Chapter 10 - Photosynthesis

Question 1

Autotrophs

Answer 1

Self-feeders

Sustain themselves without eating anything derived from other living beings

Produce organic molecules from CO2 and other inorganic raw materials from the environment (producers)

Photoautotrophs - use light to make food

Question 2

How does an organism acquire the organic compounds it uses for energy?

Answer 2

Either by creating its own food (being an autotroph), or consuming it (heterotroph)

Photosynthesis is the foundation of this process

Question 3

Heterotrophs

Answer 3

Biosphere’s consumers because they consume compounds produced by other organisms

Decomposers (bacteria) that feed on carcasses and waste, are also heterotrophs

Depend on Photoautotrophs for both food and oxygen

Question 4

Where does most photosynthesis occur?

Answer 4

The leaves of a plant , more specifically he Mesophyll - which occurs mainly in the chloroplasts

30-40 chloroplasts per Mesophyll cell

Question 5

Mesophyll

Answer 5

The tissue in the interior of the leaf where most chloroplasts are found

30–40 chloroplasts per Mesophyll cell

Question 6

Stomata

Answer 6

Pores that allows carbon dioxide in and oxygen out.

Also allows water to come out

Question 7

Stroma

Answer 7

An envelope with two membranes surrounding a dense fluid of the chloroplasts

Question 8

Thylakoids

Answer 8

Third membrane system that includes sacs which segregates the Stroma from the thylakoid space inside the sacs

Question 9

Granum

Answer 9

Stacked thylakoid stacks in columns

Question 10

Chlorophyll

Answer 10

Green pigment that gives leaves their color inside thylakoid membrane of the chloroplast

Question 11

What happens when a plant is exposed to light?

Answer 11

The green parts of the plant produce organic compounds and oxygen from carbon dioxide and water

Question 12

Photosynthesis chemical equation

Answer 12

6CO2 + 12 H2O + light energy —-> C6H12O6 + 6 O2 + 6H2O

The reverse equation of cellular respiration

Question 13

Where does O2 come from in photosynthesis?

Answer 13

H2O; not carbon dioxide like most people think

The chloroplast splits water into hydrogen and oxygen

They incorporate the electrons of hydrogen into sugar molecules and then release oxygen as a byproduct

Question 14

Photosynthesis

Answer 14

Chloroplasts capture light energy and converts it to chemical energy that is stored in sugar and other molecules

It’s a redox reaction in which H2O is oxidized (loses an electron) to become 6O2 and CO2 is reduced (gains an electron) to become C6H12O6

It’s endergonic because it uses light to aid the process.

Question 15

Explain van niel’s discovery about photosynthesis

Answer 15

He studied photosynthesis in bacteria. They make their carbohydrate from CO2, but don’t release O2.

Concluded that co2 isn’t split to make carbon and oxygen; it split its hydrogen sulfide instead. He reasoned that plants are more likely to split their h2o and use the hydrogen electrons releasing O2 as a byproduct

Question 16

Photosynthesis is reverse of cellular respiration

Answer 16

It reverses the electron flow.

Water is split and electrons are transferred along with hydrogen ions from water to co2, reducing it to sugar.

It’s endergonic because the electrons increase in potential energy as they move from water to sugar

Light provides this energy boost.

Question 17

What are the two cycles of photosynthesis

Answer 17

Light reactions (photo part)

Calvin cycle (synthesis part)

Question 18

Light reactions

Answer 18

Covert solar energy to chemical energy

Water is split providing a source of electrons and protons (H+) ions giving off O2 as a byproduct

Light absorbed by chlorophyll drives a transfer of electrons and hydrogen ions from water to NADP+ where they’re temporarily stored

Light uses solar energy to NADP+ to NADPH by adding a pair of electrons along with H+

The light reactions also generate ATP using chemiosmosis to power the additional phosphate group to ADP using phosphophorylation

Question 19

Phosphorylation

Answer 19

Using chemiosmosis to add a phosphate to ADP

Question 20

Which two compounds are converted to chemical energy in the first stage of photosynthesis?

Answer 20

NADPH and ATP

Question 21

NADPH

Answer 21

A source of electrons that reduce power that can be passed along to an electron acceptor

Question 22

Calvin cycle

Answer 22

Carbon fixation

Then reduces the fixed carbon to carbohydrate by the addition of electrons (done via NADPH)

Uses ATP convert CO2 to carbohydrate which is generated by light reactions

Referred to as dark reactions, or light independent reactions because they don’t require light directly.

Question 23

How is light used to covert solar energy into chemical energy?

Answer 23

Because chloroplasts are solar powered chemical factories…

Use thylakoids to transform lights energy into chemical energy of ATP and NADPH

Question 24

Light

Answer 24

A form of electromagnetic energy/radiation

Occurs in rhythmic waves

Question 25

Wavelength

Answer 25

Involves the distance between crests of the waves It determines the type of electromagnetic energy

Question 26

Electromagnetic spectrum

Answer 26

The entire range of electromagnetic energy or radiation

Question 27

Visible light

Answer 27

Involves all the wavelengths we can physically see Includes light waves for photosynthesis This is how we see color 380 nm - 750 nm

Question 28

Photons

Answer 28

Lights ability to function as particles as well. Particles of light

Question 29

Photosynthetic pigments

Answer 29

Pigments that Absorb light Different pigments absorb different wavelengths Wavelengths that are not absorbed are transmitted or reflected Leaves appear green because chlorophyll reflects/transmits green light

Question 30

Spectrophotometer

Answer 30

Measures a pigment's ability to absorb various wavelengths It sends light through the pigments and measures the fraction of light transmitted at each wavelength

Question 31

Absorption spectrum

Answer 31

A graph that documents pigment's light absorption versus wavelength Chlorophyll a which is violet-blue and red work best for photosynthesis 400-500 nm?

Question 32

Engelmann experiments

Answer 32

Used aerobic algae to test which wavelengths were the most suitable for photosynthesis The wavelengths that were suitable to photosynthesis caused the algae to expel excess O2 and then the aerobic bacteria would congregate around it.

Question 33

What is the main pigment of photosynthesis?

Answer 33

Chlorophyll a

Question 34

What are accessory pigments?

Answer 34

Chlorophyll b and carotenoids

Question 35

Carotenoids

Answer 35

They are responsible for photoprotection. They absorb excess light that would damage chlorophyll

Question 36

What happens when light hits chlorophyll?

Answer 36

When a pigment absorbs light, its electrons get excited and jump from one shell to one that's unstable. When the electrons fall back to their ground state, they release photons called fluorescence It gives off light and heat.

Question 37

Photosystem

Answer 37

Consists of a reaction center complex (a type of protein complex) surrounded by light harvesting complexes

Question 38

Light harvesting complex

Answer 38

Pigment molecules bound to proteins Transfer the energy of photons to the reaction center

Question 39

Primary electron acceptor

Answer 39

Exists in the reaction center and accepts excited electrons and is reduced as a result

Question 40

What are the two types of photosystems in the thylakoid membrane?

Answer 40

Photosystems 2 is the first and its chlorophyll best absorbs wavelengths that are 680 nm long Its reaction center is called P680 Photosystems 1 is best at absorbing wavelengths that are 700 nm long and its reaction center is called P700

Question 41

What are the two possible pathways during the light systems reaction?

Answer 41

Cyclical and linear Linear electron flow is the primary pathway and it involves both photosystems creates both ATP and NADPH using light energy

Question 42

What are the 8 steps in linear electron flow?

Answer 42

1. Photon hits the pigment and the energy is passed from pigment molecules until it excites P680 2. An excited electron from P680 is transferred via the primary electron transport (P680+) 3. H2O is split by enzymes and the electrons are transferred from the hydrogen atoms to P680+ thus reducing it to P680 (O2 is released as a byproduct) 4. Each electron "falls" down an electron transport chain to from the primary electron acceptor of PS 2 to PS 1 5. Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane (diffusion of H+ across the membrane drives ATP synthesis) 6. In PS 1 transferred light energy excites P700 which loses an electron (P700+ accepts an electron passed down from PS 2 through the transport chain) 7. Each electron falls down the chain from the primary electron acceptor in PS1 to ferredoxin (fd) 8. The electrons are then transferred to NADP+ and reduced to NADPH NADPH is then available for the Calvin cycle This also removed H+ from the Stroma

Question 43

Cyclic electron flow

Answer 43

Electrons cycle back from Fd to PS1 reaction center Uses only PS 1 and produces ATP, but no NADPH Don't release O2 Ie purple bacteria which have PS1 but not PS2 Evolved before linear flow and may protect the plant from light damage

Question 44

Chemiosmosis in chloroplasts vs mitochondria

Answer 44

Both generate ATP via chemiosmosis Mitochondria use food, chloroplasts use light Mitochondria pump protons into the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix In chloroplasts protons are pumped into the thylakoid space and they generate ATP as they diffuse back into the Stroma

Question 45

Calvin cycle

Answer 45

Similar to the citric acid cycle because it regenerates its starting material after molecules enter and leave the molecule It builds sugar from smaller molecules using ATP and reducing the power of electrons via NADPH Carbon enters as CO2 and releases as glyceralhyde three phosphate G3P (has to go through Calvin cycle three times for this to occur

Question 46

Three Phases of the Calvin Cycle

Answer 46

1. Carbon fixation (catalyze do by the protein rubisco) 2. Reduction 3. Regeneration of CO2 acceptor by RuBP

Question 47

Photosynthesis in hot climates

Answer 47

Plants close stomatas on hot days, which keeps H20 in, but also limits photosynthesis Closed stomatas reduces access to CO2 and causes a buildup of O2

Question 48

Photorespiration

Answer 48

rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound consumes O2 and organic fuel and releases CO2 without producing ATP or sugar 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 49

C3 plants

Answer 49

most plants | initial fixation of CO2, via rubisco, forms a three-carbon compound 3-phosphoglycerate

Question 50

C4 plants

Answer 50

minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds two distinct types of cells in the leaves of C4 plants: Bundle-sheath cells mesophyll cells

Question 51

Bundle-sheath cells

Answer 51

arranged in tightly packed | sheaths around the veins of the leaf

Question 52

mesophyll cells

Answer 52

loosely packed between the | bundle sheath and the leaf surface

Question 53

Three steps for Sugar production in C4 plants

Answer 53

1. The production of the four carbon precursors is catalyzed by the enzyme PEP carboxylase in the mesophyll cells PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low 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 54

crassulacean acid metabolism (CAM)

Answer 54

what succulent plants use to fix carbon 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

Question 55

LIGHT REACTIONS

Answer 55

``` • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere ```

Question 56

Calvin cycle

Answer 56

``` Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions ```