Study Guide Template

Biology I · Honors Semester 1 · Room 214 · Period 3

Unit 04

Study Guide & Practice Set

Cell Energy Photosynthesis & Cellular Respiration

Teacher

Ms. R. Okafor

School

Lakeview High School

Unit dates

Nov 3 – Nov 21

Unit test

Fri, Nov 21

01

Start here

Unit Overview

Every cell needs a steady supply of usable energy. In this unit you will follow one idea from start to finish: energy from sunlight is stored in sugar, then released from sugar as ATP. Photosynthesis does the storing. Cellular respiration does the releasing. Learn how they mirror each other and the rest of the unit falls into place.

Learning objectives

By the unit test, you should be able to:

1. Explain why cells use ATP as their energy currency, and how ATP releases energy when it becomes ADP.
2. Write the balanced equations for photosynthesis and cellular respiration and show that one is the reverse of the other.
3. Describe where the light-dependent reactions and the Calvin cycle happen, and what each one makes.
4. Trace a glucose molecule through glycolysis, the Krebs cycle, and the electron transport chain, with the ATP made at each stage.
5. Compare aerobic respiration with lactic acid and alcoholic fermentation.
6. Design and interpret an experiment that measures the rate of photosynthesis.

Your 5-day study plan

MonDay 1

• Read pages 3–4 and learn the glossary
• Make flash cards for the 16 key terms

TueDay 2

• Study the photosynthesis summary (p. 5)
• Draw the chloroplast from memory and label it

WedDay 3

• Study the respiration stage table (p. 6)
• Rebuild the ATP tally without looking: 2 + 2 + 28

ThuDay 4

• Review the misconceptions (p. 7)
• Do Practice Part A under test timing (12 min)

FriDay 5

• Do Parts B and C, then mark with the key
• Bring any wrong answers to Thursday tutoring

16

key terms to know cold

2

equations to write from memory

~32

ATP per glucose, aerobic respiration

14

practice questions with a full key

How to use this guide

Work through the summaries with a pencil. Cover the right column of each table and try to recall it. Do the practice questions before you open the answer key on the last page. Extra help: Thursdays, 3:15–4:00 pm in Room 214, or email r.okafor@lakeview.example.com.

02

Vocabulary

Key Terms Glossary

ATP molecule

Adenosine triphosphate. The cell’s energy currency. Breaking the bond to the third phosphate releases energy and leaves ADP.

Autotroph organism

An organism that makes its own food from inorganic molecules, usually by photosynthesis. Plants, algae, and cyanobacteria.

Heterotroph organism

An organism that gets energy by eating other organisms. Animals, fungi, and most bacteria.

Chloroplast organelle

The organelle where photosynthesis happens. Contains stacks of thylakoids surrounded by fluid called the stroma.

Chlorophyll pigment

The green pigment in thylakoid membranes. It absorbs red and blue light and reflects green light.

Thylakoid structure

A flattened membrane sac inside the chloroplast. Site of the light-dependent reactions. A stack is a granum.

Stroma structure

The fluid around the thylakoids. Site of the Calvin cycle.

Calvin cycle process

Light-independent reactions that use ATP and NADPH to fix CO2 into the 3-carbon sugar G3P, which builds glucose.

NADPH / NADH carrier

Electron carriers. NADPH carries high-energy electrons in photosynthesis; NADH (and FADH2) carry them in respiration.

Mitochondrion organelle

Organelle of aerobic respiration. The Krebs cycle runs in the matrix; the electron transport chain sits in the folded inner membrane (cristae).

Glycolysis process

First stage of respiration, in the cytoplasm. Splits one glucose into two pyruvate. Net gain: 2 ATP and 2 NADH. Needs no oxygen.

Krebs cycle process

Also called the citric acid cycle. Breaks down acetyl-CoA in the matrix, releasing CO2 and loading NADH and FADH2.

Electron transport chain process

Proteins in the inner membrane pass electrons to oxygen and pump H+ ions. The flow of H+ back through ATP synthase makes most of the ATP.

Aerobic / Anaerobic adjective

Aerobic means the process needs oxygen. Anaerobic means it does not.

Fermentation process

An anaerobic pathway that recycles NADH back to NAD+ so glycolysis can continue. Makes lactic acid (muscles) or ethanol + CO2 (yeast).

Oxidation / Reduction reaction

Oxidation is the loss of electrons; reduction is the gain. In respiration glucose is oxidized and oxygen is reduced to water.

03

Concept summary

The Big Picture

Photosynthesis and cellular respiration are two halves of one cycle. The products of one are the reactants of the other. Energy flows through the cycle (in as light, out as heat), but matter is recycled.

Photosynthesis

6CO2 + 6H2O — light → C6H12O6 + 6O2

Cellular respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + ~32 ATP (+ heat)

Side-by-side comparison

Feature	Photosynthesis	Cellular respiration
Who does it	Autotrophs: plants, algae, some bacteria	Almost all living things, including plants
Location	Chloroplast (thylakoids, then stroma)	Cytoplasm, then mitochondrion (matrix, inner membrane)
Reactants	Carbon dioxide, water, light energy	Glucose, oxygen
Products	Glucose, oxygen	Carbon dioxide, water, ATP
Energy change	Light energy → chemical energy stored in glucose	Chemical energy in glucose → ATP (about 34% captured), rest lost as heat
Electron carrier	NADP+ → NADPH	NAD+ → NADH, FAD → FADH2
When	Only in the light	All the time, day and night

Table 1. Cover the two right columns and recite each row from memory.

ATP: why cells need a “currency”

Glucose holds a lot of energy, about 686 kcal per mole: too much to spend at once. Cells break it into small, spendable amounts stored in ATP. When an enzyme removes the last phosphate (ATP → ADP + Pi), about 7.3 kcal/mol is released to power work such as muscle contraction, active transport, and building proteins.

Memory aid

ATP is a charged battery; ADP is a flat one.

Respiration recharges ADP to ATP. Cells recycle ATP constantly; they do not store it.

Mirror trick

Write one equation, then flip it.

Photosynthesis read right-to-left is respiration. Swap “light” for “ATP.”

04

Concept summary

Photosynthesis in Two Stages

Photosynthesis is a two-step relay. The first stage captures light energy and stores it briefly in ATP and NADPH. The second stage spends that ATP and NADPH to build sugar from CO2.

Stage	Where	Inputs	Outputs	Key event
1 · Light-dependent reactions	Thylakoid membranes	Light, H2O, ADP, NADP+	O2 (released), ATP, NADPH	Chlorophyll absorbs light; water is split to replace lost electrons, releasing O2.
2 · Calvin cycle	Stroma	CO2, ATP, NADPH	G3P (→ glucose), ADP, NADP+	The enzyme rubisco fixes CO2 to a 5-carbon sugar (RuBP).

Table 2. ADP and NADP+ cycle back to the thylakoids to be recharged. That is why the two stages depend on each other.

Calvin cycle bookkeeping

To make…	Turns of the cycle	CO2 fixed	ATP used	NADPH used
1 G3P (3 carbons) exported	3	3	9	6
1 glucose (6 carbons) = 2 G3P	6	6	18	12

What limits the rate?

• Light intensity: more light, faster rate, until another factor runs short.
• CO2 concentration: the Calvin cycle needs a steady supply.
• Temperature: enzymes like rubisco work fastest near an optimum; very high heat slows them.
• Water: a dry plant closes its stomata, which also blocks CO2.

Memory aid

Thylakoid = Takes in light.
Stroma = Sugar is made.

And the oxygen you breathe came from water, not from CO2: “the O2 is from H2O.”

Why are leaves green?

Chlorophyll absorbs red (about 680 nm) and blue (about 430 nm) light strongly and reflects green (about 550 nm). The reflected green light is what reaches your eyes. In autumn, chlorophyll breaks down and the yellow and orange carotenoids that were always there become visible.

05

Concept summary

Cellular Respiration, Stage by Stage

Respiration takes glucose apart in controlled steps, so energy is captured a little at a time instead of being lost as one burst of heat.

Glycolysis

Cytoplasm

+2 ATP

→

Pyruvate oxidation

Mitochondrial matrix

+0 ATP

→

Krebs cycle

Mitochondrial matrix

+2 ATP

→

Electron transport chain

Inner membrane

+~28 ATP

Stage (per glucose)	Needs O2?	CO2	NADH	FADH2	ATP made
Glycolysis	No	0	2	0	2 (net)
Pyruvate oxidation	Yes (indirectly)	2	2	0	0
Krebs cycle (2 turns)	Yes (indirectly)	4	6	2	2
Electron transport chain	Yes: O2 is the final electron acceptor	0	−10 used	−2 used	~28
Total		6	10 made	2 made	~32

Table 3. How the ~28 is reached: each NADH gives about 2.5 ATP and each FADH2 about 1.5 ATP, so (10 × 2.5) + (2 × 1.5) = 25 + 3 = 28. Older textbooks round up to 36–38. Some cells get 30, because moving glycolysis NADH into the mitochondrion costs energy. Note the 6 CO2 match the 6 carbons of glucose.

When oxygen runs out: fermentation

	Lactic acid fermentation	Alcoholic fermentation
Who	Your muscle cells in a sprint; bacteria in yogurt	Yeast; some bacteria
Pyruvate becomes	Lactate (lactic acid)	Ethanol + CO2
ATP per glucose	2 (from glycolysis only)	2 (from glycolysis only)
Real-world use	Yogurt, sauerkraut, sourdough tang	Bread rising (CO2 bubbles)

Table 4. Fermentation makes no extra ATP. Its only job is to turn NADH back into NAD+ so glycolysis can keep going.

06

Lock it in

Memory Aids & Misconceptions

OIL RIG

Oxidation Is Loss, Reduction Is Gain (of electrons).

Glucose loses electrons (oxidized). Oxygen gains them and becomes water (reduced).

ATP tally

2 + 2 + 28 = 32

Glycolysis + Krebs + electron transport chain. The chain is the “big earner” because it cashes in all the NADH and FADH2.

Krebs cycle order

Citrate Is Krebs’ Starting Substrate For Making Oxaloacetate

Citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate. (Honors only.)

Common misconceptions

Misconception

“Plants do photosynthesis, animals do respiration.”

Correct idea

Plants do both. They photosynthesize in light and respire all the time, using the glucose they made.

Misconception

“A tree gets its mass from the soil.”

Correct idea

Most of a plant’s dry mass comes from CO2 in the air, fixed into sugar in the Calvin cycle. Soil supplies water and minerals only.

Misconception

“Respiration means breathing.”

Correct idea

Breathing moves air in and out of lungs. Cellular respiration is a chemical process inside every cell. Breathing supplies its O2 and removes its CO2.

Misconception

“Mitochondria make energy.”

Correct idea

Energy cannot be created. Mitochondria convert the chemical energy in glucose into ATP, and some is lost as heat.

Misconception

“The Calvin cycle happens in the dark.”

Correct idea

It does not need light directly, but it needs ATP and NADPH from the light reactions, so in most plants it runs during the day.

07

Check yourself

Practice Questions

Part A · Multiple choice 10 questions · 1 point each

1

Where in the chloroplast do the light-dependent reactions take place?

• AStroma
• BThylakoid membranes
• COuter membrane
• DMitochondrial matrix

2

The oxygen gas released during photosynthesis comes from which molecule?

• ACarbon dioxide
• BGlucose
• CWater
• DChlorophyll

3

Which stage of aerobic respiration produces the most ATP per glucose?

• AGlycolysis
• BPyruvate oxidation
• CKrebs cycle
• DElectron transport chain

4

What is the final electron acceptor at the end of the electron transport chain?

• ANAD+
• BOxygen
• CCarbon dioxide
• DPyruvate

5

Glycolysis takes place in the…

• Acytoplasm
• Bmitochondrial matrix
• Cinner mitochondrial membrane
• Dstroma

6

Which molecule leaves the Calvin cycle and is used to build glucose?

• ARuBP
• BNADPH
• CG3P
• DAcetyl-CoA

7

Fermentation lets glycolysis continue without oxygen because it…

• Amakes 34 extra ATP
• Bregenerates NAD+ from NADH
• Cproduces oxygen
• Druns the Krebs cycle faster

8

Which organisms carry out cellular respiration?

• AAnimals only
• BPlants only
• CBoth plants and animals
• DOnly organisms without chloroplasts

9

Chlorophyll looks green because it…

• Aabsorbs green light
• Breflects green light
• Cgives off green light
• Dabsorbs all colors

10

How many CO2 molecules are released when one glucose is fully broken down in aerobic respiration?

• A2
• B4
• C6
• D12

Part B · Short answer 3 questions · 3 points each

11

Explain how photosynthesis and cellular respiration form a cycle. Name the molecules that pass between them.3 pts

12

During a 200 m sprint, a runner’s leg muscles start to burn. Explain what is happening inside the muscle cells.3 pts

13

How many times more ATP does aerobic respiration make per glucose than fermentation? Show your work and give one reason for the difference.3 pts

Part C · Data interpretation 1 question · 6 points

14

A student placed a sprig of Elodea (pondweed) in water with dissolved baking soda and counted the oxygen bubbles it released per minute. A lamp was moved to five distances. A beaker of water between the lamp and the plant absorbed heat.

Lamp distance	Trial 1	Trial 2	Trial 3	Mean
10 cm	41	44	41	42
20 cm	30	32	31	31
30 cm	18	20	19	19
40 cm	11	9	10	10
50 cm	5	4	6	5

Table 5. Oxygen bubbles released per minute.

1. Name the independent and the dependent variable. 1 pt
2. Describe the trend in the data. 1 pt
3. Explain the trend using what you know about the light-dependent reactions. 2 pts
4. Calculate the percent decrease in the mean rate from 10 cm to 30 cm. 1 pt
5. Why did the student place a beaker of water between the lamp and the plant? 1 pt

08

Mark your work

Answer Key

Part A at a glance

Q1

B

Q2

C

Q3

D

Q4

B

Q5

A

Q6

C

Q7

B

Q8

C

Q9

B

Q10

C

1

Light is captured by chlorophyll in the thylakoid membranes. The stroma hosts the Calvin cycle.

2

Water is split in the light reactions to replace electrons lost by chlorophyll; its oxygen atoms form O2 . Oxygen from CO2 ends up in glucose.

3

The electron transport chain makes about 28 of the ~32 ATP, using the NADH and FADH2 from earlier stages.

4

Oxygen accepts the electrons and H+ ions, forming water. Without it, the chain stops.

5

Glycolysis happens in the cytoplasm, which is why even cells with no mitochondria can do it.

6

G3P (glyceraldehyde-3-phosphate). Two G3P combine to make one glucose. RuBP is recycled inside the cycle.

7

Fermentation regenerates NAD+ . Glycolysis needs NAD+ to accept electrons; without it, glycolysis would stop.

8

Both. Plants respire in their mitochondria day and night, just like animals.

9

Chlorophyll reflects green light and absorbs red and blue. We see the color that is reflected.

10

6: 2 from pyruvate oxidation and 4 from the Krebs cycle, one for each carbon in glucose.

Parts B and C

11

3 pts Model answer: Photosynthesis uses CO2 and H2O with light energy to make glucose and O2. Respiration uses that glucose and O2 to make ATP, releasing CO2 and H2O, which photosynthesis can use again.

1 pt: the products of one are the reactants of the other. 1 pt: names glucose and O2. 1 pt: names CO2 and H2O.

12

3 pts Model answer: The muscles use ATP faster than blood can deliver O2. The cells switch to lactic acid fermentation, which regenerates NAD+ so glycolysis can keep making 2 ATP per glucose. Lactate builds up and contributes to the burning feeling.

13

3 pts 32 ÷ 2 = 16 times more. Fermentation stops after glycolysis. Aerobic respiration continues through the Krebs cycle and the electron transport chain, which uses O2 to cash in the NADH and FADH2. (Accept 15–19× if the student used 30 or 36–38 ATP.)

14

6 pts a) Independent: lamp distance (light intensity). Dependent: bubbles of O2 per minute. b) As distance increases, the rate falls, from 42 to 5 bubbles/min. c) Farther lamp = less light reaching the chlorophyll, so fewer electrons are excited and less water is split, releasing less O2 (2 pts). d) (42 − 19) ÷ 42 × 100 = 54.8%, about 55%. e) To keep temperature constant, so light is the only variable that changes.

Score 19 or more out of 25? You are ready.

Under 19: reread pages 5–6, redo the questions you missed, and come to Thursday tutoring.

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