Final answer:
Scientists use genetic engineering, a type of biotechnology, to alter the DNA of plants for traits like faster growth.
Step-by-step explanation:
The type of biotechnology used by scientists when they alter the DNA of a plant to make it grow faster is genetic engineering. This involves the direct manipulation of an organism's genome using recombinant DNA technology. Through genetic engineering, scientists can introduce new traits into plants, such as increased growth rate, by adding or modifying specific genes. These modified plants are known as genetically modified organisms (GMOs), and if the foreign DNA comes from a different species, the plant is considered transgenic.