Challenges on Land Water – Most found under the surface of the land Minerals – Under land surfaces Gases – Abundant in the atmosphere Support – Necessary on land Light – More available on land

Temperature – Changes are more extreme on land Reproduction – If gametes swim, this is a challenge on land Dispersal – Water is seldom available for dispersal, other methods must be explored.

Solutions: Getting Water: Diffusion, rhizoids, roots Transporting water: Xylem (vascular tissue cells) Transporting food: Phloem (vascular tissue cells) Preventing desiccation: Waxy cuticle Obtaining gases: Stomata or air pores

Obtaining sunlight: Leaves Supporting the Body: Xylem Environmental response to stimuli: Hormones Fertilization without water: Pollen Dispersal: Movement from airborne spores to seeds

Plant Characteristics What distinguishes plants? Multiellular eukaryotes Photoautotrophs Live on land Possess apical meristems in roots and shoots Embryophytes with placental transfer cells What characteristics do plants share with their green algal ancestors? Chloroplasts with chla, chlb and caretonoids Cellulose cell wall structure Food stored as starch

Why was a new mode of reproduction necessary? Disperse gametes in non-aquatic environment, on land Gametes are produced within gametangia Zygote develops into embryo within female gametangia. (embryophytes) Male gametangia = antheridia -> anthers Female gametangia = archegonia -> ovules Gametangia are protetive jacket of sterile cells that prevent gametes from drying out.

Other Adaptations Waxy cuticle – prevents dessication Stomata for gas exchange Xylem and phloem in tracheophytes Secondary compounds: Flavonoids Terpenes Tannins Have bitter taste, protect plant from UV radiation, protect plant from pathogens

Heteroorphic – sporophyte and gametophyte have different morphologies

Spore Production Sporangium found on sporophyte contains… Spore mother cell Spore mother cell undergoes meiosis … Produces spores (haploid) Spores with sporopollenin (durable outer coating) is unique to plants

Move Onto Land: What evidence is there that plants evolved from green algae (charophytes)? Homologous chloroplasts with chla, chlb and caretonoids Biochemical similarities:Cellulose cell wall structure Food stored as starch Similar cell plate formation Similar sperm structure Similar genes and rRNA’s Green algae and plants of today both evolved from a common charophyte ancestor.

Adaptations to shallow water Charophycean algae live in shallow waters If waters dry out natural selection favors land adaptations Evolutionary novelties opened up land as an adaptive zones

Advantages to Land Lots of room Lots of light and gasses Soil rich in nutrients Originally no herbivores on land

Thallus of charophyte is haploid Most algae fertilize gametes in water, this one has fertilization attached to female parent. Non-reproductive cells of the thallus grow around zygote, and zygote undergoes meiosis after it gets larger, and isreleased and grows into haploid swimmng spores. If meiosis is delayed and mitosis of 2n aygote occurs there is a multicellular diploid stage attached to haploid parent. Rudimentary sporophyte would depend on the gametophyte for nourishment and protection. Advantage to this lifecycle is that multicellular diploid can make more spores. If protection of gametes occurred then leading to the brypohytes

Possible Taxonomic Differences

Sporophyte moss

antheridia sperm antheridia

archegonium egg

Ferns To what division do ferns belong? Pterophyta What evolutionary novelty is seen in these plants? Vascualr system,with xylem, phloem and lignin What adaptive zone opens up? Getting taller

Homosporous vs. Heterosporous Vascular plants Homosporous – sporophyte produces single spore type -> bisexual gametophyte -> eggs and sperm Heterosporous – sporophyte produces different male and female spores that produce male and female gametophytes -> male releases sperm and female releases eggs Which type of plant is the fern? Fern is homosporous,

Fern sori with sporangium

Fern Frond xs with sorrus , sporangia and spores Fern sorus with sporangia