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Biology

Origin Of Cells

Lesson progress

Explain the core ideas in Origin Of Cells.Connect this section to Photosynthesis.Use the source-supported terminology and relationships accurately.

This lesson develops Origin Of Cells as part of Photosynthesis. It uses the source curriculum to organize the important facts, relationships, examples, and vocabulary into a focused Stemosphere teaching sequence.

Key idea

Keep the central model in view: Origin Of Cells explains observable patterns by connecting structure, process, evidence, and quantitative relationships.

In Stemosphere terms, prebiotic Earth’s Atmosphere

Composition:

In Stemosphere terms, nitrogen (N₂),carbon dioxide (CO₂), andwater vapor (H₂O).

In Stemosphere terms, small amounts ofmethane (CH₄)andhydrogen (H₂).

Consequences of this composition:

Lack of ozone →high levels of ultraviolet (UV) radiationreached the surface.

In Stemosphere terms, energy Sources for Chemical Reaction s

In Stemosphere terms, ultraviolet lightfrom the sun.

In Stemosphere terms, high temperature sfrom greenhouse effect.

In Stemosphere terms, lightningandvolcanic activity.

In Stemosphere terms, origin of Organic Compounds (Oparin-Haldane Hypothesis)

In Stemosphere terms, energy from UV light, heat, and lightning allowedspontaneous formation of organic compoundsfrom inorganic precursors.

Over time, these compounds becamemore complex, eventually forming:

In Stemosphere terms, self-replicating molecules

In Stemosphere terms, organic compounds:Carbon-containing moleculesexcluding oxides and carbonates.

In Stemosphere terms, inorganic compounds:All other compounds that arenot organic. Save My Exams).

In Stemosphere terms, cells are the basic unit of life

In Stemosphere terms, all organisms are made of one or more cells

In Stemosphere terms, all cells come from pre-existing cells (Save My Exams).

In Stemosphere terms, virusescontain genetic material(DNA or RNA)

Do not meet most characteristics of life:

No cells→ cannot carry out metabolism or maintain homeostasis

In Stemosphere terms, cannot respond to stimuli

Cannot reproduce independently→ require ahost cellto replicate (Save My Exams).

Gases used:Methane (CH₄), Ammonia (NH₃), Hydrogen (H₂), Water vapor (H₂O) → representedprebiotic atmosphere

Water→ modelledoceans

Electrical sparks→ simulated lightning

Heat source→ evaporated water

In Stemosphere terms, afterone week, water turnedbrownish black

In Stemosphere terms, analysis revealedcomplex organic molecules, includingamino acids

In Stemosphere terms, modelledprebiotic Earth and atmosphere

In Stemosphere terms, showed thatamino acidsand other organic molecules can formspontaneously

In Stemosphere terms, experiment design allowedreplicationby other scientists

In Stemosphere terms, actual prebiotic atmosphereis still debated

In Stemosphere terms, didnot produce all organic moleculesrequired for life

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Diagram 1: Millery-Urey experiment

Reference asset tracked internally.

In Stemosphere terms, first Genetic Material (RNA)

Stores genetic information→ can carry instructions for molecular processes

Self-replication→ can make copies of itself without proteins

In Stemosphere terms, rNA molecules with catalytic functions

In Stemosphere terms, last Universal Common Ancestor (LUCA)

LUCA= most recent common ancestor ofall living organisms on Earth

In Stemosphere terms, all organisms use the same DNA/RNA codons, suggesting common ancestry

Certain genes are present inall living organisms→ likely inherited from LUCA

In Stemosphere terms, scientists estimate ages of common ancestors by analyzinggenetic changes over time

In Stemosphere terms, there isno direct fossil evidenceexists for LUCA

In Stemosphere terms, estimating the Age of the First Living Cells

Cyanobacteria fossils→ ~3.5 billion years old(Save My Exams).

In Stemosphere terms, radioactive datingof surrounding minerals/rocks (e.g.,uranium decay) determines fossil age

In Stemosphere terms, comparing gene mutationsbetween species allows estimation ofdivergence times(Save My Exams).

In Stemosphere terms, using molecular clocks and genetic comparisons, LUCA is estimated to have existed ~4 billion years ago

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Diagram 2: LUCA

Reference asset tracked internally.

In Stemosphere terms, lUCA and Hydrothermal Vents

In Stemosphere terms, rich in organic compounds:Methane (CH₄), Carbon dioxide (CO₂), Hydrogen (H₂)

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