BIOL-112 Chapter 25

What are the shared characteristics between Green Algae (Chlorophytes/Charophytes) and Plants?

multicellularity

• cell walls with cellulose

• chloroplasts with same pigments (chlorophyll. a & b)

• storage molecule is starch

green algae along lake shores had

• more resources; less competition

• subjected to periodic dehydration

• populations with land adaptations thrive

Advantages of Land:

[CO2] higher

• light intensity higher

• more minerals

• no "herbivores"

• no competition

What are major concerns of land plants

Desiccation, Both gametes and zygotes must be protected from desiccation, Plants need to develop structural support in a medium that does not give the

same lift as water, The male gametes must reach the female gametes using new strategies,

because swimming is no longer possible

What is a key feature of the life cycle in all land plants?

It exhibits the alternation of generations.

What type of spores do land plants produce?

Walled haploid spores.

What structure do land plants have for gamete production?

Multicellular gametangia.

Where do sporophyte embryos grow in land plants?

Protected within the female gametophyte.

What type of tissue is found at the tips of roots and shoots in plants?

Apical meristem tissue.

What adaptation do land plants have to resist desiccation?

A waxy cuticle.

What are secondary compounds in plants?

Chemicals produced by plants that are not directly involved in growth, development, or reproduction.

What is the relationship between mycorrhizae and plants?

Mycorrhizae are symbiotic associations between fungi and plant roots.

Haplontic

describes a life cycle in which the haploid stage is the dominant stage

Diplontic

describes a life cycle in which the diploid stage is the dominant stage

Gametophyte

Haploid, or gamete-producing, phase of an organism

sporophyte

Diploid, or spore-producing, phase of an organism

What generation is dominant in lower plants

gametophyte

As plants evolved what happened

gametophyte generation got smaller, sporophyte generation became more dominant

What stage in the Charophyte life cycle is multicellular?

The Haploid (n) stage.

Does the charophyte life cycle represent 'Alternation of Generations'? Why or why not?

No. It lacks a multicellular diploid stage (sporophyte). The only diploid stage is a single-celled zygote.

Which cell in the charophyte life cycle undergoes meiosis, and what is the result?

The Zygote (2n) undergoes meiosis to produce 4 diverse recombinant spores (n).

How many offspring are produced from a single fertilization event in charophytes?

Only 4 recombinant spores.

What is the ploidy of gametes, zygote, and spores in charophytes?

1. Gametes: Haploid (n) 2. Zygote: Diploid (2n) 3. Spores: Haploid (n)

What are the two major characteristics of land plant spores that allow for survival out of water?

1. They are walled (protected by sporopollenin). 2. They are produced within a multicellular sporangium.

What is sporopollenin, and what is its functional purpose?

A durable polymer that makes up the walls of plant spores; it protects the spores from dehydration and damage during dispersal through the air.

Define Sporangium.

The multicellular organ of the sporophyte where spores are produced through meiosis.

In a moss like Sphagnum, describe the physical relationship between the gametophyte and the sporophyte.

The sporophyte (the stalk and capsule) grows directly out of and is nutritionally dependent on the green, leafy gametophyte.

What is the ploidy of the spores produced in the sporangium?

Haploid ($n$).

What is the container holding the red-stained dots in the longitudinal section image, and what are the dots themselves?

The container is the sporangium (or capsule); the dots are the haploid spores.

Why was the development of a 'walled' spore a critical milestone for the transition to land?

It allowed plants to disperse offspring through the dry environment of the air without the risk of the cells drying out (desiccation) before reaching a suitable habitat.

What is a gametangium (plural: gametangia)?

A multicellular organ found in land plants where gametes (sperm and eggs) are produced and protected from the environment.

What is the specific name of the male gametangium in land plants, and what does it contain?

The Antheridium (plural: antheridia). It contains and protects many sperm cells.

Why was the development of multicellular gametangia like the antheridium significant for the 'Water to Land' transition?

It provided a protective jacket of sterile tissue to keep the sperm from drying out (desiccation) before they were ready for release.

How can you visually distinguish the male gametophyte from the female gametophyte in Marchantia?

Male gametophyte: Features flat-topped, umbrella-like structures that house the antheridia. Female gametophyte: Features drooping, finger-like structures that house the archegonia.

What common structural feature do both Blasia pusilla (liverwort) and Chara vulgaris (charophyte) sperm types possess for movement?

They both possess flagella, indicating that they still require a film of water to swim to the egg for fertilization.

What is the dark, circular cluster of cells in a cross-section of a male gametophyte called?

An Antheridium packed with developing sperm.

Do gametangia (antheridia and archegonia) belong to the sporophyte or gametophyte generation?

The Gametophyte generation (n), as they are the organs that produce the haploid gametes via mitosis.

What is an archegonium (plural: archegonia)?

The multicellular female gametangium where a single egg is produced and protected.

Where does fertilization occur in bryophytes like Marchantia?

Fertilization occurs within the archegonium. The sperm must swim to the egg inside this protective structure.

What is formed immediately after fertilization within the archegonium?

A diploid (2n) zygote, which will eventually grow into the multicellular sporophyte.

What does the 'vase-shaped' structure in a microscopic cross-section of a female gametophyte represent, and what is the large cell inside?

The vase-shaped structure is the archegonium; the large cell inside is the egg, protected by a layer of sterile maternal tissue.

Why is the protection of the egg within an archegonium a vital 'Water to Land' adaptation?

It protects the delicate egg and the resulting embryo from desiccation (drying out) and physical damage in a terrestrial environment.

How are the archegonia positioned on the female gametophyte in Marchantia?

They are located on the underside of the drooping, finger-like extensions of the umbrella-shaped head.

Contrast the Antheridium with the Archegonium.

Antheridium: Male; produces and releases many flagellated sperm. Archegonium: Female; produces and retains a single non-motile egg.

What are apical meristems?

Regions of continuously dividing cells located at the tips of roots and shoots.

What is the primary functional advantage of having apical meristems in a terrestrial environment?

They allow the plant to sustain lengthwise growth, enabling roots and shoots to grow toward essential resources.

Differentiate between the targets of the Shoot Apical Meristem and the Root Apical Meristem.

Shoot: Grows upward to maximize capture of light and CO₂. Root: Grows downward to explore the soil for water and minerals.

In the microscopic cross-section of a shoot tip, what is the dome-shaped mass of cells in the center?

The central dome is the Apical Meristem; the flanking structures are developing leaves (leaf primordia).

In the microscopic cross-section of a root tip, where is the apical meristem located relative to the very end of the root?

It is located just behind the tip, often protected by a root cap.

Why were apical meristems necessary for land plants compared to their aquatic ancestors?

Land plants face spatial separation of resources, requiring a system for targeted, directional growth.

What specific type of cell division occurs at the apical meristems?

Mitosis.

What is the waxy cuticle, and what is its primary evolutionary function?

A waterproof coating on the surface of stems and leaves that prevents water loss to the air.

If the cuticle is waterproof, how does the plant obtain CO₂ for photosynthesis?

Through specialized pores called stomata.

Define stomata and the role of guard cells.

Stomata are microscopic pores; guard cells can open or close them to balance gas exchange with water conservation.

What three substances move through the stoma, and in which directions?

1. CO₂: Moves into the plant for photosynthesis. 2. O₂: Moves out of the plant as a byproduct. 3. H₂O (Vapor): Moves out of the plant.

Why is it important that stomata are controllable in most plants?

It allows the plant to save water during hot or dry conditions and open them when conditions are favorable for photosynthesis.

In the stained micrograph, identify the pink-stained layer and the opening above the blue arrow.

The pink layer is the waxy cuticle; the opening is the stoma.

Why didn't the aquatic ancestors of land plants need a waxy cuticle or stomata?

They were submerged in water, so they didn't face the risk of drying out.

Secondary Metabolites

chemicals that deter/repel/poison competitors/herbivores/parasites

Mycorrhizae

A mutualistic association of plant roots and fungus, helps water and mineral absorption, dates back to first land plants (before true roots)

What are the three phyla collectively referred to as 'Bryophytes'?

1. Marchantiophyta (Liverworts) 2. Anthocerotophyta (Hornworts) 3. Bryophyta (Mosses)

What structure do Bryophytes use for attachment to the substrate?

Rhizoids.

Which generation is the 'dominant' form in Bryophytes, and what does 'dominant' mean?

The Haploid Gametophyte (n) is dominant, meaning it is the largest and longest-lasting part of the life cycle.

What is the relationship between the diploid sporophyte and the haploid gametophyte in Bryophytes?

The sporophyte (2n) is nutritionally dependent on the gametophyte for food and water.

Why are Bryophytes typically found in moist areas?

They lack vascular tissue to transport water over long distances and possess flagellated sperm that requires a film of water to swim to the egg.

What organ within the sporophyte produces spores, and what is the ploidy of those spores?

The Sporangium produces many haploid spores (n) via meiosis.

What is the 'Archegoniophore' in liverworts and what is its role?

It is the specialized structure on the female gametophyte that bears the archegonia.

What are the two main body forms of liverworts?

Thalloid (like Marchantia polymorpha) and Leafy (like Plagiochila deltoidea).

What structure does Marchantia use for asexual reproduction?

Gemma cups, located on the surface of the thallus.

Identify the male and female gametangia in the liverwort life cycle.

Antheridia: Male structures that produce sperm; Archegonia: Female structures that contain the egg.

What are the three main parts of a mature liverwort sporophyte?

The foot, the seta (stalk), and the capsule (sporangium).

How does the sperm reach the egg in liverworts?

The sperm is flagellated and must swim through a film of water into the archegonium to fertilize the egg.

Where does the embryo develop in liverworts?

The diploid (2n) embryo develops within the archegonium after fertilization.

What physical feature gives Hornworts their common name?

The horn-like, long, and tapered shape of their sporophyte generation.

What type of environment are Hornworts particularly good at colonizing?

Moist soils.

Hornworts maintain a symbiotic relationship with which specific organism?

Nitrogen-fixing cyanobacteria.

To which major plant group do Hornworts belong?

They are seedless, nonvascular plants (Bryophytes).

Which group is considered the most numerous of the non-vascular plants?

Mosses (Bryophyta).

In what types of 'extreme' environments can mosses be found?

Mountain tops, tundra, and deserts.

Why does the moss sporophyte grow upward from the female gametophyte?

To gain elevation for spore dispersal, allowing spores to be caught and carried by the wind.

In the image of Polytrichum commune, identify the three labeled parts of the structure.

1. Capsule: The top part where spores are made. 2. Seta: The long stalk supporting the capsule. 3. Gametophyte: The green, leafy base that supports the sporophyte.

What is the ploidy (n or 2n) of the Seta and Capsule?

Diploid (2n), because they are part of the sporophyte generation.

Contrast the moss sporophyte's appearance with the liverwort sporophyte.

Moss sporophytes are typically much more prominent and persistent (often with a long seta), whereas liverwort sporophytes are usually very small and hidden under the archegoniophore.

What role do mosses play in nutrient-poor soils?

They act as 'pioneer' species, helping to establish life in environments where other plants cannot yet grow.

In which specific environments are mosses considered major primary producers?

Cold or high-altitude regions.

What are two significant reasons Sphagnum 'peat moss' bogs are important?

1. They are critical wetland ecosystems. 2. They are harvested for fuel.

Why are peatlands unique regarding biological preservation?

Because they are highly acidic and low in oxygen, some peatlands have preserved corpses for thousands of years.

Which genus is specifically associated with 'peat moss'?

Sphagnum.

What is a protonema in the moss life cycle?

A mass of green, branched, one-cell-thick filaments that develops from a germinating haploid spore.