Chpt 21 – Mosses and Ferns
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*** Plant move to land – there are new problems that plants now have to over come
o There are 5 problems
1 – the supply of water
• Plants develop ways to protect against water loss
2 – exposure to sunlight
• Plants develop ways to hold out photosynthetic cells
3 – nutrient transport
• Plants need water and nutrients to move up
• Products of photosynthesis move down
4 – gas exchange (without water loss)
• Gas exchange must take place in moist conditions
5 – reproduction (without water loss)
• So that water is no longer needed for reproduction
o As plants evolve, they become better at resolving these issues
o However, the first land plants DID NOT resolve all 5 issues
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There are only 2 phyla of plants
1 – phylum Bryophyta
o Ex) mosses, liverworts, and hornworts
o Believed to have evolved from filamentous algae
o Have alternation of generation
o Needs water for reproduction
Therefore bryophytes need to be near water to survive
o Have no internal transport system
Therefore tend to only be a few cm’s high.
o Ex) mosses
Most of the life cycle is the haploid gametophyte
Mosses have thin upright shoots that look like a stem with leaves
They are not real stems or leaves
They have thin branches called rhizoids that anchor the mosses to the ground
(these are not real roots)
Substances move through the moss by diffusion.
P. 453 copy the moss plant diagram
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Ex) liverworts
o Need constant water
o The gametophyte looks like a flat green leaf
o It produces umbrella – like structures that produce the gametes
Ex) hornworts
o Similar to liverworts
o Have horn – like structures for reproduction.
P. 454 copy the moss life cycle
Reproduction in mosses
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Mosses show alternation of generation
Part of their life cycle is with the haploid structure (gametophyte)
Part of their life cycle is with the diploid structure (sporophyte)
The majority of the mosses life cycle is with the gametophyte
o The gametophyte is the prominent feature of the moss life cycle.
At the tip of the gametophyte, when sexual reproduction occurs, there are specialized structures
that produce the gametes
o Antheridium – male reproductive structure
Produces flagellated sperm cells (gamete)
• They are motile
o Archegonium – female reproductive structure
Produces the eggs (gametes)
• Are non-motile
In order for the sperm to get to the eggs, water is needed
Once the sperm reaches the Archegonium, syngamy occurs (fusion)
A zygote (2N) is produced
The zygote grows on top of the gametophyte structure
The zygote is now called the sporophyte
At the top of the sporophyte, a capsule produces haploid spores (meiosis)
Wind or water carry the spores away
Once they find the right place, they grow into a tangled mass of filaments called the protenema
o The protenema resembles filamentous algae. (evolutionary link)
As the protenema grows, rhizoids grow and the gametophyte develops.
2- Phylum Tracheophyta –
o These are the “true” plants
They have evolved vascular tissue
o 2 types of vascular tissue (tissue for transportation)
Xylem – moves water
• has specialized cells called tracheid cells
o have thick wall
o help plants grow against gravity
phloem – moves nutrients around the plant
have evolved true roots and true leaves
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o roots and leaves have vascular tissue
o roots – function is to collect water and nutrients
anchors the plant
o leaves – function is to capture sunlight
photosynthesis
there are 3 examples
o 1 – lycophytes – known as club mosses
Look like miniature pine trees p.457
Still small, don’t grow more than 15 cm high
o 2 – sphenophytes – known as horse tails
Have leaves in rings at joints around the stem
Can grow up to 60 cm high
Has silica in them
P. 457
o 3 – fern –
Have true roots
Have underground stems called rhisomes
Have a single large leaf called a frond
Found in wet or seasonally wet area
• Still need water for reproduction
P. 459 Reproduction of ferns
Reproduction of ferns
o Have alternation of generation
o The primary stage of the life cycle is the sporophyte (2N)
o On the underside of a frond, the sporophyte produces haploid spores in a structure called
sporangia
The sporangia are grouped in clusters called sori (singular – sorus)
o The spores are released and carried by wind or water
o In the right place, the spores germinate to produce the gametophyte
o The gametophyte grows rhizoids and develops into a heart shaped structure called
prothallium –
On the prothallium, Archegonium (female) and the antheridium (male) produce
gametes
o The sperm swim to the Archegonium and fertilize an egg
o The diploid zygote grows into a sporophyte as the prothallium withers away
o P. 459 copy the fern life cycle
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Importance of mosses and ferns
Both are used in gardens
o Mosses can be added to soils to increase its ability to absorb water (peat moss)
Mosses can be used to treat burns and other wounds
After some decomposition, mosses become peat, which can be burned as a fuel
Mosses and ferns can be used as foods
o Indirectly – mosses are used to add smoky flavor
o Directly – ferns can be purchased at the grocery store as fiddle heads