30

Name _____________

Teacher ______________ Hour ____

C6H12O6

C6H12O6

as Producers

31

Learning Goals Unit 3: Plants as Producers

I will be able to:

1. Identify unique plant structures (Root Hairs, Blade, Petiole, Stem, Root). 2. Identify unique plant cell structures (chloroplast, chlorophyll). 3. Explain the function/importance of each plant structure (in relation to the process of photosynthesis). 4. Understand the relationship between pigments and light absorption/transmittance. 5. Describe the three main steps of photosynthesis:

a. Capture light energy b. Convert light energy into chemical energy c. Convert chemical energy into glucose (food)

6. Construct and understand the equation for photosynthesis (including the starting and ending places of each reactant/product).

7. Demonstrate understanding of the scientific method by creating an experiment that includes a hypothesis, procedure, data, and conclusion.

8. Relate the importance of plants and photosynthesis to the structure of an ecosystem (the plants role as the base for all other life on earth).

9. Demonstrate the following ACT college readiness standards: a. S.20.3 – Identify a control in an experiment b. S.20.4 – Identify similarities and differences between experiments c. E.20.2 – Identify key issues or assumptions in a model

Important Vocabulary:

• Root (21.3)

• Root Hairs (21.3)

• Stem (21.3)

• Blade (21.4)

• Petiole (21.4)

• *Chloroplast (4.2)

• *Chlorophyll (4.2)

• *Photosynthesis (4.2) o O2, CO2, H2O o Glucose

• *Producer/Autotroph

• *Consumer/Heterotroph

• Pigment

• Absorbance

• Transmittance

Words that are underlined and have a star* are key vocabulary words. These are the most important vocabulary words to know!

32

Plants Pre-Test What do you know about those plants anyways?

1. Label as many parts of the plant (to the right) as you can.

2. Where do plants get their “food” from so that they have energy to grow, reproduce, etc? (Be specific about where the energy comes from originally).

3. Much like plants, humans have structures that are responsible for helping to digest food. What plant structure(s) is/are responsible for:

a. obtaining (acquiring) energy?

b. storing energy?

c. using energy?

4. In addition to eating, humans breathe air. Do plants breathe? _____ What do they breathe?

5. What is photosynthesis? Give your own definition.

6. It would be a huge problem if there were no plants in our world. Give two reasons why.

7. You know that plants need light. a. What do they use it for?

b. What color light you think is most important to them.

33

Pin the Structure on the Plant? Okay, you’re not really going to ‘pin’ anything, but do you know the main structures of a plant? Your task is to place all of the plant structures in the correct place! All of the words listed in ‘Bank #1’ need to be drawn onto the bare stem below. Once you have drawn all of the structures onto the plant, match each structure with its function from Bank #2. If you get stuck on a plant structure or function, refer to your book on pages 648-652. *Use the ‘stem’ as an example of how your labels should look.

Bank #1

Root Hairs Blade Petiole Stem Root

Bank #2

A. Connects the stem to the blade. B. Greatly increases the surface area of the root, allowing for more absorption

of water and minerals. C. The broad, flat part of the leaf, used for collecting sunlight. D. Anchor plants in the soil while absorbing, transporting, and storing

nutrients. E. Supports the plant and transports materials throughout.

Stem

(E)

34

Getting Energized!!! Where does the energy come from to sustain life?

In the following exercises you will be asked to answer some questions in “Think, Pair, Share” format. In each section, follow these directions: Think: You write down your independent response. Pair: You write down your partner’s response. Share: After class discussion, write down the major themes that are agreed upon.

1) Where did you get your energy from today? Be specific. Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: _________________________________________________________________________

2) The animal products obviously came from an animal. Where did they get their energy from? Be specific. Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: __________________________________________________________________________

3) So, it all goes back to plants. But where do they get their energy from? Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: __________________________________________________________________________

4) What plant part (structure) is responsible for obtaining (getting) this energy? Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: __________________________________________________________________________

5) What do you think would happen to our planet and all living things if there were no plants? Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: __________________________________________________________________________

6) So, we are pretty dependent on plants. Do you think that plants depend on other living things for anything? If so, what thing(s)?

Think: __________________________________________________________________________

Pair: ___________________________________________________________________________ Share: __________________________________________________________________________

35

How do Plants use the Sun’s Energy? Part I Previously you have learned about how light from the sun carries energy in the form of waves, but how does a plant use this sunlight to make it’s own food? What type of food does a plant make? Is there anything else that a plant produces while making food? What else do plants need besides sunlight in order to make food? Use the space below to answer these questions to the best of your ability:

1) What does a plant need in order to survive? List as many things you can think of:

a. _______________________

b. _______________________

c. _______________________

d. _______________________

2) What type of food does a plant make? ______________________________ 3) Does the plant make any other products besides food? If so, what? _________________________

4) What is this process called? _______________________________

Part II Now that you have figured out what is used and what is made during this process, perhaps you can arrange these components in a way that can be accurate, but easy to read. Scientists use a convention called a chemical equation to do exactly this. Just like in mathematical equations, two or more things are added together to make a product. Whenever a chemical reaction occurs (like in photosynthesis) there are:

1. Things that are used up in the reaction, called reactants 2. Things that are made, called products

Scientists use an arrow to represent that a chemical change has taken place. Look at the example below that shows the production of table salt from the elements sodium and chloride:

Sodium + Chlorine � Sodium Chloride

Reactants = Product

Your Turn: In groups, use the cards provided to you by your teacher to create a chemical equation that best represents photosynthesis. Record your results below: After class discussion, write the discussed PHOTOSYNTHESIS equation below:

STOP

36

A History of Photosynthesis How do we know so much about this process?

Before we can look at the history of our understanding of this process, we need to really understand what its name means. As with so many words in biology, Photosynthesis is a word that has two smaller root words.

PHOTO – SYNTHESIS

Definition:

_____________________________________________________________________________________________

_____________________________________________________________________________________________

Read the following passages about the major contributors to the study and understanding of photosynthesis

PART 1 – Food for Plants

Aristotle

Aristotle and his followers (back in 500 BC) were perhaps the first to make and record any

observations about plant growth. They made the observation that the life processes of animals

were dependent on plants. But the question remained…where do plants get their food? Based on

their observations, Aristotle and his followers came to the conclusion that plants got all of their

necessary food directly from the soil. Somehow, the plants just sucked up all of their food from the

dirt! Aristotle’s theory was accepted up until 400 years ago.

1. What is the main idea of this passage? Write it here:

______________________________________________________________________________________

______________________________________________________________________________________

Jean Baptiste van Helmont

In 1620, a Belgian scientist named Jean Baptiste van Helmont decided to do an experiment to

test Aristotle’s theory. Van Helmont’s experiment was the first quantitative plant growth

experiment to be done that resulted in using precise measurements of mass, volume, etc to

reach a conclusion about photosynthesis. Van Helmont wrote:

37“I took an earthenware pot, placed in it 200 pounds of earth dried in an oven, soaked this with water, and

planted in it a willow shoot weighing 5 pounds. After five years had passed, the tree that had grown

weighed 169 pounds and 3 ounces. The earthenware pot was constantly wet only with rain or (when

necessary) distilled water (distilled water is purified water that contains no particles or other chemicals)

To prevent dust from flying around from mixing with the earth, the rim of the pot was kept covered with an

iron plate coated with tin and pierced with many holes. Finally, I again dried the earth of the pot, and it

was found to be the same 200 pounds minus about 2 ounces.”

2. Why did van Helmont decide to do an experiment on plants?

_______________________________________________________________________

3. Fill in the table below with the information from van Helmont’s experiment.

4. What do you think happened to the lost ounces of soil from Van Helmont’s experiment?

_____________________________________________________________________________________

5. Why do you think it was important for van Helmont to use only dry soil in his measurements?

______________________________________________________________________________________

6. Which statement below would van Helmont conclude about the soil’s role in providing food for a plant? (E.20.1)

A. Soil is the only thing that provides food for the plant. B. Water does not provide food to the plant. C. If the soil lost no mass, but the tree gained mass, then something other than soil must provided food

to the plant. Water must be the thing that provides food to the plant. D. Plant pots with rims inhibit the loss of soil, therefore, soil must be the main source of a plant’s food.

7. Does Van Helmont’s conclusion support or refute Aristotle’s original conclusion? ______________________

Part 2 – More than just water Van Helmont’s experiment was fairly elegant (simple) and provided a conclusive result—that water alone made

plants grow. He did not, however, consider what role the air had in plant growth.

Joseph Priestly

Near the end of the eighteenth century (1772) another scientist named Joseph Priestly began

making observations about plant growth. Priestly’s experiment consisted of placing a lit

candle under a bell jar so that it was air-tight. Once the candle went out, it could not be lit

Results Initial weight Final Weight after 5 years

Difference in weight

Loss or gain?

Tree

Soil

38

again. Without lifting the bell jar, Priestly tried to relight the candle by directing the sun’s beams through a magnifying

glass. Priestly then tried the experiment again, but this time, he placed a sprig of a green plant under the bell jar with

the candle. Again, the candle burned out, and could not be lit again. However, he noticed that after a few days, the

candle could once again be lit.

He noted, “I have accidentally hit upon a method of restoring air that had been injured by the burning of candles…at

least one of the restoratives that nature employs…is vegetation.” Priestly concluded that plants recycled the air to

keep it clean and pure. His proposed idea for that process worked like this:

8. Use your prior knowledge! Why did the candle in Priestly’s first bell jar go out? What is necessary for all flames to stay lit? ______________________________________________________________________________________

Jan Ingenhousz

Unfortunately for Priestly, neither he nor others could repeat the experiment and get the

same results. Therefore his theory had lost the impact that it first had. A few years later

though, in 1779, a Dutch physician name Jan Ingenhousz tried to repeat Priestly’s

experiment. For the first time in many years, he was able to show results that supported

Priestly’s work. Ingenhousz made one very important discovery in his experimentation:

The process of “purifying” the air could only occur when there was light in the room. So

by adding to Priestly’s original idea, the equation for this process would look like this:

With help from the growing field of chemistry, it was learned that the “bad” air was carbon dioxide (CO2). The “pure”

air was oxygen (O2). By applying this new information to the equation above, the new equation becomes:

“bad” air “good” air (candle won’t light) (candle will light)

plants

CO2 O2

plants

light

“bad” air “good” air (candle won’t light) (candle will light)

plants

LIGHT

39

9. Although Priestly and Ingenhousz’s experiments were essentially the same, there was one essential difference. What is the main difference between these experiments? (I.24.6) ____________________________________________________________________________________________________________________________________________________________________________

10. Based on this information, why do you think that other scientists could not replicate (copy) Priestly’s experiment? ______________________________________________________________________________________ ______________________________________________________________________________________

From this, Ingenhousz went one step further in his quest to explain and understand photosynthesis. In 1796, he had

an idea that plants were doing something other than just ‘purifying’ the air we breathe. Ingenhousz wondered if

plants could somehow also be getting the food that they needed through this process as well. He thought that

sunlight was used to split the CO2 into carbon and oxygen. He believed that the plant somehow then used the

carbon to make their food and then got rid of the O2. If we put these ideas into the equation of photosynthesis, it

becomes:

11. According to Ingenhousz’s hypothesis, what is the role of sunlight in photosynthesis?

______________________________________________________________________________________

Nicholas Theodore de Sassure

In 1804, a Swiss scientist names Nicholas Theodore de Sassure showed through careful

experimentation that water (H2O) was an essential part of the process of photosynthesis. He

remembered Von Helmont’s experiment that showed plant growth with the addition of only water to

a potted willow tree. He knew that as a plant photosynthesized, it grew and increased in mass. De

Sassure concluded that the increase in mass was more than would amount from the intake of CO2

alone. He believed that once the CO2 was split, the carbon combined with the H2O to form the

plant’s food. Therefore the new and improved equation for photosynthesis looked like:

12. How is de Sassure’s view of water different than Von Helmont’s view of water? (S.20.4)*

______________________________________________________________________________________

______________________________________________________________________________________

CO2 FOOD + O2 (oxygen)

plants

light

CO2 + H2O FOOD (CH2O) + O2 (containing C and H) (released into the atmosphere)

plants

light

40

C.B. van Niel

The above equation for photosynthesis looks like it may be complete, but C.B. van Niel

(a graduate student at Stanford) discovered that it was not quite finished. In his studies,

he found that the O2 that plants released into the atmosphere did not come from the

CO2 being broken into carbon and oxygen. Instead the CO2 stayed together and the O2

came from the splitting of H2O into hydrogen (H2) and oxygen (O2).

13. C.B. van Niel helped to show that the oxygen that plants release come from the breakdown of water into

hydrogen and oxygen. Where did people originally think this oxygen came from? (S.20.4)*

______________________________________________________________________________________

______________________________________________________________________________________

Please answer the following reading questions:

14. Describe how the ideas of Aristotle are different from how we think of photosynthesis today.

15. Describe how the following scientists each contributed to the understanding of the black box of photosynthesis (you will each be assigned to one of these people to present to the class):

a. Van Helmont

b. Priestly

c. Ingenhousz

d. De Sassure

e. C.B. van Niel

Passage 1

Germination, the initial growth of a seed, affects the yields (amount of product) farmers can obtain from their crops. Several factors are known to affect germination. The following experiments were conducted to determine the factors that influence the rate and amount of germination in corn. Experiment 1

Four samples of 100 corn seeds each were placed on moist filter paper in separate petri dishes. The petri dishes were covered and the edges taped to prevent evaporation of water. Each sample was incubated (heated) at a different temperature. The germinated seeds were counted at 7, 14, and 21 days. The results are presented in Table 1.

Experiment 2

One sample of 100 corn seeds was placed in a moist petri dish, as described in Experiment 1. Another sample of 100 corn seeds was treated with a plant hormone prior to being placed in a moist petri dish. Both samples were incubated at 35° C. The germinated seeds were counted over 7-day intervals as in Experiment 1. The results are given in Table 2.

1. In Experiment 1, how many seeds from sample 3 had germinated after 14 days? (I.13.1)

A. 35 B. 50 C. 70 D. 80

2. Which of the following factors did the researcher

vary in Experiment 1? (S.20.2) A. Sample size B. Type of seeds C. Hormone treatment D. Incubation temperature

3. Based on these experiments, which of the following practices would one most likely recommend to farmers who want to increase the germination of their corn? (E.24.1)

A. Planting germinated seeds only B. Planting when the soil temperature is

between 5° and 20°C C. Planting when the soil temperature is

between 20° and 35° C D. Planting when the soil temperature is

between 35° and 50°C

4. Which of the following conclusions concerning the germination of corn at 20° C and 35° C is consistent with the results of Experiment 1? (E.20.1)

A. No seeds are able to germinate at 20°C or 35° C

B. About half as many seeds germinate at 20°C as at 35°C

C. Twice as many seeds germinate at 20°C as at 35°C

D. All the seeds germinate at 20°C and 35°C at the end of 21 days of incubation

5. On the basis of the experimental results, one

could generalize that as the germination period increases to 21 days, germination: (I.20.2)

A. decreases at temperatures below 5°C

B. increases at temperatures between 20° and 35° C

C. increases at all temperatures D. decreases at all temperatures

6. Which of the following assumptions did the

researchers most likely make when selecting 35°C as the incubation temperature for Experiment 2? (E.20.2)*

A. Hormone activity would be inhibited at 35°C

B. The greatest number of corn seeds would germinate at 35°C

C. The lowest number of corn seeds would germinate at 35°C

D. Corn seed germination would not be affected by temperature

Table 1 Temperature Total Seeds Germinated

Sample (°C) 7 days 14 days 21 days 1 5 0 0 0 2 20 25 37 44 3 35 50 70 80 4 50 2 3 3

Table 2 Total Seeds Germinated

7 days 14 days 21 days Untreated 48 65 79 Treated 65 75 82

41

47

Photosynthesis, O2 and CO2 – How are they related?

Today you will see a set-up that includes a plant in an enclosed area and two sensors that measure O2 and CO2. Your teacher will give you data that was gathered by the Oxygen (O2) and Carbon Dioxide (CO2) sensors throughout one day. Some of the data was gathered when the plant was in the dark, and some while the plant was in the light under a box. Use the space below to make a sketch of the set-up of the plant in both the light and in the dark. Then make predictions about what trends you think you will see for the O2 and CO2 amounts measured from the plant.

Plant data measured while in the sunlight

Time of day (pm) % O2 Parts per million (ppm) CO2

2:12

2:30

3:15

4:13

4:30

5:50

6:20

Prediction for change in CO2 levels in the dark

Prediction for change in O2 levels in the dark

Prediction for change in CO2 levels in the light

Prediction for change in O2 levels in the light

Plant data measured while in the dark under box Time of day % O2 Parts per million (ppm) CO2

11:10

11:15

12:01

1:25

2:08

Plant in LIGHT Plant in DARK

42

48

Questions: Below are two graphs that each display CO2 and O2 levels while the plant was in the dark. Answer the questions for each graph.

1. Describe the trends that you observed in CO2 levels for the plant while it was in the dark. (I.16.4)

__________________________________________________________________________________________

2. Describe the trends that you observed in O2 levels for the plant while it was in the dark. (I.16.4)

__________________________________________________________________________________________

3. In both experiments, what is the independent variable? _____________________________________________

Did you know that we can graph more than one variable on a graph? It is sometimes easier to analyze data when it is all in one spot! Look at the graph below that has both %O2 and CO2 in ppm.

Now it’s your turn! You will graph both O2 and CO2 for the plant while it was in the LIGHT. Set your graph up so that it looks like the one above. Answer the questions that follow once you have graphed your data.

Parts per million (ppm) CO2

4400

4600

4800

5000

11:1

0

11:1

5

12:0

11:

252:

08

Time

Carb

on

Dio

xid

e in

part

s p

er

millio

n

Parts permillion (ppm)CO2

% O2

20.4

20.6

20.8

21

11:10 11:15 12:01 1:25 2:08

Time

% o

f O

xy

ge

n

% O2

Oxygen and Carbon Dioxide levels in the dark

20.4

20.5

20.6

20.7

20.8

20.9

21

11:10 11:15 12:01 1:25 2:08

Time

% o

f O

xyg

en

4400

4500

4600

4700

4800

4900

5000

Carb

on

Dio

xid

e (

pp

m)

% O2

Parts per million(ppm) CO2

43

49

Title: _________________________________________________________________

4. Refer to the data for the plant that was in the light. Describe the trends that you observed in CO2 levels for the

plant while it was in the light. (I.16.4)

__________________________________________________________________________________________

5. Describe the trends that you observed in O2 levels for the plant while it was in the light. (I.16.4)

__________________________________________________________________________________________

6. Compare your graph of CO2 levels in the light, to the graph of CO2 levels in the dark. What can you say about

them? ____________________________________________________________________________________________________________________________________________________________________________________

7. Compare your graph of O2 levels in the light, to the graph of O2 levels in the dark. What can you say about them?

____________________________________________________________________________________________________________________________________________________________________________________

44

KEY

50

Why can plants do photosynthesis….but other things cannot?

Remember from our first unit that all living things are made of cells . Although this is a similarity amongst all living things, there are many differences between these structures. Look at the lists below that compare plant and animal

cells, and answer the following questions

1. What cellular structures (organelles) do plant cells have that animal cells do not?

______________________________________________________________________________________

______________________________________________________________________________________

2. Read pages 103-104 in your book, and answer the following questions:

a. Which structure (organelle) is essential to a plant’s ability to do photosynthesis? _______________

b. Do animals (animal cells) contain this structure? ____________

c. What is chlorophyll, and what does it do?

d. Where can you find chlorophyll in the cell?

Cellular Structure (organelle) Present in Plant Cell? Present in Animal Cell? CYTOPLASM Yes Yes

MITOCHONDRIA Yes Yes VACUOLE Yes Yes

GOLGI APPARATUS Yes Yes CELL WALL Yes No

CELL MEMBRANE Yes Yes LYSOSOME Yes Yes NUCLEUS Yes Yes

CHLOROPLAST Yes No ENDOPLASMIC RETICULUM Yes Yes

RIBOSOMES Yes Yes

Cell Membrane Vacuoles

Cell Membrane

45

51

Light and Pigments As you just learned, plant cells have

structures that animal cells do not.

These structures are called

chloroplasts. Chloroplasts are

located in the cytoplasm of the plant

cell (see diagram to the right). This

structure, as you also learned,

contains a molecule (a group of

atoms) called chlorophyll.

Chlorophyll is a molecule that

absorbs light. We call light-

absorbing molecules pigments.

Although the most common plant pigment is chlorophyll, plants may also contain other pigments that absorb the

sun’s rays.

As we discussed earlier, energy from the sun travels to the earth in the form of waves. This energy varies in its

strength, from the warming rays of infrared to the damaging rays of ultraviolet (UV). Visible light is only a small

fraction of the total energy that comes from the sun. Visible light consists of a spectrum of colors. Each color has a

different wavelength and energy content (see the diagram below).

Sunlight, which is what our eyes

perceive as “white light”, is actually a

mixture of different wavelengths of light.

Many of these wavelengths are visible to

our eyes and make up what is known as

the visible spectrum. Our brain

interprets the different wavelengths that

travel through our eyes and optic nerves

as different colors.

46

52

Photosynthesis uses only certain wavelengths, or colors, of visible light. The green color of plants emphasizes that

fact. Not only does photosynthesis depend on particular wavelengths of light, it also works more or less efficiently

depending on the intensity of the light. The ideal intensity of light varies for different plants. Of course, many factors,

such as the availability of water and nutrients in the soil also affect photosynthesis.

Questions:

1. What is a pigment?

2. Why do you think that chloroplasts are essential to a plant’s ability to do photosynthesis?

53

Light and Pigments—How do they interact?

As you read earlier, pigments are compounds that absorb specific wavelengths of light. We also know that

photosynthesis depends upon the pigments that plants contain. Today’s demonstration will allow you to see how

various wavelengths of light are both absorbed by, and transmitted through, chlorophyll. To gather data today, we

will be using a device called a spectrophotometer. If you break this word into smaller parts, you will see that a

spectrophotometer is a device that measures information about a spectrum of light waves.

Definition for Absorbance: ______________________________________________________________________

Definition for Transmittance: _____________________________________________________________________

Data Analysis:

Use the data in the table on the next page to answer the following questions and to plot the data on the graph

provided. The wavelength in nm should be placed on the x-axis. The absorbance should be plotted on the left

vertical y-axis. The transmittance should be plotted on the right y-axis. Be sure to label or color code each line

as you draw a smooth curve through the data. Remember to include a title and labels for each axis!

Data Table:

Wavelength in nanometers (nm)

Absorbance Value

(Range 0-2)

Percent of wavelength transmitted

(Range 0-100)

400 2 1

430 1.95 .75

460 1.95 1.5

490 1.6 8.5

520 1 35

550 .99 32.5

580 1.3 19.5

610 1.9 10.5

640 1.7 7

670 1.3 17

700 1.5 4

54

Tit

le _

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

55

Questions: Use your graph to answer these questions about the spectrophotometer data:

1. Use the table below to label the appropriate wavelengths (on the graph) with their corresponding colors. Red 780 to 622 nm

Orange 622 to 597 nm

Yellow 597 to 577 nm

Green 577 to 492 nm

Blue 492 to 455 nm

Violet 455 to 390 nm

1. Which is the smallest wavelength for visible light? (I.20.1) ____________________ 2. Which is the largest wavelength for visible light? (I.20.1) ____________________ 3. Look at the graph that you made. What appears to be the relationship between absorbance and

transmittance? (I.24.4) A. There is no relationship between absorbance and transmittance B. Absorbance and transmittance are opposite of one another. As absorbance of one color of light

increases, its transmittance decreases. C. As transmittance of a color of light increases, so does its absorbance. D. As transmittance of a color of light decreases, so does its absorbance.

4. Which colors of light are absorbed the most by chlorophyll? 5. Which colors of light are transmitted the most by chlorophyll? 6. If you were going to grow plants and wanted to use the optimum wavelengths that their pigments absorb,

which wavelengths would you use? (S.24.4)

___________________________________ Explain why you chose this wavelength(s) using results from today’s data collection.

56

Packaged Sunlight—An Introduction to Photosynthesis

“Food in the human menu is hardly recognized as packaged sunlight, but that is exactly what it is…At first glance, a leaf may look as thin as paper; actually it is a spreading one-story factory with ample room between floor and ceiling for sunlight packaging material.” -Rutherford Platt “The Great American Forest”

What is this process of “packaging sunlight” or photosynthesis? What is food? Why are plants so important? What

makes them green? As scientists have studied these questions, we have found that plants play an incredibly

important role in our lives.

“What is food?” Students were asked this question in an informal survey. The most common answer was that food is

“something we eat.” Although this is true in animals, it is quite rare to see plants “eating” food. The second most

common answer to this question was that food provides us with energy and nutrients so that we can live. Therefore,

food can be described as a substance that can be broken down to provide energy. As we have studied, energy is

necessary for cellular activity. The process of breaking down “food’ (organic compounds) to provide energy for cells

is called cellular respiration. So, where do plants get the food that they break down for energy?

It is rare to see a plant go through the McDonald’s drive-through when it feels hungry. Instead, plants have the

unique ability to make the organic compounds (food) they require. How is this possible? Plants make organic

molecules through a process called photosynthesis (photo = light, and synthesis = putting together…so literally

“putting together with light”). Using sunlight as energy, plants have the ability to put together low-energy matter

(H2O and CO2) to produce high-energy matter (C6H12O6—glucose, or food!). The basic equation for

photosynthesis is:

57

As seen earlier, plants are described as autotrophs because of their ability to make their own food. Heterotrophs—

organisms that cannot make their own food—must eat other animals and plants to get the food that they need.

Reading Questions:

1. What does photosynthesis mean?

2. Write the complete balanced equation for photosynthesis:

3. a. What are the reactants in photosynthesis?

b. What are the products in photosynthesis?

4. What is a heterotroph? 5. Why is it said that all life depends on autotrophs?

6. Why is light energy important to us?

6CO2 + 12H2O C6H12O6 + 6O2 + 6 H2O

(low energy matter) (food -- glucose) (oxygen) (water)

Light energy

58

The two graphs below show the effects of light intensity and temperature on the rate of glucose production in land plants. Remember that in the photosynthesis demonstration you saw that glucose (which is stored as starch) is effected by different light conditions. Use the graphs to answer questions 1-3.

1. What happens when the light intensity rises over 9000 lumens? (Lumens are a measure of light intensity.)

2. What happens when the temperature rises past 33 degrees Celsius?

3. Write a concluding statement that describes the ideal conditions for the production of glucose in plants. Be sue to include values for both Temperature and Light Intensity.

Below is data collected on plants that had been grown under different light conditions. Examine the data table and answer questions 4-7 below.

Effects of Temperature on Glucose Production

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20 25 30 35 40 45

Temperature (degrees Celsius)

High

Lo

w

Effects of Light Intensity on Glucose Production

0

2

4

6

8

10

12

14

16

0 2000 4000 6000 8000 10000 12000 14000 16000

Light Intensity (Lumens)

High

Lo

w

Average Total Growth Over 20 Days of Adzuki Bean Plants

Photosynthesis Graphical Analysis Practice

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4. Under which type of light did a bean plant experience the most growth?

5. Under which type of light did a bean plant experience the least growth?

6. Like most other plants, Adzuki bean plants are green in color. This means that wavelengths of

_______________ light are being transmitted back to your eyes. Therefore, Adzuki bean plants must be

absorbing mostly _______________ wavelengths of light.

7. Is this consistent with the data above? Why or why not?

Day Blue Light Yellow Light Red Light Green Light

5 4.4 cm 5.2 cm 6.6 cm 3.8 cm

10 8.6 cm 11.3 cm 13.7 cm 6.3 cm

15 13.3 cm 16.8 cm 18.3 cm 8.4 cm

20 19.4 cm 23.4 cm 27.5 cm 12.3 cm

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How are plants used by humans?

This may seem like a simple question with a simple answer. However, plants and their by-products are found in more aspects of our life than we can even imagine! Below, please brainstorm and write down all of the ways in which humans depend on, or use plants. Be specific in your answers. Write your answers down under the column labeled “Think”. When you have written down as many answers as you can, sit quietly until your teacher instructs you to discuss your answers with a partner. Write down any answers from your partner that you did not have in your original list under the column titled “Pair”. We will then discuss these answers as a class. Write any remaining answers (that you and your partner did not discuss under the column labeled “Share”.

Think Pair Share

CATEGORIES of plant uses by/for humans ���� With the class, group your individual ideas into larger categories. Write them here:

Using complete sentences, answer questions 1-3 below.

8. Of all the categories listed above, which do you think is the most important or essential use of plants by humans? ____________________________________________________________________________________________

9. Why did you choose this as the most essential use of plants by humans? (ie: If humans were not able to have or

use plants in this manner, what would be the result for humans)? _____________________________________________________________________________________________________

_____________________________________________________________________________________________________

10. Do you think that plants ever depend on humans? __________ If so, how?

_____________________________________________________________________________________________________

_____________________________________________________________________________________________________

11. Look at your list of the ways in which humans use plants. List a few plant structures (parts of a plant) that are used for these purposes.

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147

Photosynthesis Concept Map

Photosynthesis

converts

into

is divided into

takes place

in

contain

which requires

chlorophyll

which

traps

and

splits

into

by-product

Light or

darkness

and

forms is

is released as a

as a

takes place

in

Word Bank some may be used more than once

CO2

chemical energy

chlorophyll

chloroplasts

glucose (C6H12O6)

H2O

H2

light

light dependent stage

light independent stage

light energy

O2

combined with

147

Bio Photosynthesis Review

1. Why are humans dependent on plants for survival?

2. Describe what photosynthesis is and write the balanced equation for photosynthesis.:

3. How are cellular respiration and photosynthesis connected and in what kinds of organisms do they occur?

4. What “ingredients” are required for photosynthesis and how does the plant get them? (Hint: Think about the equation.)

5. For each of the following scientists, describe how they contributed to our understanding of photosynthesis:

1. Why are chloroplasts

important to the process of photosynthesis? (Think about what they contain and what occurs there.)

Priestley

Ingenhousz

DeSassure

C. B. Van Niel

Van Helmont

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31

2. Explain the data that we got from the class demonstration with the spectrophotometer.

3. What are the three main steps in photosynthesis? Which are light dependent reactions? Which are light independent reactions?

a. b. c.

4. Answer the following about the light dependent reactions: a. What molecule from our photosynthesis equation is used here and what happens to it?

b. What are the products and what happens to them?

5. Answer the following about the light independent reactions:

a. What are the reactants? ________________________________________

b. What is the product? ________________________