赛达生物考试是科学考试科目中中国考生选择比较少的一项，因为在词汇和知识点上，物理和化学都相对会轻松一些。对于参加这门考试的考生来说，下面北外赛达为大家整理的是关于知识点的介绍就弥足珍贵了。

赛达是SAT subject test的通常说法（学能倾向测验），SAT2考试有别于SAT1，它是一种专项考试，考察学生某一科目的能力，故又被称为SAT SUBJECT TESTS。

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:

H2OH+ + OH–

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 charged particles.

The technical definition of an acid is that it is a hydrogen ion donor, or a proton donor, as hydrogen ions are consist of only a single proton. Acids put H+ ions into solution. The definition of a base is a little more complicated: they are H+ ion or proton acceptors, which means that they remove H+ ions from solution. Some bases can directly produce OH– ions that will take H+ out of solution. NaOH is an example of this type of base:

NaOHNa+ + OH–

A second type of base can directly take H+ out of an H2O solution. Ammonia (NH3) is a common example of this sort of base:

NH3 + H2ONH4+ + OH–

From time to time, the SAT II Biology has been known to ask whether ammonia is a base.