What are tissues?
A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue
Why does the growth of plants occur only in certain specific regions?
This is because the meristematic tissue is located only at these points.
What are the types of meristematic tissues?
Depending on the region where they are present, meristematic tissue can be classified as apical, lateral and intercalary. New cells produced by meristem are initially like those of meristem itself but as they grow and mature, their characteristics slowly change and they become differentiated as components of other tissues.
Where are the apical, lateral and intercalary meristem present?
apical- present at the growing tips of stems and roots and increases the length of the stem and the root.
lateral- the girth of the stem or root increases due to lateral meristem (cambium).
inetercalary- seen in some plants is located near the node
Define the cells of meristematic tissues
the cells of meristematic tissues are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles.
What are permanent tissues?
when the cells formed by meristematic tissues take up a specific role and lose the ability to divide, they form a permanent tissue
what is differentiation?
when the cells of meristematic tissues take up a specific function and lose their ability to divide they form a permanent tissue. This process of taking up a permanent shape, size, and a function is called differentiation
Where are simple permanent tissues generally located?
A few layers of cells beneath the epidermis are generally simple permanent tissue.
Explain parenchyma
parenchyma is the most common simple permanent tissue. It consists of relatively unspecialized cells with thin cell walls. They are living cells. They are generally loosely arranged thus large intercellular spaces are found in this tissue. It generally stores food.
Explain the types of parenchyma
in some situations the parenchyma contains chlorophyll and performs photosynthesis which is known as chlorenchyma.
In aquatic plants large air cavities are present in parenchyma to help them to float. Such a parenchyma type is called arenchyma.
What is collenchyma?
the flexibility in plants is due to another permanent tissue called collenchyma.
It allows the bending of various parts of plant like tendrils and stems of climbers without breaking. It also provides mechanical support. We can find this tissue in leaf stalks below the epidermis.
Where is the collenchyma located?
We can find the collenchyma in leaf stalks below the epidermis.
Define the structure of collenchyma tissue cells
The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space
Explain sclerenchyma
It is a tissue which makes the plant hard and stiff. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin. Often this walls are so thick that they have no internal space inside the cell.
What is lignin?
It is a substance which thicken the walls of sclerenchymatous tissue cells
Where is sclerenchyma tissue present?
It is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to plant parts.
What is the epidermis?
the outermost layer of cells is called the epidermis. This epidermis is usually made of a single layer of cells. The entire surface of the plants as an outer covering epidermis. It protects all parts of the plant
Explain the epidermis in dry habitats
In some plants living in very dry habitats, the epidermis may be thicker since the protection against water loss is critical.
Explain epidermal cells on the aerial parts of the plant
The epidermal cells on the aerial parts of the plant often secrete a waxy, water resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi.
Define the structure of epidermal cells
Since it has a protective role to play, cells of epidermal tissue forms a continuous layer without intercellular spaces, Most epidermal cells are relatively flat. Often their outer and side walls are thicker than the inner wall.
What are stomata?
Small pores in the epidermis of the leaf is called stomata. Stomata are enclosed by two kidney shaped cells called guard cells. They are important for exchanging gases with the atmosphere. Transpiration also takes place through stomata
Define the epidermal cells of the roots of plants
The epidermal cells of the roots have the function of water absorption and hence commonly bear long hair like parts that greatly increase the total absorptive surface area.
What is cutin?
In some plants like desert plants epidermis has a thick waxy coating of cutin which is a chemical substance with waterproof quality on its outer surface
What is cork?
As the plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem, located in the cortex forms a layer of cells which constitute the cork. Cells of the cork are dead and compactly arranged without intercellular spaces. They have a substance called suberin in their walls which makes them impervious to gases and water
