A student investigated the effect of root space on plant growth. The student grew two groups of plants of the same variety. Both groups received the same amount of water and sunlight and grew in the same type of soil. The plants in Group A were grown in cube-shaped containers that were 3 centimeters deep. The plants in Group B were grown in cube-shaped containers that were 10 centimeters deep. The table shows the student's observations. In one to two sentences, construct an explanation for the effect of space on plant growth. Use evidence to support your answer.