5 - Major plant lineages and bryophytes

List the 7 main divisions of land plants

• liverworts

• mosses

• hornworts

• lycophyted

• ferns

• gymnosperms

• angiosperms

What did the earliest land plants descend from and where did they live?

streptophyte green algae that lived in shallow water margins

When did the earliest land plants descend?

the end of the Silurian

State one major selection event of land plants

periodic drying selected for those best able to tolerate periods without water, eventually accumulating adaptations that allowed them to live permanently above water

List 5 features shared by all terrestrial plants

• alteration of generations

• waxy cuticle

• stomata for gas exchange

• chlorophyll a and b

• cellulose cell walls

List 3 major bryophyte lineages

• mosses

• hornworts

• liverworts

List these 3 structures of a liverwort and state whether they’re haploid or diploid

1. sporophyte (diploid)

2. gametophyte (haploid)

3. gemmae (haploid)

Discuss the diploid region of liverworts

the sporophyte undergoes meiosis to make haploid spores

Discuss the haploid region of liverworts (gametophytes) (2 points)

• gametophyte produces gametangia which are motile sperm and non motile eggs

• when mature and in wet conditions the sperm are released and swim to fertilise the eggs to form a zygote

Discuss the haploid region of liverworts (gemmae) (2 points)

• undergoes vegetative (asexual) reproduction

• during rainfall small liverworts get splashed out

List the correlating structures between mosses and liverworts

• sporophyte is comprised of capsule and seta

• gametophyte is comprised of the stem and leaves

State one difference between bryophytes and all other terrestrial plants

in bryophytes the gametophyte individual is the dominant part of the life cycle

Within bryophytes, what is the sporophyte dependent on?

the photosynthesising gametophyte

List 2 identifications of bryophytes

• small, lacking lignin and support structures

• mostly limited to moist environments

Describe tissue structure in byrophytes (3 points)

• little tissue differentiation in stems

• water can be absorbed directly through the underside of leaves/thallus as they lack waxy cuticle

• rhizoids at the base of the stem which penetrate the substrate which has no role in absorbing water/minerals

Describe sporophyte structure in byrophytes (3 points)

• developing zygote forms a “foot” which attaches to the gametophyte and absorbs sugars, minerals and water

• the upper part grows by division and expands to form a capsule

• cells inside the capsule undergo meiosis to produce haploid spores

How do sporangium behave in dry conditions?

unfurls to release spores

Why are bryophytes vulnerable to drying out?

they’re small and can’t readily store or transport water

List 4 environments that sphagnum moss can be found in

• acidic tundra bogs

• mountains

• moorlands

• peatlands

Why are peatlands ecologically important?

significant carbon stores, emitting sizeable quantities of methane

Why do peatlands act as carbon reservoirs?

the rate of plant production exceeds the rate of organic matter decomposition

What is poikilohydry within mosses and what are they adapted to?

• mosses that are unable to maintain storage of water

• adapted to drying and becoming inactive in dry conditions

What are poikilohydry mosses tolerant to during their dry phase (2 points)

extreme temperatures and UV light

What state do poikilohydry mosses undergo when dry and what does this allow them to do?

• quiescent state

• allows them to grow in inhospitable places like bare rock and deserts