cell division Flashcards
what happens during prophase 1
chromosomes condense
nuclear envelop disintegrates
nucleolus dissapears
spindle formation begins
homologous chromosomes pair up forming bivalents
movement of chromosome causes chromatids to entangle this is called crossing over
what happens during metaphase 1
same at mitosis
expect the homologous pairs of chromosome assemble along the metaphase plate of the individual chromosomes
orientation of each homologous pair on the metaphase plate is random and independent
independent assortment occurs
what happens during anaphase 1
is different from mitosis
as homologous chromosomes are pulled to opposite poles and the chromatids stay joined to each other
chromatids entangle and cross over then break and rejoin
the point at which they break and rejoin is called chiasmata
what happens during telophase 1
same as mitosis
chromosome assemble at each pole
what happens during prophase 2
the chromosomes - two chromatids condense and become visible
nuclear envelope breaks down
spindle formation begins
what happens during metaphase 2
individual chromosomes assemble on the metaphase plate
due to crossing over chromatids are no longer identical so there is independent assortment
more genetic variation
what happens during anaphase 2
chromatids of the individual chromosomes being pulled to opposite poles after division of centromeres
what happens during telophase 2
chromatids assemble at the poles
chromosomes uncoil and from chromatin again
nuclear envelope reforms
nucleolus appears
cytokinesis results in four daughter cells- haploid
genetically different due to the process of independent assortment and crossing over
what happens during prophase
chromatin fibres coil and condense to form chromosomes to be visible
protein microtubules form spindle shaped linking the poles of the cells
two centrioles migrate to opposite poles of the cells
spindle fibres attach to specific areas on the centromere
nuclear envelope disappears
nucleolus disappears
what happens during metaphase
spindle fibres form a plane in the centre called a metaphase plate and then held in position
what happens during anaphase
chromatids divide and separate
chromatids pulled to opposite poles of the cell
what happens during telophase
chromatids have reached the poles and now called chromosomes
chromosomes uncoil and are at opposite poles
nuclear envelope reforms
nucleolus is formed
cytokinesis begins
what happens in cytokinesis in animal cells
a cleavage furrow forms around the middle of the cell
the cell surface membrane is pulled inwards by the cytoskeleton and fuses around the middle
forming two cells
what happens in cytokinesis in plant cells
due to the cell wall in plant cells a cleavage furrow is not possible
therefore vesicles from the golgi apparatus begin to assemble in the same place the metaphase plate
vesicles fuse with each other and the cell surface membrane
therefore dividing the cell into two
what happens in the first growth phase - G1
proteins synthesis
organelles replicate
cell increases in size
what happens in the synthesis phase - S
DNA replication in the nucleus
what happens in the second growth phase- G2
cell continues to increase in size
duplicated DNA is checked for errors
energy stores are increased
what are stem cells?
undifferentiated cells that have the potential to differentiate and specialise into any other type of cell
what is potency?
the ability for stems cell to differentiate into any different type of cells
describe and explain totipotent stem cells
stems cells which can differentiate into any type of cell
for example : fertilised egg, zygote
they can turn into whole organisms
describe and explain pluripotent stem cells
stem cells which can form all tissue types but not whole organisms
present in early embryos
describe and explain multipotent stem cells
stem cells which can only form a range of cells within a type of tissue
describe and explain the replacement of erythrocytes
red blood cells
erythrocytes have a lifespan of 120 days
and are produced 3 billion times per kilogram per day of body mass to keep up with demand
describe and explain the replacement of neutrophils
white blood cells
essential role in the immune system
life span of only 6 hours
are produced 1.6 billion times per kilogram per hour of body mass
what are the 2 types of animal stem cells
embryonic stem cells
tissue stem cells
describe and explain the embryonic stem cells
present at a very early stage of embryo development
are totipotent
after 7 days a mass of cells, called a blastocyst
has formed and the cells are now in a pluripotent state
remain in this state until fetus is born
describe and explain the tissue stem cells
are present throughout life from birth found in bone marrow are multipotent harvested from umbilical cords of newborn babies for this invasive surgery is not needed
where are stem cells found in plant cells?
meristematic tissue
at the tip of roots and shoots
give three uses of stem cells
treats heart disease Parkinson disease type 1 diabetes spinal injuries
what are the ethics for stem cells
removal of stem cells from embryos results in destruction of embryos
many people believe life begins at conception and destruction of embryo is murder (religious objectives)
