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BY2.3 Part 2 ­ Plants




Xylem tissue transports water and mineral salts from the roots to the leaves.
Phloem tissue transports the soluble products of photosynthesis (sucrose and amino
acids) from the leaves to the other parts of the plant.

In each case the walls of tubes are thickened by…

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Stem Root




The distribution of xylem tissue differs in primary stems, leaves and roots:
In stems it occurs as part of the peripheral vascular bundles. This organisation gives flexible
support but also resistance to bending strain.
In leaves the arrangement of vascular tissues in the midrib and network of veins…

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There are 3 main pathways through which the water can move through from the roots to the xylem:

Apoplastic ­ Goes through non-living parts of the cell (through cell wall) by diffusion/osmosis
Symplast ­ goes through living parts of the cells ( cytoplasm). Cells are linked by cytoplasmic
strands that…

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The casparian strip is made from water-proof suberin and is found the on radial, lower and upper
walls, but not the tangential walls.

Therefore, the water has to take the symplast pathway ­ this means the plant selectively take up
which ions enter and leave the xylem.




Once in the…

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1. Pressure increases as temperature rises
2. Metabolic inhibitors (e.g. cyanide) that inhibit respiration cause root pressure to cease ( stops
the salts being actively secreted)
3. A decrease in O2 availability results in a reduction of root pressure



The movement of water from the root to the leaf:

Water…

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Temperature - a rise in temperature provides more kinetic energy for the movement of
water molecules. This additional energy increases the rate of evaporation of water from
the plant and speeds up the rate of diffusion of water vapour into the surrounding
atmosphere. The water potential of the atmosphere becomes…

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The reservoir is used to push the air bubble back to "0"

The air bubble moves along the capillary tube as water is absorbed by the shoot ­ measuring the
rate of transpiration

Plants can be classified on the basis of their structure in relation to the prevailing water supply,…

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reduces the water potential gradient between the leaf and the atmosphere and so
reduces the rate of diffusion of water.
Hairs - stiff, interlocking hairs trap water vapour and reduce the water potential
gradient.
Thick cuticle - the cuticle is a waxy covering over the leaf surface which reduces
water…

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phloem fibres
phloem parenchyma




The main ones are companion cells and sieve tubes.

The sieve tubes are elongated and their ends are perforated with pores. These areas are called
sieve plates.

Cytoplasmic filaments/strands containing phloem protein extend from one sieve cells to the next
through the sieve plates. The sieve…

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Unlike water in the xylem, the contents of the phloem can move up or down a plant stem, often
simaultaneously (but not in the same sieve tube)



1) Photosynthesising cells (source cells) produce glucose which is converted into sucrose,
which is loaded into the phloem sieve tube by active transport…

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