Foundations

Nitrogen fixation converts N₂ toward biologically usable reduced nitrogen; ammonification, nitrification and denitrification transform nitrogen among distinct chemical pools.

Biodiversity includes genetic, species and ecosystem dimensions.

Fossil assemblages can constrain relative age and depositional environment through observed succession and known ecological context.

Mechanical weathering changes fragment size; chemical weathering transforms or dissolves minerals through reactions such as hydrolysis and oxidation.

Dissolved inorganic carbon includes aqueous CO₂/carbonic-acid convention, bicarbonate and carbonate.

Aminoacyl-tRNA synthetases couple amino acids to cognate tRNAs using ATP-dependent activation.

Canonical eukaryotic initiation recruits a small ribosomal complex near the capped mRNA end and scans for a start codon in a suitable context.

Enhancer-bound activators can influence a promoter through protein interactions, including Mediator and chromatin-remodelling or modifying complexes.

In the canonical secretory route, SRP recognizes an emerging signal sequence and targets the ribosome–nascent-chain complex to the ER receptor and Sec61 channel.

Many nuclear-encoded mitochondrial matrix proteins carry targeting sequences recognized by TOM and transferred through the TIM23 pathway.

Rab GTPases and effectors help recruit and tether transport carriers at appropriate membranes.

An activated GPCR promotes GDP release and GTP binding on a heterotrimeric G protein's α subunit.

Activation of a receptor tyrosine kinase can create phosphotyrosine docking sites for adaptors and enzymes.

Members of the nuclear-receptor family bind suitable intracellular ligands and regulate target-gene transcription through DNA-binding and co-regulatory interactions.

A protein sequence and its chemical environment constrain a conformational energy landscape.

Rubisco's oxygenase activity produces a three-carbon phosphoglycerate and a two-carbon phosphoglycolate from RuBP.

In a common C4 route, PEP carboxylation supplies four-carbon acids that deliver CO₂ to Rubisco in a spatially separated compartment.

Chloroplast triose-phosphate exchange with inorganic phosphate connects photosynthetic fixation to cytosolic sucrose synthesis.

Symmetry, germ layers, body cavities and segmentation describe different aspects of animal organization.

Many sponges pump water through pores and feeding chambers using choanocyte flagella, capturing particles at the collars for intracellular digestion.

Cnidarians characteristically possess cnidocytes with specialized discharge organelles, tissue layers around a gastrovascular cavity and a distributed nervous system.

A typical molluscan organization comprises a mantle, visceral mass and a muscular foot whose form can be strongly modified.

Ecdysozoans replace an external cuticle through molting and ecdysis.

Echinoderms characteristically have a calcareous internal skeleton and a water vascular system associated with tube feet; typical adults are pentaradial even though their ancestry lies within bilaterian animals.

Gametogenesis combines germ-cell proliferation, meiosis and cellular differentiation.

Body heat exchange involves radiation, evaporation, convection and conduction.

Plant growth combines cell production in meristems with expansion and differentiation.

Mutation transfers allele copies between states.

If migrants form a specified fraction of a population's allele pool, the post-migration allele frequency is a weighted average of resident and migrant frequencies.

Recurrent mutation can replenish a deleterious allele that purifying selection removes.