Unit 20: Photosynthesis

Question 1

What are autotrophs?

Answer 1

“Self-feeders”- Photosynthetic organisms that make their own food from ions and molecules.

Question 2

What are heterotrophs?

Answer 2

“Different-feeders”- Non-photosynthetic organisms. Must obtain sugars from other organisms.

Question 3

Photosynthesis converts _________ energy to ______ energy.

Answer 3

Photosynthesis converts electromagnetic energy to chemical energy.

Question 4

What are oxidation-reduction (redox) reactions?

Answer 4

This involves the transfer of electrons between molecules. These processes are important for cellular respiration and photosynthesis.

Question 5

What are the two parts of a redox reaction?

Answer 5

1. Oxidation
2. Reduction

Question 6

What is oxidation?

Answer 6

Loss of electrons (or gain of oxygen, loss of hydrogen)

Question 7

What is reduction?

Answer 7

Gain of electrons (or loss of oxygen, gain of hydrogen)

Question 8

What are the two linked sets of reactions in photosynthesis?

Answer 8

1. Light- capturing reactions
2. Calvin cycle reactions

Question 9

What are light-capturing reactions?

Answer 9

Photosystem II: Sunlight energy is used to split water molecules (H₂O), releasing oxygen gas (O₂). The electrons from water are energized by light, then passed through an electron transport chain, where their energy is used to produce ATP.
Photosystem I: The electrons are finally transferred to NADP⁺, forming NADPH.

Question 10

What are Calvin cycle reactions?

Answer 10

The Calvin Cycle produces sugar from CO₂. It uses ATP (for energy) and electrons carried by NADPH to reduce CO₂ (by adding electrons and hydrogen), forming a sugar.

Question 11

Where does photosynthesis occur?

Answer 11

Photosynthesis occurs in chloroplasts.

Question 12

What are thylakoids?

Answer 12

The interior of chloroplasts are filled with flattened, vesicle-like structures called thylakoids.

Question 13

What are grana?

Answer 13

Stacks of thylakoid discs.

Question 14

What are lumen?

Answer 14

The inside space within each thylakoid.

Question 15

What is the stroma?

Answer 15

The fluid-filled space surrounding the thylakoids.

Question 16

Thylakoid membranes contain large quantities of _________.

Answer 16

pigments

Question 17

Why do chlorophylls appear green?

Answer 17

Appear green because they have photosynthetic pigments that absorb blue (430-450 nm) and red (640-680 nm) wavelengths while reflecting green.

Question 18

Why do carotenoids appear yellow/orange?

Answer 18

Absorb blue and green light (400-550 nm). Appear yellow, orange, or red because they have photosynthetic pigments that reflect these wavelengths.

Question 19

Why do Anthocyanins appear Appear purple, red, or blue?

Answer 19

Don’t have photosynthetic pigments but protective pigments.

Question 20

What is the function of Chlorophylls?

Answer 20

Primary photosynthetic pigments that capture light energy

Question 21

In Chlorophyll, what is chlorophyll a versus chlorophyll b?

Answer 21

Chlorophyll a is the primary reaction center pigment. Chlorophyll b is an accessory pigment that works alongside chlorophyll a.

Question 22

What is the function of Carotenoids, anthocyanins, and xanthophylls as accessory pigments found in chloroplasts?

Answer 22

Absorb light and pass energy on to chlorophyl.

Question 23

What is the function of anthocyanins?

Answer 23

Absorb harmful UV radiation.

Question 24

What two things do both chlorophyll a and b have in common?

Answer 24

Both are similar in structure and have two fundamental parts:
1. Long isoprenoid “tail”
2. “Head” with ring structure and magnesium atom. Light is absorbed in the head.

Question 25

What two things happen when chlorophyll absorbs a photon?

Answer 25

1. Photon's energy is transferred to bonds in the chlorophyll's head region. 2. Electron becomes "excited"- higher energy state.

Question 26

What are three possible photons chlorophyll can absorb?

Answer 26

1. Red photons 2. Blue photons 3. Green photons

Question 27

What happens when chlorophyll absorbs red photons?

Answer 27

Red photons bump an electron up one energy level.

Question 28

What happens when chlorophyll absorbs blue photons?

Answer 28

Blue photons bump an electron up two energy levels.

Question 29

What happens when chlorophyll absorbs green photons?

Answer 29

Green photons are intermediate so are not absorbed.

Question 30

When pigments absorb ______ energy, electrons become excited and jump to higher ______ levels. When these electrons fall back to their _______ state, the energy can have several fates.

Answer 30

When pigments absorb light energy, electrons become excited and jump to higher energy levels. When these electrons fall back to their ground state, the energy can have several fates.

Question 31

What happens to absorbed energy when an excited electron falls back to ground state?

Answer 31

Absorbed energy is released as heat or as combination of head and light.

Question 32

What happens to fluorescence when an excited electron falls back to ground state?

Answer 32

Fluorescence occurs when electron emits light as it falls back to its ground state.

Question 33

What is resonance energy transfer?

Answer 33

When electron drops down to lower energy level and the energy is transferred to a nearby pigment.

Question 34

What is reduction/oxidation?

Answer 34

Electron is transferred to a new compound (redox reaction).

Question 35

What two photosystems does photosynthesis use to excite electrons and capture sunlight energy?

Answer 35

1. Photosystem II 2. Photosystem I

Question 36

What are photosystems?

Answer 36

They are large complexes of proteins and pigments that are optimized to harvest light.

Question 37

Which photosystem goes first? What is its functionality?

Answer 37

Photosystem II goes first. It absorbs sunlight and uses that energy to split water molecules into hydrogen, electrons, and oxygen.

Question 38

What happens to the electrons from photosystem II?

Answer 38

After that, the now low-energy electrons reach photosystem I.

Question 39

How does photosystem I re-energize the tired electrons?

Answer 39

Photosystem I re-energizes the tired electrons by absorbing more sunlight.

Question 40

In photosystem II, how is light energy converted into chemical energy in three steps?

Answer 40

1. Light absorption- Light strikes chlorophyll, exciting an electron to a higher energy level. 2. Electron excitation- Electron is passed to to pheophytin, a pigment molecule which accepts the excited electron. 3.Electron transport- Electron is replaced from the splitting of water which releases electrons, protons (H+), and oxygen (O2).

Question 41

When converting light energy into chemical energy, what happens once the pheophytin accepts the excited electron?

Answer 41

Once pheophytin accepts the electron, it passes it down the electron transport chain (ETC). Some energy is stored in ATP.

Question 42

When converting light energy into chemical energy, what happens when the high energy electron travels down ETC?

Answer 42

Proton gradient formation- The high-energy electron loses energy as it goes. Some of this released energy drives pumping of hydrogen ions (H+) form the stroma into the thylakoid interior, building a gradient.

Question 43

What happens after this hydrogen and ion gradient is built?

Answer 43

ATP is produced- As ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production in a process called chemiosmosis.

Question 44

What happens after ATP is produced? (2 steps)

Answer 44

1. NADPH production occurs- the electron arrives at photosystem I. Photosystem I absorbs light, re-exiting the electron. 2. The high-energy electron is then transferred to ferredoxin, which reduces NADP+ to NADPH.

Question 45

What happens after NADPH production?

Answer 45

The Calvin cycle- NADPH will travel to the Calvin cycle, where its electrons are used to build sugars from carbon dioxide.

Question 46

What by-products does the Calvin cycle result in?

Answer 46

Results in the production of NADPH, ATP, and oxygen gas as a by-product.

Question 47

What is chemiosmosis?

Answer 47

Chemiosmosis is the process by which ATP is produced in plants during photosynthesis, using the energy stored in a proton (H⁺) gradient.