Photosynthesis

Question 1

Chloroplast structure ?

Answer 1

• 2-10 μm diameter
• Surrounded by a double membrane envelope - each envelope membrane is phospholipid bilayer
• outer membrane is permeable to ions/small molecules
• inner membrane has transport proteins - allow certain molecules to enter/leave chloroplast

Question 2

What is stroma?

Answer 2

Fluid filled matrix in chloroplasts (CO2,sugars,enzymes/other molecules dissolved in stroma)

Question 3

What system of membranes are found in stroma?

Answer 3

Consists of a series of flattened fluid-filled sacs - THYLAKOIDS
(contain PHOTOSYSTEMS that contain pigments,enzymes,electron carriers)
- thylakoids stack up to form GRANA —> CREATE LARGE SA
GRANA connected by stroma lamellae

Question 4

What is a photosystem?

Answer 4

System of photosynthetic pigments found in thylakoids of chloroplasts
- different pigment molecules arranged in funnel-like structures in thylakoid membrane
- large no. Pigment molecules in an arrangement —> MAX LIGHT ABSORBED

Question 5

What does the stroma also contain?

Answer 5

70S ribosomes- proteins coded for by the loop of DNA produced at 70S ribosome
Loop of DNA- codes for some chloroplast proteins
Starch grains - sugars formed during photosynthesis stored as starch in starch grains

Question 6

Where does each stage of photosynthesis take place?

Answer 6

Light dependent - thylakoids membranes of the GRANA
Light independent - in stroma

Question 7

Adaptations of chloroplasts to photosynthesis?

Answer 7

STROMA : gel-like fluid contains ENZYMES that catalyse reactions of light independent stage
- rapid transport of products from light dependent stage as surrounds GRANA/thylakoid membranes

GRANA: Granal stacks create LARGE SA-> more photosystems can be present —> max light absorption
- more space for electron carriers/ATP synthase enzymes

DNA: chloroplast DNA (cpDNA) has genes that code for some proteins/enzymes used in photosynthesis

Ribosomes: allows translation of proteins coded by cpDNA

Inner membrane of chloroplast envelope: selective transport proteins control flow of molecules between stroma/cytoplasm of plant cell (cytosol)

Question 8

2 types of pigment?

Answer 8

Chlorophylls (a/b)- absorb blue-violet/red regions of light spectrum
- reflect green
ACCESSORY PIGMENT: Carotenoids - absorb wavelengths in blue-violet region
- reflect yellow/orange

Question 9

Why are accessory pigments useful?

Answer 9

They surround primary pigment + Absorb both similar/different wavelength of light to chlorophyll
- expands the wavelength range that can be absorbed for use in photosynthesis

Question 10

What are the different photosystems?

Answer 10

Photosystem 1 (PSI) - P700
chlorophyll a which has a max absorption of light at 700nm

Photosystem 2 (PSII)- P680
Chlorophyll a has max absorption of light at 680nm

Question 11

Stages of light dependent stage of photosynthesis?

Answer 11

1. Light harvesting at photosystems
2. Photolysis of water - light energy used to breakdown water —> H+ ions, electrons, oxygen in thylakoid lumen
   Proton gradient formed due to high conc of H+ ions in lumen
   Electrons travel through electron transport chain of proteins within membrane
3. ATP produced in photophosphorylation
   Reduced NADP (NADPH) produced when H+ ions in the stroma + electrons in ETC combine with carrier molecule, NADP