What Are Plants Made Of? Crash Course Botany #2

Summary

Crash Course Botany explores the unique organs of plants, contrasting them with those of animals. Host Alexis explains that plants, evolved from single-celled organisms, have different modes of growth and organization. Stems, leaves, and roots are the main organs of vascular plants, each with specific roles like structural support, photosynthesis, and nutrient absorption. The video also delves into the botanical definitions of 'fruits' and 'vegetables,' challenging common misconceptions and highlighting the diversity and adaptability of plant life.

Takeaways

• 🌿 Plants have different organs compared to animals, adapted for their unique functions.
• 🔬 Plant organs are made up of tissues, which are groups of cells that perform similar functions.
• 🌱 Plants and animals evolved independently from single-celled organisms over a billion years ago.
• 🌳 The three main organs of vascular plants are stems, leaves, and roots.
• 🌱 Stems provide structural support and transport water and sugars throughout the plant.
• 🍃 Leaves are primarily responsible for photosynthesis, converting sunlight into energy.
• 🥕 Roots are involved in absorption of water and nutrients, and anchor the plant to the soil.
• 🥦 Many edible plant parts we consume are actually stems, leaves, or roots, not fruits.
• 🍅 Botanically, a tomato is a fruit, but it is legally considered a vegetable in the U.S. due to culinary usage.
• 🍓 True berries, according to botanical definitions, develop from a single ovary and include blueberries and cranberries.
• 🌿 The diversity of plant organs contributes to the vast array of plant life forms observed by Charles Darwin.

Q & A

What are the three main organs that comprise a plant body?

The three main organs that comprise a plant body are stems, leaves, and roots.

What is the function of apical meristems in plants?

Apical meristems are clusters of stem cells at the tip of every stem and root that continually produce the materials needed to build new body parts.

How do plants differ from animals in terms of stem cell production and organ development?

Plants are always producing new organs from the moment they germinate, while animals have most of their stem cells only fleetingly in embryos before they are used up to make organs.

What is the primary function of stems in plants?

Stems provide the structural framework of the plant, support the plant, and transport water and sugar throughout its body.

Why are leaves often flat and wide?

Leaves are often flat and wide to maximize their photosynthetic capabilities by providing more surface area for harvesting light energy.

What is the main function of roots in plants?

Roots are responsible for absorption of water and nutrients from the soil and anchoring the plant.

What is the difference between vascular and non-vascular plants?

Vascular plants have stems, leaves, and roots with vascular tissue for support and transport, while non-vascular plants, like mosses, lack such specialized tissues.

Why are tomatoes considered vegetables in the U.S. despite being botanically fruits?

In the U.S., tomatoes are legally considered vegetables because of a Supreme Court ruling in 1893 that classified them as such based on culinary usage, not botanical characteristics.

What is the botanical definition of a 'berry'?

A berry is a fleshy fruit that comes from a flower with a single ovary, according to botanical definitions.

How do plants grow and develop new organs throughout their life?

Plants grow and develop new organs through meristems, which are regions of undifferentiated cells that can continuously divide and differentiate into various cell types to form new organs.

What is the significance of phyllotaxy in plant leaves?

Phyllotaxy, or the pattern in which leaves grow around a stem, is significant because it determines the arrangement of the plant's branches and influences the plant's overall structure and light exposure.

Outlines

00:00

🧠 Plant Organs: More Than Just Artichoke Hearts

This introduction discusses the different organs in animals and plants, highlighting that plants, unlike animals, have organs such as stems, leaves, and roots that perform specific functions. The narrator, Alexis, draws comparisons between human and plant organs, noting that while animals have fixed organ systems, plants continually produce new organs throughout their life due to their unique evolutionary path. The paragraph emphasizes the continuous growth of plants via stem cells and sets the stage for exploring plant anatomy, starting with a trip to the grocery store.

05:00

🍃 The Role of Leaves and Phyllotaxy in Plant Growth

This section delves into the structure and function of leaves, explaining how they play a vital role in photosynthesis by converting carbon dioxide into sugars using sunlight. Leaves, with their wide, flat shapes, are common in the grocery store and are often attached to stems, showcasing their phyllotaxy (leaf arrangement). Examples of leaves, such as lettuce and kale, are discussed, and the paragraph explains how to differentiate between stems and leaves, using the presence of buds as a key indicator. It also touches on the complexity of organs like onions, which have layers of leaves around a modified stem.

10:02

🌱 Roots: The Hidden Powerhouses of Plants

This paragraph focuses on roots, describing their primary functions of absorption and anchorage, along with their ability to store food and exchange nutrients with fungi underground. Roots like carrots, radishes, and beets are common storage roots found in grocery stores. The paragraph explains that roots lack phyllotaxy, making them easy to identify. A surprising fact is revealed: while russet potatoes are often thought of as roots, they are actually underground stems due to their regular pattern of 'eyes,' which can grow buds, branches, and leaves.

15:06

🍎 Vegetables, Fruits, and the Botanical Terminology

This section clarifies the difference between vegetative and reproductive plant organs, noting that 'vegetable' is not a botanical term but rather a culinary one. It explains that many commonly referred-to vegetables are actually fruits, botanically speaking, because they are mature, ripened ovaries containing seeds. The paragraph uses humorous examples, such as tomatoes and strawberries, to demonstrate the confusion between culinary and botanical definitions. The famous legal case determining that tomatoes are legally vegetables in the U.S., despite being fruits botanically, is also discussed.

🥦 Have Plant Organs for Every Meal

This concluding paragraph encourages viewers to embrace a variety of plant organs in their diet, suggesting that fruits and vegetables are simply different plant parts. It teases the next episode, which will focus on plant cells and hormones, and promotes another PBS Terra series, 'Women of the Earth,' that highlights the contributions of female land stewards to climate healing. The episode closes with a fun quiz about Brussels sprouts, prompting viewers to leave their answers in the comments, and a call to support Crash Course via Patreon.

Keywords

💡Organs

In the video, 'organs' refer to the functional body parts of both plants and animals that carry out specific tasks. For animals, this includes hearts, lungs, and kidneys, whereas for plants, the main organs discussed are stems, leaves, and roots. These organs differ between plants and animals due to their evolutionary paths.

💡Stem cells

Stem cells are unspecialized cells that can develop into different types of cells. In humans, stem cells are primarily present in embryos and are used up to create organs. In contrast, plants have clusters of stem cells in apical meristems that continuously produce new organs throughout their lifetime. This reflects plants’ ability to grow indefinitely.

💡Apical meristems

Apical meristems are regions at the tips of stems and roots where plant stem cells reside. These cells continually divide to allow the plant to grow and produce new organs, such as leaves and branches. They play a crucial role in a plant's ongoing growth and development, which contrasts with animals, whose growth stops after a certain point.

💡Vascular tissue

Vascular tissue in plants is responsible for transporting water and nutrients throughout the plant body. It’s present in stems, roots, and leaves, forming a structural and functional network to support growth. This is a key component of vascular plants, distinguishing them from non-vascular plants like mosses.

💡Phyllotaxy

Phyllotaxy refers to the arrangement of leaves on a plant stem. This pattern helps botanists distinguish between plant organs, such as stems and leaves. In the video, it’s used to explain how to differentiate between a stem and a leaf by checking for a bud in the leaf axil, showing that leaves have a defined pattern.

💡Roots

Roots are plant organs primarily responsible for anchorage and nutrient absorption from the soil. They come in various shapes and sizes and can also serve functions such as food storage. The video gives examples like carrots and radishes, which are edible roots, highlighting their importance in the plant's survival.

💡Photosynthesis

Photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into sugars that fuel their growth. Leaves, with their large surface area and chloroplasts, are the primary site of this process. The video explains how this energy conversion allows plants to sustain themselves and grow.

💡Bulbs

Bulbs, like onions, are specialized plant organs that consist mostly of leaves surrounding a modified stem. These organs store food for the plant during the winter. The video uses onions as an example to show how plant organs can be more complex than they seem at first glance.

💡Storage roots

Storage roots, like sweet potatoes and beets, are roots that have evolved to store food and nutrients to help the plant survive difficult conditions like drought or winter. The video emphasizes that these roots are edible and provide vital energy reserves for plants.

💡Fruits

Botanically, fruits are ripened ovaries containing seeds, playing a key role in plant reproduction. The video humorously explains how many foods we commonly call vegetables, like cucumbers and eggplants, are technically fruits. This highlights the complexity and diversity of plant reproductive organs.

Highlights

Plants have different organs compared to animals, adapted for their unique functions.

Plant organs are made up of tissues, which are groups of cells with similar functions.

Plants and animals evolved from single-celled organisms independently over a billion years ago.

Stem cells in plants are unspecialized and can become various cell types, unlike in animals where they are mostly used in embryonic development.

Plants continuously produce new organs throughout their life from clusters of stem cells called apical meristems.

The three main organs of vascular plants are stems, leaves, and roots.

Stems provide structural support and transport water and sugar in plants.

Leaves are responsible for photosynthesis and are often flat and green to maximize light absorption.

Roots are for absorption of water and nutrients and provide anchorage to the soil.

Asparagus is an example of a plant stem that is edible when tender.

Onions are bulbs, which are mostly leaves arranged around a modified stem.

The term 'vegetable' is not botanical but refers to edible parts of plants, which can include stems, leaves, roots, and even fruits.

Fruits are botanically defined as mature, ripened ovaries containing seeds.

The tomato was legally declared a vegetable in the U.S. due to culinary usage, despite being botanically a fruit.

Many foods labeled as berries, like tomatoes and avocados, are actually berries by botanical definition.

Botanists use a precise language to describe plant organs, which can differ from everyday terminology.

Plants have diversified into a vast kingdom with unique forms due to their distinct evolutionary path.

Transcripts

Brains and hearts.

Lungs and kidneys.

No, this is not an ingredient list for a zombie cookbook.

It’s just a few of the organs that animals like us have

to keep our bodies in working order.

But plants have totally different organs

— despite what you might have heard about artichoke hearts.

And unlike most of our organs,

which you can only see with an X-ray,

you’ve come across a lot of plant organs.

You’ve seen plant organs alive,

whether growing in the woods,

beside the road,

or in your bathtub full of houseplants.

And you’ve seen them dead —

severed plant organs piled on  top of each other in bins.

There they sit beneath harsh white lights,

damp from routine mistings,

just waiting to be picked up and carried away.

Hi! I'm Alexis, and this is Crash Course Botany.

Grab your cart and coupons— we’re going to the grocery store.

[THEME MUSIC]

Like animals, plants are made up of organs,

or body parts that carry out specific functions

and consist of more than one type of tissue.

Not tissues like Kleenex;

tissues like groups of cells that look similar

and serve similar purposes in a living thing.

But plants have totally different modes of developing,

growing, and organizing their bodies.

That’s because they evolved from  the simplest form of life,

a single-celled organism,

independently of animals like us.

In other words,

it wasn’t like there were single-celled organisms that evolved into plants,

that then evolved into animals.

The evolutionary ancestors of plants and animals diverged over a billion years ago,

and then each evolved on a totally separate path.

Which explains why our bodies work so differently from plant bodies.

Like, in both plants and animals,

there are these things called stem cells.

Stem cells are special because they are unspecialized.

They have the potential to become tons of different types of cells.

They’re like the clay you use in art class.

You could make it a vase, a mug, a bust of your favorite botanist.

Love you, Linda Black Elk!

For humans and other animals,

most of our stem cells exist only fleetingly

in embryos before they get used up to make our organs.

Which is perfect because we animals are born with essentially the same body plan

that we’ll carry into adulthood.

That means the number and location of our organs

won’t really change throughout our life,

barring surgery or injury.

In contrast, plants are always producing new organs

from the second they germinate,  or begin to grow

— can’t stop won’t stop!

Clusters of stem cells, called apical meristems,

at the tip of every stem and root

continually produce the materials needed to build new body parts.

They also have lateral meristems that allow roots and stems to thicken as the plant grows.

The three main organs that comprise a plant body are stems, leaves, and roots,

and their presence is one of the defining characteristics of a category called vascular plants.

Non-vascular plants, by the way, are often low-lying plants like mosses

— and we’ll cover them in another episode.

But for now, we’re on the hunt for our rascally vasculies.

Stems provide the structural framework of the plant,

whether dainty daisy stems

or thick  tree trunks

—yes, tree trunks are stems!

Stems are typically, though not always,

found above-ground and contain vascular tissue that supports the plant

and transports water and sugar throughout its body.

As we head down the grocery aisles,

we might not find a lot of stems,

mostly because the tissues that make them strong enough to hold up a plant

are a little too tough to be tasty.

Asparagus, though, is a great example of a stem:

we harvest asparagus plants when they’re still tender,

and we often snap off the bases that have become too woody to eat.

Stems also hold a plant’s leaves —

another crucial organ —

up to the sunlight.

That lets the leaves do their main job:

photosynthesizing, or converting carbon dioxide gas into sugars,

using energy from the sun.

To maximize their photosynthetic capabilities, leaves are often flat and wide

— which gives them more surface area —

and green, which makes them more efficient at harvesting light energy.

Their veins shuttle nutrients in and out of the leaf,

and the cells in between are packed full of chloroplasts,

the cellular machines responsible for photosynthesis.

Leaves are a lot easier to find at the grocery store—

their wide, frilly shapes give them away.

Lettuce, kale, spinach, cabbage  — these are all classic leaves.

Some will still be attached to their original stems,

which show off their phyllotaxy

— or the pattern in which leaves grow around a stem.

So in asparagus, the little scales at the top of the spears

are leaves with beautiful spiral phyllotaxy.

The chunky part of kohlrabi is also a stem,

and its much larger leaves have spiral phyllotaxy as well.

At the point where each leaf meets the stem, there’s a bud,

which is a new meristem that has the potential to grow into a branch and

start producing its own stem and leaves.

Because of this, the leaf pattern determines the arrangement of the plant’s branches.

So the difference between a stem and a leaf is obvious, right?

I mean, you know which organ this is…right?

It’s trickier than you’d think!

Onions are bulbs, which means they’re mostly leaves

around a modified stem

that’s evolved to swell up and store food for the plant during the winter months.

So even an onion isn’t  very straightforward.

Hey, they have layers!

A good rule of thumb is if the plant organ is  bearing other organs, it’s probably a stem.

And the trick to telling stems apart from leaves is to look for a bud

nestled above the thing that looks like a branch.

If there’s a bud, it’s a leaf.

And now, for the third item on our list: roots.

Roots are the typically underground organs of a plant

that are responsible for absorption  and anchorage to the soil

or…the face of a cliff!

[Alexis sings a rockin' guitar lick]

Plants are pretty hardcore!

Their epidermis, or outermost layer of tissue,

produces billions of tiny hairs  that absorb water and nutrients,

and their vascular tissue transports  the nutrients up to the stem and leaves.

The longer roots grow, the more they can explore the soil and absorb the good stuff.

If the root needs to branch off,

a new root with its own meristem

busts out from the center of the old one, Alien-style.

So yeah, roots come in a variety of shapes and sizes.

Many have also evolved functions beyond anchoring and absorption

such as storing food,

providing housing for helpful organisms like bacteria,

and exchanging nutrients with fungi underground,

like swapping chicken fingers for Lunchables beneath the cafeteria table.

And many roots, we eat!

In the produce section, you’ll find carrots, radishes, beets, and sweet potatoes.

All of these foods are storage roots  that are filled with deliciousness

originally meant to help the plant through hard times,

like a dry period or cold winter.

The way to spot a root is that it should be an organ with no phyllotaxy

— meaning no pattern of leaves around it.

Now, you might be saying,

“Alexis, you’re forgetting about my favorite kind of root to eat—russet potatoes!

We’re talking the plant that birthed French fries and tater tots,

latkes and hash-browns.

The root that is  so delightfully creamy

when mashed up,

it earned a place in the Hall of Fame of Side Dishes!

Why would you neglect such a versatile food

—one that’s even been honored with its own emoji?” [Angelic voices singing]

Well, pick up a russet potato

and you’ll find those little notches in the skin, called eyes.

And from those eyes, buds, branches, and leaves can grow.

On top of that, you’ll notice the eyes are arranged in a

suspiciously regular pattern…

Yep, russet potatoes have phyllotaxy.

Which means, unlike sweet potatoes, russets aren’t roots—

they’re underground stems!

I know, mic drop.

You might be wondering why, despite

all this hanging out in the grocery store, we haven’t mentioned two very common words yet:

vegetables and fruits.

The thing is, “vegetable” isn’t actually a botanical term.

It’s just a useful regular-person  word to describe some edible plant parts.

The word “vegetable” could refer to stems, leaves, roots…

and even

—are you ready for this?—

fruits!

Okay, let’s rewind for a second.

So far we’ve only talked about vegetative plant organs,

which refers to a type of organ that contributes to a plant’s

overall growth and structure.

But plants also make reproductive organs

of a variety of different sizes, shapes, and colors,

which help them have plant  sex and create plant babies.

Botanists have a vast and precise language for describing them,

including the word “fruit,”

which refers to a mature, ripened ovary containing seeds.

[Gameshow Host Alexis]: Welcome to Not a Fruit,

[Audience applauds] where the game is to name a plant

that’s not a fruit!

[Contestant Alexis]: Cucumber!

[Gameshow Host Alexis makes a buzzer noise]

[Contestant Alexis]: Eggplant?!

[Gameshow Host Alexis]: Also [buzzer noise]

[Contestant Alexis]: Zucchini??!!

[Gameshow Host Alexis makes a buzzer noise]

Nope, [Contestant Alexis sighs]

[Gameshow Host Alexis]: all fruits!

Meanwhile, some of the things we call fruits

aren’t fruits at all!

Like, the tasty part of the strawberry is actually the base of the flower,

not the ovary.

Strawberry fruits are technically the little nubbins that we would call seeds.

[mind blown noise]

And there is one food in particular that has been the subject of the

fruit/vegetable debate for centuries.

And that’s gotta be the tomato, like Theo here.

Let’s go to the Thought Bubble…

The year was 1886.

New York was a major port city,

and wholesalers were starting to introduce the U.S. to fruits

and vegetables from other countries by

shipping them across the ocean.

But there was some controversy over shipping regulations.

Whenever anyone imported vegetables,

they had to pay a 10% tariff on them,

while fruits didn’t have the same tax.

So when a guy named John Nix received a shipment of tomatoes

from the Caribbean and was forced to pay the vegetable tariff on it,

he was not happy.

He claimed that tomatoes weren’t vegetables—

they were fruits, so he should get his money back.

Theo was having…a bit of an identity crisis.

By 1893, Nix’s case had gone all the way to the United States Supreme Court.

During the trial, the witnesses

—which were not bananas and  broccoli as you’d expect,

but humans in the produce industry—

debated multiple dictionary  definitions of “fruit” and “vegetable.”

Nobody asked the tomatoes what they thought of all this.

Ultimately, the judge declared that despite any botanical similarities to fruits,

tomatoes were vegetables because they were, quote:

“…usually served at dinner in, with, or after the soup,

fish, or meat…, and not, like fruits generally, as dessert.”

And this remains true to this day in the U.S.

Even though tomatoes are botanically fruits,

they are legally vegetables.

What can I say?

People, like tomatoes, are messy.

Thanks, Thought Bubble! [Audience applauds]

[Gameshow Host Alexis] And we’re back with everyone’s favorite game show, Name a Berry.

Where the game is… you get it.

[Contestant Alexis]: Blackberries!

[Gameshow Host Alexis makes a buzzer sound]

[Contestant Alexis]: Raspberries!

[Gameshow Host Alexis]: Additional [buzzer sound]

[Contestant Alexis]: Mulberries?!

[Gameshow Host Alexis makes a buzzer sound]

[Contestant Alexis]: I don't wanna play this game anymore

According to the botanical definition,   [crash]

a berry is a fleshy fruit that comes from a flower with a single ovary.

In a nutshell, [ripping sound] ow

blueberries and cranberries are pretty  much the only fruits with

“berry” in their name that are actually berries.

Meanwhile, tomatoes, avocados, bananas

— yep, berries.

So now we have a pretty good feel for the rulebook of botanical body-building

—as in, forming bodies made of organs, not getting swole.

Plants evolved different rules than we did,

and through variation in just a few different organ types,

they’ve diversified into a magnificent kingdom

full of, as Charles Darwin put it, “endless forms most beautiful.”

Botanists have deciphered these rules and translated them into a precise and consistent language,

one we’ll be exploring in future episodes.

Sometimes that language is at odds with how we’re used to talking about plants in our everyday lives.

But now you know that when the doctor recommends 5 servings of fruits and veggies a day,

you have a variety of plant organs to choose from.

I say go wild and have plant organs for breakfast, lunch, and dinner.

[crunch]

Next time,

we’ll be zooming in on plant cells and hormones

—the tiny structures and chemical signals

that allow plants to do amazing things.

Calling all inhabitants of Earth!

There's a new series over on PBS Terra that will make you think,

"Where would we be without women?"

Women of the Earth explores the resilient work of female land stewards across the country

and how they're leading the world toward effective climate healing.

You'll meet the powerful forces behind the practices that are healing communities

from climate change

and discover why women's contributions to our Earth are essential today.

Check out the link in our description to watch it now!

Hey, before we go, let’s branch out!

What part of the plant is a Brussels sprout?

Find the answer in the comments!

[Gameshow Host Alexis]: Thanks for watching this episode of Crash Course Botany

which was filmed at the Damir Ferizović Studio and made in partnership with PBS Digital Studios and Nature.  

If you want to help keep Crash  Course free for everyone, forever,

you can join our community on Patreon.

I don’t know what that is…