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2. Cells
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Biology
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Topics
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2. Cells
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Topics
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Understanding points
Early Earth conditions
•
High CH₄ and CO₂ concentrations due to volcanic activities and meteorite bombardment → more
greenhouse gasses
→ higher temperatures
•
UV
penetration to Earth’s surface due to lack of ozone layer and frequent lightning → triggered various chemical reactions
•
Miller-Urey Experiment:
mimicked early Earth conditions to show the synthesis of organic carbon compounds from inorganic gasses that represent the pre-biotic atmosphere
A2.1.1 Early Earth Condition
Developments required for the origin of life
A2.1 Origins of cells
Understanding points
Cell theory
1.
All living things are composed of cells
2.
Cells can only be formed by division of pre-existing cells
3.
Cell is the basic unit of all “Living things”
A2.2.1 Cell Theory
Microscopy
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A2.2 Cell structure
Understanding points
Virus
•
Virus
: non-living agents that infect host cells to reproduce inside them
•
Small and fixed size
•
Contains nucleic acid as genetic material
•
Capsid
: protein coat that encloses genetic material
•
Envelope:
viruses that infect animal cells are covered in host plasma membranes
A2.3 Viruses
Understanding points
Phospholipid bilayer
•
Phospholipids have
hydrophilic
and
hydrophobic
regions
•
Hydrophilic heads are attracted to water → face watery environment
•
Hydrophobic tails are repelled by water → arrange themselves inwards
B2.1.1 Phospholipid bilayer
B2.1 Membranes and membrane transport
Understanding points
Advantage of nucleus
•
Separation and control of transcription and translation
•
*(AHL)
double
membrane
Advantage of compartmentalization
1.
Concentrated enzymes and substrates → speed up catalysis
2.
Maintenance of ideal pH → speed up catalysis
3.
Separation of incompatible biochemical processes: e.g. lysosomes
*(AHL)
Mitochondria and chloroplast
B2.2 Organelles and compartmentalization
Understanding points
Differentiation
•
Involves the expression of some genes and not others in a cell’s genome
•
Specialised tissues can develop by cell differentiation in multicellular organisms
Stem cells
•
Totipotency
: able to divide and differentiate into any cell type
•
Only some genes are expressed in each cell type → differentiate differently
•
Stem cell therapy relies on replacing diseased tissue:
B2.3.1 Stem Cells & Differentiation
Specialization and cell size
B2.3 Cell specialization
Understanding points
Receptors
•
Signals can be
chemical
or
electrical
•
Ligand
: a molecule that binds specifically to a site on a receptor
•
Receptor: a molecule that binds with ligands to convey signals that affect cellular activity
•
The
specificity
of receptor-ligand binding is similar to enzyme-substrate interactions
Signalling chemicals
C2.1 Chemical signaling
Understanding points
Neuron
•
Cells of the nervous system
•
The speed of nerve impulse transmission is increased by:
C2.2.1 Neuron
Nerve impulse
•
Electrical signal
Resting potential
Maintained at -70mV by Na⁺/K⁺ pump
C2.2 Neural signaling
Understanding points
*(AHL) Cell Cycle
•
Interphase → Mitosis [prophase → metaphase → anaphase → telophase] → Cytokinesis
Interphase
*(AHL)
DNA replication & cell growth
G1: Mitochondria and chloroplasts grow and divide
S: DNA replication
G2: Further growth in preparation for mitosis
D2.1 Cell and nuclear division
Understanding points
Gene expression
•
Process of turning genotype into phenotype
•
The pattern of gene expression determines that cell’s route of differentiation
Regulation of gene expression
•
Internal factors
•
External factors
Epigenesis
D2.2 Gene expression
Understanding points
Solvation
•
The process of dissolving
•
Solvent
: liquids that dissolve other substances
•
Solute
: dissolved substances in solutions
D2.3.1 Solvation
Osmosis
•
Diffusion of water molecules
•
Movement of water from
high
water potential to
low
water potential (hypotonic to hypertonic)
•
Intravenous fluids and organs used in transplants must be bathed in isotonic solution (
0.9% NaCl)
to prevent osmotic damage
D2.3 Water potential
