Biology tissue chapter

Tissues for growth in plants :
Meristematic tissues :
They consist of actively deciding cells
Found in growing regions of plants like stems and roots
The site of region where new meristematic tissues are formed is called metistems
Meristems tissues are small and thin walled cells
These cells are arranged comapctly lacking intercellular space
Characteristic features of these cells are that they have a prominent nuclues , a dense cytoplasm and a cell wall
They are responsible for the growth of plants by increasing their length and girth of plant body
They help in healing injured parts and replacing them with new cells
They act as a primary tissue for development of other tissues
There are three types of meristematic tissues : apical meristem. Lateral meristem and intercalary meristem
Due to continuous cell division , meristematic tissues add new cells to the body
Some of the cells remain meristematic and some of them loses the ability to divide
The cells that lose the ability to divide undergo changes in structure and function and become permanent tissue
Thus formation of permanent tissues from meristematic tissues occurs
The process by which meristematic tissues become specialized to perform specific functions is called differentiation

Apical meristem : growth at tip of roots or shoots
This shows that roots grow only at the shoots
The tip of roots contain actively dividing cells that increase the length
Thus plant have certain growth zones at the tips of roots and shoots called apical meristem and help plants grow in length

Lateral meristem : diameter of stem and increase in girth
Plants not only increase in length but also increase in girth or thickness
The increase in girth occurs due to the presence of actively diving cells arranged in a ring or stem
These cells divide and form new cells increasing the diameter of the stem

Permanent tissues : non actively diving tissues
A different group of cells are present and each tissue performs a specific function and can be simple or complexed
There are two types : simple permanent and complex permanent
Simple permanent tissues :
These tissues support in plant height, storage , to stay upright and rigidity
There are three types of simple permanent tissues : parenchyma collenchyma and sclerenchyma
Parenchyma : storage tissue
Living cell with thin walls
Looseley packed with intracellular space
Responsible for storage of food in plants
Performs photosynthesis in green plants with chlorophyll
In aquatic plants , specialized parenchyma form spaces which help them float
Collenchyma : provides flexibility
Containing living cells with unevenly thickened corners
This tissue provides flexibility to the plant
This is why the plant can bend easily without breaking
Anima cells need to change shape and if their cells contain collenchyma tissues , they won't be able to bend easily
Sclerenchyma: hard and strong
These tissues are thick walled and tightly packed without any intracellular space between them
Contain lingin which makes the plant hard and strong
In this tissues , most of the cells are dead
This is found in stems , leaf veins and hard coverings of coconut
Thus parenchyma provides storage . Collenchyma provides flexibility and sclerenchyma provides hard and strong features

Complex permanent tissues : conducting tissues
Plants have specialized conducting tissues called xylem and phloem
They are made of different working cells
Xylem is the tissue which transports water from the roots to the different parts of plant
It also gives strength to the plant
Xylem contains tracheids , vessels , xylem parenchyma and xylem fibres
The xylem parenchyma stores water
Unlike xylem , phloem is made up of living cells
Consist of sieve tubes , phloem parenchyma , companion cells
Companion cells are specialized cells ( parenchyma )
Main function of companion cells is to maintain the loading and unloading of sugar in sieve tubes
Phloem parenchyma is responsible for storage of food

Epidermis : protective tissue
Epidermis forms the outer layers of plants
Consist of tightly packed single layer of rectangular cells
It protects all parts of the plant that provides protection against mechanical injury and invasion of parasites
These cells are covered with a cutin called cuticle
In desert plants , the epidermis of the desert plants is covered with a thick layer of cuticle to prevent water loss through transportation
The epidermis of the plant had stomata which help in gaseous exchange and transpiration
Through transpiration ,there's a transpirational pull leads to loss of water
Roots contain root hairs that increase surface area for abdorbtion of water and minerals from soil

Dermal tissue system : forms outer covering of plant and protects inner parts and reduces water loss
Ground tissue system : forms main body of plant between dermal and conducting tissues and included parenchyma collenchyma and sclerenchyma
Vascular tissue system : since xylem and phloem are called vascular tissues , they form the vascular system