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Summary - 2.1.6 Cell division, cell diversity and cellular organisation

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Provides an in depth, comprehensive and high-yield summary for A - Level biology, specifically tailored to OCR A specification. These notes compile information from the official textbook, mark schemes, and class lectures into a concise revision resource. Includes: Coverage of all points on the specification for 2.1.6 Cell Division Definitions for key terminology required by examiners Clear, labelled diagrams for complex processes

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TELOPHASE
Cell cycle Interphase and Mitosis chromatin Stem cells
⑧ ⑧
·
nuclear envelope reforms a renewing source of
grainy, S
events that take place in a cell formed by ·

Interphase dispersed&....
DNA
in
mucle us
· ↑
I




cleavage furrow forms III -
cleavage
surrou undifferentiated cells -

e.g. a zygote
cell division
·

structures in cell undistinct chromosomes disperse embryonic stem cells can turn into
⑮32 any
growth and replacementof cells

Go
.
neededfor under a microscope
.
two nuclei formed cell neededfor the foetus
centro

GIgrowth- synthesis of new organelles phase-chromosomes
S Cytokinesis not in mitosis ·totipotent
mere


I
·in
->
sister
- -

any cell in an organism including
Sor chromatic

' andproteins ↳ centrosomes
replicate to form sister ·cytoplasm divides 2 extra emb ryonic tissue
->

enzymes eg. placenta
I
- -
-


62
/Il M /

~> Cytokinesis
checkpoint I checks size, nutrients, chromatics that are identical diploidcells formed - 2n

⑰ ·pluripotent-can become any cell other


growth factors + DNA
damage if oh, cycling - PHROPHASE ·
chromosomes elongate than extra-embryonic tissue often embryonic -




entre
⑪if
k




made, cell moves to S . DNA
condenses chromatid daughter cells move multipotent-only differentiate into a


-




S61 S DNA
synthesis/replication + repair ↳ chromatics visible
par
to interphase certain
group of cells eg. blood cells
-> centrosomes now made METAPHASE ·genetically identical ↳
foundin adult tissue for growthrepair



to
G rapid growth -


checking for DNA ·nuclear envelope breaks down eachomer USES research in foetal
-

development,
damage synthesis needed for cell division
+
of molecules
·chromatics align at equator mitosis in Plants replacement of tissues such as muscle or skin,
checkpoint 2 checks cell size, DNAreplication DNA centricles move to poles cell plate instead of cleavage
+
treatment of disease diabetes or Alzheimer's -




ANAPHASE centrioles
damage if oh, cycling made + cell moves to mitosis
-
furrow new membrane t hope to use stem cells from one's tissue to -- -
·




cycling proteins that are produced to confirm completion centromeres attach to spindle fibres cell wall material made prevent rejection of immune system
-




i
·chromatics to
of a stage pulled ~&
no centrioles attach walls SOURCES embryos not needed for fertility . -
-




11
Interphase G1, S andG2 -
apart now chromosomes ·only occurs in meristem ·ethical
-




Go-where cells go if they failed a checkpoint resting cytoplasm starts dividing WVk
-
tissue Mitotic Index
with condensed chromosomes
-



Specialised tissues
·
issues t
-


cells
-




of no,
state cell held back and won't replicate apoptosis (cell
100
- - concerns total
=




Cell division and diversity
of no. cells
embryos could ↳

death) occurs ANIMAL children
be




·
controlled by genes -

proto-oncogenes + tumor suppressor -
·squamous epithelium -
thin-fast diffusion -
one cell tick

genes both involved in cancer occurance Genetic diversity -

MEIOSIS ONLY ↳
Sound in
capillary walls
cancer
group of diseases
-
a caused by cells in uncontrolled Prophase 1- Crossing over method -
ciliated epithelium-cilia -
move mucus from lungs,
cell division-cells mutate to chromatics in homologous chromosomes
leading tumours goblet cells-produce mucus

twist around each other -
create chiasmata muscle tissue -

proteins (actin+ myosin) - allow for


Meiosis
·needed for production of gametes they then break away after swapping contraction, muscle shorten when contracting
begins
·
as joelus in females -

eggs that releasemature in puberty genetic information chiasmata -> Y,M cartiledge -
stiff but flexible for movement

·begins at puberty in males -
continues throughout life Metaphase 1 + 11 PLANT
·gamete cells -n/haploid/23 chromosomes -

geneticallydifferent ·
Independant assortmentoccurs -

gives
·

epidermal layer -
epithelial +
guard cells - allow
4 daughter cells produced variation when bivalents pulled apart to through the stomata
enter and exit
are
gases
·




·


homologous pair-2 chromosomes with the same genes the separation of each pair of maternal t ·


xylem part of plant -
transport system, water-
PROPHASE I PROPHASE
II paternal chromosomes to
particular poles proof (made of lignin spirals) allows it to
carry



-




0 visible
⑪*
·chromosomes condense ·chromosomes =2 chromatics is independant of each other water without leaking
nuclear envelope breaks ↳condensetare ·phloem-part of plant transport system, carries molecules
·




anomosomestriecgromosomesintrecombination
I
homologous chromosomes nuclear envelope breaks chromatics
nutrients, sieve tube element straw-like structure
S

and
·
- -

k

METAPHASE I pair Patel- synapsis METAPHASE
II allow movementof molecules





·bivalents align chromosomes



·
at equator companion cells have mitochondria for ATP to make
SI
-




align equator

Independantassortment at etc.
W
-v
-
proteins
·




E W W

·
- e
ANIMAL
centromeres attach to andattach to
I
-

Specialised cells
·




spindle spindle sibres Red blood cell Cerythrocytel Sperm cell
ANAPHASEI ANAPHASE II biconcave shape 4 SA
acrosome-enzymes to enter PLANT
-

egg




n *
·homologous pairs pulled - chromatids pulled ↳e
faster diffusion of O2 streamlined -- movement speed Palisade cell-lots of chloroplasts for
# Al to the lots of mitochondria to
apart -
to poles poles of ·no organelles/nucleus -
more -

energy photosynthesis
↳ Sister chromatics the cell-fibres Hb
for transport of O2 move Root hair cell-lots of mitochondria -




stay together shorten small flexible narrow
·

glagella movement speed for active transport, mineralions
energy
· -
-




TELOPHASE
I TELOPHASE I I


/
capillaries -
lower 4 for osmosis, hair-like shape 4 -





·nuclear envelope reforms ·chromatics disperse White bloodcells ->
lysosomes (hydrolytic for osmosis
SA
·chromosomes disperse nuclear envelope multilobulated nucleus-squeeze enzymes) to digest Guard Cell-large vacuole allows for
· · -
-




·cleavage furrow forms * reform s through small
gaps to injection pathogens lots of water to close the stomata

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August 9, 2026
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