9 - Transport in plants Flashcards
Why do multicellular plants need a transport system?
- substances such as glucose and oxygen need to be transported to cells that do not photosynthesise.
- waste products of cell metabolism need to be removed.
- small SA:V ratio
- relatively big with high metabolic rate.
- exchange by diffusion alone would be too slow to meet metabolic needs.
- hormones need to be transported to where they are required.
What two types of tissues are part of the vascular system?
- xylem
- phloem
How are the vascular bundles arranged in a stem?
- phloem outside
- xylem inside
- cambium in between
vascular bundle around edge to give strength and support.
cambium layer contains meristem cells.
How are the vascular bundles arranged in a root?
- xylem in x structure in middle
- phloem in 4 sections around xylem
- root hair surrounding
vascular bundle in middle to help plant withstand tugging strains (e.g wind).
How are the vascular bundles arranged in a leaf?
- xylem on top
- phloem on bottom
midrib (largest middle part of leaf) is the main vein carrying the vascular tissue.
Function of xylem
- Transports water and dissolved mineral ions
- one direction movement (upwards). Water moves from roots towards leaves.
- provides structural support
- passive process
- TRANSPIRATION
Functions of phloem
- Transports organic solutes and dissolved sugars.
- bidirectional movement.
- from leaves to rest of plant.
- active process
- TRANSLOCATION
what cells are present in xylem?
- xylem vessels
- xylem fibres
- xylem parenchyma
what cells are present in phloem?
- sieve tube elements
- companion cells
- parenchyma
- phloem fibres
explain the structure of the xylem
- xylem vessels are long hollow structures formed from cells (dead) joined end to end.
- no end walls between the cells, forming a continuous hollow tube.
- thick lignified walls (lignin) help to support the xylem vessels and prevent them from collapsing inwards under the transpiration pull.
- lignin deposited in walls as spirals or distinct rings.
- water and mineral ions move in and out of xylem vessels through non-lignified pits.
explain the structure of phloem
sieve tube elements:
living cells joined end to end to form a long, hollow structure.
- sieve plates are between the cells, and are perforated to allow phloem contents through.
- no nucleus, very thin cytoplasm, very few organelles (unusual for a living cell).
Companion cells
- 1 companion cell for every sieve tube element.
- they are linked by many plasmodesmata.
- they have a nucleus and organelles.
- they carry out the living functions for both themselves and the sieve tube cells.
- e.g provide energy for active transport of solutes.
- no lignified walls
Sieve tube cells are living cells. Why are they unusual?
- no nucleus
- very thin layer of cytoplasm
- vey few organelles.
What is the phloem filled with?
- phloem sap
Which kind of plants have a vascular system consisting of xylem and phloem?
herbaceous dicotyledonous plants
Why do plants need water?
- to transport mineral ions and sugars in aqueous solution.
- water is a reactant photosynthesis
- cooling effect by transpiration
- turgor pressure.
What are the adaptations of a root hair cell?
- microscopic means they can penetrate between soil particles.
- large SA:V ratio as they are microscopic in size.
- thin surface layer provides a short diffusion and osmosis distance.
- concentration of solutes in cytoplasm of root hair cells maintains a water potential gradient between soil water and cell.
What is osmosis?
the movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane.
What are the 3 different pathways water can take from the root to the xylem?
- symplast pathway
- apoplast pathway
- vacuolar pathway
Symplast pathway (cytoplasm)
- water travels through the living parts of cells (cytoplasm)
- the cytoplasm of neighbouring cells are connected by plasmodesmata.
- osmosis