A number of examples of substances crossing membranes are given below. 1. glucose molecules into the epithelial layer lining the small intestine 2. nitrate ions from a dilute soil solution into a solution of higher concentration inside root hair cells 3. water molecules moving out of mesophyll cells and into the air spaces inside a leaf For which must oxygen be present?
- A1, 2 and 3
- B1 and 2 only
- C1 and 3 only
- D2 and 3 only