Evidences from Cell Biology and Biochemistry

• All organisms are made of cells with a basic structural plan (membrane, cytoplasm, genetic material, ribosomes). This suggests a common origin of cellular organisation.
• Fundamental cell functions (respiration, protein synthesis, energy transfer) are similar across many groups, supporting continuity of life processes.

Universal biomolecules

• DNA, RNA, proteins, enzymes and ATP are present in almost all living organisms, indicating a shared biochemical framework.
• The genetic code and 20 common amino acids are essentially the same in all organisms, strongly supporting common descent.

ATP – universal energy currency

• ATP (adenosine triphosphate) acts as the universal energy currency in cells and is used in energy‑requiring processes in all modern life.

Common metabolic pathways

• Basic metabolic pathways (e.g., respiration, glycolysis, protein synthesis) are highly conserved among different organisms.
• This conservation implies inheritance of core biochemical systems from early ancestral life forms.

Nitrogenous wastes

• Aquatic animals often excrete ammonia, whereas many terrestrial animals excrete urea or uric acid as adaptations to water availability.
• Differences are ecological adaptations; underlying nitrogen metabolism still shows deep biochemical relatedness.

Phosphagens

High‑energy phosphate compounds used to rapidly regenerate ATP:

Patterns of phosphagens help identify and group major evolutionary lineages.

Blood pigments (respiratory pigments)

Variation in pigments shows biochemical diversification, yet the overall pattern supports the grouping of organisms.

Blood groups

• Humans show A, B, AB, O blood groups; apes have A, B, AB.
• Overlap of blood group systems is used as supporting evidence for a close human–ape relationship.

Molecular homology

• Molecular homology = similarity in DNA, RNA or protein sequences between species.
• More similar sequences ⇒ fewer mutational differences ⇒ closer evolutionary relationship.

Protein sequence comparison (cytochrome c, haemoglobin, etc.)

• Proteins like cytochrome c, haemoglobin, and fibrinogen are compared across species by their amino acid sequences.
• Differences in sequence are used to construct evolutionary trees that often match those based on anatomy and fossils.

Example pattern (conceptual):

• Human vs monkey cytochrome c: few differences ⇒ close relationship.
• Human vs duck: more differences ⇒ more distant.
• Human vs yeast: many differences ⇒ very distant.

• Cell biology evidence shows that basic cell structures and organelles are similar in most organisms, indicating a common ancestral origin.
• Biochemical molecules such as DNA, RNA, proteins, and ATP are universal, supporting the idea of unity of life.
• Molecular homology, seen in similarities of DNA and protein sequences (e.g., cytochrome c), reflects the degree of evolutionary relatedness among organisms.
• Differences in biochemical compounds like phosphagens and blood pigments help distinguish major evolutionary groups while supporting their common descent.
• Metabolic processes such as protein synthesis, respiration, and ATP usage are fundamentally similar in all living organisms.
• Similarities in traits like nitrogenous waste excretion and blood groups further support evolutionary relationships, especially between humans and apes.