Module 3.1.3 Transport In Plants Flashcards
Why do plants have transport systems?
Moves substances between the leaves, stem & roots
Why is there a need for transport systems in plants?
Metabolic demands - photosynthesis happens in the leaves although many internal & underground parts of the plant dont photosynthesis & need nutrients & wastes removed
Size - some plants small but some are very large so effective transport systems required to move substances up & down the plant
SA:V - Leaves are adapted for a large SA:V (photosynthesis) but other components dont so they cannot rely on diffusion
What are dicotyledonous plants?
Plants that makes seeds that contain cotyledons - organs that act as food stores for the developing embryo plant & 1st form leaves when the seed germinates
What is the difference between herbaceous & woody dicot plants?
Herbaceous - soft tissues & live a relatively short life
Woody - hard lignified tissues & long life cycle
What are the 2 main transport vessels in herbaceous dicots?
The phloem & xylem
Where & how are the transport tissues arranged in the plant?
In vascular bundles in the leaves, stem & roots
What is the 2 main functions of the xylem?
Transport of water & mineral ions
Support
Is the xylem made from dead or living tissue?
Dead
What is the structure of the xylem?
Long hollow tube made by several columns of cells fusing together end to end
Walls contain lignin - support
What are the 2 other tissues associated in the xylem in herbaceous dicots?
Xylem parenchyma
Xylem fibres
What is the xylem parenchyma?
Tissue that stores food & contains tannin deposits (bitter chemical that protects plant tissues from attacks
What is the xylem fibres?
Tissues with long cells with lignified secondary walls to provide mechanical strength
Doesn’t transport water
What is the function of the phloem?
Transports sugars & amino acids needed for cellular respiration & synthesis of other useful molecules from the leaves to around the plant
What other supporting tissues does the phloem contain?
Fibres & sclereids - cells with extremely thick cell walls
What is the 2 components of the phloem tube?
Sieve tube element
Companion cells
What is the structure of the sieve tube element?
Hollow structure made of many cells joined end to end
Not lignifies
Walls are perforated to form sieve plates
Mature phloem cells have no nucleus
What is the function of the sieve tube element?
Lets the phloem contents through
As large appear, the tonoplast, nucleus & other organelles break down so the phloem becomes a tube filled with phloem sap
What is the structure of the companion cells
Form with sieve tube elements & linked by many plasmodesmata
Have their nucleus & all their organelles
Very active
What is the function of the companion cells
Function as a ‘life support system’ for the sieve tube cells as they have lost most of their normal cell’s functions
What are some adaptions of leaves?
Have a large SA for capturing sunlight & carrying out photosynthesis
Waxy cuticle - waterproof (prevents leaves from loosing water rapidly & constantly by evaporation from their surfaces)
Why is it important that gases move in & out of the air?
For photosynthesis to occur
What does the stomata do?
Allows CO2 & O2 to move in & out of the leaf down a concentration gradient due to diffusion
What allows the stomata to open & close?
The guard cells
What happens when the stomata are open?
Gas exchange in & out the leaf & water moves out by diffusion
What is the loss of water by diffusion?
Transpiration - inevitable consequence of gas exchange
Why do stomata need to be open all the time?
Cellular respiration happens day & night
Describe the transpiration stream
Water enters a plant by osmosis & is transported up the xylem until it reaches the leaves. Then it moves by osmosis across membranes & by diffusion in the apoplast pathway from the xylem through the cells of the lead where it evaporates from the freely permeable cellulose cell wall of the mesophyll cells into the leaves into the air spaces
What is the word equation for photosynthesis?
Water + carbon dioxide -light-> glucose & oxygen
Where does photosynthesis occur?
In chloroplasts in palisade cells
How do the reactants for photosynthesis enter the plant?
Water -> xylem vessel through osmosis
Carbon dioxide -> diffuses through the stomata of guard cels across the spongy mesophyll towards palisade cells
What are glucose & O2 used for in a plant?
The sinks (respiring tissues)
What is translocation?
The movement of assimilates e.g. sucrose from the source to the sinks of plants through the phloem
Describe translocation & active loading
The H+ ions move into the palisade cell from the companion cell, through the proton pump by active transport. This increases the concentration of the H+ ions in the palisade cell. Sucrose then moves into the companion cell through the H+ sucrose co-transporter. This is usually done by diffusion but if there is a high concentration of sucrose in the companion cell, the sucrose will be pumped across the membrane by active transport. This increases the concentration of sucrose in the companion cell. This sucrose then moves into the phloem through the plasmodesmata by diffusion which lowers the water potential of the cell. This then causes water to then move into the phloem by osmosis.
What is the difference between water potential & hydrostatic pressure?
Water potential -> the potential energy of water in the system to pure water
Hydrostatic pressure -> the concentration of molecules
Describe transpiration
Water vapour moves out of the stomata of the guard cells through evaporation which lowers the water potential. The water in the roots is cohesive so the molecules bond together with weak hydrogen bonds. Water also has an adhesive force with the xylem walls, due to it being reinforced with lignin. This causes the transpiration stream to move as one body. Furthermore, there is root pressure in the roots as water moves into the root hair cell through active transport which creates a high hydrostatic pressure which makes the water cohesive. This creates a tension & a transpiration pull where the water is pulled up the xylem from the roots to the leaves for photosynthesis.
