Question

please give correct answers​

Answer 1

EPITHELIAL TISSUES

• It consists of cells which form membranes.
• This membrane covers the body surface and the glands.
• The covering or protective tissues in the animal body are epithelial tissues.
• Epithelium covers most organs and cavities within the body.
• It also forms a barrier to keep different body systems separate.
• The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.
• The cells are tightly packed and form a continuous sheet.
• They have only a small amount of cementing material between them and almost no intercellular spaces.

These are divided into four types:-

SIMPLE

• The cells are extremely thin and flat and form a delicate lining.
• The lining of oesophagus and the mouth are covered with squamous epithelium.

STRATIFIED

• The cells are arranged in many layers to prevent wear and tear.
• Since they are arranged in a pattern of layers, the epithelium is called stratified squamous.
• The skin, which protects the body, is made of squamous epithelium.

COLUMNAR

• The columnar (meaning ‘pillar-like’) epithelium facilitates movement across the epithelial barrier.
• It is present where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present.
• In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells.
• These cilia can move, and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.

CUBOIDAL

• Cuboidal epithelium (with cube-shaped cells) forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support.
• 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.

Q: Experimentally show that cathode rays travel in straight line.

William Crookes in 1879 demonstrated that cathode rays travel in straight lines. He placed an opaque object like metal cross in the path of cathode rays in a discharge tube. It was observed that a sharp shadow of the cross was cast on the glass behind the cross. A shadow of metal cross under the circumstances can be formed only if cathode rays travel in straight lines and cannot bend round the corners of the metal cross.

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