RBSE Class 12 Biology Chapter 33-Embryonic Development in Humans. In this chapter, students can learn in detail about cleavage and morulation, blastulation, germinal layers and embryonic stages in the female reproductive system. It also deals with blastulation, grulation, formation of blastocyst in humans, implantation, parturition and different phases or stages of fetal development – first week, second week, third to sixth week, sixth to eight week, ninth to twelve week, third to fourth month, fourth to sixth month and sixth month till birth.
These important questions help students to perform exceptionally well in their exams. By practising these important questions, students can analyze their preparation, get a thorough knowledge about all the important terminologies and perform their best in the examinations.
RBSE Solutions for Class 12 are the best study material for both class assignments and other board examinations. By practising these important questions, students can gain deep knowledge about the topics explained in this chapter and also help them to be well prepared for their upcoming examinations.
RBSE Class 12 Biology Chapter 33 Important Questions
RBSE Biology Chapter 33: MCQ Type Questions
Q.1. In how many days, does the development of the heart complete in humans during the embryonic development?
(a) First week
(b) Second week
(c) Third to sixth weeks
(d) Seventh to eight weeks
Sol: (d) Seventh to eight weeks.
Q.2. Which of the following activities does not occur in humans during the first week of the embryonic stage?
(a) Implantation process
(b) Formation of blastocoel
(c) Formation of morula
(d) Formation of the primitive streak
Sol: (d) Formation of the primitive streak.
Q.3. Which germinal layer is responsible for the formation of the kidney?
(a) Ectoderm
(b) Mesoderm
(c) Endoderm
(d) None of the above
Sol: (b) Mesoderm.
Q.4. Which cavity is formed during blastulation?
(a) Active pole
(b) Inactive pole
(c) Blastocoel
(d) Amniotic cavity
Sol: (c) Blastocoel.
Q.5. How many numbers of cells are present in the morula stage?
(a) Four
(b) Eight
(c) Sixteen
(d) Thirty-two
Sol: (c) Sixteen
Q.6.Which germinal layer is responsible for the development of major parts of the eye?
(a) Ectoderm
(b) Mesoderm
(c) Endoderm
(d) None of the above
Sol: (a) Ectoderm.
Q.7. In which stage does the development of taste buds complete in humans during the embryonic development?
(a) Sixth to the eighth week
(b) Third and fourth month
(c) Fourth to the sixth month
(d) Sixth month to the eighth month
Sol: (b) Third and fourth month.
Q.8. When the number of cells becomes sixteen, then the solid phase is called _________.
(a) Morula
(b) Trophoblast
(c) Blastocoel
(d) None of the above
Sol: (a) Morula.
Q.9. In which stage does the straightening of the trunks and the development of the upper limb happen?
(a) Sixth to the eighth week
(b) Third and fourth month
(c) Fourth to the sixth month
(d) Sixth month to the eighth month
Sol: (a) Sixth to the eighth week
Q.10. What is the duration of the blastocyst stage?
(a) 2 to 3 days
(b) 4 to 5 days
(c) 5 to 6 days
(d) one to two weeks
Sol: (c) 5 to 6 days.
RBSE Biology Chapter 33: Short and Long Answer Type Questions.
Q.1.What is embryogenesis?
Sol: The development of the embryo from cell division and cell differentiation in the single-celled zygote is called embryogenesis
Q.2.Which type of cell division takes place during the cleavage?
Sol: Mitosis is the type of cell division that takes place during the cleavage, which is without the growth phase.
Q.3. What are blastomeres?
Sol: Blastomeres is a group of cells produced as a result of cleavage (cell division) of the zygote after fertilization. It is an essential part of blastula formation.
Q.4. How many blastomeres are found in the human morula?
Sol: There are around 15 to 16 blastomeres found in the human morula
Q.5. What is formed from the blastopore in humans?
Sol: Anus, the opening at the end of the alimentary canal is formed from the blastopore in humans.
Q.6.What is the difference between blastulation and gastrulation?
Sol: The difference between blastulation and gastrulation are:
| Blastulation | Gastrulation |
| Fast mitotic division of the zygote. | Slow mitotic division. |
| Cells do not show any movement. | Cell masses move from the surface of the blastula |
| A single-layered hollow blastula is formed. | Three-layered gastrula is formed. |
| Formation of blastula is called blastulation | Formation of gastrula is called gastrulation. |
Q.7. What is gastrulation?
Sol: The process of the formation of the three germinal layers from blastocyst is called gastrulation. Out of these three germinal layers, each layer forms a definite tissue, organs and the organ system.
Q.8. When and how does the blastocyst form in humans?
Sol: Blastulation:
It is the formation of blastula or blastocyst from morula- an early-stage of an embryo is known as blastulation.
In the human morula, the outer cuboidal cells become flattened when it reaches into the uterus.
These flattened cells are called Trophoblast, by which they adhere with the uterine epithelium.
Cleavage continues and clusters of cells differentiate into two distinct groups, the epithelial-like trophoblast or nutritive cells surrounding the expanding cavity and inner cell mass of formative cells of the embryo.
The cavity is called blastocoel and the embryo is known as blastocyst in humans.
Q.9. Describe gastrulation in humans.
Sol:
Gastrulation:
The process of the formation of the three germinal layers from blastocyst is called gastrulation.
During the implantation, zona pellucida disappears and the trophoblast cells become giant-sized and aggressively invade the uterine tissues and make contact informing the placenta.
The inner cell mass at this time undergoes differentiation and a layer of very flat cells appear on the interior surface of the inner cell mass that forms future endoderm. The dorsal inner cell mass is called epiblast, which is presumptive material for ectoderm and mesoderm.
The formation of the three germinal layers form a single-layered blastocyst. The blastocoel gets indistinct and a new cavity called gastric or archenteron is formed. It is called a gastrula. The method by which blastula becomes or converts into gastrula is called Gastrulation.
The mesodermal cell involutes through the primitive streak and diverges laterally and anteriorly, by occupying a position between the endoderm and ectoderm.
The epiblast also contributes some of the cells to endoderm. The cells migrate to their future places by amoeboid movements.
Q.10. How does a child born in the seventh month survive?
Sol: By the seventh month of the embryonic development, most of the vital body organs of a foetus are formed and developed. In the seventh month, the lacrimal glands are developed. This is the main reason that an embryo can survive.
Q.11.What are blastulation and implantation?
Sol: The process of the formation of the blastocyst from a morula is called blastulation. Implantation is the process of the attachment of blastocyst with the uterus wall.
Q.12.What is the gestation period?
Sol: The period from the fertilization to the parturition is called gestation period. The gestation period is about 266 days in humans.
Q.13. What is a blastocyst?
Sol: The hollow cellular mass formed during the early development, which consists of cells forming the inner cell mass, trophectoderm, and the fluid-filled cavity or the blastocoel is known as the blastocyst. The blastocyst is only found in mammals. It is formed in a process called blastulation between five to fourteen days after fertilization.
Q.14.What is parturition?
Sol: Parturition is the process of the contraction of the uterus at regular intervals that helps in the delivery of the baby at the end of pregnancy.
Q.15.What is embryology?
Sol: The branch of biology, which is involved with the study of embryos, their principles from the stage of ovum fertilization till their development is called embryology. This includes the developmental process of a single cell, embryo to a baby within an average of 266 days or 9 months. However, the term Embryology usually refers to the parental development of embryos and fetuses.
Q.16. What is the difference between Blastocyst and Embryo?
Sol: The differences between blastocyst and embryo are:
| Blastocyst | Embryo |
| It is a hollow, thin-walled structure formed during the early development of an embryo. | It is a rudimentary stage of a living being with a potential for development. |
| The process of formation of the blastocyst is called blastulation. | The processes of formation of an embryo are called gastrulation, neurulation, and organogenesis. |
| Formed by the cleavage of zygote. | Formed from the inner cell mass of the blastocyst. |
| Formed after 5-14 days after fertilization. | Formed after 2-11 weeks after fertilization. |
| Found only in mammals. | Found in both plants and animals. |
| In in-vitro fertilization, transfer of blastocyst shows a high pregnancy rate. | In in-vitro fertilization, transfer of embryos shows a low pregnancy rate. |
Q.17. What is fetal ejection reflex?
Sol: The fetal ejection reflex is also called Ferguson reflex. It occurs in the uterus of a birthing mother in which the uterus passes the signals that the fully developed fetus sends through the placenta for ejection. These signals induce muscular contractions.
Q.18. What are blastula and gastrula?
Sol: Blastula and gastrula are two multicellular embryonic stages of mammals.
The blastula is a hollow and a ball of cells formed in the early stages of development in an embryo. The blastula in mammals develops into the blastocyst and this blastocyst contains an inner cell mass, which is distinct from the blastula.
The gastrula is a stage of early embryo with three germ layers from which several organs are produced. Gastrula develops from the blastula in a process called gastrulation.
Q.19. Draw a neat labelled diagram of the embryonic stages in humans.
Sol: The embryonic stages in humans:
Q.20. What are the similarities between Blastocyst and Embryo?
Sol: The similarities between blastocyst and embryo are:
- Embryo and blastocyst are diploid structures.
- Embryo and blastocyst are formed inside the mother.
- Both are formed after the fertilization of gametes in animals.
- Both the structures possess potent cells and hence, can be used in diagnostics.
Q.21. What is the fate of the germinal layer?
Sol: Out of the three germinal layers, each layer forms definite tissues, organs and systems of the human body. The fate of these layers in embryo and adult is described in the below tabular column.
| Ectoderm | Mesoderm | Endoderm |
| Epidermis and skin derivatives | Dermis | Gastric and intestinal glands |
| Cutaneous glands | Muscular tissue | Tongue |
| The nervous system (brain and the spinal cord) | Connective tissue | Lungs, Trachea and Bronchi |
| Motor and optic nerves | Endoskeleton | Urinary bladder |
| Eye (Retina, lens and cornea) | Vascular system (Heart and blood vessels) | Primordial cells |
| Connective, Ciliary and Iris muscles | Kidney | Gills |
| Olfactory epithelium | Reproductive system (gonads) | Liver |
| Internal ear (Membranous labyrinth) | Urinary and reproductive ducts | Pancreas |
| Stomodaeum | Coelom and coelomic epithelium | Thyroid gland |
| Salivary glands | Sclerotic and choroid covering of the eye | Parathyroid gland |
| Enamel of teeth | Adrenal cortex | Thymus |
| Proctodeum | Spleen | Middle ear |
| Pituitary body | Notochord | Eustachian tube |
| Pineal gland | Parietal and visceral peritoneum | Jejunum |
| Adrenal medulla | Dentine of teeth | The lining of the vagina and urethra |
| Hypothalamus | – | Prostate gland |
Q.22. Brief out the different phases or stages of fetal development?
Sol: The stages of fetal development are as follows:
Stage -1
1st month- The heart is formed.
Stage -2
2nd month- Limbs and digits are formed.
Stage -3
3rd month (first trimester)- all the major organs are developed and the foetus is recognizable as a human being. External genitalia starts differentiating and the sex of the foetus can be determined.
Stage -4
5th month- foetus starts moving and hair on the head appears.
Stage -5
Second trimester- eyelashes and eyelids develop, the body gets covered with fine hair.
Stage -6
The third trimester- by the end of the third trimester, the child is fully developed and the body prepares for the delivery (parturition) of the infant.
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