Mineral Nutrition and Absorption
Short Questions and Answers
One mark questions with answers
1. In what form green plants mainly obtain nitrogen from the soil?
Answer: nitrate
2. Name four tracer micronutrients required by plants.
Answer: copper, zinc, molybdenum, nickel
3. Name atleast one crop for which nitrogen supplement is not required.
Answer: peas (any member of leguminosae)
4. Deficiency of which element causes dieback disease?
Answer: copper
5. Which mineral element is common in cytochrome and ferredoxin?
Answer: iron
6. Name at least two aerobic nitrogen fixers.
Answer: Azotobacter, cyanobacteria.
7. Name two asymbiotic nitrogen fixing bacteria.
Answer: Azotobacter, Clostridium
8. Name one symbiotic nitrogen fixing bacteria.
Answer: Rhizobium
9. Name one nitrifying bacteria.
Answer: Nitrosomonas
10. Name one denitrifying bacteria.
Answer: Pseudomonas
Two marks questions with answers
1. What is hydroponics?
Answer: The technique of soil-less culture used for the commercial production of many fruits and vegetables is known as hydroponics (means working with water). The quality of crop obtained in hydroponic system is better than obtained by normal soil farming.
2. What are mineral and non mineral elements?
Answer: Essential elements derived from soil are termed as mineral elements. Essential elements obtained from air or water are known as non-mineral elements e.g., C, H, O. They are building blocks of macromolecules that form the bulk of plant body. Carbon is mostly obtained from air as CO2. Hydrogen is obtained from water. Oxygen is a component of water. It is also available from air.
3. Mention two differences between macroelements and microelements.
Answer: Macro elements are present in plants in easily detectable quantities whereas microelements occur in plants in traces only. Macro elements build up the plant body and different protoplasmic constituents whereas micro elements do not have such a role.
4. What are the symptoms caused by the deficiency of copper?
Answer: The most common symptom of copper deficiency include a disease of fruit trees called ‘exanthema’ and ‘reclamation of crop plants’, found in cereals and legumes. It also causes necrosis of the tip of the young leaves (example, citrus). The disease is called ‘die back’. Copper deficiency also results in the death of fruit trees.
5. What are the major roles of zinc?
Answer: Zinc is essential for the synthesis of tryptophan- a precursor of auxins. It is an activator of several enzymes such as carbonic anhydrase, alcohol dehydrogenase, pyridine nucleotide dehydrogenase, carboxy peptidase etc.
Zinc plays an important role in protein synthesis. In its absence there is substantial increase in soluble nitrogenous compounds.
6. What are the symptoms caused by the deficiency of zinc?
Answer: The first symptom appears in the form of interveinal chlorosis of the older leaves, starting at the tips and the margins. Growth becomes stunted due to formation of smaller leaves and shortened internodes. The leaves become distorted and get clustered to form rosettes. This effect is known as ‘little leaf disease’. In maize zinc deficiency produces ‘white bud disease’ which leads to greatly reduced flowering and fruiting as well as poorly differentiated root growth.
Three marks questions with answers
1. What is the significance of hydroponics?
Answer: The technique of soil less culture is used for the commercial production of many fruits and vegetables. The quality of crop obtained in hydroponic system is better than obtained by normal soil farming. In many industrial areas where soil is not suitable for normal farming, hydroponics is a good alternative. Hydroponics can regulate pH optimum for a particular crop, control soil borne pathogens, avoid problems of weeding and obtain consistently better yield.
2. What is the role of mineral elements in plant nutrition?
Answer: Mineral elements are utilized by the plants in four basic ways.
(1). The elements may form part of structural unit, such as carbon in cellulose or nitrogen in protein.
(2). Elements may be incorporated into organic molecules important in metabolism, like magnesium in chlorophyll molecule or phosphorous in ATP.
(3). Elements may function as enzyme activators, i.e., they act as catalyst in certain enzymatic reactions.
(4). Elements in ionic form, help to maintain osmotic balance, such as potassium in guard cells.
3. What is carrier concept?
Answer: The theory of active absorption suggests the involvement of definite proteins called ‘carrier’ present in the membrane. The membrane does not allow the ions to pass through as it is. The ions form a complex with the carrier called ‘carrier ion complex’ which is capable of moving across the membrane. The ions are then released on the inner side of the membrane. The process of active transport is rapid. It accumulates the solute inside the soil. In other words the transport process will continue even if the solute concentration inside the cell is much more than the surrounding environment. To carry out this uphill transport energy is required. It is usually made available by the hydrolysis of ATP. The carriers are specific i.e., they combine with a particular type of ion.
4. Explain the mass flow theory.
Answer: According to Hylmo (1953, 1955) the ion absorption increases with increase in transpiration. The ions move in a mass flow with water from the soil solution through the root and eventually to the shoot.
This uptake depends on transpiration pull. An increase in transpiration will cause an increase in the absorption of ions. An increase in water flow due to transpiration pull also increases total uptake of ions by the roots. This is a passive process and occurs as a result of translation pull. Metabolic energy is not required for this process. The theory was supported by Kramer (1956), Russell and Barber (1960).
5. What is facilitated diffusion?
Answer: It is the movement of solute molecules or ions from one side of the membrane to other through the mediation of membrane proteins. Plasma membrane of both prokaryotic and eukaryotic cells, as well as membranes of subcellular organelles contain proteins. Many of these membrane proteins function as transport protein. These transporters translocate the molecules or ions across the membrane. This rapid protein mediated diffusion is called facilitated diffusion.The process of facilitated diffusion involve the following steps.
(1). recognition of specific substrate by transport protein
(2). translocation of solute across membrane
(3). release of solute by transport protein, and
(4). recovery of transport protein to its original condition to accept and other solute molecule.
6. What is anion respiration hypothesis?
Answer: This theory was proposed by a Lundegardh (1950 1954) According to his explanation only anions are absorbed actively i.e., anion uptake requires energy and the absorption of cations does not require energy, (i.e., they are absorbed passively). At the outer surface of membrane, the cytochrome undergoes oxidation and loses one electron and in exchange picks up an anion. This is then transported to the inner side of the membrane through the cytochrome chain and on the inner surface of the membrane the anion is released and the cytochrome gets reduced by the action of dehydrogenase involved in respiration.
The cations move passively along the electrical gradient created by the accumulation of anions at the inner surface of the membrane. The evidence in favour of Lundegardh hypothesis is that the respiration increases when a plant is transferred from water to salt solution. The increased respiration was called salt respiration or anion respiration.