Biology Video 2 - Energy Conversions: Photosynthesis and Respiration
(4)(B) investigate and explain cellular processes, including energy conversions; (9)(B) compare
reactants and products of photosynthesis and cellular respiration in terms of energy and matter
Hey, ya’ll. It’s Chucky D again. I just got a text from Juan in Austin. He said, “Hey, D, is it true that plants
breathe in the same carbon dioxide that we people breathe out?” Well, Juan, that’s what they told us
when we were kids, but it’s only kind of true.
We’re talking about energy conversions, here. That’s how all us living things, humans, plants, bacteria
get energy from the environment. The two reactions that make energy available are photosynthesis and
cellular respiration. Let’s talk about photosynthesis, ‘cuz if it wasn’t for photosynthesis, none of us
would be here.
Alright, Juan, what do plants first need to do photosynthesis? Sunlight. Easy. So here’s Mr. Sun, kickin’
out some radiant energy for our planet.
Well, what else do plants need? Water, right? Good ol’ H2O. The other reactant photosynthesis
requires is carbon dioxide, CO2.
Alright, Juan, now we know the materials that are necessary for photosynthesis. These are the
reactants. So what’s produced by photosynthesis? Well, the products. The waste product of
photosynthesis is oxygen. Crazy, huh? All-important oxygen is given off and “breathed” out in this
reaction! But don’t get confused. A lot of people think the reason plants do photosynthesis is to make
O2 for us. Spoiler alert: plants don’t care if we have oxygen or not. They do photosynthesis to make
energy!
So what energy do they make? Well they make chemical energy. A chemical l like to call sugar.
Specifically, glucose. Let’s add that to our awesome drawing. Oxygen is O2, and glucose is C6H12O6.
Don’t forget that.
Let’s draw lightning bolts coming off of glucose! Think about that for a second. That’s crazy! Plants take
in light and water and air and turn it into what? Sugar! They can make a potato out of light and air!
Crazy, alright. I’m nerding out here, but I think that’s awesome.
Okay, Juan, let’s go back to our equation and balance it. To make just one molecule of glucose, plants
need 6 molecules of water and 6 molecules of carbon dioxide to make 6 molecules of oxygen and 1
molecule of glucose.
One last thing to know about photosynthesis. All this happens in a very special part of the cell – the
chloroplast. Here’s what it looks like, I guess. So, there you go. We’ve converted solar energy into
chemical energy. Now we need to convert the energy in that sugar crystal into energy the cell can use.
Let’s do cellular respiration.
Alright, Juan from Austin, these materials are gonna seem real familiar. When animals and plants
perform cellular respiration, they break down glucose using oxygen, and they give off carbon dioxide
and water. That’s right! The reactants of respiration are the products of photosynthesis, and the inputs
of photosynthesis are the outputs of respiration. Crazy world.
Let’s look at this formula. O2 + C6H12O6 yields CO2 + H2O.
And what number of each molecule are we gonna need to balance out this bad boy? That’s right. Some
sixes and a one.
But here’s the deal. We still haven’t made any energy. All we did is make some waste products. The
point of cellular respiration is to make energy the cell can use. This energy is called ATP. Remember
that! Let’s add ATP. And this battery represents usable energy. And how much ATP does cellular
respiration make? 5? 10? Try 36 molecules of pure energy! Nice!
Now, technically, respiration can make 36 ATP’s only if there’s oxygen available. That’s called aerobic
respiration. That’s the type of respiration we normally do. This happens in the mitochondria. Here’s
what it looks like. Pretty cool, if you ask me. You’ve probably heard it called “the powerhouse of the
cell,” now you know why, Juan! Bacteria don’t have a mitochondria, so they can’t do aerobic
respiration, they can only do anaerobic respiration. So instead of making 36 ATPs they can technically
only make 4 energy molecules. Oh well.
All right, Juan. That’s a lot of info to keep straight. Let’s use this table to organize all that information
you just learned.
Alright, where do these reactions happen? Well, chloroplast for photosynthesis and mitochondria or
mitochondrion for cellular respiration. But remember, if you don’t have a mitochondria, you have to do
anaerobic respiration, and you can only make 4 measly ATPs.
What are the reactants? We know plants need CO2 and H2O. Don’t forget that solar energy!
Respiration requires O2 and glucose. Where did that glucose come from? Let’s go down to the
products.
Plants make C6H12O6 and get rid of oxygen. Respiration gets rid of CO2 and water. But remember, the
whole point is to make usable energy! 36 whole ATPs!
Finally, which organisms do these reactions? Well plants do photosynthesis. Duh! And animals do
respiration, AND SO DO PLANTS! Oh, snap! Don’t forget, Juan, first plants do photosynthesis to make
sugar, and then they do respiration to breakdown that sugar!
So, Juan, this brings us back to your text. Do plants breathe in the carbon dioxide that we breathe out?
Yes, when they do photosynthesis. But they also intake oxygen when they do respiration to make ATP.
I hope this helps out. Till next time, it’s your boy Chucky D. Bye!