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Understanding points
Early Earth conditions
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High CH₄ and CO₂ concentrations due to volcanic activities and meteorite bombardment → more greenhouse gasses → higher temperatures
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UV penetration to Earth’s surface due to lack of ozone layer and frequent lightning → triggered various chemical reactions
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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 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 Cell structure
Understanding points
Virus
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Virus: non-living agents that infect host cells to reproduce inside them
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Small and fixed size
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Contains nucleic acid as genetic material
A2.3 Viruses
Understanding points
Phospholipid bilayer
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Phospholipids have hydrophilic and hydrophobic regions
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Hydrophilic heads are attracted to water → face watery environment
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Hydrophobic tails are repelled by water → arrange themselves inwards
B2.1 Membranes and membrane transport
Understanding points
Advantage of nucleus
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Separation and control of transcription and translation
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*(AHL) double membrane
B2.2 Organelles and compartmentalization
Understanding points
Differentiation
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Involves the expression of some genes and not others in a cell’s genome
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Specialised tissues can develop by cell differentiation in multicellular organisms
Stem cells
B2.3 Cell specialization
Understanding points
Receptors
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Signals can be chemical or electrical
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Ligand: a molecule that binds specifically to a site on a receptor
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Receptor: a molecule that binds with ligands to convey signals that affect cellular activity
C2.1 Chemical signaling
Understanding points
Neuron
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Cells of the nervous system
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The speed of nerve impulse transmission is increased by:
C2.2 Neural signaling
Understanding points
*(AHL) Cell Cycle
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Interphase → Mitosis [prophase → metaphase → anaphase → telophase] → Cytokinesis
D2.1 Cell and nuclear division
Understanding points
Gene expression
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Process of turning genotype into phenotype
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The pattern of gene expression determines that cell’s route of differentiation
D2.2 Gene expression
Understanding points
Solvation
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The process of dissolving
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Solvent: liquids that dissolve other substances
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Solute: dissolved substances in solutions
D2.3 Water potential