Chapter 8

Question 1

What is photosynthesis?

Answer 1

The process whereby light energy is captured by plant, algal, or photosynthetic bacterial cells and is used to synthesize organic molecules from CO2 and H2O (or H2S).

Question 2

What are the two stages of photosynthesis?

Answer 2

1. Light reactions

2. Calvin cycle

Question 3

Define light reactions:

Answer 3

The first of two stages in the process of photosynthesis. During the light reactions, photosystem II and photosystem I absorb light energy and produce ATP, NADPH, and O2.

Question 4

Define the Calvin cycle:

Answer 4

The second stage in the process of photosynthesis. During this cycle, ATP is used as a source of energy, and NADPH is used as a source of high-energy electrons, driving the synthesis of carbohydrates using CO2.

Question 5

What are heterotrophs?

Answer 5

Organisms that cannot produce their own organic molecules by using energy from inorganic sources or light; they must obtain one or more organic compounds from their environment.

Question 6

What is an autotroph?

Answer 6

An organism that has metabolic pathways that use energy from either inorganic molecules or light to make organic molecules.

Question 7

Who are heterotrophs?

Answer 7

Most species of bacteria and protists, as well as all species of fungi and animals

Question 8

What is a photoautotroph?

Answer 8

An organism that is a type of autotroph that uses the energy from light to make organic molecules from inorganic sources.

Question 9

What are the key components of the energy cycle in the biosphere?

Answer 9

Photosynthesis uses CO2, Light, and H2O to produce O2 and organic molecules. Organic molecules are broken down into CO2 and H2O via cellular respiration to supply energy in the form of ATP. O2 is reduced to H2O.

Question 10

What is chlorophyll?

Answer 10

A photosynthetic green pigment is found in the chloroplasts of plants, algae, and some bacteria.

Question 11

Define mesophyll:

Answer 11

The internal tissue of a plant leaf; the site of photosynthesis.

Question 12

What is a thylakoid membrane?

Answer 12

A membrane within the inner membrane of a chloroplast that forms many flattened, fluid-filled tubules that enclose a single, convoluted compartment. It contains chlorophyll and is the site where the light-dependent reactions of photosynthesis occur.

Question 13

Describe the area inside the inner membrane of a chloroplast?

Answer 13

The fluid-filled region between the thylakoid membrane and the inner membrane is called the stroma. The thylakoid membrane encompasses many thylakoids stacked on top of each other to form grana (singular, granum). Every thylakoid has an enclosed compartment called the thylakoid lumen.

Question 14

Where do light reactions take place?

Answer 14

At the thylakoid membrane.

Question 15

Where does the Calvin cycle occur?

Answer 15

In the stroma.

Question 16

What are the three chemical products of light reactions?

Answer 16

O2, NADPH, and ATP

Question 17

Define wavelength:

Answer 17

The distance from one peak to the next in a sound wave or light wave.

Question 18

What is the electromagnetic spectrum?

Answer 18

All possible wavelengths of electromagnetic radiation, from relatively short wavelengths (gamma rays) to much longer wavelengths (radio waves).

Question 19

What is a photon?

Answer 19

One of the discrete particles that make up light. A photon is massless and travels in a wavelike pattern. Each photon contains a specific amount of energy.

Question 20

What wavelengths carry more energy?

Answer 20

Shorter wavelength radiation carriers more energy per unit of time than longer wavelength radiation.

Question 21

What are the three things that can happen when light hits an object?

Answer 21

1. Light passes through the object.
2. The path of the light is redirected by the object.
3. Light is absorbed by the object.

Question 22

What does the term pigment mean?

Answer 22

A molecule that can absorb light energy.

Question 23

What does it mean when light energy is absorbed?

Answer 23

Light energy in the visible spectrum can be absorbed by an atom when it boosts an electron to a higher energy level.

Question 24

What is needed for an electron to be boosted to a higher energy level?

Answer 24

In order for an electron to absorb light energy, it must overcome the difference in energy between the orbital it is in and the orbital it is going to.

Question 25

What happens when an electron absorbs energy?

Answer 25

It is said to be in an excited state and usually in an unstable condition.

Question 26

What are the four things that can happen for an electron to become stable again?

Answer 26

1. Release energy in the form of heat.
2. Release energy in the form of light.
3. Resonance energy transfer: Transfer energy (not the electron itself) to adjacent pigment molecules during photosynthesis.
4. Electron can move to another molecule where it will be stable.

Question 27

What are carotenoids?

Answer 27

A type of photosynthetic or protective pigment found in plastids that imparts a color that ranges from yellow to orange to red.

Question 28

Describe light reactions in chloroplasts:

Answer 28

First, light energy is absorbed in the light-harvesting complex in Photosystem II. Excited electrons move down the electrochemical gradient towards Photosystem I. Water is oxidized, releasing O2 and H+ to the lumen. Electrons reach PS I via the ETC, releasing energy to maintain the electrochemical gradient in the process. At PS I, they are hit by additional light energy and become highly-energized electrons. Two of these highly-energized electrons and one H+ taken from the stroma are transferred to NADP+ to produce NADH. ATP synthesis occurs via photophosphorylation.

Question 29

What is photophosphorylation?

Answer 29

The process by which the light reactions of photosynthesis produce ATP.

Question 30

What are the three things that contribute to the creation of the H+ electrochemical gradient in chloroplasts?

Answer 30

1. Oxidation of H20 adds two H+ to the thylakoid lumen.
2. Movement of high-energy electrons across the ETC creates pumps H+ into the thylakoid lumen.
3. Formation of NADPH removes H+ from the stroma.

Question 31

Define linear electron flow:

Answer 31

In the light reactions of photosynthesis, the movement of electrons from PSII to PSI and ultimately to NADP+ to form NADPH.

Question 32

What is cyclic photophosphorylation or cyclic electron flow?

Answer 32

During photosynthesis, a pattern of electron flow in the thylakoid membrane that is cyclic and generates only ATP.