2. Cells

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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 Origins of cells

Understanding points

Cell theory

All living things are composed of cells

Cells can only be formed by division of pre-existing cells

Cell is the basic unit of all “Living things”

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

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 Membranes and membrane transport

Understanding points

Advantage of nucleus

Separation and control of transcription and translation

*(AHL) double membrane

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

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

C2.1 Chemical signaling

Understanding points

Neuron

Cells of the nervous system

The speed of nerve impulse transmission is increased by:

C2.2 Neural signaling

Understanding points

*(AHL) Cell Cycle

Interphase → Mitosis [prophase → metaphase → anaphase → telophase] → Cytokinesis 

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 

D2.2 Gene expression

Understanding points

Solvation

The process of dissolving

Solvent: liquids that dissolve other substances

Solute: dissolved substances in solutions

D2.3 Water potential