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Questions and Answers
What is the primary function of cyanobacteria Nostoc found in hornworts?
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.
Hornworts have air chambers instead of mucilage.
False (B)
What structure in hornworts is responsible for the production of spores?
What structure in hornworts is responsible for the production of spores?
Sporangium
Hornwort gametophytes can be identified by having _____ large chloroplast in each cell.
Hornwort gametophytes can be identified by having _____ large chloroplast in each cell.
Match the following characteristics with their corresponding terms related to hornworts:
Match the following characteristics with their corresponding terms related to hornworts:
What structure in hornworts is responsible for producing spores?
What structure in hornworts is responsible for producing spores?
The thallus of hornworts is typically a single cell thick.
The thallus of hornworts is typically a single cell thick.
What term describes the small plants like liverwort and pennywort, which relate to the word 'wort' seen in hornwort?
What term describes the small plants like liverwort and pennywort, which relate to the word 'wort' seen in hornwort?
Hornworts produce gametes on the __________, where fertilization occurs.
Hornworts produce gametes on the __________, where fertilization occurs.
Match the following terms related to hornworts with their definitions:
Match the following terms related to hornworts with their definitions:
Which genus of hornworts is known to have a strap-like thallus with a central midrib?
Which genus of hornworts is known to have a strap-like thallus with a central midrib?
Hornworts produce numerous chloroplasts per cell, similar to mosses and liverworts.
Hornworts produce numerous chloroplasts per cell, similar to mosses and liverworts.
What is the term for the cavities within the thallus that can dry out, resulting in air-filled spaces?
What is the term for the cavities within the thallus that can dry out, resulting in air-filled spaces?
What role does Nostoc play in its relationship with hornworts?
What role does Nostoc play in its relationship with hornworts?
Hornworts have scales on the undersides of their thalli.
Hornworts have scales on the undersides of their thalli.
What characteristic shape do most hornwort sporophytes exhibit?
What characteristic shape do most hornwort sporophytes exhibit?
The sporophyte of hornworts is a structure that contains a ______.
The sporophyte of hornworts is a structure that contains a ______.
Match the following genera with their characteristics:
Match the following genera with their characteristics:
How do hornwort sporophytes grow?
How do hornwort sporophytes grow?
The sporophyte in hornworts does not contain chlorophyll.
The sporophyte in hornworts does not contain chlorophyll.
What happens to sporophyte growth when the gametophyte suffers?
What happens to sporophyte growth when the gametophyte suffers?
Where do the youngest cells of a sporophyte grow?
Where do the youngest cells of a sporophyte grow?
Pseudo-elaters mature before the spores in a sporophyte.
Pseudo-elaters mature before the spores in a sporophyte.
What happens to a sporophyte when it splits?
What happens to a sporophyte when it splits?
Hornworts’ gametophytes create a plant body known as a ______.
Hornworts’ gametophytes create a plant body known as a ______.
Match the terms with their correct descriptions regarding hornworts:
Match the terms with their correct descriptions regarding hornworts:
What is a notable feature of sporophytes from the genus Notothylas?
What is a notable feature of sporophytes from the genus Notothylas?
Hornwort gametophytes can vary in size from 1 to 2 centimeters in diameter.
Hornwort gametophytes can vary in size from 1 to 2 centimeters in diameter.
The two halves of a sporophyte usually remain joined at the very ______.
The two halves of a sporophyte usually remain joined at the very ______.
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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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