edubun
English
English한국어EspañolPortuguêsFrançaisDeutschItalianoNederlandsРусскийBahasa Indonesia日本語
Home›Biology

Plants

A 5-pound willow shoot grew into a 169-pound tree in five years while its soil lost about 2 ounces. Find out where that mass came from, change light, CO₂ and temperature in a photosynthesis lab, open a leaf, follow water from root to stoma, and see how flowers turn into seeds and fruit.

Progress

About this course

In the 1600s Jan Baptist van Helmont grew a willow in 200 pounds of dried soil. After five years the tree had gained 164 pounds, a 5-pound shoot becoming a 169-pound tree, while the soil had lost about 2 ounces. Where did the mass come from? The first unit asks you to work that out, and the rest of the course gives the pieces. In September 2026 the air at Mauna Loa held 426.07 parts per million of carbon dioxide, about 52 percent more than the roughly 280 ppm before the Industrial Revolution.

The six units begin with how photosynthesis works. In 1771 Joseph Priestley burned a candle in a closed container, put a sprig of mint inside, and a few days later a candle burned again in that air. In 1779 Jan Ingenhousz showed that this happened only in light and only with green parts. Light, CO₂ and temperature then draws curves for each factor in a lab, with dashed lines for the air before the Industrial Revolution and today. Inside a leaf notes that a leaf is often only a few cells thick yet has a waterproof coat, two kinds of food-making cells, air passages, pipes and adjustable doors. Stomata and transpiration explains that up to 90 percent of the water a plant takes up can leave as vapour. Roots, xylem and phloem notes that the three working zones of a root tip fit in roughly its first centimetre, and the last unit says at least 25,000 species of orchid have been named. In the lab you click each layer of the leaf, compare xylem and phloem, and compare water lost per CO₂ on a sunny morning and a hot, dry afternoon.

Before you start

Photosynthesis happens inside cells, in chloroplasts, so Cells is helpful if those words are new. The first unit's van Helmont willow puzzle makes more sense once you know that carbon dioxide is a gas made of atoms, which States of matter touches on.

When you finish

You will be able to explain where most of a tree's dry mass comes from, predict how light, CO₂ and temperature change the rate of photosynthesis, and label the layers inside a leaf. You can describe how stomata trade water for carbon dioxide, how xylem and phloem move water and sugar, what the Casparian strip does and why bee flowers are seldom red.

  1. 1How photosynthesis worksIn the 1600s Jan Baptist van Helmont grew a willow in 200 pounds of dried soil; after five years the tree had gained 164 pounds and the soil had lost about 2 ounces.
  2. 2Light, CO₂ and temperatureIn September 2026 the air at Mauna Loa held 426.07 parts per million of carbon dioxide, about 52 percent more than the roughly 280 ppm of the air before the Industrial Revolution.
  3. 3Inside a leafA leaf is often only a few cells thick, yet it has a waterproof coat, two kinds of food-making cells, air passages, pipes and adjustable doors.
  4. 4Stomata and transpirationUp to 90 percent of the water a plant takes up through its roots can leave again as vapour through the stomata.
  5. 5Roots, xylem and phloemAll three working zones of a growing root tip fit into roughly its first centimetre.
  6. 6Flowers, seeds and fruitAt least 25,000 species of orchid have been named, and some of them get pollinated by tricking wasps.

Related courses

  • Cells
    Every living thing is built from cells, and most of them are far too small to see. This course starts with the people who first saw cells, measures them in micrometers, takes an animal cell and a plant cell apart in 3D, and ends with how one cell becomes two. Pick an organelle in the model, cut the cell open and read the scale bar as you zoom.
  • Genetics
    A short stretch of human DNA in 3D: turn the double helix, unzip it, watch it copy itself and watch a gene being read. The course goes from genes and base pairs to chromosomes, Mendel's peas, Punnett squares, mutations and the tools used to copy, read and edit DNA. It is general information, not medical or genetic-counselling advice.
  • Evolution
    Run a natural selection lab: made-up beetles on bark of different shades, with sliders for selection pressure and mutation rate and a bar chart for each generation. The course follows Darwin and Wallace, variation and inheritance, natural selection, fossils and rock layers, family trees of life, how new species form and how humans evolved, using OpenStax Biology, the Natural History Museum in London and the Smithsonian's Human Origins Program.
  • Microbes
    In 1676 Antonie van Leeuwenhoek told the Royal Society that a single drop of pepper water held upwards of a million living creatures. Meet bacteria, archaea, fungi, protists and viruses, grow a bacterial culture on a graph, and follow how scientists proved that germs exist.
Sources for this course (16)
  • -fix5: gravity calculation corrected using rho*g*h = 1000*9.8*h Pa
  • the cited textbook has a tenfold coefficient error. Sources (checked 2026-10-17): OpenStax Biology 2e 8.1 Overview of Photosynthesis (photoautotrophs, mesophyll, stomata on the underside, guard cells, chloroplast, thylakoid, granum, stroma, two stages; openstax.org/books/biology-2e/pages/8-1-overview-of-photosynthesis)
  • 8.2 The Light-Dependent Reactions (400 to 700 nm, chlorophyll a absorbs blue and red, carotenoids, 300 to 400 chlorophylls per antenna, water split at PSII, about 10 percent of the oxygen used by the leaf's mitochondria; .../8-2-the-light-dependent-reactions-of-photosynthesis)
  • 8.3 Using Light Energy to Make Organic Molecules (RuBisCO, 3-PGA, G3P, three turns per G3P and six per glucose, "dark reaction" outdated, cacti fix CO2 at night; .../8-3-using-light-energy-to-make-organic-molecules)
  • 30.3 Roots (tap and fibrous roots, root cap, three zones in the first centimetre, root hairs, endodermis and Casparian strip; .../30-3-roots)
  • 30.4 Leaves (lamina, petiole, midrib, parallel and reticulate venation, Ginkgo, cuticle, trichomes, palisade in one to three layers, spongy mesophyll, guard cells the only epidermal cells with chloroplasts, xylem and phloem, needles and spines; .../30-4-leaves)
  • 30.5 Transport of Water and Solutes (redwoods near 116 m, turgor 0.6 to 0.8 MPa and up to 1.5 MPa = 210 psi vs tyres 30 to 34 psi, gravity -0.1 MPa per metre, -2 MPa at the leaf surface, cohesion-tension, up to 90 percent of the water lost, sources and sinks, phloem sap up to 30 percent sugar; .../30-5-transport-of-water-and-solutes-in-plants)
  • 31.3 Nutritional Adaptations (rhizobia, nodules, nitrogenase, biological fixation 65 percent of nitrogen used in agriculture, mycorrhizae in more than 80 percent of land plants, up to 20 percent of the carbon; .../31-3-nutritional-adaptations-of-plants)
  • 32.2 Pollination and Fertilization (self and cross pollination, bees cannot see red, nectar guides, bats, birds, wind, water, at least 25,000 orchid species, double fertilization 2n zygote and 3n endosperm, seed parts, scutellum, fruit types, dispersal, dormancy; .../32-2-pollination-and-fertilization)
  • Britannica, Photosynthesis: history (Priestley 1771, Ingenhousz 1779, 1782: oxygen formed at the expense of fixed air, identified the year before as carbon dioxide) (britannica.com/science/photosynthesis/History-of-the-study-of-photosynthesis)
  • Smithsonian Libraries, Ingenhousz, Experiments upon Vegetables, 1779 (library.si.edu/digital-library/book/experimentsuponv00inge)
  • van Helmont's account (200 pounds of earth, 5 pound willow, 169 pounds and about 3 ounces after five years, soil short by about 2 ounces)
  • quoted from Howe 1965 by S. G. Saupe, College of St. Benedict and St. John's University (employees.csbsju.edu/ssaupe/biol115/van_helmont.htm)
  • F. F. Blackman, Optima and Limiting Factors, Annals of Botany 19:281-296, April 1905 (doi.org/10.1093/oxfordjournals.aob.a089000)
  • NOAA Global Monitoring Laboratory, Trends in CO2 (gml.noaa.gov/ccgg/trends/: Mauna Loa September 2026 monthly mean 426.07 ppm)
  • NOAA Climate.gov, Climate change: atmospheric carbon dioxide (280 ppm or less before the Industrial Revolution of the mid-1700s, from ice cores; climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide).

Checked: 2026-10-17