A2.1:  Origins of Cell

This topic is HL only

Theme:  Unity and Diversity

The origin of life concepts demonstrate how life's earliest stages established both the fundamental unity seen across all organisms today and the incredible diversity that emerged through evolutionary processes.

Unity:

• All life began in the same harsh conditions of early Earth
• All organisms today use the same basic carbon-based chemistry.
• The cell is the basic structure that unites all life forms.
• The Last Universal Common Ancestor (LUCA) is evidenced through shared genes and the universal genetic code across all domains of life. Despite billions of years of evolution and diversification, all life retains these fundamental molecular features.
• RNA's dual role as both genetic material and catalyst in early life persists today through ribozymes in modern ribosomes. 
• The spontaneous formation of membrane-bound compartments through fatty acid vesicles represents a shared solution to creating internal chemistry distinct from the external environment.

Diversity:

• The complexity of explaining spontaneous cell origin suggests numerous different approaches to creating compartmentalized, self-replicating systems likely arose.
• Different methods for studying life's origins represent diverse attempts to understand how life could form under early Earth conditions..
• The immense timescales over which life evolved allowed for diverse chemical and biological experiments, providing vast opportunities for different evolutionary solutions to emerge and be tested. 

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What plausible hypothesis could account for the origin of life? 
• ​What intermediate stages could there have been between non-living matter and the first living cells?

Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• For what reasons is heredity an essential feature of living things? 
• What is needed for structures to be able to evolve by natural selection?​​

Key Terms to Know: all are higher level only

Amphipathic
Anabolic Reaction
Atmosphere
Bilayer
Biomarker
Carbon Compound
Catalysis
Cell
Compartmentalization
Deductive Reasoning
Emergent Property
Extraplanetary
Fatty Acid

Free- Oxygen
Hydrothermal Vent
Inorganic Molecule
Isotope
Life
LUCA
Micelle
Miller-Urey Experiment
Molecular Clock
Monomer
Organic Molecule
Ozone
Polymer

Polymerization
Pre-Biotic
Protocell
Reducing Atmosphere
Ribozyme
Ribonucleic Acid (RNA)
Self-Assembly
Self-Replicate
Self-Sustaining
Spontaneous
Stromatolite
Ultraviolet
Vesicle
Virus

AHL A2.1.1— Conditions on early Earth and the prebiotic formation of carbon compounds.

• Outline the conditions that are thought to have existed on prebiotic Earth, including atmosphere, temperature, UV radiation, volcanic activity and asteroid bombardment. 
• State that the conditions of prebiotic Earth may have caused a variety of carbon compounds to form spontaneously. ​

AHL A2.1.2— Cells as the smallest units of self-sustaining life.

• Discuss the challenges of defining matter as living or nonliving.
• Discuss the reasons why cells are considered to be living. 
• Discuss the reasons why viruses are considered to be non-living.

AHL A2.1.3— Challenge of explaining the spontaneous origin of cells.  

• Outline the intermediate stages needed for the evolution of the first cells on prebiotic Earth.
• Discuss limitations in testing hypotheses about the evolution of the first cells. 

AHL A2.1.4— Evidence for the origin of carbon compounds.

• Outline the methodology, results and conclusion that can be drawn from Miller and Urey’s experiments into the origin of biologically relevant carbon compounds.
• Discuss the benefits and limitations of the Miller-Urey apparatus as a model for a natural phenomena.

AHL A2.1.5— Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers.  ​

• Outline the cause and consequence of the spontaneous formation of membranes and vesicles by amphipathic molecules such as fatty acids and phospholipids on prebiotic Earth.

AHL A2.1.6— RNA as a presumed first genetic material.

• State that modern cells use DNA as the genetic material and enzyme proteins as catalysts of metabolism.
• List properties of RNA that suggest it was the first genetic material.
• Compare the genetic stability of RNA and DNA.
• Outline the ribosomal ribozyme as a type of RNA that is still used as a catalyst.

AHL A2.1.7— Evidence for a last universal common ancestor.

• Define LUCA.
• Discuss why the LUCA is not thought to be the first cell, but rather is thought to be the last common ancestor to all living cells.
• Explain the use of deductive reasoning to predict what genes were present in the LUCA cells.
• List characteristics of the LUCA.

AHL A2.1.8— Approaches used to estimate dates of the first living cells and the last universal common ancestor. 

• Compare the estimated dates for the evolution of the first cells and of the LUCA cells to the age of Earth.
• Describe stromatolites as the earliest direct evidence of fossilized life. 
• Outline the use of isotopes and the molecular clock for estimating dates of the first cells and of the LUCA cells. 

AHL ​A2.1.9— Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents. 

• Explain the use of deductive reasoning to predict what genes were present in LUCA cells. 
• Describe the conditions present at a white-smoker hydrothermal vent. 
• Explain how knowledge of the genes present in the LUCA cells can provide evidence that the cells lived in the vicinity of hydrothermal vents.