3.3 transport in plants Flashcards
Why do plants need a transport system?
- So large materials can be moved around plants
- So materials can be supplied quickly to fast metabolising plants
- So materials can be supplied quickly to plants w smaller SA:V
Inside to outside: cross section of a root
- xylem
- Cambium
- phloem
(4. endodermis)
Inside to outside: cross section of stem
- xylem
- cambium
- phloem
(4. packing tissue)
Top to bottom: cross section of a leaf
- Xylem
- Cambium
- Phloem
Describe the features of the phloem (3 things)
- Living, respiring tissues, providing energy for active transport
- Porous sieve plates to allow flow
- Companion cells house the organisms that could slow the flow
Describe the features of the xylem (5 things)
- Dead, lignified tissues (waterproof and strong)
- long continuous columns with no end plates or organelles (increases flow)
- Narrow (water column doesn’t break
- Patchy lignification forms bordered pits which allows lateral movement of water
- Lignin can be spiralled or ringed to allow flexibility and growth.
What does cohesion mean when talking about water?
Water attracted to other water molecules
What does adhesion mean when talking about water?
Water attracted to other substances.
What are the three ways water can pass through a plant?
apoplast
symplast
vacuolar
Describe the apoplast pathway
Water passes through plasmodesmata (this means water moves by mass flow and can carry dissolved mineral ions)
Describe the symplast pathway
Water enters the cell cytoplasm via the plasma membrane
Describe the vacuolar pathway
Like the symplast (enters through plasma membrane but can also pass through vacuoles
Describe how water will move between cells with reference to water potential (brief)
Water will move from a cell with a higher water potential to a cell with a lower water potential via osmosis.
define transpiration
The evaporation of water from leaves through stomata
What are the steps of transpiration?
- Water enters leaves via xylem and moves into cell walls of spongy mesophyll via osmosis
- Water evaporates from cell walls of spongy mesophyll
- Water diffuses out of open stomata on leaves down water vapour potential gradient.
What are the (5) factors that affect photosynthesis?
- Humidity
- Wind speed
- Temperature
- Light intensity
- Water availability
What are some precautions you should take when setting up a potometer?
Fully submerge the photometer in the water to flood any air bubbles out.
Insert plant shoot under the water so to not introduce new bubbles
Healthy shoots only so they transpire normally
Cut stem at angle increase SA
Ensure reservoir tap closed so air bubble doesn’t move
Dry leaves to unblock stomata
What are some assumptions we make when using Potometers?
- No water is used for photosynthesis
- No water is produced from respiration
- No water used to maintain turgidity
- Apparatus is sealed
Define what is meant by the transpiration stream
The overall movement of water from the soil, up the xylem, through the leaves and its evaporation out of the stomata
Outline the steps of the transpiration stream
- Evaporation of water from spongy mesophyll
- Water vapour diffuses out of leaf through stomata down water vapour potential gradient
- Osmosis of water from xylem through leaf
- Causes tension in xylem
- Cohesion of water molecules forces water up the xylem
- Tension in root xylem forces osmosis of water from root cells into xylem
Additional tension is caused by active transport of nitrate ions into root xylem causing additional osmosis of water into the xylem.
What is a xerophyte?
Plant adapted to conserve water in dry environments
What are the adaptations of xerophytes?
- Rolled leaves
- Thick cuticle
- Leaves with reduced SA:V
- Hairy leaves
- Sunken stomata
How does smaller SA:V help xerophytes?
Reduces the exchange of water vapour between the leaves and the atmosphere
How do rolled leaves help xerophytes?
Traps water vapour around the stomata
