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Plant Growth and Development NCERT Textbook With Solutions PDF Free Download
Chapter 15: Plant Growth and Development
You have already studied the organization of a flowering plant in Chapter Have you ever thought about where and how the structures like roots, stems, leaves, flowers, fruits, and seeds arise and that too in an orderly sequence?
You are, by now, aware of the terms seed, seedling, plantlet, and mature plant.
You have also seen that trees continue to increase in height or girth over a period of time.
However, the leaves, flowers, and fruits of the same tree not only have limited dimensions but also appear and fall periodically and sometimes repeatedly.
Why does the vegetative phase precede flowering in a plant? All plant organs are made up of a variety of tissues; is there any relationship between the structure of a cell, a tissue, an organ, and the function they perform?
Can the structure and the function of these be altered? All cells of a plant are descendants of the zygote.
The question is, then, why and how do they have different structural and functional attributes? Development is the sum of two processes: growth and differentiation.
To begin with, it is essential and sufficient to know that the development of a mature plant from a zygote (fertilized egg) follows a precise and highly ordered succession of events.
During this process, a complex body organization is formed that produces roots, leaves, branches, flowers, fruits, and seeds, and eventually, they die.
In this chapter, you shall also study some of the factors which govern and control these developmental processes. These factors are both intrinsic (internal) and extrinsic (external) to the plant.
Growth is regarded as one of the most fundamental and conspicuous characteristics of a living being.
What is growth? Growth can be defined as an irreversible permanent increase in the size of an organ or its parts or even of an individual cell.
Generally, growth is accompanied by metabolic processes (both anabolic and catabolic), that occur at the expense of energy.
Therefore, for example, the expansion of a leaf is growth. How would you describe the swelling of the piece of wood when placed in water?
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NCERT Solutions Class 11 Biology Chapter 15 Mineral Nutrition
1. Define growth, differentiation, development, dedifferentiation, development, redifferentiation, determinate growth, meristem, and growth rate.
Growth – it is an irreversible, permanent increase in the size of an organ or its parts or even of an individual cell. Growth is supplemented by metabolic activities taking place due to the energy.
Differentiation – The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed differentiation.
Development – All the changes that an organism goes through in its lifetime are called development.
Dedifferentiation – Plants which has lost the capacity to divide can regain the capacity under certain conditions. This phenomenon is called dedifferentiation. Example – meristem formation
Redifferentiation – Dedifferentiation produces cells that once again lose the capacity to divide but mature to perform specific functions are said to be redifferentiated.
Determinate growth – The ability of a cell, tissue, or organism to grow for a certain period is called determinate growth. In most plants, growth is indefinite, where some plants grow to a certain level and then stop growing.
Meristem – Plant tissue containing undifferentiated cells (meristematic cells) is called meristem.
Growth rate – Increase growth per unit time is called a growth rate.
2. Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
Growth is a consequence of the increase in the quantity of protoplasm. Measuring the protoplasmic growth includes several parameters, to name a few – increase in height, weight, number of cells, fresh tissue sample, length, area, volume, etc. Hence it is difficult to demonstrate any one parameter of growth throughout the life of a flowering plant.
5. What do you understand by photoperiodism and vernalization? Describe their significance.
Photoperiodism can be termed as the response of plants to periods of day/night. It is theorized that the hormonal substance that is responsible for flowering, is formed in the leaves which subsequently migrates to the shoot apices and alters them into flowering apices.
This process of photoperiodism helps in studying the response of flowering in different crop plants when the duration of exposure to light is considered.
Vernalisation is the phenomenon where the process of flowering in some plants is either quantitatively or qualitatively dependent on the exposure to lower temperatures.
In particular, it refers to promoting the flowering process by a period of lower temperatures. The process prevents precocious reproductive development late in the growing season which thereby enables the plant to have sufficient time to attain maturity.
6. Why is abscisic acid also known as stress hormone?
Abscisic acid is responsible to stimulate the closure of stomata in the epidermis and raises the tolerance of plants to different types of stresses, hence it is also called a stress hormone.
Abscisic acid is responsible to promote seed dormancy thereby ensuring the germination of seeds during favorable conditions.
This helps the seeds to withstand desiccation and to induce dormancy towards the end of the growing season in plants thereby promoting abscission of the fruits, leaves, and flowers.
7. ‘Both growth and differentiation in higher plants are open. Comment.
The ability of higher plants to retain the capacity to have an indefinite growth through their life span is because of the presence of meristems at specific locations of their body.
The cells as a result of these meristems have the capacity to divide and perpetuate on their own. This is why the growth in higher plants is open.
Few of these cells undergo differentiation always subsequent to a few rounds of cell division. Thus, differentiation is open too.
NCERT Class 11 Biology Textbook Chapter 15 Plant Growth and Development With Answer PDF Free Download