안녕하세요!

positive pressure implies "pushing down" to push water somewhere

negative pressure implies "sucking up" to pull water in a particular direction.

식물 잎에 있는 stoma를 통해 evaporation이 될수록

there is negative pressure on the xylem resulting in sucking up of water upwards

from the soil to the roots to the stems to the leaves

positive pressure의 경우는 두가지로 조금 다르게 해석할 수 있는데

1) you can talk about how nutrients and salts in the root is higher in concentration compared to the soil

causing the water to be "pushed into" the roots due to positive pressure from the environment.

OR

2) increased glucose production in leaves due to photosynthesis results in sugar buildup in top of phloem

this pulls water into the phloem causing increase in solution volume and a "positive pressure"

naturally this sugar solution will flow from a place with high pressure (in leaves) to low pressure (in roots)

where no photosynthesis occurs, resulting in a downward movement.

Because the question specifically asked you about movement of both water AND nutrients in terms of pressure

i'd be more comfortable with the second answer.

첨부파일 하나 추가할테니 한번 확인해보시고

good luck on the exam!