Class 12 biology chapter 7 - Plant Growth and Mineral Nutrition textbook solutions

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Q. 1 Multiple choice questions.
1. Which of the hormones can replace 
a. Auxin
 b. Cytokinin
 c. Gibberellins
 d. Ethylene

2. The principle pathway of water 
translocation in angiosperms is ..........
 a. Sieve cells
 b. Sieve tube elements
 c. Xylem
 d. Xylem and phloem

3. Abscisic acid controls ..................
a. cell division
b. leaf fall and dormancy
c. shoot elongation
d. cell elongation and wall formation

4. Which is employed for artificial 
ripening of banana fruits?
a. Auxin
b. Ethylene
c. Cytokinin
d. Gibberellin

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

6. For short day plants, the critical period 
is .................
a. light
b. dark/ night
c. uv rays
d. both a and c

7. Which of the following is day neutral 
a. Tomato
b. Cotton
c. Sunflower
d. Soybean

8. Essential macroelements are ............
 a. manufactured during photosynthesis
 b. produced by enzymes
 c. absorbed from soil 
 d. produced by growth hormones

9. Function of Zinc is ................
a. closing of stomata
b. biosynthesis of 3-IAA
c. synthesis of chlorophyll
d. oxidation of carbohydrates

10. Necrosis means ...............
a. yellow spots on the leaves
b. death of tissue
c. darkening of green colour in leaves
d. wilting of leaves

11.Conversion of nitrates to nitrogen is called .....................
a. ammonification
b. nitrification
c. nitrogen fixation
d. denitrification

12. How many molecules of ATP are required to fix one molecule of nitrogen?
a. 12
b. 20
c. 6
d. 16

Q. 2 Very Short Answer Questions :
1. Enlist the phases of growth in plants?
Answer : The growth in plants involves three phases, viz. meristematic, elongation and maturation. The meristematic phase consists of the constantly dividing cells of the root apex and the shoot apex.

2. Give the full form of IAA?
Answer : IAA Full Form - Indole Acetic Acid
Indole Acetic Acid (IAA) is the principal auxin in plants. This hormone is produced in cells in the apex and young leaves of a plant. IAA plays a key role in root formation and bud growth.

3. What does it mean by ‘open growth’?
Answer : Plant body retains the ability to grow throughout the life, this ability is due to the presence of meristems. The form of growth in which new cells are always being added to the plant by the action of meristems is called the open form or type of growth.

4. Which is the plant stress hormone?
Answer : Abscisic Acid—The Plant Stress Hormone. For example, researchers have long known that a hormone called abscisic acid (ABA) plays a role in how plants respond to weather stresses, such as cold and drought.

5. What is denitrification?
Answer : the loss or removal of nitrogen or nitrogen compounds specifically : reduction of nitrates or nitrites commonly by bacteria (as in soil) that usually results in the escape of nitrogen into the air.

6. Name the bacteria responsible for 
conversion of nitrite to nitrate.
Answer : The conversion of ammonia to nitrite and then to nitrate is done by the bacteria Nitrosomonas and Nitrobacter respectively. This process is called as nitrification.

7. What is role of gibberellin in rosette 
Answer : Gibberellin is one of the plant growth hormone required for the growth and development of the plants.

8. Define vernalization.
Answer : Vernalization is defined as the method of inducing early flowering in plants by treatment of their seeds at a very low temperature.

9. Define photoperiodism.
Answer : The response of plants to periods of day/night is termed photoperiodism.

10. What is grand period of growth?
Answer : the time during which a cell, organ, or organism is developing especially : that period of development characterized by rapid increase in size.

Q. 3 Short Answer Questions :
1. Write a short note on :
a. Differentiation 
b. Redifferentiation
Answer :
a. Differentiation :
The living differentiated cell which has
lost the capacity to divide, may regain the same as per the need and divide. Thus, permanent (mature) cell undergoes dedifferentiation and becomes meristematic e.g. interfascicular cambium and cork cambium are formed from parenchyma cells between vascular bundles and inner most layer of cortex, respectively.

b. Redifferentiation :
The cells produced by dedifferentiation
once again lose the capacity to divide and
mature to perform specific function. This
is called redifferentiation e.g. secondary
xylem and secondary phloem are formed from dedifferentiated cambium present in the vascular bundle.

2. Differentiate between Arithmetic and 
Geometric growth.
Answer :
Arithmatic Growth :

  1. In arithmetic growth only one daughter cells dives and all the other cells undergo differentiation and maturation.
  2. The graph obtained is a linear one.
  3. Ex: Elongation of root occurring at a constant rate.

Geometric Growth :

  1. In geometric growth the growth is proportional to the nutrients supply after which it declines. All the daughter cells divide by mitosis. This is also known as exponential growth.
  2. Represented by a sigmoid curve where the three phases are initial, exponential and stationary phases.
  3. Ex; Cells growing in a culture medium.

3. Enlist the role and deficiency symptoms of : 
a. Nitrogen 
b. Phosphorus 
c. Potassium
Answer : 
a. Nitrogen : Constituent of proteins, nucleic acids, vitamins, hormones, coenzymes, ATP, chlorophyll.

Symptoms : Stunted growth, chlorosis.

b. Phosphorus : Constituent of cell membrane, certain proteins, all nucleic acids and nucleotides required for all phosphorylation reactions.

Symptoms : Poor growth, leaves dull

c. Potassium : Helps in determining anion- cation balance in cells involved in protein synthesis, involved in formation of cell memberane and in opening and closing of stomta; increases hardness; activates enzymes and helps in maintenance of turgidity of cells.

Symptoms : Yellow edges to leaves,
 premature death.

4. What is short day plant? Give any two 
Answer : Thus, short-day plants do best in the late summer and winter, when there is less daylight to interfere with their growth. Common examples of short-day plants include chrysanthemums and poinsettia flowers, cotton, rice, and sugar cane.

5. What is vernalization? Give its significance.
Answer : It is
a low temperature (chilling) treatment that
induces early flowering in plants.
Advantages of vernalization :

  1. Crops can be produced earlier.
  2. Crops can be cultivated in regions where 
  3. they do not grow naturally.

Q. 4 Long Answer Questions :
1. Explain sigmoid growth curve with the help of diagram.
Answer :

The growth curve of any organism appears to have a sigmoidal curve which includes lag phase, log phase, stationary phase and the death phase.

  1. In Lag phase, growth rate is slow. 
  2. In Exponential (Log) phase, growth rate is faster and reaches its maximum. 
  3. In Stationary phase, growth rate gradually slows down. When a graph of rate of growth against time is plotted for three phases of growth, a sigmoid curve is obtained.

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

The relative length of the day was most crucial in the growth and development of flowers to which they coined the term photoperiodism. Based on the photoperiodic response, plants
were classified in three categories viz, Short Day Plants (SDP), Long Day Plants (LDP)
and Day Neutral Plants (DNP).

a. Short Day Plants (SDP) : 
These plants usually flower during winter
and late summer when day length is shorter than the critical photoperiod (critical photoperiod is that length of photoperiod above or below which flowering occurs). These are called long night plants because they require long uninterrupted dark period/ night for flowering. If dark period is interrupted even by a flash of light, SDP will not flower. Some of the short day plants are Dahlia, Aster, Tobacco, Chrysanthemum, Soybean (Glycine max), Cocklebur (Xanthium), etc.

b. Long Day Plants (LDP) : 
Plants that flower during summer are
called long day plants. They require longer duration of light than the critical photoperiod, for flowering. They are called short night plants as they require short dark period. When long dark period is interrupted by a brief flash of light, LD plants can flower e.g. pea, radish, sugar beat, cabbage, spinach, wheat, poppy, etc.

c. Day Neutral Plants (DNP) : 
These plants flower throughout the
year round, independent of duration of light (photoperiod). They do not require specific photoperiod to flower. Therefore, they are called Day neutral plants e.g. Cucumber, tomato, cotton, sunflower, maize, balsam, etc

3. Explain biological nitrogen fixation 
with example.
Answer : Biological Nitrogen fixation : It is carried out by prokaryotes called as ‘Nitrogen fixers’ or Diazotrophs’. It accounts nearly 70% of natural nitrogen fixation. Nitrogen fixers are either symbiotic or free living.

The cyanobacteria fix significant amount of nitrogen in specialized cells called heterocysts. Nitrogen fixation is high energy requiring process and nitrogen fixers use 16 molecules of ATP to fix each molecule of nitrogen to form ammonia.

N2+ 8H + 8e- + 16ATP 2NH3 +H2 + 16ADP + 16Pi

Ammonia is then converted into amino acids.