In the chapter “Absorption By Roots – The Process Involved” delve into how plants, specifically through their roots, take up water and essential minerals from the soil. It’s a fascinating process that’s vital for a plant’s survival and growth.
You’ll learn about root hair cells, which are tiny, delicate extensions of the epidermal cells of the root. They’re in close contact with the soil particles and the film of water surrounding them.
The chapter explains that water absorption primarily occurs through osmosis. You’ll recall that osmosis is the movement of water molecules from a region of higher water concentration (the soil water, which is a dilute solution) to a region of lower water concentration (inside the root hair cell, which has a denser cell sap) across a selectively permeable membrane. As water enters the root hair cell, it creates a pressure, pushing the water further into the root’s inner tissues – the cortex, endodermis, and eventually the xylem, which acts like a pipeline to transport water upwards to the rest of the plant.
Alongside water, roots also absorb mineral ions. This process is often more complex. While some ions might move passively with the water, the absorption of most mineral ions is an active process. This means it requires the plant to expend energy, often in the form of ATP, to move ions against their concentration gradient – from a region of lower concentration. This active transport is carried out by specific protein carriers in the cell membranes of the root hair cells.
In essence, the chapter highlights the sophisticated mechanisms – passive (osmosis for water) and active (for most mineral ions) – that roots employ to draw sustenance from the soil, forming the fundamental basis of plant life.
A. MULTIPLE CHOICE TYPE:
1)Absorption of water by the plant cells by surface attraction is called:
(a) Diffusion
(b) Osmosis
(c) Imbibition
(d) Endosmosis
Ans : c) Imbibition
2) A plant cell placed in a certain solution got plasmolysed. What was the kind of solution?
(a) Isotonic sugar solution
(b) Hypotonic salt solution
(c) Hypertonic salt solution
(d) Isotonic salt solution
Ans : c) Hypertonic salt solution
3) The state of a cell in which the cell wall is rigid and stretched by the increase in volume due to the absorption of water is called.
(a) Flaccidity
(b) Turgidity
(c) Capillarity
(d) Tonicity
Ans : b) Turgidity
4)Which one of the following is a characteristic NOT related with the suitability of the roots for absorbing water?
(a) Tremendous surface area
(b) contain cell sap at a higher concentration than the surrounding soil water
(c) Root hairs have thin cell walls
(d) Grow downward into the soil
Ans :(d) Grow downward into the soil
5) Movement of molecules of a substance from the region of their higher concentration to the region of their lower concentration without the involvement a separating membrane, is called
(a) Osmosis
(b) Diffusion
(c) active transport
(d) Capillarity
Ans : (b) Diffusion
6) Osmosis and diffusion are the same except that osmosis there is:
(a) a freely permeable membrane
(b) a cell wall in between
(c) a selectively permeable membrane in between
(d) an endless inflow of water into a cell
Ans : (c) a selectively permeable membrane in between
7) The highest water potential (capacity to move out higher concentrated solution) is that of
(a) Pure water
(b) 10% salt solution
(c) Honey
(d) 50% sugar solution
Ans : (a) Pure water
8) The space between the cell wall and plasma membrane in a plasmolysed cell is filled with.
(a) isotonic solution
(b) hypotonic solution
(c) Hypertonic solution
(d) water
Ans :(d) water
9) What is responsible for guttation?
(a) Osmotic pressure
(b) Root pressure
(c) suction pressure
(d) Capillarity
Ans : (b) Root pressure
10)The most appropriate characteristic of a semipermeable membrane is that
(a) it has minute pores
(b) it has no pores
(c) it allows the solute to pass through but not the solvent
(d) it allows a solvent to pass through freely but prevents the passage of the solute.
Ans : (d) it allows a solvent to pass through freely but prevents the passage of the solute
VERY SHORT ANSWER TYPE:
1) Name the following:
(a) The condition of a cell placed in a hypotonic solution.
(b) The process by which intact plants lose water in the form of droplets from leaf margins
(c) The process by which water enters root hairs.
(d) The term for the inward movement of solvent molecules through the plasma membrane of a cell.
(e) The process by which molecules distribute themselves evenly within the space they occupy
(f) The pressure which is responsible for the movement of water molecules across the cortical cells of the root.
(g) The pressure which is responsible for the movement of water molecules across the cortical cells of the root.
Ans : (a) Turgidity
(b) Guttation
(c) Osmosis
(d) Xylem
(e) Endosmosis
(f) Diffusion
(g) Root pressure
2) Give the equivalent terms for the following:
(a) Pressure of the cell contents on the cell wall
(b) The condition in which the cell contents are shrunken
(c) Loss of water through a cut stem
Ans : (a) Turgor pressure
(b) Flaccidity
(c) Bleeding
3) Complete the following statements:
(a) Hypotonic solution is one in which the solution kept outside the cell has lower solute concentration than ……………… the cell.
Ans : the fluids inside
(b) Active transport is one in which the ions outside the roots are ……………
Ans : (b) transported inside against their concentration gradient
(c) The bending movements of certain flowers towards the sun and the sleep movements of certain plants at night are examples of…………
Ans : (c) turgor movements
4) (a) When placed in a more concentrated solution, the cell contents will………… (shrink / swell up)
(b) The pressure by which the …………. Molecules tend to cross the semi-permeable membrane called osmotic pressure. (salt / water)
(c) Active transport is in a direction ………….. to that of diffusion. (opposite / Same)
Ans : (a) Shrink
(b) Water
(c) opposite
5) Match the items in column I with those in column II Column I Column II
| Column I | Column II |
| a) Xylem | (i) semi – permeable |
| b) Phloem | (ii) permeable |
| c) Cell membrane | (iii) downward flow of sap |
| d) Root pressure | (iv) upward flow of water |
| e) Cell wall | (v) guttation |
Ans :
| Column I | Column II |
| a) Xylem | (iv) upward flow of water |
| b) Phloem | (iii) downward flow of sap |
| c) Cell membrane | (i) semi – permeable |
| d) Root pressure | (v) guttation |
| e) Cell wall | (ii) permeable |
SHORT ANSWER TYPE:
1) Differentiate between the following:
(a) Plasmolysis and plasmolysis
(b) Turgor pressure and wall pressure
(c) Guttation and bleeding
(d) Turgidity and Flaccidity
Ans : (a) Plasmolysis and Deplasmolysis: The Dance of Water Movement
Imagine a plant cell as a small bag of water and solutes, encased in a rigid outer wall.
- Plasmolysis occurs when this plant cell finds itself in a “saltier” environment – what scientists call a hypertonic solution. Because there’s a higher concentration of water inside the cell than outside, water naturally flows out of the cell, trying to balance things. As water exits, the inner living part of the cell, known as the protoplast (which includes the cell membrane and everything inside it), begins to shrink and pull away from the sturdy cell wall. The cell goes limp and loses its firmness, a state called flaccidity. If this water loss is too severe or lasts too long, the cell can suffer irreversible damage and even die.
- Deplasmolysis is the exact opposite process, a recovery. If you take that shrunken, plasmolyzed cell and place it into a “less salty” environment, like pure water or a hypotonic solution, the tables turn. Now, there’s a higher concentration of water outside the cell. Water rushes back in, drawn by osmosis. The cell regains its original shape and firmness, becoming turgid again.
(b) Turgor Pressure and Wall Pressure: An Internal Tug-of-War
These two pressures are intimately linked and essential for a plant’s structural integrity.
- Turgor Pressure (TP) is the internal push generated by the cell’s contents. Think of the plant cell’s large central vacuole like a balloon inside a box. When the cell absorbs water, this vacuole expands, pushing the cell membrane outwards, hard against the rigid cell wall. This outward hydrostatic pressure is turgor pressure. It’s what makes healthy plant stems stand upright and leaves remain firm, preventing wilting.
- Wall Pressure (WP) is the cell wall’s reaction to this internal push. It’s the equal and opposite pressure exerted by the tough, unyielding cell wall back onto the expanding protoplast. In a fully hydrated, firm cell, the turgor pressure pushing out is perfectly balanced by the wall pressure pushing in, creating a stable, turgid state.
(c) Guttation and Bleeding: Plant “Sweat” and “Wounds”
These are both instances of fluid exuding from plants, but under different circumstances.
- Guttation is like a plant’s morning “sweat.” You’ll often see small droplets of water forming on the edges or tips of leaves, especially on herbaceous plants, early in the morning when the air is humid and there’s little wind. This happens when the plant’s roots are actively absorbing water, creating high internal pressure (root pressure), but the leaves aren’t losing much water through transpiration (evaporation). With nowhere else to go, the excess water is forced out through special pores on the leaf margins called hydathodes. The fluid isn’t pure water; it contains some dissolved minerals.
- Bleeding (of plants) is more akin to a wound weeping. This is the oozing of sap from a plant when it’s been cut or injured. When you sever a stem or damage a root, the internal pressure, primarily root pressure, can push the sap (which could be from the xylem or phloem, depending on the type of plant and where it’s cut) out of the exposed vascular tissues. This phenomenon is famously seen when maple trees are “tapped” to collect sap for syrup, or when you cut a fresh flower stem and see droplets forming on the cut end.
(d) Turgidity and Flaccidity: The Cell’s State of Firmness
These terms describe the physical condition of a plant cell based on its water content.
- Its protoplast is pressing tightly against the cell wall due to high turgor pressure. This is the healthy, rigid state of a plant cell in a well-watered environment. Turgid cells provide the structural support for non-woody plant parts, helping them stand upright and preventing wilting. It’s also vital for cell expansion and growth.
- Its protoplast has pulled away from the cell wall, and there’s little to no turgor pressure. This occurs when a cell is in an environment where it’s losing water (an isotonic or hypertonic solution). A plant whose cells are flaccid will appear wilted and droopy, as it lacks the internal pressure to maintain its shape.
2) (a) Mention whether the following statements are true (T) or false (F)
(i) A plant cell placed in a hypotonic solution gets Plasmolyzed.
(ii) Addition of salt to pickles prevents growth of bacteria because they turn turgid.
(iii) Cells that have lost their water content are said to be plasmolyzed.
(iv) Xylem is the water conducting tissue in plants.
(v) The shrinkage of protoplasm, when a cell is kept in hypotonic solution.
(vi) The cell wall of the root cell is a differentially permeable membrane.
Ans : (a) (i) False (ii)False (iii) False (iv) True (v) False (vi) False
(b) Correct the false statements by altering the last word only.
Ans : (i) A plant cell placed in hypotonic solution gets turgid.
(ii) Addition of salt to pickles prevents growth of bacteria because they turn flaccid. (iii) Cells that have lost their water content are said to be plasmolysed.
(iv) The shrinkage of protoplasm, when a cell is kept in hypertonic solution.
