Lesson two.ppt

1、Photosynthesis,Lesson two,教学内容： What is photosynthesis How light energy reaches photosynthetic cells The light-dependent reaction The light-independent reaction Oxygen: an inhibition of photosynthesis Reprieve from photorespiration: The C4 pathway 教学要求: 理解photosynthesis的定义和总反应。 了解light-dependent rea

2、ction，light-independent reaction的基本步骤。 了解photorespiration 的发生条件。 了解细胞产生ATP的两种方法。 重点： 掌握photosynthesis的总反应。 掌握light-dependent reaction，light-independent reaction发生的位点以及基本步骤。 掌握细胞产生ATP的两种方法。 难点：本课涉及大量专业词汇和生物专业的许多重要内容，因此本课的全部内容难度都比较大。,前缀 photo- photosynthesis 光合作用 photosystem 光系统 photophosphorylation 光

3、合磷酸化 photorespiration 光呼吸 photosynthetic bacteria 光合细菌 photon 光子,专业单词,专业单词,NADPH-nicotinamide adenine dinucleotide phosphate CO2-carbon dioxide ADP-adenosine diphosphate ATP- adenosine triphosphate carrier 载体 acceptor 受体 donor 供体,exergonic 放能的 endergonic 吸能的,photon 光子 electron 电子 molecule 分子,oxidati

4、on-reduction reaction 氧化还原反应,ground state 基态 excited state 激发态 stable state 稳定态,专业单词,Hydrone 水分子 Hydrogen dioxide 过氧化氢 hydropower 水电,专业单词,protist 原生生物 bacterium 细菌 fungus 真菌 virus 病毒,专业单词,glucose 葡萄糖 starch 淀粉 glycogen 糖原 cellulose 纤维素 amino acid 氨基酸（简称aa） protein 蛋白质 nucleic acid 核酸 enzyme 酶 kinase

5、 激酶,专业单词,carbohydrate 碳水化合物 Catalytic reaction 催化反应 Enzyme 酶 Chemical compound 化合物 oxidation-reduction reaction 氧化还原反应 Ferredoxin 铁氧化还原蛋白 Reoxidize 再氧化 Photophosphorylation 光合磷酸化 noncyclic photophosphorylation 非环形光合磷酸化 cyclic photophosphorylation 环形光合磷酸化 carboxylase 碳酸酵素,专业单词,复杂句子分析,During the light

6、-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.,Light striking any one of the pigment molecules is funneled to a special chlorophyll a molecule, termed a reac

7、tion-center chlorophyll, which directly participates in photosynthesis.,复杂句子分析,The photosystems of the light-dependent reactions are responsible for the packaging of light energy in the chemical compounds ATP and NADPH.,复杂句子分析,The one-way flow of electrons through photosystems and is called noncycli

8、c photophosphorylation;plants also derive additional ATP through cyclic photophosphorylation, in which some electrons are shunted back through the electron transport chain between photosystems and .,复杂句子分析,The pigment chlorophyll in plant cells absorbs photons within a particular absorption spectrum

9、-a statement of the amount of light absorbed by chlorophyll at different wavelengths.,复杂句子分析,补充材料：,Photosynthesis is the conversion of light energy into chemical energy by living organisms. The raw materials are carbon dioxide and water, the energy source is sunlight, and the end-products include gl

10、ucose and oxygen. It is arguably the most important biochemical pathway, since nearly all life depends on it. It is a complex process occurring in higher plants, phytoplankton, algae, as well as bacteria such as cyanobacteria. Photosynthetic organisms are also referred to as photoautotrophs,补充材料：,Ph

11、otosynthesis occurs in two stages. In the first phase light-dependent reactions or photosynthetic reactions (also called the Light reactions) capture the energy of light and use it to make high-energy molecules. During the second phase, the light-independent reactions (also called the Calvin-Benson

12、Cycle, and formerly known as the Dark Reactions) use the high-energy molecules to capture carbon dioxide (CO2) and make the precursors of carbohydrates. In the light reactions one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified for

13、m of chlorophyll called pheophytin, which passes the electron to a quinone molecule, allowing the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP into NADPH. In addition, it serves to create a proton gradient across the chloroplast membrane;

14、 its dissipation is used by ATP Synthase for the concomitant synthesis of ATP. The chlorophyll molecule regains the lost electron by taking one from a water molecule through a process called photolysis, that releases oxygen gas as a waste product. In the Light-independent or dark reactions the enzym

15、e RuBisCO captures CO2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson cycle releases three-carbon sugars which are later combined to form sucrose and starch.,补充材料：,In hot and dry conditions, plants will close their stomata to prevent loss of water

16、. Under these conditions, oxygen gas, produced by the light reactions of photosynthesis, will concentrate in the leaves causing photorespiration to occur. Some plants have evolved mechanisms to increase the CO2 concentration in the leaves under these conditions. C4 plants capture carbon dioxide usin

17、g an enzyme called PEP Carboxylase that adds carbon dioxide to the three carbon molecule Phosphoenolpyruvate (PEP) creating the 4 carbon molecule oxaloacetic acid. Plants without this enzyme are called C3 plants because the primary carboxylation reaction produces the three carbon sugar 3-phosphoglyc

18、erate directly in the Calvin-Benson Cycle. When oxygen levels rise in the leaf, C4 plants reverse the reaction to release carbon dioxide thus preventing photorespiration. By preventing photorespiration, C4 plants can produce more sugar than C3 plants in conditions of strong light and high temperatur

19、e. Many important crop plants are C4 plants including maize, sorghum, sugarcane, and millet. Xerophytes such as Cacti and most succulents also can use PEP Carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). They store the CO2 in different molecules than the

20、C4 plants (mostly they store it in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate which is then reduced to malate). Nevertheless, C4 plants capture the CO2 in one type of cell tissue (mesophyll) and then transfer it to another type of tissue (bundle sheath cells) so that carbon fixation may occur via the Calvin cycle. They also have a different leaf anatomy than C4 plants. They grab the CO2 at night