Biology

Photosynthesis in Plants

1,508 Questions

Photosynthesis is the biological process by which plants convert light energy into chemical energy. This page contains practice questions covering essential topics like chlorophyll, light reactions, and the pathways specific to plants. This material is crucial for medical entrance exams and academic assessments.

Chlorophyll and pigmentsLight reactionsCalvin cycleCAM plantsElectron transportPhotosynthesis factors

Photosynthesis in Plants Questions

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Engelmann's experiment with Spirogyra demonstrated that 

  1. The full spectrum of sunlight is needed for photosynthesis

  2. Only red wavelengths are effective in causing photosynthesis

  3. Only Blue wavelengths are effective

  4. Both blue and red wavelengths are effective
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Theodor Wilhelm Engelmann was a German botanist, phsiologist, microbiologist, university professor and musician, whose 1882 experiment measured the effects of different colours of light on photosynthetic activity and showed that the conversion of light energy to chemical energy took place in the chloroplast. Both blue and red wavelength are effective because the amount of oxygen released was found to be maximum in blue and red absorption bands of the chlorophyll.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

The maximum light absorbed by the chlorophyll a is at the wave length of

  1. 460 nm

  2. 500 nm

  3. 600 nm

  4. 660 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Small part of visible light in the range of 400 to 700 nm is active in photosynthesis. It is called as photosynthetically active region or PAR. The chlorophyll absorbs maximum in the blue region and red region. The blue region of PAR is near 400 nm after violet and indigo light, while the red region is near 700 nm. The blue region is centered around 460 nm, where chlorophyll a shows maximum absorption.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

The percentage of light energy utilized for photosynthesis by higher plants is 

  1. 100%

  2. 50%

  3. 10%

  4. 1 to 2%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

During photosynthesis 1 to 4% light is utilized. Photosynthesis is more in intense light and is also counted as a limiting factor. Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

The wavelength of light most absorbed during photosynthesis is 

  1. 440 nm

  2. 550 nm

  3. 660 nm

  4. 700 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Wavelength of light absorbed during photosynthesis is 440 nm (violet to blue light). It is the main function of chlorophyll molecule, which is called as the photosynthetic pigment. the violet, blue light have shorter wave length and higher energy content. 

Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Leaves appear green because they

  1. Reflect green light

  2. Absorb green light

  3. Both reflect and absorb green light

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Chlorophyll which is the abundant plant pigment absorbs red and blue light making it photosynthetically efficient. The green wavelengths are reflected giving leaves the green colour. Thus, green is the photosynthetically least efficient wavelength. 
Multiple choice botany ecosystem energy flow in food chain food chain and energy flow energy flow in ecosystem

Photosynthetically active radiation (PAR) represents which of the following range of wave length?

  1. 400 - 700 nm

  2. 500 - 600 nm

  3. 450 - 950 nm

  4. 340 - 450 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers, that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more or less with the range of light visible to the human eye.

Multiple choice biology respiration in organism human respiration the mechanism of breathing breathing and its movements

Microscopic pores in plants through which they expire air are called

  1. Stigma

  2. Thalamus

  3. Gills

  4. Stomata
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
A.Stigma - the terminal part of the gynoecium is called stigma.
B.Thalamus - The upper exapanded structure present at the tip of the pedicle.
C.Gills - the paired respiratory organ of fish and some amphibians, by which oxygen in extracted from water flowing over surfaces within or attached to the walls of the pharynx.
 D.stomata - minute pores present on the epidermis of aerial organs meant for transpiration
So, the correct option is 'stomata'.
Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Oxygen released in photosynthesis is due to 

  1. Photophosphorylation.

  2. Photolysis of water.

  3. Photorespiration.

  4. Photons.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Photosynthesis is a process which occurs in two stages. The first is the light dependent reaction where the captured energy of light is used to make the ATP and NADPH. The second stage is where the reactions independent of light use these products to capture and reduce carbon dioxide. Photolysis is part of the light dependent reaction of the photosynthesis process.  
Photosynthesis photolysis can be represented as H$ _2$A + 2 photons --> 2 e$^-$ + 2H$^+$ + A, where the chemical nature of the 'A' depends on the organism. The experiments conducted by Samuel Ruben and Martin Kamen by using radioactive isotopes helped to prove that the oxygen liberated during photosynthesis came from photolysis the water.
Thus, the correct answer is option B.
Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

During photosynthesis, oxygen is evolved from

  1. $H _{2}S$.
  2. $H _{2}O$.
  3. $CO _{2}$.
  4. $HCO _{3}$.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Photosynthesis is a redox reaction in which carbon dioxide is reduced to sugars and water is oxidised to release oxygen.

Photolysis refers to light dependent split of water molecule, which occurs during photosynthesis. The process of photolysis provides electrons for non cyclic electron flow during non cyclic photophosphorylation. Mineral ions required for the process of photolysis are manganese, calcium and chlorine.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

In the process of photosynthesis, the water molecule is broken down in

  1. Red drop.

  2. Photolysis.

  3. Phoshorylation.

  4. Carbon assimilation.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Photosynthesis is chemically a redox reaction in which carbon dioxide is reduced and water is oxidised. During light reaction phase of photosynthesis, the electron that has been donated to the electron transport chain is replaced through photolysis (light dependent splitting) of water, a process that not only yields electrons but also is the source of almost all the oxygen in Earths atmosphere. 

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Splitting of water is associated with 

  1. Photosystem I

  2. Lumpen of thylakoid

  3. Both photosystem I and II

  4. Inner surface of thylakoid membrane.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Light reaction occur inside the thylakoids, especially those of grana region. It involves two types of reaction photosynthesis of water and production of assimilation power.  The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis or photocatalytic , splitting of water, Water splitting complex is associated with the PSII, which itself is physically located on the inner surface of thylakoid  membrane. 
$4H _{2} O \rightleftharpoons 4H^{+} + 4OH^-$
$ 4OH^- \xrightarrow[Mn^{2+}, Ca^{2+}, Cl^-]{Oxygen \,\,evolving\,\, complex} 2H _{2} + O _{2}\uparrow + 4e^- $ , So, the correct answer is 'inner surface of thylakoid membrane.'.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Which statement regarding cycling flow of electrons during light reactions is false

  1. PS II is not involved in the process.

  2. ATP synthesis takes place
  3. $NADP + H^+$ is synthesised

  4. Takes place only when light of wavelength beyond 680 nm is available for excitation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cycling flow of electrons during light reactions is known as cyclic photophosphorylation. It is performed by photosystem I independently. PS II is not involved in the process. In PS I, the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called $P _{700}$, while in PS II, reaction centre has an absorption maxima at 680 nm and is called $P _{680}$. As cyclic photophosphorylation requires only PS I, so it takes place only when light of wavelength beyond 700 nm is available for excitation. This process takes place in stroma lamellae membrane. An external source of electrons is not required. There is no evolution of oxygen takes place because it is not connected with photolysis of water. Cyclic photophosphorylation produces ATP only. It operates under low light intensity, anaerobic conditions or when $CO _{2}$ availability is low. When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs, due to cyclic flow of electrons. The membrane and lamella of the grana have both PS I and PS II, the stroma lamella membrane lack PS II as well as NADP reductase enzyme. The excited electron does not pass on to $NADP^{+}$ and is cycled back to the PS I complex through the electron transport chain.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Splitting of water is associated with 

  1. Photosystem I

  2. Lumen of thylakoid

  3. Both photosystem I and II

  4. Inner surface of thylakoid membrane
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Splitting up of water or photolysis is associated with Photosystem 2 and this photosystem 2 is present only in the membrane of thylakoids. 

So,  the right answer is 'inner surface of thylakoid membrane'.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Light energy is mainly used in photosynthesis for :-

  1. Spliting of $H _2 O $
  2. For $CO _2$ reduction
  3. Activation of reaction centre to emerge $e^-$

  4. NADPH formation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The photolysis of water (H2O) in the light reactions of photosynthesis occurs in the water-splitting complex of photosystem II embedded in thylakoid membranes of chloroplasts where light is used to split water molecules as represented by the following equation:

2H2O → 4H+ + 4e- + O2

Oxygen (O2) is liberated to the atmosphere as a waste product in this process. In this way, electrons (e-) are gained to replace those lost through photoexcitation from chlorophyll a in the reaction center of photosystem II which begins noncyclic photophosphorylation.

In the light reactions, electrons lost by chlorophyll are used to generate ATP for energy, and to reduce NADP to use as a reducing agent in the Calvin cycle where monosaccharides are fixed from atmospheric carbon dioxide (CO2) and used by the plant for structure and energy.

So the correct option is 'Spliting of H2O'.