3.1.3 Transport in plants Flashcards
Why do plants need a transport system?
-Metabolic demands= need water, minerals, and sugar to survive(some parts need oxygen i.e internal/underground parts) and need to remove waste products, hormones need to be transported
-multicellular so they has a small SA: vol ratio(can’t rely on direct diffusion alone for exchange because its too slow)
-some plants are relatively large= high metabolic rate (require more efficient transport from roots to leaves)
What are dicots?
-plants that make seeds contain 2 cotyledones(organs that act as food stores for developing plant embryo and are the first leaves that from when the seed germinates)
-herbaceous dicots= soft tissue + relatively short lifecycle i.e some leaves and stems
-woody dicots= have hard lignified tissues + long lifecycle
What are the 2 types of transport system in a plant?
VASCULAR SYSTEM:
-xylem tissue= move water and soluble mineral ions upwards from root to leaf(transpiration stream) and supports plant by lignin
-phloem tissue= mainly transports assimilates(sugar/sucrose and amino acids) from the source to the sink
Location of the vascular bundles
-stem= around the edge to give strength and support, reduce bending
-roots= in the middle to provide support for root and withstand tugging winds as it pushes through soil
-leaves= makes up a network of veins to support the thin leaves and provide transport function
Difference between a transverse and longitudinal cross-section
T= sections are cut through each structure at a right angle
L= taken along the length of a structure(xylem on the inside of stem, phloem on outside)
Xylem vessel adaptations
-long tube-like, hollow structures formed from dead cells(lignin) joined end to end(no end walls to pass water up easily)
-no cytoplasm
-lignin supports the walls and prevents them collapsing inwards from transpiration pull(can be spiral or ring structure for flexibility, increases as plant gets older)
-bordered pits(small holes) in sides of wall allow water and mineral ions to move into neighbouring cells(supply them with water)
Xylem in herbaceous dicots
-have thick walled parenchyma that packs around xylem vessels, storing food and containing tannin deposits*
*bitter chemical that protect plant tissues from being attacked by herbivores
Adaptations of phloem tissue
-formed from living cells arranged in columns(can undergo active transport for translocation)
-contain sieve tube elements= form tubes for transporting sugar, very few organelles(no nucleus, thin cytoplasm layer to allow for mass flow of sap) + a sieve plate at either end(perforated walls that allow solutes to pass through)
-contain companion cells linked by plasmodesmata(channel between phloem cell wall and cytoplasm of companion), have a large nucleus, dense cytoplasm and many mitochondria–} help carry out metabolic processes to keep phloem alive i.e provide energy for active transport of solutes
why does phloem transport sucrose?
-less reactive form of sugar than glucose(original product of photosynthesis in the leaf)
-not easily used up in respiration
