Transport in plants part 2

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  • Created by: sophiee96
  • Created on: 03-04-13 11:32
The walls of the spongy mesophyll are saturated with what?
Water
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Will more water be lost on a dry, windy day, or a humid, still day?
Dry, windy
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What does a photometer measure?
The rate of water uptake
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What is the rate of water uptake much the same as? And why?
The rate of transpiration, because 99% of water taken up by a leafy shoot is lost during transpiration
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What happens to the diffusion shells in still and windy conditions?
In still air the shells remain on the leaf surface bt wind will blow them away increasing the water potential gradient
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What are the three groups plants can be categorised into in relation to the prevailing water supply?
Hydrophytes, xerophytes and mesophytes
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What types of plants are hydrophytes
Water plants
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What types of plants are xerophytes
Plants that live in condition where water is scarce
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What types of plants are mesophytes
Plants living in conditions of adequate water supplies
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What happens to the rate of transpiration in relation to the rate of water absorption if the cells of the plant are fully turgid?
They are equal
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What is the effect on photosynthesis if the plant wilts, why?
It becomes less efficient, the leaves droop so their surface area is reduced
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What type of plants are crops?
Mesophytes
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How do many trees and shrubs cope with winter?
By shedding their leaves
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What happens to many non-woody plants during winter?
Their areal parts die off, but their underground organs survive (eg bulbs, corms)
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How do annual mesophytesWater survive the winter?
As dormant seeds
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Where do xerophyte plants live?
In conditions of low water availability
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What do xerophytes adaptations try and prevent? How?
Excessive water loss, by reducing the water potential gradient between the atmosphere and the leaf
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Three conditions xerophytes may be found?
Hot, dry regions; cold regions where soil water freezes and exposed, windy conditions
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Why are sand dunes difficult for plants to survive in?
Because there is no soil, water drains away rapidly, there are high wind speeds, salt spray and lack of shade
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Four modifications marram grass shows to help it survive in the sand dunes?
Rolled leaves, sunken stomata, stiff interlocking hairs and a thick cuticle
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Why does marram grass have rolled leaves?
Because, large thin-walled epidermal cells at the bases of the grooves shrink when they loes water fro, texcess transpiration causing the leaf to roll onto itself
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What effect does rolled leaves have?
Reduces the leaf surface area from which transpiration can occur
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What is the benefit of a plant having stomta in pits or depressions?
Humid air is trapped outside the stomata, this reduces the water potential gradient between the leaf and the atmosphere so reduces the rate of water diffusion
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What do stiff, interlocking hairs do?
Trap water vapour and reduce the water potential gradient
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What is the cuticle?
A waxy covering over the leaf surface
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What does the cuticle do?
Reduces water loss
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What effect does a thicker cuticle have?
Lowers the rate of cuticular transpiration
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Where do hydrophytes grow?
Submerged or partially submerged in water
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Five adaptations of hydrophytes?
Little or no lignified support tissues, poorly developed xylem, little or no cuticle, stomata found on the upper surface of the leaves and large air spaces in stems and leaves
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Why don't hydropytes need lignified support tissues?
Because water acts as a support medium
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Why is it ok for the xylem to be poory developed?
Because the plant is suppounded by water, so there is little need for transport
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What do large air spaces in the stems and leaves form?
A reservoir of oxygen and carbon dioxide
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What do gases provide to the plant tissues when submerged?
Buoyancy
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What are the products of photosynthesis transported in?
The phloem
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When are the products transported from and to?
From the leaves (the 'source') to all the other parts of the plant where they are used (the 'sinks')
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What are the products of photosynthesis used for?
Growth or storage
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What is the transport of amino acids and sucrose in plants known as?
Translocation
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Name two soluble organic materials in plants?
Sucrose and amino acids
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What are the two main types of tissue that phloem consists of?
Sieve tubes and companion cells
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Is the phloem living tissue?
Yes
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What are the only components of phloem adapted for the longitudal flow of material?
Sieve tubes
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What cell are sieve tubes formed from?
Sieve elements
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What are the end walls of sieve tubes like?
Perforated with pores
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What are sieve plates?
The end wals of sieve tubes which are perforated with pores
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What extends from one sieve tube to the next through the pores in the sieve plates?
Cytoplasmic filaments containing phloem protein
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What happens to sieve tube organelles during their development?
They disintergrate
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Do sieve tubes possess a nucleus?
No
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Each sieve tube element is closely associated with at least one companion cell, what are three features of this companion cell?
Dens cytoplasm, large centrally placed nucleus and many mitochondria
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How are companion cells conected to sieve tube elements?
By plasmodesmata
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What is the phloem tissue concerned with?
The translocation of organic substances
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How did early experiments into phloem work?
By removing cylinders of outer bark tissue and analysing the contents above and below the tissue
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How can aphids help scientists learn about phloem?
Using radioactive tracing with labelled metabolites. Aphids insert their needle- like mouth parts into sieve tubes to feed on cell sap. The sap is under pressure as it exudes from the fine tube and is collected and analysed
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Why can scientists conclude that translocation isn't explained by diffusion?
Because it is too rapid
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What happens in radioisotope labelling?
CO2 labelled with radioactive carbon is supplied to an illuminated leaf and the radioactive carbon is fixed in the sugar produced in photosynthesis
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What does autoradiography trace?
The radioactive carbons translocation to other parts of the plant
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The leaf and tissues are placed on photographic film for 24 hours, what happens when the film is developed?
The presence of radioactivity in parts of the tissue shows up as 'fogging' of the negatives
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What does radioisotope labelling show?
That sucrose and amino acids are transported in both an upwards and downward direction - radioactivity is shown in the areal parts of the plant and the roots
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What does an autoradiograph of a transverse section of a stem of a treated plant show?
Fogging only where phloem was in contact with the film
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What does the main theory put forward to explain the transport of organic solutes known as?
The mass flow hypothesis
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What does the mass flow hypothesis (1937) suggest?
That there is a passive mass flow of sugars from the phloem of the leaf where there is the highest concentration (the source) to other areas, such as growing tissue where there is a lower concentration (the sink)
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When sugar is made what happens to the water potential?
It becomes more negative
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A source of sugar in the leaves is made by what process?
Photosynthesis
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What happens to sugar at the sink?
Its removed
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What joins the source to the sink?
The phloem
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What brings the water back to the source?
The xylem
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What does water do when the water potential becomes more negative?
It moves in by osmosis
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Other cards in this set

Card 2

Front

Will more water be lost on a dry, windy day, or a humid, still day?

Back

Dry, windy

Card 3

Front

What does a photometer measure?

Back

Preview of the front of card 3

Card 4

Front

What is the rate of water uptake much the same as? And why?

Back

Preview of the front of card 4

Card 5

Front

What happens to the diffusion shells in still and windy conditions?

Back

Preview of the front of card 5
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