Summary from last time 1 DNA evidence suggests

Summary from last time 1) DNA evidence suggests that the first land plants came from an algal scum ~1. 2 BYA in form of filamentous green alga. 2) First land plants were the Bryophytes at 515 MYA 4) Today, these plants are still restricted to moist conditions. 5) They still have swimming sperm and are dependent on water for fertilization but are assisted by animals in that process. 6) They evolved spores which allows them to survive dry conditions and they evolved ways to become dormant as mature plants in drought.

Land Plants Review • Bryophytes= Mosses, Liverworts, Hornworts – Moist environments – Swimming sperm – Homosporous- Single gametophyte – Gametophyte (n) haploid stage is dominant – Embryo (2 n) is parasitic on gametophyte – Lack xylem & phloem – Small plants

LAND PLANT EVOLUTION Eudicot Gymnosperms (Naked seeds) Non-seeds Bryophytes (Non-vascular) Seeds Tracheophytes (Vascular) Green Algae Monocot Angiosperms (Seeds in flowers and fruit) Now

Tracheophytes

Overview of Land Plants Bryophytes Tracheophytes

Advances of Tracheophytes over Bryophytes xylem and phloem lignin = wood thick waxy cuticle stomates profuse branching o increased young tissues for photosynthesis o increased areas for sporangia (as opposed to only one sporangium per sporophyte in the Bryophytes) • highly differentiated plant tissues and organs • • •

What characteristic would you expect Tracheophytes to lack? 1. 2. 3. 4. 5. 6. 7. Mitochondria Swimming sperm Embryos Gametangia Seeds Pollen None. They would have them all

First Tracheophytes Whisk Ferns Horsetails All with swimming sperm Club Mosses Ferns All lack seeds

Land Plants Review • Tracheophytes: Ferns as an example – Moist environments – Swimming sperm – Homosporous- Single gametophyte – Sporophyte (2 n) stage is dominant – Embryo (2 n) is parasitic on gametophyte – WIth xylem & phloem – Can be large plants

Sporophyte Dominant in Tracheophytes e. g. Ferns

Fern Life Cycle SORI

Fern Life Cycle

Diploid (Sporophyte generation is dominant In tracheophytes

Characteristics of Plants Alternation of generations In Bryophytes the haploid (n) generation is dominant In Tracheophytes the diploid (2 n) generation is dominant

Female pine cones Male pine cones

Where are the gametophyte (n) tissues? Answer: They are the few cells that undergo meiosis to produce the gametes

Homosporous Life Cycle e. g. Bryophytes and Ferns One kind of spore One kind of gametophyte

Heterosporous Life Cycle Seed Plants 2 kinds of spores 2 kinds of gametophytes

Land Plants Review Tracheophytes: Seed Plants; e. g. Conifers, & Flowering plants – Found in all types of environments – Sporophyte (2 n) dominant – Heterosporous= seed plants have two types of spores; two gametophytes – Gametophytes (n) are tiny and are the few cells that produce the pollen and egg – Xylem & Phloem – Can be large plants

Land Plants Review – Homosporous One type of spore – Heterosporous Two types of spores 1 gametophyte Mosses & Ferns 2 gametophytes Gymnosperms & Angiosperms

Plant Adaptations to Land • Selective advantages to land – Less competition for light and nutrients – Less predation • Problems with new environment – Physical support – Water loss and availability – Reproduction – Temperature fluctuations

How Plants Deal with Problems • Problem: Physical support • Solution: Internal support – Roots: anchor plants in soil & acquire nutrients & H 2 O

How Plants Deal with Problems • Problem: Physical support • Solution: Internal support – Stems: • Turgor pressure in cells with cell walls • Lignin = “wood” • Secondary growth—i. e. growth in width (Rings of Xylem)

How Plants Deal with Problems • Problem: Water loss & availability • Solution: Conserve & acquire H 20 – Acquire H 20 • H 20 from soil via root • Transport via xylem • Mutualism with fungus (mycorrhizae)

Fungi in Soil Mycorrhizae are probably key to the colonization of land by plants. They are found with the earliest fossils of land plants

Plants are connected to underground fungi in a mutualistic relationship

Plant Carbohydrates H 20 & minerals Fungus

Fungi form connections with many plants Fungal superhighway

Plants exchange nutrients Fungal Superhighway

When herbivores (e. g. aphids) eat plants, the plants start making distasteful and toxic chemicals to deter further destruction

When plants are attacked by herbivores they send signals the each other via the mycorrhizae. Fungal Internet

AND When plants are attacked they produce volitles (vapors) which affect other plants to produce defensive chemicals

When plants are attacked they produce volitle (vapors) which pass through the air to alert other plants

And these vapors will attract aphid predators and parasitoids Wasp laying egg in aphid

How Plants Deal with Problems • Problem: Water loss & availability • Solution: Conserve & acquire H 20 – Conserving H 20—Reduce leaf size and store water

How Plants Deal with Problems – Conserving H 20—Require large surface area for photosynthesis (leaves) • Waxy cuticle on leaves

How Plants Deal with Problems – Conserving H 20—Require large surface area for photosynthesis (leaves) • Waxy cuticle on leaves prevents water loss But what about the need for CO 2?

Water Loss in Plants • Problem: Need C 02 for photosynthesis – Holes in surface of leaf, but this means H 20 loss • Stomates & guard cells controls water loss

How Plants Deal with Problems – Conserving H 20—Require large surface area for photosynthesis (leaves) • Deciduous leaves prevent water loss during winter

How Plants Deal with Problems • Problem: Water & reproduction • Solutions: Pollen= non-swimming sperm with tough water resistant coat Carried by wind or animals

Seeds= embryo + endosperm + seed coat Seeds evolved 365 MYA in Gymnosperms Seeds found in Siberian permafrost 32, 000 years old have been germinated.

How Plants Deal with Problems Seed Dispersal • Wind – Large surface area to catch the breezes Maple seeds with wings

How Plants Deal with Problems Seed Dispersal • Wind – Large surface area to catch the breezes

How Plants Deal with Problems Seed Dispersal • Water – Seeds must float Coconuts

How Plants Deal with Problems Seed Dispersal • Animals – Caught on fur or body Cockleburs

How Plants Deal with Problems Seed Dispersal • Animals – Fruit eaten by animals & the seeds dropped at a distance from the parent plant

How Plants Deal with Problems Seed Dispersal • “Anachronistic Fruits” = Fruits whose seed dispersers are extinct. Osage orange

Osage Orange Mastodon

Why Are There Different Leaf Shapes?

Leaf Evolution & Adaptations • WHY?

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