Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions for Biology

Relaxin is the hormone secreted by the placenta.

Mark the odd one.

Which of the following statements are correct with respect to hormones secreted by the placenta?

1. The placenta secretes relaxin during the later stage of pregnancy.
2. The placenta secretes a high amount of FSH during pregnancy.
3. The placenta secretes relaxin during the initial stage of pregnancy.
4. The placenta secretes hCG and hPL during pregnancy.

The concentration of which of the following substances will decrease in the maternal blood as it flows from embryo to placenta through the umbilical cord?

The human foetus within the uterus

1. Oxygen
2. Amino Acids
3. Carbon dioxide
4. Urea

To answer the question, study the graphs below for Subjects 1 and 2 showing different levels of certain hormones.

Subject 2 has a higher level of hormone B, which is ______

Which of the following is not a function of the placenta?

Read the following and answer from given below:

Cleavage is the series of rapid mitotic divisions in the zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. An embryo with 64 blastomeres is known as a blastocyst and has a blastocoel cavity. Blastocyst gets implanted in the uterine wall and leads to preganancy.

The solid mass of cells with 16 blastomeres is called ______

Read the following and answer from given below:

Cleavage is the series of rapid mitotic divisions in the zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. An embryo with 64 blastomeres is known as a blastocyst and has a blastocoel cavity. Blastocyst gets implanted in the uterine wall and leads to pregnancy.

At which stage of embryonic development does trophectoderm develop?

Read the following and answer from given below:

Cleavage is the series of rapid mitotic divisions in the zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. An embryo with 64 blastomeres is known as a blastocyst and has a blastocoel cavity. Blastocyst gets implanted in the uterine wall and leads to pregnancy.

The correct sequence of various structures formed during embryonic development is ______

Except endocrine function, what are the other functions of placenta.

Discuss why Drosophila has been used extensively for genetical studies.

What is recombination? Discuss the applications of recombination from the point of view of genetic engineering.

Assertion: When white eyed, yellow bodied Drosophila females were hybridized with red eyed, brown-bodied males; and F₁ progeny was intercrossed, F₂ ratio deviated from 9 : 3 : 3 : 1.

Reason: When two genes in a dihybrid are on the same chromosome, the proportion of parental gene combinations is much higher than the non-parental type.

Assertion: Functional ADA cDNA genes must be inserted in the lymphocytes at the early embryonic stage.

Reason: Cells in the embryonic stage are mortal, differentiated and easy to manipulate.

Explain the formation of placenta after the implantation in a human female.

Draw a diagram showing human foetus within the uterus and label any four, parts in it.

Explain the phases in embryonic development from the morula stage till the establishment of pregnancy in a human female.

What is the basic principle of vaccination? How do vaccines prevent microbial infections? Name the organism from which hepatitis B vaccine is produced.

What are recombinant DNA vaccines? Give two examples of such vaccines. Discuss their advantages.

In the metropolitan cities of India, many children are suffering from allergy/asthma. What are the main causes of this problem. Give some symptoms of allergic reactions.