Plant Kingdom

Imagine plants started like humans started with huts. First plants had no proper house - just a mat lying on ground, no root stem leaves, that's algae. Then they made huts with leaves but still no pipes for water - that's bryophytes. Then they made houses with pipes - pteridophytes. Then tall buildings with naked seeds - gymnosperms. Finally modern flats with flowers and fruits - angiosperms. That's whole evolution story.

Why algae important? They do half of photosynthesis on earth, produce oxygen. Some haplontic life cycle - main plant is gametophyte haploid, only zygote diploid.

Imagine a plant that lives on land but needs water to have babies, like frog needs water for eggs. That's bryophytes - amphibians of plant kingdom. They live in moist shady places, walls during rainy season you see green patches - that's them.

Life cycle - very important - Haplodiplontic but gametophyte dominant. What you see green is gametophyte haploid main plant, sporophyte diploid is small and depends on gametophyte for food, like baby depends on mother, not independent. Male antheridia makes swimming sperms need water to swim to female archegonia egg. That's why they need water. Economic: Sphagnum peat moss holds water 20 times its weight, used as packing, fuel peat, prevents soil erosion.

Now imagine first plants that made pipes for water transport like you make water pipes in house. Xylem brings water up, phloem brings food down. First time true root stem leaves appear. That's pteridophytes - ferns you see, big leaves.

Very important concept - heterosporous vs homosporous. Homosporous - one type spore all same size like most pteridophytes. Heterosporous - two types spores small microspore male and big megaspore female like Selaginella Salvinia. Heterospory is first step towards seed habit - because big spore stays on plant, female gametophyte inside, makes seed-like structure. That's how seeds started evolving. Also have strobili cones, circinate vernation fiddlehead young leaf coiled like watch spring, Azolla small aquatic fern has cyanobacteria Anabaena fixes nitrogen used as biofertilizer in rice fields.

Imagine trees that make seeds but not inside fruit, seeds naked like open. No flowers, only cones. Tallest trees on earth like Sequoia redwood. That's gymnosperms - gymno means naked, sperma seed.

Life cycle - diplontic, sporophyte dominant tall tree diploid main plant, gametophyte very small inside cone, dependent. Pollination by wind, not water, so can live in dry places, big advantage. Pollen tube carries male gametes, no need water to swim. No double fertilization, no triploid endosperm, endosperm is haploid formed before fertilization nutritive. Seeds naked not covered by fruit. Economic: timber, resin, turpentine, Sequoia tallest.

Now final boss - flowering plants, most successful, 300k species, dominate earth. Angio means covered, sperma seed - seeds covered inside fruit. Have flowers, which are modified shoots for reproduction, super attractive to insects for pollination.

Biggest concepts - Double fertilization unique to angiosperms: 1 sperm + egg = 2n zygote baby plant, 1 sperm + 2 polar nuclei = 3n triploid endosperm nutritive tissue food for baby, formed after fertilization. Endosperm triploid 3n. Life cycles - main trap: Haplontic - gametophyte dominant n main plant many algae, only zygote 2n. Diplontic - sporophyte dominant 2n main plant gymnosperms angiosperms Fucus brown alga exception diplontic, only gametes n. Haplodiplontic - both dominant multicellular both n and 2n phases, bryophytes gametophyte dominant haplodiplontic, pteridophytes sporophyte dominant haplodiplontic, Ectocarpus Polysiphonia Kelps also haplodiplontic with alternation of generations.