Periodically , the lamellae become enlarged, forming flattened, membrane - enclosed vesicles called thylakoids.是什么意思？

Periodically , the lamellae become enlarged, forming flattened, membrane - enclosed vesicles called thylakoids.

片层周期性地扩展, 形成扁平的有膜为界的囊,称为类囊体.

periodically

adv. 周期性地，定期地，偶尔；

例句
Henke said. " Yoko would periodically call and speak to whoever answers. "
洋 子会定期打进来,跟接电话的人讲话,不管谁接.

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

lamellae

n. 薄层( lamella的名词复数 )，薄片，瓣，鳃；

例句
The internal lamellae originate from an invagination of the inner of double membranes surround the plastid.
片层起源于围着质体双层膜的内膜向内折伸.

become

vi. 变为，成为，变得，变成；vt. 适合，适宜，相称，相当，变成，发生；

例句
...abandoned buildings that become a breeding ground for crime.
沦为了犯罪温床的弃置楼群

enlarged

v. 扩大( enlarge的过去式和过去分词 )，扩展，扩充，放大；

例句
An enlarged prostate does not necessarily mean cancer...
前列腺肿大不一定就是癌症。

forming

n. 形成，组成，构成，编成；v. 形成，构成，产生( form的现在分词 )，是，（使）成形，结成（友谊）；

例句
Everybody knows they haven't got a hope in hell of forming a government anyway.
众人皆知他们根本就无力组建政府。

flattened

adj. [医]（水）平扁的，弄平的；v. 变平，使（某物）变平( flatten的过去式和过去分词 )，彻底打败某人，使丢脸，停止增长（或上升），（把身体或身体部位）紧贴…；

例句
The city has been flattened by heavy artillery bombardments...
城市已被猛烈的炮火夷为平地。

membrane

n. （动物或植物体内的）薄膜，隔膜，（可起防水、防风等作用的）膜状物；

例句
The Acetylcholinesterase membrane fixed by activated carrier had higher enzyme activity and longer life - span.
为建立快速的痕量有机磷类的酶法分析方法奠定了基础.

enclosed

adj. 被附上的，（用墙等）围住的，封闭的，与外界隔绝的；v. （用墙、篱笆等）把…围起来( enclose的过去式和过去分词 )，把…装入信封，附入，（尤指墙、篱笆等 ）围住；

例句
The clock stands on an oval marble base, enclosed by a glass dome.
钟放在椭圆形的大理石基座上，外罩玻璃罩。

called

v. 叫( call的过去式和过去分词 )，通电话，认为，估计；

例句
He has also called for an acceleration of political reforms.
他同时呼吁加快政治改革的步伐。