16.1 Flashcards
BLURT THE STRUCTURE OF THE ROOT OF A PLANT. (5)
Diagram template in “Bio & Chem” folder in phone.
Correct your diagram from the same folder.
Root hairs are the __________ _________ in plants that are responsible in the _____________ of water and mineral ions. (3)
(1) exchange
(2) surfaces
(3) absorption
By which process is water lost in plants? (1)
Transpiration
Each root hair is a long, thin extension of a root ______________ cell (1)
epidermal
Describe why root hairs are efficient surfaces for exchanging water and mineral ions. (4)
(1) provides a large S.A. (because they are very long extensions and occur in thousands on each root)
(2) they have a thin surface layer (so materials move rapidly)
STUDY TIP: ✍️
Always refer to osmosis and to the water potential gradient when explaining how water enters a root-hair cell from the soil
💪
How does the vacuole encourage water to move into the root hair cell by osmosis? Think about its contents. (2)
(1) it contains cell sap which consists of ions & sugars
(2) so, it has a lower water potential than the soil
When the soil is damp, why does water move by osmosis into the root hair cells? (4)
(1) the water potential of the soil is very high
(2) the root hairs have sugars, amino acids, & mineral ions dissolved inside them
(3) so the hairs / cells have a much lower water potential
(4) water moves down the water potential gradient
After water being absorbed into the root hair cell, water continues its journey across the root in 2 ways. What are they? (2)
(1) Apoplastic Pathway (cell wall)
(2) Symplastic Pathway (cytoplasm)
Water has cohesive properties. What is cohesion? (In terms of molecules) (1)
(1) the mutual attraction of molecules for one another
(In other words, it is the ability of molecules to stick to one another.)
Describe how water moves through the apoplastic pathway. (5)
(1) as water enters by osmosis into endodermal cells, it pulls more water along behind it
(2) This is due to water’s cohesive properties.
(3) This creates a tension that draws water along the cell walls of the cells of the root cortex.
(4) The mesh-like structure of the cellulose cell walls of these cells has many water-filled spaces,
(5) and so there is little or no resistance to this pull of water along the cell walls.
Describe how water moves through the symplastic pathway. (2)
(1) The water passes through the cell walls along tiny openings called plasmodesmata.
(2) Each plasmodesma is filled with a thin strand of cytoplasm
Describe how the movement of water from a root hair cell to (2 cells of) the cortex establishes a water potential gradient. (6)
(1) Water entering by osmosis inc the WP of the root hair cell.
(2) The root hair cell now has a higher WP than the first cell in the cortex.
(3) Water therefore moves from the root hair cell to the first cell in the cortex by osmosis
(4) This first cell now has a higher WP than its neighbour to the inside of the stem.
(5) Water therefore moves into the neighbouring cells by osmosis
(6) At the same time, this loss of water from the first cortical cell lowers its WP, causing more water to enter it by osmosis from the root hair cell.
When water reaches the endodermis by the apoplastic pathway, a waterproof band called the ___________ _______ in the endodermal cells prevents it progressing further along the cell wall. (2)
What is the ___________ _______ made of? (1)
What happens after that? (1)
And Why? (1)
(1) casparian
(2) strip
…
(3) suberin (the substance)
…
(4) at this point, water enters into the cytoplasm of the cell through the cell membrane.
…
(5) to allow the cell membrane to control which substances can enter the cell, therefore the xylem (e.g. pathogens)
If mineral ions and salts were to move into the xylem from the endodermal cells, by which process would they do so? (1)
And using what molecules? (1)
(1) Active transport
(2) carrier proteins
Root pressure is the force that helps to move water up the plant. How is this pressure created in the endodermal cells? (3)
(1) Mineral ions from the endodermal cells move into the xylem by active transport.
(2) This creates a lower WP in the xylem.
(3) Water now moves into the xylem by osmosis
On which type of plants does root pressure have a higher effect on water movement than the transpiration pull? Small or large plants? (1)
Small
What 3 factors are evidence that active transport of salts and mineral ions into the xylem causes root pressure?
And how would they impact root pressure if they Inc. or Dec.? (3)
(1) Temperature rises = pressure increases
(2) Metabolic inhibitors, such as cyanide, prevent most energy release by respiration and also cause root pressure to decrease
(3) A decrease in the availability of oxygen or respiratory substrates = reduction in root pressure.
“Water enters a plant from the soil. The water travels up through the plant & eventually evaporates into the air.
Describe the pathway that water takes from the soil to the endodermis.” (4)
(1) Water enters root hair (cell)
(2) water travels through the cortex
(3) By the symplastic pathway / through the cytoplasm
(4) By the apoplastic pathway / through the cell walls
“Root pressure is a force that helps to move water through the xylem. Describe how.” (3)
(1) ions actively transported into xylem
(2) lowers WP in xylem
(3) water moves into xylem by osmosis
“Give a difference, other than the route, between the symplastic and the apoplastic pathway of water movement.” (1)
A: occurs by cohesion
S: occurs by osmosis
