remember in elementary school when all you needed to know is: photosynthesis needs the sun, water and carbon dioxide to make food? Now it has come to this.

Who else zones out during the video and then has to rewatch it again...and again...

I remembered having to learn about this when I was in high school Biology so I came back to see if it would come back to me at age 37. Nope, I ended up rocking back and forth in the corner of my office in the feeble position. Then I snapped out of it... I now embrace this truth - plants turn water, sunlight, and CO2 into food using magic

I appreciate the fact that he admits this process is stupidly hard for no reason except... science😂

RIP to the people who are watching these videos who have tests the next day...

These are the notes I took. Hopefully this can further your understanding LIGHT DEPENDENT REACTIONS (STAGE 1): -Photons strike the chlorophyll in Photosystem II (PSII) and an electron absorbs the energy and gets excited (photoexcitation) -The electron travels from PSII (first protein complex of 4) along the electron transport chain (via mobile electron carriers) to harness energy. *mobile electron carriers are proteins that carry electrons along a membrane [-The chlorophyll splits a stable molecule of H2O, stealing an electron to replace the old one. Oxygen is then released from the plant. This allows us to breathe.] -The energized electrons from PSII that were picked up by the electron carriers are transported to the next protein complex, the Cytochrome Complex. -The Cytochrome Complex serves stands between PSII and PSI (all embedded in the thylakoid membrane) and uses energy from the electrons to pump hydrogen ions into the thylakoid. -Protons accumulated from the splitting of H2O and via the Cytochrome Complex now in the thylakoid then move toward the enzyme ATP synthase, which uses the energy to pack an inorganic phosphate onto ADP to create ATP. -As electrons move along the Electron Transport Chain, they lose energy -The ‘tired’ electrons become re-energized as it reaches Photosystem I and travels on another electron carrier, where all the energy is used to make NADPH. *Products of Light Dependent reactions: chemical energy in the form of ATP and NADPH, and the by-product oxygen. LIGHT INDEPENDENT REACTIONS (STAGE 2): -First phase of the Calvin Cycle is known as Carbon Fixation -Begins in the stroma (empty space of chloroplast). Involves fixing a CO2 molecule onto Ribulose Bisphosphate (RuBP) with the help of an enzyme RuBisCo. This causes the RuBP to become unstable. -This new 6-carbon chain has to break apart, creating two molecules of 3-phosphoglycerate, which occurs to three molecules of RuBP. -Second phase of the Calvin Cycle is called Reduction. -ATP combines a phosphate group onto the 3-phosphoglycerate and NADPH packs some electrons, creating 2 molecules of Glyceraldehyde 3-Phosphate (G3P). -G3P is a high energy, 3-carbon compound that plants can convert into many carbohydrates such as glucose, cellulose, or starch. (glucose=short term energy / cellulose=structure / starch=long term energy) -The last phase of the Calvin Cycle is call Regeneration. -9 ATPs and 6 NADPHs are required to convert the 3 RuBPs we started with into 6 G3Ps. However, only one G3P can leave the cycle... the other 5 G3Ps are needed to regenerate the original RuBPs, completing one round of the cycle. Hope this helps!

Watching this the day before my bio exam and realizing that I’m so gonna fail

Mitochondria are the powerhouse of the cell. That's what I've learned so far.

*hears a bunch of complicated words* *zones out* *freaks out and restarts the video*

Everyone here is cramming for AP biology but I’m just cramming for normal biology how is this fair

Good luck to everyone on their exam tomorrow! Now stop reading comments and get back to revision

This is probably the first crash course video that I've watched and then felt MORE nervous for my exam afterward

"Or more likely you want to do well on your test." Pffffttt. At this point I just want to pass.

Basically the video in text, hopefully to further your understanding. Requires water (H2O), carbon dioxide (CO2) and light. Roots of plants absorb water and transport it to the leaves through xylem, CO2 enters the plant (while O2 exits) through microscopic pores in leaves called stomata, and individual photons are absorbed from the sun in the plant by the pigment chlorophyll. **It is important that O2 levels remain low (explained later) for the Calvin Cycle (Stage 2) Inside the cell of plants are plastids called chloroplasts, which contain thylakoids (which store chlorophyll), which contain lumen inside and Stroma outside; stacks of thylakoids are called grana. Light Dependent Reactions (Stage 1) PS II (wavelength p680) -Photons strike the chlorophyll in Photosystem 2 (PS II) and an electron absorbs the energy and becomes excited (photoexcitation), but has nothing to do with this energy. -The electron travels from PS II (1st protein complex of 4) along the Electron Transport Chain (via mobile electron carriers) to harness the energy; across a series of reactions the electrons lose their energy. -The energised electrons from PS II that were picked up by electron carriers are transported to the 2nd protein complex, the Cytochrome Complex. -The cytochrome complex stands in between PS II and PS I (which are all embedded in the thylakoid membrane), and uses the lost energy from the electrons to pump hydrogen ions into the thylakoid.-Now missing an electron, the chlorophyll molecule will split a H20 molecule in cooperation with PS II to steal its electron and replenish the one it lost, the by-products of this process are hydrogen ions (single protons) and oxygen. **By-product of oxygen is the reason behind the survival of living organisms. -Protons accumulated from the splitting of H2O and via the cytochrome complex now in the thylakoid then move towards the enzyme ATP Synthase, which uses that energy to pack an inorganic phosphate (Pi) onto ADP to create ATP. PS I (wavelength p700) The 'tired' electrons becomes reenergised by some photons as it reaches Photosystem 1 (PS I) and travels on another electron carrier, where all of the energy is used to help make NADPH (similar to ATP) by an enzyme, which combines 2 electrons and 1 Hydrogen ion with NADP+. (NADP+ + 2 e- + 1 H+ = NADPH). **Products of light dependent reactions: Chemical energy in the form of ATP and NADPH, as well as the by-product O2. Light Independent Reactions/Calvin Cycle (Stage 2) **Doesn't require light energy from photons, uses energy derived from ATP and NADPH to fuel processes Carbon Fixation (1st phase of Calvin Cycle) -Begins in the Stroma (empty space of chloroplast). Involves fixing a CO2 molecule onto Ribulose-Biphosphate or RuBP (the starting and end point of the 'cycle'), with the help of an enzyme called RuBisCo (which converts inorganic carbon into organic carbon), which causes it to become unstable. -So this new 6-Carbon chain has to break apart, creating 2 molecules of 3-Phopshoglycerate, which occurs to 3 molecules of RuBP (explained later). **If RuBisCo reacts with O2 instead of CO2, it creates a toxic by-product known as phosphogycolate (process of photorespiration) believed to alter enzymatic functions. Reduction (2nd phase) -ATP combines a phosphate group onto the 3-Phosphoglycerate molecules and then NADPH packs some electrons, creating 2 molecules of Glyceraldehyde 3-Phosphate (G3P). -G3P is a high-energy, 3-carbon compound that plants can convert into many carbohydrates such as glucose, or cellulose or starch. Regeneration (3rd and last phase) -9 ATP molecules and 6 NADPHs are required to convert the 3 RuBPs started with into 6 G3Ps, however only 1 G3P can leave the cycle - with the other 5 G3Ps needed to regenerate the original 3 RuBPs, completing 1 round of the cycle. **G3P is considered the ultimate product of photosynthesis as the glucose gained from it is the energy used by all cells.

I failed Biology 3 times already, this is my 4th time taking the class. First time actually trying to seriously understand it. I’ve been watching your videos that relate to what we’re learning in class, I want to thank you for helping me earn a 92% on my first exam. I’m so grateful for you!

currently crying in bed at 3am trying to study for my AP Bio test but every single drop of will and motivation has been drained out of me.

Summary for those whom it may concern: We begin in PS2 (photosystem 2), light energy absorbed by the cholorophyll exciting electrons in it. Excited electrons move up to a higher energy level. Excited electrons move to electrons carriers forming electron transport chain (redox reactions occur). Energy is lost from electrons moving down the electron transport chain. Water is split into H+, e- and 1/2 O2 by photolysis (light energy used to break it down). Electron from the water being split is given back to PS2. Energy lost from electrons moving down electron transport chain is used to pump H+ into thylakoid from the stroma creating proton gradient. Protons move out of thylakoid down concentration gradient through ATP Synthase. Energy from this movement is used to add inorganic phosphate to ADP forming ATP. PS1: Light energy absorbed by chlorophyll exciting electrons to a higher energy level. Electron transferred to NADP along with a H+ from stroma to form reduced NADP (NADPH). - Cyclic photophosphorylation: Electrons excited by energy absorbed and passed onto electron carriers. Electrons passed back to PS1 (hence 'Cyclic')- no electrons lost)). H+ pumped into thylakoid from stroma by energy lost from electrons moving down energy levels. Proton gradient used causes high concentration of H+ in thylakoid to reduce by H+ leaving through ATP Synthase. Energy from this movement allows ---> ADP+P(i)-->ATP. NADPH and ATP used in light independant reactions.

*Replays video more than 1000 times* *Still doesn't get photosynthesis*

I have my test in an hour. So far I know electrons are involved somehow.

" you are committed to having a better, deeper understanding of our world; or more probably you'd like to do good on your test" hahahaha this Hank guy is the best

How in the hell did we figure this out?

who else is cramming the night before ap bio exam

95% of comments: studying/cramming for test 3% of comments: a summary(?) of the vid 1.99999999% of comments: some kind of thanks or 'you get me' to hank 0.00000001% of comments: this one

I need to watch this again in 0.75x speed man

guess who's cramming for finals? me

For the lazy :D GL on tests! Photosystem II captures and transfers energy. 1) chlorophyll absorbs energy from sunlight 2) energized electrons enter electron transport chain 3) water molecules are split 4) oxygen is released as waste 5 )hydrogen ions are transported across thylakoid membrane 6) Photosystem I captures energy and produces energy-carrying molecules. 7) chlorophyll absorbs energy from sunlight 8) energized electrons are used to make NADPH 9) NADPH is transferred to light-independent reactions

It took me 90 minutes to watch a 13-minute video and take a few notes so I could actually understand everything HAHAHA imma go laugh and cry at and with myself now.

Who dislikes a video of a man trying to help students with their studies lol

Why do i even go to college? This channel teaches me more in ten minutes than my professor teaches in one semester. Crash Course explains the material thoroughly, and in a simple, concise manner, while most professors simply lecture because they are required to teach a course if the university is funding their research.

"or more likley you'd like to do well on your test" I feel attacked right now this is the exact reason i'm here

Am I the only one who cracks up at this man's jokes? I'm literally dying 😂

Just to let yall know. I am not having fun doing bio hw

Wish me luck on my giant bio exam tomorrow!!! *Cries*

When Hank Green can teach you more about photosynthesis in 13min than your actual biology teacher can teach you in three weeks.

I appreciate how deeply he understands our pain😶

"Or more probably, you want to do well on your test". Yeah pretty much Edited: 8 years old and A Level biologists are still using it to teach themselves photosynthesis. You're still a freaking legend mate

Im just tryna pass biology bruh. when did religion get involved in this?

Watching Hank is like watching Khan at 2x speed.

"atp: the big daddy of cellular energy" LMAO

I remember making a model of the chloroplast for 9th-grade biology and I made it of mint Oreos, green-dyed vanilla frosting, Chocolate frosting, sprinkles, and tableware. It was everyone's favorite because we got to eat my project.

I came to learn a little bit more about photosynthesis.... I see a bunch of people complaining about religion & science, I mean really??? WHAT DOES RELIGION HAVE TO DO WITH PHOTOSYNTHESIZING?!????!?!?

Hank, you and the Crash Course team are saving my butt right now! I've got a biology test tomorrow and my teacher has one of those voices that the brain tunes out ALL OF THE TIME. Thanks for making these! SO helpful!

All the shade he is throwing at plants in this video is making my late night studying so much more enjoyable.

Who watched the whole thing like 3 times and still had no idea how photosynthesis works

I got a 93% on my test today thank you so much

In your animations, can you start to label the different things? They're kinda hard to follow when I have no idea what any of the littler orbs represent..

"Think about how chlorophyll feels." I have some advice for chlorophyll: Give in to your hate, your suffering, your anger, and turn to the dark side. Dark Plantaeus, welcome to the Sith! Now, rise as my new apprentice!

*Thanos snaps* PSII disappears, no more photosynthesis, no more life

Wish me my luck yall, got a AP bio exam tomorrow

ATP is daddy

No matter how much I read my book and rewatch these videos, nothing sticks to my head and i continue to fail my biology...... I had tried my best :( well anyone having midterms, test, etc... I wish you the best of luck!

The AP exam is tomorrow and Hank Green is the only reason I'm gonna pass

Am i the only one who watches these for genuine entertainment? ... **cricket cricket**

well....I'm screwed for biology exam tomorrow.....

I have a midterm in 1 HR and here I am

*THE BIG DADDY OF CELLULAR ENERGY*

If you teach the full name like a spell it makes it fun to say "Plastoquinone Oxidoreductase" It's one of four advanced light spells created by aurors during the rise of Voldemort to counteract his death eaters

Anyone else cramming for a Biology Test tommorow on Calvin cycle and all things photosynthesis I hope this explains electron transport carriers for me

me: why photosystem ll? hank: oh do you want the full name? me: *hears the name* photosystem ll it its!!!!

We're about to take a test in about 30 minutes May we RIP

graduation speech: "I would like to thank spell-check and hank green"

me: *has a bio final tomorrow* me: opens door to room me: opens desktop me: *typing into youtube* C'MON CRASHCOURSE! hank: or more probably you'd like to do well on your test me, actually out loud: YOU GET ME HANK

"you're going to need to know these things, I'm sorry"

The dislikes are GCSE students who dont get this because all they have to learn is carbon dioxide + water + light energy → carbohydrate + oxygen LOL

#LastMinuteAPBioKids

Why do i even bother going to school? I spend hours listening to lectures and watching slides and not understanding a thing while crash course needs just 13 miserable minutes to do the job. Jeez

Only half way threw and already have a page of notes. Also every time he says ps2 I think he mean the Sony gaming console

Parents don’t freak out over their 12 year old getting abducted by a celebrity... they’re the ones that sold us to One Direction in the first place

I just started revising Photosynthesis for my AP Bio exam tomorrow, I'm doomed.

This photosynthesis stuff is so confusing...thanks Hank for all your help, but I'm still feeling really queasy about my Bio quiz tomorrow...

Watching for my exam tmrw PRAY FOR ME!!

5:52 thank you for this iconic moment hank, thank you !!

4:55 the analogy with the mother chlorophyll freaking out about losing her electron gets kind of dark cause then to fix the problem she steals someone else's child.

Whos watching this in 2016?

Your sarcasm is absolutely off the charts... im loving it

Never have I ever been so thankful for a video in my entire life. Thank you, Crash Course!

Hank Green, I just might pass my biology test in the morning because of you.

My exam is in 2 hours and I'm just starting this now. Thank you, Crash Course!!

I love the comments on crash course, they are so relateble! XD

I'm here just because wanted to look at animations and color rather than staring at a black-and-white textbook for hours.

oh my god i have no idea what is going on in this video

#CrammingForAPBio

this was the hardest episode to watch by far. for what reason? no clue

watching this the day before my ap bio exam : )

I laughed so hard when he was talking about the 12 year old girls moms shouting "HOW DO I FIX THIS PROBLEM?" LOL

What a cool nerd

hey thank you so much for all the time, and passion, you put into these videos to help us all understand how these processes work! Just overall your animations and everything is great!

I am committed to having a better deeper understanding of our world

This video was a lot more enjoyable to watch when I didn't have a test the next day

I was so excited, my biology teacher showed this to my class, and I literally fangirled because I love Hank. He's a really good teacher and I've just been having a lot of trouble this whole year trying to understand biology in general. Now I know that I really should just crash course my material before the test, because this is easier to understand.

0:17-0:23 he admitted it I don't think even teachers would deny it

this is actually one of the best photosynthesis videos ever you just need to prep a little beforehand to understand it

A moment of gratitude for Hank Green for the hope of a decent grade on my exam tomorrow.

It goes over your head the first time, but if you break it down and make notes as you go EVERYTHING MAKES SO MUCH SENSE OMG THANKYOU HANK!!!

who's got an ap exam tomorrow

When biology became a reference of the abduction of a 12 years old by a teen idol...

Studying for my Biology Honors Semester Exam... Yay!? 0.o

I have a biology exam in under 5 hours I'm gonna fail so I'm cramming

Anyone else cramming before the ap bio exam?

Okay guys if you're craming (like I normally am when watching these) turn on closed captions (CC button, select your language), they help you focus and understand what he's saying and they're great for if you're writing notes too Hope you do well on your test!