Plant tissues

A tissue is a group of cells which are similar in structure and origin and perform a similar function. Plant tissue - plant tissue is a collection of similar cells performing an organized function for the plant. Each plant tissue is specialized for a unique purpose,and can be combined with other tissues to create organs such as flowers,leaves,stems and roots

Plant tissues are of two types:

1. Meristematic tissue
2. Permanent tissue

Meristematic Tissue

The cells of this tissue have the ability to divide and redivide to form new cells (mitosis). The newly formed cells are similar to the parent cell but as they grow their characteristics change and they differentiate. These cells, found in growing areas of plants, help in increase of length and width of plants.

Types Of Meristematic Tissue: -

1. Apical Meristem:-

Apical Meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.

2.Lateral Meristem:-

The girth of the stem or root increases due to Lateral Meristem(cambium).

3. Axillary Meristem (or intercalary meristem):-

Intercalary Meristem seen in some plants is located near the node and helps to increase the length of two nodes.

PERMANENT TISSUE

These are matured meristematic tissue. The meristematic cells form permanent tissue once they lose the ability to divide. The process by which cells arise from meristematic tissue and take up a permanent shape, size and function is called differentiation.

Permanent tissues are of three types,

1. Simple permanent tissue.
2. Protective permanent tissue.
3. Complex permanent tissue.

Two of them are:

SIMPLE PERMANENT TISSUE

This type of tissue are made of one type of cells, which are similar in origin, structure and function. Simple permanent tissues are of three types,

1. Parenchyma
2. Collenchyma
3. Sclerenchyma

PARENCHYMA

CHARACTERISTICS- it is the basic packaging tissue that fills the spaces between other tissues and is found most abundantly in plants. They have unspecialized/ undifferentiated cells with thin cell walls made of cellulose. they have large intercellular spaces as the cells are loosely packed. Cells have dense cytoplasm and nucleus and large vacuole.

FUNCTION- This tissue provide support to plants and parenchyma of stem and roots stores nutrients and water and is called as STORAGE PARENCHYMA. when it contains chloroplast having chlorophyll and performs photosynthesis, it is called CHLORENCHYMA. In aquatic plants, parenchyma has large air spaces to provide buoyancy to plants to help them float and exchange gases, it is called AERENCHYMA. Isolated parenchyma cell or group of cells are capable of producing the whole plants.

LOCATION- This type of tissue found in non woody or soft parts of roots, stem, flowers, leaves and fruits.

COLLENCHYMA

CHARACTERISTICS- The cells are living, elongated and irregularly thick at the corners made of cellulose or pectin they have very less or no intercellular spaces. The cells have a nucleus, dense cytoplasm and Large. the wall has large amount of hemicellulose and pectin in addition to cellulose. The lignin is not present.

FUNCTIONS- These cells provide flexibility (elasticity) and mechanical support to the aerial parts of the plants and allows them to bend.

LOCATION- This type of tissue is found in leaf stalks, below epidermis of leaves and stem.

SCLERENCHYMA

CHARACTERISTICS- The cells are long, narrow thick walled due to deposition of lignin. Such cell walls are called as lignified walls and have pits. These cells lack intercellular spaces due to deposition of lignin. The cells do not have a nucleus and cytoplasm and are dead.

FUNCTIONS -These cells provide rigidity and strength to plants and makes it hard and can bear stress and strains.

LOCATION- This type of cells are found in stems, around vascular bundles, in the veins of leaves.

COMPLEX PERMANENT TISSUE

This type of tissue is made up of more than one type of cells that have a common origin and work together to do a common function. Its function is to transport water, minerals and food to all parts of the plant. Complex permanent tissue is of two types,

1. XYLEM
2. PHLOEM

1. XYLEM

The cells have thick walls. Elements are tracheids, vessels, xylem parenchyma, and xylem fibers Vessels are the most important elements and are shorter and wider than tracheids. Vessels and tracheids have tube like structures that help in transporting water and minerals vertically efficiently. Conduction takes place in one direction. Xylem parenchyma stores food and helps in lateral conduction of water. In addition to transporting water and mineral salts from roots to leaves, xylem also provides support to plants and trees because of its tough lignified vessels. In xylem, only the Xylem parenchyma is living and all other elements are dead.

Bigger pink cells - Old xylem(meta xylem) Small pink cells - new xylem(proto xylem)

2.PHLOEM

Elements of phloem are sieve tubes, companion cells, phloem parenchyma and phloem fibers. Sieve tubes are tube like structures, The end walls are called sieve plates and are perforated due to presence of pores. Companion cells help in efficient functioning of sieve tubes. Phloem transports the prepared food from leaves to storage organ and from storage organ to growing regions. Hence the conduction is bi directional. In phloem all the elements are living except the phloem fibers.

phloem