植物は水と光を必要とします
I don't understand the second particle と here. I was taught 必要があります, and I don't understand this construction, the は is also confusing to me, I would have used に. Shouldn't it be:
植物に水と光(を)必要があります
Parsed as "water and light are necessary to plants"
The first と between 水 and 光 is "and".
The second と before します is part of the A + を + B + とする construction, which means "to think of A as B", "to use A as B", "to consider A B", "to make A B", and so on.
You can find other verbs that take this type of と in this answer.
So Aを必要とする can be translated very literally as "to think of A as necessary", but you can think Aを必要とする is a set phrase that just means "to require/need A".
植物は水と光を必要とします。
Plants require water and light.
植物に水と光を必要があります is ungrammatical and makes no sense (ある is the only verb in the sentence, but it's an intransitive verb that never takes を).
The main difference between these two expression is that ~を必要とする "to require something" takes noun, while ~必要がある "to need to do something" takes verb (in 連体形). So if you use 必要がある, you have to add appropriate verb like below.
植物は水と光を得る必要があります。"Plants need to get water and light."
植物に水と光を与える必要があります。"(Anybody or somebody) needs to give water and light to the plants." (This sounds bit strange if "plants" refer to those in wildlife, though)
I was taught 必要があります-- Which were you taught, 「Noun+の+必要があります」construction (eg 再検査の必要があります), or 「Verb+必要があります」 construction (eg 検査を受ける必要があります) ? ....... By the way, we also have 「Noun+が必要です」 eg 植物(に)は水と光が必要です。 – chocolate Oct 16 '23 at 14:24