USABO競賽真題！2024USABO真題及解析！

2024USABO競賽，仍然按照慣例考了10道Cell Biology題目，7道Plant Biology題目，13道Animal Biology題目，3道Ethology題目，9道Genetics題目，5道Ecology題目和3道Biodiversity題目。

考察的知識點包括：

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

 

總體而言，和往屆題目相比，難度有所增加，美國賽區(qū)平均分僅為16分。

下面挑選其中的代表性題目進行解析：

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

本題考察16S rRNA的位置，rRNA是ribosomal RNA因此位于Ribosome選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作為female sex hormone 是一種hydrophobic的steroid hormone，會結合cell內(nèi)部的receptor并形成hormone-receptor complex，進一步進入Nucleus去regulation gene expression。因此Estrogen receptor含有nuclear localization sequence 選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 是一種鑒別bacteria cell wall結構的染色法，過程需要用到Crystal violet和Safranin因此選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

本題考察花的ABC hypothesis，想要生成更多的fruit，需要在保留B gene的條件下overexpress C gene 故選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

根據(jù)植物Ethylene的triple response，ethylene越多植物越矮，題目要求選最高的，應是不響應ethylene的植株，ein，同時eto不能recover這種不響應，故選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直接連接liver，因此選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是進行一系列osmolality regulation的主要位置，因此發(fā)生最多的active transportation，因此受影響最大，本題選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故選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. 因此本題中Aphid的行為符合optimal foraging model故選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

本題考察Mammal diversity，對于mammal而言Porpoise和sheep同屬于Cetartiodactyla因此cytochrome c的similarity應最高，故選C.

USABO美國奧林匹克生物競賽是美國舉行的面向全美國的高中生進行IBO國際奧林匹克生物競賽國家隊隊員的選拔性競賽，非美國國籍學生可參加初賽，即由美國的知名大學輪流出題，以50分鐘內(nèi)答50道選擇題的形式考察整個生物學科的知識點的考試。

其內(nèi)容包括生物化學Biochemistry，分子生物學Molecular Biology， 細胞生物學Cellular Biology，發(fā)育生物學DevelopmentalBiology，微生物學Microbiology，植物學Botany，植物生理學Phytophysiology，動物學Zoology，生理學Physiology，遺傳學Genetics，基因組學Genomics，進化學Evolution，生態(tài)學Ecology，動物行為學Ethology和生物分類學Biotaxonomy?？傮w考察內(nèi)容非常廣泛，題目難度大部分屬于college level或更高，對于學生而言屬于挑戰(zhàn)性考試。

因此，對于USABO考試的受眾學生應為，將來希望在大學修習Life science相關學科的學生，包括Biological science，Bioengineering，Medicine等專業(yè)。因為USABO考試是整個美國的生物學科領域內(nèi)最高端硬核的知識類競賽沒有之一，對申請大學背景提升有極大作用。

同時，也因為其考試對于學生的生物學素質(zhì)要求過高，只推薦已開始學習AP Biology的學生參加。

主要學習方式是學習包括Campbell Biology在內(nèi)的美國大學教材，并側(cè)重于Molecular and Cell Biology部分，因為這部分是整個modern experimental 和analytical的life science的核心內(nèi)容，也是那些出題的美國大學教授們側(cè)重于考察的部分，即便是在植物學動物學乃至生態(tài)學行為學的考題中，仍然以gene expression regulation和signal transduction等molecular mechanism為考察點，因為純經(jīng)典的動植物學和分類學太過老舊，那些教授更喜歡套個植物動物的知識背景來考察他們自己研究的MCB的相關課題。同時對于MCB部分的學習也有助于關聯(lián)課內(nèi)的AP部分內(nèi)容。可以拓展知識面，對校內(nèi)課程內(nèi)容降維打擊。

在50分鐘50道題的考試方式下，要求學生有很強的閱讀能力與生物學知識面廣度，來準確作答。同時也需要通過學生整體的生物學知識體系，形成系統(tǒng)性的生物學科學觀，來分析判斷題目給出的背景信息來作答。

競賽的目的不是為了篩選看書多背書多的學生，而是真正對生命科學形成系統(tǒng)性知識理解和科學性思維的學生，因此在學習種對知識點進行總結歸納形成體系是極其重要的。