OCR As biology : casparian *****/xerophytes and marram grass / transpiration

short biology presentation covering:

role of casparian *****

xerophyte adaptations and marram grass


all adapted from OCR biology text book published by Heinemann

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  • Created by: Nicole
  • Created on: 04-01-12 18:31

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Slide 1

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Plant Presentation Number 2
role of Casparian strip / xerophytes and marram grass/
transpiration…read more

Slide 2

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Role of the Casparian strip
It blocks the apoplast path between cortex and the xylem
Ensures that water and dissolved nitrate ions have to pass into
the cytoplasm through the cell membranes ( symplast path)
There are transporter proteins in the cell membranes
The nitrate ions can be actively transported ( using active
transport which requires energy) from the cytoplasm of the
cortex cells, into the xylem
This lowers the water potential in the xylem so water from the
cortex cells follows into the xylem by osmosis
Once the water has entered the xylem it cannot pass back into
the cortex as the apoplast path of the endodermal cells is
blocked…read more

Slide 3

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Describe the role of the casparian strip (5 marks)
Describe how water is lost from the leaf ( 4 marks)
Describe how marram grass is adapted to live in dry conditions
( 5 marks)
Describe the adaptations of xerophytes ( 8 marks)…read more

Slide 4

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Xerophytes: Marram grass
Leaf rolled up to trap air inside
Thick waxy cuticle to reduce water by evaporation
Trapped air in the centre with a high vapour potential
Hairs on the lower surface reduce movement of air
Stomata in pits to trap air with moisture close to the
stomata…read more

Slide 5

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Xerophytes : general
Small leaves = reduce surface area
Densely packed mesophyll = reduce surface area
Thick waxy cuticle= reduce evaporation
Closes stomata when H2O low= reduce H2O loss
Hairs on surface= reduce difference in water vapour
potential gradient
Pits= reduce H2O potential grad
Rolls leaves= lower epidermis nt exposed = lower water
potential grad
High salt concetration in cells = low water potential
gradient between cells and leaf. = low water potential
inside…read more

Slide 6

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It is: loss of water by evaporation from the aerial parts of the plant
Water enters leaves in xylem and pass into mesophyll cells by
Water evaporates from the mesophyll cells and forms water vapour
Spongy mesophyll have air spaces that help water vapour diffuse
through the leaf tissues.
As water vapour collects in these air spaces , water potential of the
vapour rises
Water molecules will diffuse out of the leaves
The stomata are open during the day to allow gaseous exchange for
photosynthesis.…read more


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