unit 4 photosynthesis and respiration

Unit 4

Photosynthesis and Respiration

Table of Contents

Table of Contents 1

Introduction 3

Essential Questions 3

Review 4

Lesson 4.1: Photosynthesis in Plants 5 Objective 5 Warm-Up 5 Learn about It 6 Key Points 9 Web Links 9 Check Your Understanding 9 Challenge Yourself 10

Lesson 4.2: Mechanisms of Photosynthesis 11 Objective 11 Warm-Up 11 Learn about It 12 Key Points 15 Web Links 16 Check Your Understanding 16 Challenge Yourself 17

Lesson 4.3: Aerobic Respiration 18 Objectives 18 Warm-Up 18 Learn about It 19 Key Points 26 Web Links 27 Check Your Understanding 28 Challenge Yourself 28

Lesson 4.4: Anaerobic Respiration and Fermentation 30 Objectives 30 Warm-Up 30 Learn about It 31 Key Points 33 Web Links 33 Check Your Understanding 34 Challenge Yourself 35

Laboratory Activity 36

Performance Task 37

Self Check 39

Key Words 39

Wrap Up 41

References 42

Copyright © 2018 Quipper Limited 2

GRADE 9 | SCIENCE

Unit 4 Photosynthesis and Respiration

All living things on earth need energy to carry out essential life processes to survive. The sun radiates solar energy, and it is this energy that powers many essential life processes. The energy coming from the sun flows into the ecosystem. Some organisms trap energy coming from the sun to produce food. The cycle of energy transfer occurs from producers, consumers, and decomposers. As organisms feed on each other, energy and nutrients flow from one organism to another. Humans and other animals obtain energy by consuming food. At the cellular level, cells produce and consume energy in the form of adenosine triphosphate (or ATP). Cells, as the smallest unit of living organisms, degrade organic molecules in food to produce ATP. The whole process of producing food and converting it to energy occurs through photosynthesis and respiration.


Essential Questions

At the end of this unit, you should be able to answer the following questions.

● How do plants create their own food? ● How do plants synthesize energy at the cellular level? ● How do animals produce energy at the cellular level in the presence of

oxygen? ● If oxygen is absent, will animals still be able to produce energy?

Review

● An ecosystem is a community of organisms in their environment, and all the interactions within. It has two main components: the biotic and the abiotic components.

○ The biotic component is the living environment. It refers to all living organisms in the ecosystem. .

○ The abiotic component is the nonliving environment. It refers to the physical environment.

● The biotic components of an ecosystem can be classified into three groups. These are the producers, consumers, and decomposers.

○ Producers are organisms that are capable of producing their own food.

○ Consumers are organisms that are not capable of producing their own food. They rely on producers or other consumers for food.

○ Decomposers are organisms that decompose living organisms that have died.

● Food chains represent the feeding relationship between organisms. When different food chains are interlinked, a food web is formed.

● Bioenergetics is a field of Biology that discusses the production and consumption of energy and the interconnection between metabolic pathways.

● There are two main processes involved in the study of bioenergetics. These are catabolism and anabolism.

○ In catabolism, large molecules are broken down into smaller pieces. ○ In anabolism, small molecules are used to build up larger molecules.


Lesson 4.1: Photosynthesis in Plants

Objective In this lesson, you should be able to:

● describe the process of photosynthesis in plants.

Just like other living things, plants need food to survive. Without available food, plants will die. Since plants are the primary source of energy in the energy pyramid, those who eat plants such as humans will starve. How do plants make their food?

Warm-Up Where is the Source of Energy? Study the food web below.


Guide Questions:

1. What is the energy source of each organism? Trace using the food web shown.

2. How do grasshoppers and rabbits obtain their energy? How about the mouse and the bird?

3. Do grasses and grains eat any other organisms? Trace using the food web shown.

4. How do the grasses and grains obtain their energy? Identify their energy source.

Learn about It

Plants produce their food. They are known as autotrophs (also known as producers). Autotrophs produce food for the biosphere. Specifically, plants are referred to as photoautotrophs. They use sunlight to produce food. Those who consume autotrophs are known as heterotrophs (also known as consumers). Photosynthesis is the process of food-making in plants. It is also present in algae, some protists, and some prokaryotes. For plants to produce their food, they need sunlight, carbon dioxide (CO2), and water (H2O). The process produces glucose (C6H12O6), which plants consume as food, and oxygen. Solar energy is converted by plants into chemical energy. It is this chemical energy that plants consume. The chemical reaction for photosynthesis is written as


Plant Organelles in Photosynthesis Photosynthesis occurs in the leaves of plants. It specifically occurs within specialized organelles called chloroplasts. The main photosynthetic unit in the chloroplast is the thylakoid. When thylakoids are stacked in columns, it is called a granum (plural, grana). The granum is protected by two layers of membrane: the inner membrane and the outer membrane. The space between the membranes and granum is called the stroma.

Fig. 1. Structure of the chloroplast.

The green color of plant leaves is due to chlorophyll. Chlorophyll comes from the Greek word chloros meaning green, and phyllon meaning leaf. It is found on the surface of thylakoids.


The Process of Photosynthesis

1. Light energy is captured by chloroplasts found in the mesophyll cells. 2. Water enters the leaf. 3. Carbon dioxide also enters the leaf through the stomata. Stomata are tiny

pores in the leaf. 4. Glucose and oxygen are produced through a series of chemical reactions

inside the chloroplasts. 5. Glucose leaves the leaf. Oxygen also leaves through the stomata.

Fig. 2. The process of photosynthesis in plants.


Key Points

● Photosynthesis is the process of food-making in plants. ● For plants to produce their food, they need sunlight, carbon dioxide, and

water to produce glucose and oxygen. ● Photosynthesis takes place in the leaves of plants, specifically within the

chloroplasts. ● The green color of plant leaves is due to chlorophyll.

Web Links

For further information, you can check the following web links:

● Watch this video to further understand the process of photosynthesis in plants User:Elearning. 2013. ‘Photosynthesis.’ https://www.youtube.com/watch?v=3pD68uxRLkM

● A game about photosynthesis? Check this link and play the game. Mindfuel (formerly Science Alberat Foundation). n.d.. ‘Photosynthesis’ https://wonderville.org/asset/photosynthesis

Check Your Understanding

A. Identify the following.

1. These are organisms that produce their own food. 2. It is the main photosynthetic unit in the chloroplast. 3. It is the process of food-making in plants.


https://www.youtube.com/watch?v=3pD68uxRLkM

https://www.youtube.com/watch?v=3pD68uxRLkM

https://wonderville.org/asset/photosynthesis

https://wonderville.org/asset/photosynthesis

4. It is the green pigment in leaves of plants. 5. It is the entry point of carbon dioxide in leaves of plants. 6. These are molecules that plants consume as food. 7. This is the space between the membranes and the grana. 8. Where the energy captured by the chloroplasts come from. 9. Cells where the chloroplasts are mostly found in.

10. The gas that is the waste product of photosynthesis. B. Arrange the following steps in photosynthesis. Number the steps from 1 to 5

with 1 being the first.

1. Glucose leaves the leaf. Oxygen also leaves through the stomata.

______________

2. Carbon dioxide also enters the leaf through the stomata. ______________

3. Light energy is captured by chloroplasts found in the mesophyll cells.

______________

4. Water enters the leaf. ______________

5. Glucose and oxygen are produced through a series of chemical reactions inside the chloroplasts.

______________

Challenge Yourself

Answer the following questions.

1. Why is chlorophyll green? 2. How is a thylakoid different from a granum? 3. Why does glucose need to leave the leaf? 4. Some leaves of San Francisco plants are not colored green. Does this mean

that they cannot produce their food through photosynthesis? 5. Will photosynthesis in plants proceed in the absence of sunlight?


Lesson 4.2: Mechanisms of Photosynthesis

Objective In this lesson, you should be able to:

● explain the process of light-dependent and light-independent reactions in photosynthesis.

From the general reaction for photosynthesis, the process may seem to be easy. However, photosynthesis is divided into two parts: the light-dependent and the light-independent reactions. At the cellular level, how do plants synthesize their food?

Warm-Up Recalling Photosynthesis Plants make their own food through a process called photosynthesis. Trace the process of photosynthesis in the green leaf below. Label the compounds that go in and out of the leaf.


Learn about It

At the cellular level, photosynthesis is divided into two parts: the light-dependent reaction and the light-independent reaction.

Fig. 3. An overview of photosynthesis inside the chloroplast.

Light-Dependent Reaction The light-dependent reactions (or simply light reactions) occur in the thylakoids. During the reaction, sun’s light splits water and releases oxygen into the atmosphere. Light energy is converted to chemical energy in the form of ATP and NADPH (or nicotinamide adenine dinucleotide phosphate). Two photosystems inside the chlorophyll are responsible for absorbing sun’s light in the form of photons or light-carrying particles. These are photosystem I or P700 (PSI) and photosystem II or P680 (PSII).


Fig. 4. Light-dependent reaction in the thylakoid.

Steps of the Light-Dependent Reaction

1. The chloroplast absorbs and traps light from the sun. 2. Trapped light is transferred by the chlorophyll to the photosystems. 3. The photosystem uses light energy to split water into hydrogen ions (H+), and

oxide ion (O2-), and an electron. Two oxide ions combine to form a molecule of oxygen.

4. The electrons are passed through several electron carriers in an electron transport chain. During the movement of electrons, energy is gained and lost. The net energy causes the hydrogen ions to be actively pumped across the thylakoid membrane against the concentration gradient.

5. Once protons are on the other side of the membrane in an area called the lumen, they diffuse back across to the stoma through a membrane-bound protein called ATP synthase.

6. Energy is released due to the backflow of H+ down their concentration gradient. It is used to create a molecule of ATP from ADP and inorganic phosphate.

7. The electron is used to reduce NADP to NADPH along with hydrogen from photolysis. NADPH and ATP will serve as electron carriers in the next stage of photosynthesis.


Light-Independent Reaction The light-independent reaction (also known as dark reaction or Calvin cycle) occurs in the stroma. ATP produced from the light-dependent reaction is used as a source of energy and NADPH as a reducing agent to form sugar from carbon dioxide. It consists of three phases: carbon fixation, reduction, and regeneration.

Fig. 5. The light-independent reaction or the Calvin cycle.


1. Carbon fixation ○ During this phase, carbon dioxide is attached to a five-carbon sugar

(ribulose bisphosphate, RuBP). The process is catalyzed by RuBisCo, an enzyme.

○ A new six-carbon molecule is formed. ○ The six-carbon molecule splits in half to form two molecules with three

carbons each, called 3-phosphoglycerate. 2. Reduction

○ ATP and NADPH is used to convert some of the 3-carbon molecules into a sugar precursor molecule (glyceraldehyde-3-phosphate, G3P).

○ Two sugar precursor molecules can combine to form glucose or the sugar precursor can regenerate the CO2 acceptor.

3. Regeneration of CO2 Acceptor

○ The remaining 3-carbon molecule is converted again to the five-carbon sugar RuBP using ATP so the cycle can continue.

In total, the Calvin Cycle spends three molecules of CO2 and nine molecules of ATP to make one molecule of glyceraldehyde 3-phosphate.

Key Points

● Photosynthesis is divided into two parts: the light-dependent reaction and

the light-independent reaction. ● The light-dependent reactions (or simply light reactions) occur in the

thylakoids. Light energy is converted to chemical energy in the form of ATP and NADPH.

● The light-independent reaction (also known as dark reaction or Calvin cycle) occurs in the stroma. Sugar is formed from carbon dioxide.


Web Links


● Watch this video to further understand the light-dependent and lindependent reactions in photosynthesis. User:Crash Course. 2012. “Photosynthesis: Crash Course Biology #8.’’ https://www.youtube.com/watch?v=sQK3Yr4Sc_k

● To know more about the Calvin cycle, you may also watch this video: Ted-ED. 2014. “Nature’s smallest factory: The Calvin cycle - Cathy Symington.’’

https://www.youtube.com/watch?v=0UzMaoaXKaM


A. Identify the following.

1. It is the site of the light-dependent reaction. 2. It is the site of the light-independent reaction. 3. These are responsible for absorbing sun’s light inside the chlorophyll. 4. This organelle absorbs and traps light from the sun. 5. It is the enzyme that catalyzes the carbon fixation process of the light

independent reaction. 6. This product is the result of combining two oxide ions. 7. This molecule is the source of energy in the light-independent reaction. 8. This is the 3-carbon molecule formed from the splitting of the 6-carbon

molecule during carbon fixation.


https://www.youtube.com/watch?v=sQK3Yr4Sc_k

https://www.youtube.com/watch?v=sQK3Yr4Sc_k



B. Identify the number of carbon atoms in the following steps of the Calvin cycle.

Challenge Yourself


1. Will the light-dependent reaction proceed without sunlight? How about the light-independent reaction if sunlight is present?

2. In the Calvin cycle, what determines the fate of G3P? 3. On hot, sunny days, leaves close their stomata to conserve water. Hence, it

limits access to carbon dioxide and builds up oxygen inside. Is photosynthesis still possible?

4. Can photosynthesis still take place without the presence of the photosystems? Why or why not?

5. How will the production of ATP be affected if hydrogen ions are not pumped across the thylakoid membrane during the light-dependent reaction?


Lesson 4.3: Aerobic Respiration

Objectives In this lesson, you should be able to:

● describe the process of cellular respiration in animals; and ● describe the process of aerobic respiration.

Cells harvest chemical energy through cellular respiration. It could be aerobic respiration if oxygen is present, or anaerobic respiration when oxygen is absent. Both provide interesting pathways that allow cells to obtain energy. How does respiration take place in the cells?

Warm-Up Where in the Cell? Study the picture below. Locate the different parts of the animal cell and give their functions.


Learn about It

For eukaryotes, cellular respiration (often referred to as aerobic respiration) occurs in the mitochondria. For prokaryotes, it happens at the cytoplasm or inner cell surfaces. In cellular respiration, glucose (C6H12O6) and oxygen are consumed to produce carbon dioxide, and water. The process produces ATP which is used by the cells as its energy currency. ATP is a readily usable form of energy for living things. The chemical reaction for respiration is written as

Cellular respiration is the principal mode of harvesting chemical energy and ATP. It is an example of a catabolic process. Cellular respiration has three stages namely glycolysis, citric acid cycle, and oxidative phosphorylation. Glycolysis Glycolysis literally means “splitting of glucose.” Glucose, a 6-carbon sugar molecule is broken down into two molecules of pyruvate, a 3-carbon molecule, to produce ATP. It takes place in the cytosol (a part of the cytoplasm) of the cell. Glycolysis consists of two phases: the energy investment phase and the energy harvest phase. In the energy investment phase, 2 ATP molecules are used to break down glucose. In the energy harvest phase, the further degradation of glucose forms 4 molecules of ATP, 2 NADH, and 2 pyruvate molecules. NAD+ (nicotinamide adenine dinucleotide) is a coenzyme and energy carrier. Its reduced form is NADH. Electrons are usually first transferred in NADH during electron transfer. NADH is formed when free electrons and H+ combines with NAD+.


Fig. 6. The fate of glucose in glycolysis.

In glycolysis, ATP is produced directly when an enzyme transfers a phosphate group from a phosphate-containing compound to ADP (adenosine diphosphate). The process is called substrate-level phosphorylation.

Fig. 7. Substrate-level phosphorylation.

Since there are 2 molecules of ATP used and 4 molecules ATP formed, there is a net of 2 ATP molecules formed in glycolysis. Take note that during glycolysis, oxygen is not required.


The net reaction is:

Glucose + 2 NAD+ + 4ADP → 2 pyruvate + 2 NADH + 2ATP (net)

Fig. 8. Net reaction for the conversion of glucose to pyruvate in glycolysis.

Citric Acid Cycle The citric acid cycle (also known as Krebs cycle, or tricarboxylic acid cycle) completely breaks down the glucose molecule. It takes place in the mitochondrial matrix of eukaryotes. For prokaryotes, it occurs in the cytoplasm. Before the citric acid cycle can begin, the two pyruvate molecules from glycolysis are first converted to acetyl-CoA, a 2-carbon compound in the outer membrane of the mitochondria.

1. Pyruvate is first converted to acetate. 2. Acetate combines with coenzyme A (CoA) to form acetyl-CoA.

The process links glycolysis and the citric acid cycle. In the process, a molecule of NADH and CO2 is also formed from one pyruvate molecule. Since a molecule of glucose produces two pyruvate molecules, the process will yield 2 acetyl-CoA, 2 NADH, and 2 CO2 molecules. Carbon dioxide is considered as a metabolic waste in the production of ATP. However, CO2 helps maintain blood pH by binding with water to form carbonic acid.


Fig. 9. The oxidation of pyruvate to acetyl-CoA.

The net reaction is:

2 Pyruvate + 2 CoA + 2 NAD+ → 2CO2 + 2acetyl-CoA + 2NADH

When pyruvate is converted to acetyl-CoA, it is the only time that the citric acid cycle takes place in the mitochondrial matrix. The following reaction takes place in the citric acid cycle:

1. Acetyl-CoA combines with oxaloacetate to form citrate. 2. Citrate changes the arrangement of atoms to form isocitrate. 3. Isocitrate is converted to α-ketoglutarate. The process yields CO2 and NADH. 4. α-ketoglutarate is converted to succinyl-CoA. Another CO2 and NADH is

produced. 5. Succinyl-CoA is converted to succinate. The process regenerates CoA and

yields ATP. 6. Succinate loses 2 H+ and 2 electrons to produce fumarate. FADH2 is also

produced.


7. Fumarate reacts with water to form malate. 8. Malate is converted to oxaloacetate. Another NADH is produced. 9. The cycle repeats when oxaloacetate reacts with acetyl-CoA.

Fig. 10. The citric acid cycle.

The citric acid cycle produces 2CO2, 3 NADH, 1 FADH2 and 1 ATP from one pyruvate molecule. Since two pyruvates are produced from 1 glucose molecule, 4 CO2, 6 NADH, 2 FADH2 and 2 ATP molecules are produced. FADH2 is the reduced form of FAD (flavin adenine dinucleotide) and is also an energy carrier. The net reaction is:

2 acetyl CoA + 6 NAD+ + 2 FADH + 2ADP → 4CO2 + 6 NADH + 2 FADH2 + 2 ATP


Overall, the conversion of 2 pyruvate molecules to acetyl CoA and the citric acid cycle produces 6 CO2, 2 ATP molecules, 2 FADH2, and 8 NADH. The formation of ATP is by substrate-level phosphorylation.

Oxidative Phosphorylation In oxidative phosphorylation, an electron transport chain is coupled with chemiosmosis to generate ATP. It occurs in the inner mitochondrial membrane of eukaryotes. For prokaryotes, it occurs in the cell membrane. This stage uses the NADH and FADH2 produced from the first two stages. Electrons are accepted by NADH and FADH2, which act as transporters, in a series of reactions before ATP is produced. 1. Electron Transport Chain

● NADH and FADH2 lose an electron in a stepwise manner ● The transfer of electron releases huge amount of energy. ● The energy produced from the series of reaction allows protein complexes

in the inner mitochondrial membrane to pump H ions from the mitochondrial matrix to the intermembrane space.

● The protein complexes included in the chain are NADH-Q reductase (labeled as I), ubiquinone (labeled as II), cytochrome reductase (labeled as III), cytochrome C, and cytochrome oxidase (labeled as IV). NADH enters the chain at the NADH-Q reductase complex. FADH2 enters the chain at the cytochrome reductase complex.

● It produces a proton (H+) gradient across the membrane which stores energy and drives chemiosmosis.


Fig. 11. Steps within the oxidative phosphorylation stage.

2. Chemiosmosis

● ATP production is driven by the backflow of H+ in the gradient across the mitochondrial membrane.

● ATP is produced from an enzyme called ATP synthase. The ATP synthase enzyme works like a reverse ion pump for H+.

● When the ATP synthase enzyme rotates, the diffusion of H+ to the inner mitochondrial matrix couples with the bonding of ADP and an inorganic phosphate to produce ATP.

● Electrons reach H+ and oxygen molecule to form water. This step is catalyzed by cytochrome oxidase. O2 is the final electron acceptor in cellular respiration.

Glycolysis produces 2 NADH while the citric acid cycle produces 8 NADH and 2 FADH2. In total, there are 10 NADH and 2 FADH2 that enters oxidative phosphorylation. Each NADH that enters oxidative phosphorylation produces 3 molecules of ATP while for each FADH2, it produces 2 molecules ATP. Thus, in oxidative phosphorylation alone, there are 30 molecules of ATP from NADH and 4 ATP molecules from FADH2 or a total of 34 ATPs. Besides the ATP produced, there are also 6 H2O.


In this stage, ATP produced by oxidative phosphorylation is due to the transfer of phosphate groups in reactions that involves the transfer of electrons. Compared to glycolysis and the citric acid cycle, more ATP is produced by oxidative phosphorylation alone. In the whole cellular respiration process, there are 2 molecules of ATP produced from glycolysis, 2 ATP molecules from the citric acid cycle, and 34 ATP molecules from oxidative phosphorylation. A maximum of 38 ATP molecules is obtained per glucose molecule. However, some energy is consumed during the shuttling of NADH from glycolysis into the mitochondria. The actual ATP yield is around 30 to 32 ATPs per glucose only.

Key Points

● Cellular respiration (which is often referred to as aerobic respiration) takes

place in the mitochondria. In cellular respiration, glucose (C6H12O6) and oxygen are consumed to produce carbon dioxide, water, and ATP.

● The three stages of cellular respiration are glycolysis, citric acid cycle, and oxidative phosphorylation.

● In glycolysis, glucose is broken down into two molecules of pyruvate. It occurs in the cytosol.

● The pyruvate molecule is first converted to acetyl-CoA before entering the citric acid cycle.

● In the citric acid cycle (also known as Krebs cycle, or tricarboxylic acid


cycle), glucose molecule is completely broken down. It takes place in the cytoplasm.

● In oxidative phosphorylation, NADH and FADH2 act as electron transporters to produce ATP. It occurs in the inner mitochondrial membrane.

● In the whole cellular respiration process, there are 2 ATP molecules produced from glycolysis, 2 ATP molecules from the citric acid cycle, and 34 ATP molecules from oxidative phosphorylation. A maximum of 38 ATP molecules is obtained per glucose molecule.

Web Links


● Watch this video to further understand the stages of cellular respiration: McGraw-Hill Animations. 2017. ‘Cellular Respiration Glycolysis, Krebs cycle, Electron Transport 3D Animation’ https://www.youtube.com/watch?v=7J4LXs-oDCU

● Do you want to play a game? Use the board game “MousetrapTM” to visualize cellular respiration. A journal article regarding the use of the game in class can be read here: Bentley, Meg & Connaughton, Victoria. (2017). A simple way for students to visualize cellular respiration: adapting the board game MousetrapTM to model complexity. CourseSource. 4. 10.24918/cs.2017.8.

● Do you love music? Listen to a riff of “Hate It or Love It" by 50 Cent, and "On to the Next One" by Jay Z. The song is titled “Oxidate It Or Love It," performed by Derrick Davis, a student and Tom McFadden, a biology instructor at Stanford. You may listen to the song here: User:Science with Tom. 2010. ‘Oxidate It Or Love It / Electron to the Next One.’ https://www.youtube.com/watch?v=VCpNk92uswY


https://www.youtube.com/watch?v=7J4LXs-oDCU

https://www.youtube.com/watch?v=7J4LXs-oDCU

https://www.researchgate.net/publication/317059259_A_simple_way_for_students_to_visualize_cellular_respiration_adapting_the_board_game_MousetrapTM_to_model_complexity



https://www.youtube.com/watch?v=VCpNk92uswY

https://www.youtube.com/watch?v=VCpNk92uswY


A. Arrange the following steps in cellular respiration.

1. Oxaloacetate reacts with acetyl CoA to form citrate. ____________

2. Pyruvate is converted to acetyl-CoA. ____________

3. Acetyl-CoA combines with oxaloacetate to form citrate. ____________

4. ATP is produced due to transfer of phosphate groups during electron transfer

____________

5. Glucose is split into two molecules of pyruvate. ____________

B. Complete the table below.

Glycolysis Pyruvate Oxidation Citric Acid Cycle Oxidative

Phosphorylation

Location

Net ATP Yield

Reactants

Products

Challenge Yourself


1. Why do you think cells always break down glucose, a 6-carbon sugar, to produce ATP? Why not a 5-carbon sugar?

2. In the electron transport chain, electrons are passed in a stepwise manner. Why is it not possible to pass the electrons in a single step reaction?


3. In the absence of available glucose, what happens to glycolysis and citric acid cycle?

4. Calculate the amount ATP, CO2, NADH, and FADH2 produced by four glucose molecules.

5. Why is the theoretical yield for ATP not equal to 38? Is the theoretical yield of 38 ATPs achievable?


Lesson 4.4: Anaerobic Respiration and Fermentation

Objectives In this lesson, you should be able to:

● describe the process of anaerobic respiration; and ● differentiate aerobic and anaerobic respiration.

Certain organisms can survive without oxygen. When oxygen is absent, it means that there are different products that will be formed during cellular respiration. What are the products produced by anaerobic respiration?

Warm-Up A Review of Aerobic Respiration Before you proceed with anaerobic respiration, you will have a review of aerobic respiration. Procedure: Find a pair. For every stage of cellular respiration, answer the following questions. Guide Questions:

1. What are the stages of cellular respiration?

2. What are the raw materials and the products for each stage in cellular respiration?

3. Where in the cell does this stage take place? 4. How are the raw materials converted to the end products? 5. How are raw materials consumed? How many end products are produced?

Share your answers with your partner in a clear and logical manner. Politely correct your partner if he or she makes a mistake.


Learn about It

Anaerobic respiration does not rely on the presence of oxygen to produce ATP. It occurs in some bacteria. Glucose still undergoes glycolysis, citric acid cycle, and oxidative phosphorylation. Compared to aerobic respiration, the final electron acceptors in anaerobic respiration are inorganic electron acceptors other than oxygen to generate ATP. These inorganic electron acceptors may include nitrates, sulfates, and carbonates. Anaerobic respiration produces less ATP compared to aerobic respiration. Fermentation Cells, in the absence of oxygen, are still able to produce ATP through fermentation. In fermentation, sugars such as glucose are partially degraded without oxygen. Among the three stages of cellular respiration, only glycolysis can produce ATP with or without oxygen. To produce ATP, glycolysis couples with fermentation. It starts with the consumption of pyruvate, which is the end-product for glycolysis. NADH, also another end-product during glycolysis, is recycled in fermentation. Fermentation is another example of a catabolic process. Alcohol Fermentation Alcohol fermentation occurs in bacteria and fungi such as yeast. In alcohol fermentation, pyruvate produced from glycolysis is converted into ethanol.

Fig. 12. Pyruvate conversion to ethanol formation.

1. Pyruvate is converted to acetaldehyde. CO2 is produced. 2. Acetaldehyde is reduced by NADH to NAD+ to form ethanol.


The end products are two ethanol and two carbon dioxide molecules for every glucose. Two ATP molecules are also produced in the reaction.

C6H12O6 → 2 ethanol + 2CO2 + 2ATP (Energy) The process is commonly used to produce beer, wine, and other alcoholic beverages. Yeast, a fungus that undergoes alcoholic fermentation, is used to raise dough in making bread due to the production of carbon dioxide.

Lactic Acid Fermentation Lactic acid fermentation is common to some bacteria, plants and most animals. In lactic acid fermentation, pyruvate is directly reduced by NADH to form lactate as a waste product.

Fig. 13. Pyruvate reduction to lactate formation.

The end products are two lactate molecules for every glucose. Two ATPs are also produced in the reaction.

C6H12O6 → 2 lactate + 2 ATP (Energy) No carbon dioxide is produced in the reaction. When there is a buildup of lactate in animals, fatigue and cramps occur. Dairy products such as yogurt and cheese are produced by lactic acid fermentation.


Key Points

● Anaerobic respiration does not rely on the presence of oxygen to produce

ATP. ● In alcohol fermentation, pyruvate produced from glycolysis is converted

into ethanol. ● In lactic acid fermentation, pyruvate is directly reduced by NADH to form

lactate. ● Photosynthesis and respiration are two complementary processes in the

biosphere.

Web Links


● Watch this video to further understand anaerobic respiration. User:chiswickscience. 2013. ‘Respiration 2 - Anaerobic - BBC Curriculum Bites.’ https://www.youtube.com/watch?v=UoEE9-wUdZ4

● Beer is produced by alcoholic fermentation. Learn more about how beer is produced. National Geographic. 2008. ‘The Perfect Beer.’

https://www.youtube.com/watch?v=Hnl8qGOhKf4


https://www.youtube.com/watch?v=UoEE9-wUdZ4

https://www.youtube.com/watch?v=UoEE9-wUdZ4




Complete the tables below.

Table 1. Comparison between aerobic respiration, anaerobic respiration, and fermentation.

Aerobic Respiration

Anaerobic Respiration

Fermentation

Site

Pathways involved

Final electron acceptor

Reactants

Products

ATP Yield

Oxygen requirement (Present/ Absent)

Table 2. Comparison of alcoholic and lactic acid fermentation.

Alcoholic Fermentation Lactic Acid Fermentation

Reactants

Products

ATP Yield

NADH Yield

CO2 Yield


Challenge Yourself


1. Will oxidative phosphorylation occur in anaerobic conditions? If it is possible, what are the possible final electron acceptors?

2. When doing strenuous activities, the muscle cannot obtain enough oxygen that it needs. It sometimes leads to muscle cramps. How is muscle cramps related to anaerobic respiration? Is breathing enough to lessen the pain of muscle cramps?

3. Can fermentation proceed without glycolysis? 4. How does fermentation produce alcoholic drinks? 5. Why do you think animals produce most of their energy through aerobic

respiration? And why is this favorable if you consider the gases in the atmosphere of the Earth?


Laboratory Activity

Activity 4.1

Blow Up a Balloon!

Objectives At the end of this laboratory activity, the students should be able to:

● observe cellular respiration in yeast; and ● identify the starting materials and end products of cellular respiration.

Materials and Equipment

● 3 plastic bottles ● 3 balloons ● funnel ● graduated cylinder ● beakers ● straw ● active dry yeast ● sugar ● water ● limewater ● warm water bath

Procedure

1. Prepare a sugar solution first by mixing 10 grams of sugar in 200 mL warm water. Dissolve the sugar completely. Label the solution as sugar solution.

2. Prepare three plastic bottles. Label the bottles as bottle A, B, and C. 3. On bottle A, mix 100 mL of the sugar solution with 5 grams of yeast. Cover

the bottle with a balloon. 4. On bottle B, mix 100 mL water and 5 grams of yeast. Cover the bottle again

with a balloon. 5. On bottle C, add 100 mL sugar solution only. Cover the bottle with a balloon. 6. Place the three bottles in a warm water bath. Maintain the temperature at

30 oC. 7. Observe the changes in the balloon.


8. After ten minutes, gases in each balloon will be pushed out of limewater placed in a test tube. Do this by connecting a straw from the balloon to the limewater.

Guide Questions

1. What are the reactants in each of the given setups? What are the products? 2. What is the purpose of using a warm water bath? 3. In which of the three balloons did you observe any changes in size? How did

this happen? 4. What do you think is the gas in the balloon?

Performance Task

Gardening at Home Goal: Your group’s goal is to promote

do-it-yourself home gardening in urban areas (specifically high rise buildings) to solve problems on food production by applying what you have learned about photosynthesis.

Role: You are a group of young professionals

promoting DIY home gardening. Audience: Your audience are members of the

homeowners’ association of a high rise condominium unit in Makati City.

Situation: The challenge is to convince your audience to have their own home

garden by planting small plants like herbs and spices. Product, Performance, and Purpose: You will create a brochure or a presentation on the benefits of having a home garden.


Standards and Criteria Your performance will be graded by the following rubric.

Criteria Below Expectations, 0% to 49%

Needs Improvement

50% to 74%

Successful Performance 75% to 99%

Exemplary Performance

100%

Content. Detailed facts are presented well. Content related to the task.

Details not presented. Content is not related to the task.

Details are presented but not organized. There are some content that are not related to task.

Details are presented in an organized manner.Content are related to the task.

Details are presented in an organized matter that can be easily understood. Content are related to the task. Additional supporting details are presented.

Communication Skills. Presentation was done in a clear and logical manner.

Presentation was not done.

Presentation was done but in a disorganized and illogical manner.

Presentation was done smoothly but the concepts are presented in such a way that should be rearranged for better understanding.

Presentation was done clearly. Concepts were presented in a logical manner and easily understandable by the audience.

Audiovisual materials. Materials presented in a creative way but not sacrificing the accuracy of facts.

No audiovisual materials used.

Audiovisual materials are used but are messy and disorganized. There are no attention to details.

Audiovisual materials are well organized and done neatly. Some attention are paid to detail.

Audiovisual materials are well organized and done creatively. There is also a great attention to details.

Integrating concepts in photosynthesis. Subject matter is integrated and properly used in presenting facts.

No concept on photosynthesis discussed in the task.

The concept of photosynthesis was mentioned but not integrated in the task.

The concept of photosynthesis was properly integrated in the task. Concepts were properly presented in relation to the task.

The concept of photosynthesis was integrated in an organized and logical way. Additional concepts about photosynthesis related to the task were presented.


Self Check

Do a self-check on how well you learned the lessons in this unit. Place a checkmark in the appropriate box.

Check I can…

explain the process of photosynthesis that occur in the leaves of plants and at the cellular level

enumerate and explain the different processes involved in cellular respiration

count the number of ATP produced in cellular respiration

explain the process of alcohol and lactic acid fermentation

Key Words

Aerobic respiration It is a form of respiration in the presence of oxygen.

Alcohol fermentation It is a process where pyruvate is converted into ethanol.

Anaerobic respiration It is a form of respiration in the absence of oxygen

ATP It is the abbreviation of adenosine triphosphate. It is the energy currency of the cell.

ATP synthase It is an enzyme used to produce ATP in chemiosmosis.

Autotrophs They are organisms that produce their own food.

Chlorophyll It is the green pigment in leaves of plants.

Chloroplasts It is a specialized organelle in the cell where photosynthesis takes place.

Citric acid cycle It is the second step of anaerobic respiration where pyruvate is broken down to produce carbon dioxide,


NADH and FADH2. It is also known as Kreb's cycle or tricarboxylic acid cycle.

Electron transport chain

It is a series of steps where NADH and FADH2 lose electrons in a stepwise manner.

Fermentation It is a process where glucose is partially degraded in the absence of oxygen.

Glucose It is a product of photosynthesis, together with oxygen.

G3P It is a sugar precursor molecules in the light-independent reaction. It is also known as glyceraldehyde-3-phosphate.

Glycolysis It is the first step of aerobic respiration where glucose splits into two pyruvate molecules.

Granum It is a term used for thylakoids stacked in a column (plural, grana).

Heterotrophs They are organisms that consume autotrophs. They cannot produce their own food.

Lactic acid fermentation

It is a process where pyruvate is converted to lactic acid.

Light-dependent reaction

The first step of photosynthesis that occurs in the thylakoids. Energy from the sun is used to produce ATP and NADPH

Light-independent reaction

The second step of photosynthesis in the stroma. It is also called the Calvin cycle.

Mitochondria An organelle that produces most of the cell’s ATP supply.

NADPH It is the abbreviation of nicotinamide adenine dinucleotide phosphate. It is used to reduce carbon dioxide to form glucose.

Oxidative phosphorylation

It is the third step of anaerobic respiration where ATP is produced through an electron transport chain coupled with chemiosmosis.

Photons These are light-carrying particles.

Photosynthesis It is the process of food-making in plants.

Photosystems These are regions in chlorophyll that are responsible for absorbing light.


Ribulose bisphosphate

A five-carbon sugar that attaches to carbon dioxide in the carbon fixation stage of the light-independent reaction of photosynthesis.

RuBisCo It is an enzyme used to catalyze the carbon fixation stage of the light-independent reaction of photosynthesis

Stomata These are tiny pores in the leaves of plants.

Substrate-level phosphorylation

It is a process where ATP is produced directly. In the process, an enzyme transfers a phosphate group from a phosphate-containing compound to ADP

Thylakoid It is the main photosynthetic unit of the chloroplast. It is also where the light-dependent reaction takes place.

Wrap Up

Relationship between Photosynthesis and Respiration

Summary of Light-Dependent and Light-Independent Reactions of Photosynthesis


Summary of Aerobic and Anaerobic Respiration

References

Berg, J. et. al. 2012. Biochemistry. 5th ed. New York: WH Freeman. BBC. "GCSE Bitesize: Photosynthesis and respiration." 2014. Accessed May 2017.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/green_world/photosynthesisrev1.shtml.

Nelson, D. and Cox, M. 2012. Lehninger Principles of Biochemistry. 6th ed. New York:

WH Freeman.


http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/green_world/photosynthesisrev1.shtml



Pickering, W.R. 2011. Complete Biology for Cambridge IGCSE. Oxford: Oxford University Press.

Reece, Jane, et. al. 2011. Campbell Biology. 10th ed. United States: Pearson Education.


unit 4 photosynthesis and respiration

Documents