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 The liverwort has a flat, leaf-like structure haploid (1n) called a thallus. Root-like rhizoids grow from the bottom of the thallus. A slender stalk extends from the thallus, and an archegonial head sits at its top. The archegonial head has fronds, like a palm tree. The underside of the archegonial head contains protrusions called archegonia, which house the eggs. Sperm enter through a hole in the bottom of the archegonium and fertilize the egg to produce a diploid (2n) embryo. The embryo grows into a stalk. Meiosis produces haploid (1n) spores in a sac at the tip of the stalk . The sac bursts open, releasing the spores. The spores sprout, producing a new thallus and rhizoids.
The life cycle of a typical liverwort is shown. (credit: modification of work by Mariana Ruiz Villareal)

Hornworts

The hornworts    ( Anthocerotophyta ) belong to the broad bryophyte group. They have colonized a variety of habitats on land, although they are never far from a source of moisture. The short, blue-green gametophyte is the dominant phase of the lifecycle of a hornwort. The narrow, pipe-like sporophyte is the defining characteristic of the group. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant ( [link] ).

 The base of the hornwort plant, called the thallus, has a wrinkled, leaf-like appearance. The sporophytes are a cluster of slender green stalks with brown tips grows from this wrinkled mass.
Hornworts grow a tall and slender sporophyte. (credit: modification of work by Jason Hollinger)

Stomata appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to its height. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.

The lifecycle of hornworts ( [link] ) follows the general pattern of alternation of generations. The gametophytes grow as flat thalli on the soil with embedded gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. The zygote develops into a long and slender sporophyte that eventually splits open, releasing spores. Thin cells called pseudoelaters surround the spores and help propel them further in the environment. Unlike the elaters observed in horsetails, the hornwort pseudoelaters are single-celled structures. The haploid spores germinate and give rise to the next generation of gametophyte.

 In hornworts, the gametophyte is a haploid (1n) leaf-like structure with slender stalks called rhizoids underneath. Male sex organs called antheridia produce sperm, and female sex organs called archegonia produce eggs. Both male and female sex organs form just beneath the surface of the gametophyte, and are exposed to the surface as the organs mature. The sperm swims to the egg or is propelled by water. When the egg is fertilized, the embryo grows into a hollow tube-like structure called a sporophyte. Meiosis inside the sporophyte produces haploid (1n) spores. The spores are ejected from the top of the tube. They grow into new gametophytes, completing the cycle.
The alternation of generation in hornworts is shown. (credit: modification of work by “Smith609”/Wikimedia Commons based on original work by Mariana Ruiz Villareal)

Mosses

More than 10,000 species of mosses    have been catalogued. Their habitats vary from the tundra, where they are the main vegetation, to the understory of tropical forests. In the tundra, the mosses’ shallow rhizoids allow them to fasten to a substrate without penetrating the frozen soil. Mosses slow down erosion, store moisture and soil nutrients, and provide shelter for small animals as well as food for larger herbivores, such as the musk ox. Mosses are very sensitive to air pollution and are used to monitor air quality. They are also sensitive to copper salts, so these salts are a common ingredient of compounds marketed to eliminate mosses from lawns.

Mosses form diminutive gametophytes, which are the dominant phase of the lifecycle. Green, flat structures—resembling true leaves, but lacking vascular tissue—are attached in a spiral to a central stalk. The plants absorb water and nutrients directly through these leaf-like structures. Some mosses have small branches. Some primitive traits of green algae, such as flagellated sperm, are still present in mosses that are dependent on water for reproduction. Other features of mosses are clearly adaptations to dry land. For example, stomata are present on the stems of the sporophyte, and a primitive vascular system runs up the sporophyte’s stalk. Additionally, mosses are anchored to the substrate—whether it is soil, rock, or roof tiles—by multicellular rhizoids    . These structures are precursors of roots. They originate from the base of the gametophyte, but are not the major route for the absorption of water and minerals. The lack of a true root system explains why it is so easy to rip moss mats from a tree trunk. The moss lifecycle follows the pattern of alternation of generations as shown in [link] . The most familiar structure is the haploid gametophyte, which germinates from a haploid spore and forms first a protonema    —usually, a tangle of single-celled filaments that hug the ground. Cells akin to an apical meristem actively divide and give rise to a gametophore, consisting of a photosynthetic stem and foliage-like structures. Rhizoids form at the base of the gametophore. Gametangia of both sexes develop on separate gametophores. The male organ (the antheridium) produces many sperm, whereas the archegonium (the female organ) forms a single egg. At fertilization, the sperm swims down the neck to the venter and unites with the egg inside the archegonium. The zygote, protected by the archegonium, divides and grows into a sporophyte, still attached by its foot to the gametophyte.

Art connection

 In mosses, the mature haploid (1n) gametophyte is a slender, nonvascular stem with fuzzy, non-vascular leaves. Root-like rhizoids grow from the bottom. Male antheridia and female archegonia grow at the tip of the stem. Sperm fertilize the eggs, producing a diploid (2n) zygote inside a vase-like structure called a venter inside the archegonial head. The embryo grows into a sporophyte that projects like a flower from the vase. The sporophyte undergoes meiosis to produce haploid (1n) spores that grow to produce mature gametophytes, completing the cycle.
This illustration shows the life cycle of mosses. (credit: modification of work by Mariana Ruiz Villareal)

Which of the following statements about the moss life cycle is false?

  1. The mature gametophyte is haploid.
  2. The sporophyte produces haploid spores.
  3. The calyptra buds to form a mature gametophyte.
  4. The zygote is housed in the venter.

The slender seta    (plural, setae), as seen in [link] , contains tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium or capsule    .

 In the photo, setae appear as long, slender, bent stems with oval-shaped capsules at the tips.
This photograph shows the long slender stems, called setae, connected to capsules of the moss Thamnobryum alopecurum . (credit: modification of work by Hermann Schachner)

A structure called a peristome    increases the spread of spores after the tip of the capsule falls off at dispersal. The concentric tissue around the mouth of the capsule is made of triangular, close-fitting units, a little like “teeth”; these open and close depending on moisture levels, and periodically release spores.

Section summary

Seedless nonvascular plants are small, having the gametophyte as the dominant stage of the lifecycle. Without a vascular system and roots, they absorb water and nutrients on all their exposed surfaces. Collectively known as bryophytes, the three main groups include the liverworts, the hornworts, and the mosses. Liverworts are the most primitive plants and are closely related to the first land plants. Hornworts developed stomata and possess a single chloroplast per cell. Mosses have simple conductive cells and are attached to the substrate by rhizoids. They colonize harsh habitats and can regain moisture after drying out. The moss sporangium is a complex structure that allows release of spores away from the parent plant.

Art connections

[link] Which of the following statements about the moss life cycle is false?

  1. The mature gametophyte is haploid.
  2. The sporophyte produces haploid spores.
  3. The rhizoid buds to form a mature gametophyte.
  4. The zygote is housed in the venter.

[link] C.

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Questions & Answers

using fractional distillation
Mpho Reply
how can a mixture of water and ethanal be separated
Dau Reply
what is photosynthesis
Ochang Reply
Photosynthesis is the process by which plants make their own food.
Namwanje
Photosynthesis is the process by which plants manufacture their own food through sunlight, carbon dioxide and water.
Timmy
photosynthesis is the process by which green plant make a food etc . sunlight, carbon dioxide, oxygen ,gulucose.
Kaishar
Photosynthesis this is the process by which green plant can manufacture their own food with the uses of simple substances
Abibatu
Is the mitochondria the powerhouse of the cell? Or is it the Nucleus?
Akko Reply
a cow giva brith to a calf with extra tail .what the genetic name of the calf
Debrah Reply
what is atomic of biology
Henry Reply
the cell wall of bacteria is called....
Cabdicasiis Reply
peptidoglycan
Henry
peptidoglycan (also called murein), which is made from polysaccharide chains cross-linked by unusual peptides containing D-amino acids.
Henry
define alkali metals
Muhammad Reply
What's a skeletal system.
Sulemana Reply
Skeletal system is the internal framework of human body
Ayaan
thanks
Sulemana
What is Dentition
Immanuel Reply
It refers to The shape of the teeth
Yaye
it refers to the arrangements of the teeths
Ofofonono
it refers to the dental formular
Kwagala
what's the function of kidney?
Kwagala
what is microscope
Sandy Reply
hello
Tamuka
heloo
Tamuka
a microscope is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope.
Nadia
thanks
Tamuka
explain the mechanism of absorption of water and minerals by roots of plants
MARKSMAN
a microscope is a laboratory instrument used to view very tiny organisms which can not be seen by our naked eyes
Kwagala
Thanks
Aziz
what is scabex?
Aziz
what is soil
Salam Reply
God made the world Germans made constituents.discuss
MARKSMAN
it is the upper most part of the land
Joseph
soil is the uppermost layer of the earth crust that support life and serves as rigid foundation for different structures
Jamiu
What is diffusion
Abdullahi Reply
diffusion is a movement of particles from where the is high concentrated solution to where the is less concentrated solution
Lolly
diffusion is the movement of particles from a region of high concentration to a region of low concentration
Benah
Diffusion is the movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is achieve and they are evenly distributed equally
Alhassan
what are the characteristics of elements in group one?
Mohammed Reply
they have same number of valence electrons in their outermost shell
Kiran
what is microorganisms
Lolly Reply
no idea
Kataya
okay thanks
Lolly
I have found it
Lolly
so pls I need the definition
KOMOLAFE
give us definition
Kataya
these are soil organisms
Ibrahim
a Microorganism is an organism that is microscopic
Lolly
an organism that cannot be see with the eye.
Lucile

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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