2.1.6 cell division, cell diversity and cellular organisation Flashcards
draw out the entire cell cycle
2.1.6(a)
in booklet
what happens in G1
2.1.6(a)
Transcription, organelle synthesis, biosynthesis of polymers e.g. proteins
what happens in the S phase
2.1.6(a)
Semi-conservative DNA replication
what happens in G2
2.1.6(a)
Cell increases in size, protein synthesis continue
what can cells do if they are in G1
2.1.6(a)
Cells can exit the cell cycle during G1 and enter G0, a “rest” phase. Cells in G0 can also resume the cell cycle and start the G1 phase again.
what can cells do if they are in g0
2.1.6(a)
From G0, cells may undergo apoptosis (programmed cell death), differentiation and/or senescence, where they stop being able to divide
why do cells have to pass checkpoints
2.1.6(b)
This is to prevent cells from dividing by mitosis if they have damaged DNA, DNA that has not replicated correctly, or if the cell is not big enough.
what is the G1 checkpoint
2.1.6(b)
DNA is checked for damage/mutations before it replicates.
These mutations could be caused by e.g. UV light.
what is the G2 checkpoint
2.1.6(b)
The DNA that was replicated in the S phase is checked to ensure it has replicated correctly.
what is the M checkpoint
2.1.6(b)
chromosomes are checked to ensure they have correctly attached to the spindle fibres
what is the abbreviation for the stages of mitosis
2.1.6(c)
PMAT
prophase
metaphase
anaphase
telophase
what happens during interphase
2.1.6(c)
-interphase consists of G1,S,G2. These are the checkpoints the cell goes through to prepare itself for mitosis
-DNA is replicated during the S phase
-each chromosome forms an identical copy of itself to which it is attached to by a centromere
what is mitosis
2.1.6(c)
division of the nucleus into 2 new nuclei
what happens during prophase
2.1.6(c)
· Chromosomes condense and appear as X shapes as each one consists of two sister chromatids, which are identical (have exactly the same base sequence as each other).
· The nuclear envelope starts to break down.
· In animal cells, the centrioles divide and move to opposite poles of the cell forming two centrosomes. The spindle fibres begin to form and attach to the centromeres of each chromosome
what happens during the metaphase
2.1.6(c)
Chromosomes are moved by spindle fibres along a line down the equator of the cell.
This line is called the metaphase plate
what happens during the anaphase
2.1.6(c)
· The centromeres divide and the chromatids are separated
· Each chromatid becomes its own chromosome as they now have their own centromeres
· The spindle fibres shorten and the new chromosomes are pulled to opposite poles of the cell
what happens during telophase
2.1.6(c)
· The new chromosomes reach the poles
· New nuclear envelopes form around each set of chromosomes at each end
· Chromosomes de-condense forming the nucleoplasm & new nucleoli form
what is cytokinesis
2.1.6(c)
not a stage of mitosis
physical separation of the cell into 2 new daughter cells
how does cytokinesis work in animal cells
2.1.6(c)
o A cleavage furrow forms around the middle of the cell
o The cell surface membrane is pulled inwards by the cytoskeleton until it fuses in the middle
o Two daughter cells form
how does cytokinesis work in plant cells
2.1.6(c)
o Have cell walls so can’t make a cleavage furrow
o Vesicles from the Golgi assemble at the equator of the cell
o The vesicles fuse with each other and with the cell surface membrane forming a new membrane down the middle of the cell
o New sections of cellulose are deposited along the new sections of membrane
what should you do when they ask you to identify/describe a stage of mitosis
2.1.6(d)
describe what you can see which supports your identification
draw the cells as they appear in the image NOT a textbook
what can you see during interphase
2.1.6(d)
the nuclear envelope is intact
chromosomes aren’t visible
what can you see during early prophase
2.1.6(d)
nuclear envelope is disrupted
nucleolus (large dark spot) is still intact at this point
what can you see during late prophase
2.1.6(d)
nucleolus has disappeared
chromosomes continue to condense becoming visible as separate structures
what can you see during metaphase
2.1.6(d)
spindle fibres have become visible
chromosomes are organised around the middle of the cell
what can you see during early anaphase
2.1.6(d)
chromosomes are being pulled apart to opposite pole of the cell
what can you see during late anaphase
2.1.6(d)
chromosomes are still at poles of cells
spindle fibres still intact
what can you see during telophase
2.1.6(d)
chromosomes begin to decondense
new nuclear envelope starts to form
new plasma membrane forming
what can you see during cytokinesis
2.1.6(d)
New nuclear envelopes have formed New nucleoli have formed Chromosomes are decondensed Daughter cells are completely separated by the new plasma membrane + cell wall material
three ways mitosis is significant
2.1.6(e)
growth, tissue repair and asexual reproduction
how do cells grow
2.1.6(e)
All multicellular organisms grow by producing more cells that are genetically identical to each other (by mitosis) and to the parent cell that they arose from.
All the cells in the body of a multicellular organism contain all of the DNA of that organism.
how can tissues become damaged
2.1.6(e)
Tissues can become damaged by a variety of physical injuries and diseases
why do animals and plants repair there tissue
2.1.6(e)
Animals and plants repair damage to their tissues to prevent the entry of pathogens.
how do animals and plants repair there tissue
2.1.6(e)
firstly a blood clot forms which develops into a scab and skin cells under the scab divide by mitosis and cytokinesis to form new skin cells
how do plants and animals reproduce asexually
2.1.6(e)
they can reproduce asexually by mitosis
what is parthenogenesis
2.1.6(e)
Parthenogenesis is the process where an embryo develops from an unfertilised egg cell
what does asexual reproduction allow
2.1.6(e)
genetically identical offspring to be produced in large numbers
why does animals/plants asexually reproduce when conditions are favourable
2.1.6(e)
all the genetically identical offspring will be adapted to the favourable conditions so will maximise the success of that offspring (higher fitness)
what is meiosis
2.1.6(g)
Meiosis is the process where replicated chromosomes undergo two nuclear divisions to produce four haploid cells, which are genetically different to each other.
what happens is prophase 1
2.1.6(g)
Chromosomes condense
Homologous chromosomes pair up and cross over, forming chiasmata
what happens during metaphase 1
2.1.6(g)
Each pair of homologous chromosomes lines up on the metaphase plate
Independent assortment occurs – either parental chromosome can appear on either side of the plate
what happens during anaphase 1
Spindle fibres shorten, pulling homologous chromosomes to opposite poles
Chromosomes swap sections of DNA at chiasmata
Centromeres do not have to divide like they do in mitosis
what happens during telophase 1
2.1.6(g)
New nuclear envelope forms
Followed by cytokinesis
2 haploid cells are made
Each chromosome still consists of 2 sister chromatids
when do homologous chromosomes break as the chiasma
2.1.6(g)
The homologous chromosomes don’t break at the chiasmata until anaphase I where they are being pulled apart by the shortening spindle fibres.
how does the chromosomes being pulled apart by spindle fibres create new allele combination
2.1.6(g)
chromosomes swap sections of DNA at chiasma
This creates new allele combinations in the daughter cells that will eventually be inherited by the offspring.a
when does independent assortment occur and what does this create
2.1.6(g)
metaphase 1
new allele combinations in the gametes
NOTE-In a diploid cell where there are 2 pairs of chromosomes, there are 4 ways to arrange the chromosomes during metaphase I.
In a diploid cell with 2n chromosomes, there will be 2n possible ways for them to be arranged during metaphase I.
what happens during prophase 11
2.1.6(g)
Spindle fibres re-form and attach to the centromeres.