USABO竞赛真题！2024USABO真题及解析！

2024USABO竞赛，仍然按照惯例考了10道Cell Biology题目，7道Plant Biology题目，13道Animal Biology题目，3道Ethology题目，9道Genetics题目，5道Ecology题目和3道Biodiversity题目。

考察的知识点包括：

Organelle

Western Blot

Amino acid charge

Ribosomes RNA

Nucleic acid charge

Steroid hormone receptor

Plant cell wall synthesis

Gram stain

Translation initiation

Plant hormone and growth

Plant water retention

Fern indusium

Flower ABC hypothesis

Plant immunity against bacteria

Ethylene triple response

Plant heart wood and sap wood

Animal Limb development

Muscle sliding-filament model

Lymph system

Heptal portal vein

Nephron Distal Tubule

Blood components

Amino acid neurotransmitter

CD8 cytotoxic T cell

Thalamus and Cerebrum lobes

Hemoglobin Bohr effect

Hypothalamus-anterior pituitary-gonad hormone system

Resting potential

Lipid digestion

Circannual rhythm (Seasonal rhythm)

Optimal foraging model

Lethal gene

X-linked gene

Hardy-Weinberg equilibrium

Blood type ABO

Sex - influenced gene

Selections

Inherited disease

Gene conservative evolution

Virus evolution

Bottom up regulation in community

Species diversity

K-selection & r-selection

Community interspecies relationship

Phosphorus Cycle

Fungi diversity

Invertebrate water vascular system

Mammal evolutionary tree

 

总体而言，和往届题目相比，难度有所增加，美国赛区平均分仅为16分。

下面挑选其中的代表性题目进行解析：

Streptomycin is an antibiotic that works by binding to the 16S rRNA, preventing protein synthesis from occurring. Which of the following structures does streptomycin most likely directly bind to?

1. Nucleus

2. Golgi Apparatus

3. Vacuole

4. Nucleolus

5. Ribosome

本题考察16S rRNA的位置，rRNA是ribosomal RNA因此位于Ribosome选E.

Which of the following proteins most likely contains a nuclear localization sequence?

A. Kinesin

B. Collagen

C. Ubiquitin ligase

D. Phosphofructokinase

E. Estrogen receptor

Estrogen作为female sex hormone 是一种hydrophobic的steroid hormone，会结合cell内部的receptor并形成hormone-receptor complex，进一步进入Nucleus去regulation gene expression。因此Estrogen receptor含有nuclear localization sequence 选E.

A gram stain is performed to determine whether a bacterial species is gram-positive or gram-negative. Which of the following steps is part of the procedure?

I. Staining with safranin

ll. Immunoprecipitation

III. Visualization with UV light

IV. Staining with crystal violet

A.I and IV only

B.ll and Ill only

C.ll and lV only

D.I, I1I, and lV only

E.I, II, I, IV only

Gram stain 是一种鉴别bacteria cell wall结构的染色法，过程需要用到Crystal violet和Safranin因此选A.

Jonah is a farmer-scientist who cultivates a plant that produces aggregate fruit and is known to follow the ABC hypothesis. He wants to produce various mutants of this plant in an attempt to increase fruit yield. Which of the following mutant plant forms would improve fruit yield the most?

A. Constitutive expression of a cytokinin-producing gene

B. Deletion of the B gene

C. Expression of genes that increase phloem plasmodesmata

D. Overexpression of the A gene

E. Overexpression of the C gene in areas where the B gene is expressed

本题考察花的ABC hypothesis，想要生成更多的fruit，需要在保留B gene的条件下overexpress C gene 故选E.

Three plants display different mutations related to the plant hormone ethylene:

- ein: ethylene-insensitive

- eto: ethylene overproducing

- ctr: constitutive triple response

Farmer John crosses these plants with each other and with WT plants in an attempt to produce short offspring. Which of the following crosses is least likely to produce short offspring, and should thus be avoided by Farmer John?

A. WT with ctr

B. WT with eto

C. ein with eto

D. ein with ctr

E. eto with ctr

根据植物Ethylene的triple response，ethylene越多植物越矮，题目要求选最高的，应是不响应ethylene的植株，ein，同时eto不能recover这种不响应，故选C.

A red blood cell traveling between which pair of locations (in the direction of first location to second location) would have the least distance to travel?

A.Left Atrium Cardiac Muscle to Left Atrium

B. Left Lung to Right Lung

C. Liver to Adrenal Gland

D. Small Intestine to Liver

E. Stomach to Spleen

Hepatic portal vein的存在使small intestine直接连接liver，因此选D.

Ruffles has a condition where he retains too much water, causing him to feel bloated. His doctor prescribes a diuretic with the unfortunate side effect of shuttling protons through the inner mitochondrial membrane, which significantly reduces the yield of cellular respiration. Which of the following portions of the kidney would be most affected by this?

A. Proximal Convoluted Tubule

B. Descending loop of Henle

C. Ascending loop of Henle

D. Distal Convoluted Tubule

E. Collecting Duct

Nephron中的distal tubule是进行一系列osmolality regulation的主要位置，因此发生最多的active transportation，因此受影响最大，本题选D.

Which of the following statements is true about CD8?

A. It's most commonly found as an intracellular glycoprotein

B. The D1 domain can bind to MHC ll from antigen-presenting cells

C. It's a marker of cytotoxic T cells

D. It's a highly polymorphic protein

E. CD8 markers are an effective screening tool for the diagnosis of Human immunodeficiency Virus

CD8 protein是Cytotoxic T cell的marker故选C.

Aphids, herbivores with a short generation time, have been observed to run on S. niknud sap as a new food source. S. niknudsap initially had a lower cost of acquisition but greater foraging time relative to T. do sap. Which of the following would best explain the given change in aphid herbivory patterns?

A. Imprinting

B. Optimal foraging model

C. Game theory

D. Spatial learning

E. Problem-solving

According to the optimal foraging model, natural selection should favor a foraging behavior that minimizes the costs of foraging and maximizes the benefits. 因此本题中Aphid的行为符合optimal foraging model故选B.

In a BLAST sequence similarity search on the NCBI website, which of the following proteins will likely have the highest sequence similarity to Porpoise cytochrome c?

A.Human cytochrome c

B. Manatee cytochrome c

C. Sheep cytochrome c

D. Zebra cytochrome c

E. Horse cytochrome c

本题考察Mammal diversity，对于mammal而言Porpoise和sheep同属于Cetartiodactyla因此cytochrome c的similarity应最高，故选C.

USABO美国奥林匹克生物竞赛是美国举行的面向全美国的高中生进行IBO国际奥林匹克生物竞赛国家队队员的选拔性竞赛，非美国国籍学生可参加初赛，即由美国的知名大学轮流出题，以50分钟内答50道选择题的形式考察整个生物学科的知识点的考试。

其内容包括生物化学Biochemistry，分子生物学Molecular Biology， 细胞生物学Cellular Biology，发育生物学DevelopmentalBiology，微生物学Microbiology，植物学Botany，植物生理学Phytophysiology，动物学Zoology，生理学Physiology，遗传学Genetics，基因组学Genomics，进化学Evolution，生态学Ecology，动物行为学Ethology和生物分类学Biotaxonomy。总体考察内容非常广泛，题目难度大部分属于college level或更高，对于学生而言属于挑战性考试。

因此，对于USABO考试的受众学生应为，将来希望在大学修习Life science相关学科的学生，包括Biological science，Bioengineering，Medicine等专业。因为USABO考试是整个美国的生物学科领域内最高端硬核的知识类竞赛没有之一，对申请大学背景提升有极大作用。

同时，也因为其考试对于学生的生物学素质要求过高，只推荐已开始学习AP Biology的学生参加。

主要学习方式是学习包括Campbell Biology在内的美国大学教材，并侧重于Molecular and Cell Biology部分，因为这部分是整个modern experimental 和analytical的life science的核心内容，也是那些出题的美国大学教授们侧重于考察的部分，即便是在植物学动物学乃至生态学行为学的考题中，仍然以gene expression regulation和signal transduction等molecular mechanism为考察点，因为纯经典的动植物学和分类学太过老旧，那些教授更喜欢套个植物动物的知识背景来考察他们自己研究的MCB的相关课题。同时对于MCB部分的学习也有助于关联课内的AP部分内容。可以拓展知识面，对校内课程内容降维打击。

在50分钟50道题的考试方式下，要求学生有很强的阅读能力与生物学知识面广度，来准确作答。同时也需要通过学生整体的生物学知识体系，形成系统性的生物学科学观，来分析判断题目给出的背景信息来作答。

竞赛的目的不是为了筛选看书多背书多的学生，而是真正对生命科学形成系统性知识理解和科学性思维的学生，因此在学习种对知识点进行总结归纳形成体系是极其重要的。