As a science teacher in high school, I have been requested by a number of my students to describe briefly the subjects I handle in school on internet so that it would be easier for them to get access whenever they feel need it. So, as a first, I’m going to publish short description of the chapter ‘Tissues’ of class 09- NCERT(India) through this blog. If you are a school going student in indiaL(Or an enthusiastic new learner) and the syllabus you follow is CBSE, you will find this article helpful.
So what are tissues?
To get an understanding about tissues one must first know about cells. You might have studied about cells in the previous chapter. In short “Cells are the basic structural and functional units of the life”. We being multicellular organisms, there is a division of labour in our body. Which means, unlike unicellular organisms, we have separate organs and systems to carry out different functions in our body. The interestinng fact about these different organs and systems is that their cells are different, ie, different organs carry different types of cells. And this is where you find the definition of tissues! “A group of cells that come together to perform a specific function is caled a Tissue“
Different types of Tissues
We all know that all living things on earth can brought under two broad categories- Plants and Animals, Both are perfect examples for multicellular organisms. Due to the difference in their survival needs they come equipped with different types of Tissues. As you all know, plants do not move,while animals are in dire need of roaming in search of food, shelter and mate! Obviously the study of tissues involves the study of two entirely different tissues!
- Plant Tissues.
- Animal Tissues.
Most of the plant tissues are made of dead cells! Yeah, you read it right. They are dead and are efficient, because even a dead body can provide enough support and rigidity for a stationary being. Plant tissues can be broadly classified into two.
- Meristematic Tissues.
- Permnent Tissues
In a plant, not every part can get multiplied and give rise to new cells. Only a specific regions in a plant can divide and giver birth to new cells, such tissue in a plant is called Meristematic Tissue. A typical Plant contains three kinds of meristematic tissues
- Apical Meristem– These are tissues present in the tip of stems and roots. Elongation of these parts occur due to the active division of these tissues.
- Intercalary Meristem– They are present in the nodes of leaves. They facilitate the regrowth of leaves and branches.
- Lateral Meristem– These tissues found in the stems and roots are responsible for the increase in girth of these parts.
After a while, most of these newly formed meristematic tissues will differentiate into new permanent tissues having dirrent functions. The most significant change is the increase in the size of vacuole, a food storing cell organelle.
Permanent tissues are of two types- Simple Permanent Tissues and Complex permanent Tissues.
Simple permanent Tissues are generally four in number.
- Parenchyma– They are mostly covering tissues providing support to the plant. They have large intercellular space which allows them to differentiate into organs performing different functions. These tissues may contain chlorophyll and perform photosynthesis(Chlorenchyma)
- Collenchyma– They provide flexiblility to the plant. They are lossely packed and provides for the rigidity of the plant.
- Schlerenchyma– Husk of a coconut is the better example for schlerenchyma tissue. They are superhard and have no intercellular space. They contain a chemical named lignin which acts as a cementing material that binds the cells together.
- Epidermis– This is the outermost covering of a plant that protects the plant from being attacked by many environmental factors and harmful microorganisms. Stomata, the pores in plants where gas exchange takes place, is present on the surface of epidermis.
Xylem and Phloem are examples for complex permenent tissues. The main difference between simple and complex permanent tissues is that the former is made up of group of similar type of cells, whereas the latter being the combination of multiple type of cells.
- Xylem– They are tubes like tissues present in the stem of a plant. Their function is to transport food and mineral from roots to the leaves. The elements of this tissue are Tracheid, Vessel and Xylem Parenchyma.
- Phloem– Cooked food in the leaves are trasported to different parts of the plannt through these tissues. Their constituents are Sieve Tube, Sieve plate, Phloem parenchyma and companion cell.
Unlike Plant tissues, Animal tissues are charechterised by the functions that will facilitate the movement in animals. We will mainly discuss about four different types of tissues.
- Epithelial Tissue
- Connective Tissue
- Muscular Tissue
- Nervous Tissue
Epithelial Tissues are specialised covering tissues. They occupy the outer linings of all internal organs. Even our skin is made of epethelial tissues which is flat in shape and multilayered. We call them stratified squamous epithelium. In many cases, they secrete hormones and act as glands.
Blood, Bones, Cartilages, Ligaments are all examples of connective tissues. As the name indicates, connecting different body parts is the main function of these tissues. All connective tissues are embedded in a matrix. In blood, the fluid plasma is the the matrix. In bones the matrix is solid in form and is made up of calcium and phosphurus.
The main function of Muscular Tissue is to facilitate the movement, the very functionality that differentiate animals from plants. Voluntary and Involuntary muscles are present in our body. Voluntary muscles are attached with bones and are called skeleal muscles. One can easily move thesw tissues at their will. Wheres, invlountary muscles which are found in our internal organs cannot be controlled by our will.
The final and fourth important animal tissues are Nervous Tissues. They are highly responsive to stimuli and are long enough. They carry the lengthier axons and branched dendrils. Brain, spinal chord and nerves are composed of this kind of cells.(Also called Neurons)
I hope you found this article helpful. If you have any doubts regarding the portion, feel free to comment here or personally contact me!