Test your knowledge of photosynthesis with these multiple-choice questions designed for competitive exams, covering every aspect and intricate detail of the topic.
Test Your Knowledge
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1. Green plants are classified as autotrophs because they are capable of:
Green plants are called autotrophs because they make or synthesise the food they need through photosynthesis, and all other organisms depend on them for their needs.
2. Photosynthesis is considered crucial for life on Earth for which two primary reasons?
Photosynthesis is important due to two reasons: it is the primary source of all food on Earth, and it is also responsible for the release of oxygen into the atmosphere by green plants.
3. Which simple experiment demonstrates that chlorophyll (green pigment) is required for photosynthesis to occur?
The experiment to look for starch formation in two leaves – a variegated leaf or a leaf that was partially covered with black paper, and exposed to light – showed that photosynthesis occurred only in the green parts of the leaves in the presence of light.
4. Joseph Priestley's experiment in 1770, involving a burning candle, a mouse, and a mint plant in a bell jar, led him to hypothesise that:
Priestley observed that a burning candle or an animal that breathes both somehow damage the air. But when he placed a mint plant in the same bell jar, the mouse stayed alive and the candle continued to burn, leading him to hypothesise that plants restore to the air whatever breathing animals and burning candles remove.
5. Jan Ingenhousz's experiment with an aquatic plant in bright sunlight demonstrated that:
Ingenhousz showed that sunlight is essential for the plant process that somehow purifies the air fouled by burning candles or breathing animals. He also showed that it is only the green part of the plants that could release oxygen.
6. Julius von Sachs, in 1854, provided evidence for the production of glucose in plants and identified its storage form, as well as the location of the green substance (chlorophyll). Which statements are correct regarding his findings?
Julius von Sachs provided evidence for production of glucose when plants grow. Glucose is usually stored as starch. His later studies showed that the green substance in plants (chlorophyll) is located in special bodies (later called chloroplasts) within plant cells.
7. T.W. Engelmann's experiment, using a prism and aerobic bacteria with Cladophora alga, helped describe the first action spectrum of photosynthesis. He observed that bacteria accumulated mainly in the region of:
Engelmann observed that the aerobic bacteria accumulated mainly in the region of blue and red light of the split spectrum, which described the first action spectrum of photosynthesis.
8. The microbiologist Cornelius van Niel demonstrated that photosynthesis is essentially a light-dependent reaction where hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates. His inference about the source of oxygen evolved by green plants was:
Based on his studies, van Niel inferred that the O2 evolved by the green plant comes from H2O, not from carbon dioxide. This was later proved by using radioisotopic techniques.
9. The overall balanced chemical equation representing photosynthesis, incorporating the understanding that O2 is released from water, is:
The correct equation, that would represent the overall process of photosynthesis is: 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2, where the O2 released is from water.
10. In higher plants, the primary site for photosynthesis is the mesophyll cells within the leaves. Within these cells, chloroplasts align themselves along the walls to:
The chloroplasts align themselves along the walls of the mesophyll cells, such that they get the optimum quantity of the incident light.
11. Within the chloroplast, there is a clear division of labour. The membrane system (grana, stroma lamellae) is responsible for _______, while the matrix stroma is the site of _______.
The membrane system is responsible for trapping the light energy and also for the synthesis of ATP and NADPH (light reactions). In stroma, enzymatic reactions synthesise sugar.
12. Dark reactions (carbon reactions) in photosynthesis are named so because:
The dark reactions are not directly light driven but are dependent on the products of light reactions (ATP and NADPH). Hence, to distinguish the latter they are called, by convention, as dark reactions (carbon reactions). However, this should not be construed to mean that they occur in darkness or that they are not light-dependent.
13. Paper chromatography of leaf pigments reveals four main types. Which of the following correctly matches the pigment with its characteristic colour in the chromatogram?
The four pigments are: Chlorophyll a (bright or blue green), chlorophyll b (yellow green), xanthophylls (yellow) and carotenoids (yellow to yellow-orange).
14. Which pigment is considered the chief pigment associated with photosynthesis, and in which regions of the visible spectrum does it show maximum absorption?
Chlorophyll a is the chief pigment associated with photosynthesis. The wavelengths at which there is maximum absorption by chlorophyll a are in the blue and the red regions.
15. Accessory pigments (chlorophyll b, xanthophylls, carotenoids) play a vital role in photosynthesis by:
Though chlorophyll a is the major pigment responsible for trapping light, other thylakoid pigments like chlorophyll b, xanthophylls and carotenoids, which are called accessory pigments, also absorb light and transfer the energy to chlorophyll a. Indeed, they not only enable a wider range of wavelength of incoming light to be utilised for photosyntesis but also protect chlorophyll a from photo-oxidation.
16. The Light Harvesting Complexes (LHC) within Photosystem I (PS I) and Photosystem II (PS II) are made up of hundreds of pigment molecules bound to proteins. What is the function of these pigments?
Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a light harvesting system also called antennae. These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light.
17. The reaction centre chlorophyll a in Photosystem I (PS I) is designated as ______, while in Photosystem II (PS II) it is designated as ______.
In PS I the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called P700, while in PS II it has absorption maxima at 680 nm, and is called P680.
18. In the Z scheme of electron transport, electrons from Photosystem II are first picked up by a primary electron acceptor and then passed 'downhill' to an electron transport system consisting of:
In photosystem II the reaction centre chlorophyll a absorbs 680 nm wavelength of red light causing electrons to become excited and jump into an orbit farther from the atomic nucleus. These electrons are picked up by an electron acceptor which passes them to an electrons transport system consisting of cytochromes.
19. The process of splitting water molecules is associated with which photosystem, and where does it physically occur?
The splitting of water is associated with the PS II; water is split into 2H+, [O] and electrons. The water splitting complex is associated with the PS II, which itself is physically located on the inner side of the membrane of the thylakoid.
20. What are the key products of non-cyclic photophosphorylation, where both Photosystem I and Photosystem II work in series?
When the two photosystems work in a series, first PS II and then the PS I, a process called non-cyclic photo-phosphorylation occurs. Both ATP and NADPH + H+ are synthesised by this kind of electron flow.