Entrance Examination
For October 2023 and April 2024 students
Master’s Course(Specialized subjects)

Notes
lSelect and answer 3 QUESTIONS from the total 12 QUESTIONS.
The 3 QUESTIONS can be selected from any subjects.
lOne sheet should be used for each selected QUESTION. The reverse
side could be used, if necessary.
lName, examinee’s number and subject name should be written oneach answer sheet.
lQUESTION number should also be written on each answer sheet.

Division of Biosphere Science
Graduate School of Environmental Science
Hokkaido University

QUESTION No.1

Subject on Field Science

Read the following text 1) and 2) and answer the questions.
1) Biomes are the largest geographical biotic communities with certain characteristics,
and broadly correspond with climatic regions. Typically, terrestrial vegetation is classified
into 8 biomes such as tropical rainforest, savannah, desert, temperate grassland, temperate
deciduous broad-leaved forest, temperate evergreen broad-leaved forest, taiga, and tundra.
The () are considered as the main determinant factors of biomes, although otherenvironmental factors are sometimes important. In general, the primary production of
biome shows higher value with increasing these two factors. Furthermore, thebiodiversity also shows spatial variation globally, and the number of species tends to begreater at ( ) region.
Question 1-1. Select one alphabet which shows most appropriate pair of factors for.

A. soil nutrient content and annual precipitation
B. annual mean temperature and annual precipitation
C. soil nutrient content and annual mean temperature
Question 1-2. Select one alphabet which shows most appropriate term for.

A. low latitude
B. mid-latitude
C. high latitude
Question 1-3. Explain the definition of gross primary production and net primary
production in about 50 words.
2) Total soil respiration (Rs) in terrestrial ecosystems is expressed as the sum ofautotrophic respiration (Ra) and heterotrophic respiration (Rh). Bond-Lamberty et al.
(2018) mainly focused on the relationship between Rh and Rs, and they analyzed therecent trend and causes of variations in Rh and Rs by using the global dataset of carbon
flux observed between 1990 and 2014. Figure 1 shows the part of their results. Referring
the result, answer the following questions.
(Reference: Bond-Lamberty et al. 2018, Nature, 560, https://doi.org/10.1038/s41586018-0358-x)

1

Figure 1. Relationship between Rh and Rs and histogram of Rh/Rs (upper small figurein scatter plot). The data for two different periods (1990-1998 and 2007-2014) are shown.
Table indicates the result of significance test for explanation of variation in Rh/Rs. The pvalue indicates the probability that the factor is selected as the explanatory variables bychance.

Question 1-4. Select one alphabet which shows most appropriate text explaining theresult of analysis in Figure 1 (including table).
A. The relationship between the globally observed Rh and Rs was negative.
B. Rh/Rs showed constant value without spatial variation in both periods.
C. Rh/Rs tended to be rising during recent decades, and observation year affected thisvariation at over 99% probability.
D. There was no significant effect of MAT and SOC on the Rh/Rs variation.
Question 1-5. The authors in this study also found that the ratio of Rh to gross primary
production showed significant increase during recent decades. Based on the results in
Figure 1 and this finding, mention the current trend and the expected mechanism of thevariation in CO2 emission from soil in about 100 words using the following 3 keywords.
Keywords: litter, soil organic carbon, temperature

2

QUESTION No. 2 (Subject on Field Science
Read the following text 1) and 2) and answer the following questions.
1) Events that remove organisms from biotic communities and alter the availability ofresources due to natural disasters such as storms and fires or human activities are called(①). After a (①) such as a volcanic eruption or glaciation, where the existing vegetation
has been completely removed, various other species move in and the established species
gradually get replaced. This process is known as (②). In particular, (②) that occurs inplaces where the soil has not yet formed is called (③).
This kind of change is particularly evident in bare land formed by the retreat of glaciers(glacier foreland). A well-known study was conducted in Glacier Bay, Alaska. Only
limited species, such as (A) are initially growing on the bare land, but gradually
photosynthesizing (B) start to invade, which lower the pH and enable (C) to grow in thesoil. Afterward, (D) which form symbiotic relationships with (E) dominate the plantcommunity, and several decades later (F) which also form symbiotic relationships with(E) invade and form dense forests. This forest remains stable for a while, but is replacedby (G) over hundreds of years, forming a new forest.
Question 2-1. Write the terms that apply to ① to ③.
Question 2-2. Select the species that applies to A to G from the following list.
Species: dwarf shrubs (mountain avens), mosses, broadleaf trees (alder) lichens,coniferous trees (spruce), bacteria, nitrogen-fixing bacteria
Question 2-3. Species that alter the environment, as indicated by the underline,
influencing other organisms, are called “ecosystem engineers.” Name an organism that
could be an ecosystem engineer* and explain in about 30 words how that organism alters
the environment, including its ecology and impact on other species.
Note: *Any types of species are acceptable to name.
2) The following figure is modified from a research paper comparing the biomass of
microorganisms living in various environments. Answer the following questions.
(Reference: Fierer et al. 2010. Changes through time: Integrating microorganisms into
the study of succession. Research inhttps://doi.org/10.1016/j.resmic.2010.06.002)
3

Microbiology,161(8),

635–642.

Microbial biomass

algal mat（120 days）
infant intestine（200 days）
deglaciated soil（100 years）

Time
Note: The horizontal axis “Time” in the figure is the age scale of each environment in the
figure legends, with the starting point being the timing when the changes began. The
vertical axis is the change in relative biomass in each environment, and this is notquantitative for comparison with other environment.
Question 2-4. Describe how the bare land formed by the retreat of glaciers (glacierforeland) differs in the pattern of increase in biomass from other environments (no wordlimit). Also, explain the reason for this in about 40 words using the following keywords.
Keywords: oligotrophic, temperature, limitation
Question 2-5. The increase in biomass stagnates midway through the period in theinfant intestine and the algal mat. This suggests that unlimited population growth, known
as exponential growth, does not occur in nature. Instead, this type of growth is referred toas logistic growth. Explain the “carrying capacity”, which is essential to understanding
logistic growth. Additionally, explain the “logistic growth” in relation to the carrying
capacity in about 40 words.

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QUESTION No. 3 (Subject on Field Science
Read the following text 1) to 3) and answer the questions.
1) Biological classification for living organisms
Until the mid-20th century, many biologists acknowledged the existence of either two or
five kingdoms for classification of all living organisms, based on morphological and/or
developmental features. With the advance of molecular biology and phyletic analysis
theories, detailed phyletic relationship of living organisms was assessed using genetic
data. Owing to phylogenetic analyses, the Three Domain System was proposed. One ofthese domains includes a large phyletic group of Eukaryote (e.g., Plantae, Animalia, andFungi). In addition, Fungi are classified into four groups※1: Chytrids, Zygomycetes,
Ascomycetes, and () ※2.

Notes:※1

There is another theory which classifies Fungi into five groups: Chytrids, Zygomycetes,

Glomeromycetes, Ascomycetes, and (※2

In general, ().

) are known as mushrooms.

Question 3-1. Regarding the underlined words
phylogenetic relationships of the three domain are shownon the right. Answer appropriate domain names for A andB.
Question 3-2. Fill in the most appropriate term to blank ().

2) Lifecycle of Fungi
Almost all Fungi reproduce by producing spores, either sexually or asexually. In particular,
plasmogamy is the first stage for sexual reproduction in Fungi, which is characterized by
the fusion of complementary mycelium (monokaryotic = n). Heterokaryon (dikaryotic =n + n) is formed by the combination of mycelia. In particular, for () and Ascomycetes,

Karyogamy occurs at the cells after the stages of heterokaryon is maintained for a certain
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period, and hence spores (n) which retain high genetic diversity are reproduced throughmeioses.
Question 3-3. Regarding the underlined part

, explain a merit of being dikaryotic (=n + n), in about 20 words.
3) Fungi mutualism interaction with vascular land plants

Almost all vascular land plants on Earth form mycorrhizae with Fungi, developing amutualistic relationship under the ground. There is a hypothesis that mutualistic
relationship with Fungi enabled plants to be adapted to land environment because mostancient fossils of land plants have mycorrhizae.
Question 3-4. Regarding the underlined sentence, Fungi which form mycorrhizaewith vascular land plants are defined as mycorrhizal fungi, which are classified in two
types based on morphologic features of the mycorrhizae. Answer the name of these two
types of mycorrhizal fungi, and explain each morphologic feature and niche comparing
each other in about 50 words using the words “cellar walls of root cells”.
Question 3-5. Mutualistic relationship between leguminous plant (Fabaceae) andrhizobium in rhizosphere is a well-known example between land plants and other livingorganisms. Explain this relationship in about 80 words.

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QUESTION No. 4

Subject on Field Science

The following is the sentences about an experiment. Read the sentences carefully andanswer the questions.
Temperate trees become X when they are exposed to low temperature. The X
temperate trees form winter buds that are resistant to low temperature. In temperate
forests, many of the trees open the winter buds after they are exposed to the warm
temperature for a certain period in spring. On the other hand, as in the case of maple
species, it is known that small individuals show earlier bud-burst (leaf flushing) as
compared to large individuals within the same species. As the mechanisms driving sucha size-dependent difference of the bud-burst timing, two following hypotheses arethought.
Hypothesis 1: the warm temperature required for the bud-burst is less for small
individuals as compared to large individuals physiologically.
Hypothesis 2: the air temperature is warmer around the winter buds of small individuals
as compared to those of large individuals.
To test either of the hypotheses is more proper, the following field experiment was
conducted.
Experimental design: In the experimental site shown as in Figure A), we compared theprogress of the bud-burst of 1) small individuals standing at the soil (Treatment , treeheight was about 50cm), 2) large individuals standing at the soil (Treatment , treeheight was 20m), 3) small individuals which were excavated from the soil, planted in
the pots, and put on the forest floor (Treatment , tree height was about 50cm), and 4)
small individuals which were excavated from the soil, planted in the pots, and put on theplatform (Treatment , tree height was about 50cm, platform height was about 20m).
As the results of the monitoring, the results shown in the Figures B-1 4) wereobtained. Figure B-1), Figure B-2), Figure B-3) and Figure B-4) shows the data ofTreatment , Treatment , Treatment
and Treatment , respectively.
Question 4-1. Write a proper word which can fit into (X).
Question 4-2. Describe the scientific reason why the Treatment
was conducted andwhat was clarified by conducting the Treatment
in about 50 words.
Question 4-3. Based on this experiment, which of the Hypothesis 1 or 2 was
supported? Answer the supported hypothesis and describe the evidence you chose thehypothesis in about 30 words.

7

Question 4-4. What are the beneficial points of the earlier bud-burst for smaller trees
at the forest floor as compared to larger trees? Describe them by considering that earlier
bud-burst can result in the earlier start of the sunlight interception while earlier budburst can result in the increase of the late frost-damage on the opened buds within 100
words.

Notes※1 Day of the year: the sequential day number starting with day 1 on January 1st. 31st
December is shown as 365.
※2 Bud-burst rate: the relative percentage of the bud-burst among all buds within the
canopy. 0% means none of the buds opened while 100% means all of the bud opened.

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QUESTION No. 5 (Subject on Life Science)
Read the following text and answer the questions in English.
Protease is a general term for a group of ( 1 ) that catalyze the breakdown of proteins
into smaller polypeptides or single amino acids. These enzymes cleave peptide bonds
within proteins by the addition of a ( 2 ). Proteases can be classified into several types
based on their mode of action or the structure of their active center. Proteases that releasea terminal amino acid residue at the end of a target polypeptide are called ( 3 ), while
those that cleave internal peptide bonds of the protein are referred to as ( 4 ). Alternatively,
proteases are often classified into serine proteases, aspartate proteases, thiol proteases,
and metalloproteases based on the amino acid residues involved in the active center.
Most serine proteases have three catalytic residues in the active center: serine (Ser),histidine (His), and aspartate (Asp), although some may have histidine or aspartate
residues replaced by other amino acids. These three residues are not adjacent to each otherin the amino acid sequence but are spatially arranged so that they are linked by hydrogenbonds in the order Ser-His-Asp, enhancing the ( 5 ) of the oxygen atom at the γ-positionin the side chain of the serine residue.
The physiological functions of proteases are diverse, and their activities are ingeniously
regulated. In many cases, proteases are strictly regulated to function through (6)theinhibition of their activity with protease inhibitors, environmental factors such as pH, andintracellular or tissue localization. Moreover, (7)some proteases regulate the enzymatic
activity of other enzymes by selectively degrading certain parts of them.

Question 5-1. Select the appropriate word(s) in the blanks ( 1 ) - ( 5 ) from the following
options.
oxidoreductases / transferases / hydrophilic / hydrophobic / oxygen molecule / hydrogenmolecule / amino / carboxy / exopeptidases / endopeptidases / hydrolases / water molecule/ isomerases / hydrophilic / hydrophobic / nucleophilicity / electrophilicity

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Question 5-2. Regarding the underlined part (6), in general, enzyme inhibition can beeither reversible or irreversible. Explain the difference between competitive and noncompetitive inhibition among reversible inhibition in approximately 100 words.
Question 5-3. Regarding the underlined part (7), provide an example and explain it inapproximately 100 words.
Question 5-4. Trypsin, a serine protease, specifically cleaves peptide bonds on the
carboxy side of lysine and arginine in polypeptides. This substrate specificity, along withmass spectrometry, is utilized for protein identification. Explain the method in
approximately 200 words.

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QUESTION No. 6 (Subject on Life Science)
Read the following sentences and answer the questions in English.
Hemoglobin is the major protein in red blood cells that carries oxygen molecules to thetissues. It is a multi-subunit protein consisting of two α-globin chains, two β-globin chains,
and a haem containing an iron atom attached to each globin chain.
In the human genome, the β-globin locus on chromosome 11 contains a group of six(a)β-like globin genes: ε,Gγ, Aγ, ψ, δ, and β, arranged in this order. Of these, the ψ gene isa pseudogene.
Each β-like globin gene is expressed in a developmentally specific manner: (b)ε-globin
is expressed specifically during the embryonic period, while the two γ-globins are
expressed mainly during the fetal period. In addition, δ- and β-globin are expressed
postnatally—however, δ-globin accounts for only a tiny proportion and β-globin for the
majority.
The genetic disorder sickle cell disease is caused by a single-base substitution (S-type)mutation in the β-globin gene that changes the amino acid sequence. If a person ishomozygous for this mutation, the mutant hemoglobin molecules tend to aggregate into
chains in low-oxygen conditions, such as in peripheral tissues, resulting in a sickle-shaped
deformation of red blood cells. Therefore, it causes symptoms such as the formation ofblood vessel blockages and the rupture of sickled cells, whereas people who areheterozygous for the S allele do not usually have sickle cell disease.
Despite having the genotype that causes such severe symptoms, some people do notdevelop sickle cell anemia. In these human erythrocytes, γ-globin, which is expressed
only during the fetal period, is known to continue to be expressed after birth, reducing thesymptoms caused by S-type β-globin, known as hereditary persistence of fetal
hemoglobin (HPFH).
Recently, genome-wide association studies (GWASs) were used to search for the genes
responsible for HPFH. The results showed that HPFH is strongly associated with single
nucleotide polymorphisms (SNPs) in the second intron of the BCL11A gene on
chromosome 2.

11The BCL11A gene had been known to be a transcriptional regulator expressed mainly
in lymphocytes and erythroblasts, the precursors of red blood cells. Therefore, (c)when thesecond intron of the BCL11A gene, including the location of the SNPs associated with
HPFH, was deleted in erythroblast cells expressing BCL11A and β-globin, the expressionof the BCL11A gene disappeared, and γ-globin was expressed in addition to β-globin
Question 6-1. For the underline (a), how is the β-like globin gene cluster thought tohave evolved? Answer in about 50 words.
Question 6-2. For the underline (b), why is the substitution of β-globin for γ-globin
presumed to occur? Answer in about 30 words.
Question 6-3.It is known that the gene frequency of the β-globin gene mutation thatcauses sickle cell disease is significantly higher in Central Africa than in other regions.
What are the reasons for this? Answer in about 50 words.
Question 6-4.What is a genome-wide association study? Answer in about 50 words.
Question 6-5. What function is thought to exist in the second intron of the BCL11A
gene? Answer in about 30 words.
Question 6-6.For the underline (c), what is the possible function of BCL11A from thisexperiment? Answer in about 20 words

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QUESTION No. 7 (Subject on Life Science)
Read the following text and answer the questions in English.
To determine DNA sequences, the ( 1 ) method is generally utilized. First, thecomplementary base sequence of the target DNA fragment is extended by using ( 2 )substrates, and ( 3 ) substrates with different fluorescent markers for each base is added
to the extending end, causing the extension reaction to stop. The reaction products arethen separated by ( 4 ) electrophoresis according to their molecular weight, and thefluorescence is detected in the order of ( 5 ) molecular weight, thereby determining thebase sequence of the target DNA fragment. Compared to this conventional Sanger
sequencer, ( 6 ) sequencer allows rapid determination of DNA sequences in a costeffective manner. As a result, the entire ( 7 ) sequence analysis has become moreconvenient, and various genes responsible for specific biological functions are disclosed
and the existence of numerous genes with unknown functions has also been revealed.
Various methods are being employed to analyze the functions of the unknown genes,(8)such as inactivating (or activating) gene functions within a cell to understand theirroles.

Question 7-1. Select the most appropriate word(s) in the blanks ( 1 ) - ( 7 ) from theoptions below to complete the abovementioned text.
ddNTP / dNTP / dATP / next generation / next era / increasing / decreasing / dye primer /dye terminator / genome / cell / amino acid / capillary / SDS-PAGE

Question 7-2. The mechanism of synthesizing proteins from the corresponding genes
differs significantly between eukaryotes and prokaryotes. Select all the descriptions
related to eukaryotes from (a) to (d).
(a) mRNA is translated on the ribosome in the cytoplasm.
(b) Multiple genes are transcribed onto a single mRNA.
(c) Transcription occurs in the nucleus by RNA polymerase.
(d) Unnecessary proteins are degraded by the proteasome.

Question 7-3. (8) The powerful new technology called CRISPR-Cas9 system has beendeveloped to edit the genomes of cells and organisms in order to inactivate gene functions.
Explain this genome editing technique in about 60 words by using the following terms.
guide RNA(gRNA)

Cas9

double-strand break (DSB)
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Question 7-4. The CRISPR-Cas9 system is expected to be applied to improvement ofagricultural productions toward better quality and quantity. Describe the difference of
CRISPR-Cas9 system from the conventional genetic engineering in about 20 words.

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QUESTION No. 8 (Subject on Life Science)
Read the following text and answer the questions in English.
Lysosomes of animal cells are organelles containing enzymes that allow cells tohydrolyze macromolecules. Lysosomal enzymes are most active in ( 1 ) environments
within lysosomes. Hydrolytic enzyme groups are synthesized in the ( 2 ) and thentransported to the ( 3 ), where they are subsequently modified. Lysosomes undergo
intracellular digestion in a variety of situations. Amoebas, for example, take in smallorganisms and granules that serve as food through a process called ( 4 ). Among humancells, ( 5 ), one of the white blood cells, perform ( 4 ). They play a role in protecting the
body by taking in and digesting bacteria and other organisms.

Question 8-1. Write the most appropriate words in the blanks ( 1 ) through ( 5 ).
Question 8-2. Select one of the following sentences that is incorrect and write its
symbol. And correct the incorrect word(s).
Example e) photosynthesis → respirationa) Lysosomal hydrolytic enzymes may work to recycle the cell’s own organic matter.
b) Vacuolar membranes (tonoplasts) are selective for solute transport.
c) Many unicellular eukaryotes in seawater have contractile vesicles that drain excesswater out of the cell.
Question 8-3. In plant cells, certain organic compounds contained in vacuoles play arole in interactions with animals. Give two examples.
Question 8-4. A mature plant cell has a large central vacuole. Describe one possible
primary role of the central vacuole other than being a storage site for ions. In addition,
explain the advantage of having a large vacuole in the role you answered.

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QUESTION No. 9 (Subject on Aquatic and Marine Science)
Read the following text about the photosynthetic pigments in seaweeds and answer eachquestion below.
Seaweeds have unique pigments specific to each taxonomic group in addition to
the photosynthetic pigments shared with land plants. Depending on the composition ofthese photosynthetic pigments, different species dominate in the intertidal zone, which
receives direct sunlight, and the subtidal zone, which only receives weak light due toseawater. The light rapidly reduces in water, with (i) light being the most quickly reduced,
while (ii) and (iii) light can reach the deepest. The primary photosynthetic pigmentcommon to all taxonomic groups is (iv), and in green algae, chlorophyll b and (v) act aslight-harvesting (accessory) pigments. Brown algae have (vi) and (vii) as lineage-specificpigments, while red algae have (viii) and (ix) as their specific pigments. Particularly, (vii)and (ix) can efficiently absorb (ii) light that reaches deep into the sea, effectively utilizing
it for photosynthesis. Green algae, like Codium growing at the subtidal zone, possess (x),which can absorb (ii) light.
Question 9-1. Select appropriate words from the word list below to fill in the blanks (i)to (x).
blue, red, yellow, green, carotene, chlorophyll a, chlorophyll c, siphonaxanthin,phycoerythrin, phycocyanin, fucoxanthin, lutein
Question 9-2. In red algae, individuals growing at the upper and lower parts of theintertidal zone often have different body colors, even within the same species. Explain in
60 words what could have caused this phenomenon.
Question 9-3. Describe the life history of the green alga Ulva australis (Ana-aosa) andthe red alga Pyropyra yezonensis (Susabi-nori) in about 100 words using the following
keywords, focusing on changes in the ploidy, the timing of the meiosis, the shape of
reproductive cells, and differences in body size between generations.
Keywords
Ulva australis: gamete, gametophyte, sporophyte, zoospore
Pyropyra yezonensis: conospore, spermatangia, carospore, carposporangium, carpogonia,
gametophyte, sporophyte, monospores

16QUESTION No. 10 (Subject on Aquatic and Marine Science)
The following sentences mention the fishery resources and fisheries. Read the text andanswer each question.
Marine finfish are diverse but can be divided broadly into (i) and (ii). The
former inhabits the water column, whereas the latter dwells near or on the sea bottom.
(i) includes Anchovy, Mackerel, and Tuna. (ii) includes Hake, Haddock, and Cod. Mostof the world’s oceans are sparsely populated with organisms because their water has low
concentrations of dissolved nutrients and thus lower (iii). Consequently, commercially
important fish stocks tend to aggregate in two areas of the oceans: in the water of the(iv), where food abounds because of the proximity of the continents and their rich river
supply of nutrients, and in a few (v) of the world, such as off western Africa, western
United States and western South America along Peru and northern Chile. The (iv) is agently sloping shelf-like topographical area around the continent, and the (v) is an areawith currents that carry nutrients from the lower layer to the surface layer.
Ocean fishing is a big business because fish cluster in the relatively shallow
water that surrounds the continents. There they feed and breed and, for the mostcommercially important species, aggregate tightly into schools composed of thousandsand even millions of individual fish. They are relatively easy to detect with acoustic
measuring equipments. Using the equipments, vast fishing fleets deploy a variety of nets
to catch them, including stern trawl nets, purse nets, and drift nets.

Question 10-1. Fill in the blanks from (i) to (v) with the most appropriate term, anddescribe it on the answer sheet (an example of an answer, (i)-term).
Question 10-2. Regarding the underlined sentence, please explain in about 100 words
what type of acoustic measuring equipments are used to search for fish schools, and how
they work.
Question 10-3. Please explain in about 150 words the problems regarding the use ofdrift nets in sustainable use of marine biological resources.

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QUESTION No. 11 (Subject on Aquatic and Marine Science)
Answer the following questions on the Beverton-Holt and Ricker stock-recruitment
models, which are widely used in reproduction model to quantify stock-recruitment
relationships.
The Beverton-Holt stock-recruitment model is given by
R =αS/(1+βS where S: Stock R: Recruitment, α and β: constantIn this model, when S is small, R is approximately equal to (i), but as S increases, R
asymptotically approaches (ii).
While, the Ricker stock-recruitment model is given by
R =αS e -βS where S: Stock R: Recruitment, e: Napier’s constant, α and β: constantIn this model, when S is small, R is approximately equal to (iii), but at S = (iv) , R takes
the maximum value (v) and as S increases, R asymptotically approaches (vi).
Question 11-1. Choose the most appropriate number or equation from the followingthat falls into (i) to (vi) in the above description on the two stock-recruitment models(duplicate choice allowed, where e is the Napier’s constant).
(1): α, (2): β, (3): e, (4): 1/α, (5): 1/β, (6): 1/e, (7): αβ, (8): α/β, (9): β/α,(10): α/(βe), (11): β/(αe), (12): α/S, (13): β/S, (14): αS, (15): βS, (16): 1, (17): 0
Question 11-2. Schematically illustrate the Beverton-Holt and Ricker stockrecruitment models, with “Stock (S )” on the X-axis and “Recruitment (R )” on the Y-axis.
At that time, show in the diagram the numerical values or equations for (ii), (iv), (v) and(vi) of the Question 11-1.
Question 11-3. Write the meaning of the constants α and β in the Beverton-Holt stockrecruitment model in 20 words or less each, in terms of organisms.
Question 11-4. The Ricker stock-recruitment model is often adapted to salmonids
species. Give the reasons for this in about 30 words or less.

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QUESTION No. 12 (Subject on Aquatic and Marine Science)
Question 12-1. Indicate the two concepts of salinity used in oceanography and explain
each in around 100 words including definitions, units, and measurement methods.
Question 12-2. Illustrate the variation of salinity in surface oceans from 40°N to 40°S
to show how the salinity averaged for surface waters varies with latitude. Note that you
should indicate latitude on the x-axis and salinity on the y-axis with clearly indicating thescales and values on each axis. Furthermore, briefly explain why salinity shows such alatitudinal change within 100 words.
Question 12-3. Answer the residence time of sodium in the ocean using the data below
with briefly explaining the calculation process and units. The sodium concentration in theocean is assumed to be in a steady state.
Parameter

Value

Surface area of ocean

4.0×108 km2

Mean ocean depth

4000 mSalinity of seawater

35

Percentage of sodium in salt
30 % in weight
Annual freshwater flux from rivers to the
3.0×107 km3
ocean
Sodium concentration in river water*
6.0 mg/L
Note *Corrected for cyclic salt
Question 12-4. When the residence time of silicon is calculated as in Question 12-3,
it is about three orders of magnitude smaller than that of sodium. Explain the reason forthis within 100 words.

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