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Plant tissues are supportive and provide the plants with strength and support. Tissues are the building blocks of any organism be it animals or plants. Multiple tissues join together to make an organism. Tissues comprise individual cells. A group of cells that have a similar structure and perform similar functions is known as a tissue. As most plants are fixed and are stationary, they do not move around much, due to which the plant tissues are supportive and provide structural strength to the plants. Hence, the animal tissue is a lot different from the plant tissue. In this article, we will learn more about the plant tissues which include permanent tissue, chlorenchyma, collenchyma, meristematic, parenchyma, aerenchyma, xylem, phloem, and sclerenchyma.
Key Terms: Plant Tissues, Xylem, Phloem, Cells, Tissue, Parenchyma, Collenchyma, Sclerenchyma, Epidermis
What are Plant Tissues?
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A group of plant tissues can form plant tissue systems that perform special functions. A plant tissue system can be defined as a functional unit that connects all the organs of the plant. Plant tissues can be broadly categorized into two types which are as follows:
- Meristematic Tissues
- Permanent Tissues
Plant Tissue Systems
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Meristematic Tissue
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Meristematic Tissues have the ability to develop further through swift division. The majority of the growth of vegetation is supported by meristematic tissues. These plant tissues aid in the growth of the diameter and length of the plant. The meristematic cells present in these tissues are living cells and are cubical in shape having a big nucleus. The meristematic cells that become old eventually lose their ability to get distributed and convert to the permanent plant tissues. The procedure of capturing a permanent size, function, and shape is known as differentiation.
Meristematic Tissue
These cells are crammed meticulously and have no intercellular space. The plants grow only in specific areas where the meristematic tissues are located. On the basis of the location of these meristematic plant tissues, they are further classified into three categories:
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Apical Meristems
- These plant tissues exist only at the tips of roots and stems.
- When the cell division starts, this meristem helps in the enlargement of the cell and also highly influences the shape of the plants that are mature.
- They increase the length of the plant.
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Lateral Meristem
- They are found along the sides of stems and roots.
- They play an important role in increasing the diameter and width of the stems and roots.
- They increase the thickness of the plant.
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Intercalary Meristem
- They are found at the base of some young leaves or in the internodes.
- They mainly help in the enlargement of leaves and stems. They have a missing nucleus.
- The cells present in this tissue are highly active. They have dense cytoplasm along with a prominent nucleus and thin cellulose walls.
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Permanent Tissue
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Permanent tissues have cells that have lost their ability of distribution as they have gained their mature form. They are specialized as they offer flexibility, strength, and elasticity to the plant. They are derived and converted from the meristematic tissues. The cells of meristematic tissue divide to form various types of permanent tissue. Permanent tissues are classified into two categories:
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Simple Permanent Tissue
The simple permanent tissues are the plant tissues that have the same function. They are called simple as they are composed of cells that are similar in type and have a common function and origin.
They are further classified into collenchyma, parenchyma, and sclerenchyma.
1. Parenchyma
Parenchyma are polygonal living cells and have a big central vacuole. These cells have intercellular space in between them. Parenchymatous cells form ground tissue and pith.
- This plant tissue is formed of unspecialised cells that exist within the thin cell walls.
- The cells are packed loosely and have large spaces between them.
- Parenchyma that consists of chloroplasts are referred to as chlorenchyma. The chlorenchyma aids in the process of photosynthesis.
- Parenchyma that consists of huge voids of air is known as aerenchyma. The main purpose of the aerenchyma is buoyancy.
- Some parenchymatous cells act as storage chambers for the starch that is present in vegetables and fruits.
Simple Permanent Tissue
2. Collenchyma
Collenchyma are living cells that are stretched out with minor intercellular gaps. The cell walls of this plant tissue are formed of cellulose and pectin. The location of collenchyma is in the marginal region of stems and leaves. This offers flexibility, mechanical support and a structural framework to the plants.
- This contributes to the flexibility of the plant.
- It allows various parts of the plant to bend without breaking such as the stem and the leaf.
- The plant tissue provides mechanical support to the plants.
- Collenchyma is present in the leaf below the epidermis.
- Very intercellular space is present in collenchyma.
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3. Sclerenchyma
Sclerenchyma are dead cells that are elongated with the lignin deposits (a chemical substance which acts as a kind of cement and provides hardness) present in the cell wall. These plant tissues have no intercellular gap. Sclerenchyma is present in the covering of the nuts and seeds and in the veins of the leaves. They are around the vascular tissues present in the stem. These plant tissues provide the plant with strength.
- They make the plant stiff and hard.
- These plant tissues are dead.
- There is no space inside the cell.
Permanent Tissues
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Complex Permanent Tissue
Complex Tissues are the ones that are formed of multiple types of cells. All of the complex permanent tissues coordinate with each other to perform a common function. There are two types of complex permanent plant tissues such as xylem and phloem. Both of them are conducting tissue and they constitute a vascular bundle.
1. Xylem
Xylem is a plant tissue that helps in the transportation of water and dissolved substances throughout the plant. Various components of the xylem are xylem fibers, xylem parenchyma, tracheids, and vessels. Tracheids and xylem fibers are formed of lignin and it provides structural support to the plant. The plant tissue is also known as a water-conducting cell. Xylem has thick walls and most of them are dead cells. The four components of the xylem are:
- Tracheids: They are the basic conducting element of the xylem. They are unicellular and water moves from one tracheid to another through pits.
- Vessels: Vessels act as a pipeline during the process of conduction of water. They are highly capable of conduction of water.
- Xylem Fibers: They provide strength to the vessels and tracheids. They are abundantly present in the secondary xylem.
- Xylem Parenchyma: The cell wall is formed of cellulose and stores tannin, starch, and fat. They help in the radial function of the water. The walls of xylem parenchyma possesses pits.
Xylem
2. Phloem
Phloem is a plant tissue that helps in food transportation throughout the plant. The material in xylem can move in both directions. It transports food to all the parts of the plant through the leaves. It is made of four elements which are as follows:
- Sieve Tubes: They are thin wall cells or pores that facilitate the transportation of the materials.
- Companion Cells: They are thin-walled cells and are only found in angiosperms.
- Phloem Parenchyma: They are used for the storage and conduction of food in a radial direction.
- Phloem Fibers: The fibers present in the phloem are called the phloem fibers. They are not generally present in the primary phloem.
Phloem
Protective Tissues
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The protective tissues provide protection to the plants. The protective plant tissues include the epidermis and cork.
1. Epidermis
- Epidermis is a cell layer or a plant tissue that forms an outer protective layer of all the structures of the plant.
- It is perforated by the stomata at a lot of places.
- The stomata prevents the loss of water and help in the exchange of gases.
2. Cork
- Cork is the external protective tissue.
- In mature roots and stems, the cork substitutes the epidermal cells.
- No intercellular gap is present in these cells and they are lifeless.
- A chemical known as suberin is present in these plant tissues and it makes them resistant to water and gases.
Protective Tissues
Things to Remember
- Tissues refer to the building blocks of an organism be it animals or plants. Plant tissues are supportive and provide the plants with strength and support.
- A plant tissue system can be defined as a functional unit that connects all the organs of the plant.
- Meristematic Tissues have the ability to develop further through swift division and support the Majority of the growth of vegetation.
- The simple permanent tissues are the plant tissues that have the same function and are called simple as they are composed of cells that are similar in type and have a common function and origin.
- Complex Tissues are the ones that are formed of multiple types of cells that coordinate with each other to perform a common function.
- The protective tissues provide protection to the plants.
- Epidermis is a cell layer or a plant tissue that forms an outer protective layer of all the structures of the plant.
- A chemical known as suberin is present in the cork that is a protective plant tissue and this chemical makes the plant resistant to water and gases.
Sample Questions
Ques. Define meristematic plant tissues. (5 marks)
Ans. Meristematic Tissues have the ability to develop further through swift division. These plant tissues aid in the growth of the diameter and length of the plant. The meristematic cells present in these tissues are living cells and are cubical in shape having a big nucleus. On the basis of the location of these meristematic plant tissues, they are further classified into three categories:
- Apical Meristems: These plant tissues exist only at the tips of roots and stems. When the cell division starts, this meristem helps in enlargement of the cell and also highly influences the shape of the plants that are mature.
- Lateral Meristem: They are found along the sides of stems and roots. They play an important role in increasing the diameter and width of the stems and roots.
- Intercalary Meristem: The cells present in this tissue are highly active. They have dense cytoplasm along with a prominent nucleus and thin cellulose walls.
Ques. What is xylem? (5 marks)
Ans. Xylem is a plant tissue that helps in the transportation of water and the dissolved substances throughout the plant. The plant tissue is also known as a water-conducting cell. Xylem has thick walls and most of them are dead cells. The four components of the xylem are:
- Tracheids are the basic conducting element of the xylem. They are unicellular and water moves from one tracheid to another through pits.
- Vessels act as a pipeline during the process of conduction of water. They are highly capable of conduction of water.
- Xylem Fibers provide strength to the vessels and tracheids. They are abundantly present in the secondary xylem.
- Xylem Parenchyma is formed of cellulose and stores tannin, starch, and fat. They help in the radial function of the water.
Ques. What are the various types of simple permanent tissue? (5 marks)
Ans. The simple permanent tissues are the plant tissues that have the same function. They are called simple as they are composed of cells that are similar in type and have a common function and origin. They are further classified as:
- Parenchyma are polygonal living cells and have a big central vacuole. Some parenchymatous cells act as storage chambers for the starch that is present in vegetables and fruits.
- Collenchyma are living cells that are stretched out with minor intercellular gaps. It offers flexibility, mechanical support and a structural framework to the plants. It allows various parts of the plant to bend without breaking such as the stem and the leaf.
- Sclerenchyma is dead cells that are elongated with the lignin deposits (a chemical substance that acts as a kind of cement and provides hardness) present in the cell wall. They are around the vascular tissues present in the stem.
Ques. What are simple and complex plant tissues? (3 marks)
Ans. Plant tissues are classified into meristematic and permanent tissues. The permanent tissues are further divided into two categories which are simple and complex plant tissues.
- The simple permanent tissues are the plant tissues that have the same function. They are called simple as they are composed of cells that are similar in type and have a common function and origin. They are further classified into collenchyma, parenchyma, and sclerenchyma.
- Complex Tissues are the ones which are formed of multiple types of cells. There are two types of complex permanent plant tissues such as xylem and phloem. Both of them are conducting tissue and they constitute a vascular bundle. All of the complex permanent tissues coordinate with each other to perform a common function.
Ques. What is epidermis? (5 marks)
Ans. Epidermis refer to the outermost layer of the cell. The epidermis is usually formed of a single layer of cells.
- Epidermis is thicker in some plants that live in dry habitats as they provide protection against the loss of water.
- All the outer surface of the plant has epidermis as the protective layer as it protects all the organs of the plant.
- On the aerial surface of the plant, the epidermal cells secrete a water-resistant and waxy layer on the outer surface of the plant.
- Epidermis provides protection against water loss, invasion by fungi, and various types of mechanical injury.
- The small pores that are present in the epidermis of the leaf are referred to as the stomata.
- Stomata has two guard cells and encloses two kidney shaped cells. Stomata is necessary for the exchange of gases present in the atmosphere.
- The epidermal cells that are present in the roots help in absorption of the water.
- As the plants grow older, the outer protective layer of the plants undergoes various kinds of changes.
Ques. Differentiate between xylem and phloem. (5 marks)
Ans. The differences between the xylem and phloem of the plant are as tabulated below:
| Xylem | Phloem |
|---|---|
| Xylem are tube-like structures that do not have cross walls present on them. | Phloem are elongated structures that are shaped like a tube. It includes thin sieve tubes that are present between the walls of phloem. |
| Xylem plant tissues move only in a unidirectional manner. It only moves in one direction that is upwards. | Phloem plant tissues are bidirectional in nature. These tissues move both the way that is upwards and downwards. |
| The transportation of water molecules and soluble mineral nutrients from the roots to the aerial parts of any plant. | Phloem transports various nutrients and food that also include amino acids and sugar from the leaves to the organs of storage and the growing parts of the plant for growth purpose. |
| Xylem is composed of tracheids, xylem fibers, xylem parenchyma, xylem sclerenchyma, and vessel elements. | Phloem is composed of sieve tubes, phloem parenchyma, companion cells and phloem fibers. |
| Xylem is a plant tissue that helps in the transportation of water. | Phloem is a plant tissue that helps in the food transportation throughout the plant. |
Ques. Mention the classification of plant tissues. (3 marks)
Ans. A group of plant tissues can form plant tissue systems that perform special functions. A plant tissue system can be defined as a functional unit that connects all the organs of the plant. Plant tissues can be broadly categorized into two types which are as follows:
- Meristematic Tissues: Meristematic Tissues have the ability to develop further through swift division. Majority of the growth of vegetation is supported by meristematic tissues. These plant tissues aid in the growth of the diameter and length of the plant.
- Permanent Tissues: Permanent tissues have cells that have lost their ability of distribution as they have gained their mature form. They are specialized as they offer flexibility, strength, and elasticity to the plant.
Ques. What is the need of tissues in living organisms? (3 marks)
Ans. In a unicellular organism, a single cell performs all the required functions of the body. However, once an organism becomes complex, it is no longer possible for a single cell to perform all the required functions to sustain life processes of the organism. To attain all the specialization of tasks, a division of labour becomes necessary. The formation of tissues by joining of these cells result in attainment of that specialization that increases the efficiency of a living organism. Therefore, there is a need for living organisms to form complex tissues.
Ques. Name the plant tissues that specialise in conducting and transportation in plants. (3 marks)
Ans. The vascular tissues of the plants are known as xylem and phloem. Xylem is responsible for transporting minerals and water from the soil to the cells of the plant. Phloem, on the other hand, is a plant tissue that transports the dissolved sugar from the leaves where it is produced to the other plant cells.
Ques. What do you understand about the growth tissues of the plants? Explain how they are classified further and where they are located. (3 marks)
Ans.The growth tissues of the plant are referred to as meristems. Meristems refer to the tissues that help in the development and growth of plants. All the other tissues originated from the meristem plant tissues. They are formed of cells which are undifferentiated and have an intense rate of division of cells. Meristems can further be classified as primary meristems and secondary meristems which are explained as follows:
- Primary meristems are located at the apex of the stem. They are also found in the lateral buds, and the tips and base of shoots that exist within the root cap. These primary meristems are responsible for increasing the length of the plants.
- Secondary meristems are responsible for thickening the plants which is a kind of secondary growth. They are formed of the tissues that thicken the plant stems such as phellogen (cork cambium) and cambium.
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