Plant Physiology MCQ Quiz - Objective Question with Answer for Plant Physiology - Download Free PDF

The correct answer is Statement-A is incorrect but Statement-B is correct

Explanation:

• A part of a leaf is enclosed in a test tube containing some KOH soaked cotton (which absorbs CO₂), while the other half is exposed to air.
• The setup is then placed in light for some time.
• On testing for the presence of starch later in the two parts of the leaf, the exposed part of the leaf tested positive for starch while the portion that was in the tube, tested negative. This showed that CO₂ was required for photosynthesis.

The correct answer is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ 

Explanation:

• Photosynthesis is a fundamental biological process by which plants, algae, and some bacteria convert light energy into chemical energy, storing it in the bonds of glucose (a type of sugar)
• The overall chemical equation for photosynthesis in oxygen-evolving organisms is as follows 6CO₂ + 12 H₂O → C₆H₁₂O₆ + 6 H₂O + 6O₂ 

The correct answer is A - II, B - I, C - IV, D - III

Explanation:

Plant hormones, also known as phytohormones, are chemicals that regulate plant growth and development. The primary plant hormones include abscisic acid, ethylene, gibberellins, and cytokinins.​

• Abscisic acid (A - II): This hormone helps seeds to withstand desiccation. It is known for its role in inhibiting growth and promoting seed dormancy, helping seeds to survive adverse conditions by preventing premature germination.
• Ethylene (B - I): Ethylene is a gaseous hormone that promotes the formation of female flowers in cucumbers. It is also involved in fruit ripening, leaf abscission, and response to mechanical stress.
• Auxin (C - IV): Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits.
• Cytokinin (D - III): Cytokinins are involved in nutrient mobilization. They promote cell division and growth, delay leaf senescence, and work in conjunction with auxins to control various developmental processes.

Explanation:

• The C₄ cycle, also known as the Hatch-Slack pathway, is a photosynthetic process used by certain plants (e.g., maize, sugarcane, sorghum) to efficiently fix carbon dioxide (CO₂) in hot and dry conditions.
• In the C₄ cycle, the first stable product of carbon fixation is a four-carbon compound, oxaloacetic acid (OAA).
• Phosphoenolpyruvate (PEP), a three-carbon molecule, acts as the first acceptor of CO₂ in this cycle.
• CO2 combines with PEP to form oxaloacetic acid (OAA), a four-carbon compound.
• This reaction is catalyzed by the enzyme PEP carboxylase, which has a high affinity for CO2 and does not get inhibited by oxygen, making it efficient in fixing CO2 even in low concentrations.
• This process occurs in the mesophyll cells of C₄ plants, and the CO₂ fixation is catalyzed by the enzyme PEP carboxylase.

Key Points 

Other Options:

• RuBP:
  • Ribulose-1,5-bisphosphate (RuBP) is the primary acceptor of CO₂ in the C₃ cycle (Calvin cycle)
  • In the Calvin cycle, RuBP reacts with CO₂ to form two molecules of 3-phosphoglycerate (PGA).
  • This process occurs in C₃ plants or in the bundle sheath cells of C₄ plants after the initial fixation by PEP.
• PGA: PGA (3-phosphoglycerate) is an intermediate molecule formed during the Calvin cycle after the fixation of CO₂ by RuBP.
• OAA: Oxaloacetic acid (OAA) is the first stable product formed in the C₄ cycle after CO₂ is fixed by PEP and PEP carboxylase.

The correct answer is Methionine.

Explanation:

• Ethylene is a gaseous plant hormone that plays a key role in various physiological processes, including fruit ripening, leaf abscission, and response to stress.
• The biosynthesis of ethylene in plants follows a well-defined pathway known as the Yang cycle.
• Methionine, an essential amino acid, serves as the precursor for ethylene production in this pathway.
• In the Yang cycle, methionine is first converted into S-adenosylmethionine (SAM) by the enzyme SAM synthetase.
• SAM is then converted into 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase.
• Finally, ACC is oxidized by ACC oxidase to produce ethylene, along with byproducts such as carbon dioxide and cyanide.

Other Options:

• IBA (Indole-3-butyric acid): IBA is an auxin (plant hormone) that promotes root formation and growth.
• MCPA (2-Methyl-4-chlorophenoxyacetic acid): MCPA is a synthetic auxin commonly used as a herbicide to control broadleaf weeds.
• Tryptophan: Tryptophan is an amino acid that serves as a precursor for the biosynthesis of another plant hormone, indole-3-acetic acid (IAA), which is an auxin.

The correct answer is autotrophic nutrition.Key Points

• Autotrophic nutrition is the mode of nutrition in which organisms make their food themselves from simple substances.
• The process of autotrophic nutrition involves the use of light energy (in photosynthesis) or chemical energy (in chemosynthesis) to produce organic compounds.
• Autotrophs are organisms that carry out autotrophic nutrition, such as plants, algae, and some bacteria.

Additional Information

• Heterotrophic nutrition is the mode of nutrition in which organisms obtain their food by consuming other organisms or organic matter.
• Saprotrophic nutrition is a type of heterotrophic nutrition in which organisms obtain their food by decomposing dead organic matter.
• Phototrophic nutrition is a subcategory of autotrophic nutrition, in which organisms use light energy to produce their own food.

Explanation:

• Geotropism: ''Geo'' means earth & ''tropism'' means the movement of the plant due to a stimulus.
• It is the movement and growth of the plant body in response to the force of gravity. It is also called gravitropism
• It is of two types:

1. Positive geotropism: The growth & movement of the plant towards the earth's gravity i.e. downwards is called positive geotropism. Ex - roots show positive geotropism
2. Negative geotropism: The growth & movement of the plant against the earth's gravity i.e. upwards is called negative geotropism. Ex - Shoots show negative geotropism.

• So, the correct option is ''Upward growth of plant shoot is seen'' in negative geotropism.

​ Important Points  

• Exception: The roots of ''mangrove plants'' growing in marshy areas show negative geotropism. These are called pneumatophores which grow vertically upward (negatively geotropic) and come to the surface.

Explanation:

Plant Nutrients:

• Plants are also living organisms.
• The chemical components required for the growth and development of living organisms are called Nutrients.
• They are the only producers who can make food (glucose) on their own by the process of photosynthesis.
• The plant also requires some elements in its ionic form or normal forms for the growth and development of its body and to perform various metabolic activities in them.
• Plant nutrients are also known as minerals or essential elements.

Macro Nutrients:

• The nutrients which are required in large quantities than others are called macronutrients.
• The macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium.

​Micro Nutrients:

• The nutrients which are required in few quantities than others are called micronutrients.
• These include iron, manganese,copper, molybdenum, zinc, boron, chlorine and nickel.
• Iron is an essential nutrient for plant growth and development.
• Iron is a co-factor for vital enzymes which are required for the development of the plant.
• Iron is also required in the process of photosynthesis.

The correct answer is Zero.

Key Points

• The term glycolysis has originated from the Greek words, glycos for ''sugar'' and lysis for ''splitting''.
• The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway.
• In anaerobic organisms, it is the only process in respiration.
• Glycolysis occurs in the cytoplasm of the cell and is present in all living organisms.
• In this process, glucose undergoes partial oxidation to form two molecules of pyruvic acid.

​Explanation:

• The glycolysis is a common pathway for aerobic and anaerobic respiration and no oxygen O₂ is consumed during this process.
• It is a universal pathway that occurs in every living organism be it be aerobic or anaerobic.
• Therefore, the number of oxygen molecules required during glycolysis of one glucose molecule is ''Zero''

Additional Information 

• It involves a series of 10 biochemical reactions where 1 molecule of glucose is degraded to 2 molecules of pyruvic acid.
• Each step is governed by some enzyme.
• In plants, this glucose is derived from sucrose, which is the end product of photosynthesis, or from storage carbohydrates.
• Sucrose is converted into glucose and fructose by the enzyme, invertase, and these two monosaccharides readily enter the glycolytic pathway.
• Glucose and fructose are phosphorylated to give rise to glucose-6- phosphate by the activity of the enzyme hexokinase.
• This phosphorylated form of glucose then isomerizes to produce fructose-6- phosphate.
• Subsequent steps of the metabolism of glucose and fructose are the same.
• In glycolysis, a chain of ten reactions, under the control of different enzymes, takes place to produce pyruvate from glucose

The correct answer is All the Above.

Key Points

•  Hormones are regulatory substances produced in an organism.
•  Different plant hormones help to coordinate growth, development, and responses to the environment.
•  Auxin hormone - It synthesizes at the shoot tip of the plant and helps the cells to grow longer.
•  Gibberellins hormone - It helps in the growth of the stem.
•  Cytokinin hormone - It promotes cell division.
•  Auxin, Gibberellins, and Cytokinins are examples of Plant growth hormones.
•  Abscisic acid - It is a type of hormone which signals to stop growth.

 Additional Information

•  Ethylene Hormone- This hormone is a critical regulator of plant growth and development. It is best known for its effect on fruit ripening and organ abscission.

Concept:

• Nutrients are generally present in plant tissues in large amounts (in excess of 10 mmole Kg ^–1 of dry matter) and are called macronutrients.
• Examples of macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorous, sulfur, potassium, calcium, and magnesium. 
• Trace elements, that are needed in very small amounts (less than 10 mmole Kg ^–1 of dry matter) are called micronutrients.
• Examples of micronutrients are iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.

Explanation:

• Manganese plays a major role in the splitting of water to liberate oxygen during photosynthesis.
• Magnesium activates several enzymes involved in photosynthesis and respiration.
• Boron is involved in pollen germination.
• Iron activates catalase and some other enzymes.

Therefore, the correct answer is option 3.

Additional information:

• Magnesium is a constituent of the ring structure of chlorophyll and helps to maintain the ribosome structure.
• Iron is an important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes. It is reversibly oxidized from Fe²⁺ to Fe³⁺ during electron transfer.
• Boron also helps in cell elongation, cell differentiation, and carbohydrate translocation.

The correct answer is glucose.

Key Points

• The breakdown of glucose into pyruvate within a cell's cytoplasm is known as glycolysis.
• During aerobic conditions, pyruvate can diffuse into mitochondria where it joins the citric acid cycle and produces reducing equivalents in the form of NADH and FADH2.
• The electron transport chain then receives these reducing equivalents, which results in the creation of 32 ATP per molecule of glucose.
• Because the electron transport chain requires oxygen as the final electron acceptor, inadequate tissue oxygenation inhibits the process of oxidative phosphorylation.
• Under anaerobic conditions, pyruvate has a different fate.
• Instead of entering mitochondria, the cytosolic enzyme lactate dehydrogenase converts pyruvate to lactate.
• The regeneration of NAD+ from NADH is also made possible by this process.
• An oxidizing cofactor called NAD+ is required to keep the flow of glucose through glycolysis going.
• Glycolysis produces 2 ATP per glucose molecule, and thus provides a direct means of producing energy in the absence of oxygen.
• This process of breaking down glucose in the absence of oxygen is aptly named anaerobic glycolysis.

Additional Information

• Lactic acid:
  • Lactic acid is mainly produced in muscle cells and red blood cells.
  • It forms when the body breaks down carbohydrates to use for energy when oxygen levels are low. 
• Fructose:
  • Fructose is a type of sugar known as a monosaccharide.
• Citric acid:
  • Citric acid is a weak acid that is found naturally in all citrus fruits.

The correct answer is Sugarcane and Sugarbeet.

Key Points

C3 plants

• C3 plants are those where the initial product is 3-phosphoglycerate with 3 carbon atoms. These plants also known as temperate plants. 
• These plants carry out the C3 cycle to fix carbon from carbon dioxide into 3 carbon sugars.
• It is a cycle of chemical reactions where plants, over a period of time, can transform the 3 carbon compounds into nucleotides, amino acids and complex sugars(starches).
• They are highly rich in proteins.
• Approximately 95% of the shrubs, trees, and plants are C3 plants.
• Examples of C3 plants are Sunflower, Spinach, Beans, Rice, Cotton, and Sugarbeet.

C4 plants

• C4 plants are plants which cycle carbon dioxide to 4-carbon sugar compounds in order to enter the C3 or the Calvin cycle.
• The C4 plants are very productive in climatic conditions that are hot and dry and produce a lot of energy. Some of the plants that we usually consume are C4 plants such as pineapple, corn, sugar cane, etc.
• The C4 pathway is used by only 3% of the vascular plants.
• The plants are so-called because of the 4 carbon compound oxaloacetate produced during the pathway.
• About 5% of plants on earth are C4 plants.
• Examples of C4 plants are Sugarcane, Sorghum, and Maize etc

There are also a few similarities between the C3 and C4 plants:

• Both the plants fix energy from sunlight.
• Both synthesize carbohydrates.
• They are the type of dark reactions of photosynthesis.
• The site of photosynthesis is chloroplast in both types of plants.

The correct answer is Plants.

Key Points

• Phloem is a complex and living tissue.
• It is found in the root, stem and leaves of the plant.

Additional Information

• ​Two types of complex permanent tissues are found in plants -
• Xylem or Xylem and Phloem.
• Phloem -
  • This is the vascular tissue.
  • It is also called bast.
  • It is a complex permanent tissue.
  • This convection is found inside the vandal.
  • Its main function is to transport organic food made by leaves to other parts of plants.
• Xylem -
  • It is such a complex permanent tissue that is found inside the vascular bundle.
  • It plays a major role in the convection of water.
  • The process of sorption takes place from within the xylem.

Concept-

• Plant growth hormones or phytohormones are simple molecules with complex chemical composition, that regulates the growth and physiology of plants.
• Based on their functions on the living plant body, they can be classified into two groups-
  • Plant growth promoters - Eg. Auxins, Gibberellins & cytokinins.
  • Plant growth inhibitors -Eg. Abscisic acid.
• Gaseous PGR like ethylene can be put into both groups, however, it is largely an inhibitor of growth activities.

Key Points

The sub-apical elongation in plants is induced by Gibberellins.

• Gibberellins are plant growth hormones.
• It stimulates elongation of the stem, flowering, and germination.
• Gibberellin is a diterpenoid.
• There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants.
• They produce a wide range of physiological responses in plants.
• Their ability to cause an increase in length of the axis is used to increase the length of grapes stalks.

Additional Information

Auxins

• Auxins (from Greek ‘auxein’ to grow) were first isolated from human urine.
• The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.
• They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.
• Auxins like IAA and indole butyric acid (IBA) have been isolated from plants.
• NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins.
• All these auxins have been used extensively in agricultural and horticultural practices.

Cytokinins

• Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA.
• Kinetin does not occur naturally in plants.
• Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn kernels and coconut milk.
• Since the discovery of zeatin, several naturally occurring cytokinins, and some synthetic compounds with cell division promoting activity, have been identified.
• Natural cytokinins are synthesized in regions where rapid cell division occurs, for example, root apices, developing shoot buds, young fruits, etc.

Ethylene

• Ethylene is a group of plant growth regulators which are widely used for ripening fruits.
• It is also used for the production of more flowers and fruits.
• Ethylene is also used in agriculture practices to ripen fruits, germinate seeds.
• It is a gaseous hormone that stimulates transverse or isodiametric growth but retard longitudinal one.
• Ethylene is regarded as a multifunctional phytohormone that regulates both growth and senescence.
• It promotes or inhibits growth and senescence processes depending on its concentration, timing of application, and the plant species.