Q18 of 216 Page 486

It was observed that the leaves of a plant started getting wilted. Name the tissue which might have blocked. State the role of this tissue in plants.

ii. Explain opening and closing of stomata with the help of labelled diagrams.


iii. Name the physical phenomenon by which exchange of gasses occur between plant body and atmosphere.

1) The leaves of a plant started getting wilted, the tissue that might have blocked is Xylem. Wilting generally means drooping or falling due to lack of water. Xylem is responsible for water transportation, hence, it might have been blocked.


Role of xylem in plants:


i. It is a vascular tissue that helps in transportation.


ii. The xylem is responsible for the transport of water and minerals in the plants.


iii. It transports water from roots to the stem. Hence, its flow is only in one direction (unidirectional).


iv. Xylem also provides mechanical support to the plant.


v. The xylem has four different elements: tracheids, vessels, xylem fibres and xylem parenchyma.


vi. The xylem parenchyma stores food material in the form of starch.


2) Opening and closing of stomata:


• The opening and closing of stomata depend upon the guard cells.


• The guard cells are bean-shaped cells will allow as well as prevents the entry of water.


• When the water enters the guard cells, they swell. The swelling of guard cells results in the opening of the stomatal pore (also known as stomatal aperture).


• When the water flows out of the guard cells, the guard cells shrink, and the pore closes.


• The open and closed stomata are shown in the diagram below:



3) The physical phenomenon by which the exchange of gasses occur between plant body and atmosphere Respiration.


During respiration the plant uses O2 and form energy and CO2, this carbon dioxide at night is released in the atmosphere whereas during day time this carbon dioxide is used in the process of photosynthesis to form food.


More from this chapter

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16

A dry pallet common base ‘X’, when kept in open air absorbs moisture and turns sticky. The compound is also a by-product of chlor-alkali process. Identify ‘X’. What type of reaction occurs when ‘X’ is treated with strong acid? Write a balanced chemical equation for such a reaction.

ii. Can we store the ‘X’ in an aluminium container? Give reason in support of your answer.


OR


Give a suitable reason for the following statements:


i. Rain water conducts electricity but distilled water does not.


ii. We feel burning sensation in the stomach when we overeat.


iii. A tarnished copper vessel regains its shine when rubbed with lemon.


iv. The crystals of washing soda change to white powder on exposure to air.


v. An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.

 17

In the following table, six elements A,B,C,D,E and F of the modern periodic table with atomic numbers 3 to 18 are given:


i. Which of these is (a) Noble gas, (b) halogen?


ii. Which of these is the most active metal in 3rd period?


iii. Identify the most electronegative element in the third period.


iv. In the compound between B and F, what type of bond will be formed?


v. What would be the nature of oxide formed by C?

 19

i. Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions.

ii. Name the parts of the human female reproductive system where fertilisation occurs.


iii. Explain how the developing embryo gets nourishment inside the mother’s body.

 20

Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the Question s that follow, without doing any calculations:


i. What is the focal length of the convex lens? Give reason in support of your answer.


ii. Write the serial number of the observation which is not correct. How did you arrive at this conclusion?


iii. Take an appropriate scale to draw ray diagram for the observation at S.No.4 and find the approximate value of magnification.


OR


i. To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.


ii. A concave mirror produces three times magnified image on a screen. If the object is place 20 cm in front of the mirror, how far is the screen from the object?


i. For observation no.3 clearly shows that the focal length is + 15 cm.