Epithelial cells often acquire additional specialisation as gland cells which

Epithelial cells often acquire additional

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Epithelial cells often acquire additional specialisation as gland cells, which can secrete substances at the epithelial surface. Sometimes a portion of the epithelial tissue folds inward, and a multicellular gland is formed. This is glandular epithelium. Blood is a type of connective tissue. The cells of connective tissue are loosely spaced and embedded in an intercellular matrix. The matrix may be jelly like, fluid, dense or rigid. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. The plasma contains proteins, salts and hormones.
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12 RAJESH NAYAK Tendons connect bones to muscles and are another type of connective tissue. Tendons are fibrous tissue with great strength but limited flexibility. Another type of connective tissue, cartilage, has widely spaced cells. The solid matrix is composed of proteins and sugars. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx. We can fold the cartilage of the ears, but we cannot bend the bones in our arms. Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It fills the space inside the organs, supports internal organs and helps in repair of tissues. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement. striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei). involuntary muscles control such movements. They are also found in the iris of the eye, in ureters and in the bronchi of the lungs. The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles. The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. CHAPTER-7-DIVERSITY IN LIVING ORGANISMS Organisms which have ancient body designs that have not changed very much. The warm and humid tropical regions of the earth, between the tropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. This is called the region of megadiversity. Of the biodiversity of the planet, more than half is concentrated in a few countries Brazil, Colombia, Ecuador, Peru, Mexico, Zaire, Madagascar, Australia, China, India, Indonesia and Malaysia. a species includes all organisms that are similar enough to breed and perpetuate. Protista This group includes many kinds of unicellular eukaryotic organisms.
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