Class 12th Biology 2016 Set2 Delhi Board Paper Solution
Question 11
Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life.
Answer
Leuis Pasteur suggested that life is propagated only through pre-existing life forms. The swan-necked flask experiment helped him prove his point on the continuity of life. His experiment is explained step by step as follows:
Experiment was carried out by two swan-necked flasks containing nutrient broth. Broth in the both flask was boiled to kill any existing microbes and was made sterile. After sterilising, the swan neck of one of the glass was broken and the flask was left undisturbed in the open air for some time. After some time the dust particles along with bacteria in the air entered the flask with broken neck and got accumulated at the neck of the unbroken flask. The broth in the broken flask became cloudy,while the broth in the unbroken flask remain clear. Cloudiness of the broth indicated the presence of microbial life in the broken flask. Appearance of life even after sterilisation, in the broken flask concluded that life in the flask arose only from pre-exising life.Thus, it discarded the theory of spontaneous generation.
Popular Questions of Class 12th biology
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:- Why is reproduction essential for organisms? Answer
- Q:- Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals. - Q:- With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
- Q:- What is DNA fingerprinting? Mention its application.
- Q:- What is oogenesis? Give a brief account of oogenesis.
- Q:- Describe the structure of a seminiferous tubule.
- Q:- What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
- Q:- With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
- Q:- Explain the Law of Dominance using a monohybrid cross.
Recently Viewed Questions of Class 12th biology
- Q:- How do ecologists estimate the total number of species present in the world?
- Q:- Identify True/False statements. Correct each false statement to make it true.
(a) Androgens are produced by Sertoli cells. (True/False)
(b) Spermatozoa get nutrition from Sertoli cells. (True/False)
(c) Leydig cells are found in ovary. (True/False)
(d) Leydig cells synthesise androgens. (True/False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(f) Menstrual cycle ceases during pregnancy. (True/False)
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False) - Q:- Write critical notes on the following:
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment - Q:- What is meant by emasculation? When and why does a plant breeder employ this technique?
- Q:- If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
- Q:- Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:-
With the help of suitable diagram describe the logistic population growth curve.
- Q:- What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
- Q:- Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.