3.3 Transport in plants Flashcards
define dicotyldeonous plants
plants with two seeds leaves and a branching pattern of veins in the leaf.
define meristem
a layer of dividing cells, and is found just inside the endodermis.
define Phloem
transports dissolved assimilates
define vascular tissue
consists of cells specialised for transporting fluids by mass flow.
define xylem
transports water and minerals.
describe why plants need a transport system.
All living things need to take substances from, and return wastes to their enviroment, larger plants have smaller surface area to volume ratios , therfore require a specialised exchange surface and transport system.
state what every organism requirs supply of.
O2, H2O, nutrients and minerals.
describe why plants have a low demand for oxygen.
They are not very active and so respiration rate is low. and so oxygen can be obtained from diffusion.
explain how the plant derives its required sugar, water and minerals.
Sugar can not be absorb by roots and so is produce by photosynthesis in the leaves and so needs to be transported to other part of the plant. Water and minerals from the soil can be absorbed by the roots and transported up the plant.
State what makes up the vascular transport system in plants.
specialised vascular tissue, xylem and phloem.
State tissues can be found in a Dicotyledonous plants vascular bundle.
Xylem, phloem collenchyma and sclerenchyma, the two latter help to give strength and support to the plant
descirbe and suggest reasons for the apperance of the vascular bundle in a young root.
The xylem is the center core and has an X-shape to provide strength to pulling forces which roots are expose too. The phloem is inbetween the “arms” of the X-shape. The vascular bundle is surrounded in a special sheath called the epidermis. just inside the epidermis is a layer of meristem cells called the pericycle.
Describe and suggest reasons for the apperance of the vascular bundle in the stem.
the vascular bundle is found near the outer edge of the stem. In non-woody plants the bundle are serpareate and discrete.
in woody plants the bundles are separate in toung stems, but become a continuous ring in older stems. this provides strength and flexibilty.
Sclerenchyma is between the phloem and the collenchyma separeted by the cortex. between the phloem and xylem there is a layer of cambium(contains meristem cells).
Describe and suggest reasons for the apperance of the vascular bundle in the leaf.
The vascular bundle forms a midrib and veins of a leaf. A dicotyledonous leaf has a branching network of veins that get smaller as they spread away from the midrib. within each vein, the xylem is located on top of the phloem.
define companion cells
cells that help to load sucrose into the sieve tubes
define sieve tube elements
makes up the tubes in the phloem tissue that carry sap up and down the plant. the sieve tube elements are separated by sieve plates.
define xylem vessels
the tubes which carry water up the plant
state what the xylem tissue consists of
vessels to carry the water and dissolved mineral ions.
fibres to help support the plant,
living parenchyma cells which act as packing tussue to seperate and support the vessels
how do xylem vessels develop
lignin is impregnated into the walls of the cells, making the walls waterproof and so kills the cell. the ends of walls and contents of the cells decay leaving a dead column as a vessel. lignin strengthens the xylem vessel walls and prevents collapsing.
Lignin thickensing forms patterns in the cell wall, these may be spiral, annular(ring) or reticulate(network of broken rings), this prevents the xylem vessel becoming too rigid.
In someplaces in the xylem vessel lignification doesn’t take place in the cell wall leaving bordered pits and so water can pass through to living tissue.
State some adaptations of the xylem.
Adaptation for transport from root to leaf.
-They are made from dead cells aligned end to end to form a contintinous column.
-The tubes are narrow, so that the water column does no break easily and capillary action can be effective.
-Bordered pits in the lignified walls allow water to move sideways from one vessel to another.
-Lignin desposited in the walls in spiral, annular or reticulate patterns allows xylem to stretch as the plant grows.
Adaptation that don’t impede the flow of water.
-There are no cross-walls
- there are no cell ceontents
- lignin thickening prevents the walls from collapsing.
explain the structure and function of the Phloem
the Phloem is a tissue used in transport of assimilates(surcrose and amino acids) around the plant. The sucrose is dissolve in water to form sap.
The phloem is made up of the Sieve tube element and the companion cells.
describe the structure of sieve tube elements
Elongated sieve tube elements are lined up end to end to form sieve tubes. They contain no nucleus and very little cytoplasm, leaving space for massflow of sap to occur. at the ends of these sieve tube elements are perforated cross-walls called sieve plates.
these perforations in sieve plates allow movement of sap from one element to the next.
They have very thin walls.
describe the structure of companion cells.
Companion cells are found inbetween sieve tubes.
They have dense cytoplasm and a large nucleus. they also have lots of mitochondria for ATP synthesis to load assimialtes actively into sieve tubes.
define Plasmodesmata
gaps in the cell wall containing cytoplasm that connect two cells.
State the permability of water through cellulose (cell wall)
It is fully permeable.
describe the Apoplast pathway
Water passes through the spaces in the cell walls and between the cells. It does not pass through any plasma membranes into the cells. This means that the water moves by mass flow rather than by osmosis. Also dissolved mineral ions and salts can be carries with the water.
