Chapter 6

Question 1

Photosynthesis

Answer 1

• Captures light energy and uses it to convert carbon dioxide into carbohydrates.
• H2O is a byproduct of it

Question 2

Autotrophs

Answer 2

An organism that can produce its own food using light, water, carbon dioxide. Ex. Algae, Bacteria

Question 3

Heterotrophs

Answer 3

An organism that eats other plants or animals for energy and nutrients. Ex. Dogs, Humans, Birds, Fish

Question 4

Photoautotrophs

Answer 4

Organisms that carry out photosynthesis. Ex. plants

Question 5

2 Stages of photosynthesis

Answer 5

1. Light reactions
2. Calvin cycle

Question 6

Light reactions

Answer 6

Pigments absorb light to make ATP and NADPH, releasing oxygen from water.

Question 7

Calvin cycle

Answer 7

NADPH and ATP from light reactions provide energy to turn CO2 into carbohydrates.

Question 8

Chloroplasts

Answer 8

• In eukaryotes (higher plants, algae)
• photosynthesis takes place in chloroplasts

Question 9

Electromagnetic spectrum

Answer 9

The range of wavelengths of electromagnetic radiation

Question 10

Visible Light and Photons

Answer 10

• Visible light has wavelengths between about 700 nm and 400 nm
• We see the entire spectrum combined together as white light

Question 11

When photons of light hit an object, 1 of 3 things can happen. The photon can be….

Answer 11

• reflected
• transmitted
• absorbed

Question 12

Three Fates of an Excited-State Electron

Answer 12

1. Excited electrons release energy as heat or light (fluorescence) when returning to their ground state
2. An excited electron transfers energy to a nearby pigment, exciting it while the first pigment calms down.
3. The excited electron can also move to a nearby electron acceptor.

Question 13

Chlorophylls

Answer 13

The major photosynthetic pigments in plants, green algae, and cyanobacteria

Question 14

Chlorophyll A

Answer 14

It is oxidized and donates electron to primary electron acceptor

Question 15

Chlorophyll B and carotenoids

Answer 15

• They are both accesory pigments
• Donate excitation energy to chlorophyll A via inductive resonance

Question 16

Chlorophyll and Carotenoids

Answer 16

Absorb light to power photosynthesis.

Question 17

Engelmann’s experiment 1883

Answer 17

He used a glass prism to break light into a spectrum of colours

Question 18

Major Components of a Photosystem

Answer 18

1. Antenna complex
2. Reaction centre

Question 19

Antenna complex functions

Answer 19

Absorbs light energy:
* Chlorophyll a and b
* Carotenoids
- Energy moves to Reaction Center chlorophyll a through inductive resonance.

Question 20

Reaction Center

Answer 20

Pair of special chlorophyll a molecules of reaction center are bound by proteins:
* P680 in PSII
* P700 in PSI

Question 21

Photosystems I and II

Answer 21

Photosystems composed of many pigments and proteins(can be oxidized (photoreduction)

Question 22

Photosystem I used for splitting water molecules

Answer 22

P680 is reformed when P680 gains an e- from oxidation of H2O—-> Water splitting complex

Question 23

Chemiosmotic synthesis of ATP

Answer 23

• Protons (H⁺) flow from the thylakoid lumen into the stroma through ATP synthase.
• This flow drives the enzymatic formation of ATP from ADP and Pi.

Question 24

Photosynthetic Electron Transport and ATP Synthesis

Answer 24

• Electrons from P680 (Photosystem II) travel through an ETC.
• Light energy powers Photosystems II and I to produce:
  
  • NADPH (electron carrier).
  • A H⁺ gradient that drives ATP synthesis.

Question 25

Energy Levels in Thylakoid Membrane

Answer 25

- **PS II** absorbs light, allowing electrons from water to enter the **ETC**. - **PS I** absorbs more light, creating electron donors to reduce **NADP⁺**.

Question 26

Stoichiometry

Answer 26

The determination of the proportions in which elements or compounds react with one another.

Question 27

Cyclic electron transport

Answer 27

- PSI can work alone by using cyclic electron transport - Moves protons across thylakoid membrane - This cyclic electron transport converts light energy into ATP. - Generates ATP without building of NADPH

Question 28

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase)

Answer 28

- The most abundant protein on Earth. - Key provider of organic molecules for most organisms. - Converts ~100 billion tons of CO₂ into carbohydrates annually. - Makes up 50%+ of total protein in leaves. - Structure: - 8 large subunits (LSU) from the chloroplast genome. - 8 small subunits (SSU) from the nuclear genome. - Requires coordinated expression of two genomes.

Question 29

Rubisco has Carboxylase and Oxygenase Activity

Answer 29

- **Photorespiration** occurs due to Rubisco’s oxygenase activity: - Leads to a net loss of carbon. - Consumes O₂ and releases CO₂.

Question 30

Carbon-Concentrating Mechanisms (CCMs) in Algae

Answer 30

- Adapted to aquatic environments. - CO₂ levels in water are too low to saturate Rubisco’s active site. - Adding CO₂ to phytoplankton typically doesn’t boost photosynthesis rates. - Algae actively pump CO₂ into their cells to overcome this limitation.

Question 31

Dilemma of Plants in Hot, Dry Climates

Answer 31

- Stomata control gas exchange: - Open to allow CO₂ entry. - Closed to conserve water. - Balancing CO₂ uptake and water conservation is critical.

Question 32

C4 Photosynthesis

Answer 32

- Increases CO₂ near Rubisco to reduce photorespiration. - 4-carbon molecule releases CO₂ for the Calvin cycle.

Question 33

C4 in different locations

Answer 33

- PEP carboxylase binds CO₂ without oxygenase activity. - 4-carbon molecule releases CO₂ when O₂ is low. - CO₂ enters Calvin cycle via Rubisco.

Question 34

Crassulacean Acid Metabolism (CAM)

Answer 34

- C4 and Calvin cycles are separated by time in CAM plants (temporal separation). - CO₂ is captured at night via the C4 cycle (e.g., cacti, succulents). - The Calvin cycle occurs during the day using sunlight for ATP and NADPH.

Question 35

CAM Plants

Answer 35

- Stomata open at night to capture CO₂ via the C4 cycle. - 4-carbon intermediates (e.g., malate) are stored in vacuoles. - During the day, stomata close to save water; malate releases CO₂ in chloroplasts. - High CO₂ and low O₂ reduce photorespiration.

Question 36

CAM plants

Answer 36

Temporally separate the C4 pathway and the Calvin cycle (at different times of day).

Question 37

Photosynthesis vs Cellular respiration

Answer 37

- Photosynthesis occurs in plant cells with chloroplasts. - Cellular respiration occurs in all cells. - The overall reactions of photosynthesis and cellular respiration are essentially reverse of each other, with the reactants of one being the products of the other.

Question 38

C4 plant

Answer 38

Spatially separate the C4 pathway and the Calvin cycle (in different cells).