Ch. 4 BSCS Blue Study Guide
Section 1: What are autotrophs?
a. What are Autotrophs?
i. Make their own food
ii. Get their energy from nonliving sources
iii. Examples: plants, flowers, and bacteria
a. What are photoautotrophs?
i. Autotrophs that get their energy from photosynthesis
ii. Example: plants
a. What are chemoautotrophs?
i. They can’t do photosynthesis because they live in a dark or salty environment
ii. They are bacteria that get their energy from by oxidizing inorganic substances (minerals)
a. Get their energy from living organisms
deer, bears, humans
Section 2: Overview of photosynthesis
I. Visible Light
a. Energy plants absorb
b. When visible light hits an object it causes a small change in the molecules that absorbs it, this allows us to see
c. Consists of waves
i. Waves are vibrating electric and magnetic fields
ii. Wavelength determines the color and frequency the amount of energy of the wave.
The shorter the wavelength the greater the energy
I. Photoautotrophs absorption of energy
a. When visible light hits the molecules of photoautotroph the molecules capture and use the energy
b. How does photoautotroph absorb the light?
i. The pigments in their cells absorb the light
1. pigments: light absorbing substances
2. Where are they located?
the membranes called thylakoids within chloroplases
c. How do they store the energy?
i. In the thylakoids
i. What is it?
1. Organized structure in the cell membrane
ii.What is it made up of?
I. Conversion of light energy into chemical energy
i. What is it?
(fluid filled) surrounding the thylakoids .
ii What does it do?
1. Using the energy captured from visible light the enzymes in the stroma organize the sugar made by carbon dioxide, water, and energy.
2. The stroma also stores the chloroplast DNA, RNA, and the enzymes needed to make proteins
i. What is it?
1. A green pigment found in the thylakoids that photosynthesis depends on
ii. Two forms: a and b
1. What do they do?
a. Absorbs all ranges of light except green
This gives leaves their green color (green
is reflected so we see it)
When chlorophyll declines in the fall
making the leaves
different colors like red, yellow, and orange (from other pigments also
iii. Do photosynthetic bacteria (cyanobacteria) have chlorophyll?
1. No, bacteria has rhodospin instead
II. Summary of photosynthesis
a. Light reactions
i. The first step is when the pigments in the thylakoids absorb the light
ii. The second step is when the thylakoids convert it to chemical energy carried by energy rich molecules
iii. In the third step the energy rich molecules make 3-carbon sugars from carbon dioxide in a series of reactions. The reactions are called the Calvin cycle.
1. thylakoid sacs stacked together like pancakes called granum
Section 3: light reactions
I. Light reaction
a. What do they do?
i. Absorb light
ii. Convert the visible light energy into chemical energy
iii. The chemical energy powers the sugar production that occurs in the Calvin cycle
II. Photosystems (refer to figure 4)
a. What are they?
i. Two clusters of the light absorbing pigments
b. What are the two clusters called
i. photosystem I
ii. photosystem II
c. Where are they located?
i. Thylakoid membrane
d. What occurs in the photosystems?
i. Chlorophyll and the other pigments absorb light and transfer it from one molecule to the next
ii. Then they funnel the energy to the reaction center
iii. Molecules in the reaction center have so much energy that it causes the electrons to jump from molecule to another
I. These molecules are known as electron carriers.
iv. These molecules form an electric transport system between
photosystem I and photosystem II that the electrons travel on
I. Some of these molecules are in the thylakoid membrane
v. Electrons from photosystem II move through the system to replace
the lost electrons in photosystem I
vi. Photosystem II receives replacement electrons from enzymes near
the reaction center
I. What do the enzymes do?
a. Oxidize water into protons, electrons, and oxygen:
b. The oxygen gets released as gas, the protons gather into the thylakoid sac, and the electrons go to photosystem II to replace the lost electrons
vii. When the electrons from the water reach photosystem I they
receive energy from the reaction center that they use to form a
molecule called NADP+
viii. The electrons and protons combine with NADP+ to make NADPH,
this is the last step in the light reaction
e. What are the protons used for?
i. The solar energy received by photosystem II powers the transport of protons across the thylakoid membrane; this causes a high concentration of protons in the thylakoid. The difference between the concentration of protons inside of the thylakoid compared to outside the thylakoid causes potential energy
ii. Protons exit the thylakoid through an enzyme called ATP synthetase. As the protons exit they give all their potential energy to ATP synthetase
I. ATP synthetase uses this energy to create ATP from ADP and phosphate.
f. Summary of light energy being converted to chemical energy.
i. Using light energy the electrons from water help make NADP+
ii. Then the electrons and protons combine with NADP+ to make NADPH
iii. NADPH is used to create ATP which is the chemical energy that was created using light energy
NADPH and ATP is used to make sugar from
in the Calvin cycle
Section 4: The Calvin Cycle
I. Calvin cycle
a. What does it do?
i. Conserves chemical energy produced in the light reactions in the form of sugars
b. Completes photosynthesis
II. Steps of the Calvin cycle (Refer to figure 5 below)
a. 1st a molecule of carbon dioxide combines with ribulose bisphosphate (a 5-carbon sugar phosphate)
i. This step is called the carbon dioxide fixation step because “it fixes” carbon dioxide gas into an organic molecule
1. The enzyme that catalyzes this step is called rubisco
ii. From this step you get a 6 carbon molecule that changes into a 3 carbon acid called phosphoglyceric acid (PGA)
1. Plants that only use the Calvin cycle to fix carbon dioxide are called C3 plants
iii. Then the two molecules ATP and NADPH are needed during two
enzymatic steps to change PGA into a 3-carbon phosphate called
b. In the next step enzymatic reactions change PGAL into a 5-carbon sugar-
c. In the last step ATP is
used to add a second
phosphate group to the
5-carbon sugar phosphate the molecule that is produced is a starting
RuBP (ribulose bisphosphate)
I. After the Calvin cycle turns three times the product is 6 molecules of PGAL
a. 6 out of the 5 are used to regenerate RuBP
left over 5 are used to use for growth and maintenance
II. Uses if the product of the Calvin cycle
i. What do plants use it for?
1. Plants use it synthesize other compounds they need like:
a. carbohydrate polymers
b. amino acids
ii. Most of the sugars are converted to a sucrose in the cytoplasm of the leaves
1. This supplies energy to the rest of the plant
iii. The sugars are also converted to
starch for storage
1. Plants gather starch in the daylight and break it down at night to supply energy and carbon skeletons to the plant
III. Light used in the Calvin cycle
a. What is it used for?
i. Provides energy for the synthesis of ATP and NADPH
ii. To activate rubisco and other enzymes
Calvin cycle cannot operate in the dark
Section 5: Rate of Photosynthesis
I. Growth of autotrophs
a. The environment has an affect on photosynthesis which has an affect on the growth of autotrophs
i. The environment affects the growing rate of organisms
1. Rate: activity/ time unit
a. example: 2g/sec.
b. What affects photosynthesis?
i. Light intensity
1. As light intensity increases so does the rate of photosynthesis but before the light intensity is full sun the rate of photosynthesis levels off and declines
a. The decline is called photoinhibition
b. It declines because if the plants absorb too much energy to fast it converts it to oxygen. Then the oxygen can combine with water and turn into hydrogen peroxide
peroxide is dangerous to the plant’s chloroplasts
1. As temperature increases the rate of photosynthesis increases but then levels off and declines
i. Carbon dioxide concentration
1. As the concentration of carbon dioxide goes up so does the rate of photosynthesis until the rate of photosynthesis is at the maximum point then the rate of photosynthesis level off and declines
a. If the carbon dioxide concentration goes over the maximum point it doesn’t effect the rate of photosynthesis
a. Limiting factors
i. What is limiting factors?
1. When light intensity, temperature, and carbon dioxide concentration all are affecting photosynthesis one of the factors may be at an ideal level while one might be real low
a. The low factor affects the rate of photosynthesis the most
b. The low factor is called the limiting factor
1. In a forest:
a. water, temperature, light intensity, and nutrients
Section 6: Photorespiration
a. What is it?
i. When the rubisco enzyme changes carbon dioxide into sugar, sometimes rubisco can get confused between carbon dioxide and oxygen
1. How does it get confused?
a. Oxygen and carbon dioxide both are held together by a double bond, this similarity between oxygen and carbon dioxide causes rubisco to get confused between the two.
ii. When rubisco combines with carbon dioxide the product is two PGA molecules.
iii. When rubisco combines with oxygen the product is one PGA molecule and a two-carbon acid, which is transported out of the chloroplast and broken down into carbon dioxide.
iv. When rubisco combines with oxygen instead of carbon dioxide the plant doesn’t gain fixed carbon atoms it looses them. This is called photorespiration.
a. Benefits of photorespiration
i. allows organisms to recover some of the carbon in glycolate
ii. It provides a way for chlorophyll to release extra light energy which lowers photoinhibition
b. When does a plant favor photorespiration? When does a plant favor photosynthesis?
i. The levels of oxygen and carbon dioxide effect whether or not a plant does photosynthesis or photorespiration.
1. When there is more oxygen the plant does photorespiration
2. When there is more carbon dioxide the plant does photosynthesis
ii. The weather
1. When the weather is hot the plant closes its stomates to lower the loss of water. This causes the carbon dioxide level in the leaves to drop, so the plant starts to do photorespiration
iii. C4 plants
1. What are they?
Plants that have over time made adaptations
photorespiration that occurs during hot weather.
b. The system the C4 plants have evolved fixes the Carbon dioxide into a 4-Carbon acid, this is why they are called C4 plants
c. C4 plants have a bundle sheath (tightly packed mesophyll cells that surround the veins in the leaves) the mesophyll cells can distinguish the difference between oxygen and carbon dioxide
d. Because of the bundle sheath the plant can favor photosynthesis in hot weather.
a. What does it stand for?
i. Crassulacean acid metabolism (CAM)
b. What is it?
i. Specialized system discovered in desert plants like cactus
c. How does this system work?
i. The plant opens their stomates at night and then closes them during the day so they can hold water in.
Section 7: Photosynthesis and the atmosphere
I. How does photosynthesis affect the atmosphere?
a. The relationship between photosynthesis and the organisms in the environment
i. Photosynthesis takes in carbon dioxide and releases oxygen. The organisms take in oxygen and release carbon dioxide.
b. Amounts of carbon dioxide and water plants use and the amounts of oxygen and organic matter they release
i. The plants use 140 billion metric tons of carbon dioxide per year.
ii. The plant uses 110 billion metric tons of water per year .
iii. The plant produces more than 90 billion metric tons of organic nutrients per year.
iv. The plant releases more than 90 billion tons of oxygen per year.
c. The effects of the rising carbon dioxide level on earth
i. The carbon dioxide level has been rising since the 1800's.
1. The level has been rising because of people burning fossil fuels and the shrinkage of the forests. This causes a rise in the earth’s temperature.
ii. Since the 1980's the growth of C3 plants have been growing in places where C4 plants use to dominate.
1. This is happening because the rise in carbon dioxide favors C3 plants.
Section 8: Varieties of chemoautotrophs
a. What are they?
i. Bacteria that get their energy by performing chemical reactions and fix their own carbon
ii. Only certain bacteria are chemoautotrophs because chemoautotrophs have to oxidize large quantities of minerals to get enough energy to survive
iii. Chemoautotrophs grow in places where other heterotrophs and autotrophs cannot live because they don’t compete well with other organisms
b. Sources of energy
i. Their sources vary
ii. Examples: sulfur, hydrogen gas, and iron
iii. The more reduced the electrons
the more energy the chemoautotroph receives and the faster they grow
Section 9: Chemoautotrophs and the environment
I. Chemoautotroph’s role in the environment
a. Metal-oxidizing bacteria
Purify copper so that people can mine it
1. Sometimes this bacteria oxidizes the sulfur in pyrite forming sulfuric acid
2. when this acid gets washed into a stream it kills a lot of wildlife surrounding that stream
i. Bacteria that oxidizes ammonium ions to nitrite ions and then changes the nitrite to nitrate
1. plants absorb this nitrate because it is an important nutrient to the plant
c. Chemoautotrophs in the ocean
i. Chemoautotrophs are the primary producers along the ocean floor
d. Hydrogen-oxidizing bacteria
i. Where are they found?
1. in the pores of rocks that are 2,800 meters below the earths surface
food for heterotrophic fungi and bacteria that are
2,800 meters below the earth’s surface