3.1.3 ( part 2 ) - Transportation in plants Flashcards
define the term ‘assimilates’ ?
Assimilates - The products of photosynthesis that are transported through the plant
Define the term ‘translocation’ ?
Translocation - The movement of organic solutes around the plant in the phloem
Explain how assimilates are transported around the plant ?
Plants transport organic compounds/ assimilates in the phloem from the sources ( where they are made ) to the sinks ( where they are required by the plant )
Name the main sources of the plant ?
- Green leaves/ stems
- Storage organs ( e.g tubers and tap roots ) that unload stores at the start of a growth period
- Food stores in seeds when they germinate
Name the main sinks of the plant ?
- Roots that are growing/ absorbing mineral ions
- Meristems that are actively dividing
- Any part of plant that are laying food stores
What is phloem loading ?
An active process by which assimilates are moved into the phloem from the sources
describe the process of phloem loading ?
1 ) Sucrose from the sources travels through the apoplast route to the companion cell via diffusion down the concentration gradient
2 ) In the companion cells, sucrose is moved into the cytoplasm across the cell membrane through an active process
3 ) Hydrogen ions are active pumped out of companion cell using ATP
4 ) The Hydrogen ions return to companion cells down a concentration gradient via a co-transport protein. Sucrose is the molecule which is co-transported
5 ) This increases the sucrose concentration in the companion cells through the many plasmodesmata between the two linked cells
6 ) This results in build up of sucrose and water which also moves in by osmosis in companion cells
7 ) This causes the turgor pressure in companion cells to increase causing water carrying assimilates to move into tubes of sieve tube elements
8 ) Water then moves up and down the plant to regions of lower pressure such as the sinks
Explain the process of phloem unloading ?
- Sucrose is unloaded from the phloem at any point where the cells need it via diffusion or by being converted into another substance ( eg. glucose )
- This maintains curse concentration between phloem and surrounding cells
- Loss of solutes in phloem leads to increase in water potential and for water to move into surrounding cells via osmosis
What evidence is there for phloem loading/ unloading ?
- Advances in microscopes allow us to see adaptations of companion cells for active transport
- If mitochondria in companion cells are poisoned, translocation stops
- Flow of sugars is much faster than if it solely relied on diffusion indicating it is an active process
- Aphids can demonstrate the translocation process causing mass flow in phloem
Define the term ‘Xerophytes’ ?
Xerophytes - Plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment
Name examples of xerophytes ?
- Conifers
- Marram grass
Define the term ‘Hydrophytes’ ?
Hydrophytes - Plants with adaptations that enable them to survive in very water habitats or submerged or at surface of water
Name examples of hydrophytes ?
- Water lilies
- Water cress
What are some adaptations of xerophytes that help them conserve water ?
- A thick waxy cuticle
- Sunken stomata
- Reduced number of stomata
- Reduced leaves
- Haiti leaves
- Curled leaves
- Succulents
- Leaf loss
- Root adaptations ( long or shallow )
- Able to avoid the problem
Explain how a thick waxy cuticle helps xerophytes conserve water ?
this helps minimise water loss by transpiration through the cuticle
Explain how sunken stomata helps xerophytes conserve water ?
- This means stomata are located in pits
- This reduces air movement creating a humid microclimate
- This reduces the water vapour concentration gradient leading to reduced water loss via transpiration
Explain how a reduced number of stomata helps xerophytes conserve water ?
A reduced number of stomas a means the is less water loss via transpiration
Explain how reduced number of leaves helps xerophytes conserve water ?
Reduced number of leaves means there is less leaves off which water can be lost via transpiration
Explain how hairy leaves helps xerophytes conserve water ?
The hairs on the leaves create a humid microclimate reducing the water vapour potential gradient and minimising water loss via transpiration
Explain how curled leaves help xerophytes conserve water ?
The curled shape of the leaf causes all stomata to be confined in humid microclimate reducing the water vapour potential gradient leading to reduced loss of water via transpiration
Explain how succulents helps xerophytes conserve water ?
- Succulent plants store water in specialised parenchyma tissue in stems/ roots when water is in plentiful supply
- This water is used during time of drought
Explain how leaf loss helps xerophytes conserve water ?
- Some plants simply lose leaves when water is not available
- This means there are less stomata through which water can be lost via transpiration
Explain how root adaptations helps xerophytes conserve water ?
- Root adaptations help plants absorb as much water as possible from the soil
- Long plant roots can penetrate several rtes and access water a long way below the surface
- Shallow roots with a large surface area are able to absorb any available water
Explain how the ability to avoid the problem helps xerophytes conserve water ?
Some plants avoid the problem by losing leaves, becoming dormant or dying, leaving seeds behind to germinate/ grow when rain falls
