2.1.6 Cell division, cell diversity and cellular organisation

Question 1

What happens during stage G₁ of interphase?

(Growth stage 1)

Answer 1

• Cellular contents (mitochondria, chloroplasts) are duplicated
• Cell increases in size

Question 2

What happens during stage S of interphase?

(Synthesis stage)

Answer 2

Chromosomes are duplicated in nucleus

Question 3

What happens during stage G₂ of interphase?

(Growth stage 2)

Answer 3

• Cell continues to increase in size
• Energy stores increased
• Chromosomes checked for repairs

Question 4

What happens during stage G₀ of interphase?

(Resting state)

Answer 4

Cell leaves cycle temporarily or permanently

Question 5

Why does cell enter stage G₀ of interphase?

Answer 5

• Differentitation
• Damage to DNA

Question 6

What are checkpoints in interphase?

Answer 6

Requirements that have to be fulfilled before the next stage can begin

Question 7

What is checked for in the checkpoints of interphase?

Answer 7

• Cell size
• DNA damage
• DNA replication without error
• Nutrient availablity
• Chromosome attachment to spindle

Question 8

What are the three checkpoints of interphase?

Answer 8

• G₁ checkpoint
• G₂ checkpoint
• Spindle assembly checkpoint

Question 9

How many daughter cells are produced from mitosis?

Answer 9

Two genetically identical diploid cells

Question 10

How many daughter cells are produced from meiosis?

Answer 10

Four genetically different haploid cells

Question 11

What is mitosis important for?

Answer 11

• Growth and repair
• Asexual reproduction

Question 12

In terms of n what are the changes in chromosome number before, during and after for mitosis?

Answer 12

2n -> 4n -> 2n

Question 13

What type of division is meiosis known as?

Answer 13

Reduction division

Question 14

What are homologous chromosomes?

Answer 14

Matching sets of chromosomes where each one has the same genes at the same position (loci)

Question 15

What are alleles?

Answer 15

Different versions of the same gene (located in the same positions)

Question 16

What happens during meiosis I?

Answer 16

Homologous chromosomes are separated into two different cells

Question 17

What happens during meiosis II?

Answer 17

Pairs of chromatids in each daughter cell are separated to form four cells in total (similar to mitosis)

Question 18

When does crossing over occur in meiosis?

Answer 18

Prophase 1

Question 19

What is crossing over?

Answer 19

Homologous chromosomes pair up and form bivalents (occurs when chromatids entangle)

Question 20

What is independent assortment?

Answer 20

Orientation of homologous pair at equator is random and independent so different combinations of alleles face the poles

Question 21

When does independent assortment occur in meiosis?

Answer 21

Metaphase 1 and metaphase 2

Question 22

What results in genetic variation in meiosis?

Answer 22

Crossing over and independent assortment

Question 23

What is an organ?

Answer 23

Collection of tissues adapted to perform a particular function

Question 24

What is an organ system?

Answer 24

Composed of several organs working together to carry out a major function e.g. cardiovascular system

Question 25

What are stem cells?

Answer 25

Undifferentiated cells with the potential to differentiate into any specialised cell

Question 26

What are totipotent stem cells?

Answer 26

- Can differentiate into ANY type of cell - Can produce a whole organism - E.g. zygote

Question 27

What are pluripotent stem cells?

Answer 27

- Can form all **tissue types** - BUT NOT whole organisms - Present in early embryos

Question 28

What are multipotent stem cells?

Answer 28

- Can only form a range of cells within a certain type of tissue tissue - E.g. stem cells in bone marrow can form different blood cells

Question 29

Why do erythrocytes and neutrophils need to be constantly replaced?

Answer 29

They have short life spans (red blood cell has no nucleus so cannot multiply)

Question 30

What are the sources of animal stem cells?

Answer 30

- Embryonic stem cells (totipotent) - Tissue stem cells: bone marrow and umbilical cord (both multipotent)

Question 31

When do embryonic stem cells enter the pluripotent stage?

Answer 31

After seven days, when mass of cells (blastocyst) has formed

Question 32

What is the source of stem cells in plants?

Answer 32

Meristematic tissue (pluripotent) - Found in the apical meristems (tips of shoots and roots) - Found in the vascular cambium (these differentiate into cells needed in xylem and phloem)

Question 33

What are the uses of stem cells?

Answer 33

- Repairing damaged tissue - Treating neurological conditions e.g. Alzheimer’s and Parkinson’s

Question 34

In terms of n what are the changes in chromosome number before, during and after for meiosis?

Answer 34

2n -> 4n -> 2n -> n