CBSE 12TH BIOLOGY - Online Test
Q1.
Assertion: VNTR of two persons may be similar at certain sites but could be different at other sites.
Reason: A child inherits 50% of chromosomes from mother and remaining 50% from father.
Answer : Option C
Explaination / Solution:
VNTR of two persons may be similar at certain sites but could be different at other sites because a child inherits 50% of chromosomes from mother and remaining 50% from father. VNTR genes also undergoes different kinds of mutations.
Q2. Assertion: Just after implantation, embryo (inner cell mass) differentiates into ectoderm, mesoderm and endoderm.
Reason: These three layers give rise to all tissues and organs in adult human beings.
Answer : Option A
Explaination / Solution:
After implantation, embryo differentiates into outer layer called ectoderm, middle layer mesoderm and inner layer endoderm. These three layers forms the all tissues or organs of human beings.
Q3. During replication of DNA, Okazaki fragments are formed in the direction of :
Answer : Option B
Explaination / Solution:
During replication of double helix DNA, one strands having 3’ to 5’ polarity it is continuous and on other strand it is in small fraction called Okazaki fragments. The polarity of this strand is 5’ to 3’.
Q4. The process of delivery of the foetus is called
Answer : Option B
Explaination / Solution:
The process of delivery of fully developed foetus at the end of pregnancy period is called Parturition. The middle wall of uterus undergoes rigorous contraction to release baby through birth canal.
Q5. The sequence of events mentioned below is symbolized by alphabets. Choose the correct answer where the alphabets are matched with the processes.
RNA —(A)—> DNA —(B)—> DNA —(C)—> mRNA —(D)—> Polypeptide
Answer : Option C
Explaination / Solution:
The sequences of event are as follows, RNA of retrovirus change into DNA by reverse transcription. Replication of DNA produces more DNA. The DNA produce m-RNA by transcription process and m-RNA translates into specific protein.
Q6. Signal of parturition originate from
Answer : Option C
Explaination / Solution:
The signal of parturition (labour pain) originates from the placenta and movement of foetus. Some hormones like oxytocin generates ejection reflex for parturition.
Q7. During transcription, RNA polymerase holoenzyme binds to a gene promoter and assumes a saddle-like structure. What is its DNA-binding sequence?
Answer : Option D
Explaination / Solution:
Our protein-coding genes have a characteristic sequence of nucleotides, termed the TATA box, in front of the start site of transcription. The typical sequence is something like T-A-T-A-a/t-A-a/t, where a/t refers to positions that can be either A or T.
The TATA-binding protein (sometimes referred to as TBP) recognizes this TATA sequence and binds to it, creating a landmark that marks the start site of transcription
Q8. Hormone responsible for milk ejection after the birth of baby is:-
Answer : Option D
Explaination / Solution:
Lactiferous glands present inside the mammary gland start producing milk due to release of hormone oxytocin from pituitary glands.
Q9. If one strand of DNA has the nitrogenous base sequence as ATCTG, what would be the complementary RNA strand sequence?
Answer : Option A
Explaination / Solution:
If nitrogenous base sequence of DNA is as ATCTG. The complementary RNA strand should be UAGAC. Thymine of DNA is replaced by uracil (U) in RNA.
Q10. Phenomenal and rapid increase of population in a short period is called
Answer : Option C
Explaination / Solution:
Rapid increase of population in a short period of time is called population explosion. It can be checked by using contraceptive methods.
