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1、Lesson Two Photosynthesis,Warmingup Words and phrases Text Analysis Simple exercise Further references,Contents,人类对光合作用的科学研究至少已经进行了300多年，最近100年来与光合作用有关的研究已经获得了6次诺贝尔奖。时至今日，仍有许多问题需要探索。,Warmingup,Melvin Calvin, (1911-1997) Nobel Laureate, chemistry, 1961,Listen to a Photosynthesis Song and relax.,CO2H2
2、O C(H2O)nO2,光能,叶绿体,光合作用的总反应式:,光合作用是植物和藻类利用自身的叶绿素将可见光转化为能量（包括光反应和暗反应）驱动二氧化碳和水转化为有机物并释放氧气的过程。它是生物界赖以生存的生化反应过程 。,光合作用概图,类囊体,叶绿素a,H2O,1.第一阶段在叶绿体的哪一部位完成的? 2.第一阶段必有的外界条件是什么? 3. 第一阶段原料有哪些? 4. 第一阶段包括哪些步骤？产物有哪些？,第一阶段,类囊体,叶绿素a,ADP+Pi,ATP,H2O,NADPH,NADP+,H+,第一阶段是吸收光能,光解水,释放O2并形成高能量的ATP和NADPH,即将光能转化为活跃的化学能。此过程在
3、类囊体进行,同时需要光光反应,第一阶段,三碳化合物,CO2,多种酶 参与,固定,五碳化合物,(CH2O)n,NADPH,ATP,第二阶段,1.第二阶段在叶绿体的哪一部位完成的? 2.第二阶段必须有光吗? 3. 第二阶段原料有哪些? 4. 第二阶段包括哪些步骤？产物有哪些？,基质,三碳化合物,CO2,多种酶 参与,固定,五碳化合物,(CH2O)n,NADPH,ATP,第二阶段,第二阶段利用光反应产生的ATP和NADPH,固定CO2,合成糖,以稳定的化学能储存在糖中（卡尔文循环）。此过程发生在叶绿体基质中，无光也能完成暗反应,基质,也可将光合过程分为3大步骤： 1）原初反应：光能的吸收、传递和转换
4、为电能； 2）电子传递和光合磷酸化：电能转变为活跃的化学 3）碳同化：活跃的化学能再转变为稳定的化学能。,碳同化的途径 A)卡尔文循环（又叫C3途径）：是最基本、最普遍的，且只有该途径才可以生成碳水化合物. B) C4途径（又叫Hatch-Slack途径） C)景天酸代谢途径（CAM）. C4和CAM途径都是C3途径的辅助形式,只能起固定、运转、浓缩CO2的作用，单独不能形成淀粉等碳水化合物。,Glossary -about the photosynthesis The process of photosynthesis- about light-dependent reactions, li
5、ght-independent reactions, chlorophyll, photorespiration etc.,Focus in,1. Absorption spectrum bs:pn spektrm ,n.吸收光谱，吸收谱,The spectrum obtained when radiation (light, ultraviolet radiation, etc.) from a source giving a continuous spectrum is passed through a substance.,Words and phrases,物质波谱及太阳光的光谱,6,
6、叶绿素的吸收波谱,光与叶绿体的相互作用,2. Calvin-Benson cycle,卡尔文-本森循环（又叫卡尔文循环、C3途径）,卡尔文循环,C3循环中反应物及产物的生成,C3途径反应过程：羧化、还原和再生 A.羧化阶段：,RuBP,Rubisco(RuBP羧化酶),PGA（2分子） 酸能量低，不能贮存更多的能量,B.还原阶段：,PGA,DPGA,GAP （3-磷酸甘油醛）,GAP是一种三碳糖，可以稳定的贮存能量，至此，消耗的光反应的ATP和NADPH，使光能转化为稳定的化学能，光合的贮能过程结束。,GAP的出路,叶绿体内,淀粉或葡萄糖（贮存形式）,细胞质,蔗糖（运输形式）,C.更新阶段：大
7、部分GAP经一系列转化，重新形成RuBP的阶段。,C3途径的总反应式可写成： 3CO2+5H2O+9ATP+6NADPHGAP+9ADP+8Pi+6NADP+ +3H+,3. carotenoid,n.类胡萝卜素,Light-sensitive, accessory pigments that transfer absorbed energy to chlorophylls. They absorb violet and blue wave-lengths but transmit red, orange, and yellow., krtnid ,辅助色素（accessory pigment
8、）：叶绿体中的类胡萝卜素含有两种色素，即胡萝卜素（carotene）和叶黄素(lutein) 。功能为吸收和传递光能，是对叶绿素捕获光能的补充 。,连续双峰400-500nm,两个吸收峰 430-450nm蓝紫光区 640-660nm红光区,4. Chlorophyll kl:rfil ,n.叶绿素,The green substance of plants by which photosynthesis is accomplished; it is usually localized in intracellular organelles called chloroplasts.,主要有叶绿
9、素a（呈蓝绿色）和叶绿素b（呈黄绿色）,叶绿体中叶绿素的分布,5. Chloroplast kl(:)rpl:st ,n.叶绿体,A plastid in which photosynthesis is carried out. Chloroplasts occur in all photosynthetic organisms except photosynthetic bacteria and blue-green algae.,叶绿体的形态与分布,叶绿体的结构 1 双层膜：内膜为选择性屏障。 2 基质：CO2同化；淀粉形成 3 基粒：由类囊体垛叠而成的绿色颗粒。,6. photophos
10、phorylation,n. 光合磷酸化作用,The synthesis of ATP from phosphate and ADP during photosynthesis, using light energy., ,futufsfrilein ,叶绿体在光下把无机磷酸和ADP转化为ATP，形成高能磷酸键的过程。,光合磷酸化的方式,7. Cyclic photophosphorylation,n. 环形光合磷酸化作用,Cyclic photophosphorylation is coupled to cyclicelectron flow, in which ATP is the onl
11、y product., ,futufsfrilein ,环式光合磷酸化： 从PS产生的电子，经过Fd和细胞色素b6/f等后，引起了ATP的形成，降低能位，又经PC回到原来的起点P700，形成闭合回路。,8. Noncyclic photophosphorylation,n. 非环形光合磷酸化作用,Noncyclic photophosphorylation is coupled to noncyclic electron flow, the electrons being used to reduce NADP+ as well as to make ATP.,非环式光合磷酸化： PS所产生的
12、电子经过一系列的传递，在细胞色素复合体上引起ATP的形成，继而将电子传至PS，提高能位，最后用去还原NADP+。这样，电子经PS传出后不再返回。,9. C3 plant,A plant in which the light-independent reactions of photosynthesis start with a three-carbon compound. Most plants are C3 plants.,n.三碳植物,Melvin Calvin, (1911-1997) Nobel Laureate, chemistry, 1961,C3循环,C3循环中反应物及产物的生成
13、,10. C4 plant,A plant such as corn in which the light-independent reactions of photosynthesis start with a four-carbon compound.,n. 四碳植物,CO2固定的最初产物为四碳化合物的途径。,具有C4途径的植物称为C4植物。只具有C3途径的植物称为C3植物。 在农作物中，只有玉米、高粱、甘蔗、黍和粟属于C4植物。而其它的农作物，如水稻、小麦、大豆都属于C3植物，大多数树木等也属于C3植物。,C4途径需经过两种光合细胞，即在叶肉细胞的细胞质中，由PEPC催化羧化反应，形成C
14、4二羧酸， C4二羧酸运至维管束鞘细胞脱羧，释放的CO2再由C3途径同化。,C4途径反应过程：羧化、转移脱羧和再生,A.羧化阶段：场所叶肉细胞质,PEPHCO3,PEP羧化酶,OAAHOPO32,磷酸烯醇式丙酮酸,草酰乙酸,最初CO2受体,最初产物 不稳定，易转化,B.转移脱羧阶段： 按脱羧酶分为三个类型 .NADP苹果酸酶型：,OAA,苹果酸,丙酮酸,酶,CO2,叶肉细胞,维管束鞘细胞,.NAD苹果酸酶型：,OAA,天冬氨酸,丙酮酸,酶,CO2,叶肉细胞,维管束鞘细胞,C3途径,.PEP羧激酶型：,OAA,天冬氨酸,PEP,CO2,叶肉细胞,维管束鞘细胞,C.再生阶段：场所叶肉细胞,丙酮酸,
15、PEP,ATP,AMP+2Pi,丙酮酸双激酶,AMP+ATP,2ADP,11. light-dependent reactions,n. 光反应,The first stage in photosynthesis, driven by light energy. Electrons that trap the suns energy pass the energy to high-energy carriers such as ATP or NADPH, where it is stored in chemical bonds.,12. light-independent reactions,
16、n. 暗反应,The second stage of photosynthesis, also called the Calvin-Benson cycle, which does not require light. During the six steps of the cycle, carbon is fixed and carbohydrates are formed.,13. photon,n. 光子,A particle that has zero mass or charge and unit spin, the quantum of the electromagnetic fi
17、eld and carrier of the electromagnetic force., futn ,原始称呼是光量子（light quantum），其静止量为零，不带电荷 ，是电磁辐射的载体。当一个光子被分子吸收时,就有一个电子获得足够的能量从而从内轨道跃迁到外轨道,具有电子跃迁的分子就从基态变成了激发态。,14. photorespiration,n. 光呼吸,A light-dependent type of respiration that occurs in most photosynthesis plants and differs from normal( or dark )
18、 respiration., ,futu,resprein ,光呼吸是与光合作用随伴发生的吸收O2和释放CO2的过程。 整个途径要经过三种细胞器，即在叶绿体中合成乙醇酸，在过氧化体中氧化乙醇酸，在线粒体中释放CO2。由于光呼吸与光合作用两者的底物均起始于RuBP，且都受Rubisco催化，因此，两者的活性比率取决于CO2和O2的浓度比例。在O2和CO2并存的环境中，光呼吸是不可避免的。光呼吸释放的CO2可被光合再固定。,15. photosynthesis,n. 光合作用,The synthesis of organic compounds by reduction of carbon dio
19、xide using light energy absorbed by chlorophyll., ,futusinsis ,16. photosystem,n. 光系统,One of the clusters of light-trapping pigments embedded in photosynthetic membranes. Photosystem I operates during the cyclic pathway; photosystem II operates during both the cyclic and noncyclic pathways., ,futsis
20、tm ,17. Ribulose biphosphate( RuBP),n. 核酮糖二磷酸,A compound with a backbone(主链) of five carbon atoms that is required for carbon fixation in the Calvin-Benson cycle of photosynthesis.,18. thylakoid,n. 类囊体,One of a number of flattened fluid-filled sacs that form the photosynthetic lamellar system of chl
21、oroplasts, photosynthetic bacteria, and blue-green algae, ail,kid ,Review the former content：,1. Absorption spectrum bs:pn spektrm ,2. Calvin-Benson cycle,3. carotenoid,4. Chlorophyll kl:rfil ,5. Chloroplast kl(:)rpl:st ,6. Cyclic photophosphorylation,7. C3 plant,8. C4 plant, krtnid ,9. light-depend
22、ent reactions,10. light-independent reactions,11. Noncyclic photophosphorylation,12. photon,13. photophosphorylation,14. photorespiration,15. photosynthesis,16. photosystem,17. Ribulose biphosphate( RuBP),18. thylakoid, futn , ail,kid , ,futusinsis ., ,futu,respirein .,How light energy reaches photo
23、synthetic cells? The light-dependent reactions: Converting solar energy into chemical bond energy The light-independent reactions: Building carbohydrates Oxygen: An inhibitor of photosynthesis Reprieve from photorespiration: The C4 pathway,Text Analysis,Questions & Answers,What process do you think
24、the photosynthesis is?,What benefit do you think plant can gain through photosynthesis?,Photosynthesis occurs only in the chlorophyll-containing cells of green plants, algae, and certain protists and bacteria. Overall, it is a process that converts light energy into chemical energy that is stored in
25、 the form of molecular bonds.,光合作用只发生在绿色植物的含叶绿素的细胞、海藻、某些原生生物以及某些细菌中。总的来说，它是将光能转化成以分子键形成储存的化学能的过程。,From the point of view of chemistry and energetics, it is the opposite of cellular respiration. Whereas cellular respiration is highly exergonic and releases energy, photosynthesis requires energy and i
26、s highly endergonic.,从化学和热力学角度考虑，光合作用与细胞呼吸过程相反。细胞呼吸释放能量，高度放能；而光合作用需要能量，且高度吸能。,Photosynthesis starts with CO2 and H2O as raw materials and proceeds through two sets of partial reactions. In the first set, called light-dependent reactions, water molecules are split (oxidized), O2 is released, and ATP
27、and NADPH are formed. These reactions must take place in the presence of light energy.,光合作用以CO2 和H2O为原料，发生两步反应 。第一步反应叫光反应，将H2O氧化分解形成O2，同时产生ATP和NADPH，此反应必须在光照的条件下才能发生。,In the second set, called light-independent reactions, CO2 is reduced (via the addition of H atoms) to carbohydrate. These chemical e
28、vents rely on the electron carrier NADPH and ATP generated by the first set of reactions.,第二步反应叫暗反应， CO2 加H还原成碳水化合物，此反应依赖光反应中产生的电子载体NADPH，和ATP的能量供应。,光反应中,来自于太阳的光能使叶绿素产生高能电子, 然后电子通过在叶绿体类囊体膜中的电子传递链间的移动传递,并将H+质子从叶绿体基质传递到类囊体腔,建立电化学质子梯度,用于ATP的合成。光反应的最后一步是高能电子被NADP+接受,使其被还原成NADPH。光反应的场所是类囊体。概括地说光反应是通过叶绿素等
29、光合色素分子吸收光能, 并将光能转化为化学能, 形成ATP和NADPH的过程。光反应包括光能吸收、电子传递、光合磷酸化等三个主要步骤。,暗反应不需要光,是CO2固定反应。在这一反应中,叶绿体利用光反应产生的ATP和NADPH这两个高能化合物分别作为能源和还原的动力将CO2固定,使之转变成葡萄糖。碳固定反应开始于叶绿体基质, 结束于细胞质基质。,不同的植物，暗反应的过程不一样，而且叶片的解剖结构也不相同。这是植物对环境的适应的结果。暗反应可分为C3,C4和CAM三种类型。三种类型是因二氧化碳的固定这一过程的不同而划分的。,Both sets of reactions take place in
30、chloroplasts. Most of the enzymes and pigments for the light-dependent reactions are embedded in the thylakoid membrane of chloroplasts. The dark reactions take place in the stroma.,这两步反应都发生在叶绿体中。其中，光反应所需的大部分酶和色素位于叶绿体的类囊体膜上，暗反应则发生于叶绿体的基质中。,1.How light energy reaches photosynthetic cells?,The energy
31、in light photons in the visible part of the spectrum can be captured by biological molecules to do constructive work.,1.光能如何传递到光合作用细胞中？ 生化分子能捕获可见光谱中的光子能并开展一些建设性的工作。,The pigment chlorophyll in plant cells absorbs photons within a particular absorption spectrum-a statement of the amount of light absor
32、bed by chlorophyll at different wavelengths.,植物细胞中的叶绿素能吸收特定吸收光谱中的光子，这种吸收光谱指的是叶绿素在不同波长下吸收光的函数关系。,When light is absorbed it alters the arrangement of electrons in the absorbing molecule. The added energy of the photon boosts the energy condition of the molecule from a stable state to a less-stable exc
33、ited state.,光一旦被吸收就改变了吸收分子内的电子排布，增加的光子能将吸收分子由稳定的基态转变为不稳定的激发态。,During the light-dependent reactions of photosynthesis, as the absorbing molecule returns to the ground state, the “excess” excitation energy is transmitted to other molecules and stored as chemical energy.,在光反应中，随着吸收分子回复到基态，额外的激发能传递给了其他分
34、子并以化学能的形式储存起来。,All photosynthetic organisms contain various classes of chlorophylls and one or more carotenoid (accessory) pigments that also contribute to photosynthesis. Groups of pigment molecules called antenna complexes are present on thylakoids .,所有能进行光合作用的有机体都含有多种叶绿素和至少一种类胡萝卜素（一种辅助色素）。这些色素分子统
35、称为天线复合物，位于类囊体上。,Light striking any one of the pigment molecules is funneled to a special chlorophyll a molecule, termed a reaction-center chlorophyll, which directly participates in photosynthesis .,大多数聚光色素分子受光能激发后能逐一将光能传递到一个特殊状态的叶绿素a分子上，这个叶绿素a分子又叫反应中心色素，它将直接参与到光合作用中。,Most photosynthetic organisms p
36、osses two types of reaction-center chlorophylls, P680 and P700, each associated with an electron acceptor molecule and an electron donor molecule . These aggregations are known respectively as photosystem I (P700) and photosystem II (P680).,大多数能进行光合作用的有机体都具备两种类型的反应中心色素：P680和P700，二者各与一个电子受体分子和一个电子供体分
37、子协同作用。他们的聚合物分别称为光系统II和光系统I 。,The photosystems of the light-dependent reactions are responsible for the packaging of light energy in the chemical compounds ATP and NADPH.,2. The light-dependent reactions: Converting solar energy into chemical bond energy,2.光反应：将光能转化成化学能 光反应的光合系统负责将光能在化合物ATP 和NADPH中装配
38、的过程。,This packaging takes place through a series of oxidation-reduction reactions set in motion when light strikes the P680 reaction center in photosytem II.,该过程通过一系列的氧化还原反应完成，光激发位于光系统中的P680反应中心后这些氧化还原反应即可发生。,In this initial event water molecules are cleaved, oxygen is released, and electrons are do
39、nated. These electrons are accepted first by plastiquinone and then by a series of carriers as they descend an electron transport chain.,在反应的起始阶段，水分子被裂解释放出氧气，产生了电子供体。这些电子首先为质体醌所接收随后沿电子传递链被一系列载体所接收。,For each four electrons that pass down the chain, two ATP are formed. The last acceptor in the chain i
40、s the P700 reaction center of photosystem I.,每传递四个电子，即产生两个ATP。电子的终受体是光系统中的P700反应中心。,At this point incoming photons boost the energy of the electrons, and they are accepted by ferredoxin. Ferredoxin is then reoxidized, and the coenzyme NADP+ is reduced to the NADPH. The ATP generated previously and t
41、he NADPH then take part in the light-independent reactions.,ferredoxin, fere,dksin ,n. 生化铁氧化还原蛋白,这时随之而来的光子激发了电能，电子为铁氧还蛋白所接收。铁氧还蛋白被重新氧化，NADP被还原成NADPH。这些NADPH与先前产生的ATP随后参与到暗反应中。,The production of ATP from the transport of electrons excited by light energy down an electron transport chain is termed pho
42、tophosphorylation.,在光能的激发下，沿着电子传递链产生产物ATP的过程叫做光合磷酸化。,The one-way flow of electrons through photosystem II and I is called noncyclic photophosphorylation; plants also derive additional ATP through cyclic photophosphorylation, in which some electrons are shunted back through the electron transport cha
43、in between photosystems II and I.,电子通过光系统和光系统单线程传递的过程叫做非环形光合磷酸化。植物也可额外通过环形光合磷酸化产生ATP，在环形光合磷酸化的过程中，电子在光系统和光系统 中来回传递。,非环式光合磷酸化： PS所产生的电子经过一系列的传递，在细胞色素复合体上引起ATP的形成，继而将电子传至PS，提高能位，最后用去还原NADP+。这样，电子经PS传出后不再返回。,环式光合磷酸化： 从PS产生的电子，经过Fd和细胞色素b6/f等后，引起了ATP的形成，降低能位，又经PC回到原来的起点P700，形成闭合回路。,3. The light-independe
44、nt reactions: Building carbohydrates,In the light-independent reactions of photosynthesis, which are driven by ATP and NADPH, CO2 is converted to carbohydrate. The reactions are also known as the Calvin-Benson cycle.,3.暗反应：产生碳水化合物 ATP 和NADPH驱动暗反应的发生。在暗反应中二氧化碳转化形成碳水化合物，这一反应又称为卡尔文本森循环。,卡尔文循环,C3循环中反应物及
45、产物的生成,Atmospheric CO2 is fixed as it reacts with ribulose biphosphate (RuBP), a reaction that is catalyzed by the enzyme ribulose biphosphate carboxylase.,RuBP与二氧化碳气体发生反应将其固定，这一反应由RuBP羧化酶催化完成。,The reduction of CO2 to carbohydrate (fructose diphosphate) is completed via several more steps of the cycl
46、e. Finally, RuBP is regenerated so that the cycle may continue.,CO2还原成碳水化合物还需要经卡尔文循环的几步反应才能完成。最终，RuBP再生，循环得以继续。,C3途径反应过程：羧化、还原和再生 A.羧化阶段：,RuBP,Rubisco(RuBP羧化酶),PGA（2分子） 酸能量低，不能贮存更多的能量,3磷酸甘油酸,B.还原阶段：,PGA,DPGA,GAP （3-磷酸甘油醛）,GAP是一种三碳糖，可以稳定的贮存能量，至此，消耗的光反应的ATP和NADPH，使光能转化为稳定的化学能，光合的贮能过程结束。,GAP的出路,叶绿体内,淀粉
47、或葡萄糖（贮存形式）,细胞质,蔗糖（运输形式）,C.更新阶段：大部分GAP经一系列转化，重新形成RuBP的阶段。,C3途径的总反应式可写成： 3CO2+5H2O+9ATP+6NADPHGAP+9ADP+8Pi+6NADP+ +3H+,卡尔文循环,C3循环中反应物及产物的生成,4. Oxygen: An inhibitor of Photosynthesis,High levels of oxygen in plant cells can disrupt photosynthesis and can also cause photorespiration-an inefficient form
48、of the dark reactions in which O2 is fixed rather than CO2 and no carbohydrate is produced.,4.O2：光合作用的抑制剂 植物细胞中高水平的O2 能阻断光合反应的发生并引发光呼吸。光呼吸是一种无效的暗反应，反应中O2而非CO2 被固定，也没有碳水化合物的形成。,5. Reprieve from photorespiration: The C4 pathway,Most plants are C3 plants: they experience decreased carbohydrate producti
49、on under hot, dry conditions as a result of the effects of photorespiration.,5.光呼吸暂缓进行：C4途径 大多数植物属于C3植物，在炎热干旱的条件下会减少碳水化合物的形成，转而发生光呼吸。,Among C4 plants, however, special leaf anatomy and unique biochemical pathway enable the plant to thrive in arid conditions.,而C4植物却由于其独特的叶片结构和生化途径而使植物在干旱的条件下也能绽放勃勃生机。,Thus C4 plant lessen photorespir