101. Fill in the blank in the most accurate way:
Productivity is best described as the ______ of biomass production.
ⓐ. location
ⓑ. sequence
ⓒ. rate
ⓓ. source
Correct Answer: rate
Explanation: Productivity always includes the idea of speed or pace of production. It tells how much biomass is formed over a given area in a given time. Because of this, it differs from a one-time measurement of existing biomass. The time component is essential to the definition.
102. Which observation would be most useful for estimating secondary productivity in a grassland?
ⓐ. Increase in biomass of herbivores over time
ⓑ. Number of tree species present in one season
ⓒ. Concentration of dissolved minerals in soil water
ⓓ. Amount of leaf litter formed after autumn
Correct Answer: Increase in biomass of herbivores over time
Explanation: Secondary productivity deals with the formation of new organic matter by consumers. Measuring an increase in herbivore biomass over a certain period directly reflects this process. Species number and mineral concentration do not measure consumer biomass production. Litter formation is related more to detritus input than to consumer productivity.
103. Which statement about the units of primary production is correct?
ⓐ. They are expressed only in number per unit area
ⓑ. They are expressed only as total dry weight of producers
ⓒ. They never include a time component
ⓓ. They may be expressed in weight or energy per unit area per unit time
Correct Answer: They may be expressed in weight or energy per unit area per unit time
Explanation: Primary production can be measured in terms of mass or energy, depending on the purpose of the study. In either case, the unit must include area and time because production is a rate phenomenon. This allows comparison across ecosystems or seasons. The definition remains tied to photosynthetic formation of biomass.
104. A researcher records the amount of organic matter formed by aquatic plants in one hectare of wetland over one year. This measurement represents
ⓐ. standing crop
ⓑ. primary productivity
ⓒ. secondary productivity
ⓓ. decomposition efficiency
Correct Answer: primary productivity
Explanation: Aquatic plants are producers, so biomass formed by them is part of primary productivity. The measurement includes area and time, which confirms that it is a productivity estimate rather than a simple standing amount. Secondary productivity would apply to consumers instead. The question focuses on autotrophic output.
105. Which statement about gross primary productivity is correct?
ⓐ. It is the total rate of organic matter production during photosynthesis
ⓑ. It is the biomass remaining after respiratory loss in producers
ⓒ. It is the rate of biomass formation by consumers
ⓓ. It is the inorganic nutrient pool available in soil
Correct Answer: It is the total rate of organic matter production during photosynthesis
Explanation: Gross primary productivity represents the full amount of photosynthetic production before accounting for respiratory losses. It shows the total organic matter formed by producers. Part of this total is later used by the producers themselves in respiration. That is why GPP is larger than the biomass ultimately available to the next trophic levels.
106. Which equation correctly shows the relationship among GPP, respiration, and NPP?
ⓐ. NPP = GPP + R
ⓑ. GPP = NPP - R
ⓒ. NPP = GPP - R
ⓓ. R = GPP - NPP - R
Correct Answer: NPP = GPP - R
Explanation: Net primary productivity is what remains after producers use part of their photosynthetic output in respiration. Subtracting respiratory loss from gross primary productivity gives the net amount. This relationship is central to understanding how much producer biomass becomes available beyond the producers' own metabolic needs. The equation therefore links total production and usable production.
107. Which quantity is directly available to herbivores and decomposers from producer biomass?
ⓐ. Gross primary productivity alone
ⓑ. Net primary productivity
ⓒ. Total incident solar radiation
ⓓ. Respiratory loss of producers
Correct Answer: Net primary productivity
Explanation: Herbivores and decomposers depend on the biomass that remains after producers meet their own respiratory demands. That remaining biomass is net primary productivity. Gross primary productivity includes the total photosynthetic output, but not all of it is passed onward. NPP therefore represents the usable biomass for heterotrophs.
108. A plant community fixes 12,000 kcal m$^{-2}$ yr$^{-1}$ through photosynthesis and uses 4,000 kcal m$^{-2}$ yr$^{-1}$ in respiration. Its net primary productivity is
ⓐ. 4,000 kcal m$^{-2}$ yr$^{-1}$
ⓑ. 6,000 kcal m$^{-2}$ yr$^{-1}$
ⓒ. 12,000 kcal m$^{-2}$ yr$^{-1}$
ⓓ. 8,000 kcal m$^{-2}$ yr$^{-1}$
Correct Answer: 8,000 kcal m$^{-2}$ yr$^{-1}$
Explanation: Net primary productivity is obtained by subtracting respiration from gross primary productivity. Here, 12,000 minus 4,000 gives 8,000 kcal m$^{-2}$ yr$^{-1}$. This value represents the biomass energy available for consumption by heterotrophs. The calculation shows the practical use of the GPP–R–NPP relationship.
109. Which statement correctly describes the relationship between GPP and NPP?
ⓐ. GPP is the biomass available to herbivores after producer respiration
ⓑ. NPP is always greater than GPP because it includes consumer gain
ⓒ. GPP is the total photosynthetic production, whereas NPP is what remains after respiratory loss
ⓓ. NPP and GPP are identical in all green plants
Correct Answer: GPP is the total photosynthetic production, whereas NPP is what remains after respiratory loss
Explanation: Gross primary productivity includes the entire amount of organic matter produced during photosynthesis. Producers use part of that production in respiration for their own metabolic activities. The amount left after this loss is net primary productivity. That remaining biomass is the portion available for further use in the ecosystem.
110. Which component of producer output is directly available to herbivores?
ⓐ. Net primary productivity
ⓑ. Respiratory loss
ⓒ. Total incident solar radiation
ⓓ. Gross primary productivity alone
Correct Answer: Net primary productivity
Explanation: Herbivores can use only the biomass that remains after plants meet their own respiratory needs. That leftover portion is net primary productivity. Gross primary productivity includes the total photosynthetic output, but part of it is consumed by the producers themselves. NPP therefore represents the effective food resource passed to heterotrophs.
111. Which of the following is an example of secondary productivity?
ⓐ. Formation of starch by phytoplankton during photosynthesis
ⓑ. Fixation of carbon dioxide by marsh plants
ⓒ. Increase in algal biomass per square metre per month
ⓓ. Increase in body mass of grazing animals over time
Correct Answer: Increase in body mass of grazing animals over time
Explanation: Secondary productivity refers to the formation of new organic matter by consumers. Grazing animals are heterotrophs, so an increase in their body mass over time reflects consumer biomass production. Photosynthetic formation of plant or algal biomass belongs to primary productivity. The difference depends on whether producers or consumers are making the new biomass.
112. Two plant communities have the same GPP, but one has a much higher respiration rate. Compared with the other, its NPP will be
ⓐ. higher because more energy is circulating
ⓑ. lower because more of the gross production is used by producers
ⓒ. unchanged because NPP does not depend on respiration
ⓓ. equal to GPP because respiration is not subtracted
Correct Answer: lower because more of the gross production is used by producers
Explanation: Net primary productivity is calculated after subtracting respiration from gross primary productivity. When respiration is high, a larger fraction of the total photosynthetic production is consumed by the producers themselves. That leaves less biomass for growth and for transfer to heterotrophs. So higher respiration reduces NPP when GPP is unchanged.
113. Which factor can directly influence primary productivity in an ecosystem?
ⓐ. Plant species present and their photosynthetic capacity
ⓑ. Number of decomposers in the deepest soil layer only
ⓒ. Position of consumers at the top trophic level
ⓓ. Shape of the ecological pyramid alone
Correct Answer: Plant species present and their photosynthetic capacity
Explanation: Primary productivity depends strongly on the kinds of plants present and how efficiently they can photosynthesize. Different species vary in leaf structure, growth pattern, and ability to trap light and use nutrients. These differences affect how much organic matter is produced. Ecosystem productivity therefore changes with plant composition and functional ability.
114. Which condition is most likely to increase primary productivity in a plant community?
ⓐ. Better nutrient availability for producers
ⓑ. Reduction in photosynthetic activity of leaves
ⓒ. Absence of solar input
ⓓ. Complete stoppage of carbon fixation
Correct Answer: Better nutrient availability for producers
Explanation: Producers require nutrients for growth, enzyme activity, and synthesis of cellular material. When nutrient availability improves, plants can often photosynthesize and grow more effectively. This tends to increase biomass production if other conditions are also suitable. Low light or reduced photosynthetic activity would have the opposite effect.
115. If the NPP of a forest is 900 g m$^{-2}$ yr$^{-1}$ and respiration by producers is 300 g m$^{-2}$ yr$^{-1}$, what is its GPP?
ⓐ. 300 g m$^{-2}$ yr$^{-1}$
ⓑ. 1,200 g m$^{-2}$ yr$^{-1}$
ⓒ. 600 g m$^{-2}$ yr$^{-1}$
ⓓ. 900 g m$^{-2}$ yr$^{-1}$
Correct Answer: 1,200 g m$^{-2}$ yr$^{-1}$
Explanation: The relationship is $NPP = GPP - R$. Rearranging gives $GPP = NPP + R$. Adding 900 and 300 gives 1,200 g m$^{-2}$ yr$^{-1}$. This value represents the total photosynthetic production before respiratory losses are removed.
116. Consider the following statements:
Statement I: NPP is the biomass available to heterotrophs.
Statement II: NPP is obtained after subtracting producer respiration from GPP.
Which option is correct?
ⓐ. Statement I is true, but Statement II is false
ⓑ. Statement I is false, but Statement II is true
ⓒ. Both statements are false
ⓓ. Both statements are true
Correct Answer: Both statements are true
Explanation: Net primary productivity is the portion of producer biomass left after respiration. Because this remaining biomass is not used up in producer respiration, it becomes available to herbivores and decomposers. The formula $NPP = GPP - R$ captures this idea directly. Both statements describe different sides of the same concept.
117. Which measurement best represents secondary productivity?
ⓐ. Rate of new organic matter assimilation by consumers
ⓑ. Total solar energy falling on the producer surface
ⓒ. Amount of inorganic nutrient pool in the soil
ⓓ. Number of producers present in a habitat
Correct Answer: Rate of new organic matter assimilation by consumers
Explanation: Secondary productivity concerns how consumers convert ingested food into their own biomass. It is therefore measured as a rate of formation or assimilation of new organic matter by heterotrophs. Solar input and nutrient pools may affect ecosystems, but they do not define consumer productivity. The focus stays on consumer growth and biomass gain.
118. A lake receives improved nutrient input and contains producer species with high photosynthetic efficiency. The most likely outcome is
ⓐ. reduced gross primary productivity
ⓑ. complete loss of producer biomass
ⓒ. increased primary productivity
ⓓ. no change in organic matter formation
Correct Answer: increased primary productivity
Explanation: Primary productivity generally rises when nutrients are more available and producers can use light effectively. Better nutrient supply supports growth, while high photosynthetic capacity increases the rate of biomass formation. These conditions strengthen organic matter production by autotrophs. Unless another limiting factor intervenes, productivity is expected to increase.
119. Which statement about global net primary productivity is correct?
ⓐ. Oceans contribute most of the biosphere's NPP because they cover less than half of Earth's surface
ⓑ. Land contributes nothing significant because producers are absent there
ⓒ. Oceans cover about 70% of Earth's surface and contribute about 170 billion tons of dry matter annually
ⓓ. Oceans cover a large part of Earth but contribute only about 55 billion tons of dry organic matter annually
Correct Answer: Oceans cover a large part of Earth but contribute only about 55 billion tons of dry organic matter annually
Explanation: Oceanic ecosystems occupy most of Earth's surface, yet their contribution to annual net primary productivity is much lower than their area alone might suggest. Their contribution is about 55 billion tons of dry organic matter per year. This shows that area and productivity are not always directly proportional. Land ecosystems account for a large remaining share of global NPP.
120. The annual net primary productivity of the biosphere is approximately
ⓐ. 55 billion tons of dry organic matter
ⓑ. 170 billion tons of dry organic matter
ⓒ. 700 billion tons of dry organic matter
ⓓ. 17 billion tons of dry organic matter
Correct Answer: 170 billion tons of dry organic matter
Explanation: Net primary productivity at the biosphere level represents the total annual formation of dry organic matter available after producer respiration. The approximate value is about 170 billion tons. This figure gives a broad measure of the planet's biological productivity. It also helps place oceanic and terrestrial contributions in perspective.
