Solutions-Class-12-Biology-Chapter-7-Plant Growth and Mineral Nutrition-Maharashtra Board

Plant Growth and Mineral Nutrition

Maharashtra Board-Class-12th-Biology-Chapter-7

Solutions

Question 1. Multiple choice questions.

(1) Which of the hormones can replace vernalization?

(a) Auxin

(b)  Cytokinin

(c)  Gibberellins

(d)  Ethylene

Answer :

(c)  Gibberellins

(2) The principle pathway of water translocation in angiosperms is ..........

(a) Sieve cells

(b) Sieve tube elements

(c) Xylem

(d) Xylem and phloem

Answer :

(c) Xylem

(3) Abscisic acid controls ..................

(a) cell division

(b) leaf fall and dormancy

(c) shoot elongation

(d) cell elongation and wall formation

Answer :

(b) leaf fall and dormancy

(4) Which is employed for artificial ripening of banana fruits?

(a) Auxin

(b) Ethylene

(c) Cytokinin

(d) Gibberellin

Answer :

(b) Ethylene

(5) Which of the following is required for stimulation of flowering in the plants?

(a) Adequate oxygen

(b) Definite photoperiod

(c) Adequate water

(d) Water and minerals

Answer :

(b) Definite photoperiod

(6) For short day plants, the critical period is .................

(a) light

(b) dark/night

(c) uv rays

(d) both a and c

Answer :

(b) dark/night

(7) Which of the following is day neutral plant?

(a) Tomato

(b) Cotton

(c) Sunflower

(d) Soybean

Answer :

(d) Soybean

(8) Essential macroelements are ............

(a) manufactured during photosynthesis

(b) produced by enzymes

(c) absorbed from soil

(d) produced by growth hormones

Answer :

(c) absorbed from soil

(9) Function of Zinc is ................

(a) closing of stomata

(b) biosynthesis of 3-IAA

(c) synthesis of chlorophyll

(d) oxidation of carbohydrates

Answer :

(b) biosynthesis of 3-IAA

(10) Necrosis means ...............

(a) yellow spots on the leaves

(b) death of tissue

(c) darkening of green colour in leaves

(d) wilting of leaves

Answer :

(b) death of tissue

(11) Conversion of nitrates to nitrogen is called .....................

(a) ammonification

(b) nitrification

(c) nitrogen fixation

(d) denitrification

Answer :

(d) denitrification

(12) How many molecules of ATP are required to fix one molecule of nitrogen?

(a) 12

(b) 20

(c) 6

(d) 16

Answer :

(d) 16

Question 2. Very Short Answer Questions :

(1) Enlist the phases of growth in plants?

Answer :

The three phases of growth in plants :

  • Phase of cell division,
  • Phase of cell enlargement
  • Phase of cell maturation.

(2) Give the full form of IAA?

Answer :

IAA = Indole Acetic Acid.

(3) What does it mean by ‘open growth’?

Answer :

In plants the growth is indeterminate and takes place throughout the life at specific

regions having meristems.

(4) Which is the plant stress hormone?

Answer :

 Abscissic acid is the plant stress hormone

(5) What is denitrification?

Answer :

Anaerobic bacteria can convert nitrates of soil back into nitrogen gas. That process

performed by denitrifying bacteria is denitrification.

(6) Name the bacteria responsible for conversion of nitrite to nitrate.

Answer :

Nitrobacter bacteria responsible for conversion of nitrite to nitrate.

(7) What is role of gibberellin in rosette plants?

Answer :

Gibberellins promotes bolting i.e. elongation of internodes just prior to flowering in plants those with rosette habit like beet, cabbage.

(8) Define vernalization.

Answer :

The response of plant to the influence of low temperature on flowering in plants is called vernalization.

(9) Define photoperiodism.

Answer :

The response of plant to the influence of light for initiation of flowering is known as photoperiodism.

(10) What is grand period of growth?

Answer :

There are three phases of growth and the total time required for all phases to occur is called grand period of growth.

Question 3. Short Answer Questions :

(1) Write a short note on :

(a) Differentiation

Answer :

  • It is a process of maturation of cells derived from apical meristems.
  • Differentiation is a permanent change in structure and function of cells that leads to its maturation.
  • Cell undergoes major anatomical and physiological change during differentiation process.
  • In hydrophytic plants parenchyma cells develop large schizogenous cavities which help them in aeration, buoyancy and mechanical support.

(b) Redifferentiation

Answer :

  • The cells produced by dedifferentiation once again lose the capacity to divide and mature to perform specific function. This is called
  • The cells mature to perform specific function.
  • Interfascicular cambium is formed by process of dedifferentiation loses its capacity to divide.
  • Secondary xylem and secondary phloem are formed from dedifferentiated cambium present in the vascular bundle.

(2) Differentiate between Arithmetic and Geometric growth.

Answer :

Arithmetic growth Geometric growth
In arithmetic growth only one daughter cell continues to divide, while the other undergoes differentiation and maturation. In geometric growth both the daughter cells continue to divide and redivide again and again.
Rate of growth is constant. Rate growth is initially slow but later on rapid rate.
Linear curve is obtained. Exponential curve is obtained.
Mathematical expression is

L, = Lo + rt where

L, = length of time 't

L, = Length at time zero

r, = growth rate, t = time of growth

Mathematical expression is

W, = Wo® ™ where,

W, = final size,

Wo = initial size, r = growth rate, t = time of

growth E = base of natural logarithm

e.g. Elongation of root e.g. Divisions of zygote during embryo development.

(3) Enlist the role and deficiency symptoms of : a. Nitrogen b. Phosphorus c. Potassium

Answer :

(a) Nitrogen :

  • Role : Constituent of proteins as amino acids, nucleic acids, vitamins, hormones, coenzymes, ATP and chlorophyll molecule.
  • Deficiency symptoms : stunted growth and chlorosis.

(b) Phosphorus :

  • Role : Constituent of cell membrane, certain proteins, nucleic acids and nucleotides, required for all phosphorylation reactions.
  • Deficiency symptoms : Poor growth, leaves dull green

(c) Potassium :

  • Role : Determination of anion – cation balance in cell, necessary for protein synthesis, involved in formation of cell membrane, opening and closing of stomata, activates enzymes, helps in maintenance of turgidity of cells.
  • Deficiency symptom : Yellow edges in leaves, premature death.

(4) What is short day plant? Give any two examples.

Answer :

  • The plants which flower when the day length or light period is shorter than the critical photoperiod are called short day plants or SDP.
  • SDPs usually flower during winter and late summer.
  • Examples — Dahlia, Aster, Tobacco, Chrysanthemum, Soybean (Glycine max) and Cocklebur (Xanthium).

(5) What is vernalization? Give its significance.

Answer :

A low temperature or chilling treatment that induces early flowering in plants is known as vernalization.

Significance :

  • Due to chilling treatment crops can be produced earlier.
  • Crops can be grown in areas where they do not grow naturally.

Question 4. Long Answer Questions :

(1) Explain sigmoid growth curve with the help of diagram.

Answer :

When growth occurs in plants three distinct phases of growth are noticed.

  • The initial phase of cell production occurs when meristematic cells divide and new cells are formed.
  • During the cell expansion phase, freshly produced cells elongate, and there occurs cell enlargement with turgidity.
  • During the cell maturation phase, cells differentiate.
  • The growth rate differs in these three phases when compared.
  • Growth rate is sluggish in the initial phase or lag phase, but increases and reaches a maximum in the log phase or exponential phase.
  • During the stationary phase of maturation, the growth rate decreases and stabilises.
  • When this changing rate of growth is plotted against time duration in a graph a sigmoid or S-shaped growth curve is obtained.

(2) Describe the types of plants on the basis of photoperiod required, with the help of suitable examples.

Answer :

Effect of light duration on flowering of plants is known as photoperiodism.

Depending on photoperiodic response, plants are categorised into three types — Short day plants, long day plants and day neutral plants.

(1) Short day plants :

  • Plants that flower under short day length conditions are called short day plants.
  • Plants such as Dahlia, Xanthium, Soybean, Aster, Tobacco and Chrysanthemum are short day plants or SDP.
  • Short day plants require along uninterrupted dark period for flowering, Therefore, they are also called long night plants.

(2) Long day plants :

  • Plants that flower only when they are exposed to light period longer than their critical photoperiod are called long day plants or LDP.
  • Long day plants require a short dark or night period for flowering. Hence, they are also called short night plants.
  • Plants such as radish, spinach, wheat, poppy, cabbage, pea, sugar beet, etc. are long day plants.

(3) Day neutral plants :

  • Plants in which the floweri.ng is not affected by the day length period are called day neutral plants or DNP or photoneutral plants.
  • Plants such as cucumber, sunflower, cotton, balsam, maize, tomato, etc. are day neutral plants.

(3) Explain biological nitrogen fixation with example.

Answer :

  • Nitrogen fixation is the process of converting atmospheric nitrogen into nitrogenous salts and making it accessible to plants for uptake.
  • Biological nitrogen fixation occurs when live organisms participate in the nitrogen fixation process.
  • The process is mostly carried out by prokaryotic organisms, which are various types of bacteria found in soil.Nitrogen fixing organisms are known as diazotrophs or nitrogen fixers, and they fix around 70% of the nitrogen.
  • Nitrogen fixers are either free-living bacteria or symbiotic bacteria linked with higher plants, such as Rhizobium.
  • The cyanobacteria have specialized cells heterocysts which help in process of nitrogen fixation.
  • Nitrogen fixation is high energy requiring process and 16 ATP molecules are needed for fixation of one molecule of nitrogen to ammonia.
  • Soil bacteria like Nitrosomonas, Nitrosococcus convert ammonia to nitrate and the Nitrobacter convert nitrite to nitrate. This is known as nitrification, biological oxidation.
  • These bacteria are chemoautotrophic and utilize these processes for their metabolism.
  • Fabaceae plants like pea, bean have root nodules which harbour symbiotic bacterium Rhizobium which fixes nitrogen. It is host specific, soil bacteritun, Nitrogen is made available to host plant.

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