Hornworts Overview and Structure
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Questions and Answers

What is the primary function of cyanobacteria Nostoc found in hornworts?

  • Producing oil bodies
  • Absorbing water
  • Fixing nitrogen (correct)
  • Photosynthesis
  • Hornworts have air chambers instead of mucilage.

    False

    What structure in hornworts is responsible for the production of spores?

    Sporangium

    Hornwort gametophytes can be identified by having _____ large chloroplast in each cell.

    <p>one</p> Signup and view all the answers

    Match the following characteristics with their corresponding terms related to hornworts:

    <p>Mucilage = Replaces air chambers Pseudoelaters = Helps spread spores Columella = Tissue column on the capsule Near-basal meristem = Site of continuous growth in sporophyte</p> Signup and view all the answers

    What structure in hornworts is responsible for producing spores?

    <p>Sporophyte</p> Signup and view all the answers

    The thallus of hornworts is typically a single cell thick.

    <p>False</p> Signup and view all the answers

    What term describes the small plants like liverwort and pennywort, which relate to the word 'wort' seen in hornwort?

    <p>small plant</p> Signup and view all the answers

    Hornworts produce gametes on the __________, where fertilization occurs.

    <p>thallus</p> Signup and view all the answers

    Match the following terms related to hornworts with their definitions:

    <p>Thallus = The flat green sheet of hornworts Rhizoids = Structures anchoring the thallus to the substrate Chloroplasts = Responsible for photosynthesis Mucilage = Substance produced at growing tips and some cavity structures</p> Signup and view all the answers

    Which genus of hornworts is known to have a strap-like thallus with a central midrib?

    <p>Dendroceros</p> Signup and view all the answers

    Hornworts produce numerous chloroplasts per cell, similar to mosses and liverworts.

    <p>False</p> Signup and view all the answers

    What is the term for the cavities within the thallus that can dry out, resulting in air-filled spaces?

    <p>mucilage cavities</p> Signup and view all the answers

    What role does Nostoc play in its relationship with hornworts?

    <p>Provides nitrogen to the hornwort</p> Signup and view all the answers

    Hornworts have scales on the undersides of their thalli.

    <p>False</p> Signup and view all the answers

    What characteristic shape do most hornwort sporophytes exhibit?

    <p>horn-like or needle-like</p> Signup and view all the answers

    The sporophyte of hornworts is a structure that contains a ______.

    <p>spore capsule</p> Signup and view all the answers

    Match the following genera with their characteristics:

    <p>Dendroceros = Nostoc cavities easily visible Notothylas = Short and stubby sporophytes Phaeoceros = Example of a hornwort Complex thallose liverworts = Differentiated cell layers in thallus</p> Signup and view all the answers

    How do hornwort sporophytes grow?

    <p>From points above their base</p> Signup and view all the answers

    The sporophyte in hornworts does not contain chlorophyll.

    <p>False</p> Signup and view all the answers

    What happens to sporophyte growth when the gametophyte suffers?

    <p>Sporophyte growth may stop.</p> Signup and view all the answers

    Where do the youngest cells of a sporophyte grow?

    <p>At the base</p> Signup and view all the answers

    Pseudo-elaters mature before the spores in a sporophyte.

    <p>False</p> Signup and view all the answers

    What happens to a sporophyte when it splits?

    <p>It releases spores over an extended period.</p> Signup and view all the answers

    Hornworts’ gametophytes create a plant body known as a ______.

    <p>thallus</p> Signup and view all the answers

    Match the terms with their correct descriptions regarding hornworts:

    <p>Gametophyte = Sexual generation producing thallus Sporophyte = Asexual generation producing spore capsule Antheridium = Male reproductive organ Archegonium = Female reproductive organ</p> Signup and view all the answers

    What is a notable feature of sporophytes from the genus Notothylas?

    <p>They may rupture irregularly or decay</p> Signup and view all the answers

    Hornwort gametophytes can vary in size from 1 to 2 centimeters in diameter.

    <p>True</p> Signup and view all the answers

    The two halves of a sporophyte usually remain joined at the very ______.

    <p>top</p> Signup and view all the answers

    Study Notes

    Hornwort Definition

    • Hornworts are flowerless, spore-producing bryophytes that are characterized by their tapering, horn-like or needle-like spore capsules.

    Hornwort Gametophyte

    • The gametophyte is a flat, green sheet called a thallus.
    • The thallus can be strap-like, branched, or grow in a rosette shape.
    • It has a thick, central midrib with thin lateral wings that are often wavy or ruffled.
    • The thallus is attached to the substrate by rhizoids, which are anchoring structures that are superficially root-like, but without the absorptive functions of true roots.
    • The thallus contains one to a few chloroplasts per cell, most commonly just one large chloroplast per cell.
    • Growing tips are covered by mucilage, which is produced by the surface cells.
    • Mucilage cavities are formed by the breakdown of many cells into mucilage, which can dry out, resulting in air-filled cavities.
    • The mucilage cavities are connected to the exterior through slime-pores or mucilage clefts.
    • Nostoc (a cyanobacterium) can enter the mucilage cavities through the slime-pores and form a symbiotic association with the hornwort.

    Hornwort Sporophyte

    • A single thallus produces many sporophytes.
    • The sporophyte is an erect, elongated, tapering, horn-like or needle-like structure.
    • It is typically several centimeters long, but can be over 10 centimeters in length.
    • The sporophyte is constantly growing from a point just above its base.
    • The youngest cells are near the base and the oldest are at the top.
    • The sporophyte contains chlorophyll and photosynthesizes, but still depends on the gametophyte for carbohydrates.
    • The sporophyte splits along its length (from the top down) to release the spores over an extended period.

    Hornwort Reproduction

    • Hornwort reproduction occurs in an alternation of generations, with a sexual generation (gametophyte) and an asexual generation (sporophyte).
    • The gametophyte produces male and female gametes (sperm and eggs) on the thallus, and a fertilized egg develops into a sporophyte.
    • The sporophyte produces spores, which germinate to begin the cycle again.
    • Hornworts can also reproduce vegetatively if the thallus is fragmented.

    How Hornworts Differ from Liverworts

    • Hornworts lack cellular oil bodies and have mucilage instead of air chambers.
    • Hornworts have a near-basal meristem, where cells continue to divide and grow during the sporophyte's life.
    • Hornworts have a tissue column on the capsule, called a columella.
    • Hornwort gametophytes have one large chloroplast in each cell, which contributes to their color and translucency.
    • Hornwort sporophytes exist even after the gametophyte dies.

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    Lecture 4: Hornworts PDF

    Description

    Discover the fascinating world of hornworts, flowerless bryophytes that have unique spore-producing structures. This quiz covers their defining characteristics, gametophyte structure, and adaptive features. Test your knowledge on this intriguing group of plants!

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