9.1-9.5 : Transport In Plants Flashcards
Why do plants require a transport system ?
- transport system ensures that all the cells of a plant receive a sufficient amount of nutrients eg. Water,minerals and sugars to live
- low SA:V but high metabolic rate
What is the specialised transport system that plants have called ?
Vascular plants
Why do large organisms require specialised mass transport systems ?
- increasing transport distances - due to size
- SA:V ratio
- increasing levels of activity ( metabolic rate )
What are cotyledons ?
Organs that act as food stores for the developing embryo
What are dicot plants ?
Plants that make sees that contain 2 cotyledons
What are the 2 main groups of dicots ?
- Herbaceous dicots ( non woody stem ) eg. Daisies
- Woody dicots eg. Oak
What is the system of vessels in a plant called ?
Vascular system
What are herbaceous dicots vascular systems made up of and how are they arranged ?
- 2 Types of transport vessels - xylem and phloem
- arranged together in vascular bundles in the stem,roots and leaves
In the vascular bundle where are the xylem and phloem ?
Phloem = outside
Xylem = inside
Explain what is meant by increasing transport distances in regards to why large organisations require specialised mass transport systems ?
- every cell in a plant requires water, glucose and mineral ions
- the roots of a plant take in water and mineral ions while the leaves produce glucose by photosynthesis
- these molecules need to be transported to the other parts of the plant
- glucose is transported as sucrose in plants
- this large transport distance makes simple diffusion a non- viable method for transporting substances all the way from the exchange site to the rest of the organism
- diffusion wouldn’t be fast enough to meet the metabolic requirements of cells
Explain the low SA:V of plants ?
- as the size of the plant increases = SA:V ratio decreases —> due to the volume increases much more rapidly than surface area as size increases
- means it has relatively less SA available for substances to diffuse through so the rate of diffusion may not be fast enough to meet its cell requirements
- large plants therefore cannot rely on diffusion alone to supply their cells with substances such as food and oxygen and to remove waste products
- why thus they require specialised transport systems
How are plant adapted to increase SA:V ?
- plants have a branching body shape
- leaves are flat and thin
- roots have root hairs
Explain the increasing activity levels ( metabolic rates ) in regards to why plants require a specialised transport system
- larger organisms are more physically active and also contain more cells than smaller organisms
- a large number of cells results in a higher level of metabolic activity
- Thus the demand for oxygen and nutrients is greater than more waste is produced
- plant cells and tissues have a much lower metabolic rate than animal cells
- thus their demand for oxygen for aerobic respiration is reduced
What is the transpiration system ?
- Movement of water molecules and dissolve mineral ions
- xylem vessels
- passive process
What is the translocation system ?
Movement of sugars ( sucrose ) and amino acids
- phloem vessel - sieve and companion cells
- active process
What is a vascular bundle ?
- xylem and phloem are arranged in vascular bundles in the roots, stems and leaves
- there is a layer of cambium in between xylem and phloem that is MERISTEM cells which are involved in production of new xylem and phloem tissue
Describe the structure and function of vascular bundles in roots
- provides a drill like structure
- enables the plant to push down into the root
- xylem tissues is the strongest so is in the centre - X structure
- phloems in 4 separate sections
What and where is the layer of pericyclic ?
- in the endodermis around the vascular bundle of the root
- there’s a layer of meristem cells that form the pericyclic
Describe the vascular bundles in a leaf
- xylem is located on top of the phloem
- only applies to dicotyledonous plants - other plant types have a different structure
Describe the vascular bundles in stems
- xylem is located on the inside in non wooded plants
- provides additional support to the stem
- the cambium layer contains meristem cells
Explain the structure of xylem
- a DEAD tissue
- no cytoplasm + no nuclei in xylem tissue
- cell walls contain SPIRALISED lignin = gives the tissue high strength
- pits in wall ( non-lignified areas )
What is the function of xylem ?
- transports water and dissolved minerals upwards from the root hair cells to the leaves = transpiration steam
What are the adaptations of the xylem tissue ?
- very long tube like structures formed from cells joined end to end
- no end walls = making a uninterrupted tube that allows walls to pass through the middle easily
- cells are dead = no cytoplasm
- walks are thickened with a windy substance called lignin - helps to support the xylem vessels and stops them collapsing inwards
- lignin can be deposited in xylem walls in different ways eg. Distinct rings, spirals
- amount of lignin increases as the cell gets older
- water and ions move into and out of the vessels through small pits in the walls where there’s no lignin
What is the function of lignified cell walls ?
- adds strength to withstand the hydrostatic pressure = so walls do not collapse
- impermeable to water
What is the function of no end plates ?
- allows the mass flow of water and dissolved solutes as cohesive between water molecules
- adhesive between water and the walls forces are not impeded
Explain the function of having no protoplasm ( cells are dead when mature ) ?
- doesn’t impede the mass flow of water and dissolved solutes
= transpiration stream
Explain the function of having pits in wall ?
lateral movement of water allows continual flow in case of air bubbles forming in the vessels
Explain the function of a small diameter of vessels ?
Helps prevent the water column from breaking and assists with capillary action
What’s the structure of phloem tissue ?
- a living tissue
- composed of tubes of elongated cells called phloem sieve tubes
- transports assimilates ( sucrose, amino acids etc ) from the ledges to other parts of the plants
- process is called translocation
- assimilates move from one phloem cell to the next through pores in the end walls called sieve plates
- each sieve tube has an associated companion cell
What is the function of phloem tissue ?
- transports food in the form of sucrose upwards and downwards —> depending on where food is needed - bidirectional transport
- this is called translocation
What are the adaptions of phloem tissue ?
- sieve parts of the tubes are at the end walls which have lots of holes in them to allow solutes to pass through
- cytoplasm of adjacent cells is connected through the holes in the sieve plates
- lack of nucleus and other organelles in a sieve tube elements means that they can’t survive on their Own - there’s a companion cell for every sieve tube element
- companion cells carry out the living functions for both themselves and their sieve cells for eg. They provide the entertainment for the active transport of solutes
