2.3 Flashcards
mitosis
define mitosis
the process by which a cell divides to produce two genetically identical daughter cells
what is asexual reproduction
the production of genetically identical offspring from a single parent or organism
what is sexual reproduction
the production of offspring which are genetically different from the parent organism or organisms by the fusing of 2 gametes
define meiosis
a form of cell division in which the chromosome number of the original cell is halved leading to the formation of gametes
what is the order of the stages which occur in the cell cycle
G1
S
G2
mitosis
cytokinesis
what are histones
positively charged proteins involved in the coiling of DNA to form dense chromosomes in cell division
what are nucleosomes
dense clusters of DNA wound around histones
explain the structure of DNA
DNA winds around histones to form dense clusters such as nucleosomes
these then interact to produce more coiling and then supercoil to form dense chromosomes
what is interphase
the period between active cell divisions when cells increase their size and mass, replicate their DNA and carry out normal metabolic activities
what occurs in G1 phase
this is the time between the end of a previous round of cell division and the start of chromosome replication
what occurs in S phase
chromosomes replicate and become double stranded chromatids
what is a chromatid
one strand of the replicated chromosome pair that is joined to the other chromatid at the centromere
what occurs in G2 phase
the time that organelles and other materials needed for cell division are synthesized
what are cyclins
small proteins which build up during interphase and are involved in the control of the cell cycle by their attachment to cyclin-dependent kinases
what are cyclin-dependent kinases
enzymes involved in the control of the cell cycle by phosphorylating other proteins activated by attachments to cyclins
what is prophase
the first stage of active cell division where the chromosomes are coiled up and consist of two daughter chromatids joined by the centromere and nuclear membrane brakes down
what are the stages of mitosis in order
prophase
metaphase
anaphase
telophase
what is metaphase
second stage of active cell division where a spindle of overlapping protein microtubules forms and the chromatids line up on the metaphase plate
what is anaphase
third stage of active cell division where centromeres split of chromatids become chromosomes and are pulled to opposite poles of the cell by contractions of microtubules of the spindle
what is telophase
fourth stage of active cell division where a nuclear membrane forms around the two sets of chromosomes, the chromosomes unravel and spindle breaks down, the nucleoli and centrioles re-form
what are the meristem
the region of mitosis & growth in plants roots & shoots (very sensitive to stimuli)
what is dry mass and how can it be used to measure growth
dry mass- the mass of the body of an organism with all the water removed from it
must grow large samples of genetically identical organisms under similar conditions and take random samples to measure mass
what is growth and the 3 main aspects it can be defined by
growth - permanent increase in the number of cells or the mass/size of an organism
involves: cell division - mitosis
assimilation - nutrition
cell expansion - materials are incorporated into cells
explain the advantage of budding and vegetative propagation to farmers
increase plant numbers cheaply
clones are produced
cuttings can be taken to grow new plants
what is vegetative propagation
asexual reproduction of plants which forms genetically identical new plant
often used in flowering plants to survive between growing seasons
what is budding
the production by mitosis of an outgrow from the parent organism that develops into an individual organism so becomes detached
e.g. yeast cells
what is fragmentation
the use of mitosis to regenerate a whole organism from a fragment of the original
define binary fission
the splitting of one individual to form two new individuals
what is regeneration
use of mitosis to regrow a body part which has been lost
what is sporulation
production of asexual spores capable of growing to new individuals
survive adverse conditions
easily spread
common in fungi & plants
what are the advantages and disadvantages of asexual reproduction
+/ produces clones
does not rely on finding a mate
large numbers of offspring produced rapidly
-/ changes in conditions can cause total destruction of the entire population
what are plasmodesma
small gaps left between the vesicles during cytokinesis of plant cells when the cellulose cell wall begins to form
how does cytokinesis occur in plants
cellulose cell wall builds up from inside of the cell:
- remaining spindle fibers guide Golgi vesicles to the equator of the cell
- golgi vesicles fuse with all surface membrane once large vacuoles have formed
- vesicles fuse together forming cell plate
- cellulose walls with middle lamella form between cells
how does cytokinesis occur in animals
a ring of contractile fibers contract around the center of the cell until the 2 cells have been separated
what is cytokinesis
final stage in the cell cycle division of the cytoplasm at the end of mitosis to form two independent genetically identical cells
