photosynthesis and energy

Question 1

Function of chloroplast

Answer 1

Photosynthesis takes place
Absorbs light energy
Light is absorbed by complexes of pigments, such as chlorophyll
Fluid enclosed in chloroplast is called stroma + is the site of many chemical reactions resulting in the formation of complex molecules

Question 2

Structure of chloroplast

Answer 2

Network of membranes = large SA = Large SA:V
membranes form flattened sacs called thylakoids, which stack to form grana
Grana are joined by lamellae- create large SA which allows for the maxium absorbtion of light to excite electrons
Fluid enclosed is called Stroma which contains enzymes which catalyses the reactions of the light dependant stage
Contain lots of ribosomes for the translation of protiens that are used in photosynthesis

Question 3

Why leaves change colour in autumn

Answer 3

Chlorophyll breaks down, meaning green light stops reflecting
Other pigments of different colours ( that are present all year) then reflect their light

Question 4

Need for energy

Answer 4

Active transport - uptake of nitrates, phloem loading, selective reabsorption
Anabolic reactions - building of polymers: proteins, polysaccharides, and nucleic acids essential for growth
Movement - brought about by cilia, flagella, or muscle contraction
Respiration- organic molecules, glucose, are broken down into smaller inorganic ions

Question 5

What colours have: the highest light energy and longest wave length

Answer 5

ROYGBIV
violet - highest light energy
Violet to red wavelength increase

Question 6

What do pigment molecules Absorb

Answer 6

Specific wavelength (colours) of light and reflect others

Question 7

Function of pigemnts

Answer 7

Pigments arranged in light harvesting clusters to abosrb different wavelengths of light, clusters are known as photosystems
In a photosystem pigment molecues are arranged in a funnel like structre in the thylakoid membrane allowing energy to be passed down untill it reaches the primary pigment reaction centre
By having a range of pigments the range of wavelngths that can be absorbed expands

Question 8

Ps1 vs ps2

Answer 8

Ps1 known as P700 as peak absorption are wavelengths 700nm

Ps2 known as p680 as peak absorption are wavelengths 680nm

Question 9

What occurs in reaction centre

Answer 9

Photo excitation
Where electrons get boosted to higher energy levels
As they drop down chemical energy is released

Question 10

Non cyclic Light dependant reaction

Answer 10

• photolysis of water ( producing h+ and e-) 4 photos of light breaks down 1 water
• photosystem 2 absorbs the light
• excited electrons pass from primary acceptor,ps2, towards ps1 via electron transport chain
• as electrons fall to a lower energy level, whilst being transported energy is harnessed and converted from ADP to ATP
• PS1 also absorbs light. Electrons from primary pigment (p700) are excited
• carrier molecules NADP combines with these electrons ( and h+) to produce reduced NADP

Question 11

Cyclic Light dependant reactions

Answer 11

Only uses ps1
Excited electrons from ps1 chlorophyll molecule (p700) are captured by electron acceptors
It’s then passed back to ps1 via electron transport chain
During this the energy is released makes ATP from ADP and inorganic phosphate
No reduced NADP is made

Question 12

Light independent reaction detailed

Answer 12

3co2 is added 3 ribulose biphosphate to form a 3, 6 carbon molecules
This molecule is very unstable so it breaks down into 6 glycerate 3 phosphate molecules
Energy from ATP and hydrogen ( sourced from reduced NADP) are used to convert 6GP into 6TP
1 triose phosphate is removed to make glucose
5 triose phosphate is used in a regenerative reaction converting 5TP - 3RuBP to restart the cycle

Question 13

Summary of Calvin cycle

Answer 13

Fixation- co2 is fixed ( incorporated into an organic molecule, RuBP) in the first step
Reduction- gp is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP
Regeneration- RuBP is regenerated from the recycled TP
TP moleucle that is removes is used as a starting material or the synthesis of carbohydrates, lipids and amino acids

Question 14

function of light dependent reaction

Answer 14

energy from sunlight is absorbed and used to form ATP

hydrogen from water is used to reduce co enzyme NADP to reduced NADP

Question 15

where light in/dependant reactions take place

Answer 15

light dependant take place in the thylakoids

light independent reactions take place in the stroma

Question 16

stack of thylakoids

Answer 16

granum

Question 17

Products of light dependant stage of photosynthesis

Answer 17

Reduced NADP
ATP
oxygen

Question 18

Describe how thylakoids are adapted to function

Answer 18

Contains electron transporter chains
Membrane has large SA for light absorption
Contain photosystems/pigments

Question 19

How will structure of leaf change if in shady environment

Answer 19

• larger SA needed
• more chloroplasts
• more thylakoids

Question 20

How are heterotrophic organisms reliant on plants

Answer 20

• Plants produce organic molecules such as amino acids or glucose during the Calvin cycle
• heterotrophic animals must eat plants in order to attain organic molecules
• organic molecules are used by animals for respiration

Question 21

Primary pigments and accessory pigment

Answer 21

Primary - Chlorophyll a (yellow / green)

Accessory - Chlorophyll b (blue green) , carotenoids (orange), xanthophyll ( yellow)

Question 22

Advantage of having a range of accessory pigments

Answer 22

Absorb different wavelengths of light to maximising photolysis and photophosphorylation

Question 23

2 different polysaccharides that can be synthesised from end products of the light independent stage of photosynthesis

Answer 23

Amylose amylopectin starch
AND
Cellulose

Question 24

What are fat droplets in stroma used for

Answer 24

Reserve of raw material for membrane formation and phospholipids

Question 25

Why measuring co2 uptake is better or worse than measuring o2 production for measuring rate of photosynthesis

Answer 25

O2 is a waste product of photosynthesis that could be used in respiration causing us to underestimate
Co2 produced by respiration could be used in photosynthesis lowering co2 intake

Question 26

How light is harvested in chloroplast membranes

Answer 26

Pigments are found in the antenna complex
Photon ( light energy) is absorbed by pigment molecules
Electrons, from photolysis of water (ps2) or electron transport chain (ps1) are excited and move to higher energy levels and bounce between pigments
Energy is harnessed and passed to reaction centre PS2
Range of accessory pigments are needed to allow as much light to be absorbed

Question 27

How are electrons of PS1 and PS2 replace

Answer 27

PS2- photolysis of water

PS1 - replaced by electrons from the electron transport chain

Question 28

Purpose of photosynthesis vs respiration

Answer 28

Photosynthesis- trap energy

Respiration release energy

Question 29

How does wavelength effect penetration of light

Answer 29

Shorter wavelength and therefore higher frequency can penetrate more ( deep in the ocean)

Question 30

What is produced during the Calvin cycle

Answer 30

Organic molecules- lipids, amino acids, glucose

From molecule TP that is removed

Question 31

What process is prevented due to a fault at ps2

Answer 31

Non cyclic phosphorylation

Question 32

Photosynthesis and respiration equations

Answer 32

Photosynthesis: 6co2 + 6h2o ( with light energy) = 6o2 + c6h12o6
Respiration: glucose + oxygen = water + carbon dioxide + ATP

Question 33

Cyclic photophosphorylation vs non cyclic photophosphorylation

Answer 33

Photosystems involved - PS1 , PS2
photolysis of water - no, yes
Electron doner - P700 in PS1, water
Final electron acceptor- P700 in ps1, NADP
products - ATP, ATP oxygen and reduced NADP

Question 34

Factors effecting rate of photosynthesis

Answer 34

Light intensity - the greater the light intensity the faster the light dependant stage can occur producing more ATP and reduced NADP for the caliv cycle
Carbon dioxide concentration - required for the light independant stage of photosynthesis where CO2 is combined with RuBP during carbon fixation
Temperature - calvin cycle is effected by temprature as the light independant reactions are enzyme controlled. As temp increases KE of particles increases meaning there is more succeful collisions and reactions happen faster
Water availability
Presence of photosynthetic pigments

Question 35

Effects of light intensity and carbon dioxide concentration on levels of GP,TP and RuBP

Answer 35

• A decrease in light intensity causes a decrease in TP and RuBP concentration but a slight increase in GP concentration as it is not converted to TP due to lack of reduced nadp so it bulids up. RuBP conc decrease as lack of TP means RuBP will not form
• low concentration of co2 mean that RuBP is not fixed to form the unstable 6 carbon molecule, therefore TP and GP concentration decrease

Question 36

Structures in chloroplasts

Answer 36

Outer membrane 
Inner membrane 
Stroma 
Lamellae
Thylakoid 
Granum

Question 37

Source of co2

Answer 37

Hydrogen carbonate or burning fuel

Question 38

Measuring oxygen production from plant submerged in water

Factors that could effect the results

Answer 38

Co2 availability in water
Wether product is soluble in water
Air spaces in the spaces

Question 39

How water stress can reduce the rate of photosynthesis

Answer 39

Water stress stimulates stomatal closure, which decreases carbon dioxide available for photosynthesis
This means less carbon dioxide is fixed in the Calvin cycle and triose phosphate production decreases which forms starch and other organic substances