Chapter 7 - Photosynthesis

Question 1

What is the general chemical equation for photosynthesis?

Answer 1

6 CO2 + 6 H2O ——> C6H12O6 + 6O2

Question 2

How are photo-autotrophs and heterotrophs are related thru glucose, O2, H2O and CO2?
Draw a diagram of this. showing

Answer 2

Photo-autotrophs use sunlight, H2O and CO2 to make glucose and O2. Heterotrophs consume glucose and O2 and produce H2O and CO2.
See chapter 7 lecture notes, page 1

Question 3

In cellular respiration and photosynthesis which products are reduced? Which are oxidized?

Answer 3

CR: glucose is oxidized to CO2; oxygen is reduced to water
P: CO2 is reduced to glucose; water is oxidized to oxygen

Question 4

What are the: outer membrane/inner membrane, thylakoid membranes, thylakoid space, granum, stroma, chlorophyll? What organelle are they part of?

Answer 4

2 membranes surround everything.
Thy. membrane surrounds thy. space in stacks called grana (granum, singular). Stroma is fluid filling the inner membrane. Chlorophyll is the light absorbing pigment in the thy. membrane.
All parts of chloroplasts.

Question 5

What are stomata/stoma (singular) and what are they for? Are they the same as stroma?

Answer 5

Holes in the underside of leaves that carbon dioxide, oxygen, and water vapour can enter/exit through.
No! Stroma is the fluid filled inner compartment of a chloroplast.

Question 6

What is mesophyll tissue. What is a mesophyll cell?

Answer 6

Photosynthesizing tissue in a leaf.
A photosynthesizing cell that may have from 30-40 chloroplasts in it.

Question 7

What are the 2 series of reactions in photosynthesis? Where do they occur?

Answer 7

The light dependent reactions occur in the thylakoid membrane.
The Calvin Cycle (aka. dark reactions) occur in the stroma.

Question 8

What is NADP+? What does it reduce to?

Answer 8

It’s like NAD+, only with a phosphate group attached.
It reduces to NADPH.

Question 9

What are the reactants/products of light dependent reactions? What is released and reduced during these reactions? Is sugar produced?

Answer 9

Light energy is used for phosphorylation of ADP to ATP.
Water is split (and oxidized). The H reduces NADP+ to NADPH. The O is released as O2.
No sugar is produced just energy and potential energy in NADPH!

Question 10

What is carbon fixation?

Answer 10

The conversion of atmospheric carbon dioxide into organic molecules by autotrophic organisms (seen in the Calvin cycle).

Question 11

Is light a particle or wave?
What wavelengths have more or less energy?

Answer 11

Light behaves as both a particle and a wave.
Shorter wavelength = higher energy
Longer wavelength = lower energy

Question 12

Do we see the colour of wavelengths that are or are not absorbed by a surface? What about black or white? How is absorption related to heat?

Answer 12

We see what is not absorbed (aka. what is reflected back to our eyes).
i.e. Chlorophyll looks green because it does not absorb green.
Black absorbs all wavelengths of visible light; white reflects them all.
When light is absorbed, much of it is converted into heat.

Question 13

What is the electromagnetic spectrum? What part of the spectrum does the sun emit?

Answer 13

The full range of electromagnetic radiation from short gamma rays to long radio waves.
The sun emits visible light and some UV and infrared. Visible light consists of ALL of the colours together.

Question 14

Where are the photosynthetic pigments, chlorophyll a and b located within the chloroplast?

Answer 14

Photosynthetic pigments in chloroplasts are located in the thylakoid membranes.

Question 15

In addition to chlorophylls, thylakoid membranes always contain secondary light absorbing pigments. What are they called? Example?

Answer 15

Accessory pigments.
i.e. Carotenoids, which may be yellow, red or purple.

Question 16

Aside from giving us beautiful fall colours, what is primary function of accessory pigments? What is a secondary function they have?

Answer 16

They increase the range of light that can be utilized for photosynthesis by absorbing wavelengths that chlorophyll does not. They also serve to protect the cells by dissipating excessive light energy that could damage chlorophyll

Question 17

What happens to a pigment molecule’s electrons when it absorbs a photon of light? What energy state does it change from and to?

Answer 17

One of its electrons jumps to a higher energy level further from the nucleus, increasing its potential energy.
The electron has been raised from a ground state to an excited state (very unstable).

Question 18

What happens when an electron falls from an excited state to a ground state? What is released?

Answer 18

They release heat and light as they fall. Any light release will be emitted at a longer wavelength than what was absorbed.

Question 19

What is a photosystem? What are their two main parts?

Answer 19

Clusters of light-absorbing pigments of the thylakoid membrane and their associated electron carriers.
Numerous light-harvesting complexes (pigments and proteins) surrounding a reaction centre complex.

Question 20

What is the first real step in converting solar energy to chemical energy? What two components are involved?

Answer 20

The first real step occurs when an excited electron is delivered from chlorophyll a to the primary electron acceptor.

Question 21

How many photosystems are there? Which functions first?

Answer 21

There are two types
of photosystems – 1 and 2 (named in order of their discovery).
Ironically, photosystem II functions first.

Question 22

What type of chlorophyll a is found in the reaction centre of each photosystem? What do their names mean?

Answer 22

PS 2: P680 (absorbs light best at this
wavelength.)
PS 1: P700 (its maximum absorption wavelength.)

Question 23

Review the steps of light reactions. What is the path of an excited electron from the P680 of Photosystem II to NADP?

Answer 23

(Light NRG) P680 ➡ primary electron acceptor of PS 2 (water is split, P680 receives replacement electrons, O2 released) ➡ electron transport chain to PS 1 (energy pumps H+, makes gradient, make ATP) ➡ chlorophyll P700 (Light NRG) ➡ primary electron acceptor of PS 1 ➡ mini electron transport chain ➡ NADP+ (reduced to NADPH)

Question 24

What is produced by each photosystem? Which photosystems use energy from sunlight?

Answer 24

PS 2 makes ATP via chemiosmosis (and O2 is released).
PS 1 reduces NADP+ to NADPH.
Both use energy from sunlight.

Question 25

What does the electron transport chain between PS 2 and PS 1 do? Where does it get the energy to do this?

Answer 25

It contains a protein that pumps H+ ions from the stroma into the thylakoid space.
Energy is from the excited electron as it drops to a lower energy level.

Question 26

What is photophosphorylation? What enzyme is used to make ATP?

Answer 26

Phosphorylation (the attachment of a phosphate to a molecule) using energy from light (as seen in PS 2 when making ATP).
ATP synthase.

Question 27

What are ATP and NADPH used to make in the Calvin Cycle? What is entered into the cycle to make this product? How many carbons does the product have?

Answer 27

Glyceraldehyde 3 – phosphate (G3P) is made by inputting carbon dioxide (CO2). Remember it’s not the sugar glucose, but a 3 carbon sugar used to make glucose (and other stuff).

Question 28

What enzyme catalyzes the first step of the Calvin Cycle? What are some characteristics of this enzyme?
What is CO2 added to at the beginning of the cycle?

Answer 28

Rubisco (most abundant but works very slowly).
The 5- carbon sugar ribulose 1-5 bisphosphate (RuBP).

Question 29

How many turns of the Calvin Cycle does it take to generate one molecule of G3P? Why?

Answer 29

3
Each turn produces 2 G3Ps, however 6 are needed before 1 can be released. (5/6 are used to remake RuBP).

Question 30

What are the three main steps in the Calvin Cycle? When is G3P released? When are ATP and NADPH used?

Answer 30

Carbon fixation carbon from CO2 added to 5 carbon Ribulose bisphosphate (RuPB), then 6C breaks into 2 3C 3-PGA.
Reduction of 2 3-PGA to 2 G3P (which uses ATP and NADPH).
1 G3P released (after 3 cycles).
Regeneration 5 3-carbon G3Ps reconfigure into 3 RuBP (using ATP).

Question 31

How many G3Ps are needed to make 1 glucose? Can G3Ps make anything else?

Answer 31

2 G3Ps make 1 glucose.
Yes, sugars, starches, and other organic compounds (lipids, amino acids, nitrogenous bases, etc.).

Question 32

When is O2 produced and CO2 consumed in photosynthesis?
Where does the oxygen come from?
What is the CO2 made into?

Answer 32

O2 is made in the light reactions. It comes from H2O.
CO2 is consumed in the Calvin cycle and made into G3P (eventually glucose).

Question 33

What two physical factors affect the rate of photosynthesis?

Answer 33

Temperature (the lower the temp. the slower that rate).
Light availability (less light = slower rate).

Question 34

How does stomata closing affect plants?

Answer 34

Stomata close when it is very hot and dry to prevent loss of water. This also prevents CO2 from entering and oxygen from leaving causing photorespiration (in C3 plants).

Question 35

About ____ % of the carbohydrate made by photosynthesis is consumed as fuel for cellular respiration in the plant’s own mitochondria.

Answer 35

50%

Question 36

What is photorespiration?

Answer 36

When oxygen builds up, rubisco adds
oxygen instead of CO2 to RuBP to complete the Calvin cycle.
Occurs in light, consumes oxygen and releases CO2. It also consumes ATP but produces no sugar.

Question 37

What’s the difference between C3 and C4 plants?

Answer 37

C3: first products of carbon fixation are a 3-carbon compound 3-PGA.
C4: first fix CO2 into a four-carbon compound (before the Calvin cycle). Keeps internal CO2 levels high even with stomata closed. They separate the light/dark reactions in different cell types.

Question 38

What are CAM plants?

Answer 38

Many cacti and succulent are Cam plants. They only open stomata at night and fix CO2 into a four-carbon compound which is released during the day for use in the Calvin cycle. Light/dark reactions separated by time.