5A - photosynthesis and respiratoon

Question 1

what are chloroplasts?

Answer 1

the organelles in plant cells where photosynthesis occurs

Question 2

what are chloroplasts surrounded by?

Answer 2

a double-membrane envelope

Question 3

what are each of the chloroplast envelope membranes?

Answer 3

a phospholipid bilayer

Question 4

what are chloroplasts full of?

Answer 4

a fluid called stroma

Question 5

what is the stroma the site of?

Answer 5

the light-independent stage of photosynthesis

Question 6

which components are needed for light dependent reactions?

Answer 6

pigments, enzymes and electron carriers

Question 7

what are thylakoids?

Answer 7

a series of flattened fluid-filled sacs known as thylakoids

Question 8

chloroplast structure:

Answer 8

-thylakoids stack to form grana
-grana are connected by lamellae

Question 9

what is the purpose of lamellae?

Answer 9

they ensure that the stacks of grana are connected but distanced from each other

Question 10

what is the purpose of the membranes of the grana?

Answer 10

-the membranes of the grana create a large surface area to increase the number of light-dependent reactions that can occur

Question 11

what is the membrane system?

Answer 11

the site of the light-dependent stage of photosynthesis (system of membranes found in the stroma)

Question 12

what does the membrane system provide?

Answer 12

a large number of pigment molecules in an arrangement that means as much light as necessary is absorbed

Question 13

what else does the stroma contain?

Answer 13

small ribosomes, a loop of DNA, starch grains

Question 14

what is the loop of dna in the stroma needed for?

Answer 14

it codes for some of the chloroplast proteins (these are produced at the 70S ribosomes)

Question 15

where are sugars formed during photosynthesis stored?

Answer 15

as starch inside starch grains

Question 16

where does the light-dependent stage of photosynthesis occur?

Answer 16

in the thylakoid membranes and the thylakoid spaces

Question 17

what do the proteins and pigments in the thylakoids do?

Answer 17

the proteins and pigments make up an electron transport chain used to carry electrons through the membrane

Question 18

what are electrons used for? (LDR)

Answer 18

they can be used to move H­­+ ions across the membrane

Question 19

where do electrons come from? (LDR)

Answer 19

they are donated by water molecules

Question 20

what are electrons accepted by?

Answer 20

NADP molecules that form NADPH

Question 21

what do the membranes of the grana create?

Answer 21

a large surface area to increase the number of light-dependent reactions that can occur

Question 22

what are photosystems?

Answer 22

light-harvesting systems called photosystems which have chlorophyll at their centres

Question 23

photosystem description:

Answer 23

-funnel-like structures found in the thylakoid membrane
-made from accessory pigments that absorb light energy and transfer it to the primary pigment reaction centre

Question 24

why does the LDS need light?

Answer 24

they require light energy absorbed by chlorophyll to excite electrons, this raises their energy level and that energy is released to produce a small amount of ATP
from ADP (photophosphorylation)

Question 25

order of the stages in the light dependent stage:

Answer 25

1) photoionisation 2) photophosphorylation 3) photolysis of water 4) synthesis of ATP 5) photosynthesis

Question 26

what does photoionisation describe?

Answer 26

-the process of using light energy to excite electrons in chlorophyll enough so that they can leave the molecule -it leaves the chlorophyll as a positively charged ion

Question 27

photoionisation steps:

Answer 27

1) light is absorbed by pigments located in the thylakoid membrane 2) two electrons in the chlorophyll molecule are excited to a higher energy level and are emitted from the chlorophyll molecule 3) each excited electron is passed down a chain of electron carriers known as an electron transport chain (during this, chemiosmosis happens)

Question 28

what is chemiosmosis?

Answer 28

-the energy given by the electrons moving through the electron transport chain allows H­­+ ions (protons) to pass from a low concentration in the stroma to a high concentration in the thylakoid -the creation of this proton gradient across the membrane later drives the synthesis of ATP in photophosphorylation

Question 29

what has happened to the chlorophyll and electron carriers after photoionisation?

Answer 29

chlorophyll has lost electrons → oxidised, electron carrier has gained electrons → reduced (OILRIG)

Question 30

what is photophosphorylation?

Answer 30

the name for the overall process of using light energy and the electron transport chain to phosphorylate ADP to ATP

Question 31

what happens during photophosphorylation? (LDS)

Answer 31

-energetic (excited) electrons are passed along a chain of electron carriers (known as the electron transport chain) -the electron carriers are alternately reduced (as they gain an electron) and then oxidised (as they lose the electron by passing it to the next carrier) -the excited electrons gradually release their energy as they pass through the electron transport chain -the released energy is used to actively transport protons/H+ ions (through a proton pump) across the thylakoid membrane, from the stroma to the thylakoid space -