Plant Diversity I Flashcards
What was the process that lead up to the greening of the earth?
- For the first 3 billion years, land surface was largely lifeless
- Cyanobacteria existed on land ≈1.2 billion years ago
- Only ≈500 million years ago (mya), small plants, fungi, and animals emerged on land
- Now ≈290,000 living species plants
What are the advantages of living on land rather than in the water?
- In a world of water, moving onto land had distinct advantages … » Bright sunlight, unfiltered by water » More CO2 in air than in water » Soil rich in mineral nutrients » Less competition, no “predators”
What were some challenges for animals adapting to living on land? What was the result of these challenges?
» Scarcity of water
» Lack of structural support against gravity
- Plants diversity is a reflection of different adaptations to these challenges
are all plants related to algea?
Land plants are related to green algea
What is the “alternation of generations?
- an adaption in plants
- Plants alternate between two multicellular stages (“alternation of generations”)
» Includes both multicellular haploid and multicellular diploid organisms
How does the “alternation of Generations” work?
- Plants, likewise, have sperm and eggs in their life cycles, but these are produced by an intermediate stage between the adult and the offspring
- The adult generation produces spores (sporophyte), while the spore generation produces sex cells (Gametophyte)
- The spores then develop into the gametophyte generation.
How do plants protect gametes, zygotes and spores?
- Adaption of land plants
» Specialised organ for gamete production (gametangia)
• Archegonium in female plants
• Antheridium in male plants
» Multicellular, dependent embryos (“embryophytes”)
• Grow protected within the parent plant
» Tough and protected spores
• Walls more resistant to drying (thanks to sporopollenin)
• Produced protected within specialized organs (sporangium)
What is apical meristems?
- Plants need to grow above ground (CO2, light) AND below ground (water, mineral nutrients) → apical meristems
» Specialised tissue at growing tips of plant where cells divide repeatedly
» Cells produced by the apical meristem then differentiate into outer epidermis or various types of internal tissues
Give a brief summary of a plant
» Photosynthetic organisms that have adapted to life on the land
• Most live in terrestrial habitats, but a few have returned to aquatic habitats (eg, seagrass)
» Eukaryotes
» Cell walls
» Photosynthetic autotrophs
• Sunlight as source of energy for metabolism (chloroplast)
• Fix carbon from CO2 to create organic compounds
- Life on land owes its existence to plants
- Live in all but the harshest terrestrial habitats
How many forms of plants are there?
Two distinct forms:
» Vascular plants
» Non-vascular plants
How many phyla of plants are there?
10
What are the 3 phyla of Nonvascular plants (Bryophytes)?
- Bryophytes represented today by three phyla of small herbaceous (nonwoody) plants:
- Mosses (phylum Bryophyta)
- Liverworts (phylum Hepatophyta)
- Hornworts (phylum Anthocerophyta).
What are the two different types of Vascular plants?
Seedless and Seeded plants
What are the different phylums of Vascular seedless plants?
- Lycophytes (Phylum Lycophyta)
- Monilophytes (Phylum Monilophyta)
What are the different types of Vascular seeded plants?
Gymnosperms and Angiosperms
What are the different phylums of vascular seeded Gymnosperms?
- Ginkgo (phylum Ginkophyta)
- Cycads (phylum Cycadophyta)
- Gnetophytes (phylum Gnetophyta)
- Conifers (phylum Coniferophyta)
What are the different phylums of vascular seedless angiosperms?
- Flowering plants (phylum Anthophyta)
What is the predicted ancestor of all plants?
An ancestral green Alga
How long ago was the origin of land plants?
- about 470 mya
how long ago was the origin of vascular plants?
- about 425 mya
What type of plant originated 305 mya?
- extant seed plant
provide a summary of non-vascular plants
Primitive land plants
» Simple structure
» Need abundance of water
» Lack specialised conductive tissues
give a summary of liverworts
- Non-vascular plant
- About 9000 species
- Usually small (<2 cm)
- Mostly found in humid environments
Give a summary on Hornworts
- non-vascular plant
- About 100 species
- Most small, grow in humid places; some larger, grow on trees
Give a summary on mosses
- Non-vascular plant
- About 15,000 species
- The “carpet” is mostly gametophytes (haploid multicellular organism)
- Sporophytes are elongated, visible to the naked eye
What is the difference between a vascular plant life cycle and a non-vascular plant life cycle?
Unlike vascular plants, non-vascular plant life cycles are dominated by the gametophyte (haploid)
What is the life cycle of moss?
Firstly the spore germinates into a gametophyte (protonema + gametophore, anchored by rhizoid) → gametes by mitosis → fuse in archegonium → zygote → embryo → sporophyte → spores by meiosis
What is the difference between a Gametophyte and a Sporophyte?
- Gametophytes are larger and longer-living than sporophytes
» Sporophytes are typically present only part of the time
What is the first step in the general life cycle of all three phylum of Bryophyte?
- A spore germinates into a gametophyte composed of a protonema and gamete-producing gametophore
» Rhizoids anchor gametophytes to substrate
» The height of gametophytes is constrained by lack of vascular tissues
What is the 2nd step in the general life cycle of all three phylum of Bryophyte?
- Mature gametophytes produce flagellated sperm in antheridium and egg in archegonium
What is the 3rd step in the general life cycle of all three phylum of Bryophyte?
- Sperm swim through a film of water to reach and fertilise the egg
What is the 4th step in the general life cycle of all three phylum of Bryophyte?
- Bryophyte sporophytes grow out of archegonium, and are smallest and simplest sporophytes of all extant plant groups
What is the 5th step in the general life cycle of all three phylum of Bryophyte?
- Each sporophyte releases enormous number of spores
» A single moss capsule can generate over 5 million spores!
What are the parts of a Sporophyte?
» Foot
» Seta (“stalk”)
» Sporangium (“capsule”)
Draw a diagram of a Sporophyte
book
What is the Ecological significance of moss?
- Mosses colonise bare soil and rocks, and help retain nitrogen
- Peat bogs cover 3% of land surface but contain 30% of soil carbon
» Good storage, but higher temperature due to global warming is likely to dry peat moss globally, causing it to decompose → release its CO2
What are the main traits of modern vascular plants?
» Life cycles with dominant sporophyte
» Transport in specialized vascular tissues called xylem and phloem
» Well-developed roots and leaves
Draw the diagram of the xylem and pholem
book
What is the life cycle of a Vascular plant?
- Still undergo alternation of generations, but gametophyte much reduced and sporophyte greatly increased
- Dominant sporophyte
What are the two types of vascular tissues?
Xylem and Phloem
What is Xylem?
» Xylem
• Includes dead tube shaped cells (“tracheids”) that carry water and minerals up from roots
• Cell wall strengthened by lignin, provides support → enables vascular plants to grow tall
What is Phloem?
» Phloem
• Living cells that distribute sugar, amino acids and other organic products
What are the benefits of Xylem and Phloem?
- Evolutionary edge: structural support + ability to carry water and nutrients high above the ground → plants could grow higher
» Outcompete shorter plants for sunlight
» Disperse spores further
What are the leaves?
» Primary photosynthetic organ of vascular plants
» Greatly increases the surface area of vascular plants → capture more sunlight energy for photosynthesis
What are the roots of a plant used for?
» Anchor the plant, like rhizoids
» But also absorb water and nutrients from the soil
What is Phylum Lycophyta
- (“lycophytes”)
- seedless vascular plants
» Includes club mosses, spike mosses, and quillworts
• Although they’re NOT mosses!
» Most herbaceous today, but during Carboniferous period (359-299 mya), included 40 m high trees!
What is Phylum Monilophyta?
- (“monilophytes”)
- Seedless vascular plants
» Includes ferns, horsetails, and whisk ferns and their relatives
» Most widespread seedless vascular plants (12,000 species)
what is the anatomy of a Fern sporophyte?
- Horizontal stem (“rhizome”)
- Large leaves (“fronds”; leaflets called “pinnae”)
» Spore producing
sporangia on underside - Roots (can be part of the stem)
draw diagram of a fern sporophyte
book
What is unique about fern leaves?
- Unique manner of unfurling leaves (“circinate vernation”)
- Sporangia on underside (“sori”), protected by scale (“indusium”)
In relation to plants, what happened during the Devonian and Carboniferous periods?
- Ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian (419-359 mya) and Carboniferous (359 299 mya), forming the first forests
What was the result of the forests that formed during the Devonian and Carboniferous periods?
- Increased growth and photosynthesis removed CO2 from the atmosphere and may have contributed to global cooling at the end of the Carboniferous period
How are the forests that formed during the Devonian and Carboniferous periods affecting us today?
- The decaying plants of these Carboniferous forests eventually became coal … burning coal is now contributing to global warming
What are three types of local fern?
- (Platycerium bifurcatum) Elk horn - (Cyanthea cooperi) Straw treefern - (Platycerium superbum) Staghorn
What are the four main groups of plants?
» Bryophytes
» Seedless vascular plants
» Gymnosperms
» Angiosperms
