Absorption by Roots – The Processes Involved Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 4 Absorption by Roots – The Processes Involved Notes, Summary, Definition, Diagram. Absorption by Roots – The Processes Involved Notes.
4.1 ABSORPTION BY ROOTS:
The roots are important organs because of the following functions:
- Structural support to the plants to keep them firm on land
- Most important function: absorption of water and minerals from surround soil.
4.2 NEED OF WATER AND MINERALS TO PLANTS: water is part of protoplasm and has the following functions:
1.) Photosynthesis: water is used in glucose synthesis by a photosynthesis in green leaves.
2.) Transpiration: during hot climatic conditions water is lost from the leaf surface in form of vapor. This is known as transpiration.
3.) Transportation: due to the transpiration pull, nutrients move in the upward direction along with water. The water also moves from leaves to other parts to carry the food along with it.
4.) Mechanical stiffness: as water pressure develops in a cell the cells of plants become turgid and provide plant with structural support.
- Roots are the only organ in plants which help in absorption of minerals resent in soil in the form of salts or ions.
4.3 CHARACTERS OF ROOTS FOR ABSORBING WATER:
1.) large surface area of the roots: the roots of smallplants have numerous root hair on their surface. These roots if separated this can span a large surface area up to a few kilometers. Hence large surface area facilitates absorption of water
2.) root hair has larger amount of sap facilitating osmosis:the root hairs are epidermal cells containg a large sap filled vacuole. This sap has high amount of salt in it. due to which the sap serves as a solute inside the cell and helps in the inward movement of water.
3.) thin walls of the root hair:there are 2 components:
1.) Cell wall: it is thin and freely permeable to all the substances
2.) Cell membrane: it is thin and selective/ semi permeable.it allows small substances to pass through them.
4.4 ABSORPTION AND CONDUCTION OF WATER AND MINERALS:
Absorption and conduction of water and minerals in plants occurs due to the following five processes:
1.) Imbibition: it is the process driven by surface attraction. Cellulose and proteins are water loving molecules. So, when any material made of such hydrophilic substance comes in contact with water or moisture, it causes the material like wood or seed coat to swell up. This leads to development of imbibition pressure which ultimately leads to the rupture of seedcoat and facilitates germination.
2.) Diffusion: it is the free molecular movement of any kind of gas, liquid, or solvent from area of high concentration to low concentration.
Experiment to demonstrate diffusion:
- Take a beaker which is filled with water.
- Add a small cube or tablet of any dye/sugar/potassium per magnet
OBSERVATION:
- At first the dye is more concentrated near the region of the tablet.
- As time progresses diffusion occurs and causes the dye molecule to spread from area of high concentration (from tablet) to the area where concentration of the dye is less
- The diffusion movement is carried out until the dye spreads uniformly in the beaker.
3.) A. Osmosis: it is the movement of solvent / water molecules from area of higher concentration to lower concentration through a semipermeable membrane. This movement of solvent can also bedefined as movement of solvent from area of lower concentration of solute to higher concentration of solute.
a.) Endosmosis is the movement of solvent inside the cell leading to swelling of cell.
b.) Exosmosis is the movement of solvent outside the cell leading to shrinking of cell.
c.) EXPERIMENT 2:
PROCEDURE: 1.) take a thistle funnel and fill it with concentrated sugar solution. Mark the point on the thistle funnel indicating the level of water in it
2.) Use cellophane paper to cover the mouth of the funnel
3.) The thistle funnel is inverted in a beaker containg water.
4.) for purpose of setting up a control, the same experimental set up can be used but instead of concentrated sugar solution water can be used.
5.) leave the experiment setup for about 3 to 4 hours.
Observation: the water in the thistle funnel rises above the marked point whereas in the control water level remains unchanged.
IMPORTANT CONCLUSIONS: 1.) movement of water can be observed through the cellophane paper.
2.) sugar molecules do not cross the cellophane paper
d.) EXPERIMENT 3: (MODIFIED SET UP OF THE ABOVE-MENTIONED EXPERIMENT 2)
1.) Instead of taking plain water a slightly diluted sugar solution can be used. One can still observe the same results.
2.) If a rubber sheet is used instead of cellophane paper, water molecules are not able to cross the barrier. hence the water level in the thistle funnel remains constant.
3.) If muslin cloth is used as a barrier (pores of muslin cloth are larger than the cellophane paper) then both water and sugar molecules can cross the barrier
e.) IMPORTANT CONCLUSIONS:
A.) The difference in concentration can be expressed in two ways:
1.) in terms of difference in concentration of water
2.) in terms of difference in concentration of sugar
B.) the cellophane paper acts like a membrane barrier
C.) the membrane barrier should be selectively permeable
B. OSMOTIC PRESSURE: When solution and solvent are separated by means of a semipermeable membrane, OSMOTIC PRESSURE is the lowest possible pressure required to prevent the entry of pure solvent in the solution.
- TONICITY: it is the comparative concentration value. It helps in finding out the degree and direction of diffusion
I) ISOTONIC: a solution in which there is no net movement of water molecules across membrane.
II) HYPOTONIC: for a cell when endosmosis occurs, water enters the cell from outside the cell. the solution has less amount of solutes as compared to the cell. hence it is called hypotonic
III) HYPERTONIC: for a cell when exsmosis occurs, water leaves the cell from outside the cell. the solution has more amount of solutes as compared to the cell. Henceit is called hypertonic
4.) Active transport:
- It is the transport of uncharged molecules from area of low concentration to high concentration with involvement of energy.
- The direction for active transport is in opposite direction of diffusion.
- The passive transport (diffusion) does not use energy in form of ATP.
5.) Turgidity and flaccidity:
- Plant roots are in continuous contact with soil water. this soil water enters the root hair till the cell sap is more concentrated.
- Turgidity is a fully expanded state of a cell in which the cell can not gain any more fluid.
- Turgor pressure is the pressure generated on the walls of the cell because of cell content. The cell wall exerts wall pressure against the cell content.
- If the pressure on the cell exceeds the turgor pressure, the cell will rupture or burst open
- Turgor pressure = Wall Pressure, no movement of water is observed from inside or outside the cell
Plasmolysis: Any cell placed in hypertonic environment losses water. This leads to shrinkage of cell. This phenomenon is called Plasmolysis
Flaccidity: It is a process which is opposite to turgidity. When the cell is in a shrunken state it is termed as flaccid
- Use of turgidity to plants:
1.) it imparts firmness to the plant. It promotes wilting in plants. In pickle preparation and preservation of meat salting process is carried out to kill the bacteria, by enhancing plasmolysis.
2.) turgor pressure helps the germinating seed, mushroom to rise above the ground
3.) turgor pressure helps development of root pressure. root pressure is upward movement of cell sap due the increased osmosis
4.) turgor pressure is important for the process of transpiration, opening and closing of stomata
5.) turgor assists in movement of leaves that is drooping and recovery of plants like mimosa.
Imbibition is the direct diffusion of water through cellulose cell wall
4.5 ROOT PRESSURE:
Osmosisis responsible for generation of root pressure. The development of turgor pressure in plant cells leads to movement of water. The cells of plants have ability to absorb the water and send it to xylem vessel towards the center. Hence root pressure helps in movement of water from root to leaves but this is not enough to pushes the water to tall plants.
Guttation: the water in small plants can travel from the roots to the leaves with help of root pressure alone. This is called as guttation. The water drops can be seen at the end of leaves are due to guttation.
4.6 IMPORTANCE OF ROOT HAIR AND UPWARD MOVEMENT OF ABSORBED WATER AND MINERALS
1.) ABSORPTION OF WATER: Roots have specialized structure called root hair. The root hair absorbs water from soil.The plant cells have sap in them. Due to the higher concentration of sap in root hair water in the adjacent soilgets absorbed inside the root by diffusion. The entering of water makes the cell turgidand helps in movement of water toward the leaves.
2.) ABSORPTION OF MINERALS: minerals in form of ions are actively transported in the cells from the soil. The movement of the minerals up to the leaves is important to synthesize food.
4.7 EXPERIMENTS ON ABSORPTION AND CONDUCTION OF WATER IN PLANTS:
- EXPERIMENT 1
- Aim: To show water is absorbed by roots
- Take 2 test tubes and label them as control and test.
- Follow the following procedure:
Control | Test |
1.) Add water in the test tube | Add water in the test tube |
2.) Add a few drops of oil to prevent waterloss | In this tube place a small balsam plant along with its roots |
3.) | Add a few drops of oil to prevent waterloss |
4.) Observe the tube after 24 to 48 hours | Observe the tube after 24 to 48 hours |
5.) Results: no water loss | As the plant root absorb water there is water loss |
EXPERIMENT 2
- Aim: To show xylem is the channel to conduct water in plants
- Take a small sized balsam plant.
- This plant is now immersed in eosin (pink) containing solution.
- This setup is kept undisturbed for 3 – 4 hours.
- Take the plant and wash with tap water and take transverse section of the root, leaves, and stem.
- Observation:
- The water conducting xylem vessel are stained red in color.
EXPERIMENT 3
- Aim: To show xylem is the channel to conduct water in plants
- Two leafy shoot of balsam plant are taken and cut under water to avoid air bubble from entering the vascular tissue. Also dip the lower end of plantlet in water.
- Label the plant as A and B.
- For plant A, remove theoutermost ring of phloem about 3 cm (gridling).
- For plant B, remove the innermost ring of xylem keeping the phloem intact.
- Fix both the plants with their roots immersed in water and keep still for 2 days.
- Observation: the plant a is normal, plant b appears droopy and wilted.
EXPERIMENT 4
- Aim: To show phloem is the channel to conduct food material in plants
- Take a potted guava plant.
- For the same plant remove the outermost ring of phloem about 3 cm (gridling)
- Observe the plant for a few weeks
- Observation: the plant part above the gridling appears swollen and the part below the phloem is dead or weak
4.8 FORCES CONTRIBUTING TO ASCENT OF SAP
- Root pressure, capillarity, transpiration pull, adhesion are the forces contributing to ascent of sap.
- Root pressure creates pressure in the roots to push the water up in xylem sap. The pressure generated is enough to push the water in upward direction up to a certain height. This system works best in herbaceous plants.
- Transpiration pull is responsible for pulling water upwards in most of the plants. Water is lost from leaf surface due to evaporation. Due to this water loss and cohesion between water molecules the water is pulled in the upward direction from the roots creating a continuous column is created in the stem
- Adhesion is the attaching of the water molecules to cell surface. This force helps to bring together more water molecules below the leaf surface to compensate for the water loss due to transpiration.
- Capillary force is due to smaller diameterof xylem vessel which leads to the upward movement of water. This helps water to reach great height in plants.
- Downward movement of sap is mainly due to gravitational force.
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