Transport in Plants Flashcards
What is transported in the xylum?
Water
What is transported in the phloem?
Dissolved solutes such as sucrose
How is the xylum formed?
It starts off as living tissue in the protoxylum which is flexiable.
As it ages, moe lignin is added and it becomes less flexiable and impermeable to water
How is water transported from the roots to the leaves?
A transpiration stream
What is the structure of the phloem?
Made up of sieve tube elements joined together linked to companion cells by a plasmodesmata
How are companion cells adapted for their function?
Their membrane is highly folded to increase the surface area that they can transport sucrose into the cytoplasm
They have many mitochondria to supply the ATP needed for active loading
What part of the root absorbs water?
The root tip as it has more root hair cells which increase surface area
What is the purpose of root hair cells?
To increase surface area for osmosis into the plant
How does water enter the root?
Through osmosis down it’s concentration gradient into the root hair cell
What are the two routes that water can take from the root hair cells to the xylum?
Symplast pathway
Apoplast pathway
What is the symplast pathway?
Water moves by diffusion down it’s concentration gradient through the cytoplams and plasmodesmata of cells
What is the apoplast pathway?
Water is pulled between the cell walls due to it’s cohesive nature
What is the casparian strip?
A waterproof layer of waxy tissue that controlls how much water enters the xylum. Water goes into the cytoplasm of cells temporerily.
Is the movement of water a passive or an active process?
Passive
Where does water go when it reaches the leaf?
Into the spongy mesophyll cells by osmosis where it evaporates and moves out of the stomata
What is the transpiration stream?
When water evaporates, more water is pulled up into the leaf due to the cohesive nature of water. More water is then pulled through the xylum from the roots which creates a concentration gradient and means more water enters the roots through osmosis
What factors affect transpiration?
Light
Temperature
Air movement
Humidity
How does light affect transpiration?
Transpiration increases with light intensity as more of the stomata open
How does tempreture affect transpiration?
Transpiration increases with tempreture. Tempreture ncreases the ammount of evaporation from the surface of the leaf and the ammount of waer vapour that the air can take. This means there is a steeper concentration gradient between the air and the leaf so transpiration increases
How does air movement affect transpiration?
It reduces the shell of air around the leaf which keeps a steep diffusion gradient
How does humidity affect transpiration?
High humidity lowers transpiration as the concentration gradient decreases
What is the name given to the substances dissolved in the phloem?
Assimilates
What is a source?
An area of the plant with high sucrose and loads sucrose onto the phloem
What is a sink?
An area with low sucrose that removes sucrose from the phloem
What is phloem loading?
The way that sucrose is moved into the phloem
What are the two kinds of phloem loading?
Symplast pathway: Sucrose moves through the cytoplasm of the cells
Apoplast pathway: Sucrose moves through the spaces inbetween cells
How is sucrose unloaded from the phloem?
Diffusion down it’s concentration gradient
