Free Growth and Development MCQs with Answers

181. As a tree grows older, which of the following increases more rapidly in thickness?

• A. Heart wood
• B. Sap wood
• C. Phloem
• D. Cortex

Explanation: Heartwood or duramen is the dark-coloured wood near the centre of the axis formed after many years of secondary growth of the stem. A small outer region, however, remains light-coloured. It is known as sapwood or alburnum. The heartwood is formed due to changes in the elements of the secondary xylem. As secondary growth proceeds, most of the older elements of the secondary xylem lose water and become filled with organic compounds such as oils, gums, resins, tannins, and aromatic and colouring materials. The wood becomes dark-coloured due to the accumulation of these substances and is also termed duramen. The sapwood is the light-coloured region of the secondary xylem. Cells of this region are functionally active. The elements of the secondary xylem added by cambial activity are those of sapwood. But gradually most of these elements get transformed into heart wood. Thus the amount of heartwood increases as the tree grows older. The amount of sapwood, however, remains almost constant.

182. Which of the following is not true about 'sclereids'?

• A. These are groups of living cells
• B. These are found in nut shells, guava pulp, pear
• C. These are also called stone cells
• D. These are form of sclerenchyma with fibres.

Explanation: Sclereids are a type of sclerenchyma cells. They are short or irregular, their walls are very thick, and irregular and the lumen is very narrow. These are dead cells and do not perform any metabolic functions. They show different types of lignin depositions and also have pits. They are present in hard parts like the endocarp of coconut, hard seed coats fruit pulps. They are also called stone cells and are of different types as brachysclereids, osteoclereids, macrosclereids, asterosclercids, and fileform cells.

183. Which of the following meristems is responsible for extra-stelar secondary growth in the dicotyledonous stem?

• A. Interfascicular cambium
• B. Intercalary meristem
• C. Phellogen
• D. Intrafascicular cambium

Explanation: Extrastelar secondary growth means growth in the cortical region, external to stele. For extrastelar secondary growth, the cork cambium or phellogen develops in the region outside the vascular tissue. This gives rise to cork or phellem and secondary cortex or phelloderm. All three layers (i.e., cork, cork cambium, and secondary cortex) together constitute periderm. Fascicular and interfascicular cambuim occurs in the stelar regions.

184. Auxillary bud and terminal bud derived from the activity of:

• A. Lateral meristem
• B. Intercalary meristem
• C. Apical meristem
• D. Parenchyma

Explanation: Apical meristems are situated at the tips of the root and shoot. They take part in initial growth. Plants elongate and increase in height as a result of divisions in this meristem. Promeristem and primary meristem (root and shoot apices) are included in this type of meristem.

185. Chlorenchyma is known to develop in the:

• A. Cytoplasm of Chlorella
• B. Mycelium of a green mould such as Aspergillus
• C. Spore capsule of a moss
• D. Pollen tube of Pinus

Explanation: Chlorenchyma or assimilatory parenchyma are parenchymatous cells that possess abundant chloroplasts in them. They are capable of photosynthesis. A spore capsule of moss can perform photosynthesis because of the presence of chlorenchyma cells in them.

186. The apical meristem of the root is present:

• A. Only in radicals
• B. Only in tap roots
• C. Only in adventitious roots
• D. In all the roots

Explanation: Parts of typical root : root cap, meristematic growing region, zone of elongation, root hair zone, zone of meriste­matic cells. Apical meristem is terminal in position and responsible for terminal growth of the plant. Apical meristem is present at all root tips and shoot tips.

187. In a longitudinal section of a root, starting from the tip upward, the four zones occur in the following order:

• A. Root cap, cell division, cell enlargement, cell maturation
• B. Root cap, cell division,cell maturation, cell enlargement
• C. Cell division, cell enlargement, cell maturation, root cap
• D. Cell division, cell maturation, cell enlargement, root cap

Explanation: The root system of a plant develops from the hypocotyl of the embryo of a seed. The root shows the following four regions these usually merge into one another, without distinct boundaries between them. The zones, successively from the apex to the base are: (i) Root cap zone: The apex of each root is covered by a cushion of thin-walled cells known as a root cap. (ii) Region of cell division: It lies just behind the root cap. It is the main growing region of the root where active cell divisions take place. (iii) Region of elongation: The region of elongation is responsible for the growth in length of the root. (iv) Region of maturation: Epidermal cells of this region give out small, thin, cylindrical unicellular outgrowths, known as root hairs. These are the main absorbing organs of the root.

188. In a woody dicotyledonous tree, which of the following parts will mainly consist of primary tissues?

• A. All parts
• B. Stem and root
• C. Flowers, fruits and leaves
• D. Shoot tips and root tips

Explanation: The tissues which develop from apical meristem and procambium are known as primary tissues and these constitute the primary structures of the plant body. The development of the primary tissues causes the stem to grow in length and to some extent in thickness. Stem and roots in dicotyledons show secondary growth as they have the development of secondary vascular tissues (i.e., secondary xylem and secondary phloem) in them. Flowers, fruits, and leaves are primary tissues.

189. For a critical study of secondary growth in plants, Which one of the following pairs is suitable?

• A. Teak and pine
• B. Deodar and fern
• C. Wheat and maiden hair fern
• D. Sugarcane and sunflower

Explanation: Secondary growth is observed in dicots and gymnosperm. It is not observed in pteridophytes and rarely observed in monocots. Secondary growth results in increase in girth or diameter of the stem by formation of secondary tissue by the activity of lateral meristem. So for study of secondary growth, teak (angiosperm) and pine (gymnosperm) are best suited.

190. Which one of the following is not a lateral meristem?

• A. Intrafascicular cambium
• B. Interfascicular cambium
• C. Phellogen
• D. Intercalary meristem

Explanation: (d): Meristem is classified on the basis of position in plant bodies into lateral meristem, apical meristem, and intercalary meristem. Lateral meristem is present on the lateral sides, e.g., vascular cambium (fascicular and interfascicular cambium) and cork cambium (phellogen).