Question

why do water needs to germinate to a big tree

Answer 1

Seed germination. For non-dormant seeds, germination starts when a seed is provided with water as long as the temperature is appropriate. The uptake of water by dry seedis called imbibition.

This water is used by plants to fuel various reactions in cells, so that they can divide and grow. As you plants are not heterotrophs, they make their own food by a process called photosynthesis. In photosynthesis water is must. That's why wet soil is important. After a appropriate height of plants , they send their roots deeper in soil, so that soil which looks dry actually wet deeply.

Hope this will help.

Answer 2

because they need water to do photosynthesis