Plant diversity Flashcards
When did Cyanobacteria emerge? When did the others join?
1.2 billion years ago
Other fungi, algae, “plants” joined ~700 million years ago
Where is the earliest evidence of trees?
Earliest evidence of trees in Megouasag (Micmac for “red cliffs”)
Archaeopteris is a historical tree
Fossil beds are ~380 million years old
Development of lignin allowed for super rigid cell walls to support upward grow
Had fern-like leaves -> surface area allowed more efficient photosynthesis to compete with early plants
What are plants apart of?
are part of Archaeplastida
Unicellular, multicellular and/or colonial members
What are the 2 main clades of Archaeplastida ?
Green algae (paraphyletic because 2 main groups charophytes and other one) Red algae (monophyletic) -> have a holdfast, stipe(stem), blade (leaf)
Use of photosynthetic pigments allows for the adaptation to different environments and also identifies members
What did plants evolve from
Plants evolved from green algae
Green algae called charophytes are the closest relatives of plants.
Which traits in algae and plants?
Some of these traits were acquired independently and tell an incomplete story with respect to the origin of plants
Multicellularity
Photosynthetic pigments (i.e. chlorophylls)
Cell walls composed of cellulose
Charophytes
(Supergroup Archaeplastida, Green algae) are closest relatives to terrestrial plants
What evidence supports that charophytes are the closest relatives to plants?
- Rings of cellulose-synthesizing proteins (in other algae and plant organisms the cellulose forming proteins occur linearly)
Many algae produce cellulose in cell walls,but charophytes and land plants have distinctive circular rings of proteins in the plasma membrane - Flagellated sperm
In plant species that have flagellated sperm, they most resemble the sperm in charophytes compared to other algae - Formation of phragmoplast
Microtubules and associated proteins present in charophytes and land plants after cytokinesis, guiding the assembly of cell plate formation
• Molecular analyses of nuclear, mitochondrial and chloroplast DNA also support this
What are the benefits of moving to land?
Moving to land is beneficial: (unlimited Co2 nutrients from soil more light)
• Sporopollenin is a polymer that prevents desiccation (Common in charophytic algae living at the edge of shallow ponds)
• More unfiltered sunlight, carbon dioxide, nutrients in soil -> life is good!
What are the challenges of moving to land?
Water is scare, harder to disperse sperm
• Have to grow against gravity
Sporopollenin
A durable polymer that covers exposed zygotes of charophyte algae and forms the walls of plant spores, preventing them from drying out
adaptation for life on land
What are some adaptations of plants to allow for survival on land?
Accessory pigments to help with UV protection, antioxidant effects
Cuticle -> waxy layer on the outer epidermis to help prevent desiccation
Stomata (pores) -> allow exchange of carbon dioxide and oxygen (photosynthesis is efficient even more because you have regulated gas exchange)
(Can close in periods of hot, dry conditions to prevent water loss )
Formed symbiotic relationships with fungi (roots did not immediately
happen) with mycerizae
Developed meristems to allow for vertical growth
Alternation of generations life cycle
Analysis of fossilized spores shows plants colonized land ~450 million years ago
Stomata
A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.
Cuticle
A waxy covering on the surface of stems and leaves that prevents desiccation in terrestrial plant
How can plants be classified?
Plants can be broadly classified based on the presence of vascular tissues
vascular tissue
Plant tissue consisting of cells joined into tubes that transport water and nutrients throughout the plant body
What do non vascular plants include?
(bryophytes)
Liverworts
Mosses
Hornworts
What can vascular plants be divided into
comprises about 93% of all extant plant specie
Seedless vascular plants
Seedplants
What do Seedless vascular plants include?
Lycophyta (club mosses, spike mosses, quillworts
Monilophytes (ferns, horsetails, whisk ferns
What do Seedplants include?
Gymnosperms (ginkgos, cycads, gnetophytes, conifers)
Angiosperms (flowering plants)
Seedless vascular plants
An informal name for a plant that has vascular tissue but lacks seeds. Seedless vascular plants form a paraphyletic group that includes the phyla Lycophyta (club mosses and their relatives) and Pterophyta (ferns and their relatives).
Which phylum has the most species?
Angiosperms
What is an example of a grade?
A group, such as the bryophytes or seedless vascular plants, is sometimes referred to as a grade
monilophytes and lycophytes
What are the monilophytes closely related to?
even though monilophytes and lycophytes are all seedless plants, monilophytes share a more recent common ancestor with seed plants
As a result, we would expect monilophytes and seed plants to share key traits not found in lycophyte
seed
An adaptation of some terrestrial plants consisting of an embryo packaged along with a store of food within a protective coat.
gymnosperms
A vascular plant that bears naked seeds—seeds not enclosed in protective chambers.
angiosperms
A flowering plant, which forms seeds inside a protective chamber called an ovary
herbaceous
non woody liverworts (phylum Hepatophyta), mosses (phylum Bryophyta), and hornworts (phylum Anthocerophyta).
Describe the general life cycle of plants
1) Gametophyte produces haploid gametes (1n) via mitosis
2) Two gametes (1n) come together via fertilisation to produce a diploid zygote (2n)
3) The zygote (2n) develops into the multicellular sporophyte
4) The sporophyte (2n) produces unicellular haploid spores (1n) by meiosis
5) The spores (1n) develop into multicellular haploid gametophytes (1n
What are liverworts and hornworts named for?
Liverworts and hornworts are named for their shapes, plus the suffix wort
ii
Phylogenetic analyze suggest bryophytes diverged early in plant lineage evolution
Earliest spores of plants (450-470 million years ago) more similar to liverwort spores (most basal group)
~430 million years ago spores similar to mosses and hornworts showed up in the fossil record
What stage is dominant in bryophytes?
Bryophytes have a dominant haploid stage
gametophyte stage
they are usually larger and longer-living than the sporophytes
gametophyte
In organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes. (gamete producing bodies)
Protonema
threadlike filaments that develop into “buds” which grow via a meristem to produce the gametophores
Gametophore
“gamete bearer”, produces gametes via mitosis
Rhizoids
“root-like” filaments that anchor the gametophyte (not true roots)
Gametangia
produces the gametes
Archegonia
female, produces the egg
Antheridia
male, produces sperm
sporophytes
(spore producing bodies)
Bryophytes have the smallest sporophytes
Seta
stalk supporting the sporangium
Foot
absorbs nutrients from the gametophyte, supports the seta
Capsule
sporangium, produces spores via meiosis
Peristome
“teeth” on the capsule to regulate spore dispersal (open when its wet enough let some spores and close when its too dry)
Describe the bryophyte life cycle
1) Spores (1n) develop into threadlike protonema
2) Protonema (n) produces “buds” the develop into gametophytes (n)
Gametangia
Antheridia -> male, sperm
Archegonia -> female, egg
3) Sperm must swim through water to reach the egg (Gametes produced via mitosis) (need access to water for fertilization)
4) Zygote develops into a sporophyte embryo (2n)
5) Sporophyte grows a seta that emerges from the archegonium
6) Attached by the foot, the sporophyte (2n) remains nutritionally dependent on the female gametophyte (n)
7) Meiosis occurs in the 2n capsule, producing spores
Describe bryophytes
Common in moist forests and wetlands, moist bare soil
Many associate with nitrogen-fixing bacteria
Can survive harsh environments (cold, dry)
Some Sphagnum moss species comprise peat
Many bryophyte species also have a medicinal or cultural importance in many Indigenous nations
(Bandages for wounds, baby diapers)
Why are bryophytes ecologically important?
- Help retain moisture
- Help retain nitrogen within the environment
- Can tolerate complete water loss and can re-establish when moisture returns -> poikilohydric
Some Sphagnum moss species comprise peat
Preserves organisms from decaying due to the low temps, pH, and oxygen levels of peatlands
Important fuel source (Finland and Ireland uses a lot of it!)
Horticultural nutrient to help retain moisture in soils
Carbon sink -> 30% of the world’s carbon is stored in peatlands comprising 3% of Earth’s surface
What were seedless vascular plants the first to do? When did they arise?
First to grow tall due to the rigid structure of vascular tissues
Arose ~425 million years ago
Compared to nonvascular plants, Seedless vascular plants had:
- Branched sporophytes now dominant stage
- Not nutritionally dependent on the gametophyte
Still lack true roots
Vascular tissues
Xylem -> water transport, structural support
Phloem -> nutrient transport
Xylem
water transport, structural support Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from the roots to the rest of the plant.
Phloem
nutrient transport
Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.
Describe the fern life cycle
1) Sporangia release spores (n). Spores develop into a bisexual photosynthetic gametophyte antheridia and archegonia are produced on the same plant
2) Each gametophyte (n) produces antheridia and archegonia via mitosis. Sperm usually fertilizes the egg of another gametophyte
3) Sperm uses flagella to swim to the egg, attracted via positive chemotaxis to the archegonium
4) Zygote (2n) develops into a new sporophyte (2n), which grows out of the archegonium of the parent gametophyte
5) Sporophytes (2n) produce sori, clusters of sporangia (2n) which will produce spores via meiosis
What is the xylem composed of?
Composed of tracheids and vessel elements, strengthened by lignin
What is the phloem composed of?
Composed of sieve tube elements and companion cells
i
Allows plants to grow tall and still get nutrients to leaves
Allows plants to outcompete shorter plants for light
tracheid
A long, tapered water-conducting cell found in the xylem of nearly all vascular plants. Functioning tracheids are no longer living.