Q1. What kind of Change would be observed in the weight of bird-cage, weighed by a spring balance 1. when the bird is sitting inside the cage 2. when the bird is flying inside the cage? WHY?

Q2. A 1.0 gm. Seed is sown on the earth after few years it becomes one of the biggest trees in the neighbourhood! Will the weight of the earth remain same, will it increase or decrease as compared with the weight of the earth taken, when the seed was sown

Q1. If the bird is flying, the bird is pushing down on the air. The air is pushing down on the cage. If the bird is not rising, the weight of the cage should be approximagely the same whether the bird is resting or flying. If the cage were very small, some of the force might be dissipated to the earth, but we're talking first-order effects, here.

Q2. The force on the earth at the point of the tree will increase because of the mass of the tree. I'm not sure if that's what you mean by the weight of the earth or not.

Not all the air under the bird's wings will press down on the cage. Some of it will go out through the bars. In principle, the cage should be lighter, but I'm guessing it would bouncing around so much you wouldn't be able to get a good reading.

Are you talking about Earth, the planet, or some amount of soil in which the tree is growing?