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

In a cell, DNA transcription is halted when ______ 

Read the following and answer from given below:

The translation is the process of polymerization of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence bases in the mRNA. The amino acids are joined by a bond called a peptide bond. The ribosome is the site of protein synthesis.

Which ion is essential for the association of both units of the ribosome at the time of protein formation?

Which of the following glands is large-sized at birth but reduces in size with ageing?  

Which of the following is not a lymphoid tissue?

Where are B-cells and T-cells formed? How do they differ from each other?

What would happen to the immune system if the thymus gland is removed from the body of a person?

Lymph nodes are secondary lymphoid organs. Explain the role of lymph nodes in our immune response.

What does the term `memory' of the Immune system mean?

Epithelial lining of our intestine is considered as secondary lymphoid organ. Justify the statement.

Explain the role of Primary and Secondary Lymphoid organs with the help of suitable examples.

Name the secondary lymphoid organs.

What is a cistron?

State the difference between the structural genes in a Transcription Unit of Prokaryotes and Eukaryotes.

Give one example of point mutation.

Explain (in one or two lines) the function of the following:

tRNA

Explain (in one or two lines) the function of the following:

Exons

Answer the following question.
You are conducting artificial hybridization on papaya and potato. Which one of them would require the step of emasculation and why? However, for both, you will use the process of bagging. Justify giving one reason.

Answer the following question.
Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.

Name the ailments the two girls were suffering from?

Emasculation and bagging are the two important steps carried during artificial hybridization to obtain superior varieties of desired plants. Explain giving reasons, in which types of flowers and at what stages are the two processes carried out.

Answer the following question.
Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.

Why did the treatment provided to girl A required repeated visits?