Lecture 20+21 Plant , evolution of plant structure

Plant blindness

"an inability to see and distinguish the plants that surround and sustain us"

Causes of plant blindness

Visual homogeneity of plants (plants just all green)

Plants perceived as non‑threatening

Slow timescales of plant movement

Humans lack perception to detect plant motion

People identify animals faster than plants in rapid image sequences

Consequences of plant blindness

Plants treated as background for animals

Misunderstanding plant needs

Overlooking plant importance in daily life

Solutions of plant blindness

Bias awareness

Education (early, high‑quality, plant‑focused)

Engagement (interaction with plant: grow a plant, observe development)

Raising awareness among peers

Equal exposure to plants, fungi, microbes, animals

General Plant Life Cycle

Gametophyte (n) → produces gametes

Sporophyte (2n) → produces spores

moss life cycle

sperms in antheridia, eggs in archegonia at top

must have water for reporduction > fertilization by water for mobile sperm

dominant gametophyte, Sporophyte (short-lived) dependent on gametophyte for food

No vascular tissue

low humidity > open up to release spores > so the spores can travel far

fern life cycle

mostly found in tropical areas

Vascular tissue (xylem + phloem)

*Dominant sporophyte (2n) — fern plant , independent , free living gametophyte (n)—*tiny, heart‑shaped prothallus.

mainly homosporous→all the spores are of same size

Circinate vernation→ the coiled arrangement of young fern fronds (leaves), where the tip is rolled inward and gradually unrolls as the frond matures. - the coiled young fronds called (fiddleheads)

Heterospory

= production of two different kinds of spores

microsporangium produces microspores > microspores germinate into microgametophytes → produce sperm in antheridia

megasporangium produces megaspores > germinate into megametophytes → produce eggs in archegonia

large number of sperms → increase probability of fertilization

Dioecious

= male and female reproductive organs are on separate individuals of the same species.

🧬 Key evolutionary patterns

1. Gametophyte → smaller over time

2. Archegonia disappear in flowering plants

3. Sperm mobility changes

Moss & ferns: motile sperm (need water)

Gymnosperms & angiosperms: non‑motile sperm delivered by pollen tube

4. porangia (spore‑producing structures) become specialized

Moss: one capsule

Fern: many sporangia in sori

Gymnosperms: microsporangia + megasporangia

Angiosperms: anther sacs + ovules

5. more massive saporophytes

Endospory

= internal gametophyte development within the spore wall, rather than outside

opp= exospory,

Advantages of endospory

Protection - increase in genetic diversity due to many more gametophytes surviving

•This Genetic diversity increases rates of diversification (bigger pool to for selection to work on)

•Nutrition provided by sporophyte (therefore stronger, longer lived, survives without water etc)

homosporous

all the spores are of same size

Dioecious

male and female reproductive organs are on separate individuals of the same species.