Download NOTES: Kingdom Plantae I Seedless Plants (Chapter 29)

Biology 110 Section 11
J Greg Doheny
NOTES: Kingdom Plantae I
Seedless Plants (Chapter 29)
Quiz Questions:
1.
2.
3.
4.
5.
What is the name for the haploid form of a plant?
What is the name for the diploid form of a plant?
What is the name of the plant structure which produces female eggs?
What is the name of the plant structure which produces male sperm?
What is the name of a leaf on a seedless vascular plant that has been
modified to bear sporangia?
6. What is the name of the lignified vascular plant tissue that carries water and
minerals throughout the plant?
7. What is the name of the vascular plant tissue that carries sugars and amino
acids throughout the plant?
NOTES
Plants will be discussed from the oldest to the newest as follows: The earliest plants were
nonvascular, and reproduced using spores (like fungi and slime molds) rather than seeds.
Development of vascular tissues (small tubes carrying nutrients around) allowed plants to grow
taller. Evolution of spores into seeds followed, eventually diverging into Gymnosperms (‘naked
seeds’), and the more advanced Angiosperms (enclosed and fruit-covered seeds).
1. Nonvascular, seedless plants: bryophytes (mosses, liverworts and hornworts.)
2. Vascular seedless plants:
a. Lycophytes (spike mosses, club mosses, and quillworts)
b. Pterophytes (ferns, horsetails, and whisk ferns)
3. Gymnosperms: (cone plants)
4. Angiosperms: (flowering plants)
This lecture deals with the seedless nonvascular and vascular plants (Chapter 29), and the next
lecture will deal with the two types of seed-producing vascular plants. Remember, however, that
‘seedless’ plants means the plants produce spores instead of seeds, with spores being a simpler
form of seeds.
CONCEPTS:
Evolution of Land Plants from multicellular green algae: Land plants evolved from a
common flagellated protozoan ancestor, and are members of the Protist group (sub-domain)
Archaeplastida. Their closest relatives are the multicellular green algae (Chlorophytes and
Charophytes), with Charophytes being the closest. In fact, the Charophytes that grow (and often
clog) the edges of freshwater ponds are almost indistinguishable from many land plants (Figure
29.3). Charophytes live in ponds that frequently dry out at the edges. Natural selection selected
Charophytes that had developed methods of resisting desiccation. The most notable
development was a protective layer of sporopollenin protecting the spores from desiccation.
Plants display Alternation of Generations: Humans spend most of their lives as diploid
organisms with a temporary haploid phase (eggs and sperm). Fungi spend most of their lives as
haploid organisms with a temporary, transient diploid phase. In the plant life cycle, neither form
is transient. Both the haploid and diploid forms live side by side, and frequently interact. Both
the haploid and diploid forms are capable of producing spores. This is called the principle of
Alternation of Generations in plants. In primitive, non-vascular plants like mosses, the haploid
form (called the Gametophyte) is dominant, is bigger than the diploid form (called the
Sporophyte), and the sporophyte often relies on the gametophyte to live. In more advanced
plants, the opposite is true, where the gametophyte form of the plant is smaller and less
significant than the sporophyte.
As an example, ferns (seedless vascular plants) are the sporophyte version of the plant. Ferns
produce spores which drop to the ground and germinate to form gametophytes. The
gametophytes produce eggs (female gametes) in a special structure called an Archegonium, and
sperm (male gametes) in a structure called an Antheridium. The gametophytes of most
organisms are bisexual, producing both sperm and eggs, but usually do not self-fertilize. When a
sperm from the antheridium of one fern gametophyte fertilizes the egg in the archegonium of
another gametophyte, a new diploid sporophyte is produced, which then produces spores in a
structure called a sporangium, which are released and give rise to more gametophytes, and so
on. You can easily see ferns (the sporophyte), and the gametophytes are usually found
underneath the ferns, either on or in the ground, and are less visible.
SEEDLESS NONVASCULAR PLANTS:
The nonvascular plants (also known as Bryophytes) were the first plants to appear on land, and
were the only plants for about 100 million years. They do not normally grow taller than a few
centimeters due to lack of structural support tissues, and the gametophyte form is dominant.
When a sporophyte develops, it grows on top of (and inside) the gametophyte, relying on it for
nutrition. This group includes the Mosses (phylum Bryophyta), Liverworts (phylum
Hepatophyta) and Hornworts (phylum Anthocerophyta). The word ‘wort’ is an old AngloSaxton (the language that preceded English) word meaning ‘herb.’
The mosses grow as single, branched filament called a protonema (protonemata), which
includes a root-like structure called a rhizoid. Unlike higher plants, the gametophyte is not
bisexual, and there are separate male and female haploid gametophytes. Female gametophytes
carry a single egg in archegonia at the top of the plant, and male gametophytes carry many sperm
in antheridia at the top of the plant. In these plants, the sperm is flagellated, and is usually
transferred from antheridia to eggs in archegonia by water droplets. Thus, these plants must live
in damp, rainy places. When a sperm fertilizes an egg, a young sporophyte develops inside the
female gametophytes archegonium, and sprouts out of the top. The moss is green, but the
sporophyte that grows out of the top is usually a different colour, and is composed of a foot
(anchoring the sporophyte to the gametophyte), a seta (stem) and a sporangium (sometimes
called a capsule) which is filled with many haploid spores.
The Hornworts form spike-shaped sporophytes that have no stem (seta), and the Liverworts have
liver-shaped leaves, and the archegonia look like little palm trees. The sporophytes hang from
the bottom of these palm trees looking like microscopic coconuts! In all cases, the sporophytes
live inside the archegonium of the female gametophyte, and absorbs nutrition from it through the
foot. The sporophytes also have specialized pores called stomata, which are used for gas
exchange with the atmosphere, and are more important in the leafy plants to be discussed later.
Since the bryophites dominated the landscape for about 100 million years, and dead bryophites
constitute a significant portion of the carbon in the biosphere.
SEEDLESS VASCULAR PLANTS
Vascular plants have developed an internal network of tubes that carry water and nutrients
around. This is handy, because the water is found in the ground, and the leaves (needed for
photosynthesis) must be above ground. So, the plant can grow larger if there is some system to
transport water from the ground to the leaves above ground, and carbohydrates produced by the
photosynthetic leaves to other parts of the plant. Such plants have two types of vascular tissue.
Xylem is vascular tissue that primarily transports water and minerals throughout the plant, and is
reinforced for strength with lignin. The fact that lignin adds strength to the plant also allows it to
grow taller, where it has a competitive advantage in catching more sunlight. Phloem is another
form of vascular tissue that carries carbohydrates and amino acids around the plant.
The seedless vascular plants are divided into two phyla, the Lycophytes (phylum Lycophyta)
which includes the Club Mosses, Spike Mosses and Quillworts; and the Pterophytes (phylum
Pterophyta) which includes the ferns, horsetails and whisk ferns. (Note that the ‘Club Mosses’
and ‘Spike Mosses’ are not ‘true’ mosses. True mosses are nonvascular, so these names are
misnomers.) The Lycophytes and Pterophyta differ mainly in the complexity of their roots and
leaves.
Roots: the vascular plants have more elaborate roots than nonvascular plants. Bryophyte roots
(rhizoids) are fairly simple, and do not branch. Lycophyte roots can branch, but only through
bifurcation (Y shaped forks), while Pterophyte roots can have many more branches.
Leaves: Leaves are classified as either Microphylls (leaves like spikes), or Megaphylls (large
broad leaves). The Lycophytes typically have microphyllic leaves and the Pterophytes have
broader Megaphyllic leaves.
Spores: Plants can be either homosporous or heterosporous. Homosporous plants produce
spores that give rise to bisexual gametophytes, while heterosporous plants produce spores that
give rise to either male or female gametophytes. The large containers that contain the spores (on
the sporophyte version of the plant) are called sporangia (singular: sporangium). If sporangia
are found in clusters the cluster is called a sorus (plural: sori). Larger clusters of sporangia,
arranged like corn, are called strobili (singular: strobulus). Some of the Pterophytes have
modified leaves called sporophylls that are modified to bear the sporangia. (Example: the small,
brown coloured sori on the underside of fern leaves.)
The Lycophytes are often found in tropical regions growing as epiphytes (plants that grow on
the tops of other plants). By growing at the top of the forest canopy instead of the bottom, they
are able to better compete for light.
PRACTICE QUESTIONS:
Match the seedless plants to the definitions:
a. Spike mosses
d. Liverworts
g. Ferns
b. Quillworts
e. Hornworts
h. Horsetails
c. Club mosses
f.
i.
Mosses
1. Which are vascular?
2. Which are members of the phylum Hepatophyta?
3. Which are bryophytes?
4. Which are Lycophytes?
5. Which are Pterophytes?
6. Which have Xylem?
7. Which have Phoem?
Whisk ferns
Extended Matching Inventory: Match the Term to the Definiton.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
Archegonium
Bryophyte
Epiphyte
Gametophyte
Heterosporous
Homosporous
Lycophytes
Megaphylls
Microphylls
Moss
Phloem
Protonema
m.
n.
o.
p.
q.
r.
s.
t.
u.
v.
w.
Pterophytes
Rhizoid
Seta
Sporangium
Sporophylls
Sporophyte
Sporopollenin
Stomata
Strobulus
Wort
Xylem
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
The haploid form of a plant that produces eggs or sperm.
Structure containing spores.
Leaves modified to hold sporangia.
Small, spike-shaped leaves.
A plant that grows on top of another plant.
A corn cob shaped cluster of sporangia.
Name of the phylum containing the Quillworts.
Producing spores that germinate to form bisexual gametophytes.
The ‘stem’ holding up a bryophyte sporangium.
An Anglo-Saxon word meaning ‘herb.’
Vascular tissue carrying carbohydrates and amino acids throughout a plant.
Another term for seedless nonvascular plants.
Producing spores that germinate to form either male or female gametophytes.
Large, broad leaves.
Name of the phylum containing the ferns.
The primitive ‘root’ of a bryophyte.
Specialized plant pore that allows gas exchange with the atmosphere.
The single filament of a bryophyte.
Vascular tissue carrying water and minerals throughout a plant.
The layman’s term for a bryophyte.
The diploid form of a plant that produces spores.
Multicellular structure in a gametophyte that holds a female gamete (egg).
Compound that surrounds plant spores helping them to resist desiccation.
Multicellular structure in a gametophyte that holds the male gametes (sperm).