Chapter 10

Question 1

Chloroplasts

Answer 1

Leaves are the major locations of photosynthesis
Chloroplasts are found mainly in cells of the mesophyll
Each mesophyll cell contains 30–40 chloroplasts
CO2 enters and O2 exits the leaf through microscopic pores called stomata

Question 2

Chloroplast anatomy

Answer 2

• Envelope of two membranes
• Stroma – dense fluid within chloroplasts
• Thylakoids - connected sacs which compose a third membrane system
• Grana – stackes of thylakoids
• Chlorophyll - pigment which gives leaves their green colour, found in thylakoid membranes

Question 3

splitting of Water

Answer 3

-chloroplasts split H2O, put e- of H into sugar molecules and release O as a by product

Question 4

What kind of reaction is Photosynthesis?

Answer 4

a redox reaction in which H2O is oxidized and Co2 is reduced

-endergonic process

Question 5

2 stages of Photosynthesis

Answer 5

-Light reactions (the photo part) and Calvin Cycle (the synthesis part)
-The Light Reactions (in the thylakoids)
Split H2O
Release O2
Reduce the electron acceptor NADP+ to NADPH
Generate ATP from ADP by photophosphorylation
-The Calvin Cycle (in the stroma) forms sugar from CO2, using ATP and NADPH
-Begins with carbon fixation, incorporating CO2 into organic molecules

Question 6

The nature of Sunlight

Answer 6

• Light is a form of electromagnetic energy, also called electromagnetic radiation
• Travels in rhythmic waves
• Wavelength is the distance between crestsof waves
• Wavelength determines the type of electromagnetic energy
• The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation
• Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see
• Light also behaves as though it consists of discrete particles, called photons

Question 7

Photosynthetic Pigments

Answer 7

• Pigments are substances that absorb visible light
• Different pigments absorb different wavelengths
• Wavelengths that are not absorbed are reflected or transmitted

Question 8

spectrophotometer

Answer 8

measures a pigments ability to absorb various wavelengths

Question 9

absorption spectrum

Answer 9

a graph plotting a pigment’s light absorption versus wavelength

Question 10

Absorption spectrum of chlorophyll a

Answer 10

suggests that violet-blue and red light work best for photosynthesis

Question 11

action spectrum

Answer 11

profiles the relative effectiveness of different wavelengths of radiation in driving a process

Question 12

Chlorophyll a

Answer 12

main photosynthetic pigment

Question 13

chlorophyll b,

Answer 13

broaden the spectrum for photosynthesis

Question 14

carotenoids

Answer 14

absorb excessive light that would damage chlorophyll

Question 15

excitation of Chlorophyll by light

Answer 15

When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable
When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence
If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat

Question 16

Chemiosmosis in chloroplasts

Answer 16

• chloroplasts transform light energy into the chemical energy of ATP
• In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma

Question 17

Chemiosmosis in mitochondria

Answer 17

• Mitochondria transfer chemical energy from food to ATP
• In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix

Question 18

Light Reactions

Answer 18

• Are carried out by moleculesin the thylakoid membranes
• Convert light energy to thechemical energy of ATPand NADPH
• Split H2O and release O2to the atmosphere

Question 19

Calvin Cycle Reactions

Answer 19

-Take place in the stroma
-Use ATP and NADPH to convertCO2 to sugar
Return ADP, inorganic phosphate,and NADP+ to the light reactions

Question 20

What Alternative mechanisms of carbon fixation have evolved in hot, arid climates?

Answer 20

Dehydration is a problem for plants
On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesis
The closing of stomata reduces access to CO2 and causes O2 to build up
These conditions favor a process called photorespiration

Question 21

Photorespiration

Answer 21

• O2 is added instead of CO2 in the Calvin cycle, producing a two-carbon compound
• Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar
• Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle
• In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle

Question 22

C4 plants

Answer 22

minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds

Question 23

two types of C4 plants

Answer 23

• Bundle-sheath cells are arranged in tightly packed sheaths around the veins of the leaf
• Mesophyll cells are loosely packed between the bundle sheath and the leaf surface

Question 24

Sugar production in C4 plants

Answer 24

1. The production of the four carbon precursors is catalyzed by the enzyme PEP carboxylase in the mesophyll cells
2. These four-carbon compounds are exported to bundle-sheath cells
3. Within the bundle-sheath cells, they release CO2 that is then used in the Calvin cycle

Question 25

CAM plants

Answer 25

• Some plants, including succulents, use crassulacean acid metabolism (CAM) tofix carbon
• CAM plants open their stomata at night, incorporating CO2 into organic acids
• Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle