Due to imbibition of water by seed materials (starch and protein), pushes the seedlings out of the soil, thus the seed swells and imbibition pressure increases inside the seed, which contributing for germination of seeds.

Transpiration pull is the physiological phenomenon which is responsible for the upward movement of water in trees of height up to 20 m . As the water molecules transpire from stomata, it pulls water molecules up ward to the leaf from the continuous chain of water molecules carried by xylem.

This transpiration from leaf creates a pressure gradient between the atmosphere and sub-stomatal cavity and intercellular spaces of leaf. This gradient is transferred to photosynthetic cells and then on to xylem of leaf vein.

It results in a force called "transpirational pull" that can lift water upto 130 m high, through a xylem column.

The transport takes place by the cell membrane because cell membrane is semi-permeable and composed of lipids that are arranged in bilayer structure along with proteins and carbohydrate.

The lipid soluble molecules pass readily across lipid bilayer of cell membrane whereas movement of other molecules of small size is facilitated by porins, pores made up of proteins. While cell wall does not helps in transport of substances because it.

Cell wall is basically a non-living rigid structure forming outer covering over plasma membrane and it provides shape, mechanical strength and protection to the plant cell from damages and infection.

Half, The evolution of the $\mathrm{C}_4$ or plants photosynthetic system is probably one of the strategies for maximising the ability of $\mathrm{CO}_2$ while minimising water loss. $\mathrm{C}_4$ plants are twice as efficient as $\mathrm{C}_3$ plants in terms of fixing carbon in the form of glucose, but lose only half as much water as $\mathrm{aC}_3$ plant for the same amount of $\mathrm{C}_2$ fixed.

Xylem is involved in the one way transport of water and minerals from soil to root $\rightarrow$ stem $\rightarrow$ leaves. Several forces act in this mechanism like imbibition, root pressure and finally transpiration pull. There is continuous loss of water at the body surface of plants. Thus, it is a unidirectional process. Phloem's main function is to transport food from source to sink where source implies with the part of plant responsible for synthesising food and sink to those parts and organs that needs or consumes food for their growth and development. These source and sink parts of a plants may vary in different phases of its growth, thus the food need to travel in both upwards and downward direction. So, phloem shows bidirectional movement of substances.