Question 1

Where do most carbon atoms in a tree's wood come from?

Accepted Answer

CO₂ from the air. 

NOT the soil and NOT water. 

Light gives energy but no atoms.

Question 2

What are the 2 reactants and 2 products of photosynthesis?

Accepted Answer

In: CO₂ + H₂O. 

Out: sugar (C₆H₁₂O₆) + O₂. 

Light is the energy source.

Question 3

The O₂ a plant releases comes from which molecule?

Accepted Answer

Water. 

When water is split the leftover oxygen atoms pair up and leave as O₂.

Question 4

What 3 things does a plant do with the sugar it makes?

Accepted Answer

Growth / storage (starch) / its own cellular respiration

Question 5

Does photosynthesis always need a chloroplast?

Accepted Answer

No. 

Some bacteria photosynthesize with pigments in their membranes and have no chloroplasts.

Question 6

How does photosynthesis help an animal that never eats plants?

Accepted Answer

It makes the food at the bottom of every food web and the O₂ the animal breathes.

Question 7

Violet vs. red light: which has MORE energy per photon?

Accepted Answer

Violet. 

Shorter wavelength = higher frequency = more energy.

Question 8

If wavelength gets shorter what happens to frequency?

Accepted Answer

Frequency goes UP. 

They move opposite each other.

Question 9

On an absorption spectrum what do the x-axis and y-axis show?

Accepted Answer

x-axis = wavelength (color of light). 

y-axis = % of light absorbed.

Question 10

Which 2 colors does chlorophyll absorb best?

Accepted Answer

Blue and red (the two tall peaks on the absorption spectrum graph)

Question 11

Why do leaves look green?

Accepted Answer

Chlorophyll absorbs very little green so green bounces back to your eyes. 

The color you SEE is the color NOT absorbed.

Question 12

How do accessory pigments like carotenoids help?

Accepted Answer

They absorb colors chlorophyll misses so the leaf catches more total light energy.

Question 13

Why do leaves turn yellow and orange in fall?

Accepted Answer

Chlorophyll breaks down and the carotenoids that were there all along finally show.

Question 14

Where do the light reactions happen?

Accepted Answer

Thylakoid membranes 

(Room 1: the power plant)

Question 15

Where does the Calvin cycle happen?

Accepted Answer

Stroma 

(Room 2: the assembly line)

Question 16

What 2 molecules carry energy from the light reactions to the Calvin cycle?

Accepted Answer

ATP and NADPH 

(the two charged batteries)

Question 17

Which photosystem comes FIRST in the electron pathway?

Accepted Answer

Photosystem II. 

Cue: Two before One.

Question 18

Put in order: PS I re-excites / NADP⁺ forms NADPH / PS II excites / carriers build H⁺ gradient

Accepted Answer

1 PS II excites electrons → 2 carriers build H⁺ gradient → 3 PS I re-excites → 4 NADP⁺ forms NADPH. Water refills PS II.

Question 19

Which molecule replaces the electrons PS II loses?

Accepted Answer

Water (H₂O)

Question 20

What accepts electrons at the end to become NADPH?

Accepted Answer

NADP⁺

Question 21

What are the 3 products of the light reactions?

Accepted Answer

ATP + NADPH + O₂

Question 22

Where do H⁺ ions pile up during the light reactions?

Accepted Answer

Inside the thylakoid space (the lumen). 

The high side of the dam.

Question 23

Which direction do H⁺ ions flow through ATP synthase?

Accepted Answer

From the thylakoid space OUT to the stroma (high → low)

Question 24

What does the H⁺ flow through ATP synthase make?

Accepted Answer

ATP (ADP + phosphate → ATP). 

Like water spinning a turbine.

Question 25

What happens if the thylakoid membrane leaks H⁺?

Accepted Answer

No gradient → little ATP → Calvin cycle slows → less sugar

Question 26

What is the different job of ATP vs. NADPH?

Accepted Answer

ATP = energy. NADPH = electrons (reducing power) to build sugar.

Question 27

Could extra ATP fully replace missing NADPH?

Accepted Answer

No. 

ATP has energy but no electrons. 

The Calvin cycle needs NADPH's electrons to reduce carbon.

Question 28

What does rubisco do?

Accepted Answer

Attaches CO₂ to RuBP. This is carbon fixation (step 1 of the Calvin cycle).

Question 29

CO₂ (1 C) + RuBP (5 C) makes what?

Accepted Answer

An unstable 6-carbon molecule that splits into 2 molecules of 3-PGA (3 C each)

Question 30

Name the 3 phases of the Calvin cycle in order

Accepted Answer

Fixation → Reduction → Regeneration. (Dr. Suarez's diagram numbers 4 steps because 2 G3P exit at Step 3.)

Question 31

In 6 turns how many G3P form and how many leave?

Accepted Answer

12 G3P form. Only 2 leave (to make glucose / fructose / starch). 10 stay to rebuild 6 RuBP.

Question 32

Why can't the plant export every G3P?

Accepted Answer

It must use 10 G3P to rebuild 6 RuBP or the cycle stops.

Question 33

How many ATP and NADPH does 6 turns of the Calvin cycle use?

Accepted Answer

18 ATP (12 + 6) and 12 NADPH

Question 34

6 CO₂ add how many new carbon atoms and where do they end up?

Accepted Answer

6 carbons. They leave as 2 G3P (3 C each = 6 C).

Question 35

What 2 things pass through open stomata?

Accepted Answer

CO₂ comes IN and water vapor escapes OUT

Question 36

Why does a sunny leaf make LESS sugar in a drought?

Accepted Answer

Stomata close to save water → CO₂ runs low → less carbon fixed and more photorespiration

Question 37

What is photorespiration?

Accepted Answer

A pathway that starts when rubisco reacts with O₂ instead of CO₂. It reduces net carbon gain.

Question 38

What condition makes photorespiration more likely?

Accepted Answer

Low CO₂ relative to O₂ (for example when stomata close to save water)

Question 39

Can a green leaf capture lots of light but still fix carbon poorly?

Accepted Answer

Yes. If CO₂ is low rubisco reacts with O₂ more often. Light is not the limit; CO₂ is.

Question 40

What is the first stable product in a C₃ plant?

Accepted Answer

A 3-carbon molecule (3-PGA)

Question 41

C₄ plants separate the steps in ___. CAM plants separate them in ___.

Accepted Answer

C₄ = SPACE (different cells). CAM = TIME (night vs. day).

Question 42

In C₄ plants which cells run the Calvin cycle?

Accepted Answer

Bundle-sheath cells. Mesophyll cells first fix CO₂ into a 4-carbon compound (oxaloacetate).

Question 43

Why does a cactus lose less water in the daytime?

Accepted Answer

CAM: stomata open only at night to take in CO₂. In the day the stomata stay shut.

Question 44

Do C₄ and CAM plants still use the Calvin cycle?

Accepted Answer

Yes. All three types (C₃ C₄ CAM) use it.

Question 45

Give one example each: C₃ / C₄ / CAM

Accepted Answer

C₃ = most plants (wheat). C₄ = corn. CAM = cactus (Dr. Suarez's example).

Question 46

Do plants shut down at night?

Accepted Answer

No. Respiration keeps going. Only the light-driven reactions stop.

Question 47

Why is 'the Calvin cycle runs only at night' wrong?

Accepted Answer

It needs ATP and NADPH from the light reactions so it runs during the day.

Question 48

What happens to sugar production when light stops?

Accepted Answer

Light reactions stop → no new ATP or NADPH → Calvin cycle stops soon after

Question 49

Do plants carry out cellular respiration only at night?

Accepted Answer

No. Plant cells respire day AND night.

Question 50

Lab: plants in light vs. dark with an indicator. What does a no-plant control show?

Accepted Answer

That any color change is caused by the plant and not by the solution itself

Question 51

Lab: what result supports net CO₂ uptake in the light?

Accepted Answer

The indicator in the light tube shows CO₂ going DOWN compared to the dark tube and the control.

Question 52

Why might a crop improvement that works in the lab fail in a real field?

Accepted Answer

Field conditions change: heat / drought / light / pests / soil. The lab controls these.

Question 53

Memory trick: which part of the chloroplast CHARGES the batteries and which SPENDS them?

Accepted Answer

Thylakoid charges them (makes ATP + NADPH). Stroma spends them (Calvin cycle builds G3P).

Question 54

Memory trick: CO₂ + RuBP carbon math?

Accepted Answer

1 C + 5 C = 6 C → splits in half → two 3-PGA (3 C + 3 C)

Question 55

Memory trick: the Calvin cycle numbers 12 / 2 / 10?

Accepted Answer

Make 12 G3P → 2 leave → 10 recycle. Check: 10 × 3 C = 30 C = 6 RuBP × 5 C.

Question 56

Memory trick: what does each ingredient give the sugar?

Accepted Answer

CO₂ gives the Carbon. 

Water gives the electrons (and its O becomes O₂). 

Light gives the Energy.

Biology 101 Honors

Unit 3 Photosynthesis

Question	Answer
Where do most carbon atoms in a tree's wood come from?	CO₂ from the air. NOT the soil and NOT water. Light gives energy but no atoms.
What are the 2 reactants and 2 products of photosynthesis?	In: CO₂ + H₂O. Out: sugar (C₆H₁₂O₆) + O₂. Light is the energy source.
The O₂ a plant releases comes from which molecule?	Water. When water is split the leftover oxygen atoms pair up and leave as O₂.
Is light matter or energy in the photosynthesis recipe?
What 3 things does a plant do with the sugar it makes?	Growth / storage (starch) / its own cellular respiration
Does photosynthesis always need a chloroplast?	No. Some bacteria photosynthesize with pigments in their membranes and have no chloroplasts.
How does photosynthesis help an animal that never eats plants?	It makes the food at the bottom of every food web and the O₂ the animal breathes.
Violet vs. red light: which has MORE energy per photon?	Violet. Shorter wavelength = higher frequency = more energy.
If wavelength gets shorter what happens to frequency?	Frequency goes UP. They move opposite each other.
On an absorption spectrum what do the x-axis and y-axis show?	x-axis = wavelength (color of light). y-axis = % of light absorbed.
Which 2 colors does chlorophyll absorb best?	Blue and red (the two tall peaks on the absorption spectrum graph)
Why do leaves look green?	Chlorophyll absorbs very little green so green bounces back to your eyes. The color you SEE is the color NOT absorbed.
How do accessory pigments like carotenoids help?	They absorb colors chlorophyll misses so the leaf catches more total light energy.
Why do leaves turn yellow and orange in fall?	Chlorophyll breaks down and the carotenoids that were there all along finally show.
Where do the light reactions happen?	Thylakoid membranes (Room 1: the power plant)
Where does the Calvin cycle happen?	Stroma (Room 2: the assembly line)
What 2 molecules carry energy from the light reactions to the Calvin cycle?	ATP and NADPH (the two charged batteries)
Which photosystem comes FIRST in the electron pathway?	Photosystem II. Cue: Two before One.
Put in order: PS I re-excites / NADP⁺ forms NADPH / PS II excites / carriers build H⁺ gradient	1 PS II excites electrons → 2 carriers build H⁺ gradient → 3 PS I re-excites → 4 NADP⁺ forms NADPH. Water refills PS II.
Which molecule replaces the electrons PS II loses?	Water (H₂O)
What accepts electrons at the end to become NADPH?	NADP⁺
What are the 3 products of the light reactions?	ATP + NADPH + O₂
Where do H⁺ ions pile up during the light reactions?	Inside the thylakoid space (the lumen). The high side of the dam.
Which direction do H⁺ ions flow through ATP synthase?	From the thylakoid space OUT to the stroma (high → low)
What does the H⁺ flow through ATP synthase make?	ATP (ADP + phosphate → ATP). Like water spinning a turbine.
What happens if the thylakoid membrane leaks H⁺?	No gradient → little ATP → Calvin cycle slows → less sugar
What is the different job of ATP vs. NADPH?	ATP = energy. NADPH = electrons (reducing power) to build sugar.
Could extra ATP fully replace missing NADPH?	No. ATP has energy but no electrons. The Calvin cycle needs NADPH's electrons to reduce carbon.
What does rubisco do?	Attaches CO₂ to RuBP. This is carbon fixation (step 1 of the Calvin cycle).
CO₂ (1 C) + RuBP (5 C) makes what?	An unstable 6-carbon molecule that splits into 2 molecules of 3-PGA (3 C each)
Name the 3 phases of the Calvin cycle in order	Fixation → Reduction → Regeneration. (Dr. Suarez's diagram numbers 4 steps because 2 G3P exit at Step 3.)
In 6 turns how many G3P form and how many leave?	12 G3P form. Only 2 leave (to make glucose / fructose / starch). 10 stay to rebuild 6 RuBP.
Why can't the plant export every G3P?	It must use 10 G3P to rebuild 6 RuBP or the cycle stops.
How many ATP and NADPH does 6 turns of the Calvin cycle use?	18 ATP (12 + 6) and 12 NADPH
6 CO₂ add how many new carbon atoms and where do they end up?	6 carbons. They leave as 2 G3P (3 C each = 6 C).
What 2 things pass through open stomata?	CO₂ comes IN and water vapor escapes OUT
Why does a sunny leaf make LESS sugar in a drought?	Stomata close to save water → CO₂ runs low → less carbon fixed and more photorespiration
What is photorespiration?	A pathway that starts when rubisco reacts with O₂ instead of CO₂. It reduces net carbon gain.
What condition makes photorespiration more likely?	Low CO₂ relative to O₂ (for example when stomata close to save water)
Can a green leaf capture lots of light but still fix carbon poorly?	Yes. If CO₂ is low rubisco reacts with O₂ more often. Light is not the limit; CO₂ is.
What is the first stable product in a C₃ plant?	A 3-carbon molecule (3-PGA)
C₄ plants separate the steps in ___. CAM plants separate them in ___.	C₄ = SPACE (different cells). CAM = TIME (night vs. day).
In C₄ plants which cells run the Calvin cycle?	Bundle-sheath cells. Mesophyll cells first fix CO₂ into a 4-carbon compound (oxaloacetate).
Why does a cactus lose less water in the daytime?	CAM: stomata open only at night to take in CO₂. In the day the stomata stay shut.
Do C₄ and CAM plants still use the Calvin cycle?	Yes. All three types (C₃ C₄ CAM) use it.
Give one example each: C₃ / C₄ / CAM	C₃ = most plants (wheat). C₄ = corn. CAM = cactus (Dr. Suarez's example).
Do plants shut down at night?	No. Respiration keeps going. Only the light-driven reactions stop.
Why is 'the Calvin cycle runs only at night' wrong?	It needs ATP and NADPH from the light reactions so it runs during the day.
What happens to sugar production when light stops?	Light reactions stop → no new ATP or NADPH → Calvin cycle stops soon after
Do plants carry out cellular respiration only at night?	No. Plant cells respire day AND night.
Lab: plants in light vs. dark with an indicator. What does a no-plant control show?	That any color change is caused by the plant and not by the solution itself
Lab: what result supports net CO₂ uptake in the light?	The indicator in the light tube shows CO₂ going DOWN compared to the dark tube and the control.
Why might a crop improvement that works in the lab fail in a real field?	Field conditions change: heat / drought / light / pests / soil. The lab controls these.
Memory trick: which part of the chloroplast CHARGES the batteries and which SPENDS them?	Thylakoid charges them (makes ATP + NADPH). Stroma spends them (Calvin cycle builds G3P).
Memory trick: CO₂ + RuBP carbon math?	1 C + 5 C = 6 C → splits in half → two 3-PGA (3 C + 3 C)
Memory trick: the Calvin cycle numbers 12 / 2 / 10?	Make 12 G3P → 2 leave → 10 recycle. Check: 10 × 3 C = 30 C = 6 RuBP × 5 C.
Memory trick: what does each ingredient give the sugar?	CO₂ gives the Carbon. Water gives the electrons (and its O becomes O₂). Light gives the Energy.

"Know" box contains:
Time elapsed:
Retries: