Photosynthesis – Factors Affecting Photosynthesis: NEET MCQs with Answers

15 free questions on Photosynthesis – Factors Affecting Photosynthesis for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Factors Affecting Photosynthesis

Practise all 149 Photosynthesis – Factors Affecting Photosynthesis questions free Take a free timed test

Question 1

Previous-year question
With reference to the factors affecting the rate of photosynthesis, which of the following statements is NOT correct? [NEET 2017]
  1. Increasing the atmospheric CO₂ concentration up to 0.05 per cent can enhance the CO₂ fixation rate
  2. C₃ plants respond to higher temperatures with enhanced photosynthesis while C₄ plants have a much lower temperature optimum
  3. Tomato is a greenhouse crop which can be grown in a CO₂-enriched atmosphere for higher yield
  4. Light saturation for CO₂ fixation occurs at 10 per cent of full sunlight
Show answer
Answer: (B) C₃ plants respond to higher temperatures with enhanced photosynthesis while C₄ plants have a much lower temperature optimum
Explanation: The statement reverses the two groups. It is the C₄ plants that show a higher temperature optimum and respond to higher temperatures with enhanced photosynthesis, whereas C₃ plants have a much lower temperature optimum.

Question 2

Previous-year question
During the monsoon, the rice crop of the eastern states of India shows a lower yield because of the limiting factor of [AIPMT 1991]
  1. CO₂
  2. light
  3. temperature
  4. water
Show answer
Answer: (B) light
Explanation: By the principle of limiting factors, the rate of a process is set by its slowest component. Light intensity varies with latitude, altitude, season, topography and the presence of interceptors such as cloud, dust, fog and humidity. In the eastern states, heavy monsoon cloud cover sharply reduces light intensity, lowering photosynthesis and hence yield.

Question 3

Previous-year question
At temperatures above 35 °C, [AIPMT 1992]
  1. the rate of photosynthesis will decline earlier than that of respiration
  2. the rate of respiration will decline earlier than that of photosynthesis
  3. there is no fixed pattern
  4. both decline simultaneously
Show answer
Answer: (A) the rate of photosynthesis will decline earlier than that of respiration
Explanation: Photosynthetic enzymes, especially RuBisCO, and the photosynthetic machinery are more sensitive to high temperature, and photorespiration rises with temperature. Respiration keeps increasing up to higher temperatures, so above about 35 °C photosynthesis declines before respiration.

Question 4

Previous-year question
The principle of limiting factors was proposed by [AIPMT 1996]
  1. Blackmann
  2. Hill
  3. Arnon
  4. Liebig
Show answer
Answer: (A) Blackmann
Explanation: The principle of limiting factors was given by the British plant physiologist F.F. Blackmann in 1905. It states that when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest factor. Light intensity, CO₂ concentration and temperature are the chief limiting factors in photosynthesis.

Question 5

Previous-year question
Plants adapted to low light intensity have [AIPMT 2004]
  1. a larger photosynthetic unit size than sun plants
  2. a higher rate of CO₂ fixation than sun plants
  3. a more extended root system
  4. leaves modified to spines
Show answer
Answer: (A) a larger photosynthetic unit size than sun plants
Explanation: Shade-tolerant plants possess larger photosynthetic units — that is, more antenna pigment molecules per reaction centre — which lets them harvest scarce photons more effectively. However, their overall photosynthetic and growth rates remain lower than those of plants growing in full sun.

Question 6

Previous-year question
With reference to the factors affecting the rate of photosynthesis, which of the following statements is NOT correct? [NEET 2017]
  1. Light saturation for CO₂ fixation occurs at 10% of full sunlight
  2. Increasing atmospheric CO₂ concentration up to 0.05% can enhance the CO₂-fixation rate
  3. C₃ plants respond to higher temperature with enhanced photosynthesis, while C₄ plants have a much lower temperature optimum
  4. Tomato is a greenhouse crop which can be grown in a CO₂-enriched atmosphere for higher yield
Show answer
Answer: (C) C₃ plants respond to higher temperature with enhanced photosynthesis, while C₄ plants have a much lower temperature optimum
Explanation: This statement reverses the facts: C4 plants respond to higher temperatures with enhanced photosynthesis, while C3 plants have a much lower temperature optimum (NCERT). The other statements about light saturation at 10% of full sunlight, CO2 enrichment up to 0.05% and CO2-enriched greenhouse tomato are correct.

Question 7

Previous-year question
A very efficient converter of solar energy, with a net productivity of 2 to 4 kilograms per square metre or more, is the crop [1991]
  1. rice
  2. wheat
  3. bajra
  4. sugarcane
Show answer
Answer: (D) sugarcane
Explanation: Sugarcane is a C₄ plant with a long growing season, a dense canopy and a very high rate of carbon fixation, and it achieves among the highest net productivities of any cultivated crop. Rice and wheat are C₃ plants and convert solar energy considerably less efficiently.
Doing well? Create a free account to take timed tests on this topic and see your weak areas.

Question 8

Previous-year question
Maximum solar energy is trapped by [1994]
  1. growing algae in tanks
  2. planting trees
  3. growing grasses
  4. cultivating crops
Show answer
Answer: (A) growing algae in tanks
Explanation: Algae grown in tanks present an almost continuous photosynthetic surface, multiply extremely rapidly and devote nearly all their biomass to photosynthetic tissue rather than to stems and roots. Their efficiency of energy conversion per unit area is therefore higher than that of any land crop.

Question 9

Previous-year question
The greatest producers of organic matter are [1988]
  1. plants of the land area
  2. crop plants
  3. phytoplankton of the oceans
  4. forests
Show answer
Answer: (C) phytoplankton of the oceans
Explanation: Oceans cover about seven-tenths of the earth's surface, and although individual phytoplankton are minute their enormous numbers and rapid turnover make them collectively the largest producers of organic matter and the largest source of atmospheric oxygen.

Question 10

Previous-year question
Of the total incident solar radiation, the proportion that is photosynthetically active is [2012]
  1. less than 50%
  2. about 70%
  3. more than 80%
  4. about 60%
Show answer
Answer: (A) less than 50%
Explanation: Photosynthetically active radiation, the 400 to 700 nanometre band, accounts for less than half of the solar radiation reaching the earth, the remainder being largely infrared and ultraviolet. Of this available fraction plants in turn capture only two to ten per cent.

Question 11

Previous-year question
Plants adapted to low light intensity have [2003]
  1. a more extended root system
  2. a larger photosynthetic unit size than sun plants
  3. leaves modified into spines
  4. a higher rate of carbon dioxide fixation than sun plants
Show answer
Answer: (B) a larger photosynthetic unit size than sun plants
Explanation: Shade plants build larger light-harvesting antennae, with more chlorophyll molecules serving each reaction centre, so that the scarce photons are captured efficiently. Their maximum rate of fixation is lower than that of sun plants, but they saturate and reach it at much lower light intensities.

Question 12

Previous-year question
During the monsoon the rice crop of the eastern states of India gives a lower yield because of the limiting factor of [1992]
  1. temperature
  2. carbon dioxide
  3. water
  4. light
Show answer
Answer: (D) light
Explanation: Persistent cloud cover during the monsoon greatly reduces the intensity and duration of sunlight reaching the crop, so light becomes the factor nearest its minimum and photosynthesis is restricted. Water is plentiful and temperature and carbon dioxide are not limiting at that season.

Question 13

Previous-year question
The principle of limiting factors was proposed by [1994]
  1. Arnon
  2. Blackman
  3. Liebig
  4. Hill
Show answer
Answer: (B) Blackman
Explanation: Blackman's law of limiting factors states that when a process depends on several factors, its rate is governed by the one that is nearest its minimum value. Raising any other factor produces no effect until the limiting one is relieved. Liebig had earlier given a similar law of the minimum for mineral nutrients.

Question 14

Previous-year question
With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct? [NEET 2017]
  1. Increasing atmospheric CO₂ concentration up to 0.05% can enhance CO₂ fixation rate
  2. C₃ plants respond to higher temperature with enhanced photosynthesis while C₄ plants have much lower temperature optimum
  3. Tomato is greenhouse crop which can be grown in CO₂-enriched atmosphere for higher yield
  4. Light saturation for CO₂ fixation occurs at 10% of full sunlight
Show answer
Answer: (B) C₃ plants respond to higher temperature with enhanced photosynthesis while C₄ plants have much lower temperature optimum
Explanation: The statement is reversed and therefore incorrect: it is C₄ plants (not C₃) that respond to higher temperature with enhanced photosynthesis; C₃ plants have the lower temperature optimum.

Question 15

Previous-year question
With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct? (NEET UG 2017)
  1. Tomato is a greenhouse crop which can be grown in CO2 - enriched atmosphere for higher yield
  2. Light saturation for CO2 fixation occurs at 10% of full sunlight
  3. Increasing atmospheric CO2 concentration upto 0.05% can enhance CO2 fixation rate
  4. C3 plants responds to higher temperatures with enhanced photosynthesis while C4 plants have much lower temperature optimum
Show answer
Answer: (D) C3 plants responds to higher temperatures with enhanced photosynthesis while C4 plants have much lower temperature optimum
Explanation: Statement D is INCORRECT — C4 plants have HIGHER (not lower) temperature optimum than C3.

Want more Photosynthesis – Factors Affecting Photosynthesis questions?

E-GYAN NIDHI has 149 questions on this topic and 63,000+ in total, all free: timed CBT tests, NEET marking and instant analysis.

Register free Free Sunday Mock Test

More topics in Plant Physiology

↑