Photosynthesis and Cellular Respiration: Crash Course Botany #5

Summary

This Crash Course Botany episode delves into the wonders of photosynthesis and cellular respiration, explaining how plants convert sunlight, water, and carbon dioxide into glucose and oxygen. It highlights the importance of these processes in sustaining life on Earth, the role of chloroplasts and mitochondria, and how humans contribute to photosynthesis through carbon dioxide emissions. The episode also touches on the potential of biomass as a biofuel, showcasing an innovative use of discarded tomatoes to generate electricity, and emphasizing the environmental benefits of biofuels in reducing atmospheric carbon dioxide levels.

Takeaways

• 🌿 Plants grow by performing photosynthesis, a process that combines water, sunlight, and gases from the air to produce food.
• 🌞 Photosynthesis is powered by sunlight and is essential for converting light energy into chemical energy stored in glucose.
• 🍃 The process of photosynthesis has two stages: light-dependent reactions that require sunlight and light-independent reactions that occur without it.
• 🌱 Chloroplasts, containing chlorophyll, act as the solar panels of the plant, capturing light energy and facilitating photosynthesis.
• 🌳 Plants are not only the source of oxygen for us to breathe but also the foundation of Earth's biomass, making up about 80% of it.
• 🌾 The byproducts of photosynthesis, such as glucose and oxygen, are crucial for life on Earth and for the food chain.
• 🔋 Cellular respiration in plants is similar to that in animals, converting glucose into usable energy in the form of ATP, but plants can produce their own glucose.
• 🌱 Plants use glucose for various purposes, including building cellulose for structure and storing energy for later use.
• 🌱 Biomass, primarily derived from the air through photosynthesis, is a significant component of the plant's structure and can be harnessed as biofuel.
• 🔌 Biofuels, such as ethanol from corn, can be used as an alternative to fossil fuels, potentially reducing the net increase in atmospheric carbon dioxide.

Q & A

What is the main process by which plants create their own food?

The main process by which plants create their own food is photosynthesis.

What are the three main ingredients plants use for photosynthesis?

Plants use water, sunlight, and carbon dioxide from the air for photosynthesis.

What is the purpose of chloroplasts in plant cells?

Chloroplasts in plant cells contain chlorophyll and are responsible for capturing light energy to power photosynthesis.

What are the two stages of photosynthesis and what are they called?

The two stages of photosynthesis are the light-dependent reactions, also known as the 'photo' part, and the light-independent reactions, also known as the 'synthesis' part.

What is the end product of photosynthesis that plants use as food?

The end product of photosynthesis that plants use as food is glucose.

What is the byproduct of photosynthesis that is essential for human respiration?

The byproduct of photosynthesis that is essential for human respiration is oxygen.

How does cellular respiration differ between plants and animals?

In cellular respiration, animals like humans need to consume food to get glucose, while plants can produce their own glucose through photosynthesis.

What are the two main ways plants generate energy-storing molecules like ATP?

The two main ways plants generate energy-storing molecules like ATP are through aerobic respiration, which involves oxygen, and anaerobic respiration, which does not require oxygen.

What is the significance of biomass in relation to biofuels?

Biomass, such as that from plants, can be used as biofuels, which when burned, release carbon dioxide that was recently part of the atmosphere, unlike fossil fuels which release carbon that has been locked up for millions of years.

How does the process of photosynthesis contribute to the reduction of carbon dioxide in the atmosphere?

Photosynthesis contributes to the reduction of carbon dioxide in the atmosphere by converting CO2 into glucose, which is then used by plants or released as oxygen, thus not increasing the overall atmospheric CO2 levels.

What role do humans play in the process of photosynthesis?

Humans play a role in photosynthesis by exhaling carbon dioxide, which is a necessary component for plants to perform photosynthesis.

Outlines

00:00

🌿 Photosynthesis: The Magic of Plant Growth

This paragraph introduces the fundamental process of photosynthesis, explaining how plants convert sunlight, water, and carbon dioxide into glucose and oxygen. It emphasizes the importance of photosynthesis for plant growth and the Earth's ecosystem. The narrator, Alexis, sets the stage for the Crash Course Botany series by highlighting the remarkable fact that plants, which make up about 80% of the world's biomass, primarily source their building blocks from the air. The paragraph also touches on the symbiotic relationship between humans and plants, where humans contribute carbon dioxide through respiration, aiding in the photosynthesis process.

05:01

🍃 Cellular Respiration and the Journey of Glucose

The second paragraph delves into the various fates of glucose within a plant, including its role in constructing cellulose molecules for plant structure and its conversion into energy-storing molecules like sucrose and starch. It also explains the dual role of cellular respiration in plants, which is not only essential for plant survival but also provides humans with the energy they need to live. The paragraph further discusses the similarities and differences between cellular respiration in plants and animals, highlighting the efficiency of aerobic respiration and the less efficient but crucial anaerobic respiration, especially in oxygen-deprived environments like water-logged soils.

10:03

🔋 Biofuels: Harnessing Plant Power

The final paragraph explores the application of plant biomass in generating biofuels, using the example of discarded tomatoes being converted into electricity. It explains the process of how an electrochemical device, a fuel cell, can extract electrons from tomato waste, creating an electric current. The paragraph also discusses the broader use of biofuels like ethanol derived from corn, which are used in the transportation sector and for heating and electricity generation. It contrasts biofuels with fossil fuels, noting that biofuels release carbon dioxide that was recently part of the atmosphere, unlike fossil fuels which release ancient carbon, thus contributing less to climate change.

Keywords

💡Photosynthesis

Photosynthesis is a process used by plants, algae, and certain bacteria to harness energy from sunlight to convert water and carbon dioxide into glucose and oxygen. In the video, it is described as the 'magic trick' that allows plants to make their own food. The script explains that photosynthesis is essential for life on Earth, as it not only provides plants with energy but also produces the oxygen we breathe.

💡Chloroplasts

Chloroplasts are the organelles found in plant cells that contain the green pigment chlorophyll. They are the site of photosynthesis, capturing light energy and converting it into chemical energy stored in glucose. The video likens chloroplasts to 'original solar panels,' emphasizing their role in energy conversion within the plant.

💡Cellular Respiration

Cellular respiration is the process by which cells break down glucose to release energy. It is a universal process occurring in all living organisms, including plants. The video explains that while plants produce glucose through photosynthesis, they also respire, using the glucose to power their cellular activities, just like animals do by consuming food.

💡Biomass

Biomass refers to the total mass of living organisms in a given area or ecosystem. The script mentions that plants make up about 80% of the world's biomass, highlighting their abundance and the significant role they play in ecosystems. Biomass is also a source of energy, as demonstrated by the video's discussion of biofuels.

💡Chlorophyll

Chlorophyll is the green pigment present in chloroplasts that allows plants to absorb sunlight for photosynthesis. The video describes chlorophyll as the key component that enables plants to capture light energy, which is then used to power the chemical reactions involved in photosynthesis.

💡Carbon Dioxide

Carbon dioxide (CO2) is a gas that is a crucial component of the photosynthesis process. Plants absorb CO2 from the atmosphere and use it to produce glucose and oxygen. The video points out that humans contribute to the CO2 available for photosynthesis through respiration, emphasizing the interconnectedness of plant and human life.

💡Glucose

Glucose is a simple sugar that serves as the primary source of energy for most organisms, including plants. In the context of the video, glucose is produced as a result of photosynthesis and is used by plants for energy and as a building block for more complex molecules like cellulose.

💡ATP

ATP, or adenosine triphosphate, is the primary energy currency of cells. The video explains that ATP is produced during cellular respiration, where glucose is broken down to release energy. This energy is stored in ATP molecules, which can then be used to power various cellular processes.

💡Aerobic Respiration

Aerobic respiration is a type of cellular respiration that requires oxygen and produces carbon dioxide and water as waste products. The video describes it as a reversal of the photosynthesis process, where glucose and oxygen are used to generate energy in the form of ATP.

💡Anaerobic Respiration

Anaerobic respiration is a process that occurs in the absence of oxygen, producing less ATP compared to aerobic respiration. The video mentions that this process is less efficient but can be crucial for plants under oxygen-deprived conditions, such as roots in water-logged soil.

💡Biofuels

Biofuels are fuels derived from biomass, such as plants or animal waste. The video discusses how biofuels, like ethanol from corn, can be used as an alternative to fossil fuels. It highlights that biofuels have the potential to reduce net carbon dioxide emissions because the carbon they release was recently part of the atmosphere as a result of photosynthesis.

Highlights

Plants grow by making their own food through photosynthesis, utilizing water, sunlight, and gases from the air.

Photosynthesis is a process where plants convert light energy into chemical energy, storing it in glucose.

Plants are responsible for approximately 80% of the world's biomass, highlighting their ecological significance.

The primary building blocks of plant biomass come from the air, not the soil, through the process of photosynthesis.

Chloroplasts act as solar panels within plant cells, capturing light energy and converting it for use in photosynthesis.

The byproduct of photosynthesis is oxygen, which is essential for life on Earth.

Photosynthesis has two stages: light-dependent reactions that require light energy and light-independent reactions that do not.

Plants use glucose produced by photosynthesis as a building block for cellulose, which is the main construction material for plant structures.

Cellular respiration in plants is similar to that in animals, but plants can produce their own glucose through photosynthesis.

Mitochondria in plant cells are the sites of cellular respiration, where glucose is broken down to produce ATP, the energy currency of life.

Aerobic respiration in plants is efficient, producing over thirty molecules of ATP per glucose molecule.

Anaerobic respiration is less efficient and occurs in plants under oxygen-deficient conditions, such as water-logged roots.

Biomass from plants can be used as biofuel, with examples like tomato waste being converted into electricity.

Biofuels, such as ethanol from corn, can be used in vehicles and for heating, offering a renewable energy source.

The use of biofuels contributes to a reduced net increase in atmospheric carbon dioxide, potentially mitigating climate change.

Plants play a crucial role in the carbon cycle, converting CO2 into glucose through photosynthesis, which is then used or released back into the atmosphere.

The video concludes with a call to appreciate the chemical processes within plants and their importance to life on Earth.

Transcripts

Plants… grow.

Okay, yeah, you probably knew that.

In fact, you also probably know that plants grow

because they make their own food

from a combination of water, sunlight, and gases from the air.

To those of us who have to grocery-shop for food,

photosynthesis seems almost like a magic trick.

[magic noises]

But there’s a lot of work going on behind the scenes.

Inside many, many cells, inside every single leaf,

of every single plant on Earth

is a cranking, shunting, thundering workshop that never stops.

These living workshops are consumed with photosynthesis

and cellular respiration—

processes dedicated to making, breaking, and reshaping molecules

with the singular purpose of keeping a plant alive.

Though, we also have these processes to thank for our beautiful green planet,

and all the creatures who call it home.

And plants may be structured perfectly for these intricate tasks,

but they can’t do it all on their own.

This magic show includes audience participation

—that’s us.

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

[THEME MUSIC]

When you consider the amount of living stuff on this planet,

plants really do come out on top.

They make up about 80% of the world’s biomass,

or the total weight of living organisms.

But where does all that heft actually come from?

You might initially think that soil plays a big part.

After all, most plants grow in soil, and it’s similar to the solid, heavy stuff

that we use to make building materials.

But the botanical world actually does something much more remarkable.

The building blocks for all that biomass come predominantly from the air.

In this biological magic act,

plants pull microscopic carbon molecules from the atmosphere,

which become the major materials for building plant bodies, and then

—alakazam!—

we have a plant kingdom to rule the world.

Okay, it’s not that simple —

I’ll break it down for you bit by bit.

You’ll recognize this first trick as the process of photosynthesis.

The word comes from Greek and basically means

“put together with light,”

which is a fairly accurate description of what’s going on.

Nearly all of Earth’s energy comes from the Sun.

So in photosynthesis,

plant cells combine a zap of that energy

with carbon dioxide pulled from the air and water.

The end products of this chemical reaction are the sugar glucose that plants use as food,

and the byproduct, or unintended extra product, oxygen.

There are two stages to the photosynthesis process:

the “photo” part, and the “synthesis” part.

The “photo” part is more accurately known as the light-dependent reactions

because, as the name suggests,

they can only happen with the help of light energy.

Here, tiny organelles called chloroplasts inside the cells of leaves take center stage.

They contain the green pigment chlorophyll,

which is able to capture the light energy that falls on it,

and then harness that energy to do work in the plant.

So you can think of chloroplasts a bit like the original solar panels

—taking energy from the Sun and converting it to a usable form.

With the help of light energy, water molecules are split apart,

generating spare oxygen in the process.

And to be clear:

the goal of photosynthesis is to help plants thrive, full stop.

It’s really not to make oxygen for us humans to breathe.

But on the other hand,

we help plants accomplish photosynthesis, too.

Carbon dioxide is released into the air in a few different ways,

including as an unintentional byproduct for us when we exhale.

That CO2 is essential to the “photo” part of photosynthesis.

So we’re not just volunteers ready to “pick a card, any card.”

We’re full-fledged magician’s assistants.

Does this mean I get a cape?

Okay, so with the energy trapped, water split, and some CO2 absorbed,

it’s time for the “synthesis” phase of photosynthesis,

more commonly known as the light-independent reactions,

which don’t need any input from the Sun.

At this point, the energy that’s already been captured is used,

along with the split water, to convert carbon dioxide into glucose,

completing the reaction.

Can we get some applause, please?

[Poof]

Plants don’t usually disappear in a puff of smoke at the end.

Although this final stage doesn’t need light,

it does need the products of the light-dependent reactions,

which don’t last for very long inside plant cells.

So photosynthesis really only happens during the day.

In any case, the whole point of photosynthesis is

to make food for the plant in the form of glucose,

and those small sugar molecules have 

several different potential  fates inside the plant.

Some of them are used as the building blocks for much larger cellulose molecules,

which surround every cell in the plant

and are the main construction material for roots, stems, and leaves.

And some are converted to other types of molecules,

like sucrose and starch, that can save energy for later.

The rest become fuel for the other major function of the cellular workshop:

cellular respiration.

By the way, cellular respiration isn’t unique to plants.

Every living thing does it, including you and me.

It’s happening all the time – day and night,

and, in plants’ case, often at the same time as photosynthesis.

Cellular respiration is the process organisms use to transfer the energy they get from food

into the usable energy we  need to do everything we do,

like hiking up a mountain, taking a test, or plotting elaborate plant-related fan-fiction.

Oh, is that just me?

The only difference between cellular respiration in animals like us and in plants

is that we need to eat food to get our glucose fuel,

whereas plants can make their own.

And because plants can do that, they give us things to eat—

from plants themselves, to the animals that eat them.

If it weren’t for photosynthesis converting energy from the Sun to a form usable

— AKA edible —

to us, there’d be no food chains at all.

And we wouldn’t be able to power our own cellular respiration process.

So, for plants and people alike,

cellular respiration happens in organelles called the mitochondria,

often referred to (affectionately, or not) as the powerhouses of the cell.

What that old cliché actually means is that mitochondria acquire the energy needed

to power cells’ chemical reactions.

They do this by breaking down raw fuel to make special molecules known as ATP.

ATP are like rechargeable batteries —

you can fill them with energy again and again,

which can be used to power life-sustaining reactions anywhere in the plant.

And actually, in us, too.

And in every organism on Earth.

There are two main ways that plants can generate these energy-storing molecules.

The first, aerobic respiration, is the most common,

and the “aerobic” part of its name tells us that it involves oxygen.

This kind of respiration is a reversal of the photosynthesis reaction:

glucose and oxygen combine to release energy,

with water and carbon dioxide as waste products,

instead of the other way around.

That released energy can be used to make stuff happen in the plant

on a microscopic level.

But that work translates into things we can observe like

flowers growing, fruit ripening, or leaves arching toward the Sun.

And it’s efficient.

Through aerobic respiration,

each molecule of glucose can make over thirty molecules of ATP.

That’s like the energy you get from a nice, big breakfast

—a warm bowl of oatmeal, some avocado toast, and half a grapefruit. Mmm.

The other way that plants respire is by burning their glucose fuel without oxygen around,

in a process known as anaerobic respiration.

This is much less efficient than the aerobic version,

producing only two molecules of ATP for each glucose molecule used.

That’s more like a running-out-the-door- granola-bar kind of breakfast.

But it can be crucial for plants that don’t have much oxygen available.

Roots growing in water-logged soil can be heroes by using anaerobic respiration.

Aside from providing us with oxygen to breathe,

and the sugar molecules in everything we eat,

the living workshops inside plant cells have

yet another important application to us humans.

They produce biomass that can be used as biofuel.

For example, around the world,

more than 180 million tons of tomatoes are produced every year.

In my ideal world,

these would all go towards making delicious salads, pasta sauces, and ketchup.

But in reality, not every tomato makes the grade.

Some are too wonky for our supermarket shelves,

and many are rejected as waste from various sauce-making processes.

Enter environmental engineer Dr. Venkataramana Gadhamshetty

and his team in South Dakota, USA.

In 2016, they and their collaborators figured out how to give these

poor, discarded tomatoes a new lease on life,

by using them to generate electricity!

It works a bit like the lemon or potato batteries you might have made at school.

An electrochemical device called a fuel cell

helps to break down the tomato waste and extract electrons,

making an electric current.

It turns out that tomato pulp is an ideal fuel for this

because it has loads of high-energy sugars

—sugars that were originally  created by photosynthesis!

So not only are plants perfect for photosynthesis,

but some plants, like tomatoes, corn, and soybeans,

seem to be perfect for generating electricity, too.

And we’re already using the energy stored in biomass today

—every time we burn wood in an open fire,

or charcoal on a barbecue.

That energy came from the Sun, was made usable by photosynthesis,

and then, rather than eating it,

we converted it into electricity to power our lives.

In the U.S., up to 10% of the gas we put in our cars

contains a biofuel called ethanol, which comes from corn,

and other fuels from plants are increasingly being used for heating and generating electricity.

Biofuels are burned in the same way as fossil fuels,

and they do release carbon dioxide into the air.

The difference is that the carbon dioxide biofuels release

was already in the air until very recently,

when a living plant worked its photosynthesis magic to turn the CO2 into glucose.

By contrast, when we burn traditional fossil fuels,

we’re releasing carbon that’s been locked up for millions of years.

So the magic of burning biofuels

is that there’s practically no overall increase in the amount of carbon dioxide in the atmosphere

– which is good news for anyone looking to slow down the pace of climate change.

While there are pros and cons to any energy source,

it’s helpful to have a variety of options to work with,

and biofuels are just one of them, thanks to the power of photosynthesis.

So, the next time you come across a plant, whether it’s a mighty oak tree or a tiny daisy,

spare a thought for the relentless chemical industry that’s going on behind the scenes.

Photosynthesis and cellular respiration may seem as simple as some slight-of-hand,

but those amazing tricks are the result of super-efficient processes

that plants are doing all the time.

And we get to be a part of that.

We may rely on plants’ power of photosynthesis,

but we get to contribute carbon dioxide when we exhale stinky garlic breath,

and plants make it something beautiful.

Next time, we’ll unroot the great tree of life

to discover how plants evolved into the incredible organisms we know today.

Hey, before we go, let’s branch out!

What organisms make up the next largest percentage of Earth’s biomass, after plants?

Look closely to find the answer in the comments, ‘cause they’re pretty tiny!

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.