A-level生物| 光合作用、有氧呼吸作用还分不清楚？该看看了！

A-level生物| 光合作用、有氧呼吸作用还分不清楚？该看看了！

A2 生物中，对光合作用以及呼吸作用都进行了更加详细且复杂的讲述。比重比As中出现的可谓是多出了好几倍，有的学生一开始学就满头雾水，经过长期的阅读和复习，甚至有出现混淆二者的情况。这实数不该，因为在paper4中，光合作用、呼吸作用这两个章节考的主要都是死板的知识点，哪怕有一些分析，也都是在浅显的知识上稍加思考就能得出来的。可以说是必须拿到的分数。

那么下面我们开始进行整理。

一.定义

最简单的层面一定要牢牢记住，光合作用是利用太阳的能量去生产葡萄糖，油脂等大分子有机物去储存能量。而呼吸作用则是相反，他是释放能量的过程，主要能量来源就是这些大分子有机物，葡萄糖，蛋白质，油脂。二.发生细胞器

1.光合作用chloroplast2.呼吸作用mitochondria and cytoplasm

三.具体流程

那么我们先来仔仔细细的看看光合作用吧。光合作用可以分成两个大部分，light-dependent reaction and light-independent reaction。以下的文字我将用英文写，这样大家记住之后，就可以更轻松的写进试卷。1.light dependent reaction (Non-Cyclic photophosphorylation)

-Accessory pigments in PSII absorb photons of light, and the energy is passed onto primary pigment (chlorophyll?).-electrons on the primary pigmentare excited （photoactivation）to a higher energy level causing them to escape and also causes the splitting (or photolysis) of water molecules.(2H2O→O2 + 4H+ + 4e? )-O2 diffuses out of the chloroplast and into the air. Also, the protons build up in the thylakoid lumen causing a gradient to be formedand The electrons in water replace the electrons that have left the primary pigment.

-The excitedelectrons are taken up by electrons acceptor, and are passed down electron carrier chain. They are passed from PSII to carrier proteins, where the energy is used to pump protons from stroma to lumen; then to PSI, where more light energy is absorbed by the chlorophyll molecules and the electrons is excited again.

-The Electrons then recombine with a proton to form a hydrogen atom, which is taken up by the hydrogen carrier NADP forming Reduced NADP.-The combination of the water splitting and the proton pumping caused protons to build up inside the thylakoid lumen, generating a proton gradient across the thylakoid membrane. ATP is therefore photophosphorylated using the ATP synthase enzyme in exactly the same way as respiration.light dependent reaction（Cyclic photophosphorylation）-Electron photoactivated and instead of falling back into the photosystem and loosing energy as thermal energy, the excited electron is captured by electron acceptor.

-It is then passed on via a chain of electron carriers, during which, enough energy is released to synthesize ATP by chemiosmosis.-Electron then returns back to Photosystem I. (refer the above diagram)2.light independent reaction-Occurs in the stroma of chloroplast and is called the Calvin Cycle. All theATP and Reduced NADP is taken from the light dependent stage.

-Carbon dioxide binds to the 5-carbon sugar ribulose bisphosphate (RuBP) to form an unstable intermediate, this is catalysed by the enzyme rubisco. The intermediate is then broken down to form 2 molecules of (3C) glycerate phosphate (GP).-GP is reduced and activated to form triose phosphate (TP). The ATP and NADPH from the light-dependent reactions provide the energy for this step. The ADP and NADP return to the thylakoid membrane for recycling.-Most of the triose phosphate continues through a series of reactions to regenerate the RuBP using ATP and complete the cycle-Some of the triose phosphate molecules combine to form glucose, starch for storage, cellulose for cell walls and sucrose for translocation around the plant.-Others convertedto glycerol and fatty acids to produce lipids for cell membranes or acetyl coenzyme A (CoA).以上就是光合作用的所有反应细节，那么现在我们来详细看看呼吸作用的反应细节。呼吸作用的小步骤会比光合作用更多，但是不需要记住那么多语言描述。1.Glycolysisin cytoplasm大家记住这些物质的转化以及生成就好。2. link reaction in matrix要记住这里是reduced NAD 而不是NADP.3.Krebs cycle大纲没有说要记住具体详细的过程，也是一样，对于物质之间的转化清楚就好。

4.Oxidative Phosphorylation and the Electron transport chain (ETC)in Cristae-Reduced NAD and FAD are passed to the electron transport chain and they release Hydrogen which then splits up into H+ and 2e--Electrons flow down ETC release energy to pump H+ ions from the matrix to the intermembrane space producing a proton gradient and H+ then move down conc. gradient through ATP synthase and form H2O by combining with oxygen and the 2e--ADP + Pi ATP , also occurs while the hydrogen passes through the ATP synthase and uses hydrogens electrical potential energy for chemiosmosis四.撰写者的话

其实要想把生物的各个难的过程搞明白，最最重要的就是在于理解，勤于发问，并自己思考解答，或求助于同班老师，光合作用和有氧呼吸作用算是相对复杂的过程了，希望同学们有时间就打开这片小文章看一看，做到熟练。