15

Q1. Give one example of cells of plants which have undergone

Dedifferentiation

Redifferentiation

Solution

Dedifferentiation - Cells forming cork cambium and interfascicular cambium

Redifferentiation - Secondary cortex cells and phellem cells

Q2. Describe arithmetic growth.  

Solution

In arithmetic growth following mitotic cell division, only one daughter cell continues to divide while the other daughter cell differentiates and matures.     When arithmetic growth is plotted against time, it gives a linear growth curve.           The mathematical expression of arithmetic growth is     L_t = L₀ + rt,      where L_t = length at time ‘t’      L₀ = length at time zero      r = growth rate  

Q3. What is dedifferentiation? State one example.

Solution

As the cells grow and mature, they lose their capacity to differentiate. However, under certain conditions, such cells regain the capacity of division which is called dedifferentiation. Differentiated parenchymatous cells dedifferentiate to form interfascicular cambium and cork cambium.

Q4. Name the compound which is used in agriculture as a source of ethylene.

Solution

Ethephon 

Q5. Draw a well-labelled diagram indicating the germination and development of a seed.  

Solution

Germination and Development of Seed:        

Q6. State the term used for the phenomenon in which the shape of leaves of the same plant changes during its development.  

Solution

Heterophylly  

Q7. Name any two parts of the plant which synthesise natural cytokinins.

Solution

Young fruits, root apices

Q8. Name the plant growth regulator used in the brewing industry for the malting process.

Solution

Gibberellic acid

Q9. Name the phenomenon in which a growing apical bud inhibits the growth of the lateral bud.

Solution

Apical dominance

Q10. State the name of the plant growth regulator which you will use in the following cases:

To promote flowering in pineapples

To stimulate early seed production in conifers

To sprout potato tubers

To prevent leaf drop at an early age

To prepare weed-free lawns

To delay leaf senescence

Solution

To promote flowering in pineapples - Auxins

To stimulate early seed production in conifers - Gibberellins

To sprout potato tubers - Ethylene

To prevent leaf drop at an early age - Auxins

To prepare weed-free lawns - Auxins

To delay leaf senescence - Cytokinins

Q11. Abscisic acid is also known as stress hormone.

Solution

Abscisic acid inhibits seed germination. It also stimulates the closure of stomata and increases the tolerance level in plants against various stresses. Hence, abscisic acid is also known as a stress hormone.

Q12. State one example of arithmetic growth.

Solution

Elongation of the root at a constant rate is an example of arithmetic growth.

Q13. State the parameters which are considered while measuring the growth of plants.

Solution

Parameters which are considered while measuring the growth of plants are as follows:

Increase in fresh weight

Increase in dry weight

Increase in length of plants

Increase in area and volume of plants

Increase in cell number

Q14. Name the plant and its part from which auxin was isolated by F. W. Went.

Solution

Tips of coleoptiles of oat seedlings.

Q15. State the term which explains the ability of plants to respond to the environment or phases of life by following different pathways.  

Solution

Plasticity  

Q16. Differentiate between arithmetic and exponential growth.

Solution

Arithmetic Growth Geometric Growth After mitotic division, only one daughter cell divides and the other daughter cell differentiates and matures. All the daughter cells continue to divide. On plotting the growth against time, a linear curve is obtained. On plotting the growth against time, a sigmoid curve is obtained.  

Q17. How is the quantitative comparison between the growth of living beings done?  

Solution

The quantitative comparison between the growth of living beings can be done in two ways:    

Absolute growth rate: Measurement and comparison of the total growth per unit time.  

Relative growth rate: Growth of the given system per unit time expressed on a common basis.  

Q18. Name the PGR which hastens the ripening of oranges.

Solution

Ethylene

Q19. Name the PGR which is a modified form of adenine.  

Solution

Kinetin  

Q20. How does ethylene help plants to absorb more water and minerals?  

Solution

Ethylene promotes root growth and root hair formation, thus increasing the surface area of absorption which helps plants to absorb more water and minerals.  

Q21. State the functions of cytokinins.

Solution

Functions of cytokinins:

They help to overcome apical dominance.

They also promote nutrient mobilisation which results in the delay of leaf senescence.

Q22. From where was auxin isolated first? Name one natural auxin and one synthetic auxin.  

Solution

Auxin was first isolated from human urine.     Natural auxin - Indole butyric acid     Synthetic auxin - Naphthalene acetic acid  

Q23. Give three examples of dedifferentiation in plants.

Solution

1. Formation of interfacscicular cambium 2. Formation of cork cambium from fully differentiated parenchymatous cells. 3. Formation of callus by culturing the cells of pith during plant tissue culture

Q24. What type of tissues synthesise ethylene? State any two functions of ethylene.

Solution

Ethylene is synthesised in tissues which undergo senescence and in ripening fruits. It accelerates abscission in flowers and fruits. It breaks seed and bud dormancy.

Q25. Name the fungus which causes the bakanae disease in rice seedlings.

Solution

Gibberella fujikuroi

Q26. State the characteristics of cells in the elongation phase of the growth of a plant.  

Solution

Cells in the elongation phase of the growth of a plant show the following characteristics:    

They show increased vacuolation, i.e. more number of vacuoles.  

Cells are enlarged.  

There is new cell wall deposition.  

Q27. What is open form growth?

Solution

Open form growth is the growth in which new cells are always added to the plant body by the activity of meristems.

Q28. Name the phenomenon which explains the importance of low temperature and flowering in plants.

Solution

Vernalisation 

Q29. Define growth rate.

Solution

The growth rate is the increased growth per unit time.

Q30. Define development.

Solution

Development can be defined as all the changes which an organism goes through during its life cycle.

Q31. Write the mathematical expression for exponential growth.

Solution

W₁ = W₀e^rt

Q32. Define plasticity and give one example. Or How can heterophylly be an example of plasticity?

Solution

Plasticity is the ability of plants to respond to the environment or phases of life or to form different structures by following different pathways. Terrestrial plants have different shapes of leaves, and the leaves of aquatic plants also show different shapes in their life cycle.   A coriander leaf in the juvenile stage looks different from the mature leaf.

Q33. Name the three substances which were discovered and later collectively named abscisic acid (ABA).

Solution

Inhibitor B, abscission II and dormin.

Q34. Define growth. Give an example of growth in plants.

Solution

Growth is an irreversible permanent increase in the size of an organ or part or the individual cell. Expansion of leaves is an example of growth in plants.

Q35. State the chemical nature of gibberellins.

Solution

Acidic

Q36. State the three phases of the period of growth in plants, and describe the characteristic features of the cells of each phase.

Solution

The period of growth in plants has the following three phases:

Meristematic phase:

This phase is represented by the root and shoot apices. The cells of the meristematic region are rich in protoplasm and possess large conspicuous nuclei. The cell walls are thin, cellulosic, primary and show more plasmodesmata connections.

Elongation phase:

The zone of elongation is proximal to the meristematic zone. The cells show more number of vacuoles. Enlargement of cells and new cell wall deposition occur during this phase.

Maturation:

It lies proximal to the zone of elongation. The cells of this phase show more protoplasmic modifications and thickened cell walls.

Q37. Name the two processes which add to development.

Solution

The two processes which add to development are growth and differentiation.

Q38. How do gibberellins help in increasing the sugar yield?  

Solution

Gibberellins help in stem elongation in plants. In sugarcane, sugar is stored in stems. Use of gibberellin ensures an increase in the stem length of sugarcane; hence, the yield increases.  

Q39. Which PGR acts as an antagonist to gibberellins?

Solution

Abscisic acid

Q40. Describe relative growth. Also, plot a graph indicating relative growth.

Solution

In geometric growth, the progeny cells continue to divide mitotically. The initial phase, i.e. the lag phase, is very slow. After the lag phase, the growth takes place very rapidly at an exponential rate, which is called the log phase. Due to limited nutrient supply, the growth slows down leading to the stationary phase. When a graph is plotted of the growth rate against time, we get a sigmoid or S curve.   The geometric growth rate is expressed as W₁ = W₀e^rt,  where W₁ = final size (weight, height, number etc.)  W₀ = initial size at the beginning of the period  r = growth rate   t = time of growth  e = base of natural logarithm