2.3 eukaryotic cell division Flashcards
what is a chromosome
a mass of coiled dna threads and proteins
when cells divide they become more condensed and become much shorter, denser and take up stains
why do cells divide
to bring about growth and asexual reproduction
what is interphase
period of non division when the cell increase in mass and size, DNA produced, chromosomes replicate, organelles synthesised and the cell prepares for division
describe each phase of the cell cycle
G1- end of the previous round of division, start of chromosome duplication, cell material grows and develops
S- chromosomes replicate to become double stranded chromatids
G2- organelles and other materials needed for division are synthesised
M- mitosis
C- cytokinesis
what happens in prophase
chromosomes coil up and take up stains to become visible, each chromosome consists if two daughter chromatids
nucleolus breaks down, centrioles pull apart to begin to form the spindle
what happens in metaphase
the spindle is forming and chromatids move for a position on the equator of the spindle
what happens in anaphase
the centromeres that linked the two chromatids split, chromatids separate and move to opposite sides of the cell
what happens during telophase
spindle breaks down, nuclear envelopes begin to form around the two sets of chromosomes
nucleoli and centrioles reform
chromosomes unravel to become less dense
what happens during cytokinesis in plants
division of the cytoplasm, contractile fibres tighten around the centre of the cell until they are separated
what happens during cytokinesis in animals
division of the cytoplasm, contractile fibres tighten around the centre of the cell until they are separated
two identical daughter cells are formed
what does mitosis produce
genetically identical individuals or clones
two identical diploid daughter cells
what are the advantages and disadvantages of mitosis
it does not rely on finding a mate
gives rise to large numbers of offspring very quickly
however, offspring are genetically identical, doesn’t allow for variation, if living conditions change it could cause destruction for a group of genetically identical organisms
what is sporulation
the production of asexual spores that are capable of growing into new individuals
these spores can survive adverse conditions and spread over great distances
what is regeneration
form of asexual reproduction that occurs when organisms need to replace parts of their body that have been lost
what is fragmentation
a form of regeneration that happens when animals reproduce themselves asexually from fragments of their body
what is reproductive budding
when their is an outgrowth from the parent organism that produces a smaller but identical individual by mitotic cell division ]
the bud eventually detaches and has an independent existence from the parent
what is vegetative propagation and where does it occur
occurs in flowering plants and is when a plant forms a structure that develops into as fully differentiated new plant that is identical to the parent, and involves only mitotic cell division
define growth
growth is a permanent increase in the number of cells, or in the mass or size of an organism
what are the factors that growth is affected by
availability of food, temperature, light intensity, genetic make up of an organism
why is dry mass a better measurement of growth than linear measures
growth involves increase of the cell content
height and weight are deceptive
just because height has increased doesn’t mean the content of the organism has increased, and water content of cells vary which affects mass, so dry mass is the most accurate
why is it hard for scientists to measure growth accurately
must be measured with dry mass so water must be removed
if all water is removed then organism dies
it is hard and unethical to grow large samples of genetically similar organisms and take random samples to get a dry mass
what is the difference between a growth patters of an animal and the growth pattern of a plant
animals often have a relatively slow start, then a rapid period of growth until maturity where it slows down then eventually stops
plants often continuously grow throughout their lives
when does the largest amount of growth take place in the human body
during development of the embryo
how does mitosis take place in plants
it continues throughout the entire life of the plant and takes place in the meristems, and after they have divided they absorb water into their vacuoles and become more rigid
what happens when skin is damaged
rapid mitosis is triggered in the body and cells regenerate lost skin tissue
