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Question 4821Question →

An ecological survey of a protected forest reserve recorded four distinct ecological observations:

Observation	Description
I	All individuals of the mahogany tree (Khaya senegalensis) inhabiting a designated $15\text{--hectare}$ plot.
II	The combined populations of green plants, fruit bats, soil fungi, and earthworms interacting within the forest floor layer.
III	The physical soil minerals, ambient humidity, temperature, and solar radiation combined with all living organisms in the reserve.
IV	The specific micro-habitat conditions and nutritional role occupied by the pangolin (Phataginus tricuspis) as an ant-eating nocturnal mammal.

Which of the following correctly matches observations I, II, III, and IV to their corresponding levels of ecological organization and concepts?

I = Population, II = Community, III = Ecosystem, IV = Niche

I = Community, II = Ecosystem, III = Biome, IV = Habitat

I = Population, II = Ecosystem, III = Biosphere, IV = Habitat

I = Species, II = Community, III = Ecosystem, IV = Habitat

Show answer & explanation

Answer: I = Population, II = Community, III = Ecosystem, IV = Niche

Answer

Observation I corresponds to a Population, II to a Community, III to an Ecosystem, and IV to a Niche.

The correct option accurately distinguishes between the hierarchical tiers of ecological organization. A single species group in a defined region represents a population (I); the assembly of all living species forms a community (II); the combined biotic community and abiotic physical factors constitute an ecosystem (III); and the specific functional role and feeding behavior of an organism defines its ecological niche (IV).

Step-by-Step Solution

Analyze Observation I

Observation I describes a group of organisms belonging to the same species (*Khaya senegalensis*) inhabiting a specific geographic area at the same time.

By definition, a group of individuals of one species in a given area constitutes a Population.

Analyze Observation II

Observation II includes plants, animals, fungi, and earthworms (multiple species populations) interacting in one area without specifying non-living physical factors.

An assemblage of different interacting populations of organisms in a given habitat forms a Ecological Community.

Analyze Observation III

Observation III combines both living organisms (biotic factors) and non-living physical/chemical elements (abiotic factors such as soil minerals, humidity, temperature, solar radiation).

A community interacting with its non-living physical environment forms an Ecosystem.

Analyze Observation IV

Observation IV describes the functional position, feeding habits, and specific environmental adaptations of the ant-eating pangolin.

The complete functional role, position, and behavioral lifestyle of an organism within its environment defines its Ecological Niche.

Key Concept

Levels of Ecological Organization and Functional Differentiation

Question 4822Question →

Match each plant growth phenomenon or developmental regulator on the left with its corresponding physiological function or developmental outcome on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Hypocotyl rapid elongation matches with pulling cotyledons above soil in epigeal germination; Epicotyl rapid elongation matches with pushing the plumule upward while cotyledons stay underground in hypogeal germination; Gibberellin synthesis upon imbibition matches with inducing the aleurone layer to produce amylase; Ecdysone secretion matches with triggering apolysis and cuticle synthesis during ecdysis.

Hypocotyl elongation brings cotyledons above ground (epigeal germination). Epicotyl elongation elevates the plumule while keeping cotyledons below ground (hypogeal germination). Gibberellin signals the aleurone layer to produce

\alpha

-amylase during germination. Ecdysone promotes apolysis and cuticle formation during arthropod ecdysis.

Step-by-Step Solution

Analyze seedling germination types

Hypocotyl elongation lifts cotyledons above ground (epigeal), whereas epicotyl elongation leaves cotyledons underground (hypogeal).

The site of stem elongation relative to the cotyledons determines whether germination is epigeal or hypogeal.

Evaluate seed dormancy breakdown biochemistry

Imbibition activates gibberellin release from the embryo, targeting the aleurone layer.

Gibberellins stimulate gene transcription of hydrolytic enzymes like

\alpha

-amylase to break down stored endosperm starch into soluble glucose.

Analyze arthropod growth and hormonal control

Ecdysone directly controls epidermal cell division and cuticle synthesis.

Ecdysone is the primary moulting hormone in insects that coordinates shedding of the old exoskeleton.

Key Concept

Plant Germination Dynamics, Seed Mobilization Biochemistry, and Hormonal Regulation of Ecdysis

Question 4823Question →

The table below shows the distribution of weekly expenditures (in thousands of Naira, ₦'000) of a group of market traders:

Expenditure (₦'000)	Frequency ( $f$ )
10	5
20	8
30	$x$
40	4
50	3

If the mean weekly expenditure of the traders is ₦28,000 (represented as $28$ in the table units), find the value of $x$ .

Show answer & explanation

Answer: 20

Answer

The value of

x

is 20.

Using the arithmetic mean formula

\bar{x} = \frac{\sum fx}{\sum f}

, we set up the equation with the given mean of 28:

\frac{520 + 30x}{20 + x} = 28

. Cross-multiplying gives

520 + 30x = 560 + 28x

. Rearranging terms yields

2x = 40

, which gives

x = 20

Step-by-Step Solution

Sum all given frequencies including the unknown

x

to get the total frequency expression.

\sum f = 20 + x

The total number of observations is needed for the denominator of the arithmetic mean formula.

Multiply each expenditure value by its respective frequency and aggregate the terms.

\sum f x = 520 + 30x

The total weighted value of all expenditures is needed for the numerator of the mean formula.

Substitute the known mean value of 28 into the equation

\bar{x} = \frac{\sum f x}{\sum f}

and solve for

x

x = 20

Isolating

x

yields the exact missing frequency.

Key Concept

Finding a missing frequency from a frequency distribution given the arithmetic mean.

Question 4824Question →

Raising the temperature of a reaction mixture from $300\text{ K}$ to $310\text{ K}$ often doubles the rate of reaction, despite the average kinetic energy of the reactant molecules increasing by only about $3.3\%$ . Which of the following best explains this disproportionate increase in reaction rate according to collision theory?

The total collision frequency between reactant particles doubles with a

10\text{ K}

rise in temperature.

The activation energy (

E_a

) of the reaction is lowered significantly by the increase in thermal energy.

The fraction of reactant molecules possessing kinetic energy equal to or exceeding the activation energy increases exponentially.

The average kinetic energy of all reactant molecules doubles due to an increase in molecular velocity.

Show answer & explanation

Answer: The fraction of reactant molecules possessing kinetic energy equal to or exceeding the activation energy increases exponentially.

Answer

The fraction of reactant molecules possessing kinetic energy equal to or exceeding the activation energy increases exponentially.

According to collision theory and the Maxwell-Boltzmann distribution, reaction rate depends on the frequency of effective collisions—collisions possessing energy greater than or equal to the activation energy (

E \ge E_a

). The fraction of molecules satisfying this condition is expressed by

f = e^{-E_a / RT}

. Because of this exponential factor, a small increase in absolute temperature (

T

) substantially increases the proportion of high-energy molecules in the tail of the curve, roughly doubling the effective collision frequency for typical activation energies.

Step-by-Step Solution

Analyze the relationship between temperature and average kinetic energy.

Average kinetic energy is directly proportional to temperature in Kelvin (

E_k = \frac{3}{2}RT

). A rise from

300\text{ K}

310\text{ K}

yields

\frac{310 - 300}{300} = 3.33\%

increase.

This rules out explanations claiming that average kinetic energy or velocity doubles.

Analyze total collision frequency versus effective collision frequency.

Total collision frequency increases only slightly (

\propto \sqrt{T}

\approx 1.6\%

increase), whereas effective collision frequency increases dramatically.

For a collision to lead to reaction, particles must collide with energy

E \ge E_a

and correct orientation.

Apply the Maxwell-Boltzmann distribution model.

The fraction of molecules with

E \ge E_a

is proportional to

e^{-E_a / RT}

. Because of the exponential dependence on

T

, even a modest

10\text{ K}

rise significantly expands the tail of the energy distribution curve beyond

E_a

, leading to roughly double the number of successful high-energy collisions.

This accounts for the dramatic increase in reaction rate.

Key Concept

Collision Theory and Maxwell-Boltzmann Energy Distribution

Estimated Time:1m 30s

Question 4825Question →

When comparing economic systems, which of the following features primary reliance on government planning rather than the price mechanism to solve the basic economic problems of what, how, and for whom to produce?

Command economy

Free market economy

Mixed economy

Traditional economy

Show answer & explanation

Answer: Command economy

Answer

The command economy relies primarily on central government planning to allocate resources and solve basic economic problems.

In a command economy, state planners directly guide production decisions and resource allocation, replacing price signals with centralized administrative control.

Step-by-Step Solution

Identify the primary allocation mechanism described in the stem

The mechanism relies on central state planning and administrative directives.

Economic systems are categorized by how they answer the fundamental economic questions.

Compare this mechanism across economic system models

Socialist or command economies use state planning boards, while market economies rely on consumer sovereignty and the price system.

Evaluating resource allocation mechanisms is essential for comparative analysis of economic systems.

Key Concept

Comparative analysis of allocation mechanisms in economic systems

Question 4826Question →

The table below displays a consumer's utility schedule from consuming consecutive cups of tea:

Quantity (Units)	Total Utility (Utils)	Marginal Utility (Utils)
1	20	20
2	35	15
3	45	$X$
4	50	5
5	50	0
6	46	-4

Based on the table, what is the value of $X$ (the marginal utility of the 3rd unit), and at which level of consumption does the consumer reach the point of satiety?

X = 10

utils, and the point of satiety is reached at 5 units.

X = 15

utils, and the point of satiety is reached at 4 units.

X = 10

utils, and the point of satiety is reached at 4 units.

X = 15

utils, and the point of satiety is reached at 5 units.

Show answer & explanation

Answer: $X = 10$ utils, and the point of satiety is reached at 5 units.

Answer

X = 10

utils, and the point of satiety is reached at 5 units.

The marginal utility of the 3rd unit is calculated as

TU_3 - TU_2 = 45 - 35 = 10

utils. Satiety represents full consumer satisfaction, which occurs at 5 units where total utility reaches its maximum of 50 utils and marginal utility drops to zero.

Step-by-Step Solution

Calculate the Marginal Utility (

X

) for the 3rd unit consumed.

X = TU_3 - TU_2 = 45 - 35 = 10

utils.

Marginal utility measures the addition to total utility derived from consuming one extra unit of a commodity (

MU_n = TU_n - TU_{n-1}

Determine the point of satiety from the utility schedule.

Satiety occurs at 5 units of consumption, where

TU = 50

(maximum) and

MU = 0

The point of satiety is defined as the level of consumption where total utility is maximized and marginal utility becomes zero.

Key Concept

Law of Diminishing Marginal Utility and Point of Satiety

Estimated Time:1m 30s

Question 4827Question →

The following macroeconomic data (in billions of Dollars) is provided for a country in a given fiscal year:

Component	Amount ($ billions)
Consumer Expenditure ( $C$ )	500
Gross Private Domestic Investment ( $I$ )	150
Government Consumption & Investment ( $G$ )	200
Exports ( $X$ )	80
Imports ( $M$ )	100

Using the expenditure method, what is the Gross Domestic Product ( $GDP$ ) of the country?

830

billion

870

billion

1,030

billion

650

billion

Show answer & explanation

Answer: $830$ billion

Answer

830

billion

Under the expenditure approach,

GDP

is calculated as the sum of personal consumption expenditure (

C

), gross private domestic investment (

I

), government purchases (

G

), and net exports (

X - M

). Substituting the given values yields

500 + 150 + 200 + (80 - 100) = 850 - 20 = 830

billion dollars.

Step-by-Step Solution

Identify the national expenditure formula for calculating Gross Domestic Product (GDP).

GDP = C + I + G + (X - M)

The expenditure method sums private consumption, investment, government expenditure, and net exports.

Calculate Net Exports (

X - M

Net Exports

= 80 - 100 = -20

billion dollars

Imports must be subtracted from exports to derive net external trade expenditure.

Sum all expenditure components together.

GDP = 500 + 150 + 200 + (-20) = 830

billion dollars

Adding consumption, investment, government purchases, and net exports gives the total GDP.

Key Concept

Expenditure Method of Measuring GDP

Estimated Time:45s

Question 4828Question →

According to the law of diminishing returns, what eventually happens to the marginal product of a variable input as successive units of that input are added to a fixed input in the short run?

It begins to decline

It increases at an increasing rate continuously

It immediately becomes negative

It remains permanently constant

Show answer & explanation

Answer: It begins to decline

Answer

The marginal product begins to decline.

The fundamental definition of the law of diminishing returns states that when increasing amounts of a variable factor are applied to a fixed quantity of other factors, a point is eventually reached where the addition to total product (marginal product) starts to decrease.

Step-by-Step Solution

Identify the core principle of the Law of Diminishing Returns.

The law governs short-run production where at least one factor of production is fixed.

Short-run constraints limit capacity as more variable factors (such as labor) are combined with fixed capital or land.

Analyze the behavior of marginal product as variable inputs increase.

After reaching a maximum point of efficiency, each additional unit of input contributes less additional output than the previous unit.

The fixed factor becomes crowded relative to the increasing quantity of the variable factor, leading to a fall in marginal product.

Key Concept

Law of Diminishing Marginal Returns

Estimated Time:45s

Question 4829Question →

Match each utility condition or stage of consumption on the left with its corresponding mathematical and economic relationship on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Point of Satiety matches with zero Marginal Utility and peak Total Utility (

\text{MU} = 0

); Total Utility increasing at a diminishing rate matches positive but declining Marginal Utility (

\text{MU} > 0

); Onset of Disutility matches declining Total Utility (

\text{MU} < 0

); and Maximum Average Utility matches the intersection where Marginal Utility equals Average Utility (

\text{MU} = \text{AU}

Each pair correctly reflects the calculus and economic relationships governing utility curves. At satiety,

\text{TU}

reaches its maximum peak while

\text{MU} = 0

. When

\text{TU}

grows at a diminishing rate,

\text{MU}

is positive but decreasing. When consumption brings disutility (

\text{MU} < 0

\text{TU}

drops. Finally, the mathematical identity between average and marginal variables dictates that average utility is maximized where

\text{MU} = \text{AU}

Step-by-Step Solution

Analyze the derivative relationship between Total Utility (

\text{TU}

) and Marginal Utility (

\text{MU}

Marginal Utility is the first derivative of Total Utility with respect to quantity (

\text{MU} = \frac{d\text{TU}}{dQ}

Understanding

\text{MU}

as the slope of the

\text{TU}

curve allows exact matching of critical points like maxima and inflection points.

Identify the point of satiety.

When

\text{TU}

reaches its maximum, its slope is zero (

\text{MU} = 0

Point of satiety defines complete satisfaction where no more utility can be added.

Analyze the diminished growth of

\text{TU}

and negative

\text{MU}

Diminishing

\text{TU}

growth implies

\text{MU} > 0

but declining. Once

\text{MU} < 0

\text{TU}

begins falling.

This reflects the fundamental Law of Diminishing Marginal Utility.

Examine the relationship between Average Utility (

\text{AU}

) and Marginal Utility (

\text{MU}

\text{AU}

reaches its maximum where

\text{MU} = \text{AU}

When marginal value equals average value, the average value is stationary at its peak.

Key Concept

Interrelationships among Total, Average, and Marginal Utility concepts

Estimated Time:1m 0s

Question 4830Question →

The table below presents the monthly Production Possibility Schedule for a manufacturing firm in Aba producing Leather Shoes and Leather Bags using a fixed quantity of labor and raw materials:

Production Combination	Leather Shoes (hundreds of pairs)	Leather Bags (hundreds of units)
P	$0$	$150$
Q	$20$	$140$
R	$40$	$120$
S	$60$	$90$
T	$80$	$50$
U	$100$	$0$

If the plant is currently producing at Combination Q ( $20$ hundred pairs of shoes and $140$ hundred bags) and reallocates its resources to increase shoe production to Combination T ( $80$ hundred pairs of shoes), what is the average opportunity cost of producing ONE additional pair of Leather Shoes over this range? Express your answer in units of Leather Bags foregone.

Show answer & explanation

Answer: 1.5

Answer

1.5 bags foregone per additional pair of shoes

Opportunity cost measures the sacrifice of one good required to obtain an additional quantity of another good. Moving from Combination Q to Combination T increases shoe production by 60 hundred pairs (from 20 to 80 hundred pairs) while reducing bag production by 90 hundred units (from 140 to 50 hundred units). The opportunity cost per additional pair of shoes is calculated as 90 hundred bags divided by 60 hundred pairs of shoes, yielding exactly 1.5 bags foregone per pair of shoes.

Step-by-Step Solution

Determine initial production at Combination Q

Shoes =

20

hundred pairs (

2,000

pairs), Bags =

140

hundred units (

14,000

bags)

Establishes the baseline output before resource reallocation.

Determine final production at Combination T

Shoes =

80

hundred pairs (

8,000

pairs), Bags =

50

hundred units (

5,000

bags)

Identifies the new production level after expanding shoe production.

Calculate the net gain in shoe production and net loss in bag production

Additional shoes =

80 - 20 = 60

hundred pairs; Bags foregone =

140 - 50 = 90

hundred bags

Opportunity cost evaluates the sacrifice required to gain additional units of the preferred good.

Calculate the unit opportunity cost

Opportunity cost per shoe pair =

\frac{90\text{ hundred bags}}{60\text{ hundred pairs}} = 1.5\text{ bags}

Divides the total quantity of the sacrificed good by the total gain of the produced good to get per-unit real cost.

Key Concept

Opportunity Cost / Marginal Rate of Transformation

Question 4831Question →

Plants growing in the Tropical Rainforest biome face intense competition for light in the dense canopy layer, whereas plants in the Sahel Savanna face extreme water scarcity and high evapotranspiration rates. Which combination of structural adaptations correctly distinguishes tropical rainforest trees from Sahel savanna shrubs?

Broad leaves with drip tips and buttress roots in rainforest plants; reduced needle-like or thorny leaves and deep taproot systems in savanna plants.

Pneumatophores and salt-excreting glands in rainforest plants; succulent stems with broad deciduous leaves in savanna plants.

Deep taproot systems with needle-like leaves in rainforest plants; buttress roots with broad leaves in savanna plants.

Broad leaves with prop roots in rainforest plants; pioneer mosses and lichen crusts lacking vascular tissue in savanna plants.

Show answer & explanation

Answer: Broad leaves with drip tips and buttress roots in rainforest plants; reduced needle-like or thorny leaves and deep taproot systems in savanna plants.

Answer

Broad leaves with drip tips and buttress roots in rainforest plants; reduced needle-like or thorny leaves and deep taproot systems in savanna plants.

Tropical rainforest trees inhabit humid, high-rainfall environments where light is limiting near the forest floor and soils are shallow; thus, they possess broad leaves with drip tips (to prevent leaf rotting and fungal growth) and massive buttress roots for physical support. Conversely, Sahel savanna vegetation faces severe drought and intense evapotranspiration, favoring xerophytic adaptations like reduced leaf surface area (thorns/spines) to minimize water loss and long taproots to draw water from deep subterranean layers.

Step-by-Step Solution

Analyze the environmental constraints of the Tropical Rainforest biome.

High rainfall, high humidity, and dense canopy require structural adaptations such as broad photosynthetic leaves to capture low light under the canopy, drip tips to quickly shed water off leaf surfaces, and tall trunks supported by buttress roots in nutrient-poor shallow soils.

Rainforest plants prioritize light capture, rapid water drainage from leaves, and physical stability.

Analyze the environmental constraints of the Sahel Savanna biome.

Low rainfall, prolonged dry seasons, and high temperatures require xeromorphic adaptations such as reduced leaf surface area (spines/thorns/thickets) to restrict transpiration losses, thick cuticles, and extensive deep taproot systems to access deep groundwater reserves.

Savanna plants prioritize water conservation and deep moisture absorption.

Select the option that correctly contrasts these two distinct biome profiles.

The option specifying broad leaves with drip tips and buttress roots for rainforest plants paired with reduced/thorny leaves and deep taproots for savanna plants is correct.

This accurately reflects the morphological adaptations demanded by the respective abiotic conditions of each biome.

Key Concept

Morphological Adaptations to Terrestrial Biomes

Question 4832Question →

An experiment was conducted to investigate the rate of protein digestion by incubating boiled egg white with pancreatic juice under different physiological conditions. In tube 1, sodium hydrogen carbonate was added at $37^\circ\text{C}$ . In tube 2, dilute hydrochloric acid was added at $37^\circ\text{C}$ . In tube 3, sodium hydrogen carbonate was added after boiling the pancreatic juice at $100^\circ\text{C}$ . Which of the following observations and physiological explanations correctly accounts for the results?

Rapid digestion occurs only in tube 1 because trypsin and chymotrypsin require an alkaline medium provided by bicarbonate ions at body temperature.

Rapid digestion occurs only in tube 2 because pancreatic enzymes require an acidic medium to convert zymogens into active trypsin.

Digestion in tube 3 is only temporarily delayed because low-temperature inactivation can be reversed upon cooling.

Extracellular digestion occurs equally in tube 1 and tube 3 because pancreatic juice acts saprophytically on non-living substrates.

Show answer & explanation

Answer: Rapid digestion occurs only in tube 1 because trypsin and chymotrypsin require an alkaline medium provided by bicarbonate ions at body temperature.

Answer

Rapid digestion occurs only in tube 1 because pancreatic proteolytic enzymes (such as trypsin) operate optimally in an alkaline environment provided by sodium hydrogen carbonate at optimum body temperature (37°C).

Pancreatic juice contains proteolytic enzymes such as trypsinogen and chymotrypsinogen. In the duodenum, sodium hydrogen carbonate secreted in pancreatic juice neutralizes gastric acid to establish an alkaline pH (

\text{pH } 7.5 - 8.0

), which is optimal for pancreatic enzyme activity at body temperature (

37^\circ\text{C}

). Tube 1 replicates these optimal physiological conditions, leading to rapid protein hydrolysis.

Step-by-Step Solution

Analyze the components of pancreatic juice and their optimal pH environment.

Pancreatic juice contains digestive enzymes like trypsin and chymotrypsin which hydrolyze proteins in the alkaline environment of the duodenum.

Sodium hydrogen carbonate neutralizes acidic chyme from the stomach and provides the alkaline pH needed for pancreatic enzymes.

Evaluate the effect of acid in tube 2.

Hydrochloric acid lowers the pH, creating an acidic environment in which trypsin is inactive.

Pancreatic enzymes require alkaline pH, unlike gastric pepsin which functions in acidic pH.

Evaluate the effect of thermal denaturation in tube 3.

Boiling pancreatic juice at 100°C permanently denatures the active sites of its enzymes.

High temperatures break hydrogen and disulfide bonds in enzyme tertiary structure, rendering them inactive even if optimal pH is supplied.

Key Concept

Enzyme specificity, pH optima, and thermal denaturation in mammalian digestive tracts

Question 4833Question →

Match each mammalian nephron region on the left with its primary physiological function during urine formation on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Glomerulus matches with Ultrafiltration under high hydrostatic pressure; Proximal convoluted tubule matches with Selective reabsorption of glucose, amino acids, and bulk filtrate water; Loop of Henle matches with Establishment of an osmotic medullary gradient; Distal convoluted tubule matches with Hormone-regulated reabsorption of sodium and selective tubular secretion.

Each nephron section performs a distinct step in urine formation: the glomerulus filters blood plasma under pressure; the proximal convoluted tubule reabsorbs vital solutes like glucose; the Loop of Henle generates the medullary osmotic gradient; and the distal convoluted tubule carries out selective secretion and hormone-controlled electrolyte tuning.

Step-by-Step Solution

Identify the primary function of the renal corpuscle/glomerulus

High blood pressure forces water and dissolved solutes out of capillaries into Bowman's capsule (ultrafiltration).

Afferent arteriole diameter is larger than efferent arteriole diameter, creating hydrostatic filtration pressure.

Determine the main process occurring in the proximal convoluted tubule

Obligatory reabsorption of 100% glucose, amino acids, and ~65-70% of salts and water occurs here.

Epithelial lining has a microvillar brush border that maximizes surface area for active transport.

Identify the role of the hair-pin shaped Loop of Henle

Creates a hyperosmolal gradient in the renal medulla via countercurrent multiplication.

Descending limb is permeable to water, while ascending limb actively pumps out sodium and chloride ions.

Determine the functional role of the distal convoluted tubule

Fine-tunes electrolyte balance via active secretion of ions (

K^+

H^+

) and aldosterone-stimulated

Na^+

absorption.

Target region for hormonal regulation to maintain systemic pH and blood volume balance.

Key Concept

Nephron functional anatomy and urine formation processes

Estimated Time:1m 15s

Question 4834Question →

While the ABO blood group system in human populations is governed by three multiple alleles ( $I^A$ , $I^B$ , and $i$ ), any given diploid individual can inherit a maximum of two alleles, with $I^A$ and $I^B$ exhibiting codominance with each other while both display complete dominance over the allele $i$ .

True

False

Show answer & explanation

Answer: True

Answer

True

The statement accurately distinguishes between population-level multiple alleles and individual diploid genetic constitution, while correctly identifying the codominant relationship between

I^A

and

I^B

alongside their complete dominance over the recessive

i

allele.

Step-by-Step Solution

Analyze allele distribution in populations versus diploid individuals.

Multiple alleles refer to the presence of more than two allele options in a population gene pool (

I^A

I^B

i

), but diploid organisms possess only two locus copies (one maternal, one paternal).

Meiotic segregation and diploid chromosome organization restrict an individual to possessing a maximum of two alleles for any autosomal gene.

Examine the phenotypic expression pattern of heterozygous genotype

I^A I^B

Both antigen A and antigen B are independently and fully expressed on red blood cell surfaces, defining codominance.

Codominance occurs when neither allele masks the other, leading to simultaneous, distinct expression of both allele products.

Evaluate the interaction between alleles

I^A

I^B

and allele

i

Genotypes

I^A i

and

I^B i

result in blood group A and blood group B phenotypes respectively, as allele

i

produces a non-functional enzyme.

Allele

i

is recessive, so

I^A

and

I^B

exhibit complete dominance over

i

Key Concept

Multiple Alleles and Codominance in ABO Blood Groups

Estimated Time:1m 30s

Question 4835Question →

A firm operating in a perfectly competitive market faces a constant market equilibrium price of $P = \$60$ . The firm's short-run total cost function is given by $TC = Q^2 + 20Q + 100$ , where $Q$ represents output in units, resulting in a marginal cost function of $MC = 2Q + 20$ . What is the total short-run economic profit earned by this firm at its profit-maximizing output level?

$300

$200

$400

$15

Show answer & explanation

Answer: $300

Answer

The firm earns a total short-run economic profit of $300.

Under perfect competition, a firm maximizes profit by producing where price equals marginal revenue and marginal cost (

P = MR = MC

). At

P = \$60

, setting

60 = 2Q + 20

yields

Q = 20

. At

Q = 20

, Total Revenue is

TR = 60 \times 20 = \$1,200

and Total Cost is

TC = 20^2 + 20(20) + 100 = \$900

. Total short-run economic profit is

TR - TC = \$1,200 - \$900 = \$300

Step-by-Step Solution

Determine the profit-maximizing output level

Output Q = 20 units

Under perfect competition, marginal revenue equals market price (

MR = P = \$60

). Setting

MR = MC

gives

60 = 2Q + 20

, which simplifies to

2Q = 40

Q = 20

units.

Calculate total revenue (TR)

TR = $1,200

TR = P \times Q = 60 \times 20 = \$1,200

Calculate total cost (TC)

TC = $900

TC = (20)^2 + 20(20) + 100 = 400 + 400 + 100 = \$900

Compute total economic profit (π)

Profit = $300

\pi = TR - TC = \$1,200 - \$900 = \$300

Key Concept

Short-run profit maximization under perfect competition occurs where Price (Marginal Revenue) equals Marginal Cost (P = MC). Total economic profit is Total Revenue minus Total Cost.

Estimated Time:2m 0s

Question 4836Question →

In a closed chemical system at dynamic equilibrium, introducing a positive catalyst increases the rate of the forward reaction while leaving the rate of the reverse reaction unchanged, thereby increasing the overall equilibrium yield of products.

True

False

Show answer & explanation

Answer: False

Answer

False. A positive catalyst lowers the activation energy barrier for both the forward and reverse reactions equally. As a result, both rates increase by the same factor, leaving the position of equilibrium and the product yield unchanged.

The statement is false because a catalyst lowers the activation energy for both the forward and reverse pathways by the same magnitude, thereby accelerating both rates equally and leaving the equilibrium position and product yield unaltered.

Step-by-Step Solution

Analyze how a catalyst affects the activation energy (

E_a

) of a reversible reaction.

A catalyst provides an alternative reaction mechanism with a lower activation energy for both the forward and reverse directions.

Since the energy profile is lowered symmetrically by

\Delta E_a

, the energy barrier for the reverse reaction is reduced by the identical amount as the forward reaction.

Evaluate the effect of lowered activation energy on reaction rates.

The forward rate constant (

k_f

) and reverse rate constant (

k_r

) both increase by the same proportional factor.

Because both rate constants increase equally, the forward and reverse reaction rates remain equal at the new accelerated pace.

Determine the impact on the equilibrium constant (

K_c

) and product yield.

The equilibrium constant

K_c = \frac{k_f}{k_r}

and the relative equilibrium concentrations of reactants and products remain unchanged.

A catalyst only affects the kinetic rate of reaching equilibrium, not the thermodynamic stability or position of equilibrium.

Key Concept

Effect of Catalysts on Dynamic Equilibrium and Activation Energy

Estimated Time:1m 0s

Question 4837Question →

In an oligopolistic market for cement in Nigeria, a leading firm observes that if it raises its price above the prevailing market price of $₦4,000$ per bag, rival firms do not follow the price increase. Conversely, if it lowers its price below $₦4,000$ , rival firms match the price reduction immediately. Which of the following best describes the price elasticity of demand facing this firm in these two price regions?

Demand is relatively elastic above the prevailing price and relatively inelastic below it.

Demand is relatively inelastic above the prevailing price and relatively elastic below it.

Demand is perfectly elastic above the prevailing price and unit elastic below it.

Demand is unit elastic above the prevailing price and relatively inelastic below it.

Show answer & explanation

Answer: Demand is relatively elastic above the prevailing price and relatively inelastic below it.

Answer

Demand is relatively elastic above the prevailing price and relatively inelastic below it.

The correct answer correctly identifies the dual elasticity nature of the kinked demand curve. Above the prevailing price, competitors do not raise their prices, so buyers switch to rival firms, making demand relatively elastic (

E_d > 1

). Below the prevailing price, competitors match price reductions to maintain their market shares, preventing any firm from expanding sales significantly, making demand relatively inelastic (

E_d < 1

). This asymmetry explains price rigidity in oligopolistic markets.

Step-by-Step Solution

Analyze competitor reaction to a price increase above the prevailing price of

₦4,000

Because rival firms do not match price increases, buyers switch to rivals, causing a disproportionately large drop in quantity demanded (demand is elastic,

E_d > 1

Asymmetry in competitor behavior makes the upper section of the demand curve highly price-sensitive.

Analyze competitor reaction to a price reduction below the prevailing price of

₦4,000

Because rival firms immediately match price cuts to protect their market shares, the firm gains very few extra sales (demand is inelastic,

E_d < 1

Matching price cuts prevents any single firm from gaining a competitive sales advantage.

Synthesize the elasticities to describe the overall shape of the oligopolist's demand curve.

The demand curve features a kink at the prevailing price, being relatively elastic above

₦4,000

and relatively inelastic below

₦4,000

This structural difference in elasticity accounts for price rigidity in non-collusive oligopoly markets.

Key Concept

Kinked Demand Curve and Price Rigidity in Oligopoly

Estimated Time:1m 15s

Question 4838Question →

Fill in the missing chemical terms and oxidation numbers in the passage describing the reaction of hydrogen sulfide gas with an acidified oxidizing solution.

Fill in the blanks below

When hydrogen sulfide gas (

{\text{H}_2\text{S}}

) is bubbled into an acidified solution of potassium tetraoxomanganate(VII), the purple solution is decolorized because

{\text{H}_2\text{S}}

acts as a agent. During this redox process, sulfur is oxidized from an oxidation state of in

{\text{H}_2\text{S}}

to in the yellow elemental precipitate formed.

Show answer & explanation

Answer

The first blank is 'reducing', the second blank is '-2', and the third blank is '0'.

Hydrogen sulfide (

\text{H}_2\text{S}

) acts as a strong reducing agent in aqueous chemical reactions. When reacted with acidified

\text{KMnO}_4

, it reduces purple

\text{MnO}_4^-

ions to colorless

\text{Mn}^{2+}

ions, while sulfur itself is oxidized from an oxidation state of

-2

0

, forming a insoluble yellow precipitate of elemental sulfur.

Step-by-Step Solution

Determine the chemical role of

\text{H}_2\text{S}

when reacting with acidified

\text{KMnO}_4

Acidified

\text{KMnO}_4

is an oxidizing agent containing

\text{Mn}^{7+}

(purple), which is reduced to

\text{Mn}^{2+}

(colorless). Therefore,

\text{H}_2\text{S}

acts as a reducing agent.

A substance that causes reduction in another species while undergoing oxidation itself is a reducing agent.

Calculate the oxidation state of sulfur in hydrogen sulfide (

\text{H}_2\text{S}

With hydrogen in the

+1

state (

2 \times (+1) = +2

), the oxidation number of sulfur must be

-2

to make the neutral molecule sum to zero.

Sum of oxidation states in neutral compounds is zero.

Identify the oxidation state of sulfur in the elemental precipitate product.

Elemental sulfur (

S

) has an oxidation state of

0

The oxidation number of any uncombined element in its standard state is always zero.

Key Concept

Reducing properties of hydrogen sulfide gas and oxidation state changes in redox reactions

Question 4839Question →

Match each fundamental economic concept under the law of demand with its correct definition or description.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The Law of Demand matches the inverse price-quantity relationship statement. The Demand Schedule matches the tabular display of quantities demanded at various prices. The Demand Curve matches the downward-sloping graphical representation. Individual Demand matches the single consumer purchasing requirement.

Each demand term is matched to its canonical definition: the Law of Demand states the inverse price-quantity rule, the schedule is the table, the curve is the graphical plot, and individual demand relates to a single buyer.

Step-by-Step Solution

Identify the basic principle of the Law of Demand.

It specifies that higher prices lead to lower quantities demanded (inverse relationship).

This is the core definition of the law of demand.

Distinguish between tabular and graphical representations.

The schedule is tabular, while the curve is graphical.

Data in rows and columns forms a schedule; plotting it creates a curve.

Define individual demand.

It represents a single consumer's willingness and ability to buy.

Individual demand isolates one buyer, whereas market demand sums all buyers.

Key Concept

Concept and Law of Demand

Question 4840Question →

Match each chemical transformation or test involving alkanals and alkanones with its corresponding observation or principal product.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Oxidation of propanal with acidified

K_2Cr_2O_7

matches color change from orange to green yielding propanoic acid; Reduction of propanone using

LiAlH_4

matches formation of a secondary alcohol, propan-2-ol; Warming ethanal with Tollen's reagent matches deposition of a shiny silver mirror coating; Warming propanone with

I_2

in aqueous

NaOH

matches formation of a characteristic yellow precipitate of triiodomethane (

CHI_3

Each chemical process uniquely corresponds to its diagnostic observation or reaction outcome: propanal oxidizes to propanoic acid with an orange-to-green color change (

Cr^{3+}

); propanone reduces to propan-2-ol; ethanal reduces Tollen's reagent to produce a silver mirror; and propanone gives a positive iodoform test producing yellow

CHI_3

precipitate.

Step-by-Step Solution

Analyze the oxidation reaction of propanal

Propanal is an alkanal oxidized by acidified dichromate to propanoic acid (

CH_3CH_2COOH

) with dichromate reducing from orange

Cr_2O_7^{2-}

to green

Cr^{3+}

Alkanals are readily oxidized to alkanoic acids.

Determine the product of propanone reduction

Reducing propanone (

CH_3COCH_3

) with

LiAlH_4

adds hydrogen across the carbonyl double bond, converting the ketone into propan-2-ol (

CH_3CH(OH)CH_3

Reduction of alkanones yields secondary alcohols.

Evaluate the reaction between ethanal and Tollen's reagent

Ethanal oxidizes to ethanoic acid while reducing

Ag^+

ions in ammoniacal silver nitrate to elemental silver metal (

Ag

), depositing as a silver mirror.

Tollen's reagent specifically distinguishes alkanals from alkanones.

Analyze the iodoform test for propanone

Compounds containing the

CH_3C=O

group react with iodine in sodium hydroxide solution to yield triiodomethane (

CHI_3

), a yellow precipitate.

Propanone is a methyl ketone which gives a positive triiodomethane test.

Key Concept

Reactions and Distinction Tests of Alkanals and Alkanones

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