101. Purified pigments P, Q and R show the following relative absorption under equal incident light.
| Pigment | Blue region | Green region | Red region |
|---|
| P | \(88\) | \(14\) | \(72\) |
| Q | \(61\) | \(38\) | \(47\) |
| R | \(34\) | \(76\) | \(21\) |
Which conclusion is best supported by the complete dataset?
ⓐ. All photosynthetic pigments absorb every visible wavelength equally
ⓑ. Pigment concentration alone determines the wavelength of incident light
ⓒ. Each pigment has a characteristic pattern of wavelength absorption
ⓓ. A pigment that absorbs green light cannot participate in photosynthesis
Correct Answer: Each pigment has a characteristic pattern of wavelength absorption
Explanation: The rows show that the three purified pigments do not absorb the blue, green and red regions in the same proportions. Pigment P absorbs strongly in blue and red but weakly in green, while pigment R shows its greatest value in green. Pigment Q has a broader intermediate pattern. These differences demonstrate absorption specificity: the amount of light absorbed depends on both pigment identity and wavelength. Plotting absorption against wavelength for any one pigment would produce its characteristic absorption spectrum. The table does not show equal absorption across visible light, nor does it imply that green-absorbing pigments are photosynthetically useless. Different pigment spectra allow a leaf to capture a wider range of incident wavelengths than a single pigment could use alone. The decisive row combines the relevant observation with the condition needed to interpret it biologically in the stated spectral comparison.
102. A graph plots wavelength from \(400\,\mathrm{nm}\) to \(700\,\mathrm{nm}\) on the horizontal axis and the proportion of incident light absorbed by a purified pigment on the vertical axis. It has prominent peaks in blue and red regions and a trough in the green region. The graph is a:
ⓐ. carbon-dioxide response curve
ⓑ. light-saturation curve
ⓒ. photosynthetic action spectrum
ⓓ. pigment absorption spectrum
Correct Answer: pigment absorption spectrum
Explanation: The vertical axis records the proportion of incident light absorbed by a purified pigment, so the graph describes absorption rather than the rate of a biological process. The peaks identify wavelength regions where the pigment captures light strongly, while the trough marks relatively weak absorption. An action spectrum would instead place a measure such as photosynthetic rate or oxygen evolution on the vertical axis. A light-response curve would vary light intensity rather than wavelength, and a carbon-dioxide response curve would vary carbon-dioxide availability. Identifying the graph requires attention to both axes. Similar blue and red peaks may later be compared with photosynthetic performance, but the variable actually measured here fixes the graph as an absorption spectrum.
103. A chemical modification leaves a leaf pigment present at its normal concentration but greatly reduces its absorption in the blue region while leaving red absorption nearly unchanged. The most direct prediction is:
ⓐ. the pigment will begin supplying carbon atoms to carbohydrate
ⓑ. its absorption spectrum will become identical to the action spectrum
ⓒ. red light will no longer be absorbed by any pigment in the leaf
ⓓ. the pigment will capture a narrower range of useful incident light
Correct Answer: the pigment will capture a narrower range of useful incident light
Explanation: An absorption spectrum records how effectively a pigment absorbs different wavelengths. The modification selectively reduces blue-region absorption without removing the pigment or altering its red-region absorption. Its useful spectral range narrows, with less blue light captured but continued absorption in the red region. Other pigments remain unaffected, so total leaf absorption of red or blue light cannot be inferred to disappear. Pigments also do not supply carbohydrate carbon; carbon dioxide performs that role. An action spectrum measures photosynthetic performance of the whole system and need not become identical to the altered pigment spectrum. The predicted effect follows specifically from the changed wavelength sensitivity of this pigment rather than from an assumed failure of all photosynthesis.
104. Consider the following statements about an absorption spectrum.
I. It relates wavelength to the amount of light absorbed by a pigment.
II. It may be obtained using a separated pigment preparation.
III. It directly records the rate of carbon-dioxide fixation by an intact leaf.
IV. Different pigments may produce different absorption curves.
ⓐ. Statements I and III are correct; statements II and IV are incorrect
ⓑ. Statements I, II and IV are correct; statement III is incorrect
ⓒ. Statements II and III are correct; statements I and IV are incorrect
ⓓ. Statements I, II, III and IV are all correct
Correct Answer: Statements I, II and IV are correct; statement III is incorrect
Explanation: An absorption spectrum is constructed by measuring how strongly a pigment absorbs light at different wavelengths, making statement I valid. A purified or separated pigment preparation can be used to obtain such a curve, so statement II is also valid. Distinct pigments differ in their molecular properties and preferential wavelength absorption, allowing them to produce different spectra as stated in IV. Statement III describes an action measurement rather than an absorption measurement. Carbon-dioxide fixation, oxygen evolution or another photosynthetic response would reveal how effectively different wavelengths drive the process in a living system. The valid combination separates the physical property of pigment absorption from the biological performance of the complete photosynthetic apparatus.
105. Two graphs use wavelength on the horizontal axis. Graph P plots light absorbed by chlorophyll a, whereas Graph Q plots oxygen evolved by an illuminated green tissue. Graph P and Graph Q represent, respectively:
ⓐ. an absorption spectrum and an action spectrum
ⓑ. an action spectrum and an absorption spectrum
ⓒ. two action spectra measured by different methods
ⓓ. two absorption spectra of the same pigment
Correct Answer: an absorption spectrum and an action spectrum
Explanation: Graph P records the amount of light absorbed by chlorophyll a at each wavelength. Its vertical variable is a pigment property, so it is an absorption spectrum. Graph Q records oxygen evolution by green tissue, which serves as a measure of photosynthetic effectiveness. It is an action spectrum. Both graphs vary wavelength, and their peaks may resemble one another, but their vertical axes represent different variables. This distinction prevents curve shape from being used as the only basis for classification. Absorption describes entry of light energy into a pigment, whereas action describes the resulting performance of the photosynthetic system. Comparing the two can reveal which pigments contribute to the process, but comparison does not make the spectra equivalent. The vertical axes also differ, so incomplete overlap is expected even when both curves show major blue and red peaks.
106. The following observations are obtained at three wavelength regions.
| Wavelength region | Chlorophyll a absorption | Photosynthetic oxygen evolution by intact leaf |
|---|
| P | High | High |
| Q | Low | Moderate |
| R | High | High |
The moderate oxygen evolution in region Q, despite low chlorophyll a absorption, is best explained by:
ⓐ. underestimation of chlorophyll a absorption in region Q
ⓑ. independent reaction-centre activity of chlorophyll b in region Q
ⓒ. compensation by higher carbon-dioxide supply at that wavelength
ⓓ. accessory-pigment absorption followed by energy transfer
Correct Answer: accessory-pigment absorption followed by energy transfer
Explanation: Regions P and R show the expected association between strong chlorophyll a absorption and high photosynthetic activity. Region Q provides the decisive additional observation: the intact leaf still evolves a moderate amount of oxygen even though chlorophyll a absorbs weakly there. Other pigments in the photosynthetic apparatus can absorb wavelengths that chlorophyll a uses less effectively. Excitation energy captured by these accessory pigments can be transferred to reaction-centre chlorophyll a and contribute to electron excitation. The action spectrum of an intact leaf may remain above the chlorophyll a absorption curve in selected regions. The dataset demonstrates how pigment cooperation broadens the usable spectrum without making oxygen evolution independent of pigments. Comparison of absorption with oxygen evolution therefore reveals energy capture by accessory pigments rather than a pigment-independent source of oxygen.
107. Assertion: An absorption spectrum and an action spectrum measure different biological variables.
Reason: Both spectra are obtained only by measuring oxygen evolution from an intact green leaf.
ⓐ. Both the Assertion and the Reason are true, and the Reason correctly explains the Assertion
ⓑ. Both the Assertion and the Reason are true, but the Reason does not explain the Assertion
ⓒ. The Assertion is true, whereas the Reason is false and cannot explain the Assertion
ⓓ. The Assertion is false, whereas the Reason is true and cannot explain the Assertion
Correct Answer: The Assertion is true, whereas the Reason is false and cannot explain the Assertion
Explanation: The Assertion is true. An absorption spectrum measures the amount of light captured by a pigment at different wavelengths, whereas an action spectrum records the effectiveness of those wavelengths in driving a photosynthetic response. The Reason is false since oxygen evolution is one possible method for obtaining an action spectrum, not the universal method for obtaining both spectra. Pigment absorption can be measured using an isolated pigment preparation without measuring photosynthetic oxygen production. The distinction rests on the vertical variable: absorbed light for one graph and process performance for the other. Their curves may show related peaks, yet the methods and biological meanings remain different. Similarity in shape reflects functional connection rather than identity of measurement.
108. A researcher performs two measurements. In Setup P, a purified leaf-pigment extract is exposed to different wavelengths and the fraction of light absorbed is recorded. In Setup Q, an intact illuminated leaf is exposed to the same wavelengths and oxygen evolution is measured. The two setups are designed to compare:
ⓐ. respiration with transpiration
ⓑ. absorption spectra and action spectra
ⓒ. carbon fixation with mineral absorption
ⓓ. chromatography with starch hydrolysis
Correct Answer: absorption spectra and action spectra
Explanation: Setup P directly measures how much light the pigment extract absorbs at each wavelength, producing absorption-spectrum data. Setup Q measures a physiological output of photosynthesis in an intact leaf, so it produces action-spectrum data. Using the same wavelength treatments permits the two curves to be compared region by region. Close correspondence would support a role for the measured pigments in driving photosynthesis, while differences could reveal contributions from additional pigments or other whole-system effects. The experiment does not compare respiration, transpiration or mineral uptake, since none of those variables is measured. It also goes beyond chromatography, which separates pigments rather than testing their wavelength absorption and functional effectiveness. The paired design connects a pigment property with the performance of the complete photosynthetic apparatus.
109. An action-spectrum graph has wavelength on the horizontal axis and relative photosynthetic rate on the vertical axis. The curve has high peaks in blue and red regions and a broad lower region in green light. The most defensible interpretation is:
ⓐ. green light is the only effective region for photosynthesis
ⓑ. red light is reflected completely by every leaf pigment
ⓒ. wavelength has no effect on photosynthetic performance
ⓓ. blue and red light drive photosynthesis more than green light
Correct Answer: blue and red light drive photosynthesis more than green light
Explanation: The action spectrum directly relates wavelength to photosynthetic performance. High values in blue and red regions show that these wavelengths produce greater photosynthetic activity under the stated conditions. The lower green-region values indicate reduced effectiveness, not necessarily complete absence of photosynthesis. Chlorophyll pigments absorb strongly in blue and red while reflecting or transmitting more green light, contributing to this overall pattern. Accessory pigments and partial absorption can still support some activity outside the principal peaks. The conclusion must follow the relative heights of the curve rather than an absolute claim that only two colours can be used. Action spectra reveal wavelength effectiveness for the complete process, making the blue and red peaks biologically more informative than leaf colour alone. The trough is relative rather than absolute; some green light is absorbed by the combined pigment system and can still support a measurable rate.
110. A green leaf is illuminated only with green light of sufficient intensity. Compared with equal suitable blue light, its photosynthetic rate is lower but remains measurable. This result is most consistent with:
ⓐ. limited but measurable use of green light by the pigment system
ⓑ. experimental error because green light is completely reflected by leaves
ⓒ. carbon fixation under green light proceeding without photochemical reactions
ⓓ. equal photon supply making all visible wavelengths equally effective
Correct Answer: limited but measurable use of green light by the pigment system
Explanation: Green leaves appear green because a substantial fraction of green light is reflected or transmitted rather than absorbed. Absorption is not zero, however, and the combined pigment system can capture some radiation in this wavelength region. Energy absorbed by accessory pigments can be transferred to reaction-centre chlorophyll a and support electron flow, ATP formation and NADPH production. A measurable but lower rate under green illumination is therefore expected when compared with an equally suitable blue treatment. The result does not imply that carbon fixation can proceed independently of photochemical reactions, nor does equal photon supply make wavelengths biologically equivalent because pigment absorption differs. Blue and red regions are generally more effective, while green light can still contribute at a reduced efficiency. This qualifier explains why the action spectrum falls in the green region without necessarily reaching zero.
111. Evaluate the following statements about wavelength and photosynthetic effectiveness.
I. Photosynthetic rate is generally high in blue and red light.
II. The green region is usually less effective than the major blue and red regions.
III. Photosynthesis must be exactly zero at every wavelength outside the major peaks.
IV. Accessory pigments can contribute to activity at wavelengths weakly absorbed by chlorophyll a.
ⓐ. Statements I and III are correct; statements II and IV are incorrect
ⓑ. Statements II and III are correct; statements I and IV are incorrect
ⓒ. Statements I, II and IV are correct; statement III is incorrect
ⓓ. Statements I, II, III and IV are all correct
Correct Answer: Statements I, II and IV are correct; statement III is incorrect
Explanation: Action-spectrum observations show strong photosynthetic effectiveness in blue and red regions, supporting statement I. The green region commonly gives a lower rate, making statement II valid as a relative comparison. Statement III incorrectly converts lower effectiveness into complete absence. Pigments may absorb small amounts outside their strongest peaks, and accessory pigments can capture additional wavelengths. Their excitation energy can be transferred toward reaction-centre chlorophyll a, which supports statement IV. The appropriate interpretation is comparative rather than absolute: spectral peaks identify highly effective regions, while troughs indicate reduced activity. The valid set preserves both the dominant blue-red pattern and the continued contribution of the broader pigment system across visible light. Blue and red regions are highly effective, yet measurable photosynthesis can still occur at other absorbed wavelengths.
112. At equal photon supply, a leaf shows relative photosynthetic rates of \(96\) in blue light, \(72\) in red light and \(24\) in green light. Which result and interpretation are supported by these data?
ⓐ. The blue-to-green ratio is \(1:4\), so green light is more effective
ⓑ. A \(4:1\) blue-to-green ratio, with measurable photosynthesis in green light
ⓒ. The blue-to-green ratio is \(3:1\), so green light produces no photosynthesis
ⓓ. The blue-to-green ratio is \(5:1\), while red light is completely ineffective
Correct Answer: A \(4:1\) blue-to-green ratio, with measurable photosynthesis in green light
Explanation: The required comparison uses the blue value as the first term and the green value as the second. The relation is
\[
96:24=4:1
\]
This means that the measured photosynthetic rate in blue light is four times the rate in green light under the stated equal photon supply. The green value is \(24\), not \(0\), so the data do not support complete absence of photosynthesis in that region. The red value of \(72\) also shows substantial effectiveness and cannot be described as inactive. The calculation must be joined with biological interpretation: blue is markedly more effective in this dataset, yet the complete pigment system retains some ability to use green light. The result reflects relative spectral efficiency rather than an all-or-none response. The ratio is obtained from \(96:24=4:1\). The non-zero value in green light is equally important: lower effectiveness does not mean that green wavelengths are completely unusable.
113. Chlorophyll a is regarded as the chief photosynthetic pigment mainly because it:
ⓐ. forms reaction centres and matches major action-spectrum peaks
ⓑ. is the only pigment capable of absorbing any visible wavelength
ⓒ. produces starch directly without electron transfer or enzymes
ⓓ. occurs only in non-photosynthetic tissues exposed to darkness
Correct Answer: forms reaction centres and matches major action-spectrum peaks
Explanation: Chlorophyll a has a central functional position in photosynthesis. Specialised chlorophyll a molecules form the reaction centres of the photosystems, where excitation leads to transfer of a high-energy electron to a primary acceptor. Its major absorption regions also correspond closely with prominent regions of the photosynthetic action spectrum. Accessory pigments broaden light capture, but they usually transfer excitation energy toward reaction-centre chlorophyll a rather than replacing its reaction-centre role. Chlorophyll a is not the only pigment that absorbs visible light, and it does not directly manufacture starch in a single step. Calling it the chief pigment reflects its decisive position in photochemical energy conversion, not numerical abundance or exclusive absorption of every useful wavelength.
114. Assertion: Chlorophyll b is the specialised reaction-centre pigment in both photosystems.
Reason: A specialised chlorophyll a molecule forms the reaction centre of each photosystem.
ⓐ. Both the Assertion and the Reason are true, and the Reason correctly explains the Assertion
ⓑ. Both the Assertion and the Reason are true, but the Reason does not explain the Assertion
ⓒ. The Assertion is true, whereas the Reason is false and cannot explain the Assertion
ⓓ. The Assertion is false, whereas the Reason is true and cannot explain the Assertion
Correct Answer: The Assertion is false, whereas the Reason is true and cannot explain the Assertion
Explanation: The Assertion is false. Chlorophyll b functions mainly as an accessory pigment within the light-harvesting system and transfers captured excitation energy toward the reaction centre. It is not the specialised reaction-centre pigment of both photosystems. The Reason is true: each photosystem contains a special chlorophyll a molecule that performs the reaction-centre role. When sufficient excitation reaches this chlorophyll a, an electron is transferred to a primary electron acceptor, initiating photochemical electron flow. The distinction is functional rather than merely based on colour or chromatographic position. Chlorophyll b contributes valuable wavelength absorption, but chlorophyll a occupies the decisive site where excitation energy is converted into charge separation. Removing an accessory pigment narrows effective light use without necessarily destroying the reaction centre.
115. A photosystem is described as a protein-associated pigment complex containing hundreds of surrounding pigment molecules and one centrally functional chlorophyll a molecule connected to a primary electron acceptor. The surrounding pigments and the specialised chlorophyll a function, respectively, as:
ⓐ. an antenna system and a reaction centre
ⓑ. a carbon acceptor and a hydrogen donor
ⓒ. an ATP synthase and a proton channel
ⓓ. a stromal enzyme and a thylakoid lumen
Correct Answer: an antenna system and a reaction centre
Explanation: The numerous surrounding pigment molecules form the antenna or light-harvesting system. They absorb photons across a range of wavelengths and transfer excitation energy among pigments toward a specialised chlorophyll a molecule. That chlorophyll a acts as the reaction centre. Its excitation permits electron transfer to the primary acceptor, converting captured light energy into the first stable charge separation of the photosystem. The spatial description separates collection from photochemical conversion: many pigments increase the effective light-collecting area, while one specialised pigment performs the central electron-donation event. This organisation explains how accessory pigments can contribute to photosynthesis without themselves being the final reaction-centre molecule. Electron movement is sustained only when each oxidised reaction centre receives replacement electrons from the preceding source.
116. An absorption curve for purified chlorophyll a and an action-spectrum curve for an intact leaf share major blue and red peaks, but the action curve is higher than the chlorophyll a curve in some intermediate wavelengths. The mismatch most strongly indicates that:
ⓐ. action spectra measure only pigment concentration
ⓑ. chlorophyll a is absent from the intact leaf
ⓒ. accessory pigments contribute at some wavelengths
ⓓ. photosynthesis is unrelated to light absorption
Correct Answer: accessory pigments contribute at some wavelengths
Explanation: The common blue and red peaks support an important role for chlorophyll a, since strong absorption by this pigment corresponds with strong photosynthetic action. The higher action values at selected intermediate wavelengths require an additional contribution. An intact leaf contains chlorophyll b, xanthophylls and carotenoids that can absorb wavelengths used less effectively by purified chlorophyll a. Energy captured by these pigments can be transferred to reaction-centre chlorophyll a and increase photosynthetic performance. The spectra need not coincide perfectly since one curve represents a single pigment’s absorption while the other represents the output of the entire photosynthetic apparatus. The incomplete overlap is evidence of pigment cooperation rather than evidence against a connection between absorption and photosynthesis. The gap between curves is evidence of accessory-pigment contribution, not a failure of the action spectrum or a second independent reaction centre.
117. Two otherwise comparable preparations give the following results.
| Measurement | Complete pigment system | Chlorophyll a functioning without most accessory pigments |
|---|
| Use of intermediate visible wavelengths | Moderate | Low |
| Red-region activity | High | High |
| Damage under prolonged intense light | Low | High |
Which conclusion integrates all three observations?
ⓐ. Accessory pigments replace chlorophyll a as the reaction centre
ⓑ. Accessory pigments broaden light use and contribute to photoprotection
ⓒ. Accessory pigments prevent all red-light absorption by chlorophyll a
ⓓ. Accessory pigments perform carbon fixation in the thylakoid lumen
Correct Answer: Accessory pigments broaden light use and contribute to photoprotection
Explanation: The complete pigment system uses intermediate wavelengths more effectively than the preparation lacking most accessory pigments. This difference supports their light-harvesting role: they absorb wavelengths that chlorophyll a alone uses less efficiently and pass excitation energy toward the reaction centre. Both preparations retain high red-region activity, consistent with continued direct absorption by chlorophyll a. The strong-light observation adds a second function. Greater damage in the accessory-pigment-deficient preparation indicates that these pigments also help protect the photosynthetic apparatus from photo-oxidative injury. The dataset supports a dual role in broadening usable light and reducing light-induced damage. It does not transfer reaction-centre or stromal carbon-fixation functions away from chlorophyll a and stromal enzymes. The table must be interpreted as a set of linked conditions rather than as a single-cell lookup in the stated spectral comparison.
118. Accessory pigments remain able to absorb light, but a treatment blocks transfer of their excitation energy to reaction-centre chlorophyll a. The most immediate effect is:
ⓐ. carbon dioxide begins serving as the primary electron acceptor of the photosystem
ⓑ. accessory-pigment energy contributes less to charge separation
ⓒ. every photon absorbed directly by chlorophyll a is also blocked
ⓓ. accessory pigments become the enzymes of the Calvin cycle
Correct Answer: accessory-pigment energy contributes less to charge separation
Explanation: Accessory pigments expand the light-harvesting range by absorbing photons and transferring excitation energy through the antenna system toward reaction-centre chlorophyll a. The treatment leaves their absorption intact but disconnects that absorption from the reaction centre. Light captured mainly by those pigments would no longer contribute efficiently to excitation of reaction-centre chlorophyll a or to electron transfer to the primary acceptor. Direct absorption by reaction-centre or other chlorophyll a molecules is not stated to be blocked, so some photochemical activity may remain at favourable wavelengths. Carbon dioxide and Calvin-cycle enzymes belong to the biosynthetic phase and do not replace the lost antenna-to-reaction-centre energy transfer. The defect separates photon capture from productive use of the captured excitation. Reaction-centre chlorophyll can still respond to wavelengths it absorbs directly, but the usable spectrum narrows because antenna energy can no longer reach it.
119. Arrange the events by which an accessory pigment contributes to photosynthetic electron excitation.
P. An accessory pigment absorbs a photon.
Q. Excitation energy moves through the antenna pigments.
R. Reaction-centre chlorophyll a becomes excited.
S. A high-energy electron is transferred to a primary acceptor.
ⓐ. P → Q → R → S
ⓑ. Q → P → S → R
ⓒ. R → S → P → Q
ⓓ. P → R → Q → S
Correct Answer: P → Q → R → S
Explanation: The accessory pigment first absorbs a photon and enters an excited state. The excitation energy is then transferred among pigment molecules of the antenna complex rather than requiring the original accessory pigment to donate the final electron. Energy reaches the specialised reaction-centre chlorophyll a, raising it to an excited state. Only after this step can a high-energy electron pass from the reaction centre to the primary electron acceptor. The order reflects dependency: the reaction centre cannot use accessory-pigment energy before that energy has been captured and funnelled toward it, and primary charge separation cannot precede reaction-centre excitation. This sequence distinguishes energy transfer within the antenna from electron transfer beginning at the reaction centre. The pathway order can be checked by asking which event supplies the input required by the following event in the stated electron-transfer pathway.
120. Match each term with the measurement or function it represents. A Column II entry is used once.
| Column I | Column II |
|---|
| P. Absorption spectrum | 1. Photosynthetic effectiveness at different wavelengths |
| Q. Action spectrum | 2. Transfer of captured excitation toward the reaction centre |
| R. Antenna pigments | 3. Light absorbed by a pigment at different wavelengths |
| S. Reaction-centre chlorophyll a | 4. Initiation of electron transfer to a primary acceptor |
ⓐ. P-1, Q-3, R-4, S-2
ⓑ. P-3, Q-2, R-1, S-4
ⓒ. P-3, Q-1, R-2, S-4
ⓓ. P-2, Q-1, R-4, S-3
Correct Answer: P-3, Q-1, R-2, S-4
Explanation: An absorption spectrum records how much light a pigment absorbs at different wavelengths, giving P-3. An action spectrum relates wavelength to a photosynthetic response such as oxygen evolution, giving Q-1. Antenna pigments capture light and transfer excitation energy toward the reaction centre, so R-2 is appropriate. The specialised reaction-cententre chlorophyll a undergoes excitation and donates an electron to the primary acceptor, fixing S-4. The mapping follows a functional chain from wavelength absorption to energy transfer and then charge separation. It also preserves the distinction between a graph describing a pigment property and one describing the performance of the complete photosynthetic process. Accessory pigments broaden usable wavelengths by transferring excitation energy to reaction-centre chlorophyll a.
