin threads start to from a spindle between centrioles
• Chromosomes come together in their homologous pairs
• Each member of the pair consists of two chromatids
• Crossing over occurs where chromatids from different chromosomes (non-sister) wrap around each other and and may swap sections so that alleles are shuffled

Question 17

What happens in metaphase 1?

Answer 17

• Pairs of homologous chromosomes (still in their crossed over state) attach along the equator of the spindle
• Each chromosome attaches to the spindle by its centromere
• Each pair of homologous chromosomes is arranged differently with each chromosome facing opposite poles of the cell
• This arrangement is independent assortment
• The way the homologous chromosomes line up in metaphase 1 (the pole which each member of the pair is facing) determines which daughter cell they will go to in anaphase 1 (how they will independently segregate)

Question 18

What happens in anaphase 1?

Answer 18

• Members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them across the tubulin threads of the spindle
• Centromeres do not divide and each chromosome still consists of two chromatids
• Crossed over areas separate resulting in swapped areas of chromosomes and allele shuffling

Question 19

What happens in telophase 1?

Answer 19

• In most animal cells, two new nuclear membranes form around around the two sets of chromosomes and the cell divides by cytokinesis, there is a short interphase where chromosomes uncoil
• Each new nucleus contains half the amount of chromosomes but each chromosome contains 2 chromatids meaning that there is the same amount of genetic material (46 chromatids)
• In most plant cells the cell goes straight from anaphase 1 to prophase 2

Question 20

What happens in prophase 2?

Answer 20

• If the nuclear membranes have reformed then they break down again and the chromosomes condense and coil (each one consisting of 2 chromatids)
• Chromatids of each chromosome are no longer identical because of crossing over in prophase 1
• Spindle fibres form

Question 21

What happens in metaphase 2?

Answer 21

• Chromosomes attach by their centromere to the equator of the spindle
• The chromatids are randomly arranged, the arrangement determines the way they will separate in anaphase (independent segregation)

Question 22

What happens in anaphase 2?

Answer 22

• Centromeres divide
• Chromatids of each chromosome are pulled apart by motor proteins and dragged along tubulin threads of the spindle fibres to opposite poles of the cell
• The chromatids are therefore randomly segregated

Question 23

What happens in telophase 2?

Answer 23

• Nuclear envelopes form around each of the four haploid nuclei
• In animals the two cells divide forming four haploid cells
• In plants, a haploid tetrad is formed

Question 24

Are homologous chromosomes identical?

Answer 24

No, they have contain the same genes in the same order but they may not have the same alleles (versions of the gene) meaning that homologous chromosomes are not identical

Question 25

What are homologous chromosomes?

Answer 25

You have two copies of each chromosome in each cell, one from your father and one from your mother, these are homologous chromosomes

Question 26

What is independent assortment?

Answer 26

The arrangement of homologous pairs of chromosomes along the equator of the spindle in metaphase 1

Question 27

What is crossing over?

Answer 27

Homologous chromosomes cross over strands in prophase 1 and exchange genetic material and shift alleles

Question 28

What is the point that homologous chromosomes cross over at called?

Answer 28

A chiasma

Question 29

How are red blood cells specialised for their function?

Answer 29

- Biconcave shape which gives a larger surface area meaning a faster rate of exchange, have no nucleus which makes more space for oxygen molecules and are packed with haemoglobin that the oxygen can bind to

Question 30

How are neutrophils adapted for their function?

Answer 30

They have a multi-lobed nucleus so they can squeeze through gaps in the capillary walls, they also have a cytoplasm that is packed with lysosomes to digest any pathogens that the neutrophil ingests

Question 31

How are sperm cells adapted for their functions?

Answer 31

- They have an undulipodium (a type of flagellum) which helps them to swim towards the egg (ovum) - The head of the sperm contains enzymes to help burrow through the outer layer of the ovum (egg)

Question 32

What are palisade cells and how are they adapted to their function?

Answer 32

- A type of plant cell that is found near the top surface of the leaf - They're long and thin so that many of them can be packed closely together - They are filled with chloroplasts to absorb sunlight for photosynthesis

Question 33

What are guard cells and how are they adapted for their function?

Answer 33

- Found on the underside of the leaf, come in pairs and control the opening and closing of stomata

Question 34

What are root hair cells and how are they adapted to their functions?

Answer 34

They are found in the roots of the plant, they have long thin hairs attached to them to maximise their surface area, this helps them take up water and minerals from the soil more efficiently

Question 35

What is squamous epithelium and how is it adapted to its function?

Answer 35

Tissue made of smooth, flattened cells, it lines the inside of alveoli and blood cells, it maximises the rate of diffusion as it provides a large surface area and a short diffusion distance

Question 36

What is ciliated epithelium?

Answer 36

Tissue made up of ciliated cells and goblet cells, goblet cells produce mucus and ciliated cells waft the mucus away from the lungs

Question 37

What is cartilage?

Answer 37

A strong tissue that is used to make tendons, bones and connective tissue

Question 38

What is muscle tissue?

Answer 38

Many muscle cells that all contract in the same direction

Question 39

What is xylem tissue?

Answer 39

- Xylem tissue transports water and minerals from the roots to the top of the plant, many xylem elements joined end to end are joined together to form a long hollow tube - Xylem tissue is dead, the cell walls of the xylem are lined with a strong, waterproof material called lignin

Question 40

What is phloem tissue?

Answer 40

- Transports sugars (mainly sucrose) and other assimilates up and down the plant - Made of many sieve tube elements joined end to end, these tubes are separated by sieve plates - Phloem is living tissue but is supported by companion cells

Question 41

What is a tissue?

Answer 41

A group of cells

Question 42

What is an organ?

Answer 42

A group of tissues working together to perform a particular function

Question 43

What is an organ system?

Answer 43

A group of organs

Question 44

What is the significance of the cell cycle happening in such a specific sequence?

Answer 44

- It ensures that the cycle can't be reversed | - It also ensures that the DNA is only duplicated once throughout each cell cycle

Question 45

What is the function of the p53 tumour suppressor gene?

Answer 45

To trigger the two checkpoints of the cell cycle (G1/S and G2/M)

Question 46

What are the products of meiosis in plant cells?

Answer 46

A tetrad of haploid cells

Question 47

At the end of meiosis 1, how many chromosomes are there in each new daughter cell?

Answer 47

23, each with 2 chromatids meaning that the amount of genetic material is the same as the parent cell (each cell still has 46 chromatids)

Question 48

At the end of mitosis how many chromosomes does each cell have?

Answer 48

46 (23 homologous pairs), each chromosome has one chromatid meaning there is a total of 46 chromatids

Question 49

At the end of meiosis 2 how many chromosomes does each cell have?

Answer 49

23, each with one chromatid meaning a total of 23 chromatids this means the cells produced are haploid cells