Tissues

Q63. What does a neuron look like?

Ans. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. Usually each neuron has a single long part, called the axon, and many short, branched parts called dendrites. An individual nerve cell may be up to a metre long.

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Q64. Why is epidermis important for the plants?

Ans. The outermost layer of cells is called epidermis. In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical. The entire surface of a plant has this outer covering of epidermis. It protects all the parts of the plant. Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi. 

Q65. Name the different components of xylem and draw a living component.

Ans. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Only xylem parenchyma is the living component.

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Q66. Draw and identify different elements of phloem.

Ans. Phloem is made up of four types of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma.

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Q67. Fill in the blanks.
(a) ______ are forms of complex tissue.
(b) ______ have guard cells.
(c) Cells of cork contain a chemical called ______.
(d) Husk of coconut is made of ______ tissue.
(e) ______ gives flexibility to plants.
(f) ______ and ______ are both conducting tissues.
(g) Xylem transports ______ and ______ from soil.
(h) Phloem transports ______ from ______ to other parts of the plant.

Ans. (a) Xylem and phloem

(b) Stomata

(c) Suberin

(d) Sclerenchyma

(e) Collenchyma

(f) Xylem; Phloem

(g) Water; Minerals

(h) Food; Leaves

Q68. Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.

Ans. Parenchyma – It is a type of permanent tissue. The cells of this tissue are living. It consists of relatively unspecialized cells with thin cell walls.

Collenchyma - It is a type of permanent tissue. The cells of this tissue are living, elongated and irregularly thickened at the corners.

Sclerenchyma - It is a type of permanent tissue. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin (a chemical substance which acts as cement and hardens them).

Q69. Diagrammatically show the difference between the three types of muscle fibres.

Ans. Cardiac muscles cells are cylindrical, branched and uninucleate.

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Smooth muscles are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles.

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Striated muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei).

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Q70. Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body.

Ans. 

Q71. Differentiate between voluntary and involuntary muscles. Give one example of each type.

Ans.