Science 10 – Unit C - BIOLOGY
Chapter 3 - Plants
C3.3 - Leaf tissues and Gas Exchange
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Leaf Tissues and Gas Exchange
o With a waxy cuticle, how do the cells inside the plant get air?
o Plants have specialized cells which allow more efficient gas exchange within the
leaf called
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Entry of gases into the leaf
o Air enters plant cells through
o Guard cells open into ground tissue to allow for
o Movement of gas depends on the
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Stomata
o singular = stoma
o The majority of stomata on a leaf are found on the
o Depending on conditions the guard cells will open or close
 stomata must be open
 however, open stomata also allow for
 proper regulation of opening/closing is important for the survival of the plant
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Opening the stoma
o light hits the top of the leaf
 this stimulates potassium ions (K+) ions to
o there is now a higher concentration of K+ ions inside the cell
 the cell is in a
o water from the ECF floods into the cell
 cells become turgid, which causes them to
o the stoma is now open
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Closing the stoma
o when sunlight is no longer available, K+ is
 K+ diffuses back out of the guard cells
 with more K+ ions in the ECF, the guard cells are now in a
o water flows out of the guard cells by osmosis
 the cells lose turgor pressure,
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Transpiration
o Stomata allow for easy movement of gases but also
o Plants need water because…
 it is one reactant in photosynthesis
 all gas in the leaf is absorbed into the cells by
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this thin film of water causes plants to lose water vapor
Adapting to environmental conditions
o Stomata are sensitive to environmental conditions
 Plants that live in hot, dry climates have adapted to
 Plants in environments with little carbon dioxide have adapted by
o other adaptations plants can make:
 colour
 plants in tropical climates tend to be
, due to
 leaf size
 plants in tropical climates also have big broad leaves, and grow tall to

plants in very dry climates have small, specialized leaves called
 cuticle
 plants in dry climates have a very thick cuticle
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Ground tissue
o recall, the ground tissue is located
o two types of cells in the ground tissue
o Palisade tissue cells
 found
 long, rigid rectangular cells tightly packed together (maximizes number of cells in contact
with the sun)
 responsible for
o Spongy mesophyll tissue
 between palisade tissue cells and lower epidermis
 loosely packed with
 maximizes
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Lenticels
o While most gas exchange occurs through the stomata, openings through the
bark of woody plants also
o these “slashes” on the tree bark are called lenticels
Homework
o label diagram of the cross-section of a leaf
o complete summary table of plant cells, tissues and systems
o complete Section C3.3 of green workbook
Cross-section of a leaf
Put the following terms into this diagram (use page 312 for help)
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vein
upper epidermis
dermal tissue
vascular bundle
spongy layer
xylem
lower epidermis
ground tissue
guard cell
phloem
cuticle
palisade layer
stomata
Plant Cells, Tissues, and Systems
Name
Shoot System
Root System
Dermal Tissue or Epidermis
Ground Tissue
(a)
Palisade Tissue
(b)
Spongy Mesophyll Tissue
Vascular Tissue
(a)
Phloem
•
Sieve Tube Cells
•
Companion Cells
(b)
Xylem
(c)
Vascular bundles
Meristems
Specialization in Plant Cells
(a)
Root Hairs
(b)
Guard Cells
(c)
Cuticle
Definition
Function
Science 10 – Unit C - BIOLOGY
Chapter 3 - Plants
C3.4 - Transport in plants
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The challenge:
o The tallest tree recorded is a Redwood tree in California, measuring over 115m (= a 42
storey building)
o How can such a large tree transport water from its roots up into its top branches?
o We might guess it costs the tree a lot of energy!
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Transport in plants
o We have already learned about transport mechanisms which help move water in a plant
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Forces involved in moving water from roots to leaves
 Polarity of water
 plants act as pumps to deliver water from the roots to the leaves
 the properties of water help plants use it efficiently
 recall, water is a polar molecule
 the hydrogen end is
 the oxygen end is
o Cohesion
 water molecules are attracted
 when one water molecule rises up the xylem tube, it pulls
o Adhesion
 Since water is polar, it attracts itself to molecules of other substances.
 water molecules “stick” to other substances.
 this called
 in a plant the water molecules would adhere
 it is these two forces together that allow water to stay in much larger droplets
o Root pressure
 Plants actively transport minerals into the root cells
 as a result, the root becomes
 the water moving into the roots creates
 as water moves into the roots, it
 this can be tested by cutting a plant and seeing the water seep up into the cut
of the stem
o Transpirational Pull
 as water evaporates out of the leaves by transpiration, it leaves an empty space
behind it
 new water molecules will rush up to fill the void

transpiration pull refers to the pulling of water molecules up the plant by

this pull is primarily responsible for bringing water from the xylem into the ground
tissue
Transpiration depends on temperature;
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Movement of sugar in plants
o Sugar is produced in the leaves o Sugar must move in the plant to
a place where it will be used or
stored o The movement of materials in
and out of the phloem is called
the pressure-flow theory
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Homework:
o Read pages 315-321
o Label the diagram on pressureflow theory
o Complete section C3.4 in the
green workbook
Science 10 – Unit C - BIOLOGY
Chapter 3 - Plants
C3.5 - Control systems in plants
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Can plants respond to their environment?
o As humans, we can respond to stimuli in our environment.
o A stimuli is a change in the environment which creates a response within an organism
o What about plants? Can they respond to their environment?
 How do they know they know what direction their roots should go?
 How do plants grow up toward the light?
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Phototropism
o plants need to carry out photosynthesis to survive
o In order for plants to be successful, they must be efficient at gathering the materials
necessary for photosynthesis
 though not strictly a reactant, sunlight is one necessary ingredient in photosynthesis
o phototropism refers to
 photo =
; tropism =
 stems show positive phototropism because grow
 roots show negative phototropism because they grow
Darwin’s experiment on phototropism
o Charles Darwin was a scientist best known for his
o another important discovery Darwin made was in relation to phototropism
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o together with his son Francis,
Darwin set out to discover
what part of the plant was
responsible for
o he did this by setting up five
different trials
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Trial 1: the control
o the plant in trial one was not altered in any way
o this
o it also ensured that all the plants had
o Result:
Trial 2: tip removed
o suspecting that it was receptors in the stem responsible, Darwin
o Result:
Trial 3: tip covered with opaque cap
o to test if the plant was simply damaged by removing the tip, Darwin performed a third trial
o this time, the tip was
o Result:
Trial 4: tip covered with transparent cap
o to test if the plant bending was hindered by the cap, Darwin
o Result:
Trial 5: base covered by shield
o lastly, Darwin needed to verify that
responsible for phototropism
o to test this, he covered the base of the plant with an opaque shield
o Result:
Darwin’s conclusions:
o phototropism occurred most in the cells in the tip of the plant, which could most readily
access the sun’s energy
o these cells were somehow
Practice problem: in Darwin’s experiment,
o identify the manipulated variable
o identify the responding variable
o identify four controlled variables (controls)
Boysen-Jensen’s experiment
o though the Darwins had identified the cell’s tip as the photoreceptor,
o in 1913, Peter Boysen-Jensen investigated how the tip and the seedling communicated
o Boysen-Jensen snipped off the tip of the seedling and paint gelatin on the end, then put the
tip on - the seedling followed the light
o He then snipped the tip and placed a piece of thin mineral called mica in-between the tip
and the seedling - no phototropism was observed
o Peter Boysen-Jensen hypothesized that whatever was responsible for communicating
between the tip and the seedling must be able to diffuse through gelatin but not mica
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Area of elongation
o the area of the plant which bends toward the light was called
because the cells on the “dark side” of
the stem
, causing the plant to bend
Auxin
o In 1926, F.W. Went isolated the substance that was responsible for
o The substance was called
, a hormone which is produced
in a plant and then transported to cells which
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Gravitropism
o plants also respond to another stimulus: gravity
o direction of plant growth in response to gravity is called
 Stems show negative gravitropism because
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Roots show positive gravitropism because
o Mechanisms of gravitropism
 Scientist believe that plants rely on heavy starch
particles as an indicator of gravity
 If a plant is knocked over – the starch grains shift
and settle in a new location
 after movement is detected, then a growth response
results
 in this picture, the dish was turned
, then
a few days later
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Other controls
o response to touch
 some plants have the ability to respond to touch
 e.g. a pea plant responds to a rough surface by anchoring itself, allowing it to
climb
 e.g. a Venus fly trap closes when it registers the presence of an insect
o response to light availability
 e.g. Poinsettias actually respond to
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Homework
o Section review:
 Read pages 315 -328
 Complete section C3.5 in the green workbook
o Chapter review:
 prepare for a Chapter 3 key terms quiz
 p. 330 #2, 3, 7, 9-10, 12, 14, 16-20, 22-23, 25
o Unit review:
 p. 334-335 #2-5, 7-11, 13-15, 17-25