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.
what happens during metaphase 11
2.1.6(g)
Chromosomes line up on the metaphase plate.
Independent assortment of chromatid
what happens during anaphase 11
2.1.6(g)
Centromeres divide and each chromatid becomes a chromosome
Spindle fibres shorten, pulling the chromosomes apart
what happens during telophase 11
2.1.6(g)
Four haploid genetically different nuclei are formed as the nuclear envelopes re-form
Followed by cytokinesis to make gametes
what cells does meiosis result in
2.1.6(f)
Meiosis is another type of cell division that results in 4 haploid daughter cells
in order to sexually reproduce what must the organisms be
2.1.6(f)
In order to sexually reproduce, these organisms must produce haploid gametes, so that when two gamete nuclei fuse during fertilisation, a diploid zygote is produced.
how does the act of fertilisation increase genetic variation
2.1.6(f)
Fertilisation is random – in theory, any sperm can fertilise any ovum
The parent organisms may contain different allele
what 2 processes in meiosis result in 4 genetically different daughter cells
2.1.6(f)
independent assortment
crossing over
what do independent assortment and crossing over result in
2.1.6(f)
different allele combinations in each one of the 4 daughter cells
why are different allele combinations beneficial
2.1.6(f)
-its advantageous in unfavourable conditions as a small percentage of offspring will survive
-if they were all genetically identical they would all die
what does independent assortment make genetic variation
2.1.6(f)
as there’s a 50/50 chance about which way the chromosomes will face during metaphase
metaphase 1-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
metaphase 2-chromsomes line up on the metaphase plate
independent assortment of chromatids
(each chromatid is randomly arranged so it can face either pole)
how does crossing over lead to genetic variation
2.1.6(f)
prophase 1-homologous chromosomes pair up and cross over forming chiasmata
anaphase 1-when spindle fibres shorten and pull homologous chromosomes to opposite poles and chromosomes swap sections of DNA at chiasmata
what is the process by which a cell becomes specialised
2.1.6(h)
differentiation
what happens to genes during differentiation
2.1.6(h)
During differentiation, the transcription of certain genes increases or decreases.
This pattern of gene expression results(some genes being switched on/off) in permanent changes to the structure and function of the cell.
what are erythrocytes
2.1.6(h)
red blood cells
how are erythrocytes adapted for their function
2.1.6(h)
· They are very small, about 7.5μm in diameter, so they barely fit into capillaries. This means they move through capillaries slowly and this increases the time for gas exchange.
· They have a biconcave shape, giving them a high surface area for gas exchange.
· Their cytoplasm contains no nucleus, mitochondria or endoplasmic reticulum, so there is more available volume to pack with haemoglobin.
what are neutrophils
2.1.6(h)
white blood cells
how are neutrophils adapted for there function
2.1.6(h)
· Their function is to ingest pathogens by phagocytosis (a type of endocytosis)
· Their nucleus is multilobed which allows them to squeeze out of capillaries into tissues that are wounded or infected by pathogens
· They have specific receptor proteins in their cell surface membranes that can bind to antigens on pathogens
what is epithelium
2.1.6(h)
Epithelium is “lining” tissue.
The epithelium is a type of body tissue that forms the covering on all internal and external surfaces of your body.
what is the epithelium on blood vessels called
2.1.6(h)
endothelium
how are squamous epithelium cells adapted
2.1.6(h)
Squamous epithelial cells are flattened in shape, providing a very short diffusion distance.
This type of epithelium is often permeable, and occurs where small molecules need to pass quickly through membrane
what is the role of ciliated epithelial cells
2.1.6(h)
Ciliated epithelial cells work together with goblet cells to clear pathogens and dirt from the trachea, bronchi and bronchioles.
how do goblet + ciliated epithelial cells work together to discard mucus
2.1.6(h)
Goblet cells secrete mucus which traps pathogens and dirt. The ciliated epithelial cells then waft their cilia in a co-ordinated way to move this mucus towards the oesophagus, where it is swallowed
how are ciliated epithelial cells adapted
2.1.6(h)
contain many mitochondria-as the movement of cilia requires ATP from aerobic respiration
Ciliated epithelial cells also form the lining of the fallopian tubes, where they help to move the ovum (or potentially the fertilised zygote) towards the uterus.
how are sperm cells adapted for there function
2.1.6(h)
· Many mitochondria to carry out rapid aerobic respiration for ATP
· flagellum for motility
· Acrosome is a specialised lysosome containing hydrolytic enzymes that digest the protective layer of the ovum
· Head contains the haploid nucleus for fertilisation
how are palisade leaf cells adapted
2.1.6(h)
· They are long and cylindrical so they pack closely together for maximum light absorption
· They have a large vacuole so that the chloroplasts are positioned near the outside of the cytoplasm, reducing the diffusion distance for CO2
· They contain many chloroplasts
· The chloroplasts can be moved by the cytoskeleton nearer to the upper surface of the leaf when light intensity is low, but further down when it is high
what is a guard cell
2.1.6(h)
Guard cells are pairs of specialised cells with a small hole (stoma) between them
how are guard cells adapted
2.1.6(h)
· The stoma is open when the guard cells are turgid, and closed when it is flaccid
· To close the stoma, the guard cell:
o Actively transports K+ out
o H2O follows K+ by osmosis down the Ψ gradient
o The guard cell becomes flaccid
o The stoma closes
-thick inner walls and thin outer walls allows cell to bend when turgid
what are root hair cells
2.1.6(h)
Root hair cells are epidermal cells on the outer surface of young plant roots.
how are root hair cells adapted
2.1.6(h)
· The function of an RHC is to take in mineral ions and water from the soil
· Ions are actively transported from the soil into the RHC (so the RHC cell surface membrane must contain many carrier proteins)
· H2O follows the ions by osmosis down the Ψ gradient
· The RHC contains many mitochondria to produce ATP for active transport
· An RHC has a high surface area due to the root hair, increasing the rate of ion and water uptake
-thin cellulose cell wall means substances diffuse over a short distance
what is a tissue
2.1.6(i)
a tissue is a group of similar cells working together to carry out a function
what is an organ
2.1.6(i)
an organ is a group of tissues working together to carry out a function
what is an organ system
2.1.6(i)
a group of organs working together to carry out a function
what is squamous epithelium made up of
2.1.6(i)
Squamous epithelium is made up of squamous epithelial cell
where can squamous epithelial cells be found and how are they adapted
2.1.6(i)
Squamous epithelial tissue lines exchange surfaces and provides a short diffusion distance for the exchange of e.g. glucose or O2.
what is ciliated epithelium made up of
2.1.6(i)
Ciliated epithelium is made up of ciliated epithelial cells, often with goblet cells also present
what is the function of ciliated epithelium
2.1.6(i)
The function of ciliated epithelium is movement of external substances e.g. mucus with trapped pathogens, or an ovum / zygote.
what is cartilage
2.1.6(i)
Cartilage is a strong and flexible tissue
what specialised cell is cartilage made from
2.1.6(i)
made up of specialised cells called chondrocyte
what is the function of chondrocytes
2.1.6(i)
synthesise and secrete a large amount of collagen
where is cartilage found
2.1.6(i)
Cartilage is found in a variety of places where lubrication or flexible support is needed:
· In the joints e.g. the meniscus of the knee
· C-shaped rings around the trachea
· Joining ribs to the sternum
· Ears
what is muscle tissue made from
2.1.6(i)
Muscle tissue is made of muscle fibres, which are individual muscle cells
what are the three types of muscle
2.1.6(i)
· Skeletal muscle, AKA striated muscle – attached to bones by tendons
· Cardiac muscle – makes up the heart
· Smooth muscle – found in blood vessels, digestive system, etc. Contract and relax involuntarily
what is the function of vascular tissue
2.1.6(i)
The function of vascular tissue is to transport substances like water, sucrose, amino acids and mineral ions around a plant.
what is the function of xylem vessels
2.1.6(i)
· Xylem vessels carry water and ions from the roots to all parts of the plant
what is the function of phloem sieve tubes
2.1.6(i)
· Phloem sieve tubes carry sucrose from sources to sinks
what is an organ system
2.1.6(i)
A number of organs working together to carry out an overall life function is called an organ system.
what is a stem cell
2.1.6(j)
Stem cells are undifferentiated cells that are able to divide by mitosis to produce:
· New stem cells
· Various specialised cells
what is a totipotent stem cell
2.1.6(j)
These stem cells are able to divide to produce daughter cells that can differentiate into any cell type,
including extra-embryonic tissues like the placenta and umbilical cord.
what type of cells are totipotent
2.1.6(j)
A zygote and the cells of an embryo up to the 16 cell stage are totipotent.
what are pluripotent stem cells
2.1.6(j)
These stem cells can divide to produce daughter cells that can differentiate into any cell type in the adult organism, which does not include extra-embryonic tissues
what is an example of a pluripotent stem cell
2.1.6(j)
the embryonic stem cell, from after the 16-cell stage.
what is a multipotent stem cell
2.1.6(j)
These stem cells can divide to form a smaller number of specialised cell
what is an example of a multipotent stem cell
2.1.6(j)
An example is the haematopoietic stem cells in bone marrow. These can divide to form blood cells.
what type of stem cells does bone marrow contain
2.1.6(k)
The bone marrow contains haematopoietic stem cells.
what type of cells are haematopoietic
2.1.6(k)
These stem cells are multipotent
what do haematopoietic stem cells divide to produce
2.1.6(k)
· Neutrophils (RBC)
· Erythrocytes (WBC)
· All other type of blood cells including other WBCs and platelets
· New haematopoietic stem cell
where are plant stem cells found
2.1.6(l)
Plant stem cells are found in areas called meristem
where are meristems located
2.1.6(l)
Meristems are located in root and shoot tips, and in the cambium of vascular bundles
what is the cambium
2.1.6(l)
The cambium is a very thin layer of cells between the xylem and phloem.
what type of growth do meristems allow plants to carry out
2.1.6(l)
Meristems allow plants to carry out indeterminate growth throughout their lives, which is growth that doesn’t stop and doesn’t have a specific end point
how do plant stem cells in meristems differentiate into other cell types
2.1.6(l)
Stem cells in plant meristems divide by mitosis and cytokinesis and then differentiate into other cell types e.g. xylem and phloem.
what are the 5 sources of stem cells
2.1.6(m)
embryonic stem cells
foetal stem cells
umbilical stem cells
adult stem cells
induced pluripotent stem cells
what are embryonic stem cells
2.1.6(k)
totipotent cells collected from the 16-cell stage of an embryo or before. The embryo must be killed for these cells to be collected.
Usually these come from excess embryos produced during IVF, which were going to be destroyed as they had either been rejected for implantation or the parents no longer wanted to store them for future use
what are foetal stem cells
2.1.6(k)
multipotent cells obtained from miscarried or aborted foetuses
what are umbilical stem cells
2.1.6(k)
can be collected from the umbilical cord after birth, so has fewer ethical issues but also the cells are pluripotent, not totipotent
what are adult stem cells
2.1.6(k)
multipotent cells that can be collected from e.g. bone marrow, which is a painful process with potential risks and side effects
what are induced pluripotent stem cells
2.1.6(k)
Differentiated cells that are induced in a lab to un-differentiate and become pluripotent
what are the 3 uses of stem cells
2.1.6(m)
-repairing damaged tissue
-treatment of neurological diseases
-research into developmental biology
how could we repair damaged tissue using stem cells
2.1.6(m0
· Stem cells can, in theory, be directed to differentiate into any cell type
· This would allow the replacement of damaged tissues
· e.g. replace cartilage in arthritis, heal burns, cure vision and hearing loss
· Induced pluripotent stem cells could be made from the patient’s body cells. The resulting tissues would be genetically identical to the rest of their body cells and so there would be no risk of rejection.
how could we treat neurological diseases using stem cells
2.1.6(m)
· Stem cells could be directed to differentiate into neurons which could be used to treat Alzheimer’s and Parkinson’s diseases, or repair spinal cord injury.
how could we use stem cells to research into developmental biology
2.1.6(m)
· In the lab, scientists could study how stem cells differentiate into e.g. blood cells / muscle cells etc.
· This would allow the study of normal development but also enable scientists to investigate the effect of gene mutations on differentiation of certain cell types
· Different tissue types can be grown in the lab and medicines can be tested on them for effectiveness and side effects
