⭐️Energy Transfer Of Organisms - Photosynthesis

Question 1

Give 5 ways leaves are adapted for photosynthesis

Answer 1

• large surface area to absorb as much light as possible
• the cuticle and epidermis is transparent to let light penetrate to the photosynthetic mesophyll cells
• the leaves on the plant minimally overlap to avoid them shadowing each other and reducing light absorption
• the stomata open and close in response to changes in light intensity
• they are thin so diffusion distance of gases is kept short

Question 2

State and overview the three main stages of photosynthesis

Answer 2

1. Capturing of light energy by chloroplast pigments like chlorophyll
2. The light dependant reaction (LDR)
3. The light independent reaction (LID)

Question 3

Where does the LDR occur?

Where does the LIR occur?

Answer 3

LDR occurs in the thylakoid membrane

LIR occurs in the stroma

Question 4

What is photolysis?

Answer 4

The splitting of water into protons and hydroxide ions by light energy

Question 5

What is oxidation and reduction in terms of hydrogen and oxygen?

Answer 5

Oxidation is when a substance gains oxygen or LOOSES hydrogen

Reduction is when a substance looses oxygen or gains hydrogen

Question 6

What is photophosphorylation?

Answer 6

The processes of the light independent reaction to make ATP and NADPH

Question 7

Give the steps of the light dependent reaction

Answer 7

1. A photons of light are absorbed at specific wavelengths by chlorophyll a in the reaction centre of photosystem II in the thylakoid membrane
2. Electrons in the chlorophyll a are energised so they are emitted from the chlorophyll molecule causing it to be oxidised in the photoionisation of chlorophyll
3. The oxidised state initiates photolysis of water into 1/2O, 2H+ and 2e- and the 2e- replaced that lost from the chlorophyll a
4. The high energy 2e- emitted from chlorophyll a is transferred along the electron transfer chain (this accepts the excited electrons) which is made made of electron carrier proteins through redox reactions and in doing so, the electrons loose energy which is used to power the pumping of protons from the the stroma into the thylakoid lumen against their concentration gradient setting up an electrochemical gradient
5. Protons diffuse down the electrochemical gradient through ATP synthase channel which transfers energy to phosphorylate ADP to form ATP in chemiosmosis
6. The low energy electrons passed through the electron transfer chain are then transferred to photosystem I where they are transferred NADP reducing it to reduced NADP completing phosphorylation

Question 8

Give the steps of the Calvin cycle

Answer 8

1. Carbon dioxide from the atmosphere diffuses into the leaf through stomata.
2. Co2 diffuses through the cell surface membrane, cytoplasm and chloroplast membranes into the stomata of the chloroplast
3. In the stroma, the co2 combines with RuBP which has 5 carbons, in a reaction catalysed by rubisco, to produce two molecules of (GP) with each molecule containing 3 carbons
4. Reduced NADP from the LDR is used to reduce TP by donating a proton using the energy supplied by ATP
5. The NADP is reformed and goes back to the LDR to be reduced again by accepting more protons
6. 2 TP molecules are converted into organic substances that the plant requires such as starch, cellulose, glucose, lipids…
7. TP molecules are used to regenerate all of the RuBP using ATP from the LDR

Question 9

Give three ways the chloroplast is adapted to carrying out the LIR

Answer 9

1. The fluid of the stroma has all enzymes needed to carry out the LIR and the stromal fluid is membrane bound in the chloroplast so the high concentration of enzymes and substrates can be maintained
2. Stromal fluid surrounds the grana so the products of the LDR in the grana can readily diffuse into the stroma
3. It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the LIR

Question 10

When light intensity becomes the limiting factor, what happens to TP from the LIR?

Answer 10

• reduces
• no products from LDR so no/ less ATP and reduced NADP
• so GP is not converted to TP
• and existing TP is converted to RuBP

Question 11

When light intensity becomes the limiting factor, what happens to GP?

Answer 11

• increases
• no products from LDR so no/ less ATP and reduced NADP so GP is not converted to TP
• existing RuBP is converted to TP until all RuBP is used up and then it will stop

Question 12

What happens to RuBP when light intensity becomes the limiting factor?

Answer 12

• reduces
• it reacts with CO2 to form GP but there’s is no TP to replace it
• as a result of the lack of products from the LDR, no/ less ATP and reduced NADP So RuBP can’t be replaced