Chemistry with biological function.
Proteins, nucleic acids, lipids and carbohydrates participate in structure, signaling, catalysis and information storage.
Side 18
Biology
A study of living systems across scale: molecules become cells, cells become organisms, organisms reproduce and evolve, and populations interact with environments that they also transform.
organization→information→energy→regulation→evolution
06levels
05information steps
05evolution forces
18Side
Life is organized hierarchically — but causation moves both ways.
Biological explanation often shifts between molecular mechanisms and higher-level constraints such as development, environment and population structure.
Specialized intracellular machinery.
Membranes divide labor into compartments such as nucleus, mitochondria, lysosomes and endoplasmic reticulum.
Basic living unit.
Cells maintain boundaries, transform energy, regulate internal state, process information and reproduce.
Integrated multicellular system.
Tissues and organs coordinate through signaling, transport, nervous and endocrine regulation.
Individuals connected by reproduction.
Allele frequencies, demography and selection become meaningful at population scale.
Organisms + environment.
Energy flows and nutrients cycle through interacting communities and physical conditions.
Emergence does not erase mechanism.
A higher-level property can arise from lower-level interactions while still requiring its own useful description.
A cell is an active boundary.
Cells persist by controlling exchange, maintaining gradients, repairing structure and coordinating thousands of chemical reactions.
Selective boundary.
Lipid bilayers and embedded proteins regulate movement of ions, nutrients and signals.
Shape and internal transport.
Protein filaments organize form, force generation, division and movement within the cell.
Energy conversion.
In eukaryotes, mitochondria couple electron transport to ATP production.
Genome organization.
DNA is packaged, replicated and transcribed within a regulated nuclear environment in eukaryotic cells.
Protein synthesis.
Ribosomes translate messenger RNA sequences into amino-acid chains.
Sense and respond.
Receptors and intracellular pathways convert environmental or internal cues into cellular responses.
Cellular problemmaintain internal order while matter, energy and information continuously cross the boundary
Biological information is stored, copied, expressed and regulated.
The familiar DNA → RNA → protein flow is a useful backbone, but regulation and feedback make expression a dynamic network rather than a one-way pipeline.
Store hereditary sequence.
Which sequence and regulatory context?
Genes occupy genomes alongside extensive regulatory and structural DNA.
Copy before division.
How is fidelity maintained?
Polymerases and repair systems reduce but do not eliminate mutation.
Produce RNA.
Which genes are active?
Transcription factors and chromatin state help regulate when genes are expressed.
Build polypeptides.
How is sequence converted?
Ribosomes read codons and assemble amino acids according to the genetic code.
Control abundance and activity.
When, where and how much?
RNA processing, degradation, localization and protein modification all shape final function.
Gene ≠ destiny.
Phenotypes emerge from genotype interacting with developmental history, cellular state and environment.
Life runs far from equilibrium.
Organisms continually acquire energy and matter, channel them through reaction networks and regulate those flows to maintain viable internal conditions.
Metabolic logic
Catabolism
Break down.
Complex molecules are converted into smaller products while releasing usable energy.
Anabolism
Build up.
Energy is invested to synthesize cellular structures and storage molecules.
ATP
Couple reactions.
ATP frequently links energy-releasing processes to energy-requiring cellular work.
Regulatory logic
Feedback
Output regulates pathway.
Negative feedback can stabilize concentrations and physiological variables.
Hormone
Coordinate across distance.
Endocrine signals alter activity in target cells carrying appropriate receptors.
Homeostasis
Regulate around viable ranges.
Temperature, glucose, pH and ion balance are dynamically controlled rather than held perfectly constant.
Populations change across generations.
Evolution requires heritable variation and changes in the frequencies of variants through mechanisms that include selection, drift, mutation and migration.
Create new sequence variation.
Mutations introduce new genetic variants; their effects can be harmful, neutral or beneficial depending on context.
Different reproductive success.
Heritable traits affecting survival or reproduction can change in frequency across generations.
Sampling changes frequencies.
Random reproductive sampling can substantially alter allele frequencies, especially in small populations.
Variants move between populations.
Migration and reproduction can transfer alleles and reduce or reshape population differences.
Existing variation is reshuffled.
Sexual reproduction produces new combinations of alleles without necessarily creating new alleles.
Lineages diverge.
Reproductive isolation can accumulate until populations become independently evolving lineages.
Selection has no foresight.
Adaptation describes differential persistence under past and present conditions, not a process working toward predetermined goals.
No organism is studied alone for long.
Ecology asks how organisms interact with one another and with physical environments across space and time.
Population
Birth, death, immigration and emigration determine abundance and age structure.
Competition
Organisms can reduce one another’s access to limiting resources.
Predation & herbivory
Consumer-resource interactions can create feedback, oscillation and evolutionary response.
Mutualism
Interactions can increase fitness for both partners while remaining conditional on environment and partner behavior.
Food web
Energy and matter move through networks rather than simple linear chains.
Biogeochemical cycle
Carbon, nitrogen, phosphorus and water move between organisms and the physical environment.
Campbell BiologyUrry et al. · broad biological foundation
Molecular Biology of the CellAlberts et al. · cellular mechanisms
EvolutionDouglas Futuyma & Mark Kirkpatrick · evolutionary biology
EcologyBegon, Townsend & Harper · ecological principles