The sporopollenin exine surface possesses phenolic, alkane, and carboxylic acid groups. Accordingly, sporopollenins would be a promising low-cost biosorbent for the removal of heavy metals from aquatic media.

Although structures of sporopollenins from various lower and higher plant species have been investigated in previous studies, the role of the structures in the sorption of HOCs has not been examined. 

这是一篇科技论文，请问老师，the removal 和 structures 都是第一次提到，the removal加the是因为下面原因，但是为什么structures 也是被of限定，却不用加the呢？

.DET 限定词(当名词后接 of 短语或表明身份的从句时，该名词前用the) You use the at the beginning of a noun group when the first noun is followed by an 'of' phrase or a clause which identifies the person or thing.

There has been a slight increase in the consumption of meat...

肉类消费量略有增长。

Of the 9,660 cases processed last year, only 10 per cent were totally rejected.

去年受理的 9,660 宗案件中，只有 10% 被完全驳回。