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Biology-11 : 11 : Photosynthesis in Higher Plants - Flashcards

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What are the two major perspectives on biology ?
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One perspective describes life at the organismic and ecological level, while the other describes life at the cellular and molecular level.
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# Question Answer
1 What are the two major perspectives on biology ? One perspective describes life at the organismic and ecological level, while the other describes life at the cellular and molecular level.
2 Why are green plants called autotrophs? Because they synthesise their own food through photosynthesis.
3 What are organisms called that depend on green plants for food? Heterotrophs.
4 Define photosynthesis. It is a physico-chemical process by which green plants use light energy to synthesise organic compounds.
5 What is the ultimate source of energy for all living forms on Earth? Sunlight.
6 Why is photosynthesis important? It is the primary source of all food on Earth and is responsible for releasing oxygen into the atmosphere.
7 In which parts of the leaf does photosynthesis occur? In the green parts of the leaf exposed to light.
8 What experiment demonstrated that light is necessary for photosynthesis? Testing partially covered or variegated leaves for starch formation after exposure to light.
9 Why are green plants called autotrophs? Because they synthesise their own food through photosynthesis.
10 What are organisms called that depend on green plants for food? Heterotrophs.
11 Define photosynthesis. Photosynthesis is a physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds.
12 What is the ultimate source of energy for all living forms on Earth? Sunlight.
13 Why is photosynthesis important? It is the primary source of all food on Earth and is responsible for the release of oxygen into the atmosphere.
14 What did the variegated leaf experiment demonstrate? Photosynthesis occurs only in the green parts of leaves in the presence of light.
15 Who performed experiments in 1770 revealing the essential role of air in plant growth? Joseph Priestley.
16 What gas did Joseph Priestley discover in 1774? Oxygen.
17 What observation did Priestley make when a mint plant was placed in the bell jar? The mouse stayed alive and the candle continued to burn.
18 What hypothesis did Priestley propose from his experiments? Plants restore to the air whatever breathing animals and burning candles remove.
19 Who showed that sunlight is essential for the plant process that purifies air? Jan Ingenhousz.
20 What did Ingenhousz observe in aquatic plants kept in bright sunlight? Small bubbles formed around the green parts.
21 What were the bubbles observed by Ingenhousz later identified as? Oxygen.
22 Who provided evidence for the production of glucose in plants in 1854? Julius von Sachs.
23 In what form is glucose usually stored in plants? As starch.
24 What did Julius von Sachs discover about chlorophyll? He showed that chlorophyll is located in special bodies later called chloroplasts.
25 Which parts of plants did Sachs identify as the site of glucose formation? The green parts of plants.
26 Who performed experiments using Cladophora and aerobic bacteria? T.W. Engelmann.
27 Which pigments roughly match the action spectrum of photosynthesis? Chlorophyll a and chlorophyll b.
28 Who made a milestone contribution to understanding photosynthesis through studies on purple and green bacteria? Cornelius van Niel.
29 According to van Niel, what is photosynthesis essentially? A light-dependent reaction in which hydrogen from an oxidisable compound reduces carbon dioxide to carbohydrates.
30 What is oxidised to oxygen in green plants during photosynthesis? Water.
31 Which organisms do not release oxygen during photosynthesis? Some purple and green sulphur bacteria.
32 What is released instead of oxygen in sulphur bacteria during photosynthesis? Sulphur or sulphate.
33 How was it proved that oxygen released in photosynthesis comes from water? By using radioisotopic techniques.
34 Is photosynthesis a single reaction? No, it is a multistep process.
35 Where does photosynthesis mainly take place in plants? In the green leaves and chloroplasts.
36 Which cells in leaves contain a large number of chloroplasts? Mesophyll cells.
37 Why do chloroplasts align themselves along the walls of mesophyll cells? To receive optimum incident light.
38 Name the three components of the chloroplast membranous system. Grana, stroma lamellae, and matrix stroma.
39 Which part of the chloroplast is responsible for trapping light energy and synthesising ATP and NADPH? The membrane system.
40 In which part of the chloroplast are sugars synthesised? Stroma.
41 What are light-driven reactions of photosynthesis called? Light reactions or photochemical reactions.
42 Why are dark reactions also called carbon reactions? Because they depend on ATP and NADPH produced during light reactions and involve carbon fixation.
43 How many major pigments are involved in photosynthesis according to chromatographic separation? Four pigments are involved.
44 Name the four pigments found in green leaves. Chlorophyll a, chlorophyll b, xanthophylls, and carotenoids.
45 What colour does chlorophyll a appear in a chromatogram? Bright or blue-green.
46 What colour does chlorophyll b appear in a chromatogram? Yellow-green.
47 What is the colour of xanthophylls? Yellow.
48 What is the colour range of carotenoids? Yellow to yellow-orange.
49 What are pigments? Substances that have the ability to absorb light at specific wavelengths.
50 Which is the chief pigment associated with photosynthesis? Chlorophyll a.
51 In which regions of the spectrum does chlorophyll a show maximum absorption? Blue and red regions.
52 Why is chlorophyll a considered the chief pigment of photosynthesis? Because the regions where it absorbs maximum light also show the highest rate of photosynthesis.
53 What does the action spectrum of photosynthesis represent? The wavelengths at which maximum photosynthesis occurs.
54 Do the absorption spectrum of chlorophyll a and action spectrum of photosynthesis completely overlap? No, they do not completely overlap.
55 In which regions of visible light does most photosynthesis take place? Blue and red regions.
56 What are accessory pigments? Chlorophyll b, xanthophylls, and carotenoids.
57 What is the role of accessory pigments in photosynthesis? They absorb light and transfer energy to chlorophyll a.
58 How do accessory pigments help plants? They enable absorption of a wider range of wavelengths and protect chlorophyll a from photo-oxidation.
59 What are light reactions also called? Photochemical phase.
60 Which processes are included in the light reaction? Light absorption, water splitting, oxygen release, and formation of ATP and NADPH.
61 Into how many photosystems are pigments organised? Two photosystems.
62 Name the two photosystems involved in photosynthesis. Photosystem I (PS I) and Photosystem II (PS II).
63 Are PS I and PS II named according to their sequence of function? No, they are named according to the sequence of their discovery.
64 What does LHC stand for? Light Harvesting Complex.
65 What are LHCs made of? Hundreds of pigment molecules bound to proteins.
66 What is another name for the light harvesting system? Antennae.
67 What is the role of pigments in the antenna complex? They absorb different wavelengths of light to increase photosynthetic efficiency.
68 Which molecule forms the reaction centre in each photosystem? A single chlorophyll a molecule.
69 What is the reaction centre chlorophyll of PS I called? P700.
70 Why is the PS I reaction centre called P700? Because it has an absorption peak at 700 nm.
71 What is the reaction centre chlorophyll of PS II called? P680.
72 Why is the PS II reaction centre called P680? Because it has an absorption maximum at 680 nm.
73 What happens when PS II absorbs red light of 680 nm wavelength? Electrons become excited and jump to a higher orbit.
74 Where are the excited electrons from PS II transferred first? To an electron acceptor.
75 Through what system are electrons passed after leaving PS II? Through an electron transport system consisting of cytochromes.
76 Through what system are electrons transferred after leaving PS II? Through an electron transport system consisting of cytochromes.
77 In what direction do electrons move in the electron transport chain? Downhill in terms of redox potential scale.
78 Are electrons used up while passing through the electron transport chain? No, they are passed on to pigments of Photosystem I.
79 Which wavelength of light excites electrons in Photosystem I? Red light of wavelength 700 nm.
80 Why is the electron transfer pathway called the Z scheme? Because of its characteristic Z-shaped appearance on the redox potential scale.
81 How are electrons continuously supplied to PS II? By splitting of water molecules.
82 With which photosystem is water splitting associated? Photosystem II.
83 Which net product of photosynthesis is formed during splitting of water? Oxygen.
84 Which photosystem provides electrons to replace those lost by PS I? Photosystem II.
85 Where is the water-splitting complex located? On the inner side of the thylakoid membrane associated with PS II.
86 What is phosphorylation? The process through which ATP is synthesised by cells.
87 Define photophosphorylation. Synthesis of ATP from ADP and inorganic phosphate in the presence of light.
88 What is non-cyclic photophosphorylation? Electron flow involving both PS II and PS I connected through the electron transport chain.
89 What happens when only PS I is functional? Electrons circulate within the photosystem, causing cyclic photophosphorylation.
90 Where does cyclic photophosphorylation possibly occur? In the stroma lamellae.
91 Which photosystem is absent in the stroma lamellae membranes? PS II.
92 Which enzyme is absent in stroma lamellae membranes? NADP reductase enzyme.
93 What happens to the excited electron during cyclic photophosphorylation? It is cycled back to the PS I complex through the electron transport chain.
94 What is produced during cyclic photophosphorylation? Only ATP.
95 Is NADPH formed during cyclic photophosphorylation? No.
96 Under what light condition does cyclic photophosphorylation occur? When light of wavelengths beyond 680 nm is available.
97 Which hypothesis explains ATP synthesis in chloroplasts? Chemiosmotic hypothesis.
98 What is ATP synthesis linked to according to the chemiosmotic hypothesis? Development of a proton gradient across a membrane.
99 Across which membrane is the proton gradient formed during photosynthesis? Thylakoid membrane.
100 On which side of the thylakoid membrane do protons accumulate? Inside the lumen.
101 In respiration, where do protons accumulate in mitochondria? In the intermembrane space.
102 Why do protons accumulate in the thylakoid lumen? Because splitting of water occurs on the inner side of the membrane.
103 How are protons transported across the thylakoid membrane during electron transport? Through hydrogen carriers that remove protons from the stroma and release them into the lumen.
104 Where is the primary electron acceptor located in the thylakoid membrane? Towards the outer side of the membrane.
105 What happens when the hydrogen carrier transfers its electron to an electron carrier on the inner side? The proton is released into the lumen side of the membrane.
106 Where is NADP reductase enzyme located? On the stroma side of the thylakoid membrane.
107 From where are protons removed during NADP reduction? From the stroma.
108 What happens to proton concentration in the stroma during photosynthesis? It decreases.
109 What happens to proton concentration in the lumen during photosynthesis? It increases.
110 What is created due to proton accumulation in the lumen? A proton gradient across the thylakoid membrane.
111 What change in pH occurs in the lumen because of proton accumulation? A measurable decrease in pH.
112 Why is the proton gradient important in photosynthesis? Its breakdown leads to ATP synthesis.
113 How is the proton gradient broken down? By movement of protons across the membrane into the stroma.
114 What are the essential requirements for chemiosmosis? A membrane, proton pump, proton gradient, and ATP synthase.
115 Why are protons pumped into the thylakoid lumen? To create a proton gradient.
116 What activates ATP synthase enzyme? Diffusion of protons back across the membrane.
117 Along with NADPH, where is ATP used immediately? In biosynthetic reactions in the stroma.
118 What happens to oxygen produced during light reactions? It diffuses out of the chloroplast.
119 What is the biosynthetic phase of photosynthesis responsible for? Synthesis of sugars.
120 Does the biosynthetic phase directly depend on light? No, it depends on ATP and NADPH produced during light reactions.
121 What is the first stable product identified in the Calvin cycle? 3-phosphoglyceric acid (PGA).
122 How many carbon atoms are present in PGA? Three carbon atoms.
123 How many carbon atoms are present in oxaloacetic acid (OAA)? Four carbon atoms.
124 What type of molecule is RuBP? A 5-carbon ketose sugar.
125 How many carbon atoms are present in RuBP? Five.
126 Why were scientists initially searching for a 2-carbon compound as the primary acceptor? Because the first product identified was a 3-carbon acid (PGA).
127 What pathway was worked out by Calvin and his co-workers? The Calvin cycle.
128 Why is the Calvin pathway called a cyclic pathway? Because RuBP is regenerated during the cycle.
129 Into how many stages can the Calvin cycle be divided? Three stages.
130 Name the three stages of the Calvin cycle. Carboxylation, reduction, and regeneration.
131 Which is the most crucial step of the Calvin cycle? Carboxylation.
132 Which molecule is carboxylated during the Calvin cycle? RuBP.
133 Which enzyme catalyses the carboxylation of RuBP? RuBP carboxylase.
134 What are the products formed after carboxylation of RuBP? Two molecules of 3-PGA.
135 What is the more correct name for RuBP carboxylase? RuBisCO (RuBP carboxylase-oxygenase).
136 Why is RuBP carboxylase also called oxygenase? Because it also possesses oxygenation activity.
137 What occurs during the reduction phase of the Calvin cycle? Formation of glucose through a series of reactions.
138 How many turns of the Calvin cycle are required to form one molecule of glucose? Six turns.
139 What is required for regeneration of RuBP? One ATP molecule for phosphorylation.
140 Which compounds are formed during the Calvin cycle and later converted into storage products? Triose phosphate, sucrose, and starch.
141 Which energy-rich molecules produced during light reactions are used in the Calvin cycle? ATP and NADPH.
142 Why does cyclic photophosphorylation probably take place? To meet the difference in ATP and NADPH requirement in the dark reaction.
143 How many turns of the Calvin cycle are required to synthesise one molecule of glucose? Six turns.
144 What are the output molecules of the Calvin cycle? One glucose, 18 ADP, and 12 NADP.
145 How many carbon atoms are present in PEP? Three carbon atoms.
146 In which cells is PEP present? Mesophyll cells.
147 Into which compounds is OAA converted in mesophyll cells? Malic acid or aspartic acid.
148 What happens to the 3-carbon molecule produced in bundle sheath cells? It is transported back to mesophyll cells and converted into PEP again.
149 Which enzyme is absent in bundle sheath cells? PEPcase.
150 What is the full form of RuBisCO? Ribulose bisphosphate carboxylase-oxygenase.
151 How many carbon atoms are present in phosphoglycolate? Two carbon atoms.
152 Does photorespiration synthesise sugars? No.
153 What happens to ATP during photorespiration? ATP is utilised.
154 Is ATP synthesised during photorespiration? No.
155 Is NADPH synthesised during photorespiration? No.
156 Is the biological function of photorespiration clearly known? No.
157 Why is understanding factors affecting photosynthesis important? Because the rate of photosynthesis determines the yield of plants, including crop plants.
158 What are the two broad categories of factors affecting photosynthesis? Internal (plant) factors and external factors.
159 On what are plant/internal factors dependent? Genetic predisposition and growth of the plant.
160 Who proposed the Law of Limiting Factors? Blackman (1905).
161 What are the three aspects of light considered while studying photosynthesis? Light quality, light intensity, and duration of exposure.
162 Why does photosynthesis stop increasing at high light intensity? Because other factors become limiting.
163 At what level of sunlight does light saturation usually occur? At about 10% of full sunlight.
164 In nature, when is light usually a limiting factor? Mainly in shade plants or dense forests.
165 What happens if incident light increases beyond a certain point? Chlorophyll breaks down and photosynthesis decreases.
166 Which factor is considered the major limiting factor for photosynthesis? Carbon dioxide concentration.
167 Why are dark reactions temperature controlled? Because they are enzymatic reactions.
168 Are light reactions temperature sensitive? Yes, but to a much lesser extent.
169 How does habitat influence temperature optimum in plants? Tropical plants have higher temperature optima than temperate plants.
170 What effect does water stress have on leaves? Leaves wilt, reducing surface area and metabolic activity.
171 Through which structures do plants take in carbon dioxide for photosynthesis? Through stomata in the leaves.
172 What are the principal carbohydrates formed during photosynthesis? Glucose and starch.
173 In which parts of plants does photosynthesis mainly occur? Green parts, mainly the leaves.
174 Which cells in leaves contain a large number of chloroplasts? Mesophyll cells.
175 Which part of the chloroplast is the site of light reactions? Chloroplast membranes.
176 Where does the chemosynthetic pathway occur in chloroplasts? In the stroma.
177 What are the two stages of photosynthesis? Light reaction and carbon-fixing reactions.
178 What is the role of pigments in the antenna complex? They absorb light energy and funnel it to reaction centre chlorophyll molecules.
179 What are the two photosystems involved in photosynthesis? PS I and PS II.
180 What is the reaction centre pigment of PS I? P700 chlorophyll a.
181 Which wavelength of light is absorbed by P700? 700 nm.
182 What is the reaction centre pigment of PS II? P680 chlorophyll a.
183 Which wavelength of light is absorbed by P680? 680 nm.
184 What happens to electrons after absorbing light energy? They become excited and are transferred through PS II and PS I.
185 To which molecule are electrons finally transferred in the light reaction? NADP.
186 What is created across the thylakoid membrane during electron transport? A proton gradient.
187 With which photosystem is water splitting associated? PS II.
188 What type of compound is RuBP? A 5-carbon compound.
189 Which cycle converts PGA into sugars? Calvin cycle.
190 What happens to RuBP during the Calvin cycle? It is regenerated.
191 Which molecules produced in the light reaction are utilised during the Calvin cycle? ATP and NADPH.
192 Why are accessory pigments like chlorophyll b important? They help absorb additional wavelengths of light and transfer energy to chlorophyll a.
193 What happens to leaves kept in darkness for long periods? They become yellow or pale green.
194 Which pigment is considered more stable in leaves kept in darkness? Accessory pigments are relatively more stable than chlorophyll a.
195 Which leaves are usually darker green: shaded or sun-exposed leaves? Shaded leaves.
196 Why are shaded leaves darker green? Due to higher chlorophyll content for efficient light absorption.