Cell division and stem cells

Question 1

what happens in interphase? (not names of the phases in it)

Answer 1

• cell spends most of its time here
• cell is not dividing
• DNA replication
• protein synthesis
• chloroplasts grow and divide

Question 2

G1 - interphase

Answer 2

1st growth phase
- proteins making up organelles are synthesised
- cell increases in size

Question 3

S phase - interphase

Answer 3

synthesis - DNA replicated

Question 4

G2 - interphase

Answer 4

2nd growth phase
- cell increases in size
- energy stores increase
- DNA checked for errors

Question 5

mitotic phase of cell cycle

Answer 5

• mitosis - nucleus divides
• cytokinesis - cytoplasm divides and 2 cells produced

Question 6

what is G0?

Answer 6

• stage where cell moves out of cell cycle
• permanent or temporary

Question 7

reasons for g0

Answer 7

• differentiation - cell becomes specialised to carry out a particular function - unable to divide
• DNA has become damaged - enters permanent cell arrest - most cells do this as they can only divide a set no. of times

Question 8

G1 checkpoint

Answer 8

• after mitosis, at end of G1 phase before S
• checks for cell size, DNA damage, growth factors, nutrients
• if it passes checks, it is triggered for DNA replication

Question 9

G2 checkpoint

Answer 9

• end of G2 phase before mitosis
• checks for DNA damage and replication, cell size
• checks if DNA replicated without error
• if it passes checks it moves into mitosis

Question 10

spindle assembly checkpoint/ metaphase checkpoint

Answer 10

• during mitosis when all chromosomes should be attached to spindles
• checks all chromosomes attached to spindles and aligned
• mitosis won’t happen if checkpoint not passed

Question 11

mitosis definition

Answer 11

• process of nuclear division before a cell physically divides in 2
• DNA is copied into each of 2 daughter cells

Question 12

why is mitosis needed?

Answer 12

• growth
• repair
• asexual reproduction

Question 13

prophase - mitosis

Answer 13

• chromatin fibres coil up and condense to form visible chromosomes
• centriole divides and moves to opposite poles
• nucleolus disappears
• nuclear envelope disintegrates
• spindle fibres attach to centromeres and begin moving chromosomes to centre

Question 14

metaphase- mitosis

Answer 14

• each centriole is at a pole
• centrioles produce spindle fibres
• spindle fibres attach to centromere of chromosomes
• chromosomes pulled to equator

Question 15

anaphase- mitosis

Answer 15

• spindle fibres contract
• centromere divides and chromatids pulled to opposite poles of cell by centromere
• each half recieves 1 chromatid from each chromosome

Question 16

telophase- mitosis

Answer 16

• chromatids (now called chromosomes) reach poles of spindle and begin to uncoil and become less distinct
• nucleolus reformed
• nuclear envelope starts to reform at each pole

Question 17

cytokinesis in animal cells

Answer 17

• the cell divides by starting with constriction from edges of cell - a cleavage furrow forms
• cell-surface membrane pulled inwards by cytoskeleton to fuse around the middle

Question 18

cytokinesis in plant cells

Answer 18

• vesicles from golgi apparatus assemble along equator and fuse with each other and the cell membrane
• cell is divided in 2
• cell wall is laid down

Question 19

how many chromosomes does a human body cell contain

Answer 19

46 chromosomes
23 pairs of homologous chromosomes

Question 20

are gametes haploid or diploid?

Answer 20

haploid - one copy of each chromosome

Question 21

homologous chromosome

Answer 21

• 2 chromosomes with different alleles for the same gene in the same location on the chromosome
• 1 from each parent

Question 22

how is a zygote formed?

Answer 22

2 haploid cells fuse

Question 23

prophase I meiosis

Answer 23

• chromosomes condense
• nuclear envelope disintegrates
• spindle fibres begin to form
• homologous chromosomes pair up forming bivalents
• crossing over occurs - chromatids entangle

Question 24

crossing over

Answer 24

• during prophase I of meiosis
• chromatids exchange alleles so they have new combinations of alleles

Question 25

metaphase I meiosis

Answer 25

- spindle fibres attach to centromere - homologous chromosomes line up on equator - independent assortment - maternal and paternal chromosomes randomly put on either side of equator - results in genetic variation

Question 26

anaphase I meiosis

Answer 26

- homologous chromosomes pulled by spindle fibres to poles - not pulled apart - causes variation

Question 27

telophase I meiosis

Answer 27

- nuclear envelopes reform - chromosomes uncoil - cells undergo cytokinesis - cells now haploid

Question 28

prophase II meiosis

Answer 28

beginning of second division - chromosomes recondense - nuclear envelope breaks down again - spindle fibres reform

Question 29

metaphase II meiosis

Answer 29

- chromosomes lined on equator by spindle fibres - independent assortment again - more genetic variation

Question 30

ananphase II meisosis

Answer 30

- chromatids split apart by sindle fibres - chromatids move to poles of cells

Question 31

telophase II meiosis

Answer 31

- chromatids uncoil - nuclear envelopes reform - cytokinesis - 4 haploid daughter cells

Question 32

tissues definition and examples

Answer 32

collection of differentiated similar cells with specialist function - animal tissues - nervous, epithelial, muscle, connective - plant tissues - epidermis, vascular

Question 33

organ definition and examples

Answer 33

collection of tissues adapted to carry out particular function eg. heart, lungs, leaf

Question 34

organ system

Answer 34

multicellular organisms have interconnected organ systems - each system has a number of organs to carry out functions eg. digestive system, cardiovascular

Question 35

specialised cell

Answer 35

differentiated cells that carry out a particular function

Question 36

stem cells

Answer 36

- undifferentiated cells originated from mitosis or meiosis - not adapted to particular function - unspecialised and have ability to differentiate and become any cell type

Question 37

totipotent

Answer 37

- stem cells that can differentiate into any type of cell - eventually produce whole organism - eg. fertilised egg

Question 38

pluripotent

Answer 38

- form all tissue types but not whole organisms - present in early embryos - origin of all different tissue types

Question 39

multipotent

Answer 39

- can only form a range of cells within certain tissue type - eg. haematopetic stem cells in bone marrow - form types of blood cell

Question 40

how have stem cells in bone marrow adapted to erythrocytes function?

Answer 40

- only few organelles - more room for haemoglobin - life span of 120 days - replaced constantly - stemm cell colonies in bone marrow produce 3 billion erythrocytes per kg of body mass per day

Question 41

how have stem cells in bone marrow adapted to neutrophils function?

Answer 41

- live for about 6 hours - colonies of stem cells in bone marrow produce 1.6 billion per kg per hour

Question 42

embryonic stem cells

Answer 42

- present at early stages of embyonic development - totipotent - after 7 days a blastocyst (mass of cells) forms and they are pluripotent until birth

Question 43

adult stem cells

Answer 43

- bone marrow - multipotent - umbilical cord of newborn babies

Question 44

sources of plant stem cells

Answer 44

(pluripotent) - meristems - found wherever growth is occurring eg. tip of roots and shoots - between phloem and xylem - vascular cambium (can only differentiate into cells present in xylem and phloem)

Question 45

uses of stem cells

Answer 45

- heart disease - muscle tissue damaged as result of heart attack - type 1 diabetes - insulin producing cells destroyed by body - Parkinson's - shaking and rigidity caused by death of dopamine-producing cells in brain