Download App

Environmental Issues — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYEnvironmental Issues3 Marks
Question
  1. How is ozone formed in the 'stratosphere'?
  2. CFCs contribute to ozone hole formation. Explain.
✓

Answer

  1. Ozone is formed by the action of UV rays on molecular oxygen in the stratosphere.
  2.  
  • CFCs discharged in the lower part of the atmosphere move upward and reach stratosphere.
  • In the stratosphere, UV rays act on CFCs and release Cl atoms.
  • Cl atoms act as catalyst and degrade the ozone into molecular oxygen.
  • Since Cl atoms are not consumed, whatever CFCs are added to the stratosphere, they have a permanent and continuing effect on ozone levels.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "3 Marks Question" from Environmental Issues→Environmental Issues — all question types→BIOLOGY STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

Describe the process of sporulation seen in Amoeba.
→
What are the advantages of the techniques of GM crops?
→
  1. HIV and Hepatitis B are STDs. Mention any two other ways by which they can be transmitted to a healthy person.
  2. Why is early detection of STD essential? What can it lead to otherwise?
→
ion the characteristic symptoms of Dengue fever. How is the disease transmitted to others?
→
Since the origin of life on the earth, there were five episodes of mass extinction of species.
  1. How is the 'Sixth Extinction', presently in progress, different from the previous episodes?
  2. Who is mainly responsible for the 'Sixth Extinction'?
  3. List any four points that can help to overcome this disaster.
→
A person has been diagnosed to be $HIV^+$.
  1. Name the disease and the test which the person has to undergo.
  2. Write the full name of the pathogen involved and describe its structure.
  3. Which particular cells of this person are likely to get destroyed?
OR
The immune system of a person is suppressed. In the ELISA test, he was found positive to a pathogen.
  1. Name the disease the patient is suffering from.
  2. What is the causative organism?
  3. Which cells of the body are affected by the pathogen?
→
Write the symptoms of haemophilia and sickle–cell anaemia in humans. Explain how the inheritance pattern of the two diseases differs from each other.
→
Describe the major features of embryonic development at various months of pregnancy.
→
  1. What are meiocytes?
  2. If the chromosome number in meiocytes of human beings, housefly, potato, apple, dog and maize are 46, 12, 48, 34,78 and 20, respectively. What will be the chromosome numbers in gametes of these species?
→
Explain any three contraceptive devices that can be used by women for their family planning.
→