ALEVEL生物A2光合作用 有氧呼吸作用精讲 白送分还不要吗

ALEVEL生物A2中光合作用和呼吸作用的权重会比AS阶段高出不少，但很多同学在实际学习过程中会有越学越糊涂的迹象，今天就为大家从定义、发生细胞器等多个角度区分下这2个作用，争取一次弄清。

要知道ALEVEL生物A2的光合作用和呼吸作用的考核方式都很固定，如果不把这部分知识点牢牢握在手里，就等于白送分了。

一. 定义的区分

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。

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.发生细胞器的区分

1.光合作用 chloroplast

光合作用是植物、藻类等生产者和某些细菌，利用光能把二氧化碳、水变成有机物（碳水化合物）并释放出氧气的过程。 

 光合作用方程式： [公式] 二氧化碳+水=光（条件） 叶绿体（场所）=有机物（储存能量）+氧气

2.呼吸作用 mitochondria and cytoplasm

呼吸是一种气体交换，即水果吸进氧气放出二氧化碳的过程，呼吸既是消耗有机物的过程，同时，一切生命活动所需要的能量都要依靠呼吸来提供，水果采后各种合成过程的原材料也是呼吸的分解产物。所以大家不能把呼吸单纯地看作是一个消耗过程。

三. 具体流程的区分

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 pigment are 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 formed and The electrons in water replace the electrons that have left the primary pigment.

-The excited electrons 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 the ATP 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 converted to glycerol and fatty acids to produce lipids for cell membranes or acetyl coenzyme A (CoA).

以上就是ALEVEL生物A2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.Glycolysis in 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

今天对ALEVEL生物A2光合作用与呼吸作用的对比介绍就到这里。虽然这2个作用比较复杂，但只要多理解、多提问，一定能做到熟练掌握。考试时该拿的分都拿到了，终分一定不会差。

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也就是说，不管明年大考能不能正常举行，同学们都要有危机意识，一方面努力复习，面对明年大考的顺利开考。一方面要注重平时成绩的提优，在导师那里拿到更高的预估成绩。如果这对你来说压力很大，点击预约试听【ALEVEL同步培训班】，紧贴学校学习进度，每周一次解决积累的学习难点，强化答题技巧。

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