CBSE Class 12 Biology Viva Questions 2025 – The Class 12 Biology Viva is one of the practical tests in which the student is checked on the practical and theoretical aspects of the class. The following compiled list shows the common viva questions and their answers to assist the students in preparing well for the examination.
Class 12 Biology Viva Questions 2025 With Answers
1. Difference between mitosis and meiosis?
Answer: Mitosis is one of the methods of cell division that involves the division of a single parent cell into two daughter cells with an equal number of chromosomes (diploid to diploid).
Meiosis on the other hand is cell division that leads to a reduction of chromosomal numbers by half to produce four very distinct daughter cells or haploid cells which are used in sexual reproduction.
2. Explain the structure of DNA.
Answer: DNA (Deoxyribonucleic Acid) consists of two polynucleotide chains coiled around a central axis. Both strands are made of a sugar-phosphate backbone, while the nucleotides are connected to the backbone. There are four nitrogenous bases: Adenine represented by the letter ‘A’, Thymine represented by the letter ‘T’, Cytosine represented by the letter ‘C’ and Guanine represented by the letter ‘G’. For instance, adenine pairs with Thymine and Cytosine with Guanine. These bases form the sequence, they code for genetic information.
3. What are enzymes? Give examples.
Answer: Enzymes are a type of biological catalyst that reduces the rate of chemical reactions within a living organism while they are not used up in the reaction. They are proteins with a unique three-dimensional conformation. Examples include:
- Amylase – catalyses the hydrolysis of a starch to sugars.
- Lipase – frees fatty acids from glycerol, which is a type of lipid.
- Protease – an enzyme that cleaves protein into amino acids.
4. What do human beings use their respiratory systems for?
Answer: The human respiratory is actually the system for the gases to be exchanged within the human body and the environment namely oxygen and carbon dioxide. The process involves breathing in oxygen and breathing out of carbon oxide/methylene. These are the nose, trachea, bronchi, bronchioles, alveoli and the lungs.
5. What is transpiration?
Answer: Transpiration may be described as a process by which water is taken from the soil through the root into the main system of the plant and through the stomata of the leaf into the atmosphere. Its role is to serve cooling, turgidity and nutrient uptake functions to the plant.
6. Define the term ‘ecosystem’.
Answer: An ecosystem can be defined as a geographical area that is inhabited by a certain population of living organisms, that interact with their physical environment. Such as energy exchanges, nutrient recreation and the existence of species in the environment they inhabit.
7. How does xylem and phloem differ?
Answer:
- Xylem: This is essential in the transport of water as well as minerals from roots to the level of leaves. It is comprised of vessels, tracheids and fibres. A few years ago, the leading identity was makers’ stress, which came mainly from mechanical action on the body.
- Phloem: It moves the produce of photosynthesis (predominantly sucrose) from the leaves to other organs of the plant. This includes: sieve tubes, companion cells, phloem fibres as well as phloem parenchyma.
8. What is photosynthesis and how does it occur?
Answer: Photosynthesis is the energy-transforming activity using which green plants are capable of preparing for their use of the accumulated solar energy and converting it into the chemical energy of glucose which is produced with the help of carbon dioxide and water under the influence of sunlight and chlorophyll. The process occurs in two stages:
- Light-dependent reactions: Take place in the thylakoid membranes of chloroplasts and generate ATP and NADPH.
- Light-independent reactions (Calvin Cycle): ATP and NADPH are used to fix carbon dioxide into glucose in the stroma of the chloroplasts.
9. What are hormones? Which are two plant hormones and two examples of animal hormones?
Answer: Hormones are chemical substances that act as liaisons of various body activities In both active and plants. They are synthesized in one region of the body and impact predetermined cells or tissue in other regions of the body.
Plant hormones:
- Derivatives of auxins – they control growth, including cell elongation.
- Gibberellins – stimulates effects including seed germination and plant growth.
Animal hormones:
- Insulin – controls blood glucose level.
- Thyroxine controls the rate of metabolism in the body.
10. What are the roles of ribosomes within the process of the translation step of protein biosynthesis?
Answer: These are the bodies where the formation of proteins and other such polymers are formed at the cellular level. They with the help of mRNA (messenger RNA) read the genetic code and sequentially link them amino acids into proteins. Ribosomes consist of two subunits: A large subunit and a small subunit exist in their electrons micrographs. It can be free in the cytoplasm or bound with the endoplasmic reticulum making it rough endoplasmic reticulum.
11. What does it mean when it is stated that the factors are segregated?
Answer: Mendell’s Law of Segregation: Two alleles that exist for a gene separate during the formation of gametes so that the gametes bear only one allele for a gene. This helps in avoiding consanguinity and enables offspring to acquire certain attributes from each parent.
12. What is done by the kidney in the elimination process?
Answer: Through the excretion process, the kidneys filter the blood, by eliminating waste products and other substances for example water to form urine. The primary functions of kidneys include metabolic products excretion, water and electrolyte balance and acid-base equilibrium.
13. Please take time to explain what genetic drift means.
Answer: Mutation is a random process through which allele frequencies in a population are altered by random events rather than through affecting the fitness of these alleles. It has a more prominent role in the small-population genotypic makeup, and below is the process, which leads to the loss of genetic variation in such populations.
Conclusion
These viva questions are concerned with the important ideas and concepts of the CBSE Class 12 Biology. By understanding these questions, a student can be in a position to take his/her practical exam with confidence and with the best returns.
Have a good preparation!
