ABSORPTION BY ROOTS Flashcards
Why do plants need water and minerals?
- photosynthesis
- transpiration
- transportation
- mechanical stiffness
What are the characteristics of roots to absorb more water?
- large surface area
- higher concentration of cell sap
- thin walls
Define imbibition
Imbibition is a phenomenon by which living or dead plant cells absorb water by surface attraction
What are two hydrophilic substances?
substances made of
1. cellulose
2. proteins
are hydrophilic
- have a strong affinity for water
Why do wooden doors swell up on exposure to water?
Due to imbibition
What pressure causes seed coats to rupture in germinating seeds?
Imbibitional pressure
Define diffusion
The free movement of molecules from their region of lower concentration to their region of higher concentration when the two are in direct contact
Define osmosis
The movement of water molecules from their region of higher concentration to their region of lower concentration through a semi permeable membrane
What are the two types of osmosis?
- endosmosis
- exosmosis
Define endosmosis
inward diffusion of water from its region of higher concentration to lower concentration through a semi permeable membrane
Define exosmosis
The outward movement of water molecules from higher concentration to lower concentration through a semi permeable membrane
Name an impermeable membrane
rubber sheet
Name 3 semi permeable membranes
- visking bag
- animal bladder
- celophane paper
Name a freely permeable membrane
Muslin cloth
Theoretically, how long should osmosis continue?
Until both solutions become isotonic
Define osmotic pressure
The minimum pressure that must be exerted to prevent the passage of pure solvent into the solution when the two are separated by a semi permeable membrane
Define tonicity
The relative concentration of the solutions that determines the direction and extent of diffusion
What are the three types of solutions based on tonicity?
- isotonic
- hypertonic
- hypotonic
What is an isotonic solution?
A condition where the concentration of the solutes is the same and no osmosis takes place
No change in size or shape of cell
What is a hypotonic solution?
The solution in which endosmosis takes place due to higher concentration of solute
Cell size increases and cells may even burst
What is a hypertonic solution?
The solution in which exosmosis takes place due to the increased concentration of solute outside the cell
Cell size decreases and loses shape
Define active transport.
The passage of salts or ions from its region of lower concentration to higher concentration through a living cell membrane by using energy from the cell as ATP
Why can’t certain ions pass through the cell membrane easily?
Due to the higher concentration of ions maintained inside the cell to develop osmotic pressure to absorb water
These ions are forcibly transported into the cell by active transport using energy from the cell as ATP
Define passive transport
The free movement of ions or salts from their state of higher concentration to their state of lower concentration without the supply of energy from the cell
What is turgidity?
It is the state of the cell where the cell wall is rigid and stretched due to the increase in the volume of vacuoles due to absorption of water
What is turgor pressure?
The pressure of the cell contents on the cell wall
What is wall pressure?
The pressure exerted by the cell wall on the cell contents
Why is the cell in a state of balance when it is turgid?
As no more water enters or leaves the cell as the turgor pressure counter balances the wall pressure.
No absorption takes place even if there is a higher concentration of solute within the cell
What is flacidity?
The state of the cell where it is no longer tight and is shrunken, caused due to the loss of water
What is plasmolysis?
The contraction of cytoplasm from the cell wall caused due to the loss of water when the cell is placed in a hypertonic solution
The state of the cell is flaccid
What is deplasmolysis?
The swelling up of cytoplasm when placed in a hypotonic solution caused due to the absorption of water
It is the reversal of plasmolysis
Define root pressure
The pressure developed in the roots due to continuous inward movement of water through cell to cell osmosis.
It helps in the ascent of sap
Define bleeding
The loss of water or sap through a cut or injured stem
Define guttation
The loss of excessive water through the margins or tips of leaves
What are the forces contributing to the ascent of sap?
- root pressure
- capillarity - narrow diameter - capillary force
- transpirational pull - cohesion
- adhesion - suction force
Name the force contributing to ascent of sap that is important in tall trees such as pines
Adhesion
