CBSE 12TH BIOLOGY - Online Test
Q1. Enzymes called ______ add complementary nucleotides, floating inside the nucleus.
Answer : Option B
Explaination / Solution:
The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from one original DNA molecule. It is found floating freely inside the nucleus.
Q2. The dividing and undifferentiated cells are known as
Answer : Option C
Explaination / Solution:
The differentiated mass of cells is called callus. During tissue culture, callus is formed when small part of plant is kept in nutrient medium. Callus cells divide rapidly.
Q3. As per research reports, due to unchecked human activities our Earth is at present heading towards
Answer : Option B
Explaination / Solution:
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth.
Due to unchecked human activities, biologists suspect we’re living through the sixth major mass extinction. Earth has witnessed five, when more than 75% of species disappeared.
Glogal warming, greenhouse effect, deforestation, pollution of atmosphere, water and soil all contributing destruction of earth.
Q4. Corpus luteum secretes
Answer : Option D
Explaination / Solution:
The ovum released during ovulation undergoes several changes and change into corpus luteum that release two hormone, estrogen and progesterone.
Q5. Hemophilia is more commonly seen in human males than in human females because
Answer : Option A
Explaination / Solution:
Hemophilia is sex-linked recessive disease due to mutation in X-chromosome. In this disease blood clotting do not takes place in case of injury and minor cut leads to death of individual.
Q6.
The bacteria which grows anaerobically on cellulose material and produces large amount of methane along with and are collectively called
Answer : Option A
Explaination / Solution:
Methanogens are autotrophic archebacteria that use anaerobic respiration for ATP synthesis.
Methanogens use CO2 taken up from their growth environment as the carbon substrate for growth. They use some CO2 as the ultimate oxidizing agent of an electron transport chain which, by a chemiosmotic mechanism, maintains a transmembrane electrochemical ion gradient which powers ATP production.
The reducing agent that drives the electron transport chain is hydrogen also taken up from the growth environment. This hydrogen is the waste end product of the metabolism of other, heterotrophic microorganisms. Methanogens use this hydrogen and this process maintains a lowered hydrogen partial pressure in the reticulo-rumen.
It is present in dung of animals.
Q7. Ozone can be:
i. good ozone present in troposphere, and acts as shield against ultraviolet rays
ii. bad ozone is a severe pollutant in stratosphere and is dangerous to living beings.
i. good ozone present in troposphere, and acts as shield against ultraviolet rays
ii. bad ozone is a severe pollutant in stratosphere and is dangerous to living beings.
Answer : Option A
Explaination / Solution:
Ozone occurs in two layers of the atmosphere. The layer closest to the Earth's surface is the troposphere. Here, ground-level or "bad" ozone is an air pollutant that is harmful to breathe and it damages crops, trees and other vegetation. It is a main ingredient of urban smog.
The troposphere generally extends to a level about 6 miles up, where it meets the second layer, the stratosphere. The stratosphere or "good" ozone layer extends upward from about 6 to 30 miles and protects life on Earth from the sun's harmful ultraviolet (UV) rays.
Q8. Molecular scissors are
Answer : Option A
Explaination / Solution:
Restriction enzymes are also called 'molecular scissors' as they cleave DNA at or near specific recognition sequences known as restriction sites. These enzymes make one incision on each of the two strands of DNA and are also called restriction endonucleases.
Q9. Selective breeding of organisms (Animal husbandry and plant breeding programs) for specific desirable characteristics are examples of
Answer : Option C
Explaination / Solution:
In animal husbandry and plant breeding, specific desirable characteristics are obtained by selective breeding. The plants or animals having specific traits are crossed to obtain required traits. It is a kind of artificial selection.
Q10. Among desert plants, which of the following will become a limiting for primary production
Answer : Option B
Explaination / Solution:
Primary productivity is of plants depends upon availability of water, sunlight, chlorophyll, carbon dioxide etc. but in desert plants water is the main limiting factor as very less amount of water is available to plants in deserts.
