Land Plants Flashcards
Land Plants
a monophyletic group of eukaryotic phototrophs
- cells contain a nucleus, mitochondria, internal membranes, and CHLOROPLASTS
- diverges from the lineage that led to fungi and animals during the PROTEROZOIC EON
- consist of mosses, ferns, conifers, and flowering plants
Algae
aquatic, photosynthetic eukaryotes (green, brown, red) that do not have a single common photosynthetic ancestor (AKA not monophyletic)
- NOT LAND PLANTS
- Green algae and land plants share a common photosynthetic ancestor
Green Algae + Land Plants
land plants evolved from a group of green algae in the early Paleozoic era within the Phanerozoic Eon
Plants: Water Ecosystem Advantages
- plants can absorb water from their surroundings with no need for any special water-absorbing mechanisms and special tissue to prevent desiccation
- Water provides an external support structure and buoyancy to living things; living on land requires additional support to avoid falling over
- Sperm + egg can swim to each other and need no protection from desiccation
- Water filters out ultraviolet-B light that is destructive to DNA
Plant: Land Ecosystem Advantages
- Sunlight is more abundant in the air than in water. Water acts as a filter, altering the spectral quality of light absorbed by the photosynthetic pigment chlorophyll
- CO2, a required carbon source for green plants, is more readily available in the air than in water since it diffuses faster
- As they evolved before land animals, land plants had no early predators. After they were affected by the selective pressure of plant-eating animals, plants evolved adaptations to deter predation like spikes, thorns, and toxic chemicals
Universal Adaptations: Water to Land Transition
The evolution of specific adaptations in aquatic plants allowed them to transition to a terrestrial environment. They did not all evolve at once. There are ones universally present in nearly all land plants:
1. Waxy Cuticle
2. Stomata
3. Roots/root-like structures
4. Mutualistic associations with mycorrhizal fungi
5. Alternation of Generations Life Cycle
Universal Adaptations: Waxy Cuticle
covers the outer surface of the plant and prevents drying out through evaporation
- partially protects against radiation damage from UV light
- much thinner in nonvascular plants called bryophytes (mosses, liverworts, hornworts)
- prevents gas exchange
- RETAINING MOISTURE!
Universal Adaptations: Stomata (Stoma)
pores/holes which allow for exchange of gasses (O2 + CO2) between plant cells and the environment
- necessary because waxy cuticles block the free-flow of gasses
- present in all land plant lineages except liverworts
Universal Adaptations: Roots/Root-Like Structures
anchor plants to the soil and, in plants with true roots, serve as conduits for water absorptions
- all plants except bryophytes have roots
Bryophytes
have root-like structures called RHIZOIDS; their lack of true roots is one reason they can only survive in very moist environments
Universal Adaptations: Mutualistic Fungi
MYCORRHIZAL FUNGI are associated with true plant roots
- they are associated with ~80% of all land plant species
- provide additional surface area for the absorption of water and nutrients from soil
- the fungi share resources with plant roots in exchange the plant shares photosynthetic sugar
- the evolution of land plants and fungi are intertwined as fungi helped break soil to rock for plants to grow on land
Universal Adaptations: Alternation of Generations Life Cycle
includes multicellular haploid and diploid stages
- present in all land plants and some green algae
- has had alterations throughout life
Alternation of Generations
all plants have both the haploid and diploid stage:
- the haploid multicellular form (GAMETOPHYTE) is followed by a multicellular diploid form (SPOROPHYTE)
- Sporophyte produces HAPLOID SPORES, which grow into the haploid gametophyte which produces HAPLOID GAMETES. The gametes then fuse to form a DIPLOID ZYGOTE, which then grows into a multicellular sporophyte
- gametes and spores are haploid
- modified in each major land plant taxa
4 Major Land Plant Taxa
- Nonvascular Plants (Bryophytes)
- Seedless Vascular Plants
- Seeded Nonflowering Plants (Gymnosperms)
- Flowering Plants (Angiosperms)
Nonvascular Plants (Bryophytes)
tied to water throughout their entire life cycle. Their major adaptations are WAXY CUTICLE + ROOT-LIKE STRUCTURES (RHIZOIDS)
- lack true roots
- heavily dependent on water
- short because they have no mechanism for transporting water against gravity
- sperm and egg require water for mating; gametes are not protected from desiccation and the sperm swims to the egg
- GAMETOPHYTE dominated life cycle (the plant is the haploid gametophyte), and the diploid sporophyte produces haploid spores which are adapted for drying out and being dispersed to new environments
- EX: liverworts, mosses, hornworts
Seedless Vascular Plants
have 3 major adaptations that are TRUE ROOTS, VASCULAR TISSUE, and LIGNIN that allow them to out compete nonvascular lants in early colonization of life on land
- true root grow deeper into soil, allowing for better extraction of water + nutrients
- true roots form better associations with mycorrhizal fungi
- vascular tissue allows for the movement of water and sugar throughout the plant
- lignin provides structural rigidity
- SPOROPHYTE dominated life cycle (the plant is the diploid sporophyte), and the diploid sporophyte produces haploid spores adapted for dispersion + desiccation
- Tied to water for reproduction; egg and sperm are sensitive to desiccation and sperm must swim to the egg through water
- EX: lycophytes, ferns, horsetails
Vascular Tissue
xylem + phloem; consist of tube-like cells that allow for transport of water (XYLEM) from roots to leaves and the transport of sugars (PHLOEM) from leaves to plant tissues
- these plants grow taller and get more sunlight
Lignin
a rigid component of plant cell walls that provides structural rigidity and allows for higher movement of water and taller plant growth
Seeded Nonflowering Plants (Gymnosperms)
trees that grow to greater heights on land by combining the strength of lignin with secondary growth; have POLLEN and SEEDS that allow them to colonize drier habitats than nonvascular and seedless vascular plants can
- They posses ALL the adaptations in seedless vascular plants
- SPOROPHYTE dominated life cycle (the plant is the diploid sporophyte, but the haploid pores develop into pollen or and embryo sac
- EX: ginkgoes, cycads, conifers
Gymnosperm/Angiosperm Haploid Spores
develop into pollen (MALE GAMETOPHYTE) and an embryo sac (FEMALE GAMETOPHYTE)
- the sac remains on the sporophyte plant while the pollen travels by wind to get to the sac, where it produces sperm that fuses with the sac-produced egg
- the fertilized egg then develops within a seed
- in angiosperms, adaptations are used to develop the gametophytes differently
Pollen
a mechanism for delivering sperm to egg in the absence of water
- pollen produces sperm
- protects it from desiccation and provides a mean for transportation
- plants that use pollen (gymnosperms and angiosperms) rely on the wind to transport the pollen to eggs
Seeds
protect fertilized eggs (embryos) against desiccation and acts as a mean for “suspended animation” for the embryo that pauses development until environmental conditions are favorable or emergence of the embryo from see to start growing as a plant
Flowering Plants (Angiosperms)
Possess ALL seeded nonflowering plant adaptations and 4 alternations of generations adaptations: the FLOWER, DOUBLE FERTILIZATION, ENDOSPERM, and FRUIT
- SPOROPHYTE dominated life (the plant is the diploid sporophyte)
- produce pollen or an embryo sac; the male and female gametophytes develop within a flower, double fertilize, and the seed develops within a fruit
Flowers
allow pollinators to move pollen (therefore sperm) to eggs
- increases the likelihood of pollination over the use of wind
- flowers also drove the co-evolution between different flowering species and their pollinators
Double Fertilization
one sperm fertilizes the egg to create an embryo, and a second sperm fertilizes another structure next to the egg to create an ENDOSPERM
Endosperm
undergoes pseudo-development, where it increases mass and contents to create a nutrient reserve for the developing embryo to use during germination
Fruits
any structure that develops from a flower ovary and aids in seed dispersal
- they provide a mechanism for seeds to colonize new territories away from the parent plant
Origin Of: Seedless Nonvascular Plants
first land plants; land plant evolution started early PALEOZOIC ERA, when ancestors of modern plants first appear in the fossil record
- lacked leaves and roots
- lived in extremely damp environments close to water
Origin Of: Seedless Vascular Plants
appear in the middle of the PALEOZOIC ERA
- plants lacked true leaves and roots and formed low vegetation
- similar in size to modern-day mosses
- climate in the era was very wet and facilitated colonization of land by these plants
Origin Of: Seeded Vascular Plants
appear in the fossil record shortly after the appearance of seedless vascular plants
- relatively rare in the fossil record as seedless vascular plants had colonized most of the land
Carboniferous Period
fossil evidence indicates that land during this period (LATE PALEOZOIC) was dominated by trees + forests including seedless and seed-bearing plants
- seedless vascular plants formed swamp forests
- this period had extensive coal deposits because of these abundant swamp forests
GYMNOSPERM DOMINATION
Gymnosperms began to dominate the land during the LATE-PALEOZOIC era when the climate became much drier
- the dry climate allowed seed-bearing gymnosperms to outcompete seedless vascular plants and dominate the land
- many plants became extinct during the end-Permian mass extinction
- After the extinction, gymnosperms reached their greatest diversity + abundance mid-MESOZOIC (AKA Age of the Gymnosperms)
Angiosperm Appearance in Time
some fossil evidence shows that flowering plants may have first appeared during mid-MESOZOIC
- undisputed fossil evidence indicated angiosperms became dominant LATE-Mesozoic
- led to an increase of insects and pollinators
Origin Of: Grasses
fossil evidence indicates that grasses evolved early-CENOZOIC era and rapidly expanded and dominated the landscape
- this evolution correlated with the evolution of large grazing mammals and predator mammals
