3.1.3 Transport In Plants Flashcards
State 3 different tissues that make up the leaf and the roles that they each have
Phloem transport organic material away from the leaf
Xylem transports water and ions into the leaf
Palisade mesophyll is made up of leaf palisade cells, which carry out photosynthesis
State the function of xylem vessels
Vessels that transport the water and mineral ions from the roots throughout the plant
Explain why large,multicellular plants require transport system to exchange substances with the external enviornment
Large plants = low SA: V ratio which reduces the efficency of diffusion/ osmosis. Plants photosyntheise in thier leaves and get water from their roots so they require substances to travel large distances to provide all the cells with the substance they need. More efficent with a transport system
Indicate the dependent and independent variable for the test that investigate the effect of light intensity on transpiration
Dependent = water lost Independent = lignt intensity
Define the term transpiration
The loss of water vapour by evaporation, water diffuses into the atmosphere out of the plant via the stromata
Describe 2 pathways that are utilised by water molecules to travel to the xylem after being absorbed at the root
Symplast pathway which involves water moving through the cytoplasm of cells at the root through cell connections called plasmodesmata
Apoplast pathway: movement between cellulose fibres in the cell walls and intercellular spaces
Describe the forces encouraging water to travel from the roots to the leaves
Water loss at the leaf, due to transpiration creates the transpiration pull stream, forming a water potential upwards. Pulls water up the xylem via cohesion .
At the roots, cells actively transport ions into them and water follows by osmosis. Also occurs from root cells to the xylem. Pressure of water at roots is also greater than that ahead, water is pushed upwards by hydrostatic pressure
Describe 2 ways that cacti are specialised to overcome the availability of water in their enviornment
Can store water in their stems, which become swollen. Needle like leaves which reduces SA and so less water is lost by transpiration
State two substances transported by the plant tissue phloem
Sucrose
AA
Describe the mass flow theory of movement of materials in this plant tissue
Assimilates actively loaded into companion cells and diffuse into sieve tube elements, decreases WP at the source. Xylem tissue has higher WP and water moves into the sieve tube from the xylem by osmosis. Creates high hydrostatic pressure at the source, substances unloaded at the sink, increasing WP and water leaves by osmosis. Reduces hydrostatic pressure as water moves back into xylem vessels. Difference in h pressure between source and sink provides the force required to move the assimilates to where they are required.
Define translocation
Transport of assimilates through the plant from source to sink
Describe the stage of active loading in translocation
Active loading - used to move substances from surrounding cells to companion cells, against conc gradient
Stages
Companion cells actively transport H+ ions into surrounding cells (requires ATP)
Creates H+ ion gradient between surrounding cells and companion cell
H+ wants to diffuse back into companion cell
H + ions co transported with sucrose into the companion cell via co transporter proteins, H ions move down con gradient, sucrose move against conc gradient
Sucrose diffuse down conc gradient from companion cells into sieve tube elements via plasmodesmata
Explain the mass flow theory
1) sucrose moves from companion cells into STE by diffusion via plasmodesmata
2) water potential inside sieve tube elements decreases
3) Water moves into sieve tubes by osmosis from xylem, hydrostatic pressure increases at the source and end of phloem
4) pressure gradient between source and sink
5) sucrose move down the pressure gradient
6) sucrose is moved to other cells or converted to other forms I,e starch or glucose
7) removal of sucrose from phloem increases water potential at sink end
9) water moves out of sieve tube by osmosis into xylem, hydrostatic pressure decreases at sick end of phloem
How is the removal of sucrose maintained and its effect
Sucrose is used, moved to other cells or converted to other forms (e.g starch)
Removal of sucrose from phloem increases water potential at the sink end
Water therefore moves out, decrease in hydrostatic, maintains hydrostatic pressure
Why is cohesion important in water molecules
String hydrogen bonds causes water molecules to stick together, creating a continuous column of water, transpiration stream
So when tension pulls water up the xylem,whole collum of water moves upwards
