Water in plants

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  • Created by: ppogba
  • Created on: 18-08-19 12:44
Define physiology?
the branch of biology that deals with the normal functions of living organisms and their parts.
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Define Homeostasis?
the tendency towards a relatively stable equilibrium maintained by physiological processes.
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What % of plant bodies is made up of water?
95%
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What is water required for in plants?
Maintaining cell turgidity. Photosynthetic processes. Transpiration. Translocation of solutes.
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What is transpiration and how much of it accounts for total worldwide precipitation?
water is taken up by roots, travels through stems and is lost by leaves. 40%
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What are the 2 main components of the vascular system in plants?
Xylem and Phloem.
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What happens in the xylem?
unidirectional transport of water and nutrients from root to shoot
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Describe the structure of the xylem?
No end walls between cells, non-living, essentially open lignified tubes.
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What happens in the phloem?
bidirectional transport of solutes (organic molecules) between sources and sink.
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Describe the structure of the phloem?
has end walls (sieve plates). Cells are living but need support.
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Water is absorbed by root hair cells and crosses 4 major cell types before entering the xylem. What are they?
Epidermis > Cortex > Endodermis > Pericycle.
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What are the 2 water pathways that water uses to move through these 4 cell types to get to the xylem?
Apoplastic and Symplastic routes
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What is the Apoplastic route?
passage through cell walls. Largely unrestricted.
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What is the Symplastic pathway?
passage through the cytoplasm.
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What is the purpose of the Casparian *****?
it ensures all water has to follow the symplastic pathway to enter the xylem.
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What is the benefit of the symplastic pathway being the one that allows water into the xylem?
it gives the plant more control over how much water enters the xylem.
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What facilitates water transport across membranes?
water transport proteins- aquaporins
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Once in the xylem, where does the water travel to the plant?
it travels from the xylem, through the cytoplasm of the mesophyll cells, and out out of the leaf via stomata.
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Describe the Cohesion-Tension theory?
water within a plant forms a continuous column. Hydrogen bonding between water molecules is a strong cohesive force. Loss from leaves pulls water up the xylem, resulting in very high pressure (30MPa) within xylem.
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What I the effect of increased humidity on rate of transpiration? Why?
Transpiration decreases. Water in surrounding air outside leaf increases, which reduces the water potential difference between air and leaf.
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What I the effect of increased wind on transpiration rate? Why?
Transpiration increases. water in stomatal pores evaporates faster, transpiration increases and then faster movement of water through xylem.
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What is the effect of increasing light intensity on transpiration rate? Why?
Transpiration increases. P/s increases due to increased light intensity increasing. CO2 requirement increases and stomata open, allowing transpiration to increase.
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What is the effect of temperature increase on transpiration rate? Why?
Transpiration increases. Temp.increases, then p/s and CO2 requirements both increase. Stomata opens, transpiration increases.
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Boreal forests are the worlds largest terrestrial biome. What are they characterised by?
Coniferous trees- N.America and Eurasian.
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In boreal forests it can be very cold (-17C), being hard to survive here. Why is is dry here?
due to coldness, there is little water as its frozen.
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How does the water freezing cause water chains in xylem vessels to break?
water in xylem freezes and dissolved gases in xylem will form bubbles. Repeated freezing and thawing cause these air bubbles to grow and disrupt H bonding between water molecules, causing water chain to break
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What I an Embolism?
gaps in the water stream in xylem- water no longer being pulled up xylem.
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How are trees in Boreal forests adapted to be less vulnerable to embolisms?
they have narrow and short xylems
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Despite needing this adaptation to survive, what are the disadvantages to having them?
they become less efficient in conduction and transpiration rates.
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This adaptation seems to have evolved as a link to drought tolerance. How?
early trees evolved in wet, swamp conditions. To radiate northwards, they had to adapt to lower water conditions. It gave them the 'genetic toolbox' to adapt similarly to low temperature later onion their evolution.
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Other cards in this set

Card 2

Front

Define Homeostasis?

Back

the tendency towards a relatively stable equilibrium maintained by physiological processes.

Card 3

Front

What % of plant bodies is made up of water?

Back

Preview of the front of card 3

Card 4

Front

What is water required for in plants?

Back

Preview of the front of card 4

Card 5

Front

What is transpiration and how much of it accounts for total worldwide precipitation?

Back

Preview of the front of card 5
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