Tiêu đề Biology_IX_9_Review Questions.pdf ✅

ClassNotes Understanding the Concept Q#1 How would you relate the internal structure of root with the uptake of water and salts? Ans: Water and Ion Uptake: In addition to anchoring the plant, roots perform two other vital functions i. First they absorb water and salts from the soil. ii. Second, they provide conducting tissues for distributing these substances to the tissues of the stem. Root hairs provide large surface area for absorption. They grow out into the spaces between soil particles where they are in direct contact with the water. The cytoplasm of the root hairs has higher concentration of salts than the soil water, so water moves by sis into the root hairs. Salts also enter root hairs by diffusion or active transport. After their entry into the root hairs, water and salts must move through the epidermis and cortex of the root, and then into the xylem tissue in the centre of the root. Pathways through which water travels from the outside of the root to the inside: There are two pathways through which water travels from the outside of the root to the inside www.classnotes.xyz Biology ClassNotes, Inc. © 2020 1
ClassNotes i. The first of these pathways is the apoplast pathway, in which water travels along cell walls and through intercellular spaces to reach the core of the root. ii. Second route for water is the symplast pathway, in which water moves across the root hair membrane and through the cells themselves, via channels (plasmodesmata) that connect their contents. Note: Once in the xylem, the water can be carried to all the aerial parts of the plant. Q.2 Define transpiration and relate it with cell surface and with stomatal opening and closing. Ans: Transpiration: Transpiration is the loss of water from plant surface through evaporation. Opening and closing of stomata: Most plants keep their stomata open during the day and close them at night. Functions of guard cells: It is the responsibility of the stomata to regulate transpiration via guard cells. The two guard cells of a stoma are attached to each other at their ends. The inner www.classnotes.xyz Biology ClassNotes, Inc. © 2020 2
ClassNotes concave sides of guard cells that encloses a stoma are thicker than the outer convex sides. When these guard cells get water and become turgid, their shapes are like two beans and the stoma between them opens. When the guard cells loose water and become flaccid, their inner sides touch each other and the stoma closes. Function of Potassium ions in opening and closing of stomata: Recent studies have revealed that stomata actually open and close due to the movement of potassium ions in and out of guard cells. According blue wavelengths of daylight open stomata by allowing K to flow into the guard cells, from the surrounding epidermal cells. Water passively follows these ions into the guard cells, and as their turgidity increases the stoma opens. As the day progresses, guard cells make glucose. Due to higher concentration glucose, their water potential decreases and water stays in them. At the end of the day the K' flow back from guard cells to the epidermal cells and the concentration of glucose also falls. This initiates the loss of water and reduced turgor pressure in guard cells, which causes the closure of stoma. Q# 3 How do different factors affect the rate of transpiration? Ans: Factors affecting the rate of transpiration: 1. The rate of transpiration is directly controlled by the opening and closing of stomata and it is under the influence of light. In strong light the rate of www.classnotes.xyz Biology ClassNotes, Inc. © 2020 3
ClassNotes transpiration is very high as compared to dim light or no light. Other factors which affect the rate of transpiration are given below. ii. Higher temperature reduces the humidity of the surrounding and also increases the kinetic energy of water molecules. In this way it increases the rate of transpiration. The rate of transpiration doubles with every rise of 10°C in temperature. But, very high temperatures i.e. 40-45°C cause closure of stomata, so that transpiration stops and plant does not lose the much-needed water. iii. When air is dry, water vapours diffuse more quickly from the surface of mesophyll cells into leaf air spaces and then from air spaces to outside. This increases the rate of transpiration. In humid air the rate of the diffusion of water vapours is reduced and the rate of transpiration is low. iv. Wind (air in motion) carries the evaporated water from leaves and it causes an increase in the rate of evaporation from the surfaces of mesophyll. When air is still, the rate of transpiration is reduced. v. The rate of transpiration also depends upon the surface area of leaf. More surface area provides more stomata and there is more transpiration. Q#4 Transpiration is a necessary evil. Give comments? OR Describe the significance of transpiration? Ans: Significance of Transpiration: Transpiration is called a necessary evil. It means that transpiration is a potentially harmful process but is unavoidable too. i. Transpiration may be a harmful process in the sense that it There is strong requires wet surfaces from which evaporation can occur and evidence that even during the conditions of drought loss of water from the plant mild water stress results in wilting, serious desiccation and often death of the plant, results in www.classnotes.xyz Biology ClassNotes, Inc. © 2020 4