Having read the first four answers, I'll try to describe my understanding of this issue (I'm not a native speaker of English, and Russians tend to make many article usage errors, that's why this question interested me).
Imagine that you have opened a plant encyclopedia at a random page. At the top of the page, you see "Banana": the title of a long article. Then you ask your friend to read a random sentence from that article. He reads:
Bananas grow in tropical climates.
Can you guess from what part of the article this sentence is? It is most likely from the very start of the article. It's part of the basic description of bananas.
To understand fully the meaning of this sentence, you don't need to ask your friend to read a sentence preceding it, or a sentence following it. It's a very "self-contained" sentence. It conveys a generic fact.
We have a class of fruit called "bananas". Not some specific bananas, but generic bananas; an undifferentiated whole called "bananas". We have a class of climates called "tropical climates". Not some specific climates but just "tropical climates" as an undifferentiated whole.
Next, you ask your friend to read another random sentence. He reads:
Bananas grow in a tropical climate.
Now it's more likely that this sentence is not from the introductory part of the article. You feel that in order to understand the meaning of this sentence, you'd need to ask your friend to read the preceding sentence, and probably the following sentence.
He reads the sentences surrounding this sentence, and it becomes clearer:
[...] Studies have shown, however, that this technique works best when the fruit grows well in a subtropical climate. Bananas grow in a tropical climate. Not in any other. Our geneticists will need an additional decade to adapt this technique", said Dr. Moghaddam.
This sentence is not so "self-contained". You needed to read additional sentences to work out its meaning. There is a contrast between a subtropical climate and a tropical climate. Furthermore, it's a quote from speech, and sentences are 'broken apart'. Had it been a written communication, Dr. Moghaddam would've wrote:
Bananas will grow in a tropical climate, but not in any other.
Thus, the sentence with a tropical climate does not work well as a standalone sentence relaying some generic fact. This is even more evident in Ed Rutmayer's answer, where the sentence serves as a reply to a question:
-"What types of things grow in a tropical climate?"
-"Bananas grow in a tropical climate". (the answering person here stresses the word bananas using intonation (prosody))
We can construe another question:
-"What bananas do a tropical climate?"
-"Bananas grow in a tropical climate." (Here, the stress in speech falls on grow)
Thus, while the sentence with a tropical climate is not ungrammatical, it does not fit well as a "self-contained" sentence in the way the sentence with tropical climates does. The sentence with tropical climates is "more generic".
Why is it so? In my opinion, the key linguistic term to google about is "generic noun phrase". From the linguistic standpoint, we can form a generic noun phrase in several ways:
The tropical climate is the best climate for these plants. (Not some specific climate: a generic "tropical climate"; we use the definite article the)
A tropical climate is better than an arctic climate. (Not some specific tropical climate: any representative member of the class 'tropical climate'; we use the indefinite article a)
Tropical climates have been studied a lot over the last 100 years.
The problem is that there are slight differences in meaning between a 'indefinite generic' noun phrase, a 'definite generic' one, and a 'plural generic'. According to Quirk et al. (1985),
- The generic use of a picks out ANY REPRESENTATIVE MEMBER OF THE CLASS. (from Unit 5.53)
- The generic use of the zero article with both plural nouns and noncount nouns
identifies the class considered as an UNDIFFERENTIATED WHOLE. (from Unit 5.54)
- The is rather limited in its generic function. With singular heads, it is often formal or literary in tone, indicating THE CLASS AS REPRESENTED BY ITS
TYPICAL SPECIMEN (from Unit 5.55)
Furthermore, the authors of the book write (Unit 5.52) that then the noun phrase is not the subject in a clause, it could lose its generic function. They provide an example in which the 'definite generic' retains its generic nature, the 'plural generic' is somewhat changed in meaning, and the 'indefinite generic' loses its generic function.
Nora has been studying the medieval history play. ("mystery plays as a genre"; generic meaning)
Nora has been studying a medieval history play. (one specific play; the meaning is non-generic)
Nora has been studying medieval history plays. ("most likely refers to a subset of plays")
Furthermore, other parts of the sentence, such as verbs, play a role in determining whether a noun phrase is generic and what shades of 'generic meaning' it has. There's a 55-page PDF titled "Generic Noun Phrases" written by Jown Lawler that shows just how complex this issue is.