I don’t know what exact diagram your referring too but I assumed it was this diagram below as someone asked the same question before. If this is the diagram your talking about then answer is indeed ‘oxygen is used up.’
Xerophytes are plants that have adapted to arid climates. They have evolutionary developed adaptations to reduce the rate of transpiration so as to conserve water.
Among the adaptations include; thick cuticle, small, thick leaves, reducing the surface area relative to the volume of the leaf, etc.
Additionally, they use CAM pathway as an alternative photosynthetic pathway to minimize water loss.
