Breakdown of La membrane est composée d'une couche épaisse.
être
to be
une
a / an (feminine)
de
of / from / any (in negative sentences) / about (concerning)
composer
to compose
épais
thick
la membrane
the membrane
la couche
the layer
Questions & Answers about La membrane est composée d'une couche épaisse.
Why do we use d' (from de) here instead of par to introduce what the membrane is made of?
In the passive voice, the agent doing the action is usually introduced by par. However, with verbs describing a state, an emotion, or physical composition (like être composé), we use de instead. Since the membrane isn't actively being built by the layer, but rather exists in a state of being made of it, de (elided to d' before a vowel) is the right choice.
Why is there an extra e at the end of composée?
In the passive voice, the verb is formed with être + the past participle, and that past participle must agree in gender and number with the subject. Because la membrane is a feminine singular noun, you must add an e to composé.
Épaisse means "thick". What is its masculine form, and why does it change so much?
Could I use a different verb phrase to mean "is composed of" in this context?
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