Question

Answer the question which is double ticked...

Answer 1

Table of Contents

1 Plant Tissues2 Meristematic Tissue3 Permanent Tissue3.1 Simple Permanent Tissue3.1.1 Parenchyma3.1.2 Chlorenchyma3.1.3 Aerenchyma3.1.4 Collenchyma3.1.5 Sclerenchyma3.1.6 Epidermis3.2 Complex Permanent Tissue3.2.1 Xylem3.2.2 Phloem



Plant Tissues

Plants are stationary or fixed – they don’t move. Most of the tissues they have are supportive, which provides them with structural strength.Most of the plant tissues are dead, since dead cells can provide mechanical strength as easily as live ones, and need less maintenance.Animals on the other hand move around in search of food, mates and shelter. They consume more energy as compared to plants. Most of the tissues they contain are living.Another difference between animals and plants is in the pattern of growth. The growth in plants is limited to certain regions, while this is not so in animals.There are some tissues in plants that divide throughout their life. These tissues are localised in certain regions.Based on the dividing capacity of the tissues, various plant tissues can be classified as growing or meristematic tissue and permanent tissue.Cell growth in animals is more uniform. So, there is no such demarcation of dividing and non-dividing regions in animals.The structural organisation of organs and organ systems is far more specialised and localised in complex animals than even in very complex plants. This fundamental difference reflects the different modes of life pursued by these two major groups of organisms, particularly in their different feeding methods.Also, they are differently adapted for a sedentary existence on one hand (plants) and active locomotion on the other (animals), contributing to this difference in organ system design.

Meristematic Tissue

The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue, is located only at these points.Depending on the region where they are present, meristematic tissues are classified as apical, lateral andintercalary.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.



Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.The girth of the stem or root increases due to lateral meristem (cambium).Intercalary meristem is the meristem at the base of the leaves or internodes (on either side of the node) on twigs.As the cells of this tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles.

Permanent Tissue

What happens to the cells formed by meristematic tissue? They take up a specific role and lose the ability to divide. As a result, they form a permanent tissue.This process of taking up a permanent shape, size, and a function is called differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue.



Complex Permanent Tissue

The different types of tissues we have discussed until now are all made of one type of cells, which look like each other. Such tissues are called simple permanent tissue. Yet another type of permanent tissue is complex tissue.Complex tissues are made of more than one type of cells. All these cells coordinate to perform a common function.Xylem and phloem are examples of such complex tissues. They are both conducting tissues and constitute a vascular bundle.Vascular or conductive tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment.



Xylem

Xylem consists of tracheids, vessels, xylem parenchymaand xylem fibres. The cells have thick walls, and many of them are dead cells.Tracheids and vessels are tubular structures. This allows them to transport water and minerals vertically.The parenchyma stores food and helps in the sideways conduction of water. Fibres are mainly supportive in function.

Phloem

Phloem is made up of four types of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma. Sieve tubes are tubular cells with perforated walls.Phloem is unlike xylem in that materials can move in both directions in it. Phloem transports food from leaves to other Parts of the plant. Except for phloem fibres, phloem cells are living cells.


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