topic 5 photosynthesis

Topic Five : Photosynthesishttp://sodandmulch.com/wp-content/uploads/2012/03/Oak-Tree.jpg

Essential idea: Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life.

2.9 Photosynthesis

http://foodphotographyblog.com/wp-content/uploads/2014/07/Hass-Tree-Canopy.jpg

California Avocado Trees

UnderstandingsStatement Guidance

2.9 U.1 Photosynthesis is the production of carbon compounds in cells using light energy.

2.9 U.2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.

2.9 U.3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colors.

Students should know that visible light has wavelengths between 400 and 700 nanometres, but they are not expected to recall the wavelengths of specific colours of light.

2.9 U.4 Oxygen is produced in photosynthesis from the photolysis of water.

2.9 U.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

2.9 U.6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

Applications and SkillsStatement Guidance

2.9 A.1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.

2.9 S.1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

2.9 S.2 Design of experiments to investigate the effect of limiting factors on photosynthesis.

Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water.

2.9 S.3 Separation of photosynthetic pigments by chromatograph. (Practical 4)

Paper chromatography can be used to separate photosynthetic pigments but thin layer chromatography gives better results.

Photosynthesis: Capturing Energy


• Living organisms require complex carbon compounds to carry out life processes and build the structures in their cells

• Photosynthesis involves the conversion of light energy into chemical energy (carbohydrates, lipids, protein and nucleic acids).

• Chloroplasts absorb light energy from the sun and convert this energy into chemical energy (glucose) to be used by the organisms for energy.

Light energy converted into chemical energy • Producers contain

chlorophyll • Chlorophyll can trap light

energy (photons). • The chlorophyll convert this

energy into chemical energy. • The chemical energy is

transferred as bond energy (electrons)and is transferred in turn to other chemical energy stores called carbohydrates, lipids and protein.

• These molecules are called organic molecules.

Autotrophs and Chemotrophs• Carbon fixation is the process of building complex

carbon compounds. The process occurs from simple compounds (CO2) using light energy or other chemical bond energy (SO2) to form glucose (a useable form of chemical energy for living things.

PhotoautotrophsPhotoautotrophs organisms that fix carbon, using carbon dioxide as a carbon source, and combine it with water

Chemoautotrophs Chemoautotrophs provide nearly all the energy used by living systems on Earth where light is not available


Overview of Photosynthesis• Photosynthesis is a redox reaction:Photosynthesis is a redox reaction:• Carbon dioxide is reduced to sugarCarbon dioxide is reduced to sugar• Water is oxidized to molecular oxygenWater is oxidized to molecular oxygen

Carbon dioxide + Water + Light Glucose + OxygenCarbon dioxide + Water + Light Glucose + Oxygen

C6H12O6 + 6O26 CO2 + 6 H2O

Reduction

Oxidation


http://highered.mheducation.com/sites/9834092339/student_view0/chapter39/photosynthetic_electron_transport_and_atp_synthesis.html

http://highered.mheducation.com/sites/9834092339/student_view0/chapter39/calvin_cycle.html

http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/index.html

Chloroplast

• Double outer membrane

• Thylakoids is the internal membranes called which is the location of the light dependent reaction

• Grana are stacks of thylakoids

• Stroma cytoplasm that surrounding the thylakoids and grana. This is the location of the light independent reaction.

Partition of Function in the ChloroplastPartition of Function in the Chloroplast

1. The light-dependent reaction (the harvesting of light) occur on the thylakoid membrane.

2. The light-independent reaction (carbon fixation reaction or the formation of carbohydrate), which occurs in the stroma.


Photosynthesis occurs in two main phases:

1. Light Dependent Reaction A. Energy of sun is trapped by chlorophyll molecules (oxidation)

B. ADP is reduced to ATP with NADP+ reduced to NADPH, both are used to fix carbon.

C. The reaction must have light to take place.

D. This reaction takes place on the thylakoid membranes.


http://3-8photosynthesis.tumblr.com/

2.9 U.2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.

• Light from the sun is composed of a range of wavelengths.• The visible spectrum is the portion of the electromagnetic spectrum that is

visible to or can be detected by the human eye.• Electromagnetic radiation in this range of wavelengths (380 to 750 nm) is

called visible light.• All these wavelengths together form white light, with violet/blue colors having

shorter wavelengths (more energy) and red colors having longer wavelengths (less energy).

http://www.schome.ac.uk/wiki/images/3/36/EM_spectrum.jpg


http://en.wikipedia.org/wiki/Plant_anatomy#/media/File:03-10_Mnium2.jpg

Moss: Mnium stellare

• Sunlight is a mixture of different wavelengths of visible light, which we see as colors.

• The two main colors of light that are absorbed by chlorophyll are red and blue light.

• The main color that is reflected is green light, which is why most leaves look green

Pigments

• A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed).

• Chlorophyll is a complex molecule. Several modifications of chlorophyll occur among plants and other photosynthetic organisms.


Chlorophyll

Chlorophyll a• All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and

cyanobacteria) have chlorophyll a. • Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red

wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths.

• Chlorophyll a is the main photosynthetic pigment in all organisms except bacteria


Accessory pigments

• Accessory pigments absorb energy that chlorophyll a does not absorb. Accessory pigments include chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids (such as beta-carotene).

http://classroom.sdmesa.edu/eschmid/Lectur40.gif

• Pigments in the thylakoid membrane absorb light at certain wavelengths

• The light energy causes electrons held by pigments to raise to higher energy states. This converts the light energy into a form of chemical energy.

• These excited electrons are passed from pigment to pigment until the reach a molecule called the reaction center.

• The reaction center pass the electrons to electron acceptors in the thylakoid membrane


In the absence of equipment use the virtual lab and self-test quiz:http://www.phschool.com/science/biology_place/labbench/lab4/pigsep.html

Simplified Bioknowledgy protocol based on the SaPS outline: https://app.box.com/s/i8cc161713atmk7ks5zoex1psyrjir89

Thin layer chromatography for photosynthetic pigments

SAPS have published two (slightly) different protocols:•http://www.saps.org.uk/secondary/teaching-resources/189-investigation-of-photosynthetic-pigments-in-green-plants•http://www.saps.org.uk/secondary/teaching-resources/181-student-sheet-10-thin-layer-chromatography-for-photosynthetic-pigments

What pigments can you find and identify in a leaf?

Gather leaves of different types and colors and use Thin Layer Chromatography (TLC) to separate the pigments, including chlorophyll present in a leaf.

2.9 S.3 Separation of photosynthetic pigments by chromatograph. (Practical 4)

http://www.phschool.com/science/biology_place/labbench/lab4/pigsep.html

https://app.box.com/s/i8cc161713atmk7ks5zoex1psyrjir89

http://www.saps.org.uk/secondary/teaching-resources/189-investigation-of-photosynthetic-pigments-in-green-plants

http://www.saps.org.uk/secondary/teaching-resources/181-student-sheet-10-thin-layer-chromatography-for-photosynthetic-pigments




2.9 U.4 Oxygen is produced in photosynthesis from the photolysis of water..

• Chlorophyll in the thylakoid membrane is excited by light absorption.

• Electrons (e-) in the chlorophyll are energized to an excited state.

• e- captured by primary electron acceptor

• Photolysis is one of the first step the light dependent reactions of photosynthesis.

• H2O is split to replace e- O2 formed

• Water (H2O) is split by photons of light to produce 4 e- + 4H+ + O2 (lost as waste to the atmosphere)

Photolysis: Splitting a Water Molecule to produce ATP , H+ and O2

Absorption spectra are obtain

from samples of pigment.

Different wavelengths ofDifferent wavelengths of

light are passed throughlight are passed through

and the absorption isand the absorption is

measured using a colorimeter.measured using a colorimeter.

This absorption spectra for This absorption spectra for

chlorophyll shows:chlorophyll shows:

•absorption of blue light

•absorption of red light

•green light is reflected.

2.9 S.1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis

% o

f th

e m

axim

um r

ate

of

phot

osyn

thes

isThis shows the absorbance of light by photosynthetic pigments (here chlorophyll) for all the wavelengths of light.

(Edited by Chris Paine)

http://i-biology.net/

Action Spectrum: Measures the rate of Photosynthesis

•The rate of photosynthesis is

measured at different

wavelengths.

•The maximum rate are at the

blue end and red end of the

visible spectrum.

•The lowest rates are in the

yellow greens.

•Chlorophylls are absorbing blue

and red light well but not green.

2.9 S.1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis

This shows the rate of photosynthesis for all the wavelengths of light as a % of the maximum possible rate.

% o

f th

e m

axim

um r

ate

of

phot

osyn

thes

is

(Edited by Chris Paine)

http://i-biology.net/

2. The Light Independent Reaction

A. Uses the chemical energy from the LDR (ATP and NADPH2) to fix atmospheric carbon (CO2)into organic molecules such as glucose.

B. The process does not require light and can occur in both the light and dark periods.

C. This reaction takes place in the stroma


http://3-8photosynthesis.tumblr.com/

Factors that limit the rate of photosynthesis• The rate of photosynthesis can be affected by light intensity, carbon

dioxide concentration and temperature.• Under a given set of conditions only one factor will affect the rate of

photosynthesis this factor is at its minimum and is called the limiting factor.

• As has been shown photosynthesis is a process with many individual steps or stages.

• The overall rate of photosynthesis is determined by the step that is proceeding most slowly (rate-limiting step).


Light intensitya) As the intensity of light is increased the rate of reaction of photosynthesis

increases. The rate maybe limited by a lack of NADP+

(b) Light intensity has saturated the plants. The rate now remains constant for any further increase in light intensity.

(c) Note that light intensity to achieve maximum rate of photosynthesis is less than the intensity of light in summer. Light in not normally a limiting factor


Temperature• The optimum temperature in a temperate climate is about 25° C.• However. Temperature has many effects on a plant and the graph should be

treated with caution.• Temperature has just as many effects on respiration, transpiration and

translocation all of which in turn affect photosynthesis.


(a). As the concentration of CO2 is increased the rate of photosynthesis increases.

(b).The concentration of CO2 has saturated the process. The maximum rate of reaction has been achieved. Further increases in CO2 do not increase the rate. The rate is now constant.

(c) Note this is the normal concentration of CO2 in the atmosphere.! Therefore this is often the limiting factor.

Carbon Dioxide (CO2)


2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.

http://commons.wikimedia.org/wiki/File:Blue_Marble_Eastern_Hemisphere.jpg

Primordial Earth had a reducing atmosphere that contained very low levels of oxygen gas (approx. 2%).

Cyanobacteria (prokaryotes) containing chlorophyll first performed photosynthesis about 2.5 billion years ago.

Photosynthesis creates oxygen gas as a by-product (by the photolysis of water).

Oxygen levels remained at 2% until about 750 million years ago (mya). From 750 mya until the now there has been a significant rise to 20%.

Oxygen generation also allowed the formation of an ozone layer (O3). Ozone shielded the Earth from damaging levels of UV radiation. This, in turn, lead to the evolution of a wider range of organisms.

Iron compounds in the oceans were oxidized:•The insoluble iron oxides precipitated onto the seabed.•Time and further sedmentation has produced rocks with layers rich in iron ore called the banded iron formations.

Oxygen in the atmosphere lead to the production of oxidized compounds (e.g. CO2) in the oceans.

http://commons.wikimedia.org/wiki/File:Blue_Marble_Eastern_Hemisphere.jpg

Microfossils of Prokaryotes•Evident as tiny structures that look very much like cyanobacteria and other modern-day prokaryotes.

In rocks formed as long ago as ~3.5 bybpRadiocarbon dating from similar rocks suggest life formed perhaps

even 3.8 bybp•Stromatolites are layered pillow-like rock structures

Layers of prokaryotic cells and sediment Are plentiful in ancient rocks, formed large reefs Found today only in certain limited environments, such as a few hot springs

and in Shark Bay, a Western Australian location


Stromatolites• In the beginning photosynthetic systems may have resembled these

stromatolites at Shark Bay, Western Australia


• Oxygen begins to accumulate about 2.7 bya, known as the “Great Oxidation Event” – reducing → oxidizing atmosphere

• evidence in banded iron in rocks = rusting• makes aerobic respiration possible

– photosynthetic bacteria (blue-green algae)• The oxygen remained at about 2% until about 700 mya. There was then a

significant rise in oxygen until it reached about 20%.• This lead to a huge increase in species as multicellular organisms evolved


Rust band in the ocean floor created by the presence of Oxygen


Evidence for O2 production:

• Banded Iron Formations (BIF)

• BIF found in ocean sediments red bands are high in Fe2O3 and Fe3O4 (red bands)- forms when reduced iron reacts with O2


Formation of Aerobes• Bacteria which need free oxygen for their survival• Aerobes came about after onset of photosynthesis• Critical stage; allowed formation of more complex organisms.

Producing more energy from glucose than anaerobic metabolism• Out-compete anaerobes for populating the Earth• Stabilized atmosphere



http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/

Glucose production can be (indirectly) measured by a change in a plant's dry biomass.starch levels in a plant (glucose is stored as starch)can be identified by staining with iodine solution, this can be quantitated using a colorimeter.

http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/


Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?

http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg

http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.jpg







The independent variable•Only one limiting factor should be investigated at a time•The range of values should reflect conditions experienced by the organism•The range of values should allow the limiting factor to range from values that restrict photosynthesis to values that allow photosynthesis to happen at it’s optimum rate.•The increments should be sufficiently in size that a trend can be clearly detected





Dependent variable•An accurate method for measuring the rate of photosynthesis needs to be used.•Oxygen production per time unit is• recommended.

Leaf discs are a successful and easy way to measure oxygen generation by leaveshttp://www.saps.org.uk/secondary/teaching-resources/284-investigating-photosynthesis-with-leaf-discs

. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis




The control variables•These should include the limiting factors not being investigated.•Other key control variables should include any factor that affects a metabolic pathway controlled by enzymes, e.g. pH.•Ambient light should be considered as it affects the wavelength and intensity of light absorbed by the organism.•The values chosen for the control variables should be close to their optimum values so that the control variables do not limit photosynthesis.(If the control variables limit photosynthesis it may not be possible to see the impact of the limiting factor being investigated)

Nature of Science: Experimental design - controlling relevant variables in photosynthesis experiments is essential. (3.1)




The control variables - Nature of Science•Explain why it is essential to control the limiting factors not being investigated.•Evaluate which of the identified reasons are the most important.

Bibliography / Acknowledgments

topic 5 photosynthesis

Education