Photosynthesis

Question 1

What are autotrophs?

Answer 1

• self-feeders
• organisms that synthesise large organic molecules from simple inorganic molecules
• use light energy

Question 2

What are heterotrophs?

Answer 2

• organisms that obtain organic molecules by consuming other organisms

Question 3

What are photoautotrophs?

Answer 3

• any organism that carries out photosynthesis

Question 4

Summarise the compensation point:

Answer 4

• point of which rate of photosynthesis = rate of respiration
• net uptake of CO2 and 02 is zero
• different for different plant species

Question 5

What is a redox reaction?

Answer 5

• reaction that involves a transfer of electrons
• numerous involved in photosynthesis
• oxidation & reduction - oxidation of one molecule always involves the reduction of another

Question 6

What are the 3 definitions of oxidation?

Answer 6

• loss of electrons
• loss of hydrogen
• gain of oxygen

Question 7

What are the 3 definitions of reduction?

Answer 7

• gain of electrons
• gain of hydrogen
• loss of oxygen

Question 8

Why is ATP useful?

Answer 8

• releases energy quickly, in a single reaction
• hydrolysis of ATP releases ideal small amount of energy
• small & soluble, so easily transported - but cannot pass out of cell

Question 9

Summarise the structure of ATP:

Answer 9

Phosphorylated macromolecule, consisting of:
- adenine nitrogenous base
- ribose pentose sugar
- 3 phosphates

Question 10

Breakdown of ATP:

Answer 10

ATP —> ADP + Pi
- exothermic reaction

Question 11

Resynthesis of ATP:

Answer 11

ADP + Pi —> ATP
- endothermic reaction
- catalysed by enzyme ATP synthase

Question 12

What is phosphorylation?

Answer 12

• addition of a phosphate molecule
  3 types:
• photophosphorylation
• oxidative phosphorylation
• substrate-level phosphorylation

Question 13

Summarise the membrane envelope of the chloroplast:

Answer 13

• contains inner & outer membranes
• acts as a protective covering, keeping chloroplast structures enclosed

Question 14

Summarise the stroma of the chloroplast:

Answer 14

• dense fluid within chloroplast
• site of conversion of CO2 to carbohydrates

Question 15

Summarise the thylakoid membrane of the chloroplast:

Answer 15

• internal membrane system
• consisting of thylakoids = flattened sac-like membrane structures, sites of conversion of light energy to chemical energy

Question 16

Summarise the chlorophyll:

Answer 16

• green photosynthetic pigment
• within grana
• absorbs light energy

Question 17

Summarise the grana of the chloroplasts:

Answer 17

• dense stacks of thylakoid sacs = site of conversion of light energy to chemical energy
• singular = granum

Question 18

How does the structure of the chloroplast relate to its function?

Answer 18

• large surface area of thylakoid membrane = allows maximum absorption of light energy
• granal membranes have ATP synthase channels = catalyses production of ATP
• contains DNA & ribosomes = can make proteins involved in LIR of photosynthesis

Question 19

What is cpDNA?

Answer 19

Chloroplast DNA

Question 20

What does LDR stand for?

Answer 20

Light dependant reaction

Question 21

What is the LDR?

Answer 21

1st stage of photosynthesis
Converts light energy + water —> ATP + reduced NADP
In thylakoids

Question 22

What are the 4 main stages of the LDR?

Answer 22

1. Photoionisation of chlorophyll
2. Photolysis
3. Chemiosmosis
4. Production of ATP & reduced NADP

Question 23

Summarise photoionisation of chlorophyll:

Answer 23

light energy absorbed by chlorophyll
excites electrons, so they raise up energy level and leave chlorophyll (so chlorophyll has been ionised by light = photoionised)
energy from released electrons used in chemiosmosis

Question 24

Summarise photolysis of water:

Answer 24

light energy absorbed by chlorophyll splits water:
H20 —> 1/202 + 2e- + 2H+
- O2 used for respiration, or diffuses out of leave through stomata
- e- passed along electron transport chain (chemiosmosis)
- H+ picked up by NADP, reducing it to NADPH (**used in LIR)

Question 25

Summarise **chemiosmosis**:

Answer 25

Electrons move along **electron transport chain** Release **energy** at each movement, which is used to **pump protons** across chloroplast membranes, from **stroma** into **thylakoid** **Electrochemical gradient** created, so **protons** move through **facilitated diffusion**, via **enzyme ATP synthase** —> resulting in **ATP production** Some **protons** then picked up by **NADPH**, reducing it to **NADPH**

Question 26

What is the **electron transport chain**?

Answer 26

Series of **proteins** within **thylakoid membrane**

Question 27

What does **LIR** stand for*?

Answer 27

Light independent reaction

Question 28

What is the **LIR**?

Answer 28

**2nd** stage of **photosynthesis** **Calvin cycle** Converts C02 —> glucose In stroma

Question 29

What are the **3 stages** of the **calvin cycle**?

Answer 29

1. Carbon fixation (carboxylation) 2. Reduction 3. Regeneration

Question 30

Summarise **carboxylation**:

Answer 30

**CO2** leaf through stomata (through diffusion) C02 combines with **RuBP** (5C) using **enzyme rubisco** Produces unstable 6C compound Quickly splits to 2 x 3C compound called **GP**

Question 31

Summarise **reduction**:

Answer 31

**GP** reduced into different 3C compound, **triose phosphate (TP)**, using **ATP** and **H+** ions (from reduced NADP) from **LDR**

Question 32

Summarise **regeneration**:

Answer 32

**5 out of 6 TP** molecules used to **regenerate RuBP**, using **ATP** —> ADP + Pi, produced in **LDR**

Question 33

What is **TP**?

Answer 33

Triose phosphate Primary end-product of photosynthesis Key molecule for making everything plant needs: **1 out of 6** used to make **hexose sugar**

Question 34

What is a **limiting factor** in photosynthesis?

Answer 34

Factor that limits rate of photosynthesis

Question 35

What are examples of **limiting factors**?

Answer 35

Light intensity, CO2 concentration, temperature, water availability, minerals, chlorophyll, enzymes.

Question 36

What is **water stress**?

Answer 36

Condition that occurs when plant doesn’t have sufficient amount of water Roots don’t take up enough water to replace that lost in transpiration Cells loose water & become plasmolysed Roots produce abscisic acid causing stomata to close Tissues become flacid & wilt Rate of photosynthesis decreases

Question 37

How does **low light intensity** affect the **LIR**?

Answer 37

Although LIR doesn’t require light directly, **ATP** and **reduced NADP** from **LDR** won’t be produced**, meaning **GP not reduced** to **TP** **RuBP** cannot be regenerated

Question 38

How does **low CO2 levels** affect **photosynthesis**?

Answer 38

RuBP cannot combine with CO2 So no **GP** made, so no **TP** made

Question 39

How does **temperature** affect **photosynthesis**?

Answer 39

**LIR** uses many **enzymes**, which are sensitive to temperature changes Up to 30C: rate of photosynthesis increases at temp increases Above 30C: rate begins to slow due to **photorespiration** (oxygen competes with carbon dioxide for RuBPs active site) Above 45C: **enzymes denature & stomata close** to reduce water loss, so less C02. Photosynthesis stops.