Girth of stem of a plant increases due to division of cells in
- A.apical meristem only.
- B.lateral meristem only.
- C.apical and intercalary meristem.
- D.both apical and lateral meristem.
Correct answer
Explanation
The correct answer is B, lateral meristem only. The girth, or thickness, of a stem increases only through the lateral meristems, the vascular cambium and the cork cambium.
Growth in plants happens at meristems, regions of actively dividing cells. Increase in length is primary growth; increase in thickness is secondary growth. The vascular cambium runs as a ring in the stem and adds new layers of xylem inside and phloem outside, while the cork cambium forms the protective bark. This is why old trees have thick trunks with annual rings, while most monocots, such as grasses, lack a cambium and stay thin.
A is wrong because the apical meristem at the tips of stems and roots increases only their length. C is wrong because both apical and intercalary meristems add to length, not girth. D is wrong because the apical meristem plays no part in thickening; only the lateral meristem does.
Exam tip: apical and intercalary meristems add length; lateral meristem (cambium) adds girth.
Practice Questions
View allWhich one of the following features is an indication for modification of stem of a plant?
- A.Presence of 'eye' on potato
- B.'Scale' found in onion
- C.'Tendril' found in pea
- D.'Hair' present in carrot
Show answer
The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.
Read the full explanation →Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?
- A.Tungsten
- B.Copper
- C.Rubidium
- D.Aluminium
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Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.
Read the full explanation →Tooth enamel is made up of which one of the following calcium compounds ?
- A.Calcium carbonate
- B.Calcium sulphate
- C.Calcium hydroxide
- D.Calcium phosphate
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Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.
Read the full explanation →Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?
- A.Adenovirus
- B.Variola virus
- C.Aichi virus
- D.Coxsackie virus
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Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.
Read the full explanation →After fertilization, the fruit and the seed are produced by
- A.ovule and ovary, respectively
- B.ovary and ovule, respectively
- C.ovary, no ovule required
- D.ovule, no ovary required
Show answer
After fertilisation the ovary of the flower grows into the fruit, and each ovule inside it develops into a seed.
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