Alevel生物哺乳动物知识点梳理！哺乳动物的运输（上）

　　正如大家所知，Alevel生物课程的难度相对于国内生物课程的难度要稍微高一些。它不仅仅体现在实验操作性强上，更在基础知识的深度和广度上。在学习的过程中，很多同学反映不知道怎么记忆那些知识点，也不知道如何将知识点运用到实践中，在写论文时更是发愁。针对这些困难，小编为大家梳理了中英对照版本的alevel生物知识点梳理，共分为三篇，同学们可持续关注获得更多资料，那么现在就一起来看看吧！

　　A recurring theme in biological systems is the surface area to volume ratio. All cells require nutrients and most require oxygen as well. Wastes also need to be removed.

生物系统中一个反复出现的主题是表面积与体积的比率。所有的细胞都需要营养物质，而且大多数也需要氧气。废物也需要被清除。

　　With a small organism this demand can be met by simple diffusion over the body surface but larger or very active organisms need a transport system with a pump to ensure that the supply meets the demand of all cells, even those deep within the body.

　　对于一个小的生物体来说，这种需求可以通过在体表的简单扩散来满足，但较大的或非常活跃的生物体需要一个带有泵的运输系统，以确保供应满足所有细胞的需求，甚至那些在身体深处的细胞。

　　In mammals, the pump is the heart. Substances are carried in a transport medium of the blood. The blood is contained within vessels, with substances being released out of, or into the blood as it flows through certain vessels called capillaries.

　　在哺乳动物中，这个泵就是心脏。物质在血液的运输介质中被携带。血液包含在血管内，当血液流经某些被称为毛细血管的血管时，物质被释放出来或进入血液。

　　Blood vessels 血管

　　Blood is carried within a closed transport system that is made up of three types of vessel 血液是在一个封闭的运输系统内进行的，该系统由三种类型的血管组成:arteries 动脉、capillaries 毛细血管、veins 静脉

　　Arteriescarry bloodawayfrom the heart. 动脉将血液带离心脏。

　　Capillariesare the site of the exchange of materials between the blood and tissues.Veinstake blood back into the heart. 毛细血管是血液和组织之间物质交换的场所。静脉将血液带回心脏。

　　Arteries 动脉

　　Blood pumped out of the heart is at a very high pressure, so the structure of the arteries must be adapted to this. They can withst and high pressure by having very thick walls made up of elastic fibres and smooth muscle. These allow the wall to stretch as blood surges through them so that they don't burst or rupture.

从心脏泵出的血液处于非常高的压力下，因此动脉的结构必须适应这种情况。它们可以通过拥有由弹性纤维和平滑肌组成的非常厚的管壁来承受高压。这使得血管壁在血液涌入时能够伸展，从而不至于爆裂或破裂。

　　It also means that as the artery increases in diameter, the pressure is reduced a little. After they 'give', the elastic fibres recoil back inwards as the pressure falls. The artery decreases in diameter thus raising the pressure a little.

这也意味着，随着动脉直径的增加，压力会降低一些。弹性纤维在"给力 "后，随着压力的下降向内回缩。动脉的直径减小，从而使压力升高了一些。

　　The lowering of the pressure when it is high, and the raising of it when it is lower produces some smoothing out of the flow of the blood. It should be obvious though when you feel your neck or wrist that it is by no means complete - you can still feel the pulses of the flow some distance from your heart.

当压力较高时，压力降低，当压力较低时，压力升高，从而使血液流动变得更加顺畅。但当你感觉到你的脖子或手腕时，应该很明显，这绝不是完整的--你仍然可以感觉到离你的心脏有一段距离的血流脉冲。

　　A large artery will split into smaller arterioles that then branch further into many tiny capillaries. Arterioles have walls with a similar structure to arteries but have a greater proportion of smooth muscle and less elastic tissue. They do not have to withstand as high a pressure as arteries and have the ability to contract because of the smooth muscle and regulate the flow of blood to a tissue.

　　一条大动脉会分裂成更小的动脉血管，然后进一步分支成许多微小的毛细血管。动脉小管的管壁结构与动脉相似，但平滑肌的比例较大，弹性组织较少。它们不必像动脉那样承受高压力，并且由于平滑肌的存在而具有收缩能力，可以调节血液流向组织。

　　以上就是小编为大家整理的有关Alevel生物的知识点梳理，希望对大家有所帮助，祝学业有成金榜题名！如有更多有关Alevel课程辅导的需要，欢迎来联系在线客服老师，会获得更多专业的指导哦～