Cell Division

Question 1

Two phases of cell cycle?

Answer 1

Interphase
M phase

Question 2

Stages of interphase and functions?

Answer 2

G1- cell grows, new organelles and proteins are made
S- synthesis, semi conservative DNA replication
G2- further cell growth, proteins made for cell division

Question 3

What happens at G1 and G2 checkpoints?

Answer 3

G1- cell checks that chemicals needed for replication are present, check if any DNA is damaged
G2- cell checks wether all DNA has been replicated correctly

Question 4

Stages of M phase and functions?

Answer 4

Mitosis/ meiosis- nuclear division
Cytokinesis- cytoplasmic division

Question 5

Why is interphase necessary?

Answer 5

DNA is unravelled and replicated to double genetic content, so that each new cell has correct amount of DNA

Question 6

Apart from DNA content, what else is increased in interphase?

Answer 6

ATP content
Organelles

Question 7

What is mitosis used for?

Answer 7

-Growth of multicellular organisms
-Repairing damaged tissues
-Some plants, animal/ fungi use it for asexual reproduction

Question 8

Stages of mitosis?

Answer 8

Prophase
Metaphase
Anaphase
Telophase

Question 9

Structure of chromosomes in mitosis?

Answer 9

Made up of two strands ( chromatids) joined by a centromere
Two strands of one chromosome are called sister chromatids

Question 10

Why are there two strands in each chromosome of mitosis?

Answer 10

Each chromosome has already made an identical copy of itself during interphase

Question 11

What happens during prophase of mitosis?

Answer 11

-Chromosomes condense
-Centrioles move to opposite ends of cell forming spindle fibres
-Nuclear envelope breaks down, nucleolus disappears

Question 12

What happens during metaphase of mitosis?

Answer 12

-chromosomes line up down equator of cell
-spindle fibres attach to sister chromatids at centromere
-metaphase checkpoint checks that chromosomes are attached to spindle

Question 13

What happens during anaphase of mitosis?

Answer 13

-centromere divides, separating each pair of sister chromatid
-spindle fibres contract, pulling chromatids to opposite end of cell

Question 14

What happens at telophase of mitosis?

Answer 14

-chromatids are pulled to each side of cell
-they uncoil and become long
-each chromatid is now referred to as chromosome again
-new nuclear envelope form around each group of chromosomes

Question 15

What occurs in cytokinesis?

Answer 15

-cytoplasm divides to produce two genetically identical daughter cells, also identical to original cell
-chromosome number between cells is maintained

Question 16

What is G0?

Answer 16

-Where cells exit the cell cycle
-Here they can differentiate or undergo apoptosis ( programmed cell death)

Question 17

What is a homologous pair?

Answer 17

Chromosomes with the same genes, but different alleles

Question 18

What is the diploid number of normal body cells?

Answer 18

2n- each cell contains a pair of chromosomes from mother and father

Question 19

Gametes haploid number?

Answer 19

n- one copy of each chromosome

Question 20

What is a diploid cell?

Answer 20

Contains two sets of chromosomes, from each parent

Question 21

What is a haploid cell?

Answer 21

Contains one set of chromosomes

Question 22

What happens to the chromosome number of cells produced by meiosis?

Answer 22

The chromosome number halves

Question 23

What occurs in interphase of meiosis?

Answer 23

-Meiosis begins with interphase
-Cells DNA unravels and replicates to produce double armed chromosomes called sister chromatids

Question 24

What is meiosis 1?

Answer 24

Reduction division

Question 25

What happens during prophase 1?

Answer 25

-chromosomes condense -non sister chromatids on homologous pairs twist around each other (crossing over) -nuclear envelope breaks down, nucleolus disappears -centrioles move to opposite ends of cells, forming spindle fibres

Question 26

What happens during metaphase 1?

Answer 26

- homologous pairs line up down equator of cell in crossed over state - spindle fibres attach to centromeres - the random nature of they they align is called independant assortment

Question 27

What happens during anaphase 1?

Answer 27

- spindle fibres contract, pulling the pairs apart - one chromosome goes to each end of cell

Question 28

What happens in telophase 1?

Answer 28

- chromosomes uncoil, nuclear envelope forms around each group - cytokines occurs, two haploid daughter cells are produced

Question 29

What happens in meiosis 2?

Answer 29

-Prophase 2, metaphase 2, anaphase 2, telophase 2 -four haploid daughter cells are produced -each new daughter cell inherits one chromatid from each chromosome

Question 30

Two main events during meiosis that lead to genetic variation?

Answer 30

Crossing over of chromatids Independent assortment of chromosomes

Question 31

How does crossing over lead to genetic variation?

Answer 31

-During prophase 1 bits of chromatids swap over during crossing over -The chromatids still contain the same games but have different combination of alleles -each of the four daughter cells contain chromatids with different alleles

Question 32

How does independent assortment lead to genetic variation?

Answer 32

-during metaphase 1, when homologous pairs line up down equator, it is random which pair faces each side of cell -during anaphase 1, it is random which chromosome from each pair ends up in which daughter cell

Question 33

What are stem cells in the early embryo like?

Answer 33

Totipotent- they can differentiate into any cell type of the organism, including placenta/ umbilical cord

Question 34

What are stem cells?

Answer 34

Undifferentiated cells

Question 35

What are stem cells in the later embryo like?

Answer 35

Pluripotent- can differentiate into any cell type, but not form whole organisms/ extra embryonic tissues (placenta, umbilical cord)

Question 36

What are adult stem cells like?

Answer 36

Multi potent- can differentiate into only a few cell types

Question 37

What are plant stem cells like and where are they found?

Answer 37

Found in meristems (tips of roots/ shoots) Totipotent

Question 38

Uses of stem cells in medicine?

Answer 38

- researching developmental biology (how am embryo develops) - embryonic stem cells can be used to treat Alzheimer’s and Parkinson’s - to repair damaged tissues e.g. in heart disease / organ transplant

Question 39

Why is use of cells from embryos controversial?

Answer 39

Risks/ side effects not known Embryos can’t give consent Embryo can be used for fertility treatments instead of