Download Leaf Tissues and Gas Exchange

November 13, 2014
Leaf Tissues and Gas Exchange
November 13, 2014
Air can only get into the cells through passive diffusion. Plant
cells are specialized to maximize this diffusion rate.
November 13, 2014
Dermal Tissue
Guard cells allow gas exchange, they form a stomata, usually
on the underside of a leaf. They do not open all the time, or
they would lose too much water. Light triggers them to
swell and open.
When there isn't much water the guard cells close.
Guard cells control transpiration.
November 13, 2014
If there is high Humidity would there be more or less stomata?
How about in low CO2 levels?
November 13, 2014
Ground Tissue
Mesophyll tissue (Between the upper and lower epidermis)
2 types of Mesophyll
1. Palisade Tissue (on top of the leaf)
Long rigid rectangular cells that are exposed to
the sun. Photosynthesis happens in these cells.
November 13, 2014
Spongy Mesophyll
loosely packed cells, with lots of space between them.
This allows gas exchange.
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Vascular Tissue
The veins on a leaf.
xylem and phloem are here.
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Lenticels
Pores on woody stems and roots which act like stomata and
allow gas exchange.
November 13, 2014
Pg 314 #1 to 8
November 13, 2014
Transport in Plants
Cohesion and Adhesion
Cohesion:
Water is attracted to other Water molecules.
Due to its polarity.
Adhesion:
Water is attracted to other substances, Attracted to
the cell walls of the Xylem.
November 13, 2014
Root Pressure
Roots cells actively transport minerals (makes them
hypotonic) Water flows into the roots and forces water
up the stem. Because it moves from an area of high
pressure to low pressure. Root pressure pushes water a
maximum of only a few meters.
November 13, 2014
Transpiration
Evaporation of water from stomata and lenticels
creates a transpiration pull. This pulls the adjacent
water molecules up the stem.
Why is there more of a pull on a hot day?
November 13, 2014
Tonicity and the Plant Cell
Tonicity (how much solute there is)
If in a salty environment water leaves the cell, vacuoles
shrink and plant appears wilted.
If returned to fresh water vacuoles fill until turgid (full/
swollen) this is good because then green parts of the cell
are facing the sun and more photosynthesis happens.
November 13, 2014
Sugar Transport (Pressure Flow Theory)
Sugar goes from a source (where its manufactured, a
leaf) to a sink (where it's used or stored)
Sugars are actively transported into the phloem by
companion cells. then water follows, and the sugar
is pushed by water pressure to the sinks, where
pressure is lower.
November 13, 2014
Pg 322
#1,2,3,5,7,8
November 13, 2014
Control Systems
Why do stems grow up and roots grow down?
1. Phototropism
Stems exhibit positive phototropism (they grow
toward the light). Roots exhibit negative phototropism
(they grow away from the light)
November 13, 2014
2. Gravitropism
Stems grow against gravity (negative gravitropism) and roots
grow toward gravitational force (positive gravitropism).
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Pg. 328
#2,3
November 13, 2014
Pg 330
#1 to 15 and 17
I will be taking these ones in.