The episode begins with Gumball and Darwin about to leave for school when the latter points out that the week that this episode takes place in most likely has a theme for their school. Gumball, exasperated from numerous theme weeks taking place at school, airs his grievances by recounting multiple weeks of restoring everything to normal after Cake Week (followed by cake crumbs week, ant week, how to get rid of ants week, anteaters week, and how to get rid of anteaters week.)
While trying to figure out what theme the week has this time, Darwin suggests that it is Technology Week only for Gumball to remind him that the theme was already done. The latter recounts the time where they participated in that theme and tried to socialize with Bobert; however, their attempts to participate comes off as misunderstanding and somewhat offensive to the robotic student (such as assuming he knew a vacuum cleaner, or walking robotically upstairs).
Back in the present, Gumball suggests that they have not done History Week only for Darwin to remind him that he did not participate. Darwin proves this by reflecting on the time where he was dressed as a pilgrim, but Gumball was still dressed as a panda from Endangered Species Week from the week prior. In his defense, he claimed that since his costume was a thing of the past, it technically was history and claims that pandas as a species are history. Darwin sees through this façade and asks if his brother forgot, to which he admits.
Darwin begins to become anxious after realizing that they forgot what that week's theme was.
The scene cuts to Gumball and Darwin wearing a myriad of thematical costumes as they wait for the school bus; when Darwin begins to feel unsure about their attire, Gumball reassures him that they have every theme covered. When the boys get on the bus, however, they come to realize that the theme was Green Week. Rocky confirms this as he starts to drive to school and points out that he filled up the bus' gas tank with cod oil rather than diesel. Not too long after driving, the bus breaks down and Rocky realizes that he should have used sunflower oil in the engine and not cod oil.
The students begin their walk to school and just when Sarah is getting exhausted from the heat, Darwin compliments her earth-designed ice cream head by pointing out her supposed attention to detail. When he points out that the ice caps depicted in the design are melting, Sarah is quick to correct him by saying it was a hot day and sounds slightly offended by him pointing out a real world problem. Gumball then notices Tobias' green color and assumes the green theme to his body was an effort to participate in Green Week; however, he is quick to correct him by saying it is food poisoning, and vomits not too long afterwards leaving Gumball and Darwin disgusted as they walk away. To their surprise, the boys see Bobert standing on the sidewalk having not participated in the theme, but realize that he is installing updates. Teri walks by and explains that Bobert is always taking part in Green Week since he turns off every night, but takes ninety minutes to reboot every morning.
Darwin concludes that they are the only ones who have not participated, but Gumball is quick to reassure him that in his opinion there's nothing special about plants. He takes this further by coming up with a superhero scenario where the hero is named Tree Man (to the interest of Sarah, whom begins to take notes) rather than any other name that references an animal or an insect. When he calls plants pointless, Leslie gains the boys' attention and airs his grievances towards that remark. Trying to save face, Gumball quickly corrects himself and tells Leslie that he thinks plants are very important. After failing to convince Leslie that he thinks of plants in a positive manner and knows about them, Gumball laments on how his relationship with Leslie was damaged from his lack of knowledge on plants in general.
When Darwin tries to prove a point, Gumball is unable to properly recall ecosystems that have trees (for example, forgetting the name of the rainforest and calling it a big green thing.) When he recalls the rainforest, he is unable to determine whether the issue was that there was too much of it, or too little of it. Darwin informs his brother that in order to gain Leslie's forgiveness, he is going to have to become aware of plants and build knowledge on that awareness through research. Gumball agrees and the scene cuts to the library where they consult the librarian, about a book on the history of plant culture. Rather than providing a book, the Tree Librarian suggests coming to her lecture on plant history only for Gumball to decline the offer and opt to receive handwritten notes instead. When the Tree Librarian reveals a large stack of notes, Gumball asks if she has notes for the notes, but they are not any less complicated than the original notes. Exasperated, Gumball simply says that he wants a quick summary of just one word; the Tree Librarian summarizes it by saying "photosynthesis." Eventually she asks the boys to leave, but even though Gumball does not know the meaning of the word he just heard, he becomes more than willing to use it in front of Leslie to impress him.
The scene cuts to Leslie studying from a math textbook outside during his free time, but Gumball walks past him feigning a conversation with Darwin about photosynthesis. Leslie picks up on this when he is greeted by the blue cat and decides to test Gumball's knowledge about how photosynthesis works by saying it is more of a plant thing. Gumball continues to show off while trying to earn back Leslie's respect by saying that he does it out of respect for plant culture.
Leslie continues to try to see through Gumball's facade when he further notes that the sun was up for a less amount of time than when the cat claimed to have photosynthesized, but the feline reasons with the flower by saying he had his own way of bypassing the requirements to have sunlight. Leslie suggests photosynthesizing that afternoon to see if Gumball was willing to prove that he knows about plants; after three minutes of standing in sunlight, Gumball's body begins to shrivel up from the heat. Leslie eventually leaves him alone to "photosynthesize." Gumball eventually breaks out of his shriveled up body as if he was a snake, which leaves Banana Joe horrified between the time he witnessed it up until being served dinner at home.
Later that night, Gumball vents to Darwin, to the point of the latter's exhaustion, about how Leslie's successful attempts to get back at him went too far. When Darwin suggests going to sleep, he claims that he cannot get comfortable with third degree sunburns all over his body and has been shown to have been trying to get comfortable by sitting in Darwin's fishbowl with ice in it. Darwin eventually tries to reason with him that revenge was an obvious route for Leslie to take and tries to persuade his sunburned brother into forgiving the plant and moving on. Unfortunately, Gumball fails to see the true meaning behind Darwin's cryptic advice when he says to "draw a line under it."
The next day, Leslie is drinking from an orange juice carton when Gumball approaches him and reveals that for lunch, he plans on eating a bucket of soil to prove he knows about plant culture. When Leslie picks up on what Gumball is trying to accomplish, the plant refuses to be proven wrong and claims that eating soil is what plants do, but begins to regret saying that when he too is given a bucket of soil to eat. He attempts to get out of the situation by saying he already ate lunch, unfortunately Gumball was watching him for the last three hours and concludes that Leslie had no lunch. Seeing no other way out of it and not wanting to prove each other right, Gumball and Leslie eat a spoonful of the soil.
Leslie gets back at him by turning on a fire hose and explains that watering is vital for a plant's health and blasts Gumball with water with pressure that is so high that he gets blasted through a fence, down a street, through the pool room in the school and goes up the slide, interferes with a crime scene put together by the Doughnut Sheriff and two French fry officers, and interrupts a marathon by distracting a struggling runner into thinking that he will finish the race quicker with the high pressured water.
Back at school, Gumball dumps a box of bees into a classroom's window with Leslie inside. Leslie is far from welcoming of the bees' presence as they swarm him. The scene cuts to a forest where Leslie, covered in bee stings, throws bird seed at Gumball to attract hungry birds to peck at him. Gumball and Leslie are then seen underwater, with Leslie nearly drowning at the bottom of a lake as they converse about this being a plant thing.
Finally, Gumball and Leslie are shown skydiving without parachutes; this is where Gumball admits that he knows nothing about plants and the two of them finally work things out between them by pointing out that they saw through each other's facades. Upon apologizing, they become friends again and nearly fall to their deaths until Leslie sprouts seeds and floats the both of them safely towards the ground.
Leslie is still convinced that Gumball knows nothing about plants and suggests that he should go home to get milked. The episode ends with Gumball becoming offended at Leslie for such an idea.
[Gumball and Darwin grab their backpacks and are about to go to school]
Darwin: Wait, isn't there some kind of theme at school this week?
Gumball: Argh, I hate all these theme weeks! Cake week, cake crumb cleanup week, ant week, how do we get rid of ants week, anteaters week, how do we get rid of anteaters week. What is it this week?
Darwin: Technology week?
Gumball: No, that was three weeks ago.
[Flashback to three weeks ago. Gumball and Darwin are standing in the hallway with Bobert, dressed up like robots]
Gumball: Happy technology week, Bobert! Hey, who's your little friend?
Bobert: That is a vacuum cleaner. Do you assume all machines know each other?
[Gumball tries to say something to defend himself against Bobert's sound argument, but he cannot. He and Darwin silently walk away toward a flight of stairs]
Darwin: Dude, Technology week, remember?
[Gumball and Darwin move like robots. Darwin moves his cardboard robot body but gets exhausted after only four tiny steps. Gumball barely makes it up to the second step of the stairs before he falls onto his back with his arms and legs still moving, like a robot]
Bobert: Not helping.
[The flashback ends]
Gumball: Oh, we haven't done history week!
Darwin: No, you haven't done history week.
[Flashback to history week. Darwin is walking down the hall and sees Gumball dressed up like a panda]
Darwin: Why are you dressed as a panda? It's history week. Endangered species week was last week.
Gumball: Exactly. I'm dressed up as last week, that's history, right? Anyway, surely pandas are history by now.
Darwin: You just forgot, didn't you?
[The flashback ends]
Darwin: Okay, we're definitely going to mess this up again! We don't even know what the theme is!
Gumball: Don't worry, I've got this.
Darwin: I'm not sure about this.
[Gumball and Darwin are wearing multiple parts of different themed costumes]
Gumball: Ah, come on. Chill. We've got all the bases covered.
[The bus comes to a stop, and Gumball and Darwin board it]
Gumball and Darwin: Huh?
[The students already on the bus are wearing several environmentally-themed constumes]
Gumball: Oh, it's green week.
Rocky: Yeah! I even filled up the bus with cod liver oil instead of gas!
[The bus suddenly breaks down and comes to a stop]
Rocky: Wait, it's sunflower oil that works in engines. Well, looks like you're walking to school. And it was so difficult squeezing all those fish into the gas tank. [Sniffs his hand and gags]
[All the students are seen walking on the sidewalk to reach school]
Darwin: Sarah, great detail! Even your ice caps are melting.
Sarah: Actually, it's just a hot day, but thanks for pointing it out, Darwin.
[Sarah scrapes off some of her globe face-painting making it look like it's really melting. Gumball and Darwin see a tired Tobias with a green gradient over him]
Gumball: Whoa! Love the green rainbow, Tobias!
Tobias: It's not a costume... I think I have food poisoning— [Vomits]
Gumball and Darwin: [Disgusted] Ugh!
Gumball: Hey, Bobert! Thank goodness. Glad we're not the only ones who've done nothing for Green Week—
[Bobert looks like he's been shut down]
Gumball: Bobert? [Inspects his face] Installing updates?
Teri: Actually, Bobert is taking part. He turns himself off every night. Unfortunately it takes him ninety minutes to reboot.
Darwin: Oh. We are the only ones then.
Gumball: Ah, well, it's only Green Week. I mean there's nothing special about plants. Think about it. Superheroes are all named after animals and insects for a reason. [He impersonates a narrator with heroic music in the background] The city's been invaded by evil alien robots, but fear not, Tree Man will save us! [Normally] By silently standing in a field with nothing but the power of going bald annually.
Sarah: [Gasps and takes out her notebook] I can already see the merch!
Gumball: Yup, plants are pointless.
Leslie: Eh-hem! I'm a plant! I think we're pretty important!
Gumball: Leslie! Yeah, m-me too! Plants do loads of important things!
Leslie: Really? Name one.
Gumball: Only one? But there's so many!
Leslie: Okay, then give me five.
Gumball: Let's just start with one, shall we?
Leslie: Okay, then give me one.
Gumball: Uuuuuuhhhhh....... salad!
Leslie: [Unimpressed] Salad?
Gumball: Yeah...... yeah, this whole thing is coming out wrong! Lettuce-I mean let us forget about it! It's clearly thorny issue. Thorny!? Uhh, we should just nip it in the bud.
Leslie: No, let's not! That phrase is actually incredibly offensive to plants! Hmph! [Storms off in a huff]
Gumball: Leslie, wait! Let me explain!
Gumball: Ah, sorry, I got nothin'. I didn't think you'd actually turn around.
Leslie: Hmph! [Walks off]
Darwin: You wanna do it, or shall I?
Gumball: You do it.
[Darwin shoves Gumball's feet into his mouth]
Some Research on Plants
[Elmore Junior High, in the hallway]
Gumball: I can't believe Leslie thinks I don't care about plants!
Darwin: Well, do you?
Gumball: Yeah! I care loads! What about the, you know, big thing? The big green thing?
Darwin: The woods?
Gumball: No no, the other one. Bigger. The wet one.
Darwin: The rainforest?
Gumball: The rainforest! Yeah, the rainforest.
Darwin: What about the rainforest?
Gumball: Well, isn't it that there's too much of it? [Pause] Or....not enough?
Darwin: Which one?
Gumball: Too much?
Darwin: Wrong. If you wanna get Leslie to forgive you, you're going to have to do a whole lot of research.
Gumball: Oh yeah. Absolutely. I mean, that's very important, of course. [Pause] About what?
[At the school library. Gumball approaches the librarian, who is turned around at her desk.]
Gumball: Excuse me, I'm—
TreeLibrarian: Computers one, three, and four work. Please surf responsibly.
Gumball: Actually, I'm here for some books.
TreeLibrarian: [Whips around and drops her book] WHAT??!! Shh! Quiet! Sorry, I'm just excited! Kids only come here for the computers!
Gumball: Yeah, no, I wanna learn about the history of plant culture!
TreeLibrarian: Ah, you're in luck! I'm doing a lecture on plant history soon, and—
Gumball: Ooooh, sorry, I'm... busy that day.
Darwin: [Whispering] She didn't say when it was.
Gumball: Could I just have the notes?
[The librarian reaches behind her and slams a huge stack of papers onto her desk]
Gumball: Do the notes have notes?
[She reaches behind her again and slams another huge stack onto her desk]
Gumball: Could you just summarize it for me?
TreeLibrarian: You want me to summarize the entirety of plant culture and history?
Gumball: Yeah! Preferably in one word.
Gumball: One that I know?
[Back in the hallway]
Gumball: Well, I did learn one thing: the word photosynthesis. It's my way in!
Darwin: Do you even know what it means?
Gumball: [Blows raspberry] That's not the point. Like, why would you bother learning Australian when you can just wear the hat with the dangly cords and skip right to the good stuff?
Darwin: Is Australian a language?
Gumball: Hm. I guess we'll never know. Anyway, I'm gonna go talk to Leslie about sotophynthesis before I forget how to say it.
Gumball: Yep! Photosynthe-see you later! [Runs off]
An Amazing Photosynthesis Session
[In the courtyard, Leslie is reading while Gumball walks in front of him, talking on his phone]
Gumball: Yeah, yeah, totally. It was an amazing photosynthesis session. [This catches Leslie's attention] You shoulda seen me, everyone was like, slow down, you're doin' it too hard, but I was like, nah, I'm in the zone! Yeah. Cool. Speak to you later, Darwin. [His phone beeps]
Phone: Calling Darwin.
Gumball: [Frantically hangs up] Oh hey, Leslie! How's it growin', my man?
Leslie: So, you've been photosynthesizing? Isn't that more of a plant thing?
Gumball: [Stretching] Yeah, but I just respect the plant culture so much I got into it, you know?
Gumball: Yeah, I've already done, like ppphhh, eight hours today.
Leslie: But the sun wasn't up eight hours ago.
Gumball: Mmh. I got a method.
Leslie: Well, I was about to do some now, do you wanna join me?
Gumball: Cool, yeah, count me in! I might just do mine in the shade, though.
Leslie: Hah! Nice one. [Gets off the bench] Right. Let's face the sun full-on so we can really get into it!
Gumball: Oh. Yeah, of course. It's gotta be in direct sunlight, I was just kidding. That was a joke I got from....uh, Photosynthesis Weekly! MONTHLY!!
Leslie: Oh, you read PM too? What did you think of the latest issue? Controversial, right?
Gumball: I think... everything that can be said about it has been said!
Leslie: [Whispers] You're so right. Well, let's settle in, then. [Gets into position]
[Later, Leslie is happily photosynthesizing while Gumball is completely dehydrated]
Gumball: Aaahh! Gotta love that heat, right?
Leslie: Ho-ho, you wait till it really kicks in at noon!
[Noon. The sun is blistering. Gumball is even more dried out than before, while Leslie still photosynthesizes peacefully]
Gumball: How long have we got now?
Leslie: 'Bout three minutes.
Gumball: Hooooo!! Have you got any water?
Leslie: Sure! You gotta have water for the session, right?
[Leslie takes a water bottle from his backpack and hands it to Gumball, who starts to drink from it]
Leslie: What are you doing? Plants drink like this! [Pours some water into his roots] Ahhh. Allow me. [Smugly pours the rest of the water at Gumball's feet] Drink up!
[The bell rings]
Leslie: I've gotta go. But a guy your size, you're gonna wanna stay out here for at least another couple of hours, right?
[Gumball responds with a dehydrated scream]
Leslie: Oh-okay, time for me to leaf![Leans in and whispers] That's a plant joke, since I know you love plants so much. Ciao! [Walks off]
[Suddenly, two blue arms rip out from underneath Gumball's dried-up skin. A newly shed Gumball tears out, completely naked, and curls up on the ground, shivering in fear. As ominous music plays, Banana Joe, in the background, sees this, and his eyes go wide in terror. Cut to him pulling the same expression on the bus and then in the shower, still holding his ice cream which gradually melts]