OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~340 words · 2 min

Classifying life Taxonomy is the science of naming and organizing organisms into a nested hierarchy of groups, called taxa, based on shared characteristics and evolutionary relationships. Each rank in the hierarchy is broader than the one b

Biology

Biology · L3 · The Taxonomic Hierarchy

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Note~565 words · 3 min

The building blocks of life Living things are built largely from four classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Three of the four — carbohydrates, proteins, and nucleic acids — are polymers, large molecu

Biology

Biology · L3 · Biochemistry: Macromolecules and Enzymes

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Note~362 words · 2 min

Cellular Respiration in Detail Cellular respiration breaks down glucose step by step to release its stored energy as ATP. Rather than happening all at once, the process runs through three main stages, each in a different part of the cell, t

Biology

Biology · L3 · Cellular Respiration in Detail

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Note~432 words · 2 min

How the Body Regulates Temperature Human core body temperature normally stays close to 37°C, whether you're standing in the snow or lying on a beach. This stability is a form of homeostasis, and the organ in charge of it is the hypothalamus

Biology

Biology · L3 · How the Body Regulates Temperature

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Note~420 words · 2 min

Human Nutrition: Macronutrients, Energy, and Diet Every day, the body needs a steady supply of energy and building materials to keep cells working, grow new tissue, and repair damage. Three nutrients — carbohydrates, proteins, and fats — ar

Biology

Biology · L3 · Human Nutrition: Fueling the Body

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Note~500 words · 3 min

Blood Types and Transfusion Not all blood is the same. Every person's red blood cells carry (or lack) certain marker molecules called antigens on their surface, and their blood plasma carries antibodies that attack any antigen it does not r

Biology

Biology · L3 · Blood Types and Safe Transfusion

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Note~533 words · 3 min

An Introduction to Biotechnology: Cloning and GMOs Biotechnology is any use of living things, or the tools inside them, to solve a practical problem. Two of the most talked-about examples are cloning — making a genetic copy of an organism —

Biology

Biology · L3 · An Introduction to Biotechnology: Cloning and GMOs

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Note~486 words · 2 min

Respiratory Disorders The airway and the alveoli each have a job to do: the airway conducts air to the lungs, and the alveoli exchange oxygen and carbon dioxide with the blood. Different disorders disrupt this system in different places and

Biology

Biology · L3 · Respiratory Disorders

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Note~375 words · 2 min

Comparative Vertebrate Body Plans Vertebrates — animals with a backbone — are grouped into five major classes: fish, amphibians, reptiles, birds, and mammals. Every vertebrate shares the same basic body plan, but each class evolved differen

Biology

Biology · L3 · Comparative Vertebrate Body Plans

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Note~347 words · 2 min

Biodiversity Under Threat Biodiversity is the variety of life found in an area, measured at the genetic, species, and ecosystem level. It underpins ecosystem resilience, supplies food and medicine, and provides free services like clean wate

Biology

Biology · L3 · Biodiversity Under Threat

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Note~484 words · 2 min

Fungi: Decomposers, Partners, and Pathogens Fungi are a kingdom of organisms distinct from plants and animals. Instead of photosynthesizing like plants or ingesting food like animals, most fungi grow as a network of thread-like filaments ca

Biology

Biology · L3 · Fungi: Decomposers, Partners, and Pathogens

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Note~469 words · 2 min

Extremophiles: Life at the Edges Most organisms need a fairly narrow range of temperature, salinity, and pH to survive — conditions much like the ones humans are comfortable in. Extremophiles are the exception: organisms adapted to thrive i

Biology

Biology · L3 · Extremophiles: Life at the Edges

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Note~642 words · 3 min

Vaccine History and Herd Immunity Vaccination is one of the most successful ideas in the history of medicine, and it began with a single careful observation in the English countryside. This note traces that story from Edward Jenner's 1796 e

Biology

Biology · L3 · Vaccine History and Herd Immunity

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Note~484 words · 2 min

Coevolution and evolutionary arms races When two species interact closely and repeatedly over many generations — a predator and its prey, or a parasite and its host — each species can act as a selection pressure on the other. This is coevol

Biology

Biology · L3 · Coevolution and Evolutionary Arms Races

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Note~547 words · 3 min

Plant Water Relations: Turgor Pressure and Wilting Plant cells move water by osmosis just like any other cell, but one extra structure changes everything: the rigid cell wall. Because a plant cell is wrapped in a wall that its membrane cann

Biology

Biology · L3 · Plant Water Relations: Turgor Pressure and Wilting

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Note~244 words · 1 min

Photoperiodism: How Plants Sense Day Length Photoperiodism is a plant's response to the relative length of day and night. It lets a plant time major life events — most famously flowering — to the correct season, without needing to sense tem

Biology

Biology · L3 · Photoperiodism: How Plants Sense Day Length

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Note~251 words · 1 min

How Migrating Animals Navigate Many species travel enormous distances during migration — thousands of kilometers in some cases — and arrive with striking precision. That precision comes from a handful of well-studied sensory mechanisms, oft

Biology

Biology · L3 · How Migrating Animals Navigate

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Note~438 words · 2 min

Meiosis: Making Genetically Distinct Sex Cells Meiosis is the type of cell division that produces gametes — eggs and sperm. It does two things mitosis never does: it cuts the chromosome number in half, and it shuffles genetic material so th

Biology

Biology · L3 · Meiosis: Making Genetically Distinct Sex Cells

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Note~423 words · 2 min

The Other Plant Hormones Auxin isn't the only chemical messenger steering a plant's life. Four more hormones — gibberellins, ethylene, cytokinins, and abscisic acid — control everything from how tall a stem grows to how a plant survives a d

Biology

Biology · L3 · The Other Plant Hormones: Gibberellins, Ethylene, Cytokinins, and ABA

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Note~529 words · 3 min

Endocytosis and Exocytosis: Moving Bulk Material Across the Membrane Cells sometimes need to move material that is too large, or too abundant, to pass through a membrane channel or pump one molecule at a time — a whole bacterium, a mouthful

Biology

Biology · L3 · Endocytosis and Exocytosis: Moving Bulk Material Across the Membrane

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Note~522 words · 3 min

How Antibiotic Resistance Evolves It's tempting to picture antibiotics as somehow 'teaching' bacteria how to resist them. That's not what happens. Antibiotic resistance is a straightforward example of natural selection: variation already ex

Biology

Biology · L3 · How Antibiotic Resistance Evolves

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Note~537 words · 3 min

The Nitrogen Cycle in Depth Nitrogen makes up about 78% of Earth's atmosphere, yet most living things cannot use it in that form. Atmospheric nitrogen exists as N2, two nitrogen atoms locked together by an extremely strong triple bond that

Biology

Biology · L3 · The Nitrogen Cycle in Depth

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Note~437 words · 2 min

Sensory Receptor Types: Classifying by Stimulus Every sense you have — sight, hearing, touch, taste, smell, and the sense of pain — begins with a sensory receptor: a specialized cell or nerve ending built to detect one particular kind of st

Biology

Biology · L3 · Sensory Receptor Types: Classifying by Stimulus

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Note~452 words · 2 min

Asexual vs. Sexual Reproduction Across the Tree of Life Across the tree of life, organisms reproduce in two broad ways: asexually, using genetic material from a single parent, or sexually, by combining genetic material from two parents. Nei

Biology

Biology · L3 · Asexual vs. Sexual Reproduction Across the Tree of Life

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Note~573 words · 3 min

Ecological Pyramids: Energy, Biomass, and Numbers You already know that only a fraction of the energy at one trophic level passes on to the next. Ecologists use that idea to build three different kinds of pyramid diagrams, each stacking an

Biology

Biology · L3 · Ecological Pyramids: Energy, Biomass, and Numbers

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Note~685 words · 3 min

Plant Tropisms Beyond Light: Touch and Water Plants cannot walk toward what they need, but they can grow toward it. Beyond bending toward light or responding to gravity, plants also respond to touch and to moisture in the soil. These respon

Biology

Biology · L3 · Plant Tropisms Beyond Light: Touch and Water

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Note~528 words · 3 min

Animal Thermoregulation Strategies Every animal must keep its body temperature within a range where its cells can function, but different animal groups have evolved very different ways to do this. Rather than one universal solution, animals

Biology

Biology · L3 · Animal Thermoregulation Strategies

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Note~628 words · 3 min

When Immunity Misfires The immune system is normally very good at telling harmless things apart from real threats, and at telling the body's own cells apart from foreign invaders. Sometimes, though, this system gets it wrong. Two important

Biology

Biology · L3 · Allergies and Autoimmune Disease: When Immunity Misfires

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Note~602 words · 3 min

Transpiration at Ecosystem Scale: Forests and the Water Cycle A single tree loses a surprising amount of water every day, releasing it as vapor from its leaves in a process called transpiration. On its own, one tree's water loss barely regi

Biology

Biology · L3 · Transpiration at Ecosystem Scale: Forests and the Water Cycle

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Note~432 words · 2 min

Gene Editing with CRISPR: The Basics Imagine using find-and-replace in a word processor: you search for an exact phrase, and once it's found, you can delete it, fix it, or swap in something new. CRISPR-Cas9 lets scientists do something simi

Biology

Biology · L3 · Gene Editing with CRISPR: The Basics

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