Recording-2025-06-04T19:52:52.465Z

Terrestrial Plants and Life Cycle Consequences

• Organisms living on land are terrestrial plants.

• Tweaking the life cycle has consequences for the environment where plants thrive.

Liverworts: A Simple Land Plant

• Liverworts are embryophytes, considered the simplest land plants.

• They reproduce asexually and are gametophytes, whose function is to produce gametes.

• Mature liverworts spread out, with the gametophyte producing gametes.

• Archegonial heads or archegonial fours are umbrella-like structures containing archegonia, each producing an egg.

• Liverworts do not support their mass. They have a flat body that grows over the surface.

• Gas exchange occurs through unregulated pores in the liverworts' skin, leading to water loss and susceptibility to drying out. They need to bring in carbon dioxide (CO2) and release extra oxygen (O2) it doesn't use during cell respiration.

Gamma Cups and Asexual Reproduction

• Gamma cups are cup-like structures on liverworts bodies that allow asexual reproduction.

• They contain undifferentiated cells that can slough off and clone themselves.

• Plant cells are totipotent, meaning they can dedifferentiate into stem cells and redifferentiate into other cell types.

• The liverworts' asexual reproduction mechanism through gamma cups is due to the complexity of sexual reproduction.

Sexual Reproduction in Liverworts

• In nature, liverworts are found on rocks next to streams or in wet environments.

• The main plant seen is the gametophyte generation (the big green plant).

• Male plants produce anthridial heads containing individual antheridia, which release lots of sperm.

• Female liverworts produce archegonial heads or archegonial fours containing individual archegonia. Each archegonium produces and retains one egg.

• Sperm must move externally through water from one plant to another to find and fuse with the egg, forming a zygote.

• The zygote is protected in the archegonium and grows mitotically into the sporophyte.

Sporophyte Characteristics

• The sporophyte remains small and lasts only weeks before drying up.

• The sporophyte's job is to undertake meiosis to make spores.

• The sporophyte is dependent on the gametophyte parent for nutritional support, structure, and nutrients from the soil.

Spore Dispersal

• The sporophyte is inside the sporangia, where spores are produced. Strands, called elaters, inside are hydrophobic and twist upon contact with moisture, dispersing the spores. The spores are red and the elaters are greenish bluish strands.

Life Cycle Overview

• The sporophyte undergoes meiosis to make spores which are embedded in elaters.

• Spores are ejected as the sporophyte dries out, and elaters twist in the breeze.

• Spores land in a suitable environment and grow mitotically into a young gametophyte plant.

• Spores always grow to be gametophytes.

• Male gametophyte plants produce antheridiophores with antheridia, making sperm. Female gametophytes produce archegonial heads or archegonial fours containing archegonia, each with an egg.

Raindrop Britischein: A Ridiculous Mechanism

• Plants must live in extremely wet environments for this mechanism to ever be plausible.

• A raindrop must land on the antheridial head, pick up sperm, ricochet to another plant, land on the archegonial four, and allow the sperm to swim to the egg (that's produced by the archegonia) for fusion.

• The egg is retained in the gametophyte inside the archegonium, which is a general trait of the streptophytes.

• The zygote, also true of the Streptophytes, is retained in the tissue of the parent plant.

• The zygote grows mitotically into the embryonic sporophytes (embryo diploid).

• The sporophyte is inside the archegonium; attached to, protected, and nourished by its gametophyte parent.

Liverwort Facts & Context

• There are around 9,000 species of liverworts.

• There are fewer than 6,000 mammal species.

Mosses

• Mosses are a larger group with around 15,000 species, making them one of the top three most numerous plant clades (mosses, ferns, and flowering plants).

• Important innovations occur in the ancestor of the mosses and the rest of the plants, and in the diploid generation.

Key Innovations in Mosses

• Traits are appearing in the sporophyte generation.

• The two traits are stomata and a cuticle.

• They are diploid only, meaning these traits are not present in the gametophyte plant.

  • Stomata: Are for gas exchange. Guard cells control these little mouths that are are on the leaves of the plants. Plants can purse its lips to seal it shut, or open it up to take a breath (anthropomorphized).

  • Cuticle: Is a waxy layer that protects plants from drying out. (Ex. Oak leaves).

Moss Characteristics

• Mosses stand up into the air by living in colonies and pushing against each other.

• The green part is the gametophyte plant (haploid).

• The things that look like mini flowers are the sporophyte plant, which is brown and has a spore case.

• The sporophyte is attached to and dependent on its gametophyte parent, and getting nutrition from its parent as well.

• The moss gametophytes have evolved specialized cells for water and sugar transport known as hydroids and leptoids that conduct water and photosynthates through the plant (vascular-like tissues).

• Hydroids and leptoids act like vascular tissue that moves things through, but don't have lignin so they're not called vascular tissue.

• Moss has independently evolved leaf-like structures. They are not true leaves, because they lack xylem and pholem.

Moss Reproduction

• The job of the gametophyte is to make gametes via mitosis.

• The gametangia that produce sperm are antheridia. The gametangia that produce and retain the egg is archidonia.

• Sperm require external water to swim through and are disseminated via raindrop ricochet.

• Egg and sperm fuse, produce the zygote, then the sporophyte.

• The sporophyte is fancier than the liverwort sporophyte, lasting longer as a pretty sturdy plant.

• The sporophyte cannot do enough photosynthesis to feed itself because it is mostly brown. Cuticle and stomata protect it from drying out. The sporophytes produces spores via meiosis.

• Spores are surrounded by spore pollinant coating.

Moss Life Cycle

• The sporophyte plant does meiosis to make the haploid spores.

• Spores coated in spore pollen and wait until conditions become favorable. The spore is a haploid cell that can grow.

• The spore Germinates, growing multicellular, and becomes the adult multicellular gametophyte plant (half white plant).

• Gametophyte plants are bright green and do photosynthesis.

• Gametophyte plants produce gametangia, either archegonia or antheridia, to make the sperm or egg.

• The sperm (two flagella) have to swim through external water until they find an archegonium containing an egg.

• The sperm and egg fuse to make the zygote which being dipwood, grow mitotically to give rise to the sporophyte plant.

• Embryo sporophyte is retained in the archegonium, that being a key trait of why it's an embryo phyte.

• Sporophyte grows out of the archegonium to be the adult sporophyte plant.

• The sporophyte have stomata and cuticle to resist drying out and persist longer.

Cool Kinds of Mosses: Peat Bogs and Sphagnum Moss

• Peat bogs are acidic, waterlogged environments with anaerobic and low nitrogen soil.

• Sphagnum mosses are adapted to thrive in peat bogs.

• The new plants just kinda grow on top of the old ones and they smush them down.

• It becomes peat in the short term, and coal in the long term (300 million years).

• Peat is harvested for various uses, including flavoring alcohol and burning it, the is extremely unhealthy.

• Peat bogs act as carbon sinks, pulling carbon dioxide (CO_2) out of the atmosphere.

Carnivorous Plants in Peat Bogs

• Carnivorous plants do well in these environments, because there aren't any other plants, and their carbon source is sugar (photosynthesis for carbon). Then the nitrogen source is the surrounding insects.

Hornworts

• In hornworts, the diploid (sporophyte) is persistently green.

• The sporophyte can do and sustain photosynthesis for its whole life and can feed itself.

• Hornworts have these traits that are only found in the sporophytes: Stomata and cuticle to prevent drying out.

• Having the diploid be persistently green causes the diploid, the sporophyte, to be self sufficient when it comes to nutrition.

• Hornworts are a tiny group (around 100 species).

• Hornworts have a basal meristem, which, compared with the apical meristem is at the base of the plant.

• The basal meristem is this well of undifferentiated cells that's gonna allow the plant to, like, grow. The sporophyte has the actively dividing cells that are just gonna, like, push the plant right up.

• They still have a foot structure and it's not doesn't have its own rooting structure, so it stays kind of rooted into its gametophyte parent. But the sporphyte basal meristem and green phenotype means it get start growing and fed itself, so it can start growing and get it's water because of the cuticle and stomata.

• Sporophytes grow until they burst under their own mass.

• Hornworts just crumbles because there's no lignin there (cannot support a big mass).

Tracheophytes (Vascular Plants)

• The main trait of the tracheophytes is having tracheids, which come with a certain cell type called xylem cells.

• The xylem cells contain the chemical lignin.

Vascular System Characteristics

• Xylem is the specialized tissue that transports water. It is unidirectional, meaning it only sucks up water from the base of the plant roots or analogous structures coming up to the top of the plant.

• Two ways water can move is through tracheids (all tracheophytes have this) or vessel elements (some tracheophytes have this).

• Phloem transports products of photosynthesis, such as sugar and minerals. They are called sieve tube cells, and get that name because they look like a like a colander.

• Phloem has bidirectional transport, so cells are alive because transport can be bidirectional, meaning the plant has active transport properties.

• Companion cells allow metabolic work and metabolism. So if there happens to be companion cells with pholem, what that means is that in the spring, only the potato is there under the soil, and the the direction of flow can be reversed to create leaves.

What did the Tracheophyte Ancestor Look Like?

• Lignin in xylem allows the organism to get very tall.

• We find fossils of approximately half of a meter, not that mass is important.

• There are branches but no leaf structure because they don't see any leaf structure at all.

• Tips have come like enlargements where spores form via meiosis. If I can see the phases of meiosis means there inside sporangia.

• Ancestral trecheophytes had no leafe structure.

• These kind of vascular plants are traced in the siliurian era, and we find romephte fossils dating back to that time.

• Vascular plants living today don't look like this.

The Evolution of Leaves

• The structure of leaves and vascular plants, traced fights occurs twice via two independent events.

• The two events each contain leaves and each come up wit there own name. A microphills and a megafills

• Microphones have an single route, it can also be noted that macrofills have a single vine.

Names and Relationships

• The ones that have the microphytes microphylls (excuse me) these are the lycophytes. The ones that have the megaphylls (I wish they were called megaphilophytes, but they're not) they're called euphyllophytes (which is where your GTA got the true that literally means the true leaf to plants). But you're not beholden to the word root. It's just a word root. This is a made up word. Right? Someone just made it up.

Leaf Gaps

• Vacular trays allow die to be put in the xylem to see where vascular bundles travel.

• Microphils do not have these leaf gaps where megafills do.

• The leaves of like the lycophytes and the leaves of the euphyllophytes are analogous structures example of convergent evolution.

Lycophytes

• There's two species associated with this: selaginella and Lycopodium.

• In total there are around 1200 species.

• Trees used to from huge forests. Now they're all like are pretty small.

Ground Pine or Club Moss (Lycopodium)

• These guys are around. I hope you take a minute to go find them. Very lovely little plants.
  *

Sporophyte Characteristics

• It's the big plant.

• The dominant generation, that is the plant you see when you go on a walk in the woods, is a sporophyte. It's not a gametophyte.

• The sporophyte is large, green, and persistent (even with dry weather).

• It can resist drying out because there's somata cuticle happening in the diploid generation can get big cause it has trecodes.

• The sporophyte makes spores, spore bearing leaf.

Key Vocabulary

• Sporangium - Specific tissue that makes spores.

• Sporophyll - Name for these leaves that are highly modified bear

• Strobilus - Technical name for cone is strobilus.

• Spore mother cell (sporocyte) - Cell that does meiosis. Diploid cell. In the sporangium.

• Meiosis one, meiosis two to make four spore cells. Then makes haploid spores.
  *Definition for terms

• Spororphyll-- is modified leaf that contains or bears the sporangium where spores are made.

Lycopodium Life Cycle

• Sporaliff has sporium. Inside sporium there's mother cells. Has that sporophyte that will do meiosis.
  Now do haploid spores.

• Spores and released into the environment. Spores are the gametophyte

• The gametophyte is really small and brown. Has secondarily lost the ability to do photosynthesis.
  It makes those. So remember mycorrhizal is the fungus root.

• The gametophyte Does NOT have Tracheids. Don't have persisted green. Inability to have cuticle.

Means it really susceptible to dying. 2 is only going to be successful if it lives it pretty moist environment.

• The job of the gametophyte is to make gametes.

Archegonia - One archegonium produces and retains the egg. (Nothing new there)

Spermatogonia - Antheridia Sperm are released. Has to have water to swim around until it finds a archegonium.

Then the egg made a diploid zygote is PROTECTED BY TISSUES OF THE GAMETOPHYTE (the same trait from before)

• THE BABY EMBRYONIC SPOROPHYTE is also protected b=y the gametophyte

• The sporophyte is waterproof. This porfide if it's a self. Get big and smooth is go to feed and break. Gamatephy parent that we see today on the adult plant today

• These spores that are made, they're all the same size as each other. So this is something called a Homo SPORA
  *Hormo spores have spores be there but don't need can't have a few sizes

Selaginella And the Lycophytes

• Selaginella Are HEerosporous What DOES THAT MEAN
  Means gonna have fours of two different ways. Make a spore grows gamete. So all the cell line up. So has a bit can I make to do their spore mother cells.
  Make me the game the smaller gamete smaller grammy's are small the small

• So does it look like it will evolve for the same line

• Heterosporic a plant it is. Mean is it makes a gamete fight in the light and will eventually make your sex

  • Megaspore mother cell

  • Microspora mother cell

• Sporophyte inside the for for a sell the inside to support for for the

  • Meggsporeangium makes megsport

  • In microsparangeum a microphone
    Has coat of sport pollinen. And the spore is little, write, like, spore is really small, and it's gonna go to be the gametophyte, it has to crack open that coat of sporopollenin, and it grows into the gametophyte that has a name. That's called exosporic development.
    If you're a mega megaspore and a microspore, so if you're a heterosporous spore, you don't crack out of the spore coat What DOES THAT MEAN THOUGH
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    Hetero spores is a genus.

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: EUYLLOPHYTES & VanilloPhytes

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