AW- eating the sun

Question 1

Why is photosynthesis an important process on earth? (3)

Answer 1

1- converts light energy from the sun to chemical energy on Earth
2-creates almost all organic molecules that power life on Earth
3-creates almost all the O2 used for cellular respiration

Question 2

distinguish between different modes of nutrition (2)

Answer 2

Autotrophs= produce their own food using light, H2O and CO2, called the producers
Heterotrophs= eats other plants and animals for energy, called consumers

Question 3

explain where photosynthesis occurs in plants

Answer 3

• in the chloroplast light energy is able to be absorbed by chlorophyll which drives the process of photosynthesis

Question 4

describe the 2 parts of photosynthesis and what they do

Answer 4

light reactions= split H20, form O2, reduce NADP+ to NADPH and generate ATP from ADP by phosphorylation

Calvin cycle= forms sugar from CO2 using ATP and NADPH

Question 5

which molecules are involved in photosynthesis and how do they split and combine?

Answer 5

• CO2 + H20 + light energy combine to form sugar and O2
• the H2O splits to form H+ ions and releases oxygen as a product and the H+ ions form part of water
• CO2 splits to make up the products sugar and H20

Question 6

How do we know that oxygen is produced in photosynthesis from the splitting of water?

Answer 6

Due to the photosynthesis equation of purple sulfur bacteria

• instead of H2O in the reactants this bacteria has H2S hence if H2O had split to form water and part of sugar then in this equation H2S should split to form H2S and also part of sugar
• But that not what happens, Instead S is released as a product and that helps us realize that in the photosynthesis equation for plants it is actually H2O splitting to form oxygen as a product and not CO2

Question 7

explain the functions of accessory pigments

Answer 7

1- Broaden spectrum for photosynth

2- Protect from excess light

Question 8

What happens when a pigment absorbs light? in terms of electrons

Answer 8

• when a photon with sufficient energy hits light the electron absorb the energy to go from their ground state to an excited state

Question 9

How does an electron ‘fall back down’ ?

Answer 9

it emits the same amount of energy it absorbed

Question 10

Explain why plants look green?

Answer 10

due to the green pigment chlorophyll that reflects and transmits green light instead of absorbing it

Question 11

what is a Photosystem?

Answer 11

consists of a reaction-center complex surrounded by light-harvesting complexes

Question 12

Describe how , where and by what process are ATP and NADPH produced (12)

Answer 12

By the process of linear electron flow:

1- A photon hits a pigment and its energy is passed among pigment molecules until it reaches the special chlorophyll a in the reaction center complex (called P680)

2- An excited electron is then transferred from P680 to the primary electron acceptor

3-H2O is then split, and the electrons replace those lost by P680

4- Split water becomes O2 (diffuses out) and
H+ ions (lowering the pH in the thylakoid space)

5- Each electron captured by the primary electron acceptor of PS II “falls” down an electron transport chain to PS I (releasing energy along the way)

6- Movement of electrons from PS II, through the cytochrome complex, to PS I, pumps H+ ions into thylakoid space.

7-Diffusion of H+ across the membrane, into the stroma, allows ATP synthesis

8-In PS I (just like PS II), transferred light energy excites a special pair of chlorophyll a molecules (P700), which lose an electron to an electron acceptor

9-This electron is replaced by the electron passed down from PS II via the electron transport chain

10- Each electron “falls” down an electron transport chain from PS I to the protein ferredoxin (Fd)

11- The electrons are used by an enzyme (NADP+ reductase) to reduce NADP+ to NADPH

12-The chemical energy in NADPH is then available for the reactions of the Calvin cycle

Question 13

Describe how and where oxygen is produced

Answer 13

water is split to produce H+ and water as product

Question 14

Why does cyclic flow only produce ATP?

Answer 14

• Unlike in linear electron flow, Fd gives the electron back to the cytochrome complex, not NADP+ reductase so it is not reduced to NAPD
• in this process H2O does not split to release water as a product

Question 15

What is a chemoautotroph and photoautotroph?

Answer 15

• chemoautotroph= cells that create their own energy and biological materials from inorganic chemicals.
• photoautotroph= organisms that can make their own energy using light and carbon dioxide via the process of photosynthesis.

Question 16

what is a chemoheterotroph and photoheterotroph?

Answer 16

• chemoheterotroph=derives its energy from organic compounds, and needs to consume other organisms in order to live.
• photoheterotroph= make use of light energy as their energy source and use organic compounds instead of CO2

Question 17

what is chloroplast made up of?

Answer 17

• it has a double membrane

- made up of thylakoids stacked on top of each other to form a granum in the stroma(colourless fluid)

Question 18

What is stomata and what does it do?

Answer 18

• it is the valved on the underside of a leaf
• allows CO2 to diffuse in
• Allows O2 and water to diffuse out

Question 19

what does a reaction-center complex in photosystems do?

Answer 19

Contains a primary electron acceptor that accepts an excited electron from chlorophyll

Question 20

what does a light-harvesting complex in photosystems do?

Answer 20

funnel the energy of photons to the reaction center

Question 21

Describe the process of cyclic flow (5)

Answer 21

1- In PS I (just like PS II), transferred light energy excites a special pair of chlorophyll a molecules (P700), which lose an electron to an electron acceptor

2-This electron is replaced by the electron passed down from PS II via the electron transport chain

3- Each electron “falls” down an electron transport chain from PS I to the protein ferredoxin (Fd)

4- Unlike linear electron flow, Fd gives the electron back to the cytochrome complex, not NADP+ reductase

5- This generates a H+ gradient that drives ATP synthesis (as in linear electron flow), but no NAPDH or O2 are produced.