Photosynthesis

Question 1

Order the steps of photosynthesis from first to last:

i. Photosynthesis I
ii. Photosynthesis II
iii. Calvin Benson Cycle
iv. Noncyclic Photophosphorylation

Answer 1

Photosystem II comes before Photosystem I, which then proceeds to go through either cyclic photophosphorylation or Noncyclic photophosphorylation. The step that comes after Noncyclic photophosphorylation is the Calvin Benson Cycle which is also known as the C3 dark reactions.

Question 2

The Calvin Benson cycle is said to “fix” what chemically unreactive molecule

Answer 2

The Calvin Benson Cycle fixes chemically unreactive carbon dioxide. Sometimes it is best to just simplify photosynthesis by thinking about the major input and output molecules. Plants take in energy (sunlight), water, and the carbon dioxide that we breathe out, while they produce oxygen and storable energy in the form of sugars. Carbon dioxide is referred to as being chemically unreactive and is a waste product of human respiration; the good news is that plants fix our waste product into usable energy.

Question 3

Which of the following is/are different between C4 and C3 photosynthesis:
The number of carbon atoms in the first product.
The overall efficiency.
The enzymes involved.
The energy requirements.
All of the above are differences.

Answer 3

All of the above are different between C4 and C3 photosynthesis. C4 is more efficient than C3 photosynthesis because it limits the ability for oxygen to be fixed by Rubisco. The naming of C4 and C3 photosynthesis is due to the number of carbons of the first product molecule (4 in C4 and 3 in C3). The energy requirements are also different, and the enzymes involved are different because there are different steps/reactions taking place.

Question 4

Which of the following molecules is not used in photosynthesis:
ATP
PGA
PGAL
RuBP
NADH

Answer 4

NADH is not used in photosynthesis, but rather the opposite process of aerobic respiration. One way to distinguish NADH from NADPH (which is used in photosynthesis), is that NADPH has a P (Photosynthesis), whereas NADH does not.

Question 5

In which of the following ways are C4 photosynthesis and CAM photosynthesis similar:
Both use storage vacuoles to store the product of OAA.
Malic acid is transferred in both.
They both use PEP carboxylase in the fixation of CO2 to OAA.
None of above.
All of above.

Answer 5

C4 photosynthesis and CAM photosynthesis both use PEP carboxylase in the fixation of CO2 to OAA. This first step is critical and the same in both processes, however, the next steps that follow are slightly modified or different. C4 photosynthesis uses malate whereas CAM uses and stores the ionized form of malate called malic acid. Only CAM photosynthesis uses storage vacuoles to store the product of OAA, thus CAM is storing up for photosynthesis whereas C4 photosynthesis is transferring for photosynthesis… this is the key difference between the two versions of photosynthesis.

Question 6

C3 photosynthesis takes place in the __.

Answer 6

C3 photosynthesis takes place in the chloroplast. C3 photosynthesis is another name for the Calvin Benson Cycle (yes it has many names). This name is derived from the first product PGA, which is contains 3-Carbon atoms. You will also see names such as the carbon reduction cycle, Calvin Cycle, Dark Cycle, Dark reactions, Light-independent reactions. As a side note, both the light-dependent and light-independent reactions occur in the chloroplast.

Question 7

In the Calvin Benson Cycle of Reduction, going from 12 Phosphoglycerate molecules to 12 glyceride-3-phosphate molecules, how many molecules of ATP and NADPH are needed

Answer 7

In the Calvin Benson Cycle of Reduction, going from 12 Phosphoglycerate molecules to 12 glyceride-3-phosphate molecules 12 ATP molecules and 12 NADPH molecules are needed. Phosphoglycerate (PGA) and glyceride-3-phosphate (PGAL) are two important molecules used in photosynthesis, and it is important to know both their names and functions as they commonly appear.

Question 8

During the process of Chemiosmosis, what accumulates inside thylakoids?

Answer 8

Protons or H+ ions accumulate inside thyalkoids (the thylakoid compartment) during the process of chemiosmosis. The hydrogen ions come primarily from photolysis, and drive the basics of ATP production which are eventually used in the Calvin Benson Cycle. The pH on the in the thylakoid compartment is 1000 times more acidic than the outside stroma.

Question 9

Noncyclic photophosphorylation starts out with the absorption of light in

Answer 9

Noncyclic photophosphorylation starts out with the absorption of light in PS II. Photosystem II which contains the P680 pigment cluster, is the first step in the process of Noncyclic photophosphorylation. This might seem confusing as it “sounds” better if Photosystem I would come first, however, it was just discovered before Photosystem II, hence the name Photosystem I. I associate Photosystem I as being with the higher wavelength P700.

Question 10

Which of the following pigments are not used in photosynthesis to optimize energy absorption:
Carotenoid
Xanthophyll
Chlorophyll A
Chlorophyll B
All of the above are used in photosynthesis.

Answer 10

All of the above pigments are used in photosynthesis to optimize energy absorption. Xanthophyll’s are yellow pigments within the division of carotenoids (red, yellow or orange pigments—think fall color leafs). Chlorophyll A is a green pigment found in plants that absorbs light energy

Question 11

What combines with NAD+ and P+ to form NADPH

Answer 11

2 electrons combine with NADP+ and H+ to form NADPH? There is a short electron transport chain at the end of the PS I primary electron acceptor that shuttles 2 electrons down to be combined with NADP+ and H+ to form NADPH. The 2 +’s on both the NADP and H show you that they are lacking electrons (2 that is).

Question 12

The process of photosynthesis begins with

Answer 12

The process of photosynthesis begins with pigments that absorb light in plant cells. In order to be as efficient as possible, pigments work together to absorb light and efficiently use the energy produced from the excited electrons. There are two specific chlorophyll molecules in photosynthesis that participate in this absorption of energy, P680 and P700. P700 forms PS1 (photosystem 1), while P680 forms PS2 (photosystem 2). Cyclic and noncyclic photophosphorylation steps have to do with the generating of ATP from ADP and Pi from the energy that is absorbed in the pigments of the plant cells. The Calvin Benson cycle uses the ATP generated to fix carbon dioxide into energy usable molecules such as glucose.

Question 13

In order for the reactions of photosynthesis to occur, ___ are required to speed up each individual reaction and lower the activation energy barriers.

Answer 13

In order for the reactions of photosynthesis to occur, enzymes are required to speed up each individual reaction and lower the activation energy barriers. This is common in not only photosynthesis but in almost all reactions seen in the numerour biological systems.

Question 14

The enzyme Rubisco can have efficiency problems primarily because it

Answer 14

The enzyme Rubisco can have efficiency problems primarily because it is able to fix oxygen. The enzyme Rubisco is said to be the most common or abundant protein in the earth. One of the problems that arises with photosynthesis is that the enzyme which is used to fix carbon dioxide, is also able to fix oxygen. This causes competition and limits photosynthesis. Peroxisomes are used in a cell to breakdown the byproducts of Rubisco’s fixing of oxygen. This is an extra energy requirement for a cell which slows down the rate of photosynthesis. CAM along with C4 photosynthesis are slight photosynthetic modifications that aid in this potential problem.

Question 15

What is a key difference between cyclic photophosphorylation and Noncyclic photophosphorylation

Answer 15

A key difference between cyclic photophosphorylation and Noncyclic photophosphorylation is that Noncyclic photophosphorylation produces NADPH. NADPH is an energy rich molecules that is then used in the Calvin-Benson cycle of photosynthesis. Cyclic photophosphorylation simply goes down the electron transport chain again to create more ATP, whereas Noncyclic proceeds to produce NADPH. More ATP is necessary in the Calvin-Benson Cycle than NADPH, which is why cyclic photophosphorylation is important in photosynthesis.

Question 16

Which of the following would one expect to be the most acidic

Answer 16

One would expect the thylakoid compartment to be the most acidic amongst the answer choices available. Starting with a neutral pH = 7, we will go from here. Remember that the inside of the thylakoid accumulates hydrogen ions from the splitting of water in photolysis. Thus is would have more hydrogen ions or a lower pH. The outside of the thylakoid known as the stroma is less acidic or more basic because it essentially transports hydrogen ions back to the thylakoid membrane to aid in the production of energy rich products such as NADPH and ATP. A pH of 14 is not acidic, thus the answer is the thylakoid compartment.

Question 17

Why is it important to have more production of ATP then NADPH in photosynthesis

Answer 17

It is important to have more production of ATP than NADPH in photosynthesis because more ATP is needed to drive the Calvin-Benson cycle. ATP is used to convert both PGAL back to Ribulose Biphosphate and PGA to PGAL, whereas NADPH is only used in the conversion of PGA to PGAL. With the extra energy requirement of going from PGAL to Ribulose Biphosphate, more ATP is necessary.

Question 18

The fixation of oxygen is commonly called ___, while the fixation of carbon dioxide is commonly called ___

Answer 18

The fixation of oxygen is commonly called photorespiration, while the fixation of carbon dioxide is commonly called photosynthesis. There are other forms of oxygen and carbon fixation, however, these are the two main forms. The word fixing or fixation is necessary to understand, because this is really a key to understanding photosynthesis. Photosynthesis is taking something that has no energy and is potentially harmful (Carbon dioxide), and making it into something that is energy rich and useful (sugars or carbohydrates).

Question 19

Why is it hypothesized that Rubisco along with photosynthesis was more efficient in the beginning of the world according to the evolutionary theory

Answer 19

According to the evolutionary theory, there was little oxygen in the atmosphere at the beginning of the world. Because of little oxygen, it is said the photosynthesis was more efficient because Rubisco was able to only fix carbon dioxide without much competition from oxygen (which Rubisco also fixes).

Question 20

Because photophosphorylation requires light to make ATP and NADPH, it is often referred to as

Answer 20

Because photophosphorylation requires light to make ATP and NADPH, it is often referred to as light-dependent reactions. Light-dependent reactions take the energy from the sunlight and electrons from the splitting of water to make both ATP and NADPH, which are both energy rich molecules. Photophosphorylation is dependent upon light.

Question 21

Electrons move from PS I and PS II directly to

Answer 21

Electrons move from PS I and PS II directly to a primary electron acceptor. The electrons are energized or excited when the PS I and/or the PS II absorb energy from the sun, which excited the electrons and energizes them to move towards the primary electron acceptor. There are many electron acceptors in the process of photosynthesis, however, the reason the name primary is used is because it is the first electron acceptor after the excitation of electrons from the photosystems.

Question 22

When 6 ATP are used to make 6 RuBP from 10 PGAL, thus allowing additional carbon dioxide to react with RuBP and cycle again, this process is called

Answer 22

When 6 ATP are used to make 6 RuBP from 10 PGAL, thus allowing additional carbon dioxide to react with RuBP and cycle again, this process is called regeneration. In order for the cycle to continue cycling, RuBP (ribulose biphosphate) must be regenerated or recreated.

Question 23

Where do the electrons in photosynthesis that combine to form NADPH come from

Answer 23

Photolysis is the process of splitting water by light, thus forming 2 electrons along with Hydrogen and Oxygen molecules. The 2 electrons from photolysis are incorporated in NADPH and are first transported to Photosystem II.

Question 24

The major function of the Calvin Benson Cycle is to produce __.

Answer 24

The major function of the Calvin Benson Cycle is to produce glucose. Glucose is a monosaccharide of carbohydrates. It is simply a storable sugar in plants. The whole goal of the Calvin Benson Cycle is to take the energy (ATP and NADPH) from photophosphorylation along with carbon dioxide, and turn it into storable and usable energy in the form of carbohydrates such as glucose.

Question 25

Where do the dark reactions of photosynthesis tale place

Answer 25

The dark reactions of photosynthesis take place in the stroma of the chloroplast. As mentioned in another answer, another name for the dark reactions is the Calvin-Benson Cycle, or the light independent reactions. Remember that they need the products of light-dependent reactions to work, but they do not directly use light, hence the name dark reactions.

Question 26

Why is it important for there to be a pH and electrical gradient on the thylakoid membrane

Answer 26

It is important for there to be a pH and electrical gradient on the thylakoid membrane in order that ADP can be phosphorylated to ATP (ADP?ATP). The pH and electrical gradient drive the basics of ATP production which are eventually used in the Calvin Benson Cycle to make energy rich products such as glucose or fructose (storable energy for plants). The pH on the in the thylakoid compartment is 1000 times more acidic than the outside stroma, and is able to drive the production of ATP. Without ATP, there would be no carbohydrate production.

Question 27

The process of going from ADP + Pi -> ATP is called

Answer 27

The process of going from ADP + Pi à ATP is called phosphorylation. This is a good process to have a solid understanding of, as it frequently shows up in many different processes in the human body. ADP (Adenine Diphosphate) has one less phosphate group than ATP (Adenine Triphosphate). It is the additional phosphate bond in ATP that delivers energy to reactions. Phosphorylation occurs multiple times throughout the process of photosynthesis, including within both the Calvin Benson Cycle and during Photophosphorylation.

Question 28

How many H+ ions are needed to pass through an ATP synthase in order to generate one ATP

Answer 28

Three H+ ions are needed to pass through an ATP synthase in order to generate one ATP. Because ADP is recycled from the Calvin Benson cycle, ADP is energized by the passing of H+ ions through ATP synthases (which are channel proteins), generating ADP to go to ATP. ADP ? ATP

Question 29

When electrons move down the electron transport chain, they are said to:
No energy change occurs
Gain energy
Lose energy
All of above

Answer 29

When electrons move down the electron transport chain, they are said to lose energy. Notice the wording down versus up. When electrons move up they are said to gain energy. The energy that is lost as electrons move down the electron transport chain is used in the process of phosphorylation which produces about 1.5 ATP per movement down.

Question 30

Which of the following plant families are examples of C4 photosynthesis?

i. corn
ii. cacti
iii. crassulaceae
iv. sugarcane

Answer 30

Corn and sugarcane are both examples of C4 photosynthesis. Cacti and Crassulaceae are both common examples of CAM plant families. While C4 photosynthesis and CAM photosynthesis are similar, it is important to understand their differences, which includes the type of plants they would be more likely to show up in.

Question 31

Where do the light reactions of photosynthesis take place

Answer 31

The light reactions of photosynthesis take place in the Thylakoid Membrane of the Chloroplast. The thylakoid membrane contains the electron transport chain, which involves the transporting of electrons through the excitation from the sunlight and carrier proteins. The thylakoid membrane works as a barrier to create a pH difference between the stroma and the thylakoid compartment, which aids in the generation of ATP.

Question 32

What is the chief advantage of CAM photosynthesis over other forms of photosynthesis

Answer 32

The chief advantage of CAM photosynthesis over other forms of photosynthesis is that because of the storage of Malic Acid, photosynthesis can proceed with the stomata closed. When plant stomata are open, plants lose water, however, they need to be open for carbon dioxide intake. This can cause a big problem if there is either a lack of water or a hot climate (or both like the desert biome). The benefit of CAM photosynthesis is that photosynthesis can occur without the opening of the stomata because of CAM’s ability to store malic acid in a storage vacuole. This enables a plant such as the cactus to photosynthesize during the day with the stomata closed, the nearly opposite of standard C3 photosynthesis.

Question 33

Which of the following equations properly explains photosynthesis?
Glucose + 6CO2 -> 6H2O + 6O2 +energy
Sunlight + 6H2O + 6CO2 -> Glucose + 6O2
Sunlight + 6H2O + 6O2 -> glucose + 6CO2
ATP + ^O2 -> 6H2O + 6CO2 + glucose

Answer 33

Photosynthesis is the process of taking energy from the sun, carbon dioxide, and water, and converting it into usable energy in the form of sugar (example glucose) and producing oxygen. When thinking about photosynthesis, think about what plants need… water, sunlight and carbon dioxide. They turn these three things into storable sugars used for energy and the oxygen that we breathe. The opposite process of photosynthesis, aerobic respiration, is the conversion of the oxygen and glucose into energy (ATP), carbon dioxide and water.

Question 34

Within the Stroma of a Chloroplast are stacks of thylakoids which are called

Answer 34

Within the Stroma of a Chloroplast are stacks of thylakoids which are called grana. While a single stack of thylakoids is called a granum, grana is the plural form of granum which refers to multiple stacks of thylakoids. The light dependent reactions of photosynthesis occur on the membranes of thylakoids.

Question 35

How many times does the Calvin Benson cycle have to cycle in order to produce one molecule of Glucose (C6H12O6)

Answer 35

The Calvin Benson cycle has to cycle six times in order to produce one molecule of Glucose C6H12O6. The Calvin Benson cycle uses 18 ATP, 12 NADPH, 6 CO2, and 6 RuBP to create one molecule of glucose. These ratios are important to both understand and commit to memory.

Question 36

In C4 photosynthesis, which of the following is transported from mesophyll cells to the bundle sheath cells so that photosynthesis can begin more efficiently:
malate
pyruvate
rubisco
PEP carboxylase

Answer 36

Malate is transported from mesophyll cells to the bundle sheath cells so that photosynthesis can begin more efficiently In C4 photosynthesis. Carbon dioxide is first converted into oxaloacetate (OAA) and then to malate, which is transferred to bundle sheath cells and then converted back to carbon dioxide. This method of moving carbon dioxide from the mesophyll cells to the bundle sheath cells allows carbon to be fixed without competition from oxygen, thus enabling photosynthesis to be more efficient.

Question 37

Electron transport chains consist of __ that are said to carry electrons down the transport chain.

Answer 37

Electron transport chains consist of proteins that are said to carry electrons down the transport chain. These proteins more specifically referred to as carrier proteins, aid in the production of ATP. Some examples of carrier proteins in the electron transport chain are ferredoxin and cytochrome.

Question 38

Which enzyme combines with carbon dioxide to produce PGA

Answer 38

RuBP Carboxylase also known as rubisco is the enzyme that combines with carbon dioxide to produce PGA. This reaction is referred to as carboxylation. Rubisco is the most common protein on the earth, so it is a good one to tuck away in the memory bank.

Question 39

After malate is transferred to bundle sheath cells, pyruvate is then sent back to mesophyll cells and converted back to PEP (phosphoenolpyruvate). What is the energy process of going from pyruvate back to PEP?
ATP -> ADP
ATP -> AMP
Cyclic AMP -> ATP
ADP -> ATP

Answer 39

The energy process of going from pyruvate back to PEP is ATP -> AMP. This might not sound important at first glance, but it is a different energy requirement than what is seen in C3 photosynthesis. Because C4 photosynthesis has a higher energy requirement, it must be more efficient, which it is. Going from ATP to ADP versus ATP to AMP is simply one phosphate group different. It is the energy given off from the phosphate bonds that drives reactions.

Question 40

The Calvin Benson Cycle does not directly use __.

Answer 40

The Calvin Benson Cycle does not directly use light. This can be confusing, because it requires the products of the light reactions (ATP and NADPH) to function, however, it does not directly use light to carry out its processes. This is why the Calvin Benson cycle is often times termed the light-independent reactions or dark reactions. The Calvin Benson Cycle cannot however occur in the dark or without light, because it needs the products from the light reactions (ATP and NADPH to function). Make sure you understand this as it is frequently tested on.