2.1.6 Cell division, cell diversity and cellular organisation Flashcards
the cell cycle
M phase (mitosis) cytokinesis interphase (G1, S, G2) repeat cycle G0
G0 (gap 0) phase
resting phase
where differentiated cells or stem cells (waiting to divide stay) (temporary/lifetime)
may differentiate, apoptosis, senescence
M phase
cell growth stops nuclear division (mitosis) and cytokinesis (cytoplasmic division) checkpoint chemical triggers condensation of chromatin metaphase checkpoint makes sure cell can complete mitosis
senescence definition
irreversible end of cell growth
helps suppress development of cancer
G1 (gap 1) phase
“growth phase”
G1 checkpoint makes sure cell is ready to enter S phase
carries out growth and normal cell functions
makes enzymes needed for DNA replication in S phase
p53 gene (tumour suppressor) helps control phase
(aerobic respiration, biosynthesis)
biosynthesis definition
production of complex molecules within living organisms or cells
e.g. protein synthesis, organelle repair in animal cells
S (synthesis) phase
committed to complete cell cycle once entering S phase
DNA replicates (most important sequences of DNA replicated first)
chromosomes consists of a pair of identical sister chromatids
rapid (reduces chances of spontaneous mutations)
why S phase is rapid
exposed DNA base pairs more susceptible to mutagenic agents
reduces likelihood of spontaneous mutations happening
G2 (gap 2) phase
copied DNA checked by proof-reading enzymes
if not copied properly, mutations arise and new cells may not work properly / be cancerous
what happens during cytokinesis
cytoplasm cleaves (divides) to form 2 distinct daughter cells ready to begin cell cycle
importance of mitosis in life cycle
asexual reproduction: produces genetically identical offspring, mostly single-called organisms
growth: produces more genetically identical cells
tissue repair: growth factor stimulates proliferation of cells for repair
mitosis stages
just nuclear division prophase metaphase anaphase telophase
prophase method
sister chromatids coil and condense (visible under light microscope)
nuclear envelope breaks down
spindle fibres begin to form from centrioles
metaphase method
chromatids attach to spindle fibres (via centromeres)
line up on equator of cell
anaphase method
centromere of each pair of chromatids split
motor proteins on spindle fibres pull sister chromatids apart to opposite poles of cell
telophase method
separated chromosomes reach opposite poles
nuclear envelope reforms around each set of chromosomes
cell contains two nuclei genetically identical to each other and the parent cell from which they arose
cytokinesis method
plasma membrane folds inwards and “nips in” along “cleavage furrow” of cytoplasm (animal cell)
cell plates forms where equator of spindle was, new plasma membrane and cell wall laid down either side of end plate
bulge formed, nucleus goes into bulge and pinches off, leaving bud scars (budding, yeast)
importance of meiosis
produces haploid gametes for sexual reproduction
combines genetic material from two (usually) unrelated members of same species (fertilisation)
increases genetic variation
increases chances of survival of population (some individuals have characteristics to better adapt to environmental changes)
homologous chromosome definition
same genes but different alleles
allele definition
variant of the same gene
meiosis order
first meiotic division (prophase 1, metaphase 1, anaphase 1, telophase 1)
short interphase
second meiotic division perpendicular to first meiotic division (prophase 2, metaphase 2, anaphase 2, telophase 2)
cytokinesis
prophase 1
chromatin condenses and supercoils
nuclear envelope breaks down
spindle fibres form from centrioles
chromatids come together in homologous pairs
crossing over occurs (non-sister chromatids wrap around each other, may swap sections, shuffling alleles)
metaphase 1
crossed-over homologous pairs of chromatids up along equator of spindle
each attaches to spindle fibres by centromere
arranged randomly, members of each pair facing opposite poles of cell (independent arrangement)
anaphase 1
crossed-over homologous pulled apart by motor proteins along spindle fibres
crossed-over areas of homologous pairs separate (alleles are shuffled)
telophase 1
two nuclear envelopes reform around each set of chromosomes
cytokinesis then a short interphase (chromosomes uncoil)
each new nucleus contains half number of original set of chromosomes
each chromosomes made up of 2 chromatids
in most plant cells, goes straight from anaphase 1 to prophase 2
prophase 2
nuclear envelopes break down if reformed previously
chromosomes coil and condense (made up of 2 non-identical chromatids)
spindles form
metaphase 2
chromosomes attach by centromeres to equator of spindle
chromatids of chromosomes randomly arranged
anaphase 2
centromeres divide
chromatid of each chromosome pulled apart by motor proteins along tubulin threads on spindle towards opposite poles
chromatids randomly segregated
telophase 2
nuclear envelope reforms around each of 4 haploid cells
two cells divide to form 4 haploid cells (animals)
tetrad of 4 haploid cells formed (plants)
how meiosis produces genetic variation
crossing over prophase 1 shuffles alleles
independent assortment of chromosomes in metaphase 1 randomly distributes maternal and paternal chromatid pairs (either one of the homologous pair can face either end of the cell)
independent assortment of chromatids in metaphase 2 further random distribution of genetic material
gametes produced fuse with random gamete of another member of same species
important of differentiation/specialisation
direct diffusion with environment not sufficient for multicellular organisms’ innermost layer of cells
also smaller SA:V ratio
also more active (need more nutrients and faster waste exchange for more aerobic respiration)
zygote definition
when an ovum(egg cell) is fertilised by sperm cell
haploid nuclei fuse to form diploid nucleus to form totipotent stem cell
how cells differentiate
certain genes are expressed or switched off changes in: -proportion of different organelles -shape of cell -contents of the cell
totipotent definition
can differentiate into any cell
pluripotent definition
can differentiate into 200 different cell types
multipotent definition
can differentiate into a limited range of cells
differentiation definition
changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function
clone definition
genetically identical cells or organisms derived from one parents (e.g. asexual reproduction)
vegetative propagation definition
plants asexual reproduction
how bacteria divide
binary fission not mitosis (no nucleus)
how RBCs differentiate
enucleated (lose nucleus) and other organelles (maximises space for haemoglobin, adds flexibility to squeeze through capillaries)
filled with haemoglobin
shape becomes biconcave (larger SA for faster gas exchange)
how neutrophils differentiate
produce more lysosomes (why it looks grainy, more phagocytosis)
nucleus becomes multi-lobed (flexibility of cell)
how sperm cells differentiate
becomes haploid (so zygote is diploid) tail (undilipodium) formed (helps sperm cell to move towards egg more mitochondria (more energy to move flagellum) shape becomes long and thin (more streamlined for ease of movement) acrosome formed (contains enzymes so sperm can penetrate egg for fertilisation)
how root hair cells differentiate
hair-like structure (larger SA for AT/diffusion of minerals and water) thinner cell wall (shorter diffusion distance) more mitochondria (more energy for AT) no chloroplast (no photosynthesis so not needed)
how palisade cells differentiate
contain more chloroplast (more photosynthesis) contain cytoskeleton threads and motor proteins (moves chloroplasts up and down depending on sunlight intensity) larger vacuole (pushes chloroplast to peripheries of cell, shorter diffusion distance of CO2) long and cylindrical (packed tight together, shorter diffusion distance for CO2 between cells)
how guard cells differentiate
thickened, more rigid inner wall than outer wall (allows closing and opening of stomata)
4 main tissue types in human body
epithelial (lining) tissue connective tissue (holds structure together and provide support) muscle tissue (cells contract and cause movement) nervous tissue (cell conduct electrical impulses)
epithelial tissue in animals features
specialised for protection, absorption,filtration excretion, secretion
short cell cycles (divide 2-3 times a day)
smooth but may have cilia
made up of almost all cells
no blood vessels (nutrients via diffusion from tissue fluid in connective tissue)
cells very close together (continuous sheets)
connective tissue features
blood, bone, cartilage, tendons, ligaments skin
non-living extracellular matrix (proteins, polysaccharides) that separates cells, allows to withstand forces
cartilage features
chondroblasts: immature, divide by mitosis, secrete extracellular matrix, develop into chondrocytes that maintain matrix
hyaline cartilage: forms embryonic skeleton, covers ends of long bones (adults), joins ribs to sternum, in nose, trachea and larynx (voice box)
fibrous cartilage: disc between vertebrae in spine and knee joint
elastic cartilage: makes up outer ear and epiglottis (flap over larynx)
muscle tissue features
well vascularised
muscle cells = fibres (contain myofilamentd made up of actin and myosin to allow for contraction)
functions of muscle
skeletal muscle: allows movement of bones
cardiac muscle: makes up walls of heart to pump blood around body
smooth muscle: walls of intestine, blood vessels, uterus, urinary tracts to allow substances to move
organ definition
collection of tissues working together to perform the same function(s)
tissue definition
collection of cells working together to complete the same function(s)
organ system definition
collection of organs working together to perform the same specific function(s)
epidermis tissue in plant features
flattened cells
guard cells
no chloroplasts
form protective covering over leaves, stems roots
sometimes walls impregnated with cutin to form waxy cuticle
vascular tissue in plants functions
xylem vessels: carry water and minerals up the plant
phloem sieve tube: transfer sucrose and other assimilated up and down the plant
meristematic tissue features
contains stem cells
all other plant tissue derive from here then differentiate
found at root tips, shoot tips, cambium of vascular bundle
cells: thin cell walls with cellulose, no chloroplasts, do not have large vacuole, divide by mitosis and differentiate into other types of cells
how cambium cells differentiate into xylem vessels
lignin deposited into cell walls
reinforced and makes it waterproof, also kills cells
end walls break down
forms continuous column with wide lumens to carry water and minerals better
lose all organelles, less resistance for water and minerals to travel through
how cambium cells differentiate into phloem sieve tubes/companion cells
sieve tubes lose most of organelles, sieve plates develop between them
companion cells retain organelles, continue functions to provide ATP for active loading of sugars into sieve tubes
plant organs functions
leaf: photosynthesis
root: anchorage in soil, absorption of mineral ions and water, storage (of carbohydrates)
stem: support, holds leaves up so exposed to more sunlight, transportation of water, minerals, sucrose, assimilates
flower: sexual reproduction
organs systems in animals for movement
skeleton and skeletal muscles to contract and mod bones
nervous system to instruct muscles to contract
circulatory system to being glucose + oxygen to respiring tissue, carry away CO2 and waste
respiratory system to transfer oxygen from atmosphere to blood
digestive system to absorb glucose from food eaten
excretory system to remove waste produced of metabolism from body
sources of stem cells
embryonic stem cells
stem cells in umbilical-cord blood
specific adult stem cells found around the adult body
induced pluripotent stem cells reprogrammed in laboratories by switching on certain key genes to turn undifferentiate cells
uses of stem cells in research and medicine
bone marrow transplants to treat diseases in blood and immune system or restore blood system after treatment
drug research (can test on human tissue rather than animal tissue so more accurate and humane)
developmental biology, improves current medics technology with better understanding of cell types
regenerative medicine (implanting cells to grow into organs in the patient so no need for immunosuppressants if own cells)
repair/replacement of damaged/lost tissues
roel of embryonic stem cells in development of embryo
undifferentiated
can differentiate into any cell type
renewing source of cells
why embryonic stem cells seen as unethical
embryo discarded/killed
embryo cannot give consent
debate about when life begins
why foetal stem cells seen as unethical
obtained from miscarried/aborted foetuses
why umbilical cord stem cells more ethical
umbilical cord detached from infant at birth anyway
why bone marrow harvesting seen as unethical
harvesting bone marrow painful / risky
donor babies conceived specifically to provide bone marrow transplant for sibling
applications of adult cell cloning
recreate and save endangered species
produce spare tissues/organs
produce elite/best animals
