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  • [查看全文]SATII生物专题分析——Cell Replication
    Eukaryotic cell replication is a process by which cells duplicate their genetic material and then divide to yield two daughter cells. In this section, we will discuss one type of cell reproduction called mitosis that produces an exact copy of the original cell, including an exact replication of DNA. In the next chapter, we will move on to discuss meiosis, a different form of cell replication that leads to the creation of sex cells. Millions of rounds of mitosis take place during the development of large multicellular organisms. Three separate tasks must be completed for a successful round of mitosis:DNA packaged into chromosomes must replicate. Copies of the chromosomes and organelles must migrate to opposite ends of the cell. The cell must physically split into two separate cells. The cell cycle is the recurring sequence of events that includes...
  • [查看全文]SATII生物专题分析——Enzymes
    Some chemical reactions simply happen when the two reactants come into contact. For example, you may be familiar with the bubbly volcano that forms when baking soda and vinegar are placed together in a glass. This reaction is spontaneous because it does not require outside energy to force it to occur. Most reactions, however, require energy. For example, the chemical reactions that produce a cake do not take place when baking soda, flour, and the other ingredients of a cake are simply left in a pan on the kitchen counter. Heat is required to break the existing chemical bonds in the ingredients so that they can undergo chemical reactions and combine with each other in new ways.In the laboratory, chemists use heat to create the activation energy needed to get nonspontaneous reactions started. Animals, however, can’t rely on internal Bunsen bur...
  • [查看全文]SATII生物专题分析——Acids and Bases
    Sometimes atoms give their electrons up altogether instead of sharing them in a chemical bond. This process is known as disassociation. Water, for instance, dissociates by the following formula: The hydrogen atom gives up a negatively charged electron, gaining a positive charge, and the OH compound gains a negatively charged electron, taking on a negative charge. The H+ is known as a hydrogen ion and OH– ion is known as a hydroxide ion. The disassociation of water produces equal amounts of hydrogen and hydroxide ions. However, the disassociation of some compounds produces solutions with high proportions of either hydrogen or hydroxide ions. Solutions high in hydrogen ions are known as acids, while solutions high in hydroxide ions are known as bases. Both types of solution are extremely reactive—likely to form bonds—because they contain so many ...
  • [查看全文]SATII生物专题分析——The Cell Membrane
    SAT是Scholastic Aptitude Test的缩写,是申请几乎所有美国大学必须参加的考试。通常,希望继续接受高等教育的高中生需要参加SAT考试,并且SAT考试得分是获取奖学金的重要标准之一。大部分美国大学要求SAT作为录取的条件并根据SAT得分授予奖学金。 The cells of all organisms, prokaryotic and eukaryotic alike, are surrounded by a thin sheet called the cell membrane. This barrier keeps cellular materials in and foreign objects out. The membrane is key to the life of the cell. By regulating what gets into and out of the cell, the membrane maintains the proper chemical composition, which is crucial to the life processes the cell carries out. Structure of the Cell Membrane The cell membrane is made up of two sheets of special fat molecules called phospholipids, placed on top of each other. This arrangement is known as a phospholipid bilayer. Phospholipid molecules naturally arrange in bilayers becaus...
  • [查看全文]SATII生物专题分析——Chemical Bonds
    SAT是Scholastic Aptitude Test的缩写,是申请几乎所有美国大学必须参加的考试。通常,希望继续接受高等教育的高中生需要参加SAT考试,并且SAT考试得分是获取奖学金的重要标准之一。大部分美国大学要求SAT作为录取的条件并根据SAT得分授予奖学金。 The connections between the atoms in a compound are called chemical bonds. Atoms form bonds by sharing their electrons with each other, relying on the power of electric charge to keep themselves attached. Molecules and compounds can also bond with each other. Important bonds between atoms are covalent and ionic bonds. Bonds between molecules or compounds are called dipole-dipole bonds. Covalent bonds Bonds formed through the more or less equal sharing of electrons between atoms are known as covalent bonds.If the electrons in a covalent bond are shared equally, the resulting bond is called a nonpolar covalent bond. When one atom pulls the shared electro...
  • [查看全文]SATII生物部分资料附翻译(三)
    Polypeptides All proteins are made of chains of some orall of these 20 amino acids. The bond formed between two amino acids bydehydration synthesis is known as a peptide bond. A particular protein has a specific sequence of amino acids, which is known as its primary structure.Every protein also winds, coils, and folds in three-dimensional spacein specific and predetermined ways, taking on a unique secondary(initial winding and coiling) and tertiary structure (overall folding).In harsh conditions, such as high temperature or extreme pH, proteinscan lose their normal tertiary shape and cease to function properly.When a protein unfolds in harsh conditions, it has been denatured.血脂 血脂是碳水化合物但不溶于水。他们是有别于其他生物大分子的特点在长的链上碳与氢相连。这种链不溶于水,因为他们非极性。 甘油三酯 甘油三酸酯的构成为三条长链烃末端连有不饱和脂肪酸,叫做甘油。 因为他们包括3个脂肪...
  • [查看全文]SATII生物部分资料附翻译(二)
    Disaccharides Disaccharidesare carbohydratedimers. These dimers are formed from two monomers by dehydrationsynthesis. Any two monosaccharides can form a disaccharide. Forexample, maltose is formed by the dehydration synthesis of two glucosemolecules. Sucrose, common table sugar, comes from the linkage of onemolecule of glucose and one of fructose.二糖二糖化合物,这些二聚体是由两个单体脱水缩合形成。任何两个单糖可以形成一个糖。举例来说,麦芽糖是由脱水合成二葡萄糖分子。蔗糖,淀粉,是由葡萄糖和果糖组成的。 Polysaccharides Polysaccharides can consist of as few asthree and as many as several thousand monosaccharides. Depending ontheir structure and the monosaccharides they contain, polysaccharidescan function as a means of storing excess energy or provide structuralsupport. When cells ingest more carbohydrates thanthey need for fuel, they link the sugars together to formpolysaccharides. The str...
  • [查看全文]SATII生物部分资料附翻译(一)
    The Molecules of Life The elements involved in life processes can, and do, form millions ofdifferent compounds. Thankfully, these millions of compounds fall intofour major groups: carbohydrates, proteins, lipids, and nucleic acids.Though all of these groups are organized around carbon, each group hasits own special structure and function.分子的生活生命过程所涉及的元素可以形成数百万种不同化合物。这些化合物有:碳水化合物,蛋白质,脂类,核酸.所有这些周围都是由碳的结构组成,每组hasits?拥有特殊的结构和功能。 Carbohydrates Carbohydrates are compounds that havecarbon, hydrogen, and oxygen atoms in a ratio of about 1:2:1. If you’restuck on an SAT II Biology question about whether a compound is acarbohydrate, just count up the atoms and see if they fit this ratio.Carbohydrates are often sugars, which provide energy for cellularprocesses. Like all of the biologically importantclasse...