Solution of multiple choice questions in biology competition
1. Forward deduction method
Forward deduction is to directly infer or calculate the answer according to the known conditions of the topic, and then compare it with the alternative answer given in the topic, and the same is the selected answer. This method is often used to solve multiple-choice questions whose answers are determined by calculation or whose test objectives belong to recitation level.
For example, a couple with normal behavior, the first child gave birth to an albino son, then the probability that the second child and the third child are albino is.
a 1/4 B 1/8 C 1/ 16D 1/9
Albinism is an autosomal recessive genetic disease. The couple with normal behavior gave birth to an albino son in their first child, so it can be concluded that both genotypes must be heterozygotes (Aa). Therefore, the probability of having an albino child in the second birth should be 1/4. The probability of giving birth to an albino child in the third fetus is also 1/4. So the probability that the second child and the third child are albinos should be1/4×1/4 =116. So you should choose C.
2. Inverse method
Inverse deduction is derived from alternative answers, and the answer that meets the meaning of the question is the selected answer. This method is mostly used for multiple-choice questions with more alternative answer information.
For example, pea safflower is dominant to white flowers. The following parental combinations can produce offspring with the same phenotype but different genotypes by crossing with the following strains.
Homozygous white flowers and homozygous safflower
Homozygous white flowers and hybrid safflower hybrid safflower and homozygous safflower
There is a situation that "the phenotype is the same but the genotype of the offspring is different" in the problem-solving stalk, so D is considered first.
The genotype of heterozygous safflower is Rr, and the genotype of homozygous safflower is RR. Rr can produce R and R gametes, Rr can produce R gametes, and individuals with RR and RR genotypes can appear in their offspring, and their phenotypes are all safflower, which just conforms to the meaning of stem. So you should choose d.
3. Push forward and backward and usage
The combination of forward push and backward push is to push forward from the stem of the question, get an intermediate conclusion, and then push back from the alternative answer. The answer that matches the intermediate conclusion is the selected answer. This method is suitable for more complicated multiple-choice questions.
Hairy legs (F) are more dominant than bare legs (F). Pea crown (E) is dominant over single crown (E). At present, there is a rooster A and two hens B and C. These three chickens are pea crowns, which are crossed with A, B and C respectively. The characteristics of their descendants are as follows:
(1) A× B→ hairy pea crown, naked pea crown
(2) A × C → hairy pea crown, hairy single crown
The genotype of rooster a is.
A F
According to the answer, rooster A's personality is a hairy pea crown, from which it can be inferred that the genotype of rooster A is F, E, A, B, C and D, all of which are consistent with them, and then four alternative answers are deduced one by one, and B is contradictory to (1). D is in contradiction with (2). A contradicts (1) and (2). Only c is consistent with (1)(2). So you should choose C.
4. Exclusion method
Exclusion means that according to the conditions given by the stem and the questions raised, the unreasonable answers in the alternative answers are excluded one by one, and the rest are alternative answers. This method is suitable for various forms of multiple-choice questions.
In plant cells, a large number of organelles that produce ATP are.
A chloroplast b ribosome c golgi d mitochondria
Chloroplast decomposition can produce some ATP in photosynthesis, but not a lot of ATP; Ribosomes can not only produce a lot of ATP, but also consume ATP in the process of synthesizing protein. The activity of Golgi apparatus also consumes ATP. Only mitochondria can produce a large amount of ATP during aerobic respiration. So, the answer to this question is D.
5. Comprehensive analysis method
For some multiple-choice questions that are difficult to judge the correct answer directly, it is often necessary to carry out detailed analysis, rigorous reasoning and correct judgment to get the correct answer. This method is called comprehensive analysis. This method is often used to solve complex multiple-choice questions.
Among the parents, grandparents and grandparents of a color-blind boy, except his grandfather, everyone else has normal color vision. The boy's color blindness gene comes from.
Grandpa a, grandma b, grandpa c, grandma d.
Color blindness is a recessive sex-linked genetic disease, and the genotype of color-blind boys is XbY. According to the cross-genetic characteristics of sex-linked inheritance, the boy's color blindness gene comes from his mother. According to his mother's normal color vision, we can know that his mother's genotype is XBXb, and according to his grandfather's normal color vision (no color blindness gene), we can know that his mother's pathogenic gene comes from his grandmother. Therefore, the correct answer to this question is D.
6. Matters needing attention in answering biological questions
1. Check the problem carefully.
Careful examination of questions is the premise of correct answer. After seeing a test question, we must first understand the meanings of all the concepts involved in the topic and the functions of some important words, and eliminate the confusion of superficial phenomena, so as to ensure an accurate understanding of the meaning of the question.
Graft the branches of a hairless peach tree onto a hairy peach tree. The genotype of hairless peach plants is aa, and that of hairy peach plants is AA. In the case of selfing, the genotype of the embryo cell of the seed on the next branch is AA.
A Aa B AA and Aa C AA D AA and Aa
We must first understand the concept of grafting. Grafting belongs to asexual reproduction. Aa and AA do not cross, but AA and AA intersect, so it is impossible to produce. The correct answer can only be C. If you don't analyze it carefully, you may mistake A for aa and AA hybrids.
Get to the point
A test question, whether it is itself or its related content, will contain many factors. In the process of solving the problem, we should eliminate the interference of secondary factors and grasp the key to solve the problem so that the problem can be solved smoothly.
Hundreds of years ago, there were dense forests on the Loess Plateau in China, which later became barren hills. The main reasons are as follows.
A cold current in the north invaded B, and excessive land reclamation destroyed the ecological balance.
C many years of drought, bare earth crust movement frequently.
This topic focuses on the basic knowledge of ecological balance. There are two reasons for destroying the ecological balance: one is natural factors, such as earthquakes, volcanic eruptions, floods and droughts, landslides and so on. Second, human factors, such as human unreasonable exploitation and utilization of nature and environmental pollution. Man-made factors are the main causes of barren hills and hills. So you should choose B.
Step 3 master the law
The answers to some questions are regular. Mastering and applying the rules will make the answer quick and accurate. For example, answering genetic questions has the following rules.
(1) The number of gametes produced by an individual is equal to the product of the number of gametes formed by each pair of genes.
The gamete types produced by individuals with genotype A, B, B, C and C are calculated as follows: A → 2, B → L, C → 2 and D → 2, so the gamete types produced by this individual are 2× 1× 2× 2 = 8.
(2) When parents of any two genotypes cross, the number of offspring genotypes produced is equal to the product of the number of genotypes produced by parents.
Calculation of genotype number of offspring produced by an ABB BC × an ABB BC. Because A a×A a has three genotypes for offspring, B b×B b has three genotypes for offspring and C c×c c has two genotypes for offspring, the number of genotypes produced by AA× AA× AB× BC is 3× 3× 2 = 18.
(3) When parents of any two genotypes cross, the number of sub-phenotypes produced is equal to the product of the number of sub-phenotypes produced by a single cross of parent genes.
Calculation of phenotype number of an ABB BC× an ABB BC. Because A a×A a has two phenotypes, B b×B b has two phenotypes and C c×c c has two phenotypes, so AA× AB× AB× BC has 2× 2× 2 = 8 phenotypes.
(4) The proportion of individual genotypes in offspring is equal to the product of the occurrence probability of each pair of genotypes in individual genotypes.
Calculation of genotype A a B b×A a B B ratio in Aa a B B hybrid offspring Because Aa a genotype individuals account for 1/4 in AA A A hybrid offspring and BB B genotype individuals account for 1/2 in BB B hybrid offspring, AA A genotype individuals account for1/4 x/kloc-in all offspring.
(5) The individual phenotype ratio of offspring is equal to the product of the phenotype ratio of each pair of genes in the individual phenotype.
Calculation of the proportion of phenotype a B in the offspring produced by AA B× AA B Because phenotype A accounts for 65,438+0/4, phenotype B accounts for 4/4, and phenotype A B individuals account for 65,438+0/4× 4/4 = 65 in the offspring produced by AA B× AB.
Problem-solving process of biology short answer questions
The process of solving biological short problems is the process of applying knowledge, which basically belongs to the process from known to unknown. So it is not exactly the same as the process of acquiring new knowledge. From the perspective of thinking, the process of answering questions includes five links: generalization, association, recall, judgment and answer. Let's take the process of solving a problem as an example to illustrate.
For example, a partition with small holes divides the tank into two chambers, and phospholipid molecules are introduced into the small holes of the partition to form a film. The solution with low potassium ion concentration is added to the left chamber of the tank, and the solution with high potassium ion concentration is added to the right chamber. (1) The positive electrode and the negative electrode are inserted into the left and right chambers respectively. It is found that potassium ions cannot enter the right cavity from the left cavity because. (2) If a small amount of valinomycin (polypeptide) is added to the left ventricle at this time, it is found that potassium ions can enter the right ventricle from the left ventricle because. (3) If the electrode is removed at this time, as a result, potassium ions cannot enter the right ventricle from the left ventricle because. (4) The above experiments prove that.
1. Summary
Generalization is to summarize and refine the materials provided by the topic. So as to find the focus of the problem, and finding the focus is the basis for solving the problem correctly. By analyzing and summarizing the experimental steps, experimental phenomena and questions raised in the above examples, it can be concluded that the focus of the problem is the conditions required for the reverse concentration gradient movement of potassium ions.
2. Lenovo (brand name of computer)
Association is to start from the focus of the problem, find out the connection with the learned knowledge, and then determine the combination point of the problem and knowledge. Finding the right combination point is a key step to solve the problem successfully. In the above example, the combination of problem and knowledge is to actively transport substances into three forms of cells.
remember
Memory is to find out the specific content that combines some knowledge. For the above example, it is necessary to recall the principle of active transportation, that is, under the condition of providing energy, with the assistance of the carrier, the substances selected for absorption are transported from the low concentration side to the high concentration side.
judge
Judgment is to judge the questions in the exam according to the relevant theoretical knowledge. In (1), due to the lack of carriers, active transportation cannot be completed. The failure to complete the active transportation in (3) is due to the lack of energy. Because (2) it has energy and carrier, and can complete active transportation.
answer
Answering a question is to describe the answer to the question with standardized biological terms and concise language. The answer of the previous example: (1) There is no carrier on the phospholipid membrane, and potassium ions cannot enter the right ventricle from the left ventricle through active transport; (2) Potassium ions are transported from the left ventricle to the right ventricle by using valinomycin as the carrier and the energy provided by the electrode plate; (3) insufficient energy, unable to carry out active transportation; (4) Active transportation is characterized by the need for carriers, energy consumption, and substances from low concentration to high concentration.