3.1.3 - Transport In Plants (set A - The Need For Transport Systems In Multicellular Plants) Flashcards
Explain why plants require transport systems?
- ensures that all the cells of a plant receive a sufficient amount of nutrients (eg water,minerals and sugars)
- important as plants are multicellular and have relatively small SA:V ratios with high metabolic rates
Explain what vascular plants are - why is a system needed?
Plants with a specialised transport systems
- needed due to relatively small SA:V ratio and high metabolic rates - need to provide sufficient amount of nutrients
Explain why large organisms require specialised mass transport systems - give three reasons?
– Increasing transport distances (due to size) - decreases diffusion rates
– Surface area: volume ratio - less diffusion across surface
– Increasing levels of activity (metabolic rate) - more substances needed and waste produced
Explain why plants need a specialised mass transport system - mention transport distance?
- all cell requires substances,nutrients and mineral ions to function
- molecules need to be transported all the way from the exchange site to other parts of the plant (root and leaves)
- simple diffusion is non-viable (big distance)
Explain why plants need a specialised mass transport system - mention SA:V?
- As the size of a plant increases, its surface area to volume ratio decreases - this is because volume increases much more rapidly than surface area
- has relatively less SA available for substances to diffuse through - rate of diffusion will not be fast enough to meet cells demands (supply of substances and removal of waste)
Explain why plants need a specialised mass transport system - mention SA:V?
- As the size of a plant increases, its surface area to volume ratio decreases - this is because volume increases much more rapidly than surface area
- has relatively less SA available for substances to diffuse through - rate of diffusion will not be fast enough to meet cells demands (supply of substances and removal of waste)
Explain why plants need a specialised mass transport system - mention metabolic rate?
Larger organisms are more physically active and contain more cells - have a higher level of metabolic activity have a greater demand for oxygen and nutrients as well as production of waste products
- metabolic demand is less than animals
Explain how glucose is transported and why?
glucose is combined with fructose forming sucrose (more efficient transport medium)
- if it was transported as glucose it would be taken in by surrounding cells
What are cotyledons - what is their function?
organs that act as food stores for the developing embryo plants and for the first leaves when the seed germinates
- dicotyledonous plants (dicots) make seeds that contain 2
Explain how plants are adapted to increase SA:V - give 3 ways?
- plants have a branching body shape
- leaves are flat and thin
- roots have root hairs
Explain what dicotyledonous (dicot) plants are, give the name of the 2 main groups?
- plants that make seeds that contain 2 cotyledons (organs that act as food stores)
- herbaceous dicots (non-woody stem) - soft tissues and relatively short life cycle
- woody dicots (eg oak) - hard lignified tissues with long life cycle
Explain the vascular system of a dicot plant?
A plant has a series of transport vessels running through the roots,stems and leaves - the system is known as the vascular system
- made up of xylem and phloem
Explain how the vascular bundle is positioned in the roots of herbaceous plants - include xylem and phloem?
- in the roots the vascular bundle is found in the centre, the centre core is the xylem tissue which helps roots withstand the pulling strain during transpiration
- on the edge of the centre core is the phloem tissue
Explain how the vascular bundle is positioned in the stems of herbaceous plants - include xylem and phloem?
- vascular bundles are located around the outside - xylem tissue is found on the inside (helps support the plant)
- phloem found on outside closest to the epidermis
- provides strength and support for the stem
Explain how the vascular bundle is positioned in the leaves of herbaceous plants - include xylem and phloem?
- vascular bundles form midrib, with veins spreading from centre in parallel lines - xylem tissue is found on upper side (closest to upper epidermis)
- phloem tissue found on the lower side (closest to lower epidermis)
Outline 3 functions of xylem tissue in plants?
- vascular tissue that transports dissolved minerals and water around plants
- structural support
- food storage
Outline 4 cell types which make up the xylem?
- tracheids (long,narrow tapered cells with pits)
- vessel elements (thicken cell walls - no end plates
- xylem parenchyma (thicker walled and stores food)
- xylem fibres (provide mechanical strength)
Outline and explain the function of lignified cell walls in xylem?
- adds strength to withstand hydrostatic pressure so vessels do not collapse
- impermeable to water, prevents water leaking
Outline and explain the function of lack of end plates and non-lignified regions/pits in xylem?
- allows the mass flow of water and dissolved solutes as cohesive and adhesive forces are not impeded
- lateral movement of water, allows continual flow in case of air bubbles forming in the vessels
Outline and explain the function of dead cells and small diameter of vessels in xylem?
- doesn’t impede the mass flow of water and dissolved solutes
- small diameter helps prevent water column from breaking and assist with capillary action
Outline the structure of xylem?
- largely non-living tissue
- made up of several types of cells which are mostly dead - involved in providing mechanic strength and forming lignin spirals
- xylem vessels are main structures which are long, hollow structures made by columns of cells fusing together end to end
- spirals of lining running around lumen - helps reinforce xylem vessels preventing them from collapsing
Outline the main function of phloem?
- transport organic compounds, particular sucrose from the source (leaf) to the sink (roots) - transport can occur up and down the plant
Outline the components of the phloem?
- involves various cell types - including parenchyma (for storage) and strengthening fibres
- made mainly of sieve tube elements and companion cells
- contain living cells
Outline the structure of phloem?
- sieve tubes made from many cells joined end to end - forming a long, hollow structure
- cells are not lignified - areas between the cells, the walls become perforated forming sieve plates with pores (allowing continuous movement)
- companion cells linked to sieve tube elements by plasmodesmata (channels through cell wall linking cytoplasm to adjacent cells)control metabolism of sieve tube elements
Explain the function of mature cells in phloem having no nucleus,vacuoles or ribosomes - outline the importance of thin cytoplasm?
- maximises the space for the translocation of organic compounds
- reduces friction to facilitate movement of substances
Outline the function of sieve plates with sieve pores - and the function of cellulose cell walls?
- allows the continous movement of substances
- strengthens the wall to withstand the hydrostatic pressure that moves the substances
Explain why the nucleus and other organelles are present in phloem companion cells, why are their large numbers of mitochondria present?
- nucleus provides metabolic support to several tube elements - helps with loading and unloading of assimilates
- mitochondria - provide ATP for active transport of assimilates into or out of companion cells
Explain the function of transport proteins in the plasma membrane of companion cells - and the presence of channels in the cell wall?
- move assimilates into and out of the sieve tube elements
- channels link to sieve tube elements which allows organic compounds to move from the companion cells into sieve tube elements
Compare the difference in features between xylem and phloem - give 4 and explain the differences?
- cell wall material of xylem is lignin and cellulose - in phloem its only cellulose
- end walls are only present in phloem as sieve plates with sieve pores
- direction of flow for xylem is only one way (upwards) whereas for phloem its two ways
- xylem the cells are dead and hollow in phloem they are living (companion cells)
