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Memory tricks for plants, hormones & photosynthesis

From auxins to alternation of generations — plant biology is packed with lists and processes that respond perfectly to mnemonics. Lock in the key concepts before your next exam.

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🌱 Plant Biology

Memory Tricks

Proven mnemonics — fast to learn, hard to forget.

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Plant Hormones
ACEGI — Auxin, Cytokinin, Ethylene, Gibberellin, Abscisic acid
5 major plant hormones — "A Clever Elephant Grows Apples"
The 5 major plant hormones: Auxin (IAA) — promotes cell elongation, phototropism, apical dominance. Cytokinin — promotes cell division, delays aging. Ethylene (gas) — fruit ripening, leaf drop, stress response. Gibberellin — stem elongation, seed germination, fruit development. Abscisic acid (ABA) — stress hormone, closes stomata during drought, seed dormancy.
📖 Full Lesson →Difficulty: Intermediate
Auxin and phototropism
Light causes auxin to migrate to shaded side of stem → more elongation on shaded side → stem bends toward light. Apical dominance: auxin from apical bud suppresses lateral bud growth. Remove apex → lateral branches grow (why pruning bushes makes them bushy).
Ethylene as a gas
Only gaseous plant hormone. "One bad apple spoils the barrel" — ethylene released by ripe fruit triggers ripening in neighbors. Used commercially to ripen tomatoes after shipping. Also triggers abscission (leaf/fruit drop) and senescence.
ABA — the stress hormone
Abscisic acid rises during drought → guard cells lose K⁺ → stomata close → reduces water loss. Also maintains seed dormancy — seeds won't germinate until ABA degraded. Antagonist to gibberellin (GA (gibberellin) promotes germination, ABA inhibits it).
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🃏 Plant Hormones
ACEGI
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🃏 Answer
ACEGI — Auxin, Cytokinin, Ethylene, Gibberellin, Abscisic acid
Auxin and phototropism — Light causes auxin to migrate to shaded side of stem → more elongation on shaded side → stem bends toward light. Apical dominance: auxin from apical bud suppresses lateral bud growth. Remove apex → lateral branches grow (why pruning bushes makes them bushy).
Ethylene as a gas — Only gaseous plant hormone. "One bad apple spoils the barrel" — ethylene released by ripe fruit triggers ripening in neighbors. Used commercially to ripen tomatoes after shipping. Also triggers abscission (leaf/fruit drop) and senescence.
ABA — the stress hormone — Abscisic acid rises during drought → guard cells lose K⁺ → stomata close → reduces water loss. Also maintains seed dormancy — seeds won't germinate until ABA degraded. Antagonist to gibberellin (GA (gibberellin) promotes germination, ABA inhibits it).
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Flower Parts
SCAPE — Sepal, Corolla (petals), Androecium (stamens), Pistil, Everything else
Sepals → Petals → Stamens (male) → Pistil/Carpel (female) — from outside to inside
Flower parts from outside to inside: Sepals (calyx) — green leaf-like, protect bud. Petals (corolla) — attract pollinators. Stamens (androecium = male) — filament + anther (produces pollen/microgametophytes). Pistil/Carpel (gynoecium = female) — stigma (receives pollen) + style + ovary (contains ovules/megagametophytes). Perfect flower = has both stamens and pistil.
📖 Full Lesson →Difficulty: Beginner
Pollination vs Fertilization
Pollination: pollen lands on stigma. Fertilization: pollen tube grows through style to ovule — sperm fertilizes egg. Double fertilization (angiosperms only): one sperm + egg = zygote (2n); second sperm + polar nuclei = endosperm (3n — food for seed).
Monocots vs Dicots
Monocots: 1 cotyledon, parallel leaf veins, flower parts in 3s, scattered vascular bundles (grass, corn, lily). Dicots (eudicots): 2 cotyledons, branching veins, flower parts in 4s or 5s, ring of vascular bundles (roses, oaks, beans).
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🃏 Flower Parts
SCAPE
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🃏 Answer
SCAPE — Sepal, Corolla (petals), Androecium (stamens), Pistil, Everything else
Pollination vs Fertilization — Pollination: pollen lands on stigma. Fertilization: pollen tube grows through style to ovule — sperm fertilizes egg. Double fertilization (angiosperms only): one sperm + egg = zygote (2n); second sperm + polar nuclei = endosperm (3n — food for seed).
Monocots vs Dicots — Monocots: 1 cotyledon, parallel leaf veins, flower parts in 3s, scattered vascular bundles (grass, corn, lily). Dicots (eudicots): 2 cotyledons, branching veins, flower parts in 4s or 5s, ring of vascular bundles (roses, oaks, beans).
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Photosynthesis Pathways
C3 Fixes First · C4 Concentrates · CAM at Night — "Cold, Concerned, Cautious"
C3 (most plants) · C4 (hot climate crops) · CAM (desert succulents)
Three photosynthesis strategies: C3 — RuBisCO fixes CO₂ directly to 3-carbon compound (3-PGA). Problem: photorespiration in hot/dry conditions. C4 — pre-fix CO₂ in mesophyll to 4-carbon compound, concentrate it in bundle sheath cells around RuBisCO. Corn, sugarcane, sorghum. CAM — fix CO₂ at night (stomata open), store as malate, release during day. Cacti, succulents, pineapple. Minimizes water loss.
📖 Full Lesson →Difficulty: Intermediate
Why C4 and CAM evolved
Photorespiration: RuBisCO can fix O₂ instead of CO₂ (wasteful) — worsens in hot, dry conditions when stomata close. C4 concentrates CO₂ around RuBisCO → less photorespiration. CAM separates CO₂ fixation (night) from Calvin cycle (day) → stomata closed during hot day = no water loss.
Examples to remember
C3: wheat, rice, soybeans, most trees (85% of plant species). C4: corn (maize), sugarcane, sorghum, many grasses. CAM: cacti, agave, pineapple, jade plant, most succulents. C4 crops are more productive in tropical climates — hence corn's dominance in warm regions.
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🃏 Photosynthesis Pathways
C3 vs C4 vs CAM plants — how do they differ?
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🃏 Answer
C3 Fixes First · C4 Concentrates · CAM at Night — "Cold, Concerned, Cautious"
Why C4 and CAM evolved — Photorespiration: RuBisCO can fix O₂ instead of CO₂ (wasteful) — worsens in hot, dry conditions when stomata close. C4 concentrates CO₂ around RuBisCO → less photorespiration. CAM separates CO₂ fixation (night) from Calvin cycle (day) → stomata closed during hot day = no water loss.
Examples to remember — C3: wheat, rice, soybeans, most trees (85% of plant species). C4: corn (maize), sugarcane, sorghum, many grasses. CAM: cacti, agave, pineapple, jade plant, most succulents. C4 crops are more productive in tropical climates — hence corn's dominance in warm regions.
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Plant Tissue Types
DEVG — Dermal, Epidermis/Vascular, Ground — "Don't Eat Very Green plants"
3 tissue systems: Dermal (skin) · Vascular (transport) · Ground (everything else)
Three plant tissue systems: Dermal tissue — epidermis (outer protective layer), cuticle (waxy waterproofing), stomata (gas exchange via guard cells), root hairs (water absorption). Vascular tissue — Xylem (water/mineral transport, dead cells, one-way up), Phloem (sugar transport, living cells, bidirectional). Ground tissue — Parenchyma (photosynthesis/storage), Collenchyma (flexible support), Sclerenchyma (rigid support — fibers, sclereids).
📖 Full Lesson →Difficulty: Intermediate
Xylem vs Phloem
Xylem: dead at maturity, tracheids + vessel elements, moves water UP by transpiration pull (cohesion-tension). Phloem: alive, sieve tubes + companion cells, moves sugars in BOTH directions (source to sink). Pressure-flow hypothesis: high pressure at source (leaves), low at sink (roots/fruit).
Stomata mechanics
Guard cells control stomatal opening. K⁺ enters guard cells → water follows osmosis → cells swell → stomata open. ABA → K⁺ leaves → stomata close (drought response). Open during day (CO₂ in, O₂ out), close at night (except CAM (Crassulacean Acid Metabolism) plants). 90% of water loss via transpiration through stomata.
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🃏 Plant Tissue Types
DEVG
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🃏 Answer
DEVG — Dermal, Epidermis/Vascular, Ground — "Don't Eat Very Green plants"
Xylem vs Phloem — Xylem: dead at maturity, tracheids + vessel elements, moves water UP by transpiration pull (cohesion-tension). Phloem: alive, sieve tubes + companion cells, moves sugars in BOTH directions (source to sink). Pressure-flow hypothesis: high pressure at source (leaves), low at sink (roots/fruit).
Stomata mechanics — Guard cells control stomatal opening. K⁺ enters guard cells → water follows osmosis → cells swell → stomata open. ABA → K⁺ leaves → stomata close (drought response). Open during day (CO₂ in, O₂ out), close at night (except CAM (Crassulacean Acid Metabolism) plants). 90% of water loss via transpiration through stomata.
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Alternation of Generations
Sporophyte makes Spores · Gametophyte makes Gametes — "SPores from SPOROphyte · GAMetes from GAMEtophyte"
Diploid (2n) sporophyte → meiosis → haploid spores → gametophyte → gametes → fertilization → sporophyte
Plants alternate between two multicellular generations: Sporophyte (2n, diploid) — the dominant generation in vascular plants (the plant you see). Makes spores by meiosis. Gametophyte (n, haploid) — reduced in vascular plants. Makes gametes by mitosis. Fertilization restores diploid. Trend in evolution: sporophyte becomes dominant, gametophyte becomes reduced (mosses → ferns → gymnosperms → angiosperms).
📖 Full Lesson →Difficulty: Intermediate
Mosses vs ferns vs seed plants
Mosses: gametophyte dominant (the green mat). Sporophyte = brown stalk on top. Ferns: sporophyte dominant (the frond you see). Gametophyte = tiny heart-shaped prothallus. Seed plants: sporophyte dominant. Gametophyte microscopic (pollen = male gametophyte; embryo sac = female gametophyte).
Seed structure
Seed = embryo + endosperm + seed coat. Embryo: sporophyte embryo with cotyledons. Endosperm (3n in angiosperms): food supply. Seed coat: protective. Seeds allow dispersal away from parent and dormancy until conditions are right. Major evolutionary advantage over spores.
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🃏 Alternation of Generations
Sporophyte vs gametophyte — which makes what?
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🃏 Answer
Sporophyte makes Spores · Gametophyte makes Gametes — "SPores from SPOROphyte · GAMetes from GAMEtophyte"
Mosses vs ferns vs seed plants — Mosses: gametophyte dominant (the green mat). Sporophyte = brown stalk on top. Ferns: sporophyte dominant (the frond you see). Gametophyte = tiny heart-shaped prothallus. Seed plants: sporophyte dominant. Gametophyte microscopic (pollen = male gametophyte; embryo sac = female gametophyte).
Seed structure — Seed = embryo + endosperm + seed coat. Embryo: sporophyte embryo with cotyledons. Endosperm (3n in angiosperms): food supply. Seed coat: protective. Seeds allow dispersal away from parent and dormancy until conditions are right. Major evolutionary advantage over spores.
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Vascular vs Non-Vascular
BANF — Bryophytes (mosses), Angiosperms, Non-vascular have No xylem/phloem, Ferns have Fronds
Non-vascular: mosses/liverworts (no true roots/stems/leaves) · Vascular: ferns, gymnosperms, angiosperms
Plant groups: Non-vascular (Bryophytes) — mosses, liverworts, hornworts. No xylem/phloem, no true roots/stems/leaves, limited to moist environments, gametophyte dominant. Vascular (Tracheophytes) — have xylem and phloem. Seedless vascular: ferns, horsetails. Seed plants: Gymnosperms (naked seeds — conifers, cycads) and Angiosperms (enclosed seeds — flowering plants, most diverse).
📖 Full Lesson →Difficulty: Beginner
Gymnosperms vs Angiosperms
Gymnosperms: "naked seeds" — seeds not enclosed in fruit (conifers, cycads, ginkgo). Pollen cones (male) and seed cones (female). Wind pollinated. Angiosperms: "enclosed seeds" — ovule enclosed in ovary that becomes fruit. Flower for pollination, fruit for seed dispersal. 80% of plant species.
Key adaptations to land
Cuticle (waxy, prevents desiccation). Stomata (gas exchange while limiting water loss). Vascular tissue (transport and support against gravity). Seeds (protected embryo, food supply, dormancy). Pollen (male gametophyte dispensed without water — key to land colonization).
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🃏 Vascular vs Non-Vascular
BANF
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🃏 Answer
BANF — Bryophytes (mosses), Angiosperms, Non-vascular have No xylem/phloem, Ferns have Fronds
Gymnosperms vs Angiosperms — Gymnosperms: "naked seeds" — seeds not enclosed in fruit (conifers, cycads, ginkgo). Pollen cones (male) and seed cones (female). Wind pollinated. Angiosperms: "enclosed seeds" — ovule enclosed in ovary that becomes fruit. Flower for pollination, fruit for seed dispersal. 80% of plant species.
Key adaptations to land — Cuticle (waxy, prevents desiccation). Stomata (gas exchange while limiting water loss). Vascular tissue (transport and support against gravity). Seeds (protected embryo, food supply, dormancy). Pollen (male gametophyte dispensed without water — key to land colonization).
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Water Transport
TACT — Transpiration, Adhesion, Cohesion, Tension pull water up xylem
Water evaporates from leaves → tension pulls water column → cohesion holds it together → adhesion to walls
Water moves up plants by transpiration pull (cohesion-tension theory). Transpiration: water evaporates from stomata → creates tension (negative pressure) at top of xylem. Cohesion: hydrogen bonds hold water molecules together — allows tension to pull entire column. Adhesion: water sticks to xylem walls — helps support column and capillary action. Water pulled up passively — no energy required by plant!
📖 Full Lesson →Difficulty: Intermediate
Root pressure
Active mineral uptake into roots → water follows osmosis → creates positive root pressure that pushes water up. Minor contributor compared to transpiration pull. Guttation: root pressure forces water out of hydathodes at leaf edges at night (not dew — guttation is pure water from xylem).
Factors affecting transpiration
Temperature (↑ = ↑transpiration). Humidity (high humidity = ↓transpiration). Wind (↑ = ↑transpiration). Light (opens stomata). Water availability. A large tree can transpire 100+ gallons of water per day. Wilting = water loss exceeds uptake.
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🃏 Water Transport
TACT
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🃏 Answer
TACT — Transpiration, Adhesion, Cohesion, Tension pull water up xylem
Root pressure — Active mineral uptake into roots → water follows osmosis → creates positive root pressure that pushes water up. Minor contributor compared to transpiration pull. Guttation: root pressure forces water out of hydathodes at leaf edges at night (not dew — guttation is pure water from xylem).
Factors affecting transpiration — Temperature (↑ = ↑transpiration). Humidity (high humidity = ↓transpiration). Wind (↑ = ↑transpiration). Light (opens stomata). Water availability. A large tree can transpire 100+ gallons of water per day. Wilting = water loss exceeds uptake.
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Tropisms
PHGT — Phototropism (light), Hydrotropism (water), Gravitropism (gravity), Thigmotropism (touch)
Plants grow toward or away from environmental stimuli — directed by auxin redistribution
Plant tropisms — directional growth responses: Phototropism: stems grow toward light (positive), roots grow away (negative). Auxin migrates to shaded side → more elongation. Gravitropism (geotropism): roots grow down (positive), stems grow up (negative). Amyloplasts (starch grains) sediment to detect gravity. Hydrotropism: roots grow toward water. Thigmotropism: growth in response to touch — tendrils wrap around supports, trees thicken in wind.
📖 Full Lesson →Difficulty: Beginner
Auxin and tropisms
Charles Darwin (with son Francis) discovered phototropism in coleoptiles. Went Cholodny-Went model: auxin redistributes to shaded side, causing differential growth. High auxin → more elongation in stems (but inhibits root elongation — roots are more sensitive to auxin).
Nastic movements
Non-directional responses (not tropisms): Thigmonasty — Mimosa pudica folds leaves when touched (turgor change, not growth). Photonasty — flower opening/closing with light. Nyctinasty — sleep movements (bean leaves fold at night). Seismonasty — rapid response to mechanical stimulation.
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🃏 Tropisms
PHGT
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🃏 Answer
PHGT — Phototropism (light), Hydrotropism (water), Gravitropism (gravity), Thigmotropism (touch)
Auxin and tropisms — Charles Darwin (with son Francis) discovered phototropism in coleoptiles. Went Cholodny-Went model: auxin redistributes to shaded side, causing differential growth. High auxin → more elongation in stems (but inhibits root elongation — roots are more sensitive to auxin).
Nastic movements — Non-directional responses (not tropisms): Thigmonasty — Mimosa pudica folds leaves when touched (turgor change, not growth). Photonasty — flower opening/closing with light. Nyctinasty — sleep movements (bean leaves fold at night). Seismonasty — rapid response to mechanical stimulation.
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Seed Germination
WAR — Water, Air (O₂), Right temperature — the 3 requirements for germination
Imbibition → enzyme activation → radicle emerges first → shoot follows
Seed germination requires WAR: Water (imbibition — seed absorbs water, swells, activates enzymes). Air (O₂ for cellular respiration — seeds need energy). Right temperature (each species has optimal range — vernalization: some seeds need cold period first). Process: water absorbed → ABA degraded, GA rises → amylases activated → starch → sugar → energy → radicle (embryonic root) emerges first → shoot follows (hypocotyl/epicotyl).
📖 Full Lesson →Difficulty: Beginner
Phytochrome and light
Some seeds also require light for germination. Phytochrome: pigment that detects red vs far-red light. Pr (red-absorbing) ⇌ Pfr (far-red absorbing). Pfr is active form — promotes germination, inhibits stem elongation, promotes flowering (in some plants). Sunlight rich in red → Pfr predominates → plant "knows it's day."
Dormancy mechanisms
Seed coat impermeability (physical dormancy — must be scarified). Chemical inhibitors (ABA — must be washed away by rain). Afterripening (dry storage at cool temp). Stratification (cold + moist period — mimics winter). Adaptations prevent germination in unfavorable conditions.
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🃏 Seed Germination
WAR
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🃏 Answer
WAR — Water, Air (O₂), Right temperature — the 3 requirements for germination
Phytochrome and light — Some seeds also require light for germination. Phytochrome: pigment that detects red vs far-red light. Pr (red-absorbing) ⇌ Pfr (far-red absorbing). Pfr is active form — promotes germination, inhibits stem elongation, promotes flowering (in some plants). Sunlight rich in red → Pfr predominates → plant "knows it's day."
Dormancy mechanisms — Seed coat impermeability (physical dormancy — must be scarified). Chemical inhibitors (ABA — must be washed away by rain). Afterripening (dry storage at cool temp). Stratification (cold + moist period — mimics winter). Adaptations prevent germination in unfavorable conditions.
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Photoperiodism
Short-Day plants flower in SHORT days (long nights) · Long-Day plants flower in LONG days (short nights) · Day-Neutral plants don't care
It's actually NIGHT LENGTH that matters — phytochrome detects darkness duration
Photoperiodism: plant flowering response to day/night length. Short-day plants (SDPs): flower when night exceeds critical length — chrysanthemums, poinsettias, cannabis. Long-day plants (LDPs): flower when night is shorter than critical length — spinach, iris, wheat. Day-neutral: flower regardless — tomatoes, roses, dandelions. Key: it's actually night length (not day length) that matters — brief light flash interrupting the dark period can prevent SDP flowering.
📖 Full Lesson →Difficulty: Intermediate
The night-length trick
Classic experiment: interrupt the dark period of a SDP with a brief red light flash → prevents flowering (Pfr formed → inhibits SDP flowering). Follow with far-red light → reverses effect → SDP flowers again. Proves it's phytochrome detecting night length, not day length.
Florigen — flowering signal
Leaves detect the photoperiod → produce florigen (a protein, FT (Flowering Locus T — a mobile protein that triggers flower development)) → travels through phloem to apical meristem → triggers flower development. Grafting experiments: graft SDP (Short Day Plant) leaf onto LDP (Long Day Plant) in wrong conditions → still flowers (florigen is systemic).
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🃏 Photoperiodism
Short-day vs long-day vs day-neutral plants?
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🃏 Answer
Short-Day plants flower in SHORT days (long nights) · Long-Day plants flower in LONG days (short nights) · Day-Neutral plants don't care
The night-length trick — Classic experiment: interrupt the dark period of a SDP with a brief red light flash → prevents flowering (Pfr formed → inhibits SDP flowering). Follow with far-red light → reverses effect → SDP flowers again. Proves it's phytochrome detecting night length, not day length.
Florigen — flowering signal — Leaves detect the photoperiod → produce florigen (a protein, FT (Flowering Locus T — a mobile protein that triggers flower development)) → travels through phloem to apical meristem → triggers flower development. Grafting experiments: graft SDP (Short Day Plant) leaf onto LDP (Long Day Plant) in wrong conditions → still flowers (florigen is systemic).
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