Adaptations for Transport (Plants)

Roots

Adapted to absorb water and minerals by having their surface area increased by the presence of root hairs
Freely permeable and soil water soaks into the walls of the root hair cells and travels across the walls of the cells of the cortex and the spaces be

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Osmosis

Water also enters the cell via osmosis
Moves through the cytoplasm of adjacent cells via the plasmodesmata
Symplast pathway
Water can also travel from vacuole to vacuole, it is known as the vacuolar pathway

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Root Hair

Extensions of the epidermal cells
Increase the surface area of the root in contact with the soil water
Only found near the growing tip of the root
Replaced by the exodermis in older roots

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Xylem

Made of 4 types of cells
Vessels - there are the main conducting cells and are lignified to give strength and to waterproof them
Trachieds - more primitive than vessels they overlap and have pits to allow the transpiration stream to move between tracheids

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Phloem

Sieve tubes - cylinidical cells placed end to end, the cell walls joining them are perforated by pores and are known as sieve plates. Cytoplasmic filaments stretch from one sieve cell to the next through the sieve plates. Lack most organelles, but have nu

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Enderm

The apoplast pathway is blocked at the endodermis by the Casparian ***** made of waterproof suberin

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Apoplast Pathway

Blocked at the endodermis by the Casparian ***** which is made of water-proof suberin
Water enters the pericycle via the symblast pathway
It reaches vasculkar tissue (stele) it enters the xylem vessels via the apoplast pathway
Some evidence that salts may

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Casparian *****

Blocks the apoplast pathway at the endodermis with a water proof band of suberin within the cell wall

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Water Loss

Large quantities of water lost from the stomata through transpiration must be replaced from the soil
Vacuoles of root hair cells has a lower water potential than the surrounding soil water so water enters them by osmosis
Minerals are actively pumped into

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Vessels

Main conducting cells
Lignified to give strength and to waterproof them

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Tracheids

More primitive than vessels they overlap
Have pits to allow the transpiration stream to move between tracheids
Lignified

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Fibres

Provide support

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Parenchyma

Living, packing tissue

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Transpiration

Evaporation of water from the leaves of plants pulls up a column through the plant from the surrounding soil
Provides the water needed for photosynthesis - transpiration pull
Large cohesive forces between the polar water molecules
Adhesive forces which ex

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Potometer

Used to measure the rate of water uptake
Caused of water uptake include transpiration and photosynthesis

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Rate of Transpiration

Depends on several factors
Key importance to plants as they need to balance water loss through stomata with the need for gaseous exchange for photosynthesis
Factors that alters the concentration gradient between leaf and the surrounding air will affect tr

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Temperature

Rising temperature increases the kinetic energy of water molecules and the rate of evaporation from the walls of the mesophyll cells
If stomata open it also increases the rate of diffusion into the surrounding atmosphere

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Humidity

Measure of how much water vapour is in the air surrounding the leaves
High levels of humidity decrease the concentration gradient between the saturated air within the leaves and the surrounding air and slows the transpiration stream

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Light Intensity

In bright light the plant want to open stomata for photosynthesis

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Hydrophyte

Grows either partially or wholly submerged in water
Water provides much of the necessary support
Little or no lignified tissues
Very limited xylem as all cells are close to a supply of water
Leaves do not need to limit water loss so lack a cuticle
Leaves

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Xerophytes

Evolved to in areas of low water availability and have developed adaptations to reduce water loss
Low water availability may be found in desert regions, cold regions and exposed windy locations

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Adaptations of Marram Grass

Rolled leaves - the undersides of the leaves are held inside the rolled leaves reducing the exposure of the stomata to the wind
Sunken stomata - located in depressions to maintain a humid layer of air next to their openings and therefore reduce the concen

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Xerophytic Adaptations

Cacti with their succulent stems to store water
Close stomata during the daylight and their leaves are reduced to spines
Pine trees also reduce their leaf size to needles

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Mesophytes

Plants that have evolved to live in regions with an adequate water supply
If they lose excessive water in the day they can close their stomata, but they can usually balance their water loss in the day by taking up more water at night
Adapted to survive th

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Translocation

The products of photosynthesis are transported about the plant as sucrose
Along with amino acids and other soluble organic materials this is known as translocation
Takes place in the phloem tissue

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Sieve Tubes

Cylindrical cells placed end to end
Cell walls joing them are perforated by pores and are known as sieve plates
Cytoplasmic filaments stretch from one sieve cell to the next through the sieve plates
Lack most organelles
Numerous plasmodesmata to connect t

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Companion Cells

Have a dense cytoplasm
Many mitochondria

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Two Types of Phloem Tissue

Phloem fibres
Phloem parenchyma

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Ringing Experiment

Sap in the phloem is under pressure
Moves too fast to be explained by simple diffusion
First experiment investigating translocation involved 'ringing'
The removal of phloem tissue (bark) and analysing the contents of the bark above and below the ring

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Aphids Experiment

Feeding aphids which have had their stylets removed to remain in the plant
The sap that exudes from the aphids' stylets can be analysed

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Radiolabelling Experiment

Radioactive 14CO2 is supplied to an illuminated leaf
The transport of the radioactive 14C is monitored by placing the plant on photographic film
Where radioactivity is present the film fogs

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Rates of Translocation

Observed rates of 25-1100cm h-1

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Mass Flow Hypothesis

Involves sucros being loaded into the phloem by the companion cells at the source
Unloaded where it is needed for growth or stroage - the sink

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Issues with the Mass Flow Hypothesis

Does not account for the presence of the sieve plates which would impede flow
Bidirectional flow has been observed in radiolabelling experiements
Flow is stopped if respiratory poisons enter the phloem suggesting an active process
It doesn't provide a rol

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Mass Flow Explained

Cells of the leaf make sucrose by photosynthesis
Sucrose is actively taken up by phloem companion cells
Companio cells pass the sucrose into the sieve tubes
At the sink the phloem companion cells remove sucrose from the sieve tubes
The companion cells pas

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Mass Flow Explained Part Two

Water is drawn into the sieve by osmosis
Causes build up of hydrostatic pressure at the top of the sieve tube which results in the movement of water and sucrose from source to sink
The sucrose is removed at the sink and used up or converted to starch for

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Complete Understanding

We do not completely understand the process
Other theories have been created
Cytoplasmic streaming is where different solutes are transported along different filaments

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Get Revising

Adaptations for Transport (Plants)

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