Correct Answer – Option 2 – carbon dioxide

Plants absorb carbon dioxide to generate food and oxygen. Hence, option 2 is the correct answer.

Plants do not absorb dissolved nitrogen to generate oxygen. Hence, option 1 is incorrect.

Enzymes and hormones are not freely available in water. Hence, options 3 and 4 are incorrect.

Correct Answer – Option 1 – producing glucose

Plants use carbon dioxide and sun light, to break nutrients into simple sugars such as glucose for and in the process generate oxygen. The observation of bubbles of oxygen in the tube shows the production of glucose. Hence, option 1 is correct.

Plants do not make protein. Hence, option 2 is incorrect.

Plants do not release energy from water. Hence, option 3 is incorrect.

Active transport does not lead to the production of oxygen. Hence, option 4 is incorrect.

Correct Answer – Option 3 – a feedback mechanism

The statement in the question describes circulation of message to generate reaction i.e. a feedback mechanism.

The reaction of the pituitary gland to release hormone 2 on drop of blood pressure and in reaction to this gland B is stimulated to increase blood pressure and this in turn leads to the reduction in the release of hormone 2. This mechanism does not take place by DNA base substitution, or manipulation of genetic instructions or an antigen-antibody reaction. Hence, options 1, 2 and 4 are incorrect.

Correct Answer – Option 3 – an enzyme

An enzyme acts as a catalyst accelerating a reaction. In the above diagram an enzyme helps the break down of the starch molecule into simple sugars. Hence, option 3 is correct.

An antibody, a receptor molecule or a hormone do not help in breaking a starch molecule into simple sugars. Hence, options 1, 2 and 4 are incorrect.

Correct Answer – Option 1 – simple sugars

Starch is digested into simple sugars. Hence, option 1 is the correct answer.

Starch cannot be broken down into fats, amino acids or minerals. Hence, options 2,3 and 4 are incorrect.

Correct Answer – Option 3 – Photosynthetic rate in the algae is greatest in blue light

Photosynthetic activity by algae leads to generation of oxygen. The graph above shows maximum oxygen production at the point of exposure of blue light to algae. Hence, we can interpret that under the influence of blue light photosynthetic rate in algae is highest.

Oxygen production increases as the wavelength of light increases from 550 to 650nm. Hence, option 1 is incorrect.

Correct Answer – Option 1 – The ecosystem will change until a new stable community is established

The tsunami affected the marine ecosystem hence, leading to change. This change will be in process until a new stable community will be established.

However, there is no assurance of continuation or extinction of ecological succession neither the extinction of organisms. Hence, options 2,3 and 4 are incorrect.