OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~504 words · 3 min

Mass Extinction and the Rise of New Life Species go extinct all the time — old species disappearing as new ones evolve is the normal, ongoing 'background' rate of extinction. A mass extinction is different: it is a sharp spike far above tha

Biology

Biology · L3 · Mass Extinction and the Rise of New Life

@openstem

Note~458 words · 2 min

Ecology, evolution, and the web of life Ecology and evolution are inseparable: ecological interactions drive natural selection, and evolutionary changes reshape ecological communities. Together they explain how life is distributed, why biod

Biology

Biology · L4 · Ecology, evolution, and the web of life

@openstem

Note~472 words · 2 min

Cellular respiration: glycolysis, Krebs cycle, and oxidative phosphorylation Cellular respiration is the process by which cells extract energy from organic molecules, principally glucose (C₆H₁₂O₆), and store it as ATP. The overall reaction:

Biology

Biology · L4 · Cellular respiration: glycolysis, Krebs cycle, and oxidative phosphorylation

@openstem

Note~441 words · 2 min

Photosynthesis: light reactions and the Calvin cycle Photosynthesis is the process by which photosynthetic organisms convert light energy into chemical energy stored in organic molecules. Overall equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O

Biology

Biology · L4 · Photosynthesis: light reactions and the Calvin cycle

@openstem

Note~446 words · 2 min

Nervous system: neurons, synapses, and action potentials The nervous system enables rapid communication between cells. In vertebrates, it is divided into the central nervous system (CNS: brain + spinal cord) and the peripheral nervous syste

Biology

Biology · L4 · Nervous system: neurons, synapses, and action potentials

@openstem

Note~1092 words · 5 min

Sensory Physiology and Transduction Mechanisms Every sense organ solves the same underlying problem: convert some feature of the physical or chemical world into a change in membrane potential that the nervous system can interpret. Despite t

Biology

Sensory Physiology and Transduction Mechanisms

@openstem

Note~1114 words · 6 min

Cell Signaling and Cell Cycle Regulation Multicellular life depends on cells communicating accurately with one another and responding appropriately to their internal state. Two systems make this possible: signal transduction pathways that c

Biology

Cell Signaling and Cell Cycle Regulation

@openstem

Note~931 words · 5 min

Molecular genetics and gene expression: from DNA to protein Gene expression is the multistep process that converts information stored in DNA into a functional product, most often a protein. Each step — transcription, RNA processing, and tra

Biology

Biology · L4 · Molecular genetics and gene expression

@openstem

Note~1263 words · 6 min

Biotechnology and recombinant DNA technology Biotechnology uses living cells and their molecular machinery to solve practical problems — manufacturing medicines, diagnosing disease, improving crops, and correcting genetic disorders. Nearly

Biology

Biology · L4 · Biotechnology and recombinant DNA technology

@openstem

Note~830 words · 4 min

Population genetics Population genetics studies how allele and genotype frequencies change within a population over time. Its central tool is the Hardy-Weinberg model, which predicts what those frequencies would look like if no evolutionary

Biology

Biology · L4 · Population Genetics

@openstem

Note~959 words · 5 min

Cardiovascular Physiology Cardiovascular physiology examines how the heart generates blood flow and how the body regulates blood pressure moment to moment. Two ideas anchor this chapter: cardiac output, the volume of blood the heart pumps p

Biology

Biology · L4 · Cardiovascular Physiology

@openstem

Note~1063 words · 5 min

Respiratory Physiology Respiratory physiology examines how the mechanical act of breathing moves air, how gases cross into and out of the blood, and how the nervous system continuously adjusts breathing to match the body's metabolic demands

Biology

Biology · L4 · Respiratory Physiology

@openstem

Note~767 words · 4 min

Renal physiology: filtration, reabsorption, and hormonal control The kidneys maintain fluid, electrolyte, and acid-base homeostasis through three basic processes acting along each nephron: filtration (bulk movement of plasma into the tubule

Biology

Biology · L4 · Renal physiology: filtration, reabsorption, and hormonal control

@openstem

Note~1122 words · 6 min

Endocrine physiology: hormone signalling and the pituitary axes The endocrine system coordinates body-wide physiology through chemical messengers released into the blood. How a hormone acts on its target cell is set almost entirely by one p

Biology

Biology · L4 · Endocrine physiology — hormone signalling and the pituitary axes

@openstem

Note~725 words · 4 min

Musculoskeletal physiology: motor control and bone homeostasis Skeletal muscle and bone are both dynamic tissues under continuous physiological control. Muscle force is graded by how the nervous system recruits motor units and by the contra

Biology

Biology · L4 · Musculoskeletal physiology: motor control and bone homeostasis

@openstem

Note~1320 words · 7 min

Microbial Genetics and Pathogenesis Bacteria evolve fast, and not only through mutation. A single bacterial cell can acquire a fully functional gene — for antibiotic resistance, for a toxin, for a new metabolic pathway — from another cell o

Biology

Biology · L4 · Microbial Genetics and Pathogenesis

@openstem

Note~1228 words · 6 min

Plant Physiology and Hormones Unlike animals, plants cannot move to escape unfavorable conditions or seek out resources, so they rely on a set of chemical messengers — plant hormones — and directional growth responses to adjust their form a

Biology

Biology · L4 · Plant Physiology and Hormones

@openstem

Note~1354 words · 7 min

Community and Ecosystem Ecology A biological community is not simply a list of species sharing a location — it is a network of interactions in which each species' presence, abundance, and behavior are shaped by its neighbors. Community ecol

Biology

Community and Ecosystem Ecology

@openstem

Note~1122 words · 6 min

Enzyme Kinetics and Metabolic Pathways Cells run on chemistry, but nearly all of that chemistry is too slow to sustain life without catalysis. Enzyme kinetics gives biologists a quantitative language for describing how fast an enzyme works

Biology

Enzyme Kinetics and Metabolic Pathways

@openstem

Note~1118 words · 6 min

Neurobiology: The Action Potential and Synaptic Transmission Neurons communicate using two linked electrical and chemical processes. Within a single neuron, information travels as an action potential — a stereotyped, self-propagating change

Biology

Neurobiology: The Action Potential and Synaptic Transmission

@openstem

Note~1203 words · 6 min

Developmental Biology: From Fertilization to Body Plan Developmental biology asks how a single fertilized egg, with no apparent structure beyond its own molecular contents, reliably builds a complex, patterned, multicellular organism. The a

Biology

Developmental Biology: From Fertilization to Body Plan

@openstem

Note~781 words · 4 min

Animal Behavior and Ethology Ethology asks why animals behave as they do, treating behavior as a trait shaped by natural selection just like morphology or physiology. Behavior sits on a spectrum from rigidly innate to highly flexible and le

Biology

Animal Behavior and Ethology

@openstem

Note~559 words · 3 min

Biogeography Biogeography asks why organisms are distributed across the globe as they are, and answers draw on both deep geological history — continents moving, seas rising and falling — and ongoing ecological processes of colonization and

Biology

Biogeography

@openstem

Note~598 words · 3 min

Biomechanics and Animal Locomotion Animal movement is governed by the same physics that governs any mechanical system: levers convert muscle force into limb motion, muscle itself has intrinsic force-generating limits that depend on both its

Biology

Biomechanics and Animal Locomotion

@openstem

Note~561 words · 3 min

Classical Genetics and Inheritance Patterns Mendel's laws of segregation and independent assortment describe the simplest possible inheritance case: one gene, two alleles, complete dominance, and genes on different chromosomes. Real inherit

Biology

Classical Genetics and Inheritance Patterns

@openstem

Note~596 words · 3 min

Comparative Vertebrate Anatomy Comparative anatomy asks how the same underlying structures have been modified across vertebrate lineages to serve different functions, and how convergent pressures have produced similar solutions from entirel

Biology

Comparative Vertebrate Anatomy

@openstem

Note~667 words · 3 min

Conservation Biology Conservation biology applies ecological and genetic theory to the practical problem of preventing extinction. Two threads run through the field: quantifying how and why small or declining populations are especially vuln

Biology

Conservation Biology

@openstem

Note~540 words · 3 min

Digestive Physiology Digestion breaks large, structurally complex macromolecules into small units simple enough to absorb, and does so through a tightly coordinated sequence: acid unfolds and begins digesting protein in the stomach, hormona

Biology

Digestive Physiology

@openstem

Note~619 words · 3 min

DNA Repair Mechanisms DNA is under constant chemical and physical assault — spontaneous hydrolysis, oxidative damage from metabolism, UV radiation, replication errors — and cells maintain a suite of dedicated repair pathways, each specializ

Biology

DNA Repair Mechanisms

@openstem

Note~566 words · 3 min

Enzyme Regulation and Allostery Metabolic flux must respond to a cell's changing needs on a timescale of seconds, far faster than gene expression can act. Allosteric regulation provides this speed: reversible, non-covalent binding of small-

Biology

Enzyme Regulation and Allostery

@openstem