Photosynthesis revision

For F214 January 25th 2010

Revising photosynthesisBasic knowledge

1) Explain the similarities and differences between an autotroph and a heterotroph

2) Describe the relationship between photosynthesis and respiration in living organisms

3) Write the overall chemical equation for photosynthesis4) Name the 2 sets of reactions involved in

photosynthesis and state where exactly each occurs5) Explain why the very large surface area provided by

the grana is important in photosynthesis6) Draw a diagram of a chloroplast and label it to show

how it is adapted for photosynthesis

Autotrophs

• Autotrophs are organisms that can synthesise complex organic molecules such as

carbohydrates, lipids, proteins, DNA, RNA, vitamins

from inorganic molecules, using an energy source.

Heterotrophs

• Heterotrophs digest complex organic molecules into simpler, soluble ones. They then synthesise molecules they need from these.

Examples of heterotrophs are

Animals Fungi Some bacteria

Photosynthesis: 2 stage process

• Takes place in chloroplasts

CHLOROPHYLLLight

Water

Oxygen

Carbon dioxide

Carbohydrate

The cells and tissues of a leaf

Chloroplasts under LM and EM

1. Chloroplasts in an Elodea leaf using LM

2. Chloroplasts in a maple leaf using TEM

3. TEM of a single chloroplast

Chloroplast

Revising photosynthesis Light dependent reactions

1) List the products of the light dependent reaction2) Distinguish between an absorption spectrum

and an action spectrum3) State the wavelength of visible light at which

least photosynthesis takes place. Why is this?4) State the role of accessory pigments in a

photosystem5) Describe the different roles of photosystems 1

and 26) Describe the similarities and differences

between cyclic and non-cyclic photophosphorylation

Photosynthesis biochemistry p17 workbook p63 textbook

The light dependent stage on the thylakoid membranes of the chloroplast

Using light energy to make ATP (= photophosphorylation)

Also produces reduced NADP (= coenzyme NADPH)

There are 2 parts – cyclic and non-cyclic photophosphorylation

Light harvesting clusters or photosystems p12-13 workbook, p61 textbook

Quite complex animation!• http://www.learnerstv.com/animation/animation.php?ani=179&cat=biology• http://www.uic.edu/classes/bios/bios100/lectures/ps01.htm(useful info!)

cyclic photophosphorylation

chlorophyll a in photosystem I

P 700

excited electrons 2e-

electron acceptor + chain of electron carriers

ADP + Pi ATP

2e-

photosystem II P680 photosystem I P700

e- e-

ADP + Pi ATP

NADP + H+

reducedNADP

photolysis of water

H2O OH- + H+

oxygen O2

NonNon-cyclic photophosphorylation

Non-cyclic photophosphorylation p

http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html

Making ATP by photophosphorylation and chemiosmosis (needed in the light independent stage)

p14

A photon of light hits a chlorophyll molecule2 electrons get excited!They are released from chlorophyll to electron acceptorsThey travel along electron carriers on thylakoid membranesEnergy released during electron transport is used to pump

H+ into thylakoid space between membranesH+ (proton) gradient is formedH+ move down gradient through ATP synthase enzymes

making ATP So ATP is made using light energy = photophosphorylation

http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atpsynthase_an.html

The role of water in the light dependent stage

• Light energy makes it split = photolysis• Produces hydrogen ions (protons) +

electrons + oxygen atoms

• Hydrogen ions ATP synthase • Hydrogen ions reduce NADP• Electrons electron acceptors and

carriers• Oxygen waste product (but needed in

respiration)

Revising photosynthesisLight independent reactions / Calvin cycle

1) Explain the term carbon dioxide acceptor2) Describe the reaction catalysed by the

enzyme rubisco3) State the roles of ATP and reduced

NADP in the Calvin cycle4) List the possible fates of triose phosphate

formed in the Calvin cycle. Which is the most likely to happen?

CO2 RuBP

RuP

ATP

ADP

2x GP ATP ADP+

Pi

NADPH NADP

2x Triose P

Hexose sugar

2 x3C

5C

5C

2 x3C

6C

RUBISCO

Revising photosynthesisLimiting factors

• Explain what is meant by a limiting factor• List 3 factors that could limit the rate of photosynthesis

at a high concentration of carbon dioxide• Explain why the rate of photosynthesis increases as

the light increases from low to high.• Explain why increasing the light intensity does not

produce a continuous increase in the rate of photosynthesis

• Exaplin why at low light intensities temperature changes have little effect on the rate of photosynthesis

• Describe how to investigate experimentally the factors that affect the rate of photosynthesis. Include how you will make the data valid and reliable.

How did Engelmann explain these results?

Light intensity and the compensation point refer to bicarbonate indicator expt