CBSE 12TH BIOLOGY - Online Test
Q1. Cancer cells can be easily be destroyed by radiations due to
Answer : Option A
Explaination / Solution:
Radiation therapy targets the DNA inside the cell by making them unable to divide and reproduce. Cancer cells perform unlimited cell division. Now, when their dividing ability is targeted, naturally they respond more. Newly formed cells can be easily destroyed by radiation of high frequency. They stop dividing. Thus, the tumour shrinks.
However, the adjoining normal cells also get affected by radiation but they can repair themselves more effectively.
Q2. Which one of the following is not a part of a transcription unit in DNA?
Answer : Option A
Explaination / Solution:
Transcription is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA).
Transcription of DNA requires a promoter, the structural gene to be transcripted and a terminator. The inducer is not required during transcription of DNA.
Q3. Tissue culture technique was first performed successfully by
Answer : Option B
Explaination / Solution:
plant tissue culture is the technique of in vitro maintaining and growing cells, tissue or organs in nutrient medium. Tissue culture technique was first performed successfully by White in 1932.
Q4. How many species in the world are facing threat of extinction?
Answer : Option B
Explaination / Solution:
Nearly 700 species have become extinctin recent times and more than 15,500 species (of which > 650 are from India) which includes amphibians, gymnosperms, reptiles, birds and mammals etc. currently face the threat of extinction.
The causes of high extinction rates at present include habitat (particularly forests) lossand fragmentation, over-exploitation, biological invasions andco-extinctions.
Q5. Wall of uterus has ------- layers of tissues.
Answer : Option C
Explaination / Solution:
The wall of uterus has three layers of tissues. The outer most layer is called perimetrium followed by myometrium and innermost glandular tissue is endometrium.
Q6. A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc × AaBbCc, the phenotypic ratio of the offspring was observed as 1 : 6 : x : 20 : x : 6 : 1. What is the possible value of x?
Answer : Option B
Explaination / Solution:
Polygenic trait controlled by three genes will form 8 types of gametes. Combination of 8 types of gametes of male and female each result into 64 types of zygote in different ratio. So, possible value of x is 15 (1:6:15:20:15:6:1).
Q7. A nitrogen fixing microbe associated with Azolla in rice fields is
Answer : Option A
Explaination / Solution:
A number of microbes are present in rice field, Azolla and Anabaena are two common bacteria found in rice field that fix the atmospheric nitrogen.
Q8. DDT is a
Answer : Option C
Explaination / Solution:
DDT is a non-biodegradable pollutant used as pesticides in agricultural field. It pollutes the air, water and soil if used in form of spray.
Q9. Thermostable DNA polymerase is isolated from bacterium
Answer : Option D
Explaination / Solution:
Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated by Chien et al. in 1976.Its name is often abbreviated to Taq Pol or simply Taq. It is frequently used in the polymerase chain reaction (PCR), a method for greatly amplifying the quantity of short segments of DNA. It remain active during high temperature induced denaturation of double stranded DNA.
Q10. According to Darwin, evolution is
Answer : Option B
Explaination / Solution:
According to Charles Darwin, evolution is a very slow and gradual process. He believed that evolution took place over a very long period of time. When we talk about time period in evolution we usually refer to billions of years. The generation of a species from another takes a long period of time. It is a very steady process as the changes and adaptation take long time to stabilise and give rise to a new species.
