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 Multiple Choice QuestionsMultiple Choice Questions


The function of leghaemoglobin during biological nitrogen fixation in root nodules of legumes is to

  • convert atmospheric N2 to NH3

  • convert ammonia to nitrite

  • transport oxygen for activity of nitrogenase

  • protect nitrogenase from oxygen


protect nitrogenase from oxygen

Rhizobium is the nitrogen fixing bacteria present in root nodules of leguminous plants. Roots of a legume secrete chemical attractants flavonoids and betaines. Bacteria collect over the root hairs, release nod factors that causes curling of root hairs around the bacteria, degradations of cell wall and formation of an infection thread enclosing bacteria. The infected cortical cells differentiate and start dividing. It produces swelling of nodules and the infected cells enlarge. Bacteria stop dividing and form irregular polyhedral structures called bacteroids. The host cells develops a pinkish coloured pigment called leghaemoglobin. It is an oxygen scavenger and protects nitrogenase from oxygen. Symbiotic nitrogen fixation requires co-operations of 'Nod' genes of legumes, 'nod' 'nif' and 'fix' genes of bacteria.


Leghaemoglobin helps in

  • imparting colour to floral petals

  • protecting nitrogenase from O2

  • destroying bacteria

  • transport of food in plants


protecting nitrogenase from O2

Leghaemoglobin is a pinkish pigment present inside the root nodules of nitrogen fixing plants like legumes. It is an oxygen scavenger and is related to blood pigment haemoglobin. It protects nitrogen fixing enzyme nitrogenase from oxygen. The most important bacteria present inside the nodules is Rhizobium.


Which among the following is a rootless plant?

  • Nymphaea

  • Sagittaria

  • Ceratophyllum

  • Vallisneria



All the given options are hydrophytes in nature which grow in extremely wet or watery conditions. But among them only in Ceratophyllum roots are completely absent even in embryonic stage. They remain under water completely Nymphaea is a rooted hydrophyte with floating leaves.

Vallisneria is rooted submerged hydrophyte and Sagittaria is rooted emergent hydrophyte.


Hydroponics is

  • nutrient less culture

  • water less culture

  • soilless culture

  • none of these


soilless culture

Hydroponics is a subset of hydroculture, which is a method of growing plants without soil by using mineral nutrient solutions in a water solvent. It is useful in areas having thin, infertile and dry soils. They conserve water. It can regulate pH optimum for a particular crop, control soil borne pathogens, avoid problems of weeding and obtain consistently better yield.


The enzyme responsible for atmospheric nitrogen fixation is

  • nitrogenase

  • hydrogenase

  • oxygenase

  • carboxylase



Enzyme nitrogenase plays a key role in N, fixations and remains active only during anaerobic condition. It is made up of two protein subunits :

i) non-heme iron protein or Fe-protein or dinitrogen reductase.

ii) Iron molybdenum protein or Mo-Fe protein or dinitrogenase


Insects captured by insectivorous plants fulfil their requirements of

  • enzymes

  • oxygen

  • nitrogen

  • water



The insectivorous plants grow in nitrogen deficient soil and their nitrogen requirement is fulfilled by capturing and digesting the insects.


Examination of blood of a person suspected of having anaemia, shows large, immature, nucleated erythrocytes without haemoglobin. Supplementing his diet with which of the following is likely to alleviate his symptoms?

  • Thiamine

  • Folic acid and cobalamine

  • Riboflavin

  • Riboflavin



Anaemia refers to any condition in which there is an abnormally low haemoglobin concentration and/or blood cell count. The most common cause is deficiency of iron which is an essential element of haemoglobin molecule.
Thus, the iron compounds in the diet will help to alleviate the symptoms of anaemia.
Thiamine (vitamin B1), deficiency causes beri-beri.
Riboflavin (vitamin B2) deficiency causes cheilosis and skin diseases.



The deficiencies of micro-nutrients, not only affects growth of plants but also vital functions such as photosynthetic and mitochondrial electron flow. Among the list given below, which group of three elements shall affect most, both photosynthetic and mitochondrial electron transport ?

  • Cu, Mn, Fe

  • Co, Ni, Mo

  • Mn, Co, Ca

  • Ca, K, Na


Cu, Mn, Fe

Micronutrients are minerals obtained from the soil and present in plant tissues at concentrations usually less than 3 μ mol g-1 dry matter. Copper (Cu), Manganese (Mn) and Iron (Fe) are the micronutrients which affect both photosynthesis and mitochondrial electron transport as they are the main constituents of various electron carriers.


Which one of the following elements is not an essential micronutrient for plant growth?

  • Mn

  • Zn

  • Cu

  • Cu



Ca is essential macronutrient for plant growth. It is constituent of middle lamella, activator of enzymes, connected with chromosome formation and many aspects of metabolism



Which of the following is correct set of micronutrient for plants?

  • Mg, Si, Fe, Cu, Ca

  • Cu, Fe, Zn, B, Mn

  • Mg, Fe, Zn, B, Mn

  • Mo, Zn, Cl, Mg, Ca


Cu, Fe, Zn, B, Mn

Plants require nutrients for proper growth and development. There are 16 elements which are required for plant and are termed as essential elements. They are as follows:

Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulphur (S), Potassium (K), Magnesium (Mg), Calcium (Ca), Iron (Fe), Copper (Cu), Boron (B), Zinc (Zn), Manganese (Mn), Molybdenum (Mo) and Chlorine (Cl).

The essential elements are categorised into 2 groups, 

  1. Macro- nutrients: These are required by plants in large quantities. eg, C, H, O, N, S, P, K, Ca and Mg.
  2. Micro- nutrients: These are required by plants in very small quantities. eg, Fe, Cu, B, Mn, Ni, Mo and Cl.