Vascular Plants = Winning! - Crash Course Biology #37

Summary

This script explores the remarkable world of vascular plants, highlighting their evolutionary success since their emergence 420 million years ago. It delves into their unique conductive tissues, which facilitate the transport of nutrients and water, enabling growth and adaptation. The script also touches on the three main organs of plants—roots, stems, and leaves—and their crucial roles in photosynthesis and water absorption. The importance of plants in the ecosystem, including their role in the water cycle and food chain, is emphasized, showcasing their vital contribution to life on Earth.

Takeaways

• 🌿 Yarrow is a flowering plant with astringent properties, named after Achilles who used it for treating soldier wounds.
• 🌱 Snakegrass, also known as horsetail, has a unique feature where it can be popped apart and reassembled.
• 🌲 Ponderosa pine is a favorite tree with a distinct butterscotch smell on warm days and can grow hundreds of feet tall.
• 🌳 Vascular plants are diverse and important, with a history dating back 420 million years, and have found success through resource exploitation.
• 🌞 Vascular plants convert sunlight into food, absorb nutrients directly from the soil, and often involve third parties in reproduction.
• 🚀 The defining trait of vascular plants is their conductive tissues that transport food and water throughout the plant, allowing for growth and adaptation.
• 🌳 The largest, most massive, and oldest living organisms are all vascular plants, including the redwood, a quaking aspen grove, and a seagrass patch.
• 🔬 Vascular plants have specialized tissues: dermal for protection, vascular for conduction, and ground tissues for photosynthesis and food storage.
• 🌱 Herbaceous plants undergo primary growth and are typically small, soft, and flexible, often dying back to the roots or completely after one season.
• 🌳 Woody plants experience secondary growth, growing wider and taller with the development of woody tissues, including shrubs, lianas, and trees.
• 🌿 Vascular plants are organized into three main organs: roots for absorption and storage, stems for support and transport, and leaves for gas exchange and photosynthesis.

Q & A

What is the scientific name of the yarrow plant and why is it named so?

The scientific name of yarrow is Achillea, which comes from Achilles, the Greek hero. It is said that Achilles used yarrow on the wounds of his soldiers due to its natural astringent properties.

What is the common name for snakegrass and why is it called popgrass by kids?

Snakegrass is also known as horsetail. It is called popgrass by kids because the plant can be easily popped apart and then put back together again.

What unique characteristic does the ponderosa pine have when sniffed on a warm day?

On a warm day, ponderosa pine has a unique characteristic where it smells like butterscotch.

What is the defining trait of vascular plants that contributed to their evolutionary success?

The defining trait of vascular plants that contributed to their evolutionary success is the presence of conductive tissues that can transport food and water from one part of the plant to another.

How did vascular plants exploit resources around them to find success?

Vascular plants found success by converting sunshine into food, absorbing nutrients directly through the soil without the costly process of digestion, and enlisting the help of third parties for reproduction.

What are the three main types of tissues that define vascular plants?

The three main types of tissues that define vascular plants are dermal tissues, vascular tissues, and ground tissues.

What is the primary function of the xylem in plants?

The primary function of the xylem in plants is to carry water and dissolved minerals from the roots up to the leaves.

How do plants manage to defy gravity and transport water upwards?

Plants defy gravity by using the process of evapotranspiration. As water evaporates from the leaves, it creates negative pressure inside the xylem, which draws more water upward.

What is the role of stomata in the leaf and how do they function?

Stomata are tiny openings in the leaf epidermis that allow for gas exchange. They are surrounded by guard cells that regulate their size and shape, opening to let carbon dioxide in and water evaporate during photosynthesis and evapotranspiration.

What is the role of the phloem in vascular plants?

The phloem is responsible for transporting sugars, such as glucose, which are products of photosynthesis, throughout the plant to parts that need energy or storage.

How do tree rings form and what can they tell us?

Tree rings form due to the growth of sclerenchyma cells in the xylem. In warm, wet years, these layers grow thick, while in cold, dry years they are thin. Scientists can use tree rings to determine the age of a tree and understand the climate history it has experienced.

Outlines

00:00

🌿 The Evolution and Importance of Vascular Plants

This paragraph introduces various vascular plants, such as yarrow, snakegrass, and ponderosa pine, and highlights their diverse shapes, sizes, and properties. It delves into the evolutionary success of vascular plants since their emergence 420 million years ago, attributing their success to their ability to efficiently exploit resources, convert sunlight into food, and reproduce with the help of third parties. The key evolutionary breakthrough for vascular plants is identified as the development of conductive tissues, which enabled them to grow larger, store food, and spread rapidly. This breakthrough led to plants dominating Earth long before the appearance of animals and setting world records for size, mass, and age. The paragraph also touches on the specialization of tissues in vascular plants, including dermal, vascular, and ground tissues, and explains primary and secondary growth in plants.

05:00

💧 The Journey of Water in Vascular Plants

This paragraph explores the role of water in vascular plants, starting with its absorption through root hairs and its movement through the dermal tissue. It explains the function of the epidermis, including the cuticle that prevents water loss and trichomes that protect against insects. The paragraph then describes the vascular tissue xylem, which carries water and minerals upwards from the roots, and the process of evapotranspiration that creates negative pressure, drawing water upwards against gravity.

Keywords

💡Vascular Plants

Vascular plants are a group of plants that have specialized tissues for conducting water and nutrients. These tissues include xylem and phloem, which allow the plants to grow larger and more complex. In the video, vascular plants are highlighted for their evolutionary success and the ability to transport resources efficiently.

💡Xylem

Xylem is a type of vascular tissue in plants responsible for transporting water and dissolved minerals from the roots to the rest of the plant. The video explains how xylem creates negative pressure through evapotranspiration, drawing water upwards and allowing plants to grow tall and robust.

💡Phloem

Phloem is the vascular tissue that transports sugars and other metabolic products downward from the leaves. The video discusses how the phloem carries glucose, produced during photosynthesis, throughout the plant, ensuring that all parts of the plant receive the necessary nutrients.

💡Photosynthesis

Photosynthesis is the process by which green plants use sunlight to synthesize foods from carbon dioxide and water. It involves chlorophyll and generates oxygen as a byproduct. The video emphasizes photosynthesis as a critical function of ground tissues in leaves, turning sunlight into food.

💡Evapotranspiration

Evapotranspiration is the process of water evaporation from plant leaves, creating a negative pressure that pulls more water up through the xylem. The video highlights how this process not only aids plant growth but also plays a significant role in Earth's water cycle and climate regulation.

💡Dermal Tissue

Dermal tissue forms the outer protective layer of a plant, preventing water loss and damage. The video describes the various functions of the dermal tissue, including the presence of cuticles, trichomes, and root hairs that help plants interact with their environment.

💡Ground Tissue

Ground tissue is involved in photosynthesis, storage, and support, comprising most of the plant's bulk. The video describes how ground tissue, especially in the mesophyll of leaves, contains chloroplasts for photosynthesis and provides structural support.

💡Mesophyll

Mesophyll is the inner tissue of a leaf, containing many chloroplasts where photosynthesis takes place. The video details how mesophyll cells are arranged to maximize gas exchange and light absorption, essential for the plant's food production.

💡Cuticle

The cuticle is a waxy layer covering the epidermis of leaves and stems, preventing water loss. The video mentions the cuticle's role in maintaining hydration in plants and protecting them from environmental stress.

💡Stomata

Stomata are small openings on the leaf surface that allow gas exchange. Guard cells regulate their opening and closing to balance water loss and CO2 intake. The video explains how stomata are crucial for photosynthesis and evapotranspiration, facilitating the plant's respiration and water management.

Highlights

Yarrow is a flowering plant with astringent properties, named after the Greek hero Achilles who used it for treating wounds.

Snakegrass, also known as horsetail, has a unique feature where it can be popped apart and reassembled.

Ponderosa pine is a favorite tree with a butterscotch scent on warm days and can grow hundreds of feet tall.

Vascular plants are diverse and important, exploiting resources through photosynthesis and nutrient absorption without digestion.

Vascular plants have a third-party involvement in reproduction, highlighting their evolutionary success.

The defining trait of vascular plants is their conductive tissues, allowing for efficient food and water transport.

Vascular plants' ability to move substances internally was a significant evolutionary breakthrough, enabling growth and adaptation.

Plants dominated Earth before animals, holding world records for size, mass, and age, such as the redwood and the quaking aspen grove.

Vascular plants have specialized tissues including dermal, vascular, and ground tissues, each with distinct functions.

Primary growth in plants involves the development of basic tissues and is characteristic of herbaceous plants.

Secondary growth allows vascular plants to increase in width and height through the development of woody tissues.

The three main organs of vascular plants are roots, stems, and leaves, each with a crucial role in the plant's life cycle.

Plants are designed around water absorption and transport, with dermal tissues playing a key role in this process.

Xylem is the vascular tissue responsible for water and mineral transport from roots to leaves.

Evapotranspiration is a key process where water is evaporated from leaves, creating negative pressure that draws water upward.

Plants contribute to the water cycle by transpiring large amounts of water, making the atmosphere habitable.

Sclerenchyma cells in woody plants provide structural support through their thick lignin cell walls.

The leaf's mesophyll tissue contains parenchyma cells with chloroplasts, where photosynthesis occurs.

Stomata are tiny openings in leaves that regulate gas exchange, essential for evapotranspiration and photosynthesis.

Phloem is the vascular tissue that transports glucose, produced during photosynthesis, throughout the plant.

Plants are vital for the water cycle and the food chain, emphasizing their importance in sustaining life on Earth.

Transcripts

This is yarrow, a flowering plant

found all over the Northern Hemisphere.

Its feathery leaves have natural astringent properties,

and its scientific name, Achillea, comes from Achilles, the Greek

hero, who is said to have used it on the wounds of his soldiers.

And this is snakegrass, also known as horsetail or, to the kids,

popgrass, because you can just pop it apart, and then put it

back together again. Although on top there, it's dead now.

And this is a ponderosa pine, one of my favorite trees.

They can grow hundreds of feet tall,

and on a warm day if you sniff it, it smells like butterscotch.

They all have different shapes, sizes, and properties,

but each of these things is a vascular plant, one of the most

diverse and, dare I say, important families in the tree of life.

Since their predecessors first arrived on the scene some

420 million years ago, vascular plants have found tremendous

success through their ability to exploit resources all around them.

They convert sunshine into food. They absorb nutrients directly

through the soil without the costly process of digestion.

And they even enlist the help of some friends when it comes

to reproduction, so often when they're doing their thing it

involves a third party. Which, y'know, good for them.

But these things alone can't

explain vascular plants' extraordinary evolutionary success.

I mean, algae was photosynthesizing

long before plants made it fashionable.

And as we learned last week, nonvascular plants have reproductive

strategies that are tricked out six ways from Sunday.

So, like, what gives?

The secret to vascular plants' success is in their defining trait:

conductive tissues that can take food and water

from one part of a plant to another part of a plant.

This may sound simple enough, but the ability to move stuff

from one part of an organism to another was a

huge evolutionary breakthrough for vascular plants.

It allowed them to grow exponentially larger,

store food for lean times, and develop some fancy features

that allowed them to spread farther and faster.

It was one of the biggest revolutions in the history of life on Earth.

The result? Plants dominated Earth long before

animals even showed up.

And even today, they hold most of the world records:

The largest organism in the world is a redwood

in Northern California, 115 meters tall.

Bigger than 3 blue whales laid end to end.

The most massive organism is a grove of quaking aspen in Utah,

all connected by the roots, weighing a total of 13 million pounds.

And the oldest living thing?

A patch of seagrass in the Mediterranean

dating back 200,000 years.

We've spent a lot of time congratulating ourselves

on how awesomely magnificent and complex the human animal is,

but you guys, I gotta hand it to you.

So you know by now, the more specialized tissues an organism has,

the more complex they are and the better they typically do.

But you also know that these changes don't take place overnight.

The tissues that define vascular plants didn't evolve all at once,

but today we recognize three types

that make these plants what they are.

Dermal tissues make up their

outermost layers and help prevent damage and water loss.

Vascular tissues do all of that

conducting of materials I just mentioned.

And the most abundant tissue type, ground tissues,

carry out some of the most important functions of plant life,

including photosynthesis and the storage of leftover food.

Now, some plants never go beyond these basics.

They sprout from a germinated seed,

develop these tissues, and then stop.

This is called primary growth, and plants that are limited

to this stage are herbaceous.

As the name says, they are "like herbs"

small, soft and flexible, and typically they die down to the root,

or die completely, after one growing season.

Pretty much everything you see growing in a backyard garden:

herbs, flowers, broccoli and that kind of stuff,

those are herbaceous.

But a lot of vascular plants go on to secondary growth,

which allows them to grow not just taller but wider.

This is made possible by the development of additional tissues,

particularly woody tissues.

These are your woody plants, which include shrubs,

bark-covered vines called lianas, and of course, your trees.

But no matter how big they may or may not grow,

all vascular plants are organized into three main organs,

all of which you are intimately familiar with, not just because

you knew what they were when you were in second grade,

but also because you probably eat them every day.

First, the root. It absorbs water and nutrients,

and serves as a pantry of leftover food, and of course,

keeps the plant anchored in the ground.

Next, the stem. It contains structures that transport fluids,

stores nutrients, and also is home to specialized cells

called meristems that are responsible for creating new growth.

But their most important task is to support the last organ:

The leaf. This, of course, is where the plant exchanges gases

with the atmosphere and collects sunlight to manufacture food,

with the help of water and minerals collected through the root

and sent up through the stem.

Now, each of these organs contains all three tissues,

which together work to absorb, conduct, and exploit

one of the world's most important molecules: water.

So, since plants are pretty much designed around water,

let's follow some H2O to see how plants make the most of it.

First, as with most organisms, nothing can get in or out of a plant

without getting past the skin, in this case the dermal tissue.

In smaller, non-woody plants, most of this is just a thin layer

of cells called, fittingly, the epidermis.

Naturally, this is great for keeping the outside out

and the inside in, but the epidermis can also sport

some snazzy features in different parts of the plant.

In leaves and stems, for example, it often has a waxy outer layer

called a cuticle that helps prevent water loss.

On some leaves, or on pods that hold those valuable seeds,

the epidermis can sprout hairlike structures called trichomes

that help keep insects at bay and secrete toxic or sticky fluids.

The same secretions that make the yarrow useful for first aid,

for instance, are also what discourage

ants from using it for lunch.

Finally, in the roots, the epidermis has similar features called

root hairs that maximize the root's surface area for absorption,

just like we've seen in our own organ systems.

This, of course, is where the plants generally absorb the water they need.

By the way, the cells that make up this dermal tissue

are the most basic, essential building blocks of vascular plants,

called parenchyma, or "visceral flesh," cells.

These are the most abundant plant cells, found not just in roots

but also in stems, leaves, and flowers.

They're thin and flexible and can perform all kinds

of functions depending on their location.

Now, after passing through the skin of the root and through

its starchy cortex, or outer layer, water arrives in the first of

two kinds of vascular tissue: the xylem.

The xylem's main function is to carry water and dissolved

minerals from the root up to the leaves.

But, like, how? How, by Zeus' beard,

can plants make water defy gravity?

Well, a lot of the reason is that, up top, the plant is continuously

evaporating water through a process called evapotranspiration.

As water evaporates from the leaves, which I'll explain

in greater detail when we get up there, it creates negative

pressure inside the xylem, which draws more water upward.

Plants can transpire truly staggering amounts of water,

and it's because of this that our atmosphere is habitable.

A single acre of corn gives off about 3,000 gallons

of water every day. A large oak tree, just one tree,

can transpire 40,000 gallons in a year.

Only 1% of the water that plants absorb is actually used by plants,

mostly in photosynthesis.

The rest is slowly, and invisibly released, providing one

of Earth's most crucial functions, transporting water from

the soil into the atmosphere, where it then returns to the

surface as rain, making all life possible. Yeah.

Chew on that as we continue up the xylem.

And as we get higher in the plant, we begin to encounter

a greater diversity of cells, designed not only for moving stuff

around but also for providing structural support.

For instance, elongated cells with thicker cell walls,

called collenchyma, help hold up the plant body, especially

in herbaceous plants and young structures like new shoots.

Celery is mostly made up of these cells,

so you already know what they taste like.

In larger, woody plants, you also find sclerenchyma cells,

especially in the xylem.

These have even thicker cell walls made from lignin,

a super-strong polymer that makes wood woody.

What's weird about sclerenchyma cells, though,

is that most of them when they reach maturity, they die.

They just leave behind their hearty cell walls as a support

structure, and new cells form a fresh layer during the next

growing season, pushing the old, dead layer outward.

In warm, wet years these layers grow thick, while in cold,

dry years they're light and thin.

These woody remains form tree rings, which scientists can use not

only to track the age of a tree but also the

history of the climate that it lived in.

Now, at the top of the xylem, water arrives at

its final destination: the leaf.

Here, water travels through an increasingly minuscule network

of vein-like structures until it's dumped into a new

kind of tissue called the mesophyll.

As you can tell from its name, meso meaning "middle"

and phyll meaning "leaf," this layer sits between the

top and bottom epidermis of the leaf, forming the bacon

in the BLT that is the leaf structure.

This, my friends, marks our entry into the ground tissue.

I'm sure you're as excited about that as I am.

Despite its name, ground tissue isn't just in the ground,

and it's actually just defined as any tissue that's either

not dermal or vascular.

Regardless of this low billing, though, this is where the money is.

And by money I mean food.

The mesophyll is chock full o' parenchyma cells of various shapes

and sizes, and many of them are arranged loosely to let CO2 and

other materials flow between them.

These cells contain the photosynthetic organelles,

chloroplasts, which as you know host the process of photosynthesis.

But, where is this CO2 coming from?

Well, some of the neatest features on the leaf are

these tiny openings in the epidermis called stomata.

Around each stoma are two guard cells connected at both ends

that regulate its size and shape.

When conditions are dry and the guard cells are limp,

they stick together, closing the stoma.

But when the leaf is flush with water, the guard cells plump up

and bow out from each other, opening the stoma to allow water

to evaporate and let carbon dioxide in.

This is what allows evapotranspiration to take place,

as well as photosynthesis.

And you remember photosynthesis: Through a series of brain-wrackingly

complicated reactions sparked by the energy from the sun,

the CO2 combines with hydrogen from the water to create glucose.

The leftover oxygen is released through the stomata,

and the glucose is ready for shipping.

Now, if you've been paying attention, you noticed that earlier

I said that there are two kinds of vascular tissue,

and here the circle is made complete as the sugar

exits the leaf through the phloem.

The phloem is mostly made of cells stacked in tubes

with perforated plates at either end.

After the glucose is loaded into these cells,

called sieve cells or sieve-tube elements,

they then absorb water from the nearby xylem to form a rich,

sugary sap to transport the sugar.

This sweet sap, by the way, is what gives the

ponderosa its delicious smell.

By way of internal pressure and diffusion,

the sap travels wherever it's needed, to parts of the plant

experiencing growth during the growing season, or down to the root

if it's dormant, like during winter, where it's stored until spring.

So now that you understand everything that it takes for vascular

plants to succeed, I hope you see why plants = winning.

And I'm not just talking about them sweeping the contests for

biggest, heaviest, oldest living things.

Though, again, congrats on that, guys.

Plants are not only responsible for, like, making rain happen,

they're also the first and most important link in our food chain.

That's why the world's most plant-rich habitats,

like rain forests and grasslands, are so crucial to our survival.

When those habitats change, everything changes:

weather, food supply, even the incidence of natural disasters.

So I, for one, welcome our plant overlords, because they've done

a great job so far, making life on Earth possible.

But, I know you're curious, how do different kinds of plants

make more plants? That's all about the birds and the bees,

which is what we'll be talking about next week.

Thank you for watching this episode of Crash Course Biology.

And of course, thank you to everyone who helped

put this episode together.

If you want to review anything, there's a table of contents

over there, just click, and you can go see the part of the

episode that you want to reinforce inside of your brain head.

And if you have any questions, we'll be on Facebook or Twitter,

or of course, down in the comments below.

And we'll see you next time.