Gas exchange of the Flowering plants.pdf

Gas exchange of the Flowering plants

1. IconsCC –The Pink Group
Copyright © 2017 Henry Exham

2. Copyright © 2018 Henry Exham
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2.40BUnderstandtheroleofdiffusioningasexchange.
2.41BUnderstandgasexchange(ofcarbondioxideandoxygen)inrelation
torespirationandphotosynthesis.
2.42BUnderstandhowthestructureoftheleafisadaptedforgasexchange
2.43BDescribetheroleofstomataingasexchange.
2.44BUnderstandhowrespirationcontinuesduringthedayandnight,but
thatthenetexchangeofcarbondioxideandoxygendependsonthe
intensityoflight.
2.45BPractical:investigatetheeffectoflightonnetgasexchangefroma
leaf,usinghydrogen-carbonateindicator.
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2g –Gas exchange –Flowering plants
Objectives

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•Gaseous exchange in plants occurs through the
stomatain the leaves.
•The gases move by diffusion(from an area of high
concentration to low concentration).
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2g –Gas exchange –Flowering plants
Gas exchange in plants
O
2
CO
2
O
2
O
2
CO
2
During photosynthesis,
carbon dioxide enters
the leaf and oxygen
exitsthe leaf.
During respiration,
oxygen entersthe
leaf and carbon
dioxide exits the leaf.

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2g –Gas exchange –Flowering plants
Gas exchange in plants
O
2
O
2
CO
2
CO
2

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•Respiration occurs in plants 24 hours a day.
•However photosynthesis only occurs when
sunlight is available.
•Therefore the net exchange of gasses depends
on how much light is available.
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2g –Gas exchange –Flowering plants
Gas exchange in plants

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2g –Gas exchange –Flowering plants
Gas exchange in plants
0 12 24 186
Time from midnight (Hours)
Rate of reaction
Photosynthesis
Respiration

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2g –Gas exchange –Flowering plants
Leaf adaptations for gas exchange
•Broadso large surface area for diffusion
•Thinso short diffusion distance
•Air spaces allow gases to easily move to all cells
•Lots of stomata
•Plant can control the opening and closing of stomata
using the guard cells

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•As already mentioned there is an indicator which
is used to measure the amount of carbon dioxide.
•It’s called Hydrogen-carbonate indicator.
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Investigating the effect of light on net gas exchangePRACTICAL

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Investigating the effect of light on net gas exchangePRACTICAL
Normal CO
2
is orange High CO
2
is yellowLow CO
2
is purple
IncreaseIncreaseDecreaseDecrease

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•You can use this apparatus to show how light
affects gas exchange.
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Investigating the effect of light on net gas exchangePRACTICAL
1.Put three leaves all of the same size into
tubes with the same volume of hydrogen-
carbonate indicator.
2.Have a fourth tube with the indicator in
but no leaf as a control experiment.

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Investigating the effect of light on net gas exchangePRACTICAL
3.Wrap one tube in aluminium foil
4.Wrap another in muslin
5.Now shine a bright light onto the
tubes and leave them for 45 minutes.
6.Can you predict the results?

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2g –Gas exchange –Flowering plants
Investigating the effect of light on net gas exchangePRACTICAL
The tube which was covered with foil has had
no light and therefore the leaf has not been
photosynthesising but only respiring.
Therefore producing CO
2
.
The tube with no cover has been
photosynthesising a lot and therefore using
up the CO
2
in the tube.
The tube with muslin has had some light so
overall no change in CO
2
.
The control tube has had no leaf in it and
therefore no change in CO
2
.
ControlFoilNo
cover
Muslin

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1.Plants do both respiration and photosynthesis
2.Plants respire only during daylight hours
3.Gases move in and out the leaf via the xylem
4.Leaves are thin to minimize diffusion distance
5.CO
2
is produced during photosynthesis
6.Photosynthesis happens 24 hours a day
7.Hydrogen-carbonate indicator turns yellow when CO
2
levels increase
8.Hydrogen-carbonateindicator is purple with atmospheric CO
2
levels
9.Plants can open and close their stomata
10.Most stomata are on the bottom of the leaf
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CONCEPT CHECK –True or false

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1.Plants do both respiration and photosynthesis
2.Plants respire only during daylight hours
3.Gases move in and out the leaf via the xylem
4.Leaves are thin to minimize diffusion distance
5.CO
2
is produced during photosynthesis
6.Photosynthesis happens 24 hours a day
7.Hydrogen-carbonate indicator turns yellow when CO
2
levels increase
8.Hydrogen-carbonateindicator is purple with atmospheric CO
2
levels
9.Plants can open and close their stomata
10.Most stomata are on the bottom of the leaf
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2g –Gas exchange –Flowering plants
CONCEPT CHECK –True or false

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Q: Describe the graph showing the net gas exchange in a plant
over 24 hours
(3 marks)
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CONCEPT CHECK –Exam style question
Photosynthesis
Respiration
Time from midnight (Hours)
Rate of reaction (AU)
0 12 24 186
10
5

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Q: Describe the graph showing the net gas exchange in a plant
over 24 hours
(3 marks)
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2g –Gas exchange –Flowering plants
CONCEPT CHECK –Exam style question
Time from midnight (Hours)
Rate of reaction (AU)
0 12 24 186
10
5
Photosynthesis
Respiration
The rate of respiration stays approximately
the same/constant for 24 hour;
This is at about 2AU;
Photosynthesis increases at 5 hours;
It plateaus between 10-15 Hours;
This is at 9AU;
It then decreases back to 0AU at 22 hours;