The contractile vacuole expels excess fluid from the cell.
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<h3>⇝ <u>Epidermis</u> :</h3>
Protective tissues includes epidermis & cork. Epidermis is basically a simple permanent tissue, protective in function. It forms one-cell-thick covering over all the parts of plant.
<h3>⇝ <u>Characteristics of Epidermis</u> : </h3>
- Epidermis is formed of living cells, arranged in a single layer.
- In aerial parts, epidermis is covered with a waterproof and noncellular waxy covering called cuticle.
- Cells form a continuous layer, but in leaves epidermis has small openings called stomata.
- Each stoma is guarded by a pair of bean-shaped guard cells which govern opening & closing of stomatal aperture.
<h3>⇝ <u>Functions of Epidermis</u> :</h3>
- Epidermis protects the underlying tissues from mechanical injury, chemicals & infection.
- Cuticle of epidermis protects against water loss & desiccation. It checks the rate of transpiration & evaporation and prevents wilting.
- Stomata in the epidermis of leaves help in gaseous exchange during respiration & photosynthesis.
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The period of Convalescence is the time during which the person regains health and fully recovers.
Explanation:
- Diseases that can spread from one person to other are called infectious disease.
- Disease development is divided into Incubation period, Prodromal period, period of illness, Decline period, and period of Convalescence.
- During incubation period the pathogen enters the host body and starts multiplying itself. But the signs of diseases are unnoticeable.
- Then comes the prodromal period, when the pathogen keeps multiplying itself and some signs of disease are observed but they are not obvious
- After the prodromal period comes the period of illness when the patient exhibits obvious signs of sickness.
- As the period of illness is over the symptoms of disease start to cease and the the number of pathogen decrease in body.This period is the period of decline.
- Finally comes the period of Convalescence when the person returns to his pre-disease state and is completely healthy. (except irreversible damage caused by the disease)
