Transcript Unit9

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
Unit 9
Photosynthesis in Green Plants
Unit 9: Photosynthesis in Green Plants
Understand:
1.
2.
3.
4.
5.
6.
7.
8.
9.
The anatomy and cell parts of the common
plant cell.
The role of the chloroplast and mitochondria
during photosynthesis and respiration.
The role of the leaf and the palisade cell during
photosynthesis.
That the substrates for photosynthesis are
water and carbon dioxide.
That the products of photosynthesis are
glucose and oxygen.
That
light
energy
is
essential
for
photosynthesis to occur.
That the overall rate of photosynthesis is
determined by limiting factors including carbon
dioxide, light intensity, light colour and
temperature.
That plants use glucose to make other
molecules.
That plants can respond to stimuli like light,
gravity and moisture.
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Keywords:
Leaf,
Tissue,
Organ,
Cell,
Palisade,
Photosynthesis, Substrates, Water, Carbon
dioxide, Products, Glucose, Oxygen, Light,
Energy, Intensity, Limiting, Factors, Light,
Temperature, Colour, Rate, Tropism &
Stimuli.
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Levels of organisation in plants
In plants, as in animals, similar cells performing similar f__________ are organised into
tissues. Leaf palisade tissue consists of identical palisade cells functioning together to enable
photosynthesis to occur. Other tissues found in green l________ also support photosynthesis. A
leaf is an organ made up of many different tissues. Different organs work together as part of the
entire plant organism. There are four distinct organs in a typical plant: The root system, the
stem system, the leaf system and the reproductive system. Name the function of each of the four
organ systems found in green plants ?
Cells, tissues, organs and organ systems in plants:
Word bank: functions leaves
Cells
Tissues
Organs
Organism
Cells
are
highly
specialised and are
designed to do their job
within the plant. List 3
specialised cells found
in green plants ?
Tissues like the palisade
layer or stomata tissue
are a collection of cells
working together to
perform specific tasks in
the plant.
Organs are a collection
of tissues like the leaf.
Many separate organs
build an organ system.
List 3 organs in the
plant ?
The are four organ
systems that support life
in plants. All perform
specific roles. Which of
these systems does not
support photosynthesis ?
Diagram
Notes
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Plant leaf system
A number of cells and tissues within the plant leaf play a role during photosynthesis, whereby
water and carbon dioxide combine during photosynthesis to form g_______ and o_________.
Palisade cells containing chloroplast are the main site of glucose production. Xylem tissue
supplies water from the root and phloem tissue transports glucose made during photosynthesis
around the plant. Gaseous exchange during photosynthesis and respiration is controlled by the
stomata cells. Why are the stomata cells found only on the underside of the leaf ?
Plant leaf system:
Stomata cells
Word bank: glucose oxygen
Xylem tissue
Plant leaf
Leaf system
Diagram
A
B
C
E
Notes
Stomata found on the
underside of the plant
leaf allows gaseous
exchange and water
transpiration. They open
during the day and
remain closed during the
night.
The
xylem
tissue
transports water and
minerals like nitrates
from the root system to
the leaf system via the
plant stem. Phloem
tubes transport sugary
sap all around the plant.
D
The leaf is a collection
of tissues:
A: Upper epidermis
B: Palisade layer
C: Spongy mesophyll
D: Lower epidermis
E: Stomata
The leaf system is a
collection of leaves
that work together
producing glucose and
oxygen from water and
carbon dioxide using
the energy from the sun
during daylight hours.
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Specialised cells in plants
Like animals, plants have many different s____________ cells performing different
functions. Green plants have many examples of specialised cells that are designed for
functions like photosynthesis, growth, reproduction, taking in w______ and minerals from
the soil. The leaf palisade cell is a good example of a specialised cell in plants. It is well
designed for photosynthesis, for example it contains many chloroplasts organelles, rich in
chlorophyll. Where is the palisade tissue located in the plant ?
Specialised cells:
Word bank: specialised water
Palisade cell
Root hair cell
Stomata cell
Pollen cell
Green leaves contain
many palisade cells
which are rich in
chloroplasts that enable
photosynthesis
to
occur. Why do root
cells not have these
cell parts ?
The root hair cell has
a large surface area to
volume ratio, so that it
can absorb water and
minerals from the soil.
Name two of these
mineral salts found
dissolved in water ?
The stomata cells
controls the exchange
of CO2 and oxygen
during photosynthesis.
They close during the
night. At what time
during the day does
CO2 enter the leaf ?
Pollen cells, normally
transferred to the
female carpel by bees
and other insects carry
genetic information to
create a new plant
when it fuses with the
female ovule.
Diagram
Notes
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The common plant cell
Plant cells, like animals cells are made from many cell parts or organelles, each with a
specific function. The common plant cell has some similarities and some differences to
animal cells. This reflects differences in the way plants and animals feed and support
themselves. The most important cell part is green c____________ containing chlorophyll
which allows photosynthesis to occur.
Common plant cell:
Word bank: chloroplast
Cell part
Function (complete)
Nucleus
Control cells activities and contains DNA
Cytoplasm
_______________________ ?
Membrane
_______________________ ?
Vacuole
_______________________ ?
Cell wall
_______________________ ?
Chloroplast
_______________________ ?
Mitochondria
_______________________ ?
Lysosome
_______________________ ?
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Mitochondria and chloroplast organelles
If you view plant and animals cells under a microscope, you can see tiny dots in the
cytoplasm. These are the mitochondria. Cellular r____________ occurs in the
mitochondria, releasing energy from glucose molecules. Plants also have green
c____________ containing chlorophyll where water and carbon dioxide are combined
to form glucose and o_________ during photosynthesis. Why do muscle cells contain
more mitochondria than skin cells ?
Mitochondria and chloroplast:
Word bank: respiration chloroplast oxygen
Mitochondria
Chloroplast
Diagram
Matrix
Membrane
Matrix
Membrane
Function in the cell
To respire glucose with oxygen To produce glucose using CO2 and water. All
providing cell energy. All living cells green plants have these organelles.
have these organelles.
Equation
C6H12O6 + 6O2
Animal or plant
Animal and plant
6H2O
+ 6CO2
6H2O
+ 6CO2
Plant only
_____ + _____
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Plants as producers one
Plants are called producers because they produce all the World’s biomass via a process called
photosynthesis. Plants use energy from the s_____ to combine carbon dioxide and w________
to form g__________ and oxygen. This reaction produces millions of tonnes of living matter
that nourishes all other living organisms in the animal kingdom. The oxygen that plants release
into the atmosphere is used in cellular r_____________ by all living organisms. How can we
determine the biomass of a plant ?
Plants as producers:
Word bank: sun water glucose respiration
Photosynthesis in action
Plant yield
Plant yield: (kg per hectare)
Diagram
C6H12O6
6H2O
Chloroplast
Energy
Glucose
14000
6CO2
6O2
10000
6000
2000
Plant cells
Notes
Green chlorophyll contained in
palisade chloroplasts are able to
use light energy to enable carbon
dioxide and water to combine to
form glucose and oxygen.
<1000
Plants only use a small fraction of the sunlight energy, they
receive every year. Despite this, sugarcane produces up to
200 tonnes of glucose per year per hectare. The most
productive areas are the equatorial regions that receive the
most sunlight energy.
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Plants as producers two
The glucose produced during photosynthesis in green plants is used to make plant
c____________, lipids and proteins. Every year over 70,000,000 kJ of sunlight energy falls
on every metre squared of land. Plants only use about 90,000 kJ/m2/year of l_______
energy during photosynthesis, however they produce over 132 billion tonnes per annum of
biomass. Overall plant yields depend on a number of factors including light availability,
soil quality, rainfall levels and competition. How could you determine the yields of
different crops over time ?
Plant yield and biomass:
Crop
Word bank: carbohydrates light
Sugarcane
Corn
Rice
Wheat
Sugarcane,
rich
in
glucose can produce a
yield of up to 9000 kg
per acre.
Corn, rich in proteins
and carbohydrates can
produce a yield of up to
5500 kg per acre.
Rice, rich in carbohydrates can produce a
yield of up to 3000 kg
per acre
Wheat, rich in carbohydrates and sugars can
produce a yield of up to
2500 kg per acre.
Diagram
Notes
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Plants as producers three
Plants are extremely efficient at transforming the energy carried by light to chemical
energy trapped in glucose molecules, which are produced during p_____________. Their
efficiency is about 80%, far higher than typical values for herbivores and carnivores. Only
a small fraction of the c__________ energy they produce in the form of glucose is lost
through respiration or waste. How could you determine the amount of glucose that is used
during cellular respiration in plants ?
Plants using light energy:
Word bank: photosynthesis chemical
Plants use of light energy
Diagram
Light energy
10,000kJ
1
Process
Biomass: Energy contained
8,000 kJ 1 in the tissues of the plant
(available for the next level.)
Respiration: Energy used in
1,500 kJ 2 cellular respiration by all
plant cells.
2
3
Notes
500 kJ
Waste: Energy contained in
3 the waste materials found in
leaves.
The transfer of energy from the sun’s rays to the glucose
found in plant leaves is achieved during photosynthesis.
Plants are highly adapted and efficient at transforming light
energy to chemical energy. Over 132 billions tonnes of plant
biomass is produced globally every year.
Only a very small fraction of
energy is used for respiration
or lost as waste. Plants are
almost 80% efficient as
producers.
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Plants as producers four
Plant leaves contain many palisade cells containing green c___________. Palisade cells
use e______ from sunlight during photosynthesis to make g________ and oxygen. This
palisade cell layer is found near to the surface of the leaf. Here it can absorb all the
sunlight that falls on the leaf’s surface. How could you design an experiment to show that
light is an essential factor for photosynthesis ?
Plants using light energy:
Word bank: chloroplasts energy glucose
Anatomy of the plant leaf
Process
Diagram
A
B
F
G
C
D
E
Notes
The transfer of energy from the sun’s rays to the glucose found in plant
leaves is achieved during photosynthesis. Plants are highly adapted
and efficient at transforming light energy to chemical energy. Over 132
billions tonnes of plant biomass is produced globally every year.
A: Upper epidermis
B: Palisade layer
C: Spongy mesophyll
D: Lower epidermis
E: Stomata
F: Xylem
G: Phloem
Give a function of the leaf tissue.
Say how each part helps
photosynthesis ?
Only a very small fraction of
energy is used for respiration or
lost as waste. Plants are almost
80% efficient as producers.
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Plants as producers five
Every tissue found in green leaves, supports the production of glucose during
photosynthesis. Palisade cells containing green c___________ have enzymes which use
light energy to combine water and carbon dioxide forming glucose and oxygen. The xylem
transports w______ from the root. Phloem tubes transport glucose to the rest of the plant.
Stomata cells allows carbon dioxide from the atmosphere and promote transpiration. The
spongy mesophyll allows carbon dioxide to diffuse quickly to the palisade cells. Why are
the palisade cells filled with chloroplast found in the upper part of the leaf ?
Plants leaf structure and anatomy:
Word bank: chloroplast water
Parts of the leaf
Cuticle
Upper epidermis
Palisade layer
Spongy mesophyll
Lower epidermis
Stomata
Guard cells
Xylem
Phloem
Give a function for each
tissue found in green leaves.
Say how each part helps
photosynthesis ?
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Photosynthesis and its equation one
Photosynthesis, the process whereby l______ energy is used by palisade cells found in green
leaves to combine carbon dioxide and water to produce glucose and oxygen. This is the
equation for the whole process.
Carbon dioxide
+
Water
Light and chlorophyll
Glucose
+
Oxygen
From the equation we can see there are three requirements:
 Light
 Chlorophyll
 Substrates: Carbon dioxide and water
Requirements for photosynthesis:
Light
Chlorophyll
Word bank: light
Carbon dioxide and water
Diagram
Carbon dioxide
Notes
Light is used to provide the
energy
required
during
photosynthesis to combine
water and carbon dioxide
producing
glucose
and
oxygen.
Green chlorophyll found in the
leaf palisade layers uses light
energy to form glucose and
oxygen. It contains a very
complicated series of enzymes
that act as catalysts.
Water
Carbon dioxide, absorbed by the
leaf and water absorbed by the
root hair cells are essential
substrates that are used during
photosynthesis making glucose
and oxygen.
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Photosynthesis and its equation two
From the equation for photosynthesis, we can determine the raw materials required during
photosynthesis. Glucose production in green leaves will only occur if w_______ and
carbon dioxide are supplied to the chloroplasts inside leaf palisade cells.
6CO2
+
Carbon dioxide
6H20
C6H12O6 + 6O2
water
light and chlorophyll
Glucose
Oxygen
Raw materials and photosynthetic products:
Substrate
Carbon dioxide
Water
Word bank: water
Glucose
Oxygen
Diagram
6 molecules of CO2
Notes
Carbon dioxide is
taken in during day
light hours through the
leaf stomata cells from
the atmosphere.
6 molecules of H2O
Water is taken from the
soil by the root hair
cells, through the
xylem and into the leaf
space.
1 molecule of glucose
Glucose
produced
during photosynthesis
is transported by the
phloem to all parts of
the plant.
6 molecules of O2
Oxygen is taken out
through the leaf during
daylight hours and
released
into
the
atmosphere.
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Photosynthesis and its equation three
Reactions that take in energy from their surroundings in the form of heat or light are
called endothermic reactions. Although these types of reactions are not as common as
exothermic reactions, there are several examples. An important example of an
endothermic reaction is photosynthesis, whereby light e_________ is used to combine
water and carbon dioxide to form glucose and oxygen.
Energy changes during photosynthesis:
Word bank: energy
Photosynthesis in green plants
Key
6O2
C6H12O6
H2O
6H2O 6CO2
Products
Potential energy
Activation energy
Substrates
Progress of reaction
C6H12O6
Net energy taken
in during reaction
O2
CO2
In this reaction H2O
and CO2 substrates
are combined in the
plant leaf cells using
light
energy
to
produce
glucose
(C6H12O6) and O2.
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Photosynthesis and its equation four
Sunlight, carbon dioxide, water and g______ chlorophyll are all essential for
photosynthesis to take place inside a green leaf. Proving that these are essential, however
requires experimentation. A series of experiments were carried out and are summarised in
the table below. In brief, plants with no access over 48 hours to sunlight, chlorophyll or
carbon dioxide were tested for starch in their l________. For each experiment, complete
the results and give an explanation ?
Factors required for photosynthesis:
1: No light
Word bank: green leaves
2: No chlorophyll
3: No carbon dioxide
Diagram
Complete
Results
Complete
Show leaf after
testing
with
iodine solution.
Explanation
Starch is shown by a blue black colour when in contact
with iodine. What does this
experiment prove ?
________________________ ________________________
________________________ ________________________
_______________________ ? _______________________?
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Limiting factors for photosynthesis
From the equation for photosynthesis, we can also determine the limiting factors affecting
the r_______ of glucose production in green leaves. The rate of photosynthesis speeds up
as light intensity increases, but only up to a point. The overall rate may also be limited by
the concentration of carbon dioxide, the temperature or even the colour of light. Factors
that can affect the rate of photosynthesis are called limiting factors.
Limiting factors:
Word bank: rate
Light intensity
Temperature
CO2 Concentration
Colour of light
Diagram
Equation
6CO2
+
Carbon dioxide
Notes
Light from the sun is
used to provide the
energy
required
to
combine H2O and CO2
during photosynthesis.
6H20
water
C6H12O6
light and chlorophyll
The
higher
the
temperature the more
often H2O and CO2
molecules collide into
each other.
Glucose
The
greater
the
concentration of CO2
the greater the rate of
photosynthesis in green
plants.
+ 6O2
Oxygen
Red and blue light are
absorbed by plants,
whereas green light is
reflected and not used
during photosynthesis.
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Limiting factors light intensity one
During photosynthesis, molecules of water and carbon dioxide collide, form new chemical bonds
producing glucose and oxygen. The energy required to form these new bonds in glucose is provided
by light energy. The rate of p____________ increases when the amount of light energy increases, but
only up to a point. Other factors, like carbon dioxide concentration and temperature also affect the
overall rate of photosynthesis. These are called limiting f__________. The factor in shortest supply
will always be the limiting factor.
Affect of light intensity on the rate of photosynthesis:
Experiment
1
2
3
Distance (m)
0.1m
0.2m
0.3m
Diagram
0.1m
0.2m
Word bank: photosynthesis factors
Time
(seconds)
Oxygen
bubbles at
0.1m
Oxygen
bubbles at
0.2m
Oxygen
bubbles at
0.3m
30
23
11
3
60
45
22
7
90
67
32
12
120
109
45
17
150
134
65
22
180
157
76
27
210
189
88
32
240
210
109
37
270
245
123
42
300
269
134
45
0.3m
1: Plot a graph of distance (m) versus rate of oxygen production ?
2: Is there a relationship between light intensity and rate of photosynthesis ?
3: What is this relationship ?
4: What are the other limiting factors in this experiment ?
5: How could you test out you answer for question 4 ?
6: Why is important to control the temperature of the water ?
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Limiting factors light intensity two
During the night, no photosynthesis takes place, just plant respiration. At dusk and dawn when
the light intensity is low, the rate of respiration and photosynthesis are roughly the same.
During the day, when there is greatest l______ energy, there is a net production of glucose and
oxygen. The stomata cells, found on the underside of the leaf open during daylight hours when
photosynthesis occurs and partially close during the night. Stomata are opened and closed by
the guard cells changing shape. These guard cells contain chloroplasts, which provide the
energy for stomata opening and closing.
Affect of light intensity on stomata opening and closing:
Diagram
Oxygen
MicrobeGlucose
Body
temp CO2 Use
Night
Daylight
Dusk
Night
normal
37oC
0
12am
Notes
Dawn
Word bank: light
2
Closed
48 am
6 time hrs
days 8
12pm
Open
10
12
8pm 14
12am
Closed
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Limiting factors CO
2
concentration
The rate of photosynthesis increases when the concentration of carbon dioxide increases,
but only up to a point. Other factors, like l______ intensity and temperature also affect the
overall rate of photosynthesis in green plants. These are called limiting factors. The factor
in shortest supply will always be the limiting factor.
Affect of CO2 concentration on the rate of photosynthesis:
Experiment
1
2
3
CO2 (%)
0.1%
0.25%
0.5%
Time
(seconds)
Diagram
0.1m
0.1% CO2
0.1m
0.25% CO2
0.1m
0.5% CO2
1 :Plot a graph of CO2 concentration (%) versus rate of oxygen production ?
2: Is there a relationship between CO2 (%) concentration and the rate of
photosynthesis ?
3: What is this relationship ?
4: What are the other limiting factors for this experiment ?
Word bank: light
Oxygen
bubbles at
0.1% CO2
Oxygen
bubbles at
0.25% CO2
Oxygen
bubbles at
0.5% CO2
30
19
31
43
60
38
54
65
90
68
101
134
120
102
167
201
150
140
223
256
180
180
324
378
210
230
430
498
240
256
489
578
270
298
545
645
300
323
595
702
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Limiting factors temperature
The rate of photosynthesis in green plants increases when temperature is increased, but only up to a
point, due to other limiting factors like carbon dioxide concentration and light intensity. This is
because the two substrates; water and carbon dioxide have a higher kinetic energy, therefore colliding
more often and with greater f_______ inside the palisade cell chloroplasts. Very high temperatures
stop photosynthesis altogether. This is because, like other enzyme catalysed processes, plant enzymes
are denatured when subjected to very high temperatures.
Affect of temperature on the rate of photosynthesis:
Experiment
1
2
3
Temp (oC)
25oC
35oC
45oC
Word bank: force
Time
(seconds)
Diagram
0.1m
0.1m
25oC
35oC
0.1m
Oxygen
bubbles at
25oC
Oxygen
bubbles at
35oC
Oxygen
bubbles at
45oC
30
19
38
2
60
38
70
3
90
68
128
4
120
102
189
7
150
140
287
11
180
180
356
15
210
230
456
19
240
256
502
22
270
298
615
25
300
323
689
32
45oC
1: Plot a graph of temperature (oC) versus rate of oxygen production ?
2: Is there a relationship between temperature and rate of photosynthesis ?
3: What is this relationship ?
4: What are the other limiting factors ?
5: Why, when the temperature was increased to 45oC in expt 3, was the rate of
photosynthesis very low ?
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Limiting factors colour of light
The rate of photosynthesis can also be affected by the colour of light. This is because green
chlorophyll absorbs r____ and b_____ light and reflects green. When green light is reflected,
the light energy is not available to the chloroplasts during the formation of g__________ and
oxygen from carbon dioxide and water. Why are many of the seaweeds found deep below the
water’s surface red ?
Affect of light colour on the rate of photosynthesis:
Expt.
1
2
3
4
Colour
of light
White
Blue
Green
Red
Word bank: red blue glucose
(seconds)
White
light at
25oC
30
19
10
4
5
60
38
20
6
11
90
68
34
10
24
120
102
49
12
35
150
140
67
16
48
180
180
100
19
60
210
230
120
24
89
240
256
130
30
99
270
298
140
35
123
300
323
159
42
134
Time
Blue
light at
25oC
Green
light at
25oC
Red
light at
25oC
Diagram
White
Blue
Green
Red
1: Plot a graph of colour of light versus rate of oxygen production ?
2: Is there a relationship between colour of light and rate of photosynthesis ?
3: What is this relationship ?
4: What are the other limiting factors ?
5: Why is the rate of photosynthesis not zero for green light ?
6: Show in a diagram using a green plant leaf, what colours are absorbed and
reflected during photosynthesis ?
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Plant use of glucose general overview
During photosynthesis in green plants, only glucose (C6H12O6) is manufactured. This
glucose is then used by green plants for a number of uses including respiration, fruit
production, g________ and repair. Plants are able to take a simple molecule like glucose
and manufacture all the other types of molecules, including enzymes, l________, proteins
and carbohydrates. They really are food factories and essential to all other animal life. Why
is the word producers a good term to use when describing plants ?
Affect of light intensity on the rate of photosynthesis:
Diagram
Light energy
Word bank: growth lipids
Respiration
Respiration
6H2O
C6H12O6
Mitochondria
Energy
6O2
6CO2
Cells
Photosynthesis
Growth & reproduction
Assimilation
6H2O
C6H12O6
Chloroplast
Light energy
6O2
6CO2
Cells
Notes
During the day there is a net production of glucose and oxygen by plants as the result of
photosynthesis. This glucose is then used during respiration or assimilated and used in the
manufacture all the other molecules like proteins, carbohydrates and lipids.
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Plant use of glucose reproduction
Pollination is the transfer of pollen, the male sex cells from the a_________ of the stamen by
b____ or insects to the surface of the female c_________. Once the pollen sex cells have
landed on the female carpel, pollination has been achieved. Flowering plants contain both
female and male reproductive organs and can either self or cross pollinate. Following
fertilisation, where the ovule and pollen cell fuse, the seed begins to develop surrounded by the
swollen ovule which forms the f_______. It is the function of the fruit to disperse the seed.
What is this organ’s role in the plant life cycle ?
Plant reproductive system:
Word bank: anther bees carpel fruit
Pollen cells
Female carpel
Male anther
Reproductive system
Pollen, the male sex
cells contain the paternal
genes and are held on
the anther which is part
of the male stamen.
The egg cells or ovules
contain the maternal
genes and are held in the
ovule, part of the female
carpel.
The stamen is the plant
male reproductive organ
which contains many
millions of microscopic
pollen cells.
Flowering plants have
both male and female
reproductive
organs.
Plants can self or cross
pollinate.
Diagram
Notes
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Plant use of glucose fruits and tubers
It is the function of the fruit to disperse the seed. Fleshy fruits like apples, pears, oranges and
tomatoes contain lots of sugar as a reward for a_________ and insects. These animals and
insects, by eating fruit containing seeds, help spread the seeds prior to g_____________ during
the following spring. Also roots tubers swollen with carbohydrates, like those found in carrots,
turnips and potatoes act as a food reserve for new growth in the following spring. The sugar or
carbohydrates contained in the fruit or root tubers is made during photosynthesis and is
transported by the phloem tubes from the leaf.
Plant fruits and tubers:
Apples
Word bank: animals germination
Oranges
Potatoes
Carrots
Diagram
Notes
Fruits, root vegetables and nuts all contain sugar or carbohydrates made from sugar produced
during photosynthesis. These plant products all contain stored chemical energy which animals
then eat, digest and assimilated into their own bodies. Without plants, there would be no food
chains and no oxygen, another product of photosynthesis.
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Tropisms in plants one
Plants can respond to environmental stimuli like light, gravity and water. Unlike humans
and other animals, plants cannot move themselves because they lack a skeletal m________
system. Plants can, however grow towards or away from a light source. Plant shoots grow
towards the light, whereas plant roots grow towards gravity and moisture. If you
germinated a seed in space with zero gravity, what would the growth response of the root
be like ?
Plant reproductive system:
Growing towards the light
Word bank: muscle
Response to light in plant shoots
Auxin accumulates on the dark side of
the shoot causing cell elongation and
the subsequent bending of the shoot
towards the light source
In the picture above, the tree clearly grows towards the primary source of light. Plants respond to light by using a
hormone called auxin. Auxin causes cell elongation and is broken down by sun light. The non-illuminated side therefore
elongates bending the shoot towards the sunlight. If the sun is overhead, the shoot continues to grow in an upwards
direction. Why do we germinate seeds in the dark ?
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Tropisms in plants two
Plants must grow in one direction or another to respond to stimuli like light, moisture or even
gravity. They can’t simply m_______ because thy don’t have a nervous or muscle system. The
following experiments help us understand the role auxin plays in controlling a plant’s response.
Look at the three different scenarios and predict where auxin is found and how this affects plant
growth ?
Plant reproductive system:
Word bank: move
Scenario one
Scenario two
The shoot responds to the light
by growing towards the light.
Auxin is found on the dark side
(right hand side) and causes cell
elongation.
The tip of the shoot is covered
with foil. Auxin is present on
both sides and in equal amounts.
The shoot continues to grow
upwards.
Scenario three
Diagram
Notes
The bottom of the shoot is
covered. The tip of the shoot
where auxin is found is still able
to respond to the light stimulus,
by growing towards it.
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Extension questions and homework
1:
Define the following terms: Photosynthesis, Substrates, Products, Glucose, Oxygen, Limiting factors & Ratelimiting-factors.
2:
Look at the diagram of the three types of leaf tissue. Complete the table.
Stomata
Tissue
Xylem tubes
Function the in the green leaf
Palisade cells
How is it specialised
Stomata
Xylem
Palisade cells
3:
Answer the following:
a) How does water and carbon dioxide arrive at the palisade cell for photosynthesis.
b) How is sugar transported around the plant.
c) Sugar is also used by all plant cells during respiration to produce energy for life processes in the plant. Compare
photosynthesis and respiration.
d) During the day do plants respire.
e) How could you prove your answers in part (c) by performing an experiment. Explain all the steps.
f) Explain why the leaf cuticle is transparent. What other role does the cuticle play.
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4:
Look at the information in the table below. It shows the diameter of the stomata cells over a 24hr period:
Time (hr)
00.00
06.00
08.00
10.00
12.00
14.00
16.00
18.00
20.00
22.00
Diameter (cm)
0.01
0.1
0.15
0.25
0.40
0.40
0.25
0.20
0.10
0.01
a) Explain why the diameter changes over this 24 hr period
b) At midday the light intensity is strongest. How do the stomata cells react to this.
c) At dawn and dusk, is the rate of respiration and photosynthesis the same.
5:
a) Other than water and carbon dioxide, plants also need minerals (e.g. phosphates, nitrates and potassium) what are
these minerals used for and how do the plants obtain them.
b) Show how a specialised root hair cell takes in minerals like nitrates from the soil.
c) Do the minerals given in part (a) give any energy value to the plant.
d) Compare those minerals that plants require for healthy growth to the minerals and vitamins we require in our
own diet.
e) Somebody observed that wheat grows taller and gives a higher yield when the field is closer to a coal burning
power station. Suggest a reason for this.
f) Explain why grass doesn’t need cutting during the winter months when the average daily temperature is below
6oC.
6:
Complete the following:
Plants produce ____________ and oxygen during photosynthesis. This all takes place in the chloroplast found in the
_______________ cells. The active chemical in the chloroplast is called _____________. It is able to use light
energy to form new chemical bonds between water and carbon dioxide.
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7:
a) Plants and crops need mineral salts for healthy growth. Give the name of three of these mineral salts.
b) A farmer wants to increase his crop yield by using fertilisers. The able below shows how mass of crop produced
from a field depends on the quantity of nitrogen used.
Amount of nitrogen (kg)
0
100
200
300
400
500
600
700
Crop yield (tonnes/hectare)
6
7.5
12
14
15.5
16
15
13
(i) What is the maximum mass of crop that could be produced using nitrogen fertilisers.
(ii) Explain why using 700kg/hectare of fertilisers actually decreases crop yield compared to your answer in part (i).
(iii) Large amounts of fertilisers dissolve in water. When it rains fertilisers can accumulate in rivers and ponds.
Explain why this is a problem.
(iv) Some consumers prefer organically grown crops. State two advantages and disadvantages of eating organically
grown crops.
8:
a) Explain the difference between ‘peat culture’ and ‘nutrient film’ hydroponics.
b) What are the benefits of intensive farming to the (i) farmer and (ii) consumer.
c) What are the disadvantages of intensive farming to (i) the consumer (ii) biodiversity (iii) the environment.
9:
Complete the following:
Water passes into the root hair cell by ___________. Mineral salts like _____________ potassium and phosphate
are taken up by active transport. A root hair cell has a ____________ surface area to help water and mineral salt
uptake. Water is then transported through the ___________ tubes by capillary action to the leaf tissue. Palisade cells
require water during photosynthesis to manufacture glucose. Water is lost through the leaves thorough the
_____________. They are opened during the day and close at night when no p______________ takes place.
Internet:
Go to google.co.uk and find out about fertilizers and how they provide essential minerals for healthy plant growth.
Look at how the fertilizers are rated (N:P:K value) and what role each mineral plays in healthy plant growth.