The correct option is C Respiratory activities in plants
Plant physiology is a subdiscipline of botany concerned with the functioning or physiology of plants. Fundamental processes such as photosynthesis, respiration, plant nutrition, plant hormone functions, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, environmental stress physiology, seed germination, dormancy and stomata function and transpiration, both parts of plant water relations are studied under plant physiology.