Final answer:
Companion cells are essential for phloem transport in plants. They have a high number of mitochondria and cell membrane infoldings to support their function.
Step-by-step explanation:
Companion cells are specialized cells found in the phloem of plants. They are closely connected to sieve tube elements and play a crucial role in supporting their function of transporting sugars and other organic compounds throughout the plant.
The structure of companion cells includes a high number of mitochondria, which are responsible for generating energy in the form of ATP. The presence of mitochondria allows companion cells to meet the high energy demands of active transport processes involved in loading and unloading sugars to and from the sieve tube elements.
In addition, companion cells have cell membrane infoldings, which increase the surface area of the cell membrane. This allows for a larger number of transport proteins to be embedded in the membrane, enhancing the efficiency of nutrient exchange between companion cells and sieve tube elements.