BIOL-214 #7: Major Patterns of Plant Evolution

1. What evolutionary transitions did primitive plants go through when they transitioned from water to land?

2. What is one requirement that all plants need?

• Evolutionary transitions

  1. Avoid desiccation (drying out)

     • stunted growth or failed blooms

     • Structures: Waxy cuticle & stomata

  2. Dispersing reproductive cells into the air

     • Male gametes need to reach the female gametes using new strategies (swimming is not possible, land is dry)

     • Gametes & zygotes must be protected from desiccation

  3. Structural support

     • Land plants maintain stability via roots (anchor them into the soil)

     • Rigid stems & woody tissues provide solid support

  4. Capturing & filtering sunlight

     • Air does not filter out mutagenic solar radiation

• Water

  • Plants are still fully dependent on water

  • Require a moist environment for reproduction

1. From which major group did land plants arose from?

2. What 3 algae groups are included in Archaeplastida

1. Archaeplastida

2. Archaeplastida groups

   1. Red algae: Rhodophyta

   • Green algae

     • Shares common characteristics with land plants

       • Using chlorophyll and carotene (absent from other types of algae

     • Chlorophyta

     • Charaphyta

List the adaptive traits plants developed in chronological order (from the phylogenetic tree in the slides)

1. Embryo Protection

   • sheltered from desiccation & other environmental hazards

2. Apical Growth

   • Apical meristem: mitotically active undifferentiated (totipotent) tissue found in the buds & growing tips of roots in plants

     • generate organs (leaf & stems) & reproductive organs

3. Vascular Tissue

   • main transport systems of plants

   • Before: all plant cells had access to water (moist environment)

   • After: dry environment, need a system to bring water to all cells

4. Megaphyllus

5. Seeds

6. Flowers/Double Fertilization/Endosperm/Fruit

How is desiccation a danger for plants?

1. Most small molecules dissolve & diffuse in the cytoplasm

2. Majority of the chemical reactions of metabolism take place

3. Provides buoyancy to organisms

   • Plants need to develop structural support in a medium that does not give the same “life” as water

4. Requires protection from mutagenic solar radiation

   • Air does not filter out UV rays of sunlight

5. Male gametes must reach the female gametes

What advantages does land offter to plants?

1. Sunlight is abundant

   • Water acts as a filter

     • alters the spetrual quality of light absorbed by chlorophyll

2. CO₂ is more readily available in air than in water

   • diffuses faster in air

3. Land plants evolved before animals

   • No predators threatened plant life

   • Once animals appeared, plants developed strategies to deter predation

     1. Spines

     2. Thorns

     3. Toxic chemicals

How did early land plants combat dryness?

1. Tolerance

   • Mosses can dry out to a brown & brittle mat, but quickly absorb water when it rains or floods

2. Colonize environments with high humidity, where droughts are uncommon

   • Ferns (early lineage of plants) thrive in damp & cool places

3. Resistance to desiccation, rather than tolerance

   • Plants moved away from moist/aquatic environments

   • Cacti & succulents minimize the loss of water so they can survive in extremely dry environments

1. How did plants colonize new & dry environments?

2. What are the 4 most successful adaptations of plants?

3. Are these adaptations present in green algae

• Development of new structures

  • Gave plants the advantage when colonizing new & dry environments

• Successful adaptations of plants

  1. Alternation of generations life cycle

     • plants alternate between two different life stages, or generations, in their life cycle; a haploid stage called gametophyte and a diploid stage called sporophyte

  2. Apical meristem tissue in roots & shoots

     • absent in mosses

  3. Evolution of a waxy cuticle

     • Resist desiccation

  4. Cell Walls with Lignin

     • to support structures off the ground

• NOT present in green algae even though land plants are closely related to them

1. What is the alternation of generations?

2. What does a dominant life cycle mean?

3. What is a haplontic life cycle?

4. What is a diplontic life cycle?

5. What is a haplodiplontic life cycle?

• Alternation of generations life cycle

  • plants alternate between two different life stages, or generations, in their life cycle

• Dominant life cycle

  • Stage in which the organism spends most of its time

  • Stage in which most mitotic cell reproduction occurs (multicellular stage)

• Haplontic life cycle

  • The haploid stage is the dominant stage

  • The only diploid is the zygote

    • undergoes immediate meiosis to restore the haploid state

• Diplontic life cycle

  • The diploid stage is the dominant stage

  • The only haploid cells are the gametes

    • combine to restore the diploid state at their earliest convenience

  • Ex: humans

• Haplodiplontic life cycle

  • Haploid & diploid stages alternate

Developmental sequence

1. What is the multicellular haploid form in alt. of generations?

2. What is the multicellular diploid form in alt of gen?

Developmental sequence

1. Gametophyte: multicellular haploid form

   • gives rise to the gametes (reproductive cells) by mitosis

   • Can be the most obvious phase of the life cycle of the plant

     • Pollen grain in seed plants

2. Sporophyte: multicelluar diploid form

   • Seed plants: sporophyte phase can be a towering tree

1. Why must the land plant protect the embryo?

2. How does the female gametophyte provide protection?

3. What is an embryophyte?

1. Embryo must be sheltered from desiccation & other environmental hazards

2. Provides protection & nutrients to the embryo as it develops into the new sporophyte

   1. Embryophyte: other name for land plant; embryo is protected & nourished by the sporophyte

What do pollen grains contain? How are pollen grains protected?

1. Plant Sperm

2. Fuel for survival

• Protected by a sheath (prevents dessication)

1. Is the sporophyte of seedless plants diploid or haploid?

2. What does the sporophyte do?

3. What does sporangia mean?

4. What are sporocytes?

5. What happens when the haploid spore germinates in a hospitable environment?

6. Summary

1. Diploid sporophyte

   • Results from the syngamy (fusion) of two gametes

2. The sporophyte bears the sporangia

3. Sporangia (s. sporangium): vessel for spores

   • reproductive sac in which spores are formed

4. Sporocytes: mother diploid cell that produces haploid spores by meiosis

   • Haploid spores are later released by the sporangia & disperse in the environment

5. Haploid spore germinates → generates a multicellular haploid gametophyte by mitosis

   • haploid gametophyte give rise to gametes by mitosis

   • haploid gametophyte supports the diploid zygote formed from the fusion of gametes and the resulting young diploid sporophyte

6. The sporophyte generation produces a gametophyte as its offspring → gametophyte generation produces a sporophyte

1. What are homosporous plants?

2. Which plants are homosporous? What is their gametophyte?

3. What are heterosporous plants? What are their male & female spores called?

1. Homosporous plants: produce only one type of spore & the resultant gametophyte produces male & female gametes

   • usually on the same individual

2. Homosporous plants: non-vascular

   • (Haploid) Gametophyte: dominant generation in the life cycle

3. Heterosporous plants: produce two types of spores

   • Male spore: microspore (smaller size) → develop into male gametophyte

   • Female gametophyte: m egaspore (larger size) → develop into female gametophyte

   • Diploid Sporophyte is the dominant generation

1. What is sporopollenin?

2. Where is it found?

3. Is sporopollenin found in other plants?

1. Sporopollenin: Tough polymer surrounding the spores of seedless plants

   • Long chains of organic molecules related to fatty acids & carotenoids (causes yellow color)

   • Resistant to chemical & biological degradation

2. Sporopollenin location: walls of pollen grains

3. Sporopollen also found in charophyte Coleochaetes spores

1. What are gametangia?

2. What are female gametangia called?

3. What are male gametangia called?

4. Where does the embryo develop?

1. Gametangia: a sex organ or cell in which gametes are produced & are covered by protective tissue

   • prominent in seedless plants, but are absent in seed plants

   • Outgroup feature (exists in nonvascular plants) because it still uses water

     • most ancesterial form of reproduction

2. Archegonia: female gametangia

   • produces one egg

3. Antheridia: male gametangia

   • produces many sperm

   • seedless plants produce sperm with flagella (swim in moist environments) to the archegonium

4. Embryo develops inside the archegonium as the sporophyte

1. What is the apical meristem? Where is it located?

2. What is the apical meristem made out of?

3. How does elongation of the shoots & roots help the plant?

4. What is the lateral meristem?

1. Apical meristem:

   • small region of cells capable of rapid division (mitotically active zone) and growth in the root and shoot tips in plants

   • Root

     • Needs a root cap to protect the fragile apical meristem

     • Apical meristem: addition of new cells in a root

       • grow downwards & deeper

         • access to resources

   • Tips

     • Grow outwards & taller

2. Apical meristem is made out of:

   • Undifferentiated (totipotent) cells that continue to proliferate throughout the life of the plant

   • Meristematic (totipotent) cells give rise to all specialized tissues of the organisms

3. Elongation of the shoots & roots

   1. Access to additional space & resources

   2. Light for the shoot

   3. Water & minerals in the case of roots

4. Lateral meristem

   • Separate meristem that produces cells that increase the diameter of tree trunks

Devloping a shoot → compete for light → land plants needed more rigid molecules in their stems → What do plants need now?

Evolution of vascular tissue (transport tissue/plumbing system) AND apical meristems (obtaining resources- sunlight, CO₂, etc)

• The vascular system contains two types of conductive tissue:

  1. Xylem

  2. Phloem

• Adaptations against droughts, support a larger plant body, supply with resources for growing tissues

1. What is xylem tissue?

2. How is xylem tissue reinforced?

3. What is the phloem tissue?

4. Til where do vascular tissues extend into the root of land plants?

1. Xylem tissue:

   • Storage & long-distance transport of water and nutrients

   • Transfer of water-soluble growth factors

2. Reinforced with lignin

   • Tough hydrophobic polymers help prevent the seepage of water across the xylem cell walls

   • Addes strength of the tissues supporting the plant

     • Plants can grow taller → reach more sunlight

3. Phloem: transports food (sugar) derived from photosynthesis throughout the entire plant

   • Stores excess sugars (carrots, potatoes) in the roots

   • soil acts a buffer for drastic changes

4. Vascular tissues extend into to root of land plants

   • root system evolved to take up water & minerals from the soil → anchor the increasingly taller shoot in the soil

• What two structures help maintain moisture (avoid desiccation) in plants?

  1. What is a cuticle? What is its function?

  2. What are stomata? What functions do they have?

1. Cuticle:

   • waxy, waterproof cover that protects the leaves & stems from desiccationwaterproof

   • Prevents intake of CO₂ needed for the synthesis of carbohydrates throughout photosynthesis

     • Needs stomata to allow CO₂ access

2. Stomata

   • pore found on the epidermis (skin) of plants

   • Function

     1. Regulate the traffic of gasses

        1. CO₂ & water access (photosynthesis)

        2. Dispose waste productions (oxygen)

     2. Control dehydration

What functions do these structures have?

1. Cuticle

2. Epidermis

3. Palisade

4. Vein

5. Spongy mesophyll

6. Stomata

7. Lower Epidermis

1. Cuticle

   • waxy, waterproof cover that protects the leaves & stems from desiccation

2. Epidermis

   • first layer of protection against drought, ultraviolet light, and pathogen attack

3. Palisade

   • Chloroplast-rich cells for photosynthesis

     • tall to maximize amount of chloroplasts & UV light coming through

4. Vein

   1. Water access to plants

   2. Sugar movement

   3. Nutrients from the soil

   • Contains xylem & phloem tissues

5. Spongy mesophyll

   • allow for the interchange of gases (CO ₂) that are needed for photosynthesis

6. Stomata

   • regulate gas exchange between the plant and environment and control of water loss

7. Lower Epidermis

   • to regulate gas exchange and to help prevent water loss

1. How does the stoma maintain moisture in plants?

2. What functions do guard cells have?

3. What risk do guard cells do when they open/close?

Individual control during photosynthesis

• Stoma are surrounded by a pair of guard cells

Guard cell function

1. Store water (act as a vacuole)

2. Open & close stomata

   • Swollen with water: open

   • Flaccid: close (conserve water)

Calculated Risk

• Risk desiccation (bad) in exchange for CO₂ (good: photosynthesis)

How did the synthesis of protective flavonoids and other pigments help land plants?

Absorb UV wavelengths of light & protect the aerial parts of plants from photodynamic damage

1. How do plants protect themselves from predators?

2. What a metabolite?

3. How did metabolites evolve over time?

• Synthesize a large range of poisonous secondary metabolites

• Metabolites: complex organic molecules with foul smells & unpleasant taste

• Metabolite Evolution

  1. Deter animals via smell and unpleasant taste

  2. Lure animals for assistance in dispersing pollen grains, fruit, or seeds

What are the geological eras?

1. Paleozoic

   1. Cambrian

   2. Ordovician

      • Colonization of land by the ancestors of modern land plants

      • Fossilized cells, cuticles, & spores

   3. Silurian

   4. Devonian

      • Vascular plants

      • Ferns, horsetails, and seed plants populated the landscape → give rise to trees & forests

   5. Carboniferous

      • enriched the atmosphere with oxygen (give rise to aerobic animals to colonize dry land)

   6. Permian

• What are extinct species?

• What characteristics did extinct vascular plants have?

• What are extant species?

• Extinct species: no longer existing species

  • Extinct vascular species:

    • NO true leaves and roots

    • formed low vegetation mats (moss-like)

• Extant species: still living species

1. In what group are green algae & land plants grouped together?

2. How is Strepotphyta divided? What are land plants?

3. How are embryophytes divided?

• Streptophyta (charophytes): subphylum in which green algae & land plants are grouped together

  • Charophytes

  • Embryophytes: land plants

    • Vascular

      • Seedless plants

        • Lycophytes

          • Club mosses

          • Quillworts

          • Spike Mosses

        • Prerophytes

          • Whisk ferns

          • Horsetails

          • Ferns

      • Seed plants: Spermatophytes

        • Gymonosperms

        • Angiosperms

    • Non-vascular

      • Seedless plants: Bryophytes

        • Liverworts

        • Hornworts

        • MOsses