Solved Exercise, Bio-12, Ch-19


(i) The influence of notochordal cells on the ectodermal cells to become nervous system was called _______. (embryonic induction)

(ii) _______ is a condition in which individuals have small skull. (microcephaly)

(iii) Growth is accompanied by two factors:

(a) increase in _______ (b) increase in _______. (length, thickness)

(iv) _______ are the regions where growth is initiated by the proliferation of cells. (Meristems)


Q.02: Indicate True or False:

(i) Primary growth leads to increase in length, while secondary growth leads to increase in width. (TRUE)

(ii) The plants in which flowering is not at all effected by the day length are called day neutral plants. (TRUE)

(iii) The somatic mesoderm soon splits in the middle to form two layers: (a) Outer parietal layer (b) Inner visceral layer. (FALSE)

CORRECT: The lateral plate mesoderm splits in to two sheet like layers: (a) somatic mesoderm (b) splanchnic mesoderm

(iv) In the clear cytoplasmic area, cytoplasm contains information essential for development. (FALSE)

CORRECT: In the gray crescent area, cytoplasm contains information essential for development.

(v) The phase of cell movement and rearrangement is called cleavage. (FALSE)

CORRECT: The phase of cell movement and rearrangement is called gastrulation.


(i) Growth rate is influenced by.

(a)  Hormones

(b)  Water

(c)  Vitamins

(d) All a, b, c

EXPLANATION: Growth rate is influenced by both external and internal factors including hormones, water & vitamins etc.

(ii) Neurula is the stage in which embryo has:

(a)  Blastocoele

(b)  Neural tube

(c)  The germ layers

(d) Archenterons

EXPLANATION: The neurula stage is characterized by the formation of the neural tube in the developing embryo. The neural tube is a precursor to the central nervous system, including the brain and spinal cord.

(iii) The mesodermal cells do not invaginate but migrate medially and caudally from both sides and midline thickening called:

(a)  Henson’s node

(b)  Primitive streak

(c)  Epiblast

(d) Hypoblast

EXPLANATION: During gastrulation, mesodermal cells migrate medially and caudally from both sides to form a midline thickening called the primitive streak. This process contributes to the formation of the three germ layers in embryonic development.

(iv) The negative physiological changes in our body are called:

(a)  Degeneration

(b)  Abnormalities

(c)  Aging

(d) Regeneration

EXPLANATION: Aging refers to the negative physiological changes that occur in our bodies over time, leading to a decline in biological functions and an increased vulnerability to diseases and death.


Organizer and Inducer Substance:

Hans Spemann and Hilde Mangold’s experiments on embryonic induction in 1924 clearly showed that only the cells from the dorsal lip of blastopore were capable of inducing a complete embryo. This area corresponds to the presumptive area of notochord, somites and prechordal plate. Spemann designated the dorsal lip area the ‘primary organizer’ because it was the only tissue capable of inducing development of secondary embryo in the host.


A fertilized egg contains cytoplasmic components that are unequally distributed within the egg. “These different cytoplasmic components are believed to have morphogenetic determinants that control the functioning of a specific cell type. This is now called differentiation.”

Embryonic Induction:

“The capacity of some cells to evoke a specific development response in other is widespread phenomenon in development, called embryonic induction.”


“Growth is the permanent and irreversible increase in size that occurs as an organism mature.”


“The progressive changes which are undergone before an organism acquires its adult form constitute embryonic development.”


“Meristems are young tissues or group of cells that retain the potential to divide.”

In higher plants, the entire plant body is not capable of growing but growth is limited to certain regions known as growing points.

“These growing points consist of groups of cells which are capable of division, these growing points are called meristems.”

These meristematic cells are located at the stem and root.


Consult textbook at page 117.

Consult textbook at page 117 — 118.

Consult textbook at page 110 — 113.

Consult textbook at page 106 — 107.

Consult textbook at page 113 — 116.

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