Class 12th Biology 2016 Set1 Delhi Board Paper Solution
Question 13
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:- Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
- Q:- Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
- Q:- Correct the following statements:
(a) Surgical methods of contraception prevent gamete formation.
(b) All sexually transmitted diseases are completely curable.
(c) Oral pills are very popular contraceptives among the rural women.
(d) In E. T. techniques, embryos are always transferred into the uterus. - Q:- List the harmful effects caused by alcohol/drug abuse.
- Q:- Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.
- Q:- Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
- Q:- The second trophic level in a lake is-
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes - Q:- What is oogenesis? Give a brief account of oogenesis.
- Q:- In our society the women are often blamed for giving birth to daughters.
Can you explain why this is not correct? - Q:- Compare and contrast the advantages and disadvantages of production of genetically modified crops.