Lecture 12 Flashcards
Plants (embryophytes) are members of
Archaeplastida, sister group to charophyte algae
List the similarities between plants and algae
- Eukaryotic photoautotrophs
- Multicellularity
- Alternation of generations
- Plastid which has a cyanobacterial ancestry
- Cellulose cell walls
How is cyanobacterial ancestry acquired
Directly by primary endosymbiosis or indirectly by secondary endosymbiosis
Distinguishing feature of plants vs algae
Plants occupy land while all algae are aquatic
What is the major advantage of land
- Easier access to sunlight
- Sunlight gets absorbed extremely easily by water
- Better access to soil, minerals
Earth’s dense atmosphere (statosphere/ troposphere) is about
50 km thick
- 50% of sunlight from outer space reaches earth’s surface after travelling through this atmosphere
What happens once sunlight enters water
50% of it gets lost/ absorbed after the first 10 meters
terrestrial habitat
any environment that exists on land—as opposed to in water (aquatic habitat) or air. It includes places where organisms live and interact with their surroundings on the Earth’s surface
Challenges of terrestrial habitats
- Lack of water
- Limited water supply for photosynthesis
- No protection against desiccation (loss of moisture)
- Less support against gravity
- No water for spores and sperms to swim in
Dispersal of spores and sperms is completely
Water dependent for Brown algae since they can swim in the water to disperse
What does sporangia of algae develop
Surface of blade to produce zoospores
What specialized tissues did plants evolve to occupy above and under the ground
Leaves: Acquire sunlight and CO2 from above ground
Roots: Acquire water and minerals from underground
Vascular system: Transports these products through plant body
Plant dispersal mechanisms that do not depend on water
Pollens: Male gametophyte packaged into shelled structures to disperse sperms via air/animals
Seeds: Developing embryo packaged with a protective coating + food source, dispersal via air/animals
List the multistep process in how plants evolved land conquering traits
Step 1: Mosses; Basic traits to persist on land
Step 2: Ferns; traits to combat gravity
Step 3: Pines; traits to reproduce without water
Step 4: Flowers; traits to take full advantage of the terrestrial environment
- During this process, the alternation of generation changed from a gametophyte-dominated cycle to an extremely sporophyte dominated cycle
List all the non vascular plants
- Liverworts
- Mosses
- Hornworts
List all the seedless vascular plants
Lycophytes (club mosses)
Monilophytes (ferns)
Seed plants
Gymnosperms
Angiosperms
Explain step 1 of plant evolution
Representative plant: Moss
Group name: Non vascular plants (bryophytes)
Land conquering trait: Anti desiccation mechanisms
Sperm dispersal: Water
Dominance of life cycle: Gametophyte
Other members: Liverworts
Explain step 2 of plant evolution
Representative plant: Ferns
Group name: Seedless vascular plants
Land conquering traits: Vascular system and tissue specialization
Sperm dispersal: Water
Dominance of life cycle: Extremely sporophyte
Other members: Club mosses, horsetails
Explain step 3 of plant evolution
Representative plant: Pines
Group name: Gymnosperms: Vascular seed plant
Land conquering trait: Pollen, ovule, seed
Sperm dispersal: Mainly wind
Dominance of life cycle: Extremely sporophyte
Other members: Spruces, firs
Explain step 4 of plant evolution cycle
Representative flower: Flowers
Group name: Angiosperms: Vascular flowering seed plants
Land conquering trait: Flower and fruit
Sperm dispersal: Wind or animal
Dominance of life cycle: Extremely sporophyte
Others members: too many to list..?
About 90% of plant species are
Angiosperms: It shows how successful their strategy to occupy diverse niches on land
- Other plants are also competitive and effective (pine forest) but not as diverse
Mosses and protection from desiccation
Use of sporopollenin to cover the spores for protection against desiccation; remember charophyte algae covers their zygotes
Cuticles: Waxy polymer covering plant body for protection against desiccation
Stomata: Pores on plant surface for CO2 and O2 exchange… Closes in dry conditions to preserve water
- Traits allow mosses to persist on land
Mosses and protection from desiccation pt2
- Lack of further specialized tissues limit mosses from growing tall
- No hardened tissues to support body against gravity
- No vascular structure to transport water and nutrients throughout the body
- No true root; Moss use rhizoids to anchor onto surface, rhizoids do not transport water
Moss life cycle
- Gametophyte dominated alternation of generations
- Moss gametophyte: The green ‘mossy’ things which we typically of as a moss
Moss sphorophyte
Appendages which grow out from the gametophyte
- Has the sporangium (the spore producing tissue) at the end
- Completely dependent on the gametophyte for growth and survival
- Usually has a shorter life than the gametophyte
Explain the process of moss life cycle
- Moss spores grow into protonemata
- Protonemata produces buds which grows into full female or male gametophytes
- Male gametophytes produces sperm. female gametophyte produces eggs
- Flagellated sperms swim to eggs
- Fertilized zygote grows into sporophyte
- Is nurtured by female gametophyte
- Mature sporophyte releases spores while still being attached to the female gametophyte
How does the moss life cycle depend on water
- Fertilization depends on water since sperms need to swim through the water to reach the egg
- Absence of vascular tissue: All parts of the moss gametophyte needs to directly absorb water from the environments
- Mosses usually grows in humid and moist habitats for these reasons
Moss protonemata looks very similar to
charophyte algae
Ferns and differentiated organs
Roots: Anchors plant to ground while absorbing water and nutrients from soil
Leaves: Primary photosynthetic organ with a large surface area
Stem: Connect leaves to roots while making the plant taller since taller plants have better exposure to light and chances of dispersing their offspring over longer distance
Vascular system of ferns
Vascular structure allows nutrient transportation in plant body
Xylem: Transport water and minerals
- xylem cells are dead at functional maturity
- Cell walls strengthened by lignin to provide mechanical strength
Pholoem: Transport sugars through the body
Ferns no longer need
all parts of its body to absorb water directly from the environment
- Leaves can stay dry while they receive water via the vascular system
Sporophyll vs sporangia
Sporophyll: Leaves of vascular plants which have been modified to produce spores
Sporangium: Reproductive tissue located on the sporophyll which actually produces the spores
Explain the process of fern life cycle
- Spores grows into a bisexual gametophyte
- Gametophyte produces both the sperm producing organ and the egg producing organ. Sperm swims through moisture to reach the egg
- Fertilization of egg by sperm to produce the zygote
- Zygote develops into a sporophyte while it is supported by the gametophyte
- Mature sporophyte is independent from parental gametophyte. It produces spores from sporangia
Ferm gametophyte is much smaller than
the sporophyte
- Fern sporophytes do not require complete “wetness” to acquire water for photosynthesis however fern gametophytes still depend on water for fertilization
Fern sperms
swim to the egg for fertilization
