Chapter 13: Plant Growth and Development Short Questions | biology Class 11 CBSE

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Chapter 13: Plant Growth and Development Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Define growth as used in the context of plant biology and state why swelling of wood in water is not considered growth.

Growth is an irreversible permanent increase in size of an organ, its parts, or an individual cell.
It is accompanied by metabolic processes (anabolic and catabolic) that occur at the expense of energy.
Swelling of wood in water is a reversible physical process with no metabolic activity, so it does not qualify as growth.

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Question 2

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Why is plant growth described as indeterminate or open?

Plants retain the capacity for unlimited growth throughout their life due to the presence of meristems at specific locations in their body.
Meristematic cells have the capacity to divide and self-perpetuate, continuously adding new cells to the plant body — a pattern called open form of growth.
Unlike animals, plants do not have a fixed final size; growth can continue as long as meristematic activity persists.

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Question 3

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Distinguish between primary growth and secondary growth in plants.

Primary growth results from the activity of root apical meristem and shoot apical meristem, contributing to elongation of the plant along its axis.
Secondary growth results from the activity of lateral meristems — vascular cambium and cork-cambium — which appear later in dicotyledonous plants and gymnosperms.
While primary growth increases the length of the plant, secondary growth increases the girth (thickness) of stems and roots.

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Question 4

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List any four parameters used to measure growth in plants.

Growth can be measured as an increase in fresh weight or dry weight of the plant or organ.
Increase in length or area is used for organs such as roots (length) and leaves (surface area).
Increase in volume and cell number also serve as measurable parameters for growth.
The appropriate parameter varies: pollen tube growth is measured by length, while growth of a dorsiventral leaf is measured by increase in surface area.

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Question 5

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Describe the characteristics of cells in the meristematic phase of growth.

Cells in the meristematic phase are located at the root apex and shoot apex and are constantly dividing.
These cells are rich in protoplasm and possess large, conspicuous nuclei.
Their cell walls are primary in nature — thin, cellulosic, and with abundant plasmodesmatal connections.

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Question 6

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What changes characterise cells in the elongation phase of growth?

Cells in the elongation phase are located proximal to the meristematic zone (just behind the apex).
They show increased vacuolation and cell enlargement as their defining features.
New cell wall material is deposited during this phase to accommodate the increase in cell size.

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Question 7

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Write the mathematical expression for arithmetic growth and explain each term.

The expression for arithmetic growth is: Lt = L0 + rt
Lt is the length at time 't', L0 is the length at time 'zero', and r is the growth rate or elongation per unit time.
In this model, only one daughter cell continues to divide after mitosis while the other differentiates; plotting length against time gives a linear (straight-line) curve.

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Question 8

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Write the formula for exponential growth and identify the term that reflects the efficiency of the plant.

The formula for exponential growth is: W1 = W0 e^rt, where W1 is the final size, W0 is the initial size, r is the growth rate, t is time of growth, and e is the base of natural logarithms.
The term 'r' is the relative growth rate and is also called the efficiency index, measuring the ability of the plant to produce new plant material.
In this growth pattern, both progeny cells following mitosis retain the ability to divide, leading to exponential increase.

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Question 9

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Differentiate between absolute growth rate and relative growth rate.

Absolute growth rate is the measurement and comparison of total growth per unit time without reference to the initial size of the system.
Relative growth rate is the growth of a given system per unit time expressed on a common basis, such as per unit initial parameter.
Two leaves of different sizes showing the same absolute increase in area will have different relative growth rates — the smaller leaf has a much higher relative growth rate.

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Question 10

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What is a sigmoid growth curve? Name the phases it consists of.

A sigmoid or S-curve is a characteristic growth curve of living organisms growing in a natural environment, obtained by plotting a growth parameter against time in geometric growth.
It consists of three phases: an initial slow lag phase, a rapid exponential (log) phase where growth increases rapidly, and a final stationary phase where growth slows due to limited nutrient supply.
The sigmoid curve is typical for all cells, tissues, and organs of a plant.

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Question 11

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State the role of water and oxygen as essential conditions for plant growth.

Water is required for cell enlargement: turgidity of cells facilitates extension growth, and the water status of the plant is intimately linked to growth and development.
Water also provides the medium for enzymatic activities necessary for growth.
Oxygen helps in releasing metabolic energy that is essential for all growth activities in the plant.

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Question 12

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Define differentiation in plants. Give one example of structural changes that occur during differentiation.

Differentiation is the process by which cells derived from meristems undergo structural changes in their cell walls and protoplasm to mature and perform specific functions.
For example, to form a tracheary element, cells lose their protoplasm entirely.
These cells also develop a very strong, elastic, lignocellulosic secondary cell wall to carry water over long distances even under extreme tension.

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Question 13

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What is dedifferentiation? Give one example from plants.

Dedifferentiation is the phenomenon where living differentiated cells that had lost the capacity to divide regain the capacity of division under certain conditions.
An example is the formation of interfascicular cambium and cork cambium from fully differentiated parenchyma cells.
Dedifferentiation restores meristematic activity in cells that had previously completed their differentiation.

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Chapter 13: Plant Growth and Development | Short Questions

Define growth as used in the context of plant biology and state why swelling of wood in water is not considered growth.

Why is plant growth described as indeterminate or open?

Distinguish between primary growth and secondary growth in plants.

List any four parameters used to measure growth in plants.

Describe the characteristics of cells in the meristematic phase of growth.

What changes characterise cells in the elongation phase of growth?

Write the mathematical expression for arithmetic growth and explain each term.

Write the formula for exponential growth and identify the term that reflects the efficiency of the plant.

Differentiate between absolute growth rate and relative growth rate.

What is a sigmoid growth curve? Name the phases it consists of.

State the role of water and oxygen as essential conditions for plant growth.

Define differentiation in plants. Give one example of structural changes that occur during differentiation.

What is dedifferentiation? Give one example from plants.

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