Lecture 12: Mosses and Ferns Flashcards
Plants (Embryophytes) are the member of ___, sister group to ___
Archaeplastida
Charophyte algae
Similarity of plants and algae
- Eukaryotic photoautotrophs
- Multicellularity (all plants are multicellular, many algae are also multicellular)
- Alternation of generations (all plants have alternation of generation, as well as many algae)
- Plastid which has a cyanobacterial ancestry (acquired directly by primary endosymbiosis or indirectly by secondary endosymbiosis)
- Cellulose cell walls (in all plants, and in many other algae like brown algae and charophytes)
Plants occupy __, while all algae are __
land
aquatic
Major advantage of land
easier access to sunlight
How does sunlight interact with water
- Sunlight gets absorbed extremely easily by water
- Earth’s dense atmosphere (Stratosphere /
Troposphere) is about 50 km thick - 50% of sunlight from outer space reaches Earth’s surface after travelling through this atmosphere
- Once sunlight enters water, 50% of it gets lost/absorbed after the first 10 meters
Challenge of terrestrial habitat
- Lack of water (…obviously)
- Limited water supply for photosynthesis
- No protection against desiccation
- Less support support against gravity
- No water for spores and sperms to
swim in - Brown algae spores/sperms can swim in water to disperse
- Many plants must use an alternate method
Plants evolved traits to live on land
- Specialized tissues to occupy above- and under-ground
- Dispersal mechanisms which do not depend on water
What specialized tissues did plants evolve?
- Leaves: acquire sunlight and CO2 from above ground
- Roots: acquire water and minerals from underground
- Vascular system: transports these products through plant body
What dispersal methods did plants evolve?
- 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
Plants evolved land-conquering traits in multi-step process
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
How did Alternation of generation change within this process
During this process, the Alternation of Generation changed from a gametophyte- dominated cycle to an extremely sporophyte dominated cycle
Step 1: Mosses
Group name: Nonvascular plants (bryophytes)
Land trait: Anti-desiccation mechanisms
Sperm Dispersal: Water
Dominance of life cycle: Gametophyte
Other members: Liverworts, hornworts, etc.
Step 2: Ferns
Group name: Seedless vascular plants
Land trait: Vascular system and tissue specialization
Sperm Dispersal: Water
Dominance of life cycle: Sporophyte
Other members: Club mosses, Horsetails, etc.
Step 3: Pines
Group name: Gymnosperms: Vascular seed plant
Land trait: Pollen, ovule and seed
Sperm Dispersal: Mainly wind
Dominance of life cycle: Extremely Sporophyte
Other members: Spruces, Firs, Cycads, Ginkgo, etc.
Step 4: ‘Flowers’
Group name: Angiosperms: Vascular flowering seed plants
Land trait: Flower and fruit
Sperm Dispersal: Wind or Animal
Dominance of life cycle: Extremely Sporophyte
Other members: too many to list
About _ of plant species are Angiosperms
90%
Mosses: Protection from desiccation
Use of sporopollenin to cover the spores for protection against desiccation Remember, charophyte algae cover their zygotes
Cuticles: Waxy polymer covering plant body for protection against desiccation (different from an animal cuticle)
Stomata: Pores on plant surface for CO2 and O2 exchange & Closes in dry conditions to preserve water
Disadvantages due to Moss structure
- 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
- Mosses use rhizoids to anchor onto surface
- Rhizoids do not transport water
___ dominated alternation of generations
Gametophyte
Moss gametophyte
The green, ‘mossy’ things which we typically think of as a ‘moss’
Moss sporophyte
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
Moss life cycle: gametophyte dominated
- Moss spores grows into protonemata
- Protonemata produces buds which grows into full female or male gametophytes
- Male gametophyte produces sperms, female gametophyte produces eggs
- Flagellated sperms swim to eggs
- Fertilized zygote grows into sporophyte…
- …while being nurtured by female gametophyte
- Mature sporophyte releases spores while still being attached to the female gametophyte
How does moss life cycle depends on water
Fertilization depends on water since sperms need to swim through water to reach the egg
Absence of vascular tissue
in another words, all parts of moss gametophyte needs to directly absorb water from the environment
Mosses usually grows in __ habitats
humid and moist
Moss protonemata looks very similar to the
charophyte algae
What differentiates ferns from moss
Vascular system and differentiated organs
Roots
Anchors plant to ground while absorbing water and nutrients from soil
Leaves
Primary photosynthetic organ with a large surface area (usually)
Stems
Connect leaves to roots while making the plant taller
Taller plants have better exposure to
light; In addition, a taller plant has a better chance to disperse their offspring over a longer distance (many angiosperms have changed this rule, though)
Vascular structure allows __ in plant body
nutrients transportation
Xylem
transport water and minerals;
* Xylem cells are dead at functional maturity
* Cell walls strengthened by lignin to provide mechanical strength
Phloem
transport sugars etc. throughout the body
Sporophyll (plural, sporophylls)
Leaves of vascular plants which have been modified to produce spores
Sporangium (plural, sporangia)
Reproductive tissue located on the sporophyll which actually produces the spores
“Sporophytes have leaves, some leaves are (1). (1) produce (2) and the (2) produces spores”
(1) Sporophylls
(2) sporangia
“Sporophytes have leaves, some leaves are sporophylls. Sporophylls produce sporangia and the sporangia produces spores”
Fern life cycle: sporophyte dominated
- 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.
Fern __ is much smaller than the __
gametophyte
sporophyte
Fern fertilization
Fern sperms swim to the egg for fertilization.
Fern sporophytes do not require complete ‘wetness’ to acquire water for photosynthesis.
However, fern gametophyte still depends on water for fertilization.
