郑州十大评价好的A-level培训学校名单榜首一览，认准郑州新航道A-Level培训学校，新航道针对不同学员的不同层次学习需求，设置一站式计划，G5学霸计划，国际班互补计划课程体系。并且有针对性的制定课程和教学方式，开设的课程有数学、进阶数学、物理、化学、生物、经济学、会计学等。紧抓中国学生理科优势，进行课程组合化、配备海量国际背景的教师和专业学习管理师团队、双管齐下、奠定每一位学员的留学之路。欢迎来电咨询和试听课程。

　　下面新航道老师给大家分享：什么是A-Level生物中的光合作用？有哪些常见考点？

　　提到A-level生物，给人的感觉就是关于一些基因、细胞等方面的问题，学好A-level生物，非常关键的一步是要把基本知识点掌握，其中，光合作用是A-level生物考试中很重要的一个部分。下面，锦秋小编带着大家一起来了解一下A-level生物中的光合作用。

　　Photosynthesis revision光合作用要点概述

　　Part 1 Pigments and the Absorption of Light  色素与光吸收

　　At GCSE, you will have used the the following equation:

　　This shows that carbon dioxide and water are turned into glucose and oxygen in a plant, using light as energy. The glucose made may be used to make other substances or it may be used in respiration. The oxygen may diffuse out through the stomata or it may be used in respiration.

　　CO2吸收位置：The carbon dioxide enters the plant by stomata (in the leaves) or lenticels (in the stem). The water enters through the roots and moves up through the plant in xylem vessels.

　　Light is required as an energy source for the reaction and chlorophyll is necessary to absorb the light.

　　Light energy is necessary but it must be harvested and trapped by the photosynthetic pigments to be of any use.

　　叶绿素分类

　　Chlorophyll absorbs light from the visible part of the electromagnetic part of the spectrum, but there are several types of chlorophyll:

　　• chlorophyll a

　　• chlorophyll b

　　• chlorophyll c

　　• bacteriochlorophyll (found in photosynthetic bacteria!)

　　There are also other families of pigments, such as the carotenoids.

　　不同色素的吸光强度都不一样. 不同部位的色素吸光强度也不一样. Not all wavelengths of light are equally absorbed and different chlorophylls absorb more strongly in different parts of the visible spectrum.

　　Absorption and Action Spectrums

　　The action spectrum shows the rate of photosynthesis at different wavelengths.

　　The absorption spectrum shows how strongly the pigments absorb at different wavelengths.

　　The absorption spectrum and action spectrum show that the wavelengths that are most strongly absorbed (red and blue) are the ones that cause photosynthesis to proceed at the fastest rate. Green is not strongly absorbed; rather it is reflected, causing leaves to look green.

　　The shorter the wavelength, the more energy it contains. During photosynthesis the light energy is converted into chemical energy. The absorbed light excites electrons in the pigment molecules and the energy can be passed on to be used by the plant.

　　Photosystems

　　The pigments are arranged in funnel shaped photosystems that sit on the thylakoid membranes in the chloroplasts.

　　In each photosystem, several hundred pigment molecules, called accessory pigments, are clustered around a particular pigment molecule, known as the primary pigment.

　　The various accessory pigments absorb light of different wavelengths and pass the energy down the photosystem. Eventually the energy reaches the primary pigment that acts as a reaction centre.

　　There are 2 types of photosystem:

　　• Photosystem One - PS I:

　　• Its primary pigment is a molecule of chlorophyll a with an absorption peak at 700nm. It is called P700

　　• Photosystem Two - PS II:

　　• Its primary pigment is a molecule of chlorophyll b with an absorption peak at 680nm. It is called P680

　　PS I are situated next to PS II on the thylakoid membrane.

　　Part 2 Light Dependant Reactions 光反应

　　The first reactions of photosynthesis require light energy, and are called light dependant reactions.

　　The aim is to produce ATP from ADP and inorganic P and harvest hydrogen so that carbon dioxide can be reduced to form a carbohydrate in the second series of reactions. The production of ATP using light is called photophosphorylation.

　　It will be useful if you refer to the Respiration Learn-it, and refresh your memory about electron carriers and the Chemiosmotic theory, as both reappear here.

　　There are many electron carriers involved, but the one that you must know about for the exams is NADP (nicotinamide adenine dinucleotide phosphate).

　　When light is absorbed by PS I and PS II, electrons in the chlorophyll molecule are boosted to higher energy levels. They are emitted and passed on to electron carriers.

　　The loss of electrons from PS II causes the splitting of water. The water gives up its electrons to PS II to fill the gap.

　　This leaves oxygen, which is given off as waste, and hydrogen ions. (See later in this Learn-it for loss of electrons from PS I).

　　The electrons are passed through a series of electron carriers at successively lower energy levels. This means that energy is released and used to form ATP out of ADP and P.

　　This occurs in a similar way to ATP production in mitochondria. The energy is actually used to pump hydrogen ions from the stroma across the thylakoid membrane. This creates an electrochemical gradient.

　　As the hydrogen ions diffuse back down the concentration gradient they flow through proteins. Part of each protein is ATP synthetase.

　　The energy released as the hydrogen ions diffuse down the concentration gradient is used to synthesize ATP. The electron eventually reaches PS I and fills the space.

　　Non-Cyclic Photophosphorylation

　　The electrons from PS I may also pass onto an electron carrier and then combine with the hydrogen ions (from the water) to reduce NADP to NADPH.

　　This reduced NADP is used in the next series of reactions.

　　Note: No ATP has been made during this process.

　　This process is called non-cyclic photophosphorylation.

　　Cyclic Photophosphorylation

　　However, if there is plenty of NADPH, something different happens.

　　The electron from PS I is passed to the electron carriers used in PS II. ATP is formed and the electrons return to PS I to fill the space. This makes PS II redundant as no electrons are needed from there to fill the space in PS I. Only PS I is active. This is called cyclic photophosphorylation.

　　To summarise, in cyclic photophosphorylation:

　　• No PS II is involved.

　　• No oxygen is evolved.

　　• No NADPH is made.

　　• ATP is still made.

　　Part 3 Light-Independent reactions 暗反应

　　Calvin cycle

　　These reactions can occur in the light or the dark. They need ATP for energy to drive the reactions, and they need NADPH for reducing power. They occur in the stroma of the chloroplast and are called the Calvin cycle.

　　Carbon dioxide combines with a 5-carbon sugar called ribulose bisphosphate (RuBP) to form a 6-carbon sugar. This process is known as carbon fixation and is catalysed by the enzyme ribulose bisphosphate carboxylase (rubisco).

　　This 6-carbon sugar is unstable and breaks down to form two 3-carbon sugars. These are converted into triose phosphates using the energy from ATP and using the hydrogen from reduced NADP.

　　Most of this triose phosphate is used to regenerate RuBP, but some is used to produce 6-carbon sugars from which complex carbohydrates, amino acids and other substances are made.

　　For every twelve 3-carbon sugars (36 carbons):

　　Two of the 3-carbon sugars form 1 x 6-carbon sugar (6 carbons)

　　Ten of the 3-carbon sugars form 6 x 5-carbon sugars (RuBP) (30 carbons)