Chapter 3B : Photosynthesis and Cellular Respiration

Question 1

What is photosynthesis?

Answer 1

Photosynthesis is the process by which plants use the radiant energy of sunlight trapped by chlorophyll to build carbohydrates from carbon dioxide and water.

Question 2

Write the full chemical equation for photosynthesis.

Answer 2

12H2O + 6CO2 + sunlight —> C6H12O6 + 6O2 + 6H2O

Question 3

What type of reaction is photosynthesis classified as?

Answer 3

Anabolic + Endergonic reaction .

Question 4

Where does photosynthesis occur in a cell?

Answer 4

In an organelle known as the chloroplasts.

Question 5

Describe the structure of the chloroplasts.

Answer 5

The chloroplasts has a double membrane, with an inner and outer one. It is filled with an aqueous fluid known as the stroma. Within the chloroplasts, there are disc-like structures, known as thylakoids. Chlorophyll and lumen are found inside the thylakoid. One stack of thylakoids is known as a granum, multiple stacks are called grana. Structures known as lamella connects the stacks. Ribosomes and DNA are also found inside the chloroplasts.

Question 6

What wavelength of light is used to drive photosynthesis?

Answer 6

Around 400-700nm.

Question 7

Name the color of light that is the preferred energy source for photosynthesis.

Answer 7

Red and violet light.

Question 8

What are the two stages of photosynthesis?

Answer 8

The light dependent and independent (Calvin Cycle) stage.

Question 9

Where does the light dependent stage of photosynthesis occur?

Answer 9

In the thylakoid membrane of the grana in the chloroplast.

Question 10

State the inputs of the light dependent stage of photosynthesis.

Answer 10

Light energy, water, NADP+, ADP+Pi.

Question 11

State the outputs of the light dependent stage of photosynthesis.

Answer 11

Oxygen (waste product), NADPH, ATP.

Question 12

Describe the entire process of the light dependent stage of photosynthesis in as much detail as possible.

Answer 12

Light hits photosystem II, which excites an electron that moves off through the membrane to drive a chain of redox reactions, known as the electron transport chain. A water molecule is also split with a water-splitting enzyme, to produce oxygen, protons and electrons (2H2O –> 4H+ + 4e- + O2). The oxygen can be used for cellular respiration by the plant or diffuses into the atmosphere through stomata in the leaf surface. The protons/hydrogen ions diffuse into the lumen to drive ATPsynthase. The electrons move through the membrane by mobile electron carriers to the cytochrome complex and then to photosystem I. As the electrons move through the cytochrome complex on the thylakoid membrane, more H+ ions are pumped into the lumen from the stroma. The high concentration of H+ ions in the lumen is used to make ATP from ADP+Pi via ATPsynthase. Photosystem I is also hit by light, which excites an electron to move off through the membrane, and the electron is replaced by the electron that comes from Photosystem II. The highly energized electron from photosystem I is transferred to NADP+reductase, which reduces NADP+ to NADPH (NADP+ +2e- + 2H+ –> NADPH + H+). The ATP and NADPH carry the protons, electrons and energy needed in the next stage of photosynthesis - the light independent stage.

Question 13

How does the shape and structure of leaves equip them to carry out photosynthesis?

Answer 13

• The flat shape provides a larger surface area to be exposed to sunlight.
• The presence of stomata/pores on the leaf surface provide access for carbon dioxide to enter the cell.
• The xylem vessels in the vascular tissue enable the transport of water to photosynthetic cells.
• The thinness and the presence of internal air space in the leaf enables the ready diffusion of carbon dioxide to photosynthetic cells.
• The presence of many chloroplasts in photosynthetic cells enables it to trap sunlight energy.

Question 14

Where does the light-independent stage of photosynthesis occur?

Answer 14

Inside the stroma of the chloroplast.

Question 15

State the inputs of the light-independent stage of photosynthesis.

Answer 15

Carbon dioxide (from the atmosphere), ATP and NADPH (both from the previous stage).

Question 16

State the outputs of light-independent stage of photosynthesis.

Answer 16

Water, NADP+, ADP+Pi and glucose/2G3P

Question 17

Describe the light independent stage of photosynthesis in as much detail as possible.

Answer 17

The light-independent reaction occurs inside the stroma of chloroplasts. This stage is not dependent on light, but it is dependent on the previous stage occurring. Three carbon dioxide molecule are incorporated into three RuBP molecules (5 carbon compound) through the help of the enzyme Rubisco, to form six 3-PGAs. This is known as the carbon fixation. Through the input of ATP and NADPH from the light dependent stage, the six 3-PGA is reduced to form six G3Ps. The products/outputs of this reaction include ADP+Pi and NADP+. One of the G3P molecule leaves the cycle and is ready for use by the cell (two G3Ps will form glucose which can be used for cellular respiration or to form other carbohydrates such as starch or cellulose). Through the input of ATP, the five remaining G3Ps are regenerated/rearranged to form three RuBP, and an output of ADP+Pi. The cycle continues as more carbon dioxide diffuses into the cell.

Question 18

Define cellular respiration.

Answer 18

Cellular respiration is a series of energy releasing reactions that breakdown organic compounds found in food, releasing chemical energy and transferring it to a form usable by cells, which is ATP.

Question 19

Write the full chemical equation for cellular respiration.

Answer 19

C6H12O6 + 6O2 –> 6CO2 + 6H2O + ATP

Question 20

What type of reaction is cellular respiration classified as?

Answer 20

Catabolic + exergonic reaction.

Question 21

Name the types of cellular respiration.

Answer 21

Aerobic and anaerobic respiration.

Question 22

What is the preferred source of chemical energy for cells?

Answer 22

Glucose.

Question 23

Where does cellular respiration occur in a cell?

Answer 23

The mitochondrion.

Question 24

True or False.

The rate of cellular respiration depends on the state of the organism.

Answer 24

True.

Question 25

State examples of what energy from cellular respiration is needed for?

Answer 25

• The growth and repair of the body
• Movement, such as muscle contraction
• Neural transmission
• Active transport across cell membranes
• The translocation of sugar in plants
• The synthesis of complex molecules, such as hormones and enzymes.

Question 26

What is a poison that stops ATPsynthase from working?

Answer 26

Cyanide.

Question 27

True or False.

The transfer of glucose to ATP molecules is 100% energy efficient.

Answer 27

False.

It is 40% energy efficient and the remaining 60% is lost as heat energy.

Question 28

Describe the structure of the mitochondria.

Answer 28

The mitochondria has a double membrane, the inner (cristae) and outer membrane. It has several folds, and the inner membrane space is known as the matrix. Ribosomes and DNA are also found in the mitochondria.

Question 29

Define aerobic respiration.

Answer 29

The chemical breakdown of glucose in the presence of oxygen.

Question 30

Define anaerobic respiration.

Answer 30

The chemical breakdown of glucose without the presence of oxygen.

Question 31

Compare the two types of cellular respiration.

Answer 31

• Aerobic respiration is an oxygen requiring process. It produces 36/38 mol of ATP per mol of glucose, it has a slower rate of ATP production, but it is sustain indefinitely, which is a more efficient energy transfer process and the end products are carbon dioxide and water.
• Anaerobic respiration does not require oxygen. It produces 2 mol of ATP per mol of glucose used, it has a faster rate of ATP production, but it is sustained over a short period of time only, which is a less efficient energy transfer process and the end products are lactic acid in humans, ethanol and carbon dioxide in plants and yeast.

Question 32

State the three stages of cellular respiration.

Answer 32

Glycolysis, the Krebs Cycle and the electron transport chain.

Question 33

State the inputs and outputs of glycolysis.

Answer 33

Inputs: Glucose, 2 ATP, 2 NAD+, 4 ADP+Pi
Outputs: 2 pyruvate, 2 NADH, 4 ATP (net of 2 ATP produced)

Question 34

Describe the stage of glycolysis in as much detail as possible.

Answer 34

Glycolysis occurs in the cytosol of cells, and requires the input of glucose, NAD+ and ADP+Pi. This stage does not require oxygen and involves a series of ten chemical reactions all controlled by a specific enzyme, and these enzymes are in solution in the cytosol. During glycolysis, 2 ATP is used to breakdown one molecule of glucose into two molecules of a 3-carbon compound known as pyruvate/pyruvic acid. 4 ATP is produced in this stage, and thus a net of 2 ATP is produced. Hydrogen atoms are also removed from the glucose molecule. These hydrogen atoms and their electrons are collected by the acceptor molecule NAD+. When acceptor molecules are carrying hydrogens, they are termed “loaded” acceptors or NADH. A total of 2 NADH is produced in this stage. Thus, the outputs of this stage include two pyruvates, ATP and NADH.

Question 35

State the inputs and outputs of the Krebs cycle.

Answer 35

Inputs: 2 pyruvate/glucose - 2 Acetyl CoA, 8 NADH+, 2 FAD+, 2 ADP+Pi
Outputs: 6 CO2, 8 NADH, 2 FAD, 2 ATP

Question 36

Describe the Krebs cycle in as much detail as possible.

Answer 36

The Krebs Cycle occurs in the inner membrane space (matrix) of the mitochondrion. The pyruvate molecule enters the mitochondrion matrix where with the help of coenzyme A it is oxidized to form Acetyl CoA (2 carbon compound), producing carbon dioxide and NADH. The Acetyl CoA will be the starting point for the Krebs Cycle. It will then combine with a 4 carbon compound (oxaloacetate) to form a 6 carbon compound, known as citrate/citric acid. In the process of recycling citrate back to oxaloacetate, 3 NADH, 2 CO2, FADH2 and ATP is produced.

Question 37

State the inputs and outputs of the electron transport chain.

Answer 37

Inputs: 6 O2, 8 NADH, 2 FADH2
Outputs: 6H2O, 8 NAD+, 2 FAD+, 32 ATP

Question 38

Describe the electron transport chain in as much detail as possible.

Answer 38

The electron transport chain occurs in the cytochrome complex embedded in the cristae/inner membrane of the mitochondrion. The inputs include the NADH, FADH2 from the Krebs Cycle and oxygen molecules. The NADH and FADH2 carry the electrons and H+ ions needed to drive the electron transport chain. As the electrons move through the membrane, H+ ions are pumped to the outside of the cell. This results in a protein gradient that drives the synthesis of ATP from ADP+Pi via ATPsynthase. Some of the hydrogen ions also combine with oxygen to form water molecules. The resulting products are water, NAD, FADH2 and ATP.

Question 39

True or False.

Most of the ATP produced is from the electron transport chain.

Answer 39

True.

Question 40

What are NAD+, FAD+ and NADP known as?

Answer 40

Uncharged carrier molecules.

Question 41

What are NADH, FADH2 and NADPH known as?

Answer 41

Charged carrier molecules.

Question 42

Name the limiting factors that control the rate of photosynthesis.

Answer 42

Concentration of carbon dioxide, availability of water, light intensity, temperature, light wavelength.

Question 43

What is the purpose of additional photosynthetic pigments?

Answer 43

To enable light of different wavelengths to be absorbed, which increases the capacity of light absorption by the plant, and increases the rate of photosynthesis.

Question 44

Name one structural feature of chloroplasts or mitochondria and outline how it supports the endo-symbiotic theory for the origin of these organelles.

Answer 44

Chloroplasts have a double-membrane, indicating that this organelle was independent but engulfed by a eukaryotic cell, which had to wrap a membrane around it to do so. They also have ribosomes and DNA.

Question 45

Explain the importance of the presence of these ribosomes in chloroplasts.

Answer 45

Ribosomes are used for protein synthesis of the enzymes that are used to catalyze photosynthetic reactions.