1. CELL THEORY
A. Cells are the smallest units of life
B. Living organisms are composed from one or more cells
C. Cells come from pre existing cells.
2. PASTEUR’S EXPERIMENTS (1850S)
A. He used four different experiments to show spontaneous generation
i.
He boiled up a nutrient broth in a flask and left it open > went bad due to bacterial growth
ii.
Repeated first experiment but sealed the flask after heating > sterile
iii.
Repeated first experiment using an open swan neck flask > sterile
iv.
Broke off the swan neck > broth went bad
3. SURFACE AREA TO VOLUME RATIO
A. An organism increases in size the SA:V decreases
B. Metabolism of a cell is linked to it mass:volume ratio
C. Surface area provides the exchange surface for heat and substances
D. More cytoplasm = more heat and waste products = greater demand for oxygen and nutrients
E. Organisms and cells develop strategies to cope with SA:V problems
i.
Plant cells develop a large central vacuole
ii.
Intestinal cells and proximal convoluted tubule cells have microvilli
iii.
Leaf palisade cells are column shaped
4. FUNCTIONS OF LIFE
A. Metabolism – all the chemical pathways that take place in the cell to build up molecules (anabolism) or break
down molecules (catabolism)
B. Response – reactions given to stimuli to help survival
C. Homeostasis – maintaining a constant internal environment
D. Growth – increasing the cell size or number of cells
E. Reproduction – producing offspring, can be sexual or asexual
F. Nutrition – taking in nutrients for growth and energy
G. Excretion – removal of waste products from metabolism
5. CELL DIFFERENTIATION
A. To become different and therefore specialise in a particular function
B. Cells in a multicellular organism are produced by mitosis – all chromosome and complete genome
C. Most genes are switched off. The genes that are on are associated with respiration (to stay alive) and those
with the particular function of the cell
D. Differentiation in groups of cells produces specialised tissues
6. EMERGENT PROPERTIES
A. Only in multicellular organisms
B. Arise from the interaction of differentiated cells
C. Cells form tissues, tissues form organs, organs form organ systems > whole organism is better than the sum of
its parts
7. STEM CELLS
A. Undifferentiated cells, retaining the capacity to divide and to differentiate along different pathways eg: during
embryonic development
B. Some tissues retain stem cells to continue producing new cells or replacing damaged cells
C. Some stem cells have the potential for therapeutic use
i.
Stargardt’s disease – replace the RPE (retinal pigment epithelium) cells, human embryonic stem cells into
affected area, cells survive and multiply, improvement in patients eyesight
ii.
Leukaemia – cancer of WBC and/or bone marrow cells, chemotherapy kills all mutated and normal BMC,
stem cells collected from donor BM or umbilical cord blood introduced into the patients blood > migrate
to BM to produce healthy leucocytes
D. Ethics with stem cells
i.
Adult tissues
A. Autologous harvesting is the least controversial – cells from patient
B. Other cases see cells from a donor, with the decision to donate their cells
ii.
Umbilical cord blood
A. Blood is easily collected with no harm to child or mother
B. The blood can be frozen for long term storage
C. Likely to be genetically different from patient if not treated
iii.
Embryonic stem cells
A. Most controversial – pluripotent differentiate into nearly all cell types = greatest potential for
therapeutic uses
B. Not accumulated any mutations, however there is a risk of them developing into tumours
C. Likely to be genetically different from patient if not treated
D. Cannot be used after 14 days
8. ELECTRON MICROSCOPES
A. Higher resolution than light microscopes
B. Can see very small objects (non-living), eg: organelles, membranes and viruses
C. Only shades of grey unless they are artificially coloured
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9. 1PROKARYOTIC CELLS
A. Simple structure and no membrane bound nucleus
B. No membrane bound organelles, non compartmentalised
C. Divide by binary fission
10.
EUKARYOTIC CELLS
A. 2Contain membrane bound organelles, compartmentalised
B. Organelles carry out specific functions
C. Animal cells
i.
Have centrioles
ii.
May have glycogen granules
iii.
May have phagocytic vesicles
STRUCTURE
FUNCTION
80S RIBOSOMES
SITE OF PROTEIN SYNTHESIS
SECRETORY VESICLE
CONTAINS ENZYMES, HORMONES OR
NEUROTRANSMITTERS
LYSOSOME
STORE OF HYDROLYSING ENZYMES THAT
ARE RELEASED IF THE CELL DIES.
ALSO USED BY PHAGOCYTES TO DIGEST
INGESTED PARTICLES.
PHAGOCYTIC VESICLE
CONTAINS INGESTED PARTICLE
(BACTERIA)
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ROUGH ENDOPLASMIC RETICULUM
TRANSPORT AND PACKING INTO VESICLES
OF PROTEIN SYNTHESISED BY THE
ATTACHED RIBOSOMES
NUCLEUS
CONTAINS CHROMOSOMES THAT CARRY
THE GENETIC INFORMATION
NUCLEAR ENVELOPE
A DOUBLE MEMBRANE WITH NUCLEAR
PORES TO ALLOW EXCHANGE BETWEEN
CYTOPLASM AND NUCLEOPLASM
NUCLEAR PORE
ALLOWS EXCHANGE OF SUBSTANCES
BETWEEN THE NUCLEOPLASM AND
CYTOPLASM
CENTRIOLES
INVOLVED IN SPINDLE FIBRE FORMATION
DURING CELL DIVISION
GOLGI APPARATUS AND VESICLES
MODIFIES AND REPACKS PROTEINS FROM
THE RER INTO VESICLES
MITOCHONDRION
SITE OF OXIDATIVE OR AEROBIC
RESPIRATION.
D. Plant cells
i.
Have a cellulose cell wall
ii.
Mature cells may have a large central vacuole
iii.
Photosynthesising cells have chloroplasts
iv.
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May have starch grains
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STRUCTURE
FUNCTION
80S RIBOSOMES
SITE OF PROTEIN SYNTHESIS
ROUGH ENDOPLASMIC RETICULUM
TRANSPORT AND PACKING INTO VESICLES
OF PROTEIN SYNTHESISED BY ATTACHED
RIBOSOMES
CHLOROPLAST
SITE OF PHOTOSYNTHESIS
VACUOLE
CONTAINS WATER, SALTS AND WASTE
PRODUCTS
NUCLEUS
CONTAINS CHROMOSOMES THAT CARRY
GENETIC INFORMATION
NUCLEAR ENVELOPE
A DOUBLE MEMBRANE WITH NUCLEAR
PORES TO ALLOW EXCHANGE BETWEEN
CYTOPLASM AND NUCLEOPLASM
NUCLEAR PORE
ALLOWS EXCHANGE OF SUBSTANCES
BETWEEN THE NUCLEOPLASM AND
CYTOPLASM
GOLGI APPARATUS AND VESICLES
MODIFIES AND REPACKS PROTEINS FROM
THE RER INTO VESICLES
MITOCHONDRION
SITE OF OXIDATIVE/AEROBIC RESPIRATION
11.
COMPARING PROKARYOTIC AND EUKARYOTIC CELLS
A. Naked DNA, DNA in cytoplasm, DNA circular, no membrane bound structures, plasmids present, ribosomes
smaller 70S
B. DNA wrapped around special proteins, DNA enclosed by a nuclear envelope, DNA linear, membrane bound
structures such as mitochondria/ER and Golgi apparatus present which compartmentalise functions, no
plasmids, ribosomes larger 80S
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12.
COMPARING PLANT AND ANIMAL CELLS
A. Cellulose cell wall, mature cells usually only contain a large central vacuole, no cholesterol in the plasma
membrane, no centrioles, store starch, may contain chloroplasts
B. No cellulose cell wall, no large central vacuole but small vacuoles may be present in the cytoplasm,
cholesterol in the plasma membrane, centrioles present, store glycogen, never contain chloroplasts.
13.
MEMBRANES
A. Cytoplasm is surrounded by the plasma membrane
B. Eukaryotic cells have several membranous substances providing compartments
C. Double membrane is an envelope
D. Membranes are partially permeable
E. Membrane structure
i.
Phospholipids – hydrophilic head and hydrophobic tails, bilayer
ii.
Proteins – highly variable in structure, position and function, some with a carb chain > glycoprotein
Cholesterol – up to 50% membrane, reduces membrane fluidity, reduces permeability to some substances
iii.
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iv.
Glycoproteins
F. The phospholipid bilayer
i.
Amphipathic
ii.
The phospholipids form a bilayer
iii.
Water solution on each side of membrane, hydrophilic part next to the solution
iv.
The major force causing the formation of the bilayer is the hydrophobic interaction
v.
Flexible, easily broken and rejoined bilayer due to only forces
vi.
Saturated fatty acid chains make a membrane less fluid as they are packed tighter together
vii.
Cholesterol can make animal membranes less fluid by reducing tail movement
G. The proteins
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i.
Surface proteins = peripheral
ii.
Partially embedded = integral
iii.
Some on the outer surface are called glycoproteins
iv.
Hormone receptors, active transport, facilitated diffusion channel, electron carriers, immobilised enzymes,
cell adhesion, cell to cell communication
H. Davson-Danielli Model (1935)
I.
i.
Phospholipid bilayer in the centre, proteins coat both surfaces, evidence from electron micrographs, later
added protein lined channels through the phospholipid bilayer
ii.
Problems – proteins exposed to hydrophilic surfaces on both sides = unstable, lipid soluble substances
cannot pass through, membranes around different organelles have different functions so cannot have the
same structure, membranes are bifacial
Singer-Nicholson Model (1972)
i.
14.
Fluid mosaic model, from observations on electron microscope, proteins on surface of bilayer not
continuously, proteins move freely over surface, some proteins move from one side to another
TRANSMEMBRANE TRANSPORT
A. Simple diffusion
i.
Through the air, across membrane with oxygen, lipids and steroid hormones, passive, random, high
concentration to a low concentration using molecular kinetic energy
B. Facilitated diffusion
i.
Can't go through bilayer > integral protein channels with hydrophilic core, have a binding site, can be
gated to control the flow
C. Osmosis
i.
Diffusion of water, passive, low solute concentration to high solute concentration, water moves by
osmosis/simple diffusion through phospholipid bilayer and facilitated diffusion through channels.
D. Determining osmolarity of a tissue
i.
Hypertonic = cell loses water through osmosis and shrinks
ii.
Hypotonic = cell gains water and swells (plasmolysis), animal cells can burst not plant
iii.
Isotonic = remain unchanged as no osmosis takes place
E. Active transport
i.
Always uses energy from ATP, Hydrolysed to ADP + Pi, Transports against concentration gradient,
requires integral transport protein, change in protein shape, specific binding site for specific substance,
some transport two substances at the same time > same direction = symport or different directions =
antiport
F. Endocytosis
i.
Taking substance into cells, phagocytosis takes in particles and solution, energy from ATP is required,
plasma membrane folds inwards to form a vesicle which buds off
G. Exocytosis
i.
Removes substances from cells, includes secretion of useful substances or excretion of waste, vesicle in
the cytoplasm joins the plasma membrane and bursts
H. Transport vesicles
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i.
15.
Vesicles bud off of rER, move through cytoplasm and join to one side of Golgi apparatus, bud off other
side of Golgi apparatus, move to plasma membrane for secretion of contents, may remain in cytoplasm as
a lysosome and fuse with a phagocytic vesicle
THE ORIGIN OF CELLS
A. Cells can only be formed from pre existing cells
B. The first cells must have arisen from non-living material
C. The origin of eukaryotic cells can be explained by the endosymbiotic theory
D. The endosymbiotic theory
16.
i.
Eukaryotic cells arose from combinations of different types of prokaryotic cell
ii.
Battle between host and invader – bacterium inside other bacterium
iii.
Endosymbiotic theory states that neither host nor invader win and form mutualism
iv.
Mitochondria are an example as they have their own DNA and way of living inside a cell
CELL DIVISION
A. Called cytokinesis, preceded by nuclear division (mitosis or meiosis), cycling are involved in the control of
the cell cycle
B. Cell cycle
i.
17.
Interphase, mitosis and cytokinesis
MITOSIS
PHASE
PROPHASE
METAPHASE
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KEY POINTS

REPLICATED DNA CONDENSES BY
SUPERCOILING AND IS THEN VISIBLE
UNDER A LIGHT MICROSCOPE

SPINDLE MICRO TUBULES START TO
FORM

NUCLEAR ENVELOPE BREAKS DOWN

MICRO TUBULE NETWORK COMPLETED

MICRO TUBULES ATTACH TO
CENTROMERES
ANAPHASE
TELOPHASE

CHROMOSOMES MOVE TO THE EQUATOR
OF THE CELL

CENTROMERES SPLIT

MICROTUBULES CONTRACT

CHROMOSOMES PULLED T O OPPOSITE
POLES

CHROMOSOMES UNCOIL

MICRO TUBULES BREAK DOWN

NUCLEAR ENVELOPE REFORMS
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18.
DIFFERENCE BETWEEN CHROMOSOME AND CHROMATID
A. Sister chromatids – chromosome
B. Two chromosomes
19.
CELL DIVISION AND CANCER
A. Uncontrolled cell division
B. Can spread via both blood and lymph
C. Mutagens – causes mutation of a cells genome, eg: X-rays, hydrogen peroxide, nickel, viruses
D. Oncogenes – genes that can turn into a normal or tumour out cell, involved in the cell cycle, prevent death and
allow the cell to survive and divide, may need another gene to mutate to cause cancer
E. Metastasis – spread of cancer from one part of the body to another, primary stays in the same place, may
become metastatic, can then lodge in another part of the body and cause a secondary tumour
20.
CORRELATION BETWEEN SMOKING AND INCIDENCE OF CANCER
A. 1/5 of all cancer cases, causes more that 4/5 cases of lung cancer
21.
MEIOSIS
A. Most cells are diploid, have two sets of chromosomes in each cell nucleus
B. Chromosomes are in pairs, each parent contributed to one pair
C. Haploid cell has one set of chromosomes
D. Meiosis is a reduction division
i.
One parent results in 4 daughter nuclei
ii.
One or more of these nuclei differentiate into a gamete
E. Halving of chromosome number allows for sexual life cycle with fusion of gametes
F. Genetic variety
PHASE
PROPHASE 1
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KEY POINTS

REPLICATED DNA START S TO CONDENSE
BY SUPERCOILING

REPLICATED CHROMOSOMES PAIR UP
INTO THEIR HOMOLOGOUS PAIRS TO
FORM A BIVALENT (SYNAPSIS)

SUPERCOILING/CONDENSATION
COMPLETED
METAPHASE 1
ANAPHASE 1
TELOPHASE 1
METAPHASE 2
ANAPHASE 2
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SPINDLE MICRO TUBULE START TO
FORM

NUCLEAR ENVELOPE BREAKS DOWN

MICRO TUBULE NETWORK COMPLETED

MICRO TUBULES ATTACH TO
CENTROMERES

BIVALENTS MOVE TO EQUATOR AND
ALIGN IN A RANDOM WAY

CENTROMERES DO NOT SPLIT

MICRO TUBULES CONTRACT

HOMOLOGOUS CHROMOSOMES PULLED
TO OPPOSITE POLES

FIRST CELL DIVISION STARTS *

MICRO TUBULE NETWORK COMPLETED

MICRO TUBULES ATTACH TO
CENTROMERES

CHROMOSOMES MOVE TO THE EQUATOR

CENTROMERES DO SPLIT
*
CYTOKINESIS 1
PROPHASE 2

*
TELOPHASE 2
CYTOKINESIS 2

MICRO TUBULES CONTRACT

CHROMOSOMES PULLED T O OPPOSITE
POLES

CHROMOSOMES UNCOIL

SPINDLE FIBRE NETWORKS BREAK
DOWN

NUCLEAR ENVELOPE REFORMS

SECOND CELL DIVISION INTO HAPLOID
CELLS
G. 6* The spindle fibre network breaks down and two new ones begin to form, often at right angles to the first
one.
H. Sexual reproduction
I.
Meiosis – crossing over in P1, maternal and paternal alleles between non sister chromatids of homologous
chromosomes / bivalents line up on the equator in a random way
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J. Also from random fertilisation of gametes
22.
NON-DISJUNCTION
A. When separation of homologous chromosomes or sister chromatids fails to occur
B. Can happen at anaphase of first or second division
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23.
AGE AND NON-DISJUNCTION
A. Association between maternal age and chromosome 21 non-disjunction
B. Associated with meiosis 1 and meiosis 2 errors
24.
KARYOTYPING
A. Arranging chromosomes according to their size and banding pattern
B. Used in pre-natal diagnosis of abnormalities, observing major changes in chromosome structure due to
mutations, changes in chromosome numbers
C. Foetal cells collected through amniocentesis or chronic villus sampling
D. Risks – small risk of injuring foetus or causing a miscarriage
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