Tag: photosynthesis

Questions Related to photosynthesis

$CO _{2} : NADPH _{2} : ATP$ ratio for $C _{4}$ plants is

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  1. $1 : 2 : 3$

  2. $2 : 3 : 4$

  3. $1 : 2 : 5$

  4. $1 : 5 : 10$

Show answer
Correct Option: C
Explanation:

In C$ _4$ pathway for production of one molecule of glucose we require 12 NADPH$ _2$, 30 ATP and 6CO$ _2$ are required.

CO$ _2$ : NADPH$ _2$ : ATP =  6 : 12 : 30

CO$ _2$ : NADPH$ _2$ : ATP =  1 : 2 : 5

Read the given statements and select the correct option. 
Statement 1 : Crassulacean acid metabolism occurs in succulent plants which grow in xeric conditions. 
Statement 2 : Stomata are generally sunken in succulent plants. 

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. Both statements are correct

  2. Statement 1 s correct but statement 2 is incorrect.

  3. Statement 1 is incorrect but statement 2 is correct.

  4. Both statement are incorrect.

Show answer
Correct Option: A
Explanation:

Crassulacean acid metabolism is a mechanism of photosynthesis involving double fixation of $CO _2$ which occurs in succulents belonging to Crassulaceae, Cacti, Euphorbias and some other plants of dry habitats. Here, the stomata remains closed during the daytime and opens only at night, e.g Sedum,Kalanchoe,Opuntia. Sunken stomata are deep seated stomata in which subsidiary cells lie above the guard cells.  So, the correct answer is 'Both statements are correct'.

Internal source of CO2 in CAM plants is

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. Oxaloacetic acid

  2. Malic acid

  3. RUBP

  4. PEPA

Show answer
Correct Option: A
Explanation:

In  CAM plant, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect CO$ _{2}$. This CO$ _{2}$ is fixed into oxaloacetate by PEP carboxylase, which is then converted to malate. The CO$ _{2}$ is stored as malate in vacuoles at night, and then in the daytime, it is transported to chloroplasts where it is converted back to CO$ _{2}$, which is then used during photosynthesis.  

So, the correct option is 'Oxalo acetic acid'.

In CAM plants, $ C{ O } _{ 2 } $ acceptor is

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. RuBP

  2. PEP

  3. OAA

  4. PGA

Show answer
Correct Option: B
Explanation:

Crassulacean Acid Metabolism (CAM) is a specialised photosynthetic process which is characterized by the following criteria given by  Osmond (1978) and Cluge and Tuge (1978). These are:

  1. CO$ _2$ uptake takes place mainly at night
  2. stomata are open during the night and closed during the day when CO$ _2$ uptake is mostly negligible.
  3. Malate accumulates at night by carboxylation of PEP.
  4. Decarboxylation of malate during the day yields CO$ _2$ which is fixed up by RuBP carboxylase. 
During the night time when the stomata are open, the CO$ _2$ is absorbed and fixed by phosphoenol pyruvic acid (PEP, 3C) in presence of enzyme PEP carboxylase. As a result of this PEP gets converted into oxaloacetic acid (OAA, 4C).
So the correct option is 'PEP'

In CAM plants the site of  light reaction and glucose synthesis are 

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  1. Mesophyll, Bundle seath

  2. Bundle sheath, Mesophyll

  3. Mesophyll, Mesophyll

  4. Bundle seath, Bundle seath

Show answer
Correct Option: B

Which of the following metabolic cycle is an adaptation against Glycolate metabolism?

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. Crassulacean acid metabolism

  2. Co-operative photosynthesis

  3. Reductive pentose phosphate pathway

  4. Photochemical reaction

Show answer
Correct Option: A

In CAM plants, the acceptor of ${CO _2}$ is

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. Pyruvic acid.

  2. Oxaloacetate.

  3. Phosphoenol pyruvate.

  4. Nucleic acid.

Show answer
Correct Option: C
Explanation:
  • Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions.
  •  At low temperatures (frequently at night), plants using CAM open their stomata, CO2 molecules diffuse into the spongy mesophyll's intracellular spaces and then into the cytoplasm. Here, they can meet phosphoenolpyruvate (PEP), the CO2 acceptor.
  • Hence, In CAM plants, the acceptor of CO2 is Phosphoenolpyruvate. 
  •  So, the correct answer is 'Phosphoenol pyruvate'.

The plant adaptation not suitable for hot and dry climates is
I. CAM
II. Mycorrhizae
III. ${C} _{4}$ photosynthesis

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. I only

  2. II only

  3. I and II

  4. I and III

  5. I, II, and III

Show answer
Correct Option: B
Explanation:

Spatial separation of carbon dioxide fixation and RUBISCO activity in mesophyll and bundle sheath cells of $C _4$ plants respectively avoids photorespiration by concentrating $CO _2$ in bundle sheath cells to scale down the oxygenase activity of RUBISCO and increase the RUBISCO efficiency. The increased RUBISCO efficiency allows higher rates of photosynthesis even when stomata are closed for the longer time as well as reduces photorespiration and water loss. CAM plants reduce water loss by opening the stomata at night only. Mycorrhizae are the symbiotic fungi that reside in roots of higher plants and increase soil fertility by nitrogen fixation; it does not impart any adaptive feature to plant to cope with hot and dry conditions. 

Therefore, the correct answer is option B.

The internal source of $C{ O } _{ 2 }$ in CAM plants is

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. Oxalo-acetic acid

  2. Malic acid

  3. RUBP

  4. PEPA

Show answer
Correct Option: A
Explanation:

Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO$ _2$). So the correct option is 'Oxalo-acetic acid'.

In which of the following respects the photosynthetic adaptations of $C _4$ plants and CAM plants are similar?

botany photosynthesis cam cycle cam plants photosynthetic cycle

  1. In both cases, stomata normally close during the day

  2. Both types of plants make their sugar without the Calvin cycle

  3. In both cases, an enzyme other than rubisco carries out the first step in carbon fixation

  4. Neither $C _4$ plants nor CAM plants have grana in their chloroplasts

Show answer
Correct Option: C
Explanation:

$C _4$ and CAM  plants are plants that use certain special compounds to gather carbon dioxide (CO 2 ) during photosynthesis. Exploitation of dry and arid habitats required adaptations in the form of $C _4$ and CAM photosynthesis, which independently evolved many times during periods of low atmospheric $CO _2$ levels carried out by carried out by a non-rubisco enzyme, PEP carboxylase, that has no tendency to bind $O _2$.

So, the correct option is, 'In both cases, an enzyme other than rubisco carries out the first step in carbon fixation'.