5.6 Photosynthesis

Question 1

the interrelationship between the process of
photosynthesis and respiration

Answer 1

both are important in cycling carbon dioxide and oxygen in the atmosphere
the products of one process are the raw materials for the other

Question 2

autotroph

Answer 2

uses light or chemical energy to synthesise large organic molecules from smaller imorganic ones

Question 3

heterotroph

Answer 3

obtain energy/ large organic molecules from autotrophs

Question 4

two types of autotrophs and what energy they use

Answer 4

chemoautotrophs - uses chemical energy
photoautotrophs - uses light energy

Question 5

equation for photosynthesis

Answer 5

6CO2 + 6H20 + energy from photons -> C6H1206 + 6O2

Question 6

what is photosynthesis

Answer 6

process of converting light energy from sunlight into chemical energy to synthesise large organic molecules

Question 7

photon

Answer 7

a particle of light (each countains a quantum of energy)

Question 8

main product of photosynthesis and what its converted/stored as

Answer 8

monosaccharide sugar - coverted to disaccharides for transport and starch for storage

Question 9

what is photosynthesis an example of (explain it)

Answer 9

carbon fixation - process by which carbon dioxide is converted to sugars

Question 10

what does photosynthesis/ carbon fixation help regulate

Answer 10

carbon dioxide levels in the atmosphere and oceans

Question 11

what happens during respiration

Answer 11

glucose/ other organic molecules are oxidised to produce carbon dioxide and water and releases chemical energy

Question 12

explain why heterotrophs use respiration

Answer 12

obtain energy from it by digesting the larger complex organic food to smaller molecules , energy released can be used in the organisms metabolism

Question 13

explain what the compensation point is

Answer 13

when photosyntheis and respiration proceed at the same rate so there is no net gain or loss of carbohydrate

Question 14

what is the compensation period

Answer 14

the time taken for a plant to reach its compensation point

Question 15

why does repiration not vary much but photosynthesis does across a 24 hour period

Answer 15

photosynthesis = dependant on sunlight for energy
respiration = oxygen always present
varies due to heat = increase enzyme activity

Question 16

state the structure of a chloroplast

Answer 16

outer and inner membrane (double)
stroma
granum
thylakoids
(intergranal) lamallae

Question 17

granum

Answer 17

inner part of chloroplast made of stacks of thylakoid membranes where the light dependant stage of photosynthesis takes place

Question 18

photosynthetic pigment

Answer 18

pigment that absorbs specific wavelengths of light and traps the energy associated with the light

Question 19

photosystem

Answer 19

system of photosynthetic pigments found in thylakoids that create a funnel shaped structure, to trap photons and is funnelled to the primary pigment reaction centre

Question 20

stroma

Answer 20

fluid filled matrix of chloroplasts where the light independant stage of photosynthesis

Question 21

thylakoid

Answer 21

flattened membrane bound sacs that contain photosynthetic pigments or photosystems and is the site of the light dependant stage

Question 22

Role in DNA in plants for photosynthesis

Answer 22

Loop of DNA contains genes that code for some of the proteins needed
Proteins assembled at the chloroplasts ribosomes

Question 23

What is chlorophyll

Answer 23

Light capturing photosynthetic pigment that absorb wavelengths of light

Question 24

Name types of chlorophyll

Answer 24

Chlorophyll a
Chlorophyll b
Chlorophyll carotenoids
Phaeophytin

Question 25

What is the absorption spectrum

Answer 25

Shows the wavelengths of light absorbed by different photosynthetic pigments

Question 26

What wavelength of light can the different types of chlorophyll absorb and describe the shape of the graph

Answer 26

A = 400 to 725 nm - double peak , highest one at 425 and slighlty smaller one at 700 B = 400-500nm and around 640nm - high peak at 450 and smaller peak at 650 Carotenoids = 400-500nm - very small curve Xanthophylls = 375-550nm - sharp spike (triangle) bacteriochlorophyll = up to 850nm - widest range, highpeak at 800 and peak at 350

Question 27

what light wavelength can PS1 and PS2 absorb

Answer 27

PS1= 700nm PS2= 680nm

Question 28

Describe how to separate photosynthetic pigments using chromatography

Answer 28

Scraping/ mashing leaf Using two microscope slides Spot the chromophyll onto a slide coated with a thin layer of chromatography material Solvent separates pigments as they have different Rf values

Question 29

what photosystems are used in non cyclic and cyclic photophosporylation

Answer 29

non cyclic = PS2 and PS1 cyclic = PS1

Question 30

Where are photosynthetic pigments found

Answer 30

photostems In thylakoid membranes

Question 31

name the steps of light dependant stage of photosynthesis

Answer 31

light harvesting photolysis photophosphorylation formation of reduced NADP

Question 32

describe photolysis

Answer 32

splitting of water using light energy splits it into protons, electrons and oxygen 2H20-> 4H+ + 4e- + O2

Question 33

name the two types of photophosphorylation and what photosystems it uses

Answer 33

non cyclic - PS1 and PS2 cyclic - only PS1

Question 34

what does non cyclic and cyclic photoposhorylation produce

Answer 34

non cyclic - ATP, oxygen and reduced NADP cyclic - smaller quantities of ATP

Question 35

describe cyclic photophosphorylation

Answer 35

only uses PS1 as light energy strikes PS1= pair of electrons get excited = passes to an electron acceptor = goes down electron transport chain = passes back to PS1

Question 36

describe non cyclic photophosphorylation

Answer 36

PS1 and PS2 used electrons get excited passess to electron acceptor molecule and goes down the ETC (electrons in PS2 get replaced by e- produced by photolysis) sets up a proton (H+) gradient (proton pump ase- release energy) known as chemiosmosis electrons move to PS1 from PS2 , replaces e- lost by light in PS1 higher conc. of H+ ions inside the thylakoid space - sets up gradient - protons diffuse down the gradient through channels associated with ATP synthase enzymes = flow of protons causes ADP + Phosphate = ATP as protons pass through channel they are accepted with electrons lost from PS1 by light - NADP becomes reduced catalysed by NADP reductase

Question 37

how has light energy been converted to chemical energy

Answer 37

in the form of ATP by photophosphorylation

Question 38

what products from LDS are used in the light independant stage

Answer 38

ATP and reduced NADP

Question 39

what is the LIS stage called

Answer 39

the calvin cycle

Question 40

what does the LIS produce

Answer 40

6 turns of the cycle = 2TP molecules which is made into carbohydrates ( starch etc)

Question 41

main stages of the calvin cycle

Answer 41

RuBisCO catalyses CO2 and RuBP creates an unstable 6carbon compund which splits into two 3 carbon compounds (2GP) the C02 is now fixed GP is reduced to 2 TP by hydrolysis of 2ATP and reoxidation of 2NADPH from LDS some of the TP is used to form hexose sugars (1/6) some of the TP is used to regenerate RuBP and the cycle starts again (5/6) 6 turns of the cycle makes 2TP as a product and 6RuBP

Question 42

uses of triose phosphate

Answer 42

used to synthesise organic compounds 2TP can make 1 glucose - glucose converted to starch, sucrose, cellulose - some used to synthesise amino acids, fatty acids and glycerol

Question 43

how does daylight impact the LDS and LIS

Answer 43

light needed in the LDS to produce ATP AND reduced NADP for the LIS - continuously needed in the LDS hydrogen ions are pumped into the thylakoid space = raises pH to 8 = optimum for enzyme RuBisCO in daylight = magnesium ion concentration increases in the stroma = act as a cofactor for RuBisCO the LIS stage doesn't directly use light but needs to use the products created by light

Question 44

GP TP RuBP RuBisCO

Answer 44

glycerate phosphate triose phoshpate ribulose bisphosphate ribulose bisphosphate carboxylase oxygenase

Question 45

name limiting factors of photosynthesis

Answer 45

light intensity C02 concentration temperature

Question 46

describe how light intensity can impact photosynthesis

Answer 46

as light intensity increases the rate of photosynthesis increases when there is little light - GP cannot be reduced to TP as LDS products not produced - TP levels fall and GP accumlates - RuBP cannot be regenerated

Question 47

describe how C02 concentration can impact photosynthesis

Answer 47

if C02 levels decrease (below 0.01%) then RuBP cannot acept it and accumulates GP cannot be made so TP not made

Question 48

describe how temperature can impact photosynthesis

Answer 48

as temp increases the ROP increases if no other factors are limiting above 30 = growth rates reduce due to photorespiration = 02 competes with C02 for Rubisco enzyme = less C02 fixed and GP formed = so less TP produced above 45 = enzymes denature = reduce levels of GP and TP and eventually RuBP as not being regenerated

Question 49

define water stress

Answer 49

a condition a plant experiences when water supply becomes limiting

Question 50

describe how water stress can impact photosynthesis

Answer 50

not enough water available = roots cannot take up enough to reduce water lost through transpiration = cells lose water and become plasmolysed = stomata closes = tissues become flaccid and wilt = ROP decreases

Question 51

how can you measure the rate of photosynthesis

Answer 51

using a photosynthometer

Question 52

limitations of using a photosynthometer

Answer 52

oxygen produced can be used in respiration dissolved nitrogen in gas needs to be air tight/ no air bubbles

Question 53

how do you collect results of a photosynthometer

Answer 53

gas given off by the plant is collected in the capillary tube can be measured against the scale length of bubble x (pie)r*2 = volume of gas collected