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

Single Choice Answer Type Questions

1. Which of the hormones can replace vernalization?

1. Auxin

2. Cytokinin

3. Gibberellins

4. Ethylene

Ans: The correct Option is (c) Gibberellins

• The hormone that can take up the role of vernalization is gibberellins. 

• They are hormones produced by plants that aid in controlling a variety of plant functions, such as stem growth, dormancy, flower development, and flowering. 

• They belong to the longest hormone classes. 

• Gibberellins are the hormones that promote growth and will aid in the tall and elongated growth of plants.

2. The principal pathway of water translocation in angiosperms is ..........

1. Sieve cells

2. Sieve tube elements

3. Xylem

4. Xylem and phloem

Ans:  The correct Option is (d) Xylem and phloem

• Xylem and phloem are the primary pathways for the transport of water in angiosperms.

• Plants have vascular tissues called xylem and phloem that aid in the distribution of food and water to every part of the plant. 

• Phloem and xylem tissues will function as a single bundle. Phloem moves in both directions, but xylem only moves in one.

3. Abscisic acid controls ..................

1. cell division

2. leaf fall and dormancy

3. shoot elongation

4. cell elongation and wall formation

Ans: The Correct Option is (b) leaf fall and dormancy.

Abscisic acid is a hormone found in plants that aids in the development and accelerates rapid cell growth in plants. The acid also regulates the stomatal closure's activity and organ size. The ability of the plants to handle environmental challenges is crucial.

4. Which is employed for the artificial ripening of banana fruits?

1. Auxin

2. Ethylene

3. Cytokinin

4. Gibberellin

Ans. The Correct Option is (b) Ethylene

• Banana fruits are artificially ripened using ethylene. 

• It is a hormone that stimulates plants and aids in the artificial ripening of fruits. 

• A flavourless, flameless gas with an odour of sweetness is ethylene. 

• To give the fruits an artificial hue and hasten their ripening, ethanol is sprinkled on them. 

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

1. Adequate oxygen

2. Definite photoperiod

3. Adequate water

4. Water and minerals

Ans. The Correct Option is (b) Definite photoperiod

• The following is necessary to encourage plants to flower: Definite photoperiod

• Depending on how much light there is during the day and at night, the length of the light period, known as the photoperiod, affects the activities of the plants. 

• The level of floral bloom will depend on the photoperiod. Therefore, the photoperiod affects the flowering level.

6. For short-day plants, the critical period is .................

1. Light

2. dark/ night

3. UV rays

4. both a and c

Ans. The Correct Option is (b) dark/ night

• The crucial time for short-day plants is dark/night.

• The essential period permits the plants to develop within a specific amount of time. 

• The time it takes for plants to bloom or flower during a specific period is referred to as the key period. 

• During times of darkness, plants blossom more intensely.

7. Which of the following is a day-neutral plant?

1. Tomato

2. Cotton

3. Sunflower

4. Soybean

Ans. The Correct Option is (a) Tomato

• Tomatoes are a day-neutral plant since neither intense sunlight nor complete darkness is necessary for their growth. 

• The limited light is sufficient for the fruits to bloom. 

• The tomato is a fruit that, unlike plants with short or long days, engages in the ripening process during a neutral day.

8. Essential macroelements are ............

1. manufactured during photosynthesis

2. produced by enzymes

3. absorbed from soil

4. produced by growth hormones

Ans. The Correct Option is (c) absorbed from the soil

• Essential minerals found in soil are known as macro elements. 

• With the aid of their roots, soil-based plants take in these components. 

• Therefore, various elements like potassium and chlorine will be concentrated in the roots.

9. Function of Zinc is ................

1. closing of stomata

2. biosynthesis of 3-IAA

3. synthesis of chlorophyll

4. oxidation of carbohydrates

Ans.  The Correct Option is (c) synthesis of chlorophyll

Zinc is an element that is crucial for the development of plants. In plants, it aids in the production of chlorophyll. Chlorophyll aids in food preparation. Zinc increases the concentration of chlorophyll, which has the potential to capture atmospheric carbon dioxide.

10. Necrosis means ...............

1. yellow spots on the leaves

2. death of tissue

3. darkening of green colour in leaves

4. wilting of leaves

Ans. The Correct Option is (b) death of tissue

The phenomenon of necrosis causes the tissues of plants to die and the body's organs to become feeble. The blood supply to the various parts is likewise decreased in this situation. In this situation, the blood flow will be obstructed.

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

1. Ammonification

2. Nitrification

3. nitrogen fixation

4. denitrification

Ans. The Correct Option is (d) denitrification

• The process of denitrification converts nitrate to nitrogen gas, releasing bioavailable nitrogen and reintroducing it to the atmosphere. 

• Denitrification produces dinitrogen gas (N2) as its undeniable end product, however other somewhat vaporous forms of nitrogen do occur. 

• Some of these gases, such as nitrous oxide (N2O), are thought of as nursery gases because they react with ozone and worsen air pollution.

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

1. 12

2. 20

3. 6

4. 16

Ans. The Correct Option is (d) 16

A total of 16 ATP molecules are needed to repair one nitrogen molecule.

Very Short Answer Questions

1. Enlist the phases of growth in plants.

Ans. 

Plant Growth Stages:

1. The Meristematic Stage: A plant's root and shoot pinnacle have constantly dividing cells. They relate to the meristematic stage of growth. These cells feature thick cell walls that contain cellulose and huge centres that are rich in cellular components.

2. Extension Phase: The cells in the region immediately following the meristematic area provide evidence for the period of prolonging. Cell broadening, enlarged vacuole formation, and new cell wall deposition are characteristics of the cells in this zone.

3. Developing Stage: The time of development is located just outside the expansion period, yet far from the peak. The cells in this region reach their largest sizes in terms of cellular composition and cell wall thickness. 

2. Give the full form of IAA?

Ans. The main auxin in plants is called indole acetic acid (IAA). Cells in a plant's zenith and young leaves produce this hormone. IAA plays a significant role in both root and bud development.

• IAA is mostly produced in the cells of a plant's apex (bud) and its exceedingly young leaves.

• Several independent biochemical routes allow plants to produce IAA. While four of them begin with tryptophan, there is another metabolic pathway that is independent of this amino acid.

• IAA is primarily made by plants from tryptophan using indole-3-pyruvic acid.

• In Arabidopsis thaliana, IAA is further supplied from tryptophan via indole-3-acetaldoxime.

• The most well-known naturally occurring auxin class plant hormone is indole-3-acetic acid (IAA, 3-IAA). It is the most well-known auxin and has been the focus of extensive research by plant physiologists.

3. What does it mean by ‘open growth’?

Ans. Open growth is the type of growth when meristem activity continuously adds new cells to the plant body. 

• Plants can develop continuously throughout their lives because of the meristems that are present in their bodies. 

• Cells in meristems have the ability to divide and self-replicate. 

• Plants have the capacity to develop continuously throughout their lives because of the meristems that are present in their bodies.

4. Which is the plant stress hormone?

Ans. Abscisic Acid is regarded as the stress hormone because it is produced in unfavorable conditions like a drought or a water shortage.

• Physiological Effects of Abscisic Acid: Buds go into dormancy as winter approaches due to abscisic acid. Several seeds have abscisic acid accumulation which appears to be a factor in seed dormancy.

• Senescence: Senescence is generally induced by ABA (Thiemann). Stomatal closure is connected to the start of senescence. As senescence begins, the ABA content of aged leaves will grow significantly.

• Flowering: Gibberellins' effect on flowering in long-day plants is mitigated by ABA, which accumulated in the leaves during the brief winter days. For plants with extended days, this ABA serves as the blooming matter. On the other hand, ABA causes flowering in plants within short days.

5. What is denitrification?

Ans. The process of denitrification converts nitrate to nitrogen gas, releasing bioavailable nitrogen and reintroducing it to the atmosphere. 

• Denitrification produces dinitrogen gas (N₂) as its undeniable end product, however other somewhat vaporous forms of nitrogen do occur. 

• Some of these gases, such as nitrous oxide (N₂O), are thought of as nursery gases because they react with ozone and worsen air pollution.

• Most of the time, denitrification proceeds by reducing a mixture of the accompanying intermediate structures in a stepwise manner: NO₃⁻ → NO₂⁻→ NO + N₂O → N₂

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

Ans. After nitrogen gas is transformed into nitrite, Nitrobacter bacteria are utilized to convert nitrite to nitrate. 

• The fixation and conversion of nitrogen are assisted by these whole microorganisms.

• Nitrobacter bacteria first transform nitrogen gas into nitrite (NO₂), and Nitrobacter next transforms nitrite into nitrate (NO₃^-), a nutrient for plants. 

• During the osmosis process, plants retain ammonium and nitrate, which are then converted into nitrogen-containing natural atoms like amino acids and DNA.

7. What is the role of gibberellin in rosette plants?

Ans. A stem that resembles a consolidated plate is known as a rosette stem. Gibberellin deficiency is the reason for the predisposition for rosettes. When radish rosette plants are treated with gibberellic acid, the stem lengthens. In rosette plants, shooting also typically occurs during the start of Powering.

As a result, along the internodes of the rosette plants, the stein maintains an extraordinarily short length.

8. Define vernalization.

Ans. Vernalization, or its artificial equivalent, is the induction of a plant's flowering process through exposure to the extended cold of winter. 

• This phrase is frequently used to refer to flavored plants that need a cold dormancy to produce new shoots and leaves, but its use is discouraged.

• This makes sure that procreative growth and seed generation takes place in the spring and winter rather than during the season. 

• Commonly, the amount of required cold is given in chill hours.

9. Define photoperiodism.

Ans. Photoperiodism is an organism's response to the length of the night or a quantity of darkness. 

• The organic reactions of plants to the varying lengths of daylight and nighttime can even be used to define photoperiodism. 

• The photoperiods are divided into three groups: day-neutral plants, long-day plants, and short-day plants.

• Both plants and animals experience it. 

10. What is a grand period of growth?

Ans: A grand period of growth is the overall time frame in which maximum growth occurs to complete all phases of growth.

Short Answer Questions

1. Write a short note on:

1. Differentiation

2. Redifferentiation

Ans:  

(a) Differentiation

• The cells derived from the cambium, root apical meristem (RAM), and shoot apical meristem (SAM) differentiate and grow to carry out specific roles. Differentiation is the term used to describe this display that spurs development. 

• Their cell wall and cellular substance both go through a few significant ancillary alterations. 

• For instance, to produce a treacherous component, the cells shed their cellular substance while developing a strong, flexible, lignocellulosic auxiliary cell wall, which is best suited to transport water over great distances while being put under extreme pressure.

(b) Redifferentiation

• Cells and tissues that undergo dedifferentiation are those that have lost the ability to differentiate as a result of dedifferentiation.

• However, development and even separation in plants are both open because, for instance, the identical apical meristem cells provide ascent to xylem, phloem, filaments, and other structures, while cells and tissues emerging from the same meristem have different structures at different developmental stages.

• The area of the cell within determines the final structure that forms when a cell or tissue emerges from the same meristem.

2. Differentiate between Arithmetic and Geometric growth.

Ans: The differences are given below:

3. Enlist the role and deficiency symptoms of:

1. Nitrogen

2. Phosphorus

3. Potassium

Ans. 

(a) Nitrogen:

• Role: Plants need nitrogen to produce proteins, nucleic acids (DNA and RNA, among others), and chlorophyll.

• Deficiency Symptoms: General chlorosis of lower leaves, moderate development delays, and, in severe cases, the rot of more experienced leaves are signs of insufficient Nitrogen. Plants short in nitrogen will mature earlier, which usually lowers crop quality and output.

(b) Phosphorus:

• Role: For the reactions of ATP (vitality), sugars, and nucleic acids in plants, phosphorus is necessary. 

• Deficiency Symptoms: Plants with low phosphorus typically develop dull green leaves and stems and appear hampered.  Young plants, which have a more notable relative interest for P than additionally developed plants, are more likely to exhibit the negative effects of phosphorus deficiency.

(c) Potassium:

Short-day plants are those that require less sunshine than their essential photoperiod. Distinct plants have a different critical photoperiod. The duration of day/night light exposure necessary for plants to flower is known as photoperiod, and this phenomenon is referred to as photoperiodism. Once the crucial photoperiod is exceeded, the short-day plant is unable to blossom. These plants include chrysanthemums, rice (Oryza sativa), and many others.

4. What is a short-day plant? Give any two examples.

Ans. Short-day plants need less light than is necessary for them to begin flowering. 

• Such day-shortening plants include chrysanthemum, rice, and soybean. Photoperiodism is the term for this occurrence.

• Short-day plants are those that require less sunshine than their essential photoperiod. Distinct plants have a different critical photoperiod. 

• The duration of day/night light exposure necessary for plants to flower is known as photoperiod, and this phenomenon is referred to as photoperiodism. 

• Once the crucial photoperiod is exceeded, the short-day plant is unable to blossom. 

• These plants include chrysanthemums, rice (Oryza sativa), and many others. 

5. What is vernalization? Give its significance.

Ans. With the use of low temperatures, vernalization aids plants in preventing them from generating premature grains. Instead of becoming mature too soon, this enables them to have enough time to fulfil their full potential. When exposed to cold, biennial plants that typically flower and then perish in the second season respond with photoperiodic flowering.

• Less temperature is required for plants to blossom, either in quantity or quality. Vernalization is the name given to this phenomenon.

• This trait gives them the necessary time to mature and prevents them from growing too quickly.

• Winter and spring variations are available in both wheat and barley. The winter variety, in contrast to the spring type, produces mature seeds during the flowering season if planted in the spring. Thus, they are planted in the autumn and harvested in the middle of the summer.

Long Answer Question

1. Explain the sigmoid growth curve with the help of a diagram.

Ans. 

Sigmoid Growth Curve 

In the case of unlimited resources, the increase concerning time is represented graphically by a J-shaped exponential growth curve. In a perfect world, resources should not be unlimited.

As the number of species increases, members compete more fiercely for the scarce resources that are available, giving rise to the ideas of reproduction and survival of the fittest.

The carrying capacity (K) is nature's limit or the greatest number of species that may coexist in a given habitat with sufficient resources.

Logistic growth refers to growth like this with carrying capacity.

The formula below depicts the Verhulst-Pearl Logistic curve, also known as the Sigmoid growth curve, which is a graphical representation of this condition;

\[\dfrac{{dV}}{{dt}} = rN\left( {\dfrac{{K - N}}{N}} \right)\]                

Where N = Population density at time t

r = Intrinsic rate of natural increase

K = Carrying capacity 

The graph initially displays a lag phase, followed by the phases of acceleration and deceleration. The density eventually decreases as a result of survival of the fittest once the growth density surpasses the carrying capacity, creating an S-shaped curve.

2. Describe the types of plants based on photoperiod required, with the help of suitable examples.

Ans: Varying plants have different photoperiods and depending on the season, there are various plant varieties. A plant cannot initiate blooming if the critical photoperiod is exceeded or decreased. Different plants require a different amount.

Long Day Plants: Long-day plants are those that bloom beyond the required photoperiod, such as in the summer. Below this photoperiod (winter), where light intensity and temperature are low, such plants never flower.

Short Day Plants: These are the species of plants that bloom in seasons with lower photoperiods, including autumn and winter. Take rice, sugar cane, chrysanthemums, cotton, etc. as examples.

Day-neutral plants: Day-neutral plants are the third category. These are the plants that are photoperiod independent. The initiation of flowering is reliant on additional elements like soil, minerals, etc.

• The amount and length of light that particular plants get affects how they respond in terms of flowering. Depending on this phenomenon, plants are divided into three categories: long days, short days, and day-neutral plants.

• Short-day plants bloom below the essential photoperiod, while long-day plants bloom above it. However, day-neutral plants do not exhibit this relationship between blooming and photoperiod.

3. Explain biological nitrogen fixation with examples.

Ans: Because nitrogenase is present, biological things can turn nitrogen into ammonia. Microbes that are symbiotic or free-living can fix nitrogen. Azotobacter and Beijernickia are examples of free-living microorganisms. The most typical symbiotic association is between legumes and the Rhizobium bacteria. Rhizobium are symbionts that can fix atmospheric nitrogen since they are free-living bacteria. Rhizobia proliferate, colonise the area around roots, adhere to the root hairs, and eventually form a root nodule that supplies essential biochemical elements like nitrogenase and leghemoglobin. Since nitrogenase is a very sensitive oxygen-sensitive enzyme, anaerobic conditions are necessary for it to function. These conditions are established and kept up by the root nodules. The reaction that fixes nitrogen is very endothermic. By way of the host cell's respiration, energy is supplied.

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

By adhering to the root cells of the host plant, such as legumes, the microorganisms such as rhizobium generate nitrogenase enzyme, which helps to convert atmospheric nitrogen into ammonia. The host cell supplies the reaction with the high energy it needs to proceed.

Importance of Maharashtra Board Class 12 Biology Chapter 7 Plant Growth and Mineral Nutrition

This chapter defines and explains what growth is. It is a process where cells multiply and increase in size to increase the overall quality and quantity of an organism. The same explanation stands true for the plants too.

Plants show a unique style of growth. They increase in body mass but in different stages. Also, the growth depends on the age of a plant. It is also a permanent change that cannot be reversed at any cost.

Unicellular plants show growth at the cell level. Multicellular plants show different types of growth based on their locations, age, organs, etc. It means that unicellular plants show uniform growth whereas multicellular plants show variable rates of growth at the same time.

This chapter will also explain the phases of growth where cells divide and increase in number. In the other phases, cells get bigger in size and contribute to the volume of a plant. There are two different types of cell division explained in this chapter. To get a hold of the concepts, refer to the Maharashtra Board Class 12 Biology Solutions Chapter 7 Plant Growth and Mineral Nutrition.

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Download Plant Growth and Mineral Nutrition Class 12 Solutions PDF

Get your Plant Growth and Mineral Nutrition Class 12 Solutions PDF download today and complete your study material for this chapter. Get the best assistance from these notes to resolve your doubts. Grab the concepts of growth, cell division, mineral nutrition, etc. in plants and score better in the exams.