The curve in bananas is due to how they grow.
Banana plants produce leaves that develop into a pseudostem and produce fruit. The bud forms in the bottom part of the plant and grows up through the centre of the pseudostem to the top. The arrow-shaped bud pushes through the top of the plant and its weight then causes it to change direction and grow towards the ground.
Each cluster of bananas is covered by a thick hood like bract (a modified leaf) that makes it difficult for the bananas to grow. It descends downward and grows towards the earth.However, when the fruit begins to mature, layers of bracts fall off. Then the bananas, which were straight at the origin, begin to push upwards in the direction of the sun. This growth away from the pull of gravity is known as negative geotropism.