Difference between gymnosperm and angiosperm is as follows

Gymnosperm	Angiosperm
Gymnosperms lacks vessels in their xylem. Phloem lacks companion cells.	Vessels present in the xylem. Phloem possesses companion cells.

Modification of Epidermal Cells

The epidermal tissue has the following modifications

(i) Root hair

Structure	Function
Unicellular hairs are the extensions of epidermal cell of roots in the root hair zone.	It increases the surface area for absorption of water and minerals.

(ii) Epidermal Appendages

Structure	Function
These are called trichomes and are epidermal cell modifications. There may be unicellular or multicellular.	Some performs for stinging produces and some glandular secretions.

The meristematic tissue is responsible for the rapid growth of such mowed lawn grass. When the apex of grass is cut frequently, it leads to the growth of the lateral branches, that makes it more bushy.

Plants use water for several metabolic process as photosynthesis, transpiration and respiration. Plants die when watered in excess, because excess water removes the air trapped between the soil particles. So, plant roots do not get $\mathrm{O}_2$ for respiration. Once root cells die, water and mineral absorption is stopped and this leads to gradual death of a plant.

Concentric Rings The concentric growth rings are called annual rings. These rings are formed due to the secondary growth. Secondary growth occurs in dicot trees due to the activity of cambium which is a meristematic tissue. The rate of activity of cambium is more in spring so wood formed has larger wider xylem cells, whereas wood formed in winter has narrower and smaller xylem elements. This results in the formation of two rings called growth rings.

By counting these rings, age of the tree can be determined. This branch of science is known as dendrochronology or growth ring analysis.