Function of companion cells is :
1. Loading of sucrose into sieve elements
2. Providing energy to sieve elements for active transport
3. Providing water to phloem
4. Loading of sucrose into sieve elements by passive transport

The translocation of organic solutes in sieve tube members is supported by:

1. root pressure and transpiration pull

2. P-proteins

3. mass flow involving a carrier and ATP

4. cytoplasmic streaming