ICSE Class 9 Biology Chapter 03 Tissues Plant and Animal Tissues

Tissues - Plant And Animal Tissues

Syllabus: Tissues: Types of plant and animal tissues.

A brief understanding of their location, basic structure and functions, with examples. A brief understanding of their role in different physiological processes in plants and animals.

A single cell working on its own would achieve very little inside an animal or a plant. So, many similar cells lying side by side work together as a team to perform the same function. Such groups are called tissues. We will describe here only the more common plant and animal tissues.

Tissues - The Teams Of Workers

A tissue is a group of similar cells performing a specific function.

Most plants and animals possess a tissue system. The human body, for example, has an epithelial tissue covering the skin, the muscular tissue made up of muscle cells which by contraction bring about movements. In a plant, the conducting tissue conducts water upwards from the soil to the aerial parts and food prepared from the leaves to the lower parts.

Relationship between tissue, organ, organ system and organism. Several tissues together contributing to some specific function inside the body constitute an organ (such as tongue having epithelial cells, nerve cells, muscle cells, etc.). Many organs acting together to perform a specific life process constitute an organ system (such as the digestive system). Organ systems together constitute the organism (e.g. the root system and the shoot system constitute the plant, an organism).

Plant Tissues

Plant tissues are basically of two types-

A. Meristematic tissue (cells can multiply to produce new cells) (Gk. meristos; divided).

B. Permanent tissue (non-dividing cells and specialised).

A. Meristematic Tissue Or Meristem

Found at all growing points of a plant, such as the tips of roots, stems and branches (Fig. 3.1).

Also present between the bark and the wood of trees where it leads to growth in the diameter of the stem.

Chief characteristics of meristematic tissue:

(1) Cells are small.

(2) Cells are usually cubical.

(3) Cell wall is thin.

(4) Nuclei are large.

(5) Vacuoles almost absent.

(6) Cells tightly packed with almost no intercellular spaces.

(7) The cells actively divide adding new cells to the plant.

(8) New cells thus produced are transformed into mature permanent tissues.

The meristematic tissue can be classified into two categories: Apical meristem and Cambium or lateral meristem.

Fig. 3.1 A- Longitudinal section of stem tip, together with the differentiating leaves and the axillary buds. B-Meristematic cells undergoing cell division in the root tip of an onion.

Teacher's Note

When you observe a plant growing taller each season, you're seeing meristematic tissue at work - similar to how your body grows taller during childhood through cell division in your growth plates.

(i) Apical or Terminal. This is located near the tips of roots and stems and also in the growing young leaves near the tips of stems, as well as on the tips of axillary buds.

(ii) Cambium or Lateral meristem. This is situated below the bark and is responsible for increase in the diameter of the stem.

B. Permanent Tissues

Permanent tissues are made up of cells which have lost their ability to divide. They take a permanent shape to perform some permanent functions. They may be living (nucleus present) or dead (nucleus absent).

According to the function performed the permanent tissues are of three types: Protective, Supporting and Conducting.

1. Protective Tissue

Cells with thick walls.

Found on the surface of roots, stems and leaves.

Examples: Epidermis of leaves which secretes a waxy water-proof material. Cork cells in the barks contain another strong water-proof material.

2. Supporting Tissue

Supporting tissue is of several types. The three most important ones are (a) parenchyma, (b) collenchyma, and (c) sclerenchyma.

(a) Parenchyma

Large thin walled cells, oval, circular or polygonal in shape.

Usually a single large vacuole (Fig. 3.2A)

Found in soft parts of plants, such as in the cortex (outer region) and in the pith (central region)

May store food as in potatoes (Fig. 3.2B)

Provide temporary support to the plant

Some parenchymatous cells, particularly in the leaf, contain chloroplasts and are termed chlorenchyma (chloros: green). Chlorenchyma helps the leaf to produce food by photosynthesis.

(b) Collenchyma

Made up of cells which are elongated and the cell wall is thickened at the corners. (Fig. 3.3).

It is found in the leaf stalks and below the epidermis of stems. The tissue helps to support the parts of a plant.

Fig. 3.3 Collenchyma. A-Longitudinal view. B-Cross section.

(c) Sclerenchyma

Composed of long, narrow cells, which have become dead; these cells develop very thick walls due to the deposition of lignin. This tissue provides strength to plant parts. It is found in stems and veins of the leaves (Fig. 3.4).

Fig. 3.4 Sclerenchyma. A-Longitudinal section; B-Cross section.

The above three categories namely, parenchyma, collenchyma and sclerenchyma, are grouped as simple tissues, each being made up of one type of cell.

Fibres and stones

Ropes, mats and certain textiles are made from plant fibres such as those of linen and hemp. These fibres are the sclerenchyma cells.

The hard walnut shells and the gritty masses in the skin and the pulp of pears are made up of sclerenchyma cells, here known as stone cells.

Teacher's Note

When you bite into a pear and feel the gritty texture, you're actually crunching on stone cells - a perfect example of sclerenchyma providing structural support in fruit.

3. Conducting Tissue

Conducting tissue, also called the vascular tissue, provides a passage for water and dissolved materials to move up and down in the plant. The xylem and phloem are the two types of conducting tissues.

(a) Xylem cells are elongated and thick-walled. These cells are somewhat in the form of tubular passages (Fig. 3.5). They provide for upward movement of water and dissolved materials absorbed from the soil by the roots to other parts of the plant. Older xylem (xylo: wood) tissue forms the wood and does not participate in transport. You can determine the age of a tree by counting its annual rings which actually are the xylem rings (Fig. 3.6). The xylem tissue consists of tracheids and vessels, also called tracheary elements, and xylem parenchyma respectively.

Fig. 3.7 A variety of shapes of tracheids (xylem elements)

Xylem Vessels or tracheae are long tube-like structures meant for transporting water, and dissolved minerals. They are made up of elongated cells placed end to end. Their cell walls are quite hard, thick and lignified. Transverse walls get dissolved and make a continuous water pipe.

Xylem parenchyma consists of living parenchyma cells associated with the xylem. These cells serve for the storage of food (sugars and starch), and also help in the conduction of water and minerals.

(b) Phloem cells (phloos: bark) provide a passage for the downward movement of food manufactured in the leaves to various parts of the plant. They also provide for the upward movement of the prepared food towards the growing new leaves. The phloem consists of sieve tubes, companion cells, phloem parenchyma cells and phloem fibres (Figs. 3.5, 3.8).

Fig. 3.8 Phloem cells. A-Longitudinal section, B-Cross-section.

Sieve Tubes: Made up of elongated cells placed end to end forming a long tube. The transverse walls are perforated and called sieve plates. They help in the transport of food from leaves to storage organs and other parts of the plant.

Companion cells: Living parenchyma cells closely associated with sieve tube cells. They help in the functioning of the sieve tube cell.

Phloem parenchyma: Parenchymatous tissue found associated with phloem. Mainly concerned with storage of starch, fat and other organic food material.

Phloem Fibres: Sclerenchymatous tissue found associated with phloem. They mainly provide support.

The xylem and phloem collectively form the vascular bundles. The veins of leaves are examples of vascular bundles. They are in continuity with the conducting tissues of stem and root.

The above two tissues, xylem and phloem, are also termed complex tissues being made of more than one type of cells working together as a unit.

Summary Of Plant Tissues

Teacher's Note

Think of the xylem and phloem in plants like the arteries and veins in your body - one carries water and minerals up, while the other transports nutrients down to where they're needed most.

Progress Check

1. What are the two basic types of plant tissues?

2. Give the technical terms for the following:

(i) The category of plant tissues that have lost their ability to multiply.

(ii) The kind of plant cells with thin walls and usually a single large vacuole.

(iii) Elongated cells which are thickened at the corners.

(iv) The two types of tissues which provide the upward movement of water and dissolved materials from the roots to other parts of the plant.

3. Mention if the following statements are true (T) or false (F).

(i) Phloem cells carry manufactured food from leaves to other parts.

(ii) Veins of leaves have both xylem and phloem.

(iii) The older xylem tissue does not participate in transport.

(iv) The sclerenchyma consists of actively dividing cells.

3.3 Animal Tissues

The main kinds of animal tissues are as follows:

1. Epithelial tissue

2. Connective tissue

3. Muscle tissue

4. Neural tissue

1. Epithelial Tissue

Epithelial tissue is a thin, protective continuous sheet of cells.

Location: It covers the surface of the body and lines the various body cavities and internal organs, including the blood vessels. Examples: The outermost layer of skin and the lining surfaces of the mouth, nose, lungs, stomach, etc.

Shape: Epithelial cells may be flat, cuboidal or columnar in shape.

In all cases the cells of the epithelial tissue fit tightly together leaving no space between the cells.

Function: The epithelial tissue functions for protection (as on skin), absorption, secretion (as in intestine), sensory perception, etc. Its five structurally distinct categories are as follows:

(a) Squamous epithelium (Fig. 3.9 A) is composed of cells, which are thin, flat with prominent nuclei closely packed. Examples: Found lining the mouth and nasal cavities, blood vessels and lymph vessels.

The squamous epithelium protects the underlying parts from mechanical injury, germs, harmful chemicals, and drying up.

(b) Stratified epithelium (Fig. 3.9 B): Found in the skin and the cornea. It is composed of several layers (strata) of the same or different kinds of epithelial cells.

(c) Cuboidal epithelium (Fig. 3.9 C) is found in some parts of kidney tubules and in some glandular ducts such as those of salivary glands, pancreatic duct.

(d) Columnar epithelium (Fig. 3.9 D) contains vertically arranged cylindrical or brick-like cells. These cells are usually tall in size. Columnar epithelium is generally found in the inner lining of the stomach and intestines.

(i) Ciliated columnar epithelium (Fig. 4.9 E): At some places in the body, such as in the lining of the trachea (wind pipe), the columnar epithelium is ciliated. The cells of ciliated epithelium have thread-like protoplasmic projections called cilia, at their free ends. The cilia constantly keep lashing and move the materials which enter these regions.

(ii) Glandular epithelium (also a kind of columnar epithelium) contains some large cells which secrete certain chemical substances. Such cells are common in the lining of the stomach and the intestine. At certain places in the body the glandular epithelium is folded inward to form compact, hollow or tubular glands, for example, the sweat glands, tear glands or the liver.

Fig. 3.9 Different kinds of epithelial tissue in the animal body

Teacher's Note

Your skin's outer layer is stratified epithelium - multiple layers of cells that protect you from cuts, bacteria, and the environment, replacing itself completely every few weeks.

This is a preview of the first 3 pages. To get the complete book, click below.