Plant Physiology MCQ

High atmospheric humidity means large amount of water vapour in the surrounding atmosphere. There would be no more space in the atmosphere to hold more water vapours. So rate of transpiration decreases.

Seismonasty is the nastic response of a plant to touch or vibration. It is also known as thigmonasty.

Gibberelins promote seed germination. They stimulate the production of hydrolytic enzymes such as amylases, lipases, proteases. These enzyme solubilise the reserve food material and helps in germination.

Cryptochromes are flavoproteins that are sensitive to blue light. They are present in both plants and animals and are involved in their circadian rhythms.

In C₄ plants special anatomy is present called kranz anatomy and Calvin cycle occurs in stroma of bundle sheath chloroplasts.

The osmotic potential is the amount of solute or minerals/ions, soil has more osmotic potential than roots, so ions move into the roots. To balance the solute potential, water also moves into the roots, which leads to absorption of water from soil by roots.

Guard cells are not joined to each other by plasmodesmata.

Cytochromes are heme-containing proteins. They have Fe centres.

Ascent of sap is the mechanism by which water travels in a plant against gravity. Assimilation means the process of absorption and digestion of nutrients by an organism. Somatic embryos are also known as artificial seeds. Asphyxiants destroy pests by causing them respiratory distress.

ACC oxidase catalyses the last step in ethylene biosynthesis i.e. the conversion of ACC to ethylene in the cytosol. 

Photorespiration in plants involves three organelles - chloroplast, peroxisome and mitochondria. Here, glycolate converts into glycine in peroxisomes and this glycine is converted into serine giving off CO₂ in the process. This CO₂ is produced in mitochondria.

The process of converting organic nitrogen to ammonia is ammonification. It occurs during the process of decomposition of plants and animals by fungi and bacteria.

Photorespiration is the process in which the enzyme Rubisco binds to O₂ instead of CO₂. This reaction has 3 organelles where intermediate steps occur. These are chloroplast, mitochondria and peroxisome.

Active transport takes place against concentration gradient. It is an endergonic process.

Abscisic acid is also called abscism. It is a plant hormone which has carotenoid as a precursor. ABA functions in many plant developmental processes, including bud dormancy. ABA is an isoprenoid plant hormone, which is synthesized in the plastidal 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, unlike the structurally related sesquiterpenes, which are formed from the mevalonic acid-derived precursor farnesyl diphosphate, the C15 backbone of ABA is formed after cleavage of C40 carotenoids in MEP.

Sufur is a component of cysteine and methionine.

Nitrogenase undertakes catalysis of all these reactions.

2H₂O → 2H₂ + O₂
∴ 2 molecules of water given are one molecule of oxygen and 2 molecules of hydrogen.

The C4 cycle which involves PEP requires 2 ATP. The C₃ cycle which is common in all plants requires 3 ATP.
Therefore, total ATP required to fix one molecule of CO₂ in C4 plants is 5ATPs.

The reaction is as follows:
 Thus 4 protons and 4 electrons are released to evolve 1 molecule of oxygen.

Glucose is a 6C molecule 1 C is fixed in each turn of the Calvin cycle so 6 turns are needed to make 1 glucose molecule.