Plant and Animal Tissues

Chapter 15

Plant and Animal Tissues

Plant Tissues

• Depending upon their oripin, structure and physiology, the plant tissues can be classified as follows:

• (I) Meristematic or embryonic tissues

• (II) Permanent tissues

• (I) Meristematic Tissues: They have the following characters.

• 1. The cells are small and isodiametric in nature.

• 2. The cells are very compact and without any intercellular spaces.

• 3. The cells are thin walled, normally cubical and with prominent nucleus.

• 4. Vacuoles in meristematic tissues are very small or even may be absent.

• 5. Their cells have capacity to multiply.

• 6.The newly formed cells due to enlargement and also due to morphological differentiation get transformed or changed into permanent tissue. Meristematic tissues in the plants are located at the growing points i.e. tips of the shoots and roots, between the bark and the wood of trees, in the bark themselves and also in any part of the plant wheresoever extensive growth of the plant takes place.

• (A) Simple Permanent Tissues:

• As described above, this consists of only one type of cells forming homogeneous structure. These are further sub-classified as

• (1) Epidermis, (2) Parenchyma, (3) Sclerenchyma, (4) Collenchyma, (S) Cork.

• 1. Epidermis: It is a type of simple permanent tissue forming the outermost layer of plant structure and normally only one cell thick and is made up of parenchyma. It occurs as surface layer of leaves, flowers, fruits, seeds and younger parts of roots and stems.

• Its function is to conserve the moisture supply to the inner tissues and offer protection to certain extent against mechanical infection.

Animal Tissues

• The outer nuclear membrane bears ribosomes which may continue with the membrane of endoplasmic reticulum.

• Mitochondria:

• Within the cytoplasm, there are numerous double layered elongated bodies present called mitochondria. It is composed largely of proteins and lipids. Each mitochondrion is composed of tubular or paired Ameia called cristae. It is the site for carbohydrate and lipid (fat) metabolism i.e., respiration.

• Golgi Apparatus:

• The Golgi apparatus (body) is compact and consists of parallel membrane plates and tubules. It is the site for enzyme secretion.

• Endoplasmic Reticulum and Ribosomes:

• Within the cytoplasm of the cell is an extensive network of membrane arranged in plates and tubules, collectively known as the endoplasmic reticulum. It is the site for biochemical synthesis and intracellular transport of molecules. The endoplasmic reticulum present is attached to the nuclear membrane and the plasma-membrane. On the membrane of endoplasmic reticulum, there are small round bodies present called ribosomes. It is the site for protein synthesis. The endoplasmic reticulum with the ribosomes is called the rough endoplasmic reticulum, while devoid of ribosomes it is called the smooth endoplasmic reticulum.

• Lysosomes:

• The lysosomes are small vesicular structures containing homogeneous fluid. It is composed of a single layer and contains digestive enzymes for intracellular digestion.

• Microtubules:

• These are tubular structures composed of globular protein and held for intracellular transport.

• Microfilaments:

• These are protein filaments in the cytoplasm meant for contraction and motility of then cell.

• The animal cell is responsible to perform functions like motility, digestion, metabolism, growth, reproduction and irritability.

• Animal Tissues:

• The animal body is composed of cells which are grouped together to form a tissue. An organ of the body consists of various tissues of common function. The tissues may be simple or compound. A simple tissue is a combination of similar cells while different kinds of cells together form a compound tissue. Simple tissues can be broadly classified into four groups

• 1. Epithelial, 2. Muscular, 3. Connective, and 4. Nervous.

• 1. Epithelial Tissues:

• Epithelial tissue is a group of cells present on the free surface of organs or lining of cavities. The cells are compound, arranged with little intercellular space. The functions of epithelial tissues are protection, absorption, secretion, excretion, reproduction etc.

• Epithelia are classified according to their shape and the arrangement of cells.

• These are grouped into simple and stratified epithelia. The simple epithelia are

• (a) Squamous, (b) Collumnar, (c) Cuboidal and (d) Ciliated. The stratified epithelia are

• (i) stratified squamous, (ii) stratified columnar and (iii) stratified transitional.,

• A. Simple Epithelium:

• (a) Simple Squamous Epithelium: It consists of a single layer of flattened cells. The nucleus is oval and present in the Centre of the cell. This type of epithelium can be obtained from the skin of frog or Bowman's capsule and Henle's loop of mammal.

• (i) Stratified Squamous Epithelium:

• It consists of three layers of cells. The first layer consists of flattened and fusiform cells, the second polygonal cells and the third basal cuboidal cells. The outermost layer is cornified. The cells of the basal layer consist of spherical nuclei. This type of epithelium is found in the esophagus and epidermis.

(i) Supporting or Skeletal Tissue:
It consists of bone, cartilage and hyaline cartilage. The cartilage is found on the tip of the bones of girdles and limbs. These are also found in the trachea and the larynx. The cartilage with yellow elastic fibers in the matrix is called cartilage and is found in the external ear and the nose. The hyaline cartilage consists of many elastic fires (Fig. 15.14 (b)). Most part of the endoskeleton is made of bones. The bone comprises the hardest tissues.

• (ii) Fluid or Blood Tissue:

• Blood is called fluid conductive tissue. Blood is present in vessels, like the arteries and the veins. The blood consists of plasma in which corpuscles are suspended. These are erythrocytes (R.B.C.) and leucocytes (W.B.C.). The plasma corresponds to matrix did the corpuscles, to the cells. The corpuscles are round and nucleated in frog and non-nucleated in mammal. The leucocytes are irregular in shape with nuclei inside.

• 1. Nervous Tissue:

• Nervous tissues are formed by nerve cells and nerve fibres. Thèse can be divided into

• (a) nerve cells or neurons, (b) medulated nerves and (c) non-medulated nerves.

• (a) Neurons: The neurons are found in the brain, spinal cord and nerve ganglia. A typical neuron has a large cell body containing a nucleus. From the cell body several fine nerves develop called dendrites. A single Iang nerve arising from the cell body is called axon. The axon conducts impulses away from the cell body while dendrites towards the cell body. The axon is covered by a sheath called the medullary sheath. The medullary sheath is not continuous but is broken in the middle. The breaks are called nodes of Ranvier. The modulated nerve is an axon covered by modulated sheath, which is the sheath covered by a layer called neurolemma. It is a sample layer of nucleated cells and is known as white nerve fiber. At intervals, the sheath breaks to form nodes of Ranvier.