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 facade 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's gas tank with another kind of oil rather than diesel. Not too long after driving, the bus breaks down and Rocky realizes that he should've used sunflower oil in the engine and not fish 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's 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 said 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; 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 suggest 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.
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?
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.
Are Plants Pointless?
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.
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 texture all over him.]
Gumball: Whoa! Love the green rainbow Tobias!
Tobias: It's not a costume... I think I have food poisoning--[vomits]
Gumball & 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 90 minutes to reboot.
Darwin: Oh. We are the only ones then.
Darwin: You wanna do it, or shall I?
Darwin: Well, do you?
Darwin: The woods?
Darwin: The rainforest?
Darwin: What about the rainforest?
Darwin: Which one?
Darwin: Wrong. If you want Leslie to forgive you, you're going to have to do a whole lot of research.
Darwin: She didn't say when it was.
Darwin: Do you even know what it means?
Darwin: Is Australian even a language?
Drawing A Line Under It
Darwin: Yes. Can we please just go to sleep?
Darwin: Look, you upset him and he got you back. Maybe you should just draw a line under it.
Darwin: Good. I feel like we're on different pages here.
It’s a Plant Thing
[ Leslie is drinking from an orange juice carton during lunch. Gumball approaches him.]
Gumball: Mind of I join you? [grinning evilly]BUDDY?
Leslie: Don't you usually have lunch with Darwin?
[ Gumball opens of a box full of bees, releasing them into the classroom.]
Gumball: Naw, it's a plant thing!
Leslie: [offscreen] But are they dangerous??
Gumball: That's fine as long as you don't aggravate them. After all, Bees are just overweight wasps!
[ Gumball closes the window, puts sunglasses on leaves Leslie in the classroom, freaking out as the bees swarm his face.]
Leslie: Ahh! Aaah! Oh!.. AAAAHH!!!
[Leslie; covered in bee stings throws bird seed at Gumball to attract woodpeckers to peck at him.]
Gumball: Don't tell me. Plant thing?
Leslie: Guess so.
[Leslie is chained to the bottom of the lake while Gumball wear scuba gear]
Leslie: Plant thing?
[Finally, Gumball and a evil grinning Leslie are shown skydiving]
Gumball:--AAH! OKAY! I GIVE IN! I might not know anything about plants, but skydiving without a parachute is definitely NOT A PLANT THING!
Leslie: Aha! So you admit it! You DON'T know anything about plants!