Growth is an important factor in every living entity. It is an irreversible and ever-increasing process which can be expressed in any these parameters – area, length, size, volume, cell number, etc and requires the involvement of increased protoplasmic material. Meristems are the site of growth in plants. In higher plants, however, growth is indeterminate. There are three principle stages of growth – the log, the lag, and the senescent stage. Cells reach the stage of differentiation when they lose their capacity to divide. Learn in detail about the growth and hence developmental stages of a plant.
Very Short Answer Type Questions
Q.1. Fill up:
a) A stage of growth that is the rapid and maximum is _________
b) ________ present in the apical bud in more numbers causes apical dominance as displayed in dicotyledonous plants.
c) Sites of photoperiodic perception in vegetative plants are _______
A.1. a) Log phase of an S-curve/Exponential b) IAA/Auxin c) Leaves.
Q.2. List the PGS (Plant growth substances) that needs to be used to have practical applications in the following:
a) Improve yield of sugarcane
b) Increase lateral shoot growth
c) The basis for the sprouting of potato tuber
d) Hinder seed germinationA.2. a) Gibberellin/Gibberellic acid b) Cytokinin c) Ethylene d) Abscisic acid
Q.3. List three physiological processes in plants that are affected by light.
A.3. Photosynthesis, phototropism, and photoperiodism.
Q.4. a) Write two functions of the phytohormone – Gibberellins
b) The seedling disease in rice caused by Gibberellin is due to which feature of it?
A.4. a) It is utilized to accelerate the malting phenomena in brewing industries. They facilitate bolting in cabbages, beetroot and several plants with rosette habitat. b) Internode elongation.
Q.5. Name the plant growth regulator that needs to be applied to improve the number of female flowers in a cucumber plant field.
Q.6. Where in plants are the below hormones manufactured?
A.6. a) Apical buds and shoot tips b) Young leaves and root tips c) Root tips (meristematic zones).
Short Answer Type Questions
Q.1. Write the structural features of
a) Meristematic cells near the root tip
b) The cells in the elongation zone of the root
A.1. a) They are characterized by the following:
- Big conspicuous nucleus
- Rich protoplasm
- The cell wall is cellulosic and thin – basic in nature
- Less number of vacuoles
- Large numbers of mitochondria
- Plentiful plasmodesmata
b) Cells in the elongation zone are defined by:
- Extended dimension
- Increased vacuolation
- New cellulosic cell walls are collected
Q.2. Is there a difference in the growth pattern of plants and animals? Do all parts of the plant grow endlessly? List the regions of the plant that can grow endlessly, if no.A.2. Yes, they differ. Plant growth is different as plants have the potential to grow indefinitely during their lifetime. They exhibit this property because of the presence of meristems at certain parts of the plant body. These cells of the meristems have the ability of division and grow constantly. The plant body is made up by the cells which lose the capacity to divide. The growth form, where cells are constantly added to the body of the plant through the action of meristems is referred to as the open form of growth.
Q.3. Explain the following with examples from various plant tissues
a) Differentiation – It is permanent in structure, size, function, and composition of cells, tissues or organs. For instance, meristematic tissues give rise to new cells that mature and get differentiated into special tissue or plant organ. For example – formation of treachery element results in the loss of cell protoplasm. To carry water at a stretch under extreme tension, they develop an elastic, strong, lignocellulosic secondary cell wall.
b) De-differentiation – Under certain conditions, the cells that have dropped the capability to divide can regain the capacity, this process is referred to as de-differentiation. For example – the development of meristems – the cork cambium from completely transformed parenchyma cells.
c) Re-differentiation – During de-differentiation, before-mentioned tissues/meristems after division generate cells that lose the ability to divide once more but mature to take up certain functions. They get re-differentiated. Example – secondary cortex.
Q.4. Why is it difficult to designate any effect to a single hormone during experimentation?
A.4. Several hormones have an antagonistic and synergistic impact with each other. Hence it becomes difficult.
Q.5. Where are plant hormones formed? How are the hormones passed to the specific site of activity?
A.5. The plant hormones are produced by several tissues like the root tips, shoot tips, leaves, meristematic tissues, and apical buds, etc. The presence of vascular tissues like phloem and xylem help in the translocation of hormones to sites of activity.
Q.6. What are Plant growth regulators?
A.6. Plant growth regulators also referred to as phytohormones or plant hormones. They are a group of organic compounds, which functions by controlling and modifying the physiological processes like the growth, development, and movement of plants.
Q.7. Which plant hormone is used to manipulate and stimulate the maturation of sugarcane crop?
A.7.Ethylene, the ripening hormone in plants helps in maturation of sugarcane crops by increasing the storage of sucrose in plants.
Q.7. What are the functions of Auxins in plant growth?
A.7. Auxins are one of the most important plant hormones. These plant hormones are generally produced at the tips of stems and roots. In all vascular plants, auxins play a vital role in:
- Cell division.
- Plant propagation.
- Promoting flowering in plants.
- Initiation of roots and stem cuttings.
- Prevent premature dropping of fruits and leaves.
Long Answer Type Questions
Q.1. Winter varieties, when planted in spring, do not produce flowers or mature grains within the span of a flowering season. Explain.
A.1. In some plants, flowering is either qualitatively or quantitatively reliant on subjection to lower temperatures, the process is referred to as vernalization. This limits advanced reproductive development rate in maturing season thereby allowing them to have enough time to gain maturity. Vernalisation promotes flowering by a span of low temperatures. Some plants like wheat, barley have two types of varieties – spring and winter varieties. The spring variety is planted in the spring and flowers, producing grains towards the termination of the growing season. While the winter varieties, when planted in spring fail to flower or generate mature grains within the flowering season, this is why they are planted in autumn. Over winter, they germinate and turn out as small seedlings, restarting development in the spring and are gathered in mid-summer.
Q.2. Several variations of wheat are cultivated in autumn and harvested in the next midsummer.
a) Give reason
b) What is the flowering in lower temperatures referred to as?
c) Name the plant hormone that can substitute for the cold treatment.
a) If planted in spring, winter varieties do not flower or generate mature grains in a span of the flowering season, hence they are cultivated in autumn. Over winter, they sprout and come out as tiny seedlings, resuming growth in the spring and are collected in mid-summer.
Q.3. List a hormone that:
a) Is in nature, gaseous.
b) Is in charge of phototropism.
c) Influences femaleness in cucumber flowers.
d) Is utilized to kill weeds(dicots).
e) In long-day plants, induces flowering.
A.3. a) Ethylene(C2H4)
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