生物专业英语.ppt
生物医学工程专业英语精品PPT课件
➢ Structured abstract
➢ Non-structured
（4、5、6、8 elements）
Lesson2 “Abstract”
第二讲 “摘要”
Lesson2 “Abstract”
❖I. Importance of “abstract” ❖II. Writing about “abstract” ❖III. Reading about “abstract”
I. Background
Importance of Abstract
II. Writing about “abstract”
Part1.Requirement
❖ IfGtheenreeraalrererqeuqirueemstesn，ts
From form:
Writinfgonatb，olouctaatibons，tract in waocrcdonrudmanbecre（w30it0h）, trheqeurierFleeermgvos:materonunbtcctjetsoucnr。teitveen, ts: (“call fmoretphoadpse,re”tc. or “aIuntshtrFosurrecosnt”mtieon)lnacenf，ogruteangsee：
Informational Function
（meaning of abstract：refining；miniature；highly condensed summary and conclusion）
A，Read articles on the most rapid, make up for lack of title B，facilitate the establishment of literature database
生物专业英语(共62张PPT)
光合作用以二氧化碳和水为原材料并经历两步化学反应。
第一步，称光反应，水分子裂解 (被氧化)，释放氧气，并形成ATP和 NADPH（还原型烟酰胺腺嘌呤二核苷酸磷酸）。
此反应必须在存在光能的条件下进行。
2022/9/25
9
Introduction
光合作用只发生在含有叶绿素的绿色植物细胞、藻类、某些原生生 物和细菌之中。
总体来说，这是一个将光能转化成化学能的过程，其能量以分子 键形式贮存。
从化学和能量学角度来看，它是细胞呼吸作用的逆反应。
但是细胞呼吸作用是高度放能，释放能量的过程，而光合作用需 要能量, 并且是高度吸能的过程。
在光合作用的光反应中，当捕光分子回到基态时，额外的激发能 被转移到其它分子中并且以化学能的形式贮存。
•All photosynthetic organisms contain various classes of
chlorophylls and one or more carotenoid pigments that also contribute to photosynthesis.
captured by biological molecules to do constructive work.
生物分子能捕获可见光谱中光子的能量。
The pigment chlorophyll in plant cells absorbs photons within a particular absorption spectrum—a statement of the amount of light absorbed by chlorophyll at different wavelengths.
生物专业英语上传PPT精选文档
Professional Words and Phrases
(Continued)
classification [klæsifi'keiʃən] n. 分类，类别
biochemistry ['baiəu'kemistri] n. 生物化学
molecular biology 分子生物学
molecular level 分子水平
Chapter 1 Biology
1.1 What is Biology? 1.2 The Origin of Life 1.3 The Significance of Biology in Your Life 1.4 The History of Biology– Additional Reading
microorganism [maikrəu'ɔ:gənizəm] n. 微生物
well-being ['wel'bi:iŋ] n. 健康，福利
agriculture ['ægrikʌltʃə] n. 农业
livestock ['laivstɔk] n. 家畜，牲畜
ecology [i:‘kɔlədʒi] n. 生态学
1
ቤተ መጻሕፍቲ ባይዱ
1.1 What is Biology?
Biology is the study of life. Alongside physics and chemistry, biology is one of the largest and most important branches of science. At the highest level, biology is broken down based on the type of organism being studied: zoology, the study of animals; botany, of plants; and microbiology, of microorganisms. Each field has contributed to mankind or the Earth’s wellbeing in numerous ways. Most prominently: botany, to agriculture; zoology, to livestock and protection of ecologies; and microbiology, to the study of disease and ecosystems in general.
生物专业英语课件 Biology
Biology: The Science of Our Lives Biology literally means "the study of life". Biology is such a broad field, covering the minute workings of chemical machines inside our cells, to broad scale concepts of ecosystems and global climate change. Biologists study details of the human brain, the composition of our genes, and even the functioning of our reproductive system. Biologists recently all but completed the deciphering of the human genome, the sequence of deoxyribonucleic acid (DNA) bases that may determine much of our innate capabilities and predispositions to certain forms of behavior and illnesses. DNA sequences have played major roles in criminal cases (O.J. Simpson, as well as the reversal of death penalties for many wrongfully convicted individuals), as well as the impeachment of President Clinton (the stain at least did not lie). We are bombarded with headlines about possible health risks from favorite foods (Chinese, Mexican, hamburgers, etc.) as well as the potential benefits of eating other foods such as cooked tomatoes. Informercials tout the benefits of metabolism-adjusting drugs for weight loss. Many Americans are turning to herbal remedies to ease arthritis pain, improve memory, as well as improve our moods.Can a biology book give you the answers to these questions? No, but it will enable you learn how to sift through the biases of investigators, the press, and others in a quest to critically evaluate the question. To be honest, five years after you are through with this class it is doubtful you would remember all the details of meatbolism. However, you will know where to look and maybe a little about the process of science that will allow you to make an informed decision. Will you be a scientist? Yes, in a way. You may not be formally trained as a science major, but you can think critically, solve problems, and have some idea about what science can and cannot do. I hope you will be able to tell the shoe from the shinola.Science and the Scientific MethodScience is an objective, logical, and repeatable attempt to understand the principles and forces operating in the natural universe. Science is from the Latin word, scientia, to know. Good science is not dogmatic, but should be viewed as an ongoing process of testing and evaluation. One of the hoped-for benefits of students taking a biology course is that they will become more familiar with the process of science.Humans seem innately interested in the world we live in. Young children drive their parents batty with constant "why" questions. Science is a means to get some of those whys answered. When we shop for groceries, we are conducting a kind of scientific experiment. If you like Brand X of soup, and Brand Y is on sale, perhaps you try Brand Y. If you like it you may buy it again, even when it is not on sale. If you did not like Brand Y, then no sale will get you to try it again.In order to conduct science, one must know the rules of the gameplay! Which is precisely what one does with some computer or videogames (before buying the cheatbook). The scientific method is to be used as a guide that can be modified. In some sciences, such as taxonomy and certain types of geology, laboratory experiments are not necessarily performed. Instead, after formulating a hypothesis, additional observations and/or collections are made from different localities.Steps in the scientific method commonly include:1.Observation: defining the problem you wish to explain.2.Hypothesis: one or more falsifiable explanations for theobservation.3.Experimentation: Controlled attempts to test one or morehypotheses.4.Conclusion: was the hypothesis supported or not? After thisstep the hypothesis is either modified or rejected, whichcauses a repeat of the steps above.After a hypothesis has been repeatedly tested, a hierarchy of scientific thought develops. Hypothesis is the most common, with the lowest level of certainty. A theory is a hypothesis that has been repeatedly tested with little modification, e.g. The Theory of Evolution. A Law is one of the fundamental underlying principles of how the Universe is organized, e.g. The Laws of Thermodynamics, Newton's Law of Gravity. Science uses the word theory differently than it is used in the general population. Theory to most people, in general nonscientific use, is an untested idea. Scientists call this a hypothesis.Scientific experiments are also concerned with isolating the variables. A good science experiment does not simultaneously test several variables, but rather a single variable that can be measured against a control. Scientific controlled experiments are situations where all factors are the same between two test subjects, except for the single experimental variable.Consider a commonly conducted science fair experiment. Sandy wants to test the effect of gangsta rap music on pea plant growth. She plays loud rap music 24 hours a day to a series of pea plants grown under light, and watered every day. At the end of her experiment she concludes gangsta rap is conducive to plant growth. Her teacher grades her project very low, citing the lack of a control group for the experiment. Sandy returns to her experiment, but this time she has a separate group of plants under the same conditions as the rapping plants, but with soothing Led Zeppelin songs playing. She comes to the same conclusion as before, but now has a basis for comparison. Her teacher gives her project a better grade.Theories Contributing to Modern BiologyModern biology is based on several great ideas, or theories:1.The Cell Theory2.The Theory of Evolution by Natural Selection3.Gene Theory4.HomeostasisRobert Hooke (1635-1703), one of the first scientists to use a microscope to examine pond water, cork and other things, referredto the cavities he saw in cork as "cells", Latin for chambers. Mattias Schleiden (in 1838) concluded all plant tissues consisted of cells. In 1839, Theodore Schwann came to a similar conclusion for animal tissues. Rudolf Virchow, in 1858, combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory. Thus there is a chain-of-existence extending from your cells back to the earliest cells, over 3.5 billion years ago. The cell theory states that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells.Figure 1. JamesWatson (L) andFrancis Crick (R),and the model theybuilt of thestructure ofdeoxyribonucleicacid, DNA. While amodel may seem asmall thing, theirdevelopment of theDNA model fosteredincreasedunderstanding of howgenes work. Imagefrom the Internet.In 1953, American scientist James Watson and British scientist Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had (then) recently been deduced to be the physical carrier of inheritance. Crick hypothesized the mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the central dogma. Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" of proteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins).Homeostasis is the maintainence of a dynamic range of conditions within which the organism can function. Temperature, pH, and energy are major components of this concept. Theromodynamics is a field of study that covers the laws governing energy transfers, and thus the basis for life on earth. Two major laws are known: the conservation of matter and energy, and entropy. These will be discussed in more detail in a later chapter. The universe is composed of two things: matter (atoms, etc.) and energy.These first three theories are very accepted by scientists and the general public. The theory of evolution is well accepted by scientists and most of the general public. However, it remains a lightening rod for school boards, politicians, and television preachers. Much of this confusion results from what the theory says and what it does not say.Development of the Theory of EvolutionModern biology is based on several unifying themes, such as the cell theory, genetics and inheritance, Francis Crick's central dogma of information flow, and Darwin and Wallace's theory of evolution by natural selection. In this first unit we will examine these themes and the nature of science.The Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman philosopher Lucretius (99-55 B.C.) coined the concept that all living things were related and that they had changed over time. The classical science of their time was observational rather than experimental. Another ancient Greek philosopher, Aristotle developed his Scala Naturae, or Ladder of Life, to explain his concept of the advancement of living things from inanimate matter to plants, then animals and finally man. This concept of man as the"crown of creation" still plagues modern evolutionary biologists (See Gould, 1989, for a more detailed discussion).Post-Aristotlean "scientists" were constrained by the prevailing thought patterns of the Middle Ages -- the inerrancy of the biblical book of Genesis and the special creation of the world in a literal six days of the 24-hour variety. Archbishop James Ussher of Ireland, in the late 1600's calculated the age of the earth based on the geneologies from Adam and Eve listed in the biblical book of Genesis. According to Ussher's calculations, the earth was formed on October 22, 4004 B.C. These calculations were part of Ussher's book, History of the World. The chronology he developed was taken as factual, and was even printed in the front pages of bibles. Ussher's ideas were readily accepted, in part because they posed no threat to the social order of the times; comfortable ideas that would not upset the linked applecarts of church and state.Figure 2. Archbishop JamesUssher. Image from the Internet.Often new ideas must "come out of left field", appearing as wild notions, but in many cases prompting investigation which may later reveal the "truth". Ussher's ideas were comfortable, the Bible was viewed as correct, therefore the earth must be only 5000 years old. Geologists had for some time doubted the "truth" of a 5,000 year old earth. Leonardo da Vinci (painter of the Last Supper, and the Mona Lisa, architect and engineer) calculated the sedimentation rates in the Po River of Italy. Da Vinci concluded it took 200,000 years to form some nearby rock deposits. Galileo, convicted heretic for his contention that the Earth was not the center of the Universe, studied fossils (evidence of past life) and concluded that they were real and not inanimate artifacts. James Hutton, regarded as theFather of modern geology, developed the Theorythe basis of modern geology and paleontology. According to Hutton's work, certain geological processes operated in the past in much the same fashion as they do today, with minor exceptions of rates, etc. Thus many geological structures and processes cannot be explained if the earth was only a mere 5000 years old.The Modern View of the Age of the EarthRadiometric age assignments based on the rates of decay ofsuggest the earth is over 4.5 billion years old. The Earth is thought older than 4.5 billion years, with the oldest known rocks being 3.96 billion years old. Geologic time divides into eons, eroas, and smaller units. An overview of geologic time may be obtained at /help/timeform.html.Figure 3. The geologic time scale, hilighting some of the firsts in the evolution of life. One way to represent geological time. Note the break during the precambrian. If the vertical scale was truly to scale the precambrian would account for 7/8 of the graphic.。
生物专业英语PPT
The genomic formula of the alien chromosomes in TE253 was 2 St + 8 J S + 2 J + 2 J-St.
The problem which haven't solved
We are presently developing chromosome addition and substitution(替换) lines to identify(确认) the chromosome location of the powdery mildew and stripe rust resistance(抗性) genes.
The problem need to be solve
In this study, we determined the genomic composition of a partial amphiploid TE253 by GISH probed with St genomic DNA from Ps. strigosa and evaluated its resistance to both powdery mildew and stripe rust as well. 我们通过基因组原位杂交探测从Ps. Strigosa到St基 因组确定了局部TE253基因的组成，并且还评估了 对白粉病和条锈病的抗性。
The method of the study
Cytogenetic Analyses(细胞遗传学分析）
其基本原理是用不同荧光物质分别标记病变细胞DNA 和正常细胞然后与正常中期细胞染色体杂交。 荧光原位杂交技术 用荧光物质标记特异性DNA探针，与中期细胞染色体 或间期细胞核杂交，鉴别和确定出生缺陷、肿瘤细胞 染色体异常，分辨率可达50~500kb。
生物-专业英语作业纯英文献ppt
Result
A CRISPR–Cas9 mutagenesis construct was designed to simultaneously generate knockout mutants in both AtDMP8 and AtDMP9 (Fig. a).
Homozygous dmp8, dmp9 and dmp8dmp9 mutants were selfpollinated and seed sets were examined. The seed set was reduced slightly in dmp8 (95.6%; average: 45.3 seeds per silique), even more so in dmp9 (70.9%; average: 32.2 seeds per silique) and even further in dmp8dmp9 (48.4%; average: 21.4 seeds per silique) (Fig. c,d)
These data confirm previously reported defects in the seed set and during development, and the proposed roles for AtDMP8 and AtDMP9 in fertilization.
Content
1 Summary 2 Background 3 Results 4 Discussion
Summary
Summary
➢ ZmPLA1/MTL/NLD is conserved in monocots and has been used to extend the system from maize to other monocots, but no functional orthologue has been identified in dicots, while ZmDMP-like genes exist in both monocots and dicots.
《生物专业英语》PPT课件
gene [dʒi:n] 基因
A unit of heredity located on a chromosome and composed a sequence of DNA nucleotides.
heredity [hə‘redɪti:] 遗传 nucleotide ['nu:kli:ə,taɪd] 核苷酸
dihybrid cross [dai‘haibrid]双因子杂种杂交
A cross between individuals that differ with respect to two specified gene pairs.
differ with 与...不一致 specified 指定的 respect 关系
particular 特殊的, 特别的 allelic 等位基因的
homozygous [,hɔmə'zaiɡəus] 纯合的
A diploid organism that has two identical alleles for particular characteristic.
identical 同一的, 同样的
incomplete dominance [, inkəm'pli:t 'dɔmənəns] 不完全显性
The condition in which two allelic genes have a different effect when
they are together as a heterozygote in a diploid cell than either of
germ plasm theory 种质学说
A substance thought to be transmitted in the gametes (germ cells) in an unchanged form from generation to generation. The germ plasm was believed to be unaffected by the environment and to give rise to the body cells.
生物专业英语课件
Biology: The Science of Our LivesBiology literally means "the study of life". Biology is such a broad field, covering the minute workings of chemical machines inside our cells, to broad scale concepts of ecosystems and global climate change. Biologists study details of the human brain, the composition of our genes, and even the functioning of our reproductive system. Biologists recently all but completed the deciphering of the human genome, the sequence of deoxyribonucleic acid (DNA) bases that may determine much of our innate capabilities and predispositions to certain forms of behavior and illnesses. DNA sequences have played major roles in criminal cases (O.J. Simpson, as well as the reversal of death penalties for many wrongfully convicted individuals), as well as the impeachment of President Clinton (the stain at least did not lie). We are bombarded with headlines about possible health risks from favorite foods (Chinese, Mexican, hamburgers, etc.) as well as the potential benefits of eating other foods such as cooked tomatoes. Informercials tout the benefits ofmetabolism-adjusting drugs for weight loss. Many Americans are turning to herbal remedies to ease arthritis pain, improve memory, as well as improve our moods.Can a biology book give you the answers to these questions? No, but it will enable you learn how to sift through the biases of investigators, the press, and others in a quest to critically evaluate the question. To be honest, five years after you are through with this class it is doubtful you would remember all the details of meatbolism. However, you will know where to look and maybe a little about the process of science that will allow you to make an informed decision. Will you be a scientist? Yes, in a way. You may not be formally trained as a science major, but you can think critically, solve problems, and have some idea about what science can and cannot do. I hope you will be able to tell the shoe from the shinola.Science and the Scientific MethodScience is an objective, logical, and repeatable attempt to understand the principles and forces operating in the natural universe. Science is from the Latin word, scientia, to know. Good science is not dogmatic, but should be viewed as an ongoing process of testing and evaluation. One of the hoped-for benefits of students taking a biology course is that they will become more familiar with the process of science.Humans seem innately interested in the world we live in. Young children drive their parents batty with constant "why" questions. Science is a means to get some of those whys answered. When we shop for groceries, we are conducting a kind of scientific experiment. If you like Brand X of soup, and Brand Y is on sale, perhaps you try Brand Y. If you like it you may buy it again, even when it is not on sale. If you did not like Brand Y, then no sale will get you to try it again.In order to conduct science, one must know the rules of the game(imagine and having to discover the rules as you play! Which is precisely what one does with some computer or videogames (before buying the cheatbook). The scientific method is to be used as a guide that can be modified. In some sciences, such as taxonomy and certain types of geology, laboratory experiments are not necessarily performed. Instead, after formulating a hypothesis, additional observations and/or collections are made from different localities.Steps in the scientific method commonly include:1.Observation: defining the problem you wish to explain.2.Hypothesis: one or more falsifiable explanations for theobservation.3.Experimentation: Controlled attempts to test one or morehypotheses.4.Conclusion: was the hypothesis supported or not? After thisstep the hypothesis is either modified or rejected, which causes a repeat of the steps above.After a hypothesis has been repeatedly tested, a hierarchy of scientific thought develops. Hypothesis is the most common, with the lowest level of certainty. A theory is a hypothesis that has been repeatedly tested with little modification, e.g. The Theory of Evolution. A Law is one of the fundamental underlying principles of how the Universe is organized, e.g. The Laws of Thermodynamics, Newton's Law of Gravity. Science uses the word theory differently than it is used in the general population. Theory to most people, in general nonscientific use, is an untested idea. Scientists call this a hypothesis.Scientific experiments are also concerned with isolating the variables. A good science experiment does not simultaneously test several variables, but rather a single variable that can be measured against a control. Scientific controlled experiments are situations where all factors are the same between two test subjects, except for the single experimental variable.Consider a commonly conducted science fair experiment. Sandy wants to test the effect of gangsta rap music on pea plant growth. She plays loud rap music 24 hours a day to a series of pea plants grown under light, and watered every day. At the end of her experiment she concludes gangsta rap is conducive to plant growth. Her teacher grades her project very low, citing the lack of a control group for the experiment. Sandy returns to her experiment, but this time she has a separate group of plants under the same conditions as the rapping plants, but with soothing Led Zeppelin songs playing. She comes to the same conclusion as before, but now has a basis for comparison. Her teacher gives her project a better grade.Theories Contributing to Modern Biology Modern biology is based on several great ideas, or theories:1.The Cell Theory2.The Theory of Evolution by Natural Selection3.Gene Theory4.HomeostasisRobert Hooke (1635-1703), one of the first scientists to use a microscope to examine pond water, cork and other things, referred to the cavities he saw in cork as "cells", Latin for chambers. Mattias Schleiden (in 1838) concluded all plant tissues consisted of cells. In 1839, Theodore Schwann came to a similar conclusion for animal tissues. Rudolf Virchow, in 1858, combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory. Thus there is a chain-of-existence extending from your cells back to the earliest cells, over 3.5 billion years ago. The cell theory states that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells.Figure 1. James Watson (L)and Francis Crick (R), andthe model they built of thestructure ofdeoxyribonucleic acid,DNA. While a model may seema small thing, theirdevelopment of the DNAmodel fostered increasedunderstanding of how geneswork. Image from theInternet.In 1953, American scientist James Watson and British scientist Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had (then) recently been deduced to be the physicalcarrier of inheritance. Crick hypothesized the mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the central dogma. Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" of proteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins). Homeostasis is the maintainence of a dynamic range of conditions within which the organism can function. Temperature, pH, and energy are major components of this concept. Theromodynamics is a field of study that covers the laws governing energy transfers, and thus the basis for life on earth. Two major laws are known: the conservation of matter and energy, andbe discussed in more detail in a later chapter. The universe is composed of two things: matter (atoms, etc.) and energy.These first three theories are very accepted by scientists and the general public. The theory of evolution is well accepted by scientists and most of the general public. However, it remains a lightening rod for school boards, politicians, and television preachers. Much of this confusion results from what the theory says and what it does not say.Development of the Theory of EvolutionModern biology is based on several unifying themes, such as the cell theory, genetics and inheritance, Francis Crick's central dogma of information flow, and Darwin and Wallace's theory of evolution by natural selection. In this first unit we will examine these themes and the nature of science.The Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman philosopher Lucretius (99-55 B.C.) coined the concept that all living things were related and that they had changed over time. The classical science of their time was observational rather than experimental. Another ancient Greek philosopher, Aristotle developed his Scala Naturae, or Ladder of Life, to explain his concept of the advancement of living things from inanimate matter to plants, then animals and finally man. This concept of man as the "crown of creation" still plagues modern evolutionary biologists (See Gould, 1989, for a more detailed discussion). Post-Aristotlean "scientists" were constrained by the prevailing thought patterns of the Middle Ages -- the inerrancy of the biblical book of Genesis and the special creation of the world in a literal six days of the 24-hour variety. Archbishop James Ussher of Ireland, in the late 1600's calculated the age of the earth based on the geneologies from Adam and Eve listed in thebiblical book of Genesis. According to Ussher's calculations, the earth was formed on October 22, 4004 B.C. These calculations were part of Ussher's book, History of the World. The chronology he developed was taken as factual, and was even printed in the front pages of bibles. Ussher's ideas were readily accepted, in part because they posed no threat to the social order of the times; comfortable ideas that would not upset the linked applecarts of church and state.Figure 2. Archbishop JamesUssher. Image from the Internet.Often new ideas must "come out of left field", appearing as wild notions, but in many cases prompting investigation which may later reveal the "truth". Ussher's ideas were comfortable, the Bible was viewed as correct, therefore the earth must be only 5000 years old.Geologists had for some time doubted the "truth" of a 5,000 year old earth. Leonardo da Vinci(painter of the Last Supper, and theMona Lisa, architect and engineer) calculated the sedimentation rates in the Po River of Italy. Da Vinci concluded it took 200,000 years to form some nearby rock deposits. Galileo, convicted heretic for his contention that the Earth was not the center of the Universe, studied fossils (evidence of past life) and concluded that they were real and not inanimate artifacts. James Hutton, regarded as the Father of modern geology, developed thepaleontology. According to Hutton's work, certain geological processes operated in the past in much the same fashion as they do today, with minor exceptions of rates, etc. Thus many geological structures and processes cannot be explained if the earth was only a mere 5000 years old.The Modern View of the Age of the Earth Radiometric age assignments based on the rates of decay ofnot discovered until the late 19th century, suggest the earth is over 4.5 billion years old. The Earth is thought older than 4.5 billion years, with the oldest known rocks being 3.96 billion years old. Geologic time divides into eons, eroas, and smaller units. An overview of geologic time may be obtained at .--Figure 3. The geologic time scale, hilighting some of the firsts in the evolution of life. One way to represent geological time. Note the break during the precambrian. If the vertical scale was truly to scale the precambrian would account for 7/8 of the graphic.--。
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-----Preventing gene exchange
Sometimes the differences that produce prezygotic isolation involve mechanical isolation . That is , mating is physically impossible between members of different species because genitals of males and females are structurally incompatible or because molecules on the surfaces of sperm and egg fail to bind . A final type of prezygotic mechanism is temporal isolation , in which time-related environmental cues that trigger reproductive processes are different for related species.
the second and subsequent generations after a cross show reduced reproductive success .
-----Preventing gene exchange
In postzygotic isolating mechanisms mating occurs, but the resulting hybrid organism is inviable or sterile. In a
2. Preventing gene exchange
Two general types of mechanisms operate to block the exchange of gene . The first general type is made up of prezygotic isolating mechanisms - mechanisms that prevent the formation of zygotes . Prezygotic isolation falls into two categories: ecological and behavioral . In the first case, two related group may become adapted to slightly different environments _ perhaps varying soil types or food sources. Over time , these genetic differences become so great that successful cross-fertilization can no longer take place . In behavioral isolation , related groups evolve differing behaviors-such as species mating rituals-that restrict the exchange of genes to members of the same group.
cyclic
Lesson 9
The origin of species
1.The biologists define a species
Modern biologists generally define a species as group of actually or potentially interbreeding populations that is reproductively isolated from other such groups . Members of species can interbreed with each other , but they cannot breed with organisms belonging to another species . One advantage of the standard of reproductive isolation is that it is very precise . Notice ,however , that it can only be applied to organisms that reproduce sexually . Asexual reproducers, including most prokaryotes, many plants, and some animals, must be classified into species on the basis of physical (biochemical or morphological) traits.
In postzygotic isolating mechanisms mating occurs, but the resulting hybrid organism is inviable or sterile. In a
special case of hybrid sterility termed hybrid breakdown ,