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Photosynthesis
Which is more important?
The carnivore or the plant?
Introduction
– Ecosystems:
• A self-sufficient system consisting of a community of interacting
organisms and the abiotic factors of their habitat
– What does self-sufficient mean?
• The organisms are interdependent and ALL rely on Producers
– Producers are autotrophs
– There are two types of autotrophs • Photosynthetic: plants, phytoplankton and some bacteria
• Chemosynthetic: some bacteria: synthesis organic molecules
using energy released from exergonic reactions
– Where do you find chemoautotrophs and why?
Photosynthesis 6CO + 6H O  C H
2
2
6 12O6
+ 6O2
• What is reduced?
– CO2 (H atoms are added, or it is fixed (incorporated into organic
molecules)
• What type of energy change reaction is happening?
– Endergonic reaction, the products are at a higher energy level than
the reactants.
• Where does the energy come from?
– Light
Two important molecules
ATP –
Reduced NADP -
Adenosine triphosphate
= Universal energy currency
Nicotinamide adenine
dinucleotide phosphate
= Reducing power
Photosynthesis
• 6CO2 + 6H2O  C6H12O6 + 6O2
• Where does the H come from to reduce the CO2?
– From water.
• So what has to happen to the water? What is this process
called?
• Photolysis: splitting of water using light energy
• Glucose is a chemical energy store. What happens to it
during respiration?
– Energy is released when it is oxidised during respiration
Importance of Photosynthesis
– Why is it so important?
• Energy from the sun is trapped by autotrophs and can then be passed
along food chains
– Other than respiration, what is glucose used for in plants?
• Cellulose, starch, proteins, lipids, phospholipids, DNA, RNA (add to
balanced symbol equation of photosynthesis- showing what happens
after photosynthesis)
– Cellulose, starch and lipids need no additional elements (they
also consist of C, H and O)What is needed to produce
• proteins?
– Nitrates (sulphur for some amino acids)
• Phospholipids?
– Phosphates
• DNA and RNA?
– Both Nitrates and Phosphates
– What happens to O2? What is the significance of this?
– It is released as a waste product: the composition of atmospheric gases has
changed as a result of photosynthesis: this makes aerobic respiration possible
Leaf structure– Where does most photosynthesis take place?
• In palisade layer of the leaf
– Review how a leaf is adapted to its function.
– Complete Activity 5.06a- Leaf Structure
NADP
• Nicotinamide adenine dinucleotide diphosphate
– A co-enzyme
– Works together with enzymes in processes like
photosynthesis and respiration where there are lots
of steps (and enzymes) involved
– Has two forms: an oxidised and a reduced form
– Oxidised: NADP (oxidised) or NADP+
– Reduced: NADP (reduced) or NADPH2
– Are electron transfer molecules: transferring e- from
1 molecule to another
How photosynthesis works
Light dependent stage
Light independent stage
Reactants
Products
Water, oxidised NADP,
ADP and Pi
Reduced NADP, ATP, and
carbon dioxide
Reduced NADP, ATP,
Oxygen
Glucose, oxidised
NADP, ADP and Pi
Photolysis using light
energy
Reduction of CO2
Reactions
+
The two stages of Photosynthesis
– Where does the Hydrogen come from to reduce the CO2?
• from the photolysis of water.
– Do CO2 and water make direct contact so that the H can be
transferred from the water to CO2? Explain.
• No, the reduced co-enzyme NADP transfers the H
– What transfers the energy from light to the carbohydrate fuel
glucose?
• ATP and reduced NADP
• Complete Activity 5.06b Summary of
Photosynthesis (Q14)
• Q 5.12
Light Dependent reactions-pages 18-20
– What is a pigment? Which pigment is
involved in photosynthesis?
• Absorbs light at certain wavelengths and reflects
all other wavelengths of light
• Chlorophyll is the main one, but there are other
pigments
Which colours are absorbed?
Reflected?
5.06c- Light Reactions
Complete # 1-3
Extension 5.3 Light Dependent
Reactions
Read the top paragraph
As well as chlorophyll accessory pigments
are present too: They absorb light and pass
energy onto chlorophyll
The reaction takes place where the
chlorophyll is.
What is a photosystem?
Arrangement of photosynthetic pigments
in the membrane
Two Photosystems• Photosystem I where chlorophyll absorbs
at 700nm wavelength
• Photosystem II where chlorophyll
absorbs at 680nm wavelength
• Identify with an arrow the higher energy level
• Identify the light striking the photosystems.
• Label the electron carriers
• What happens when light is
absorbed by the chlorophyll in
the reaction centre?
• Where in plant cell is the
electron transport chain?
• What is the purpose of the
electron transport chain? Define
photophosphorylation
• Add the NADP and reduced
NADP to the diagram.
Compare the diagram above with
figure 5.22.
• Where did the electrons and H+
ions come from?
Extension 5.3 Light Dependent Reactions for the
more ambitious.
– Compare cyclic and non-cyclic photophosphorylation• What happens to the electrons in– Cyclic
– Non-cyclic
• Reactants and Products?
– Cyclic
– Non-cyclic
• Answer # 1-6
Chemiosmosis
read page 21
• As electrons pass along the electron carriers, energy
released is used to pump H+ into the thylakoid space.
• H+ concentration builds up, pH drops to about 5
• There is now a pH gradient between inside the
thylakoid space and the stroma, which is about pH 8.
• Chemiosmosis then happens, H+ ions diffuse across the
selectively permeable thylakoid membrane down a
concentration gradient back into the stroma. This
diffusion powers the phosphorylation of ADP via ATP
synthase.
Photosynthesis video. Use light dependent first part only.
https://www.youtube.com/watch?v=joZ1EsA5_NY
• How do the pair of elections move from the chlorophyll to the
electron transport system?
• How are the electrons lost from the chlorophyll replaced?
• How is ATP synthesized when electrons pass between b and
c?
• NADP is not shown here. What is its role in the light
dependent stage of photosynthesis?
Light independent reactions
1. Carbon fixation.
CO2 converted to organic
carbon. Carried out by
RuBisCo enzyme.
2. Reduction.
H is added by NADPH
made during the light
reactions. Requires energy
input ie. ATP.
3. Regeneration of RuBP.
Requires ATP. Therefore
the cycle can begin again.
Light independent reactions-
Read pages 22-
24
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
Complete Activity 5.06d The Calvin Cycle
Simplified Calvin Cycle
Activity 5.6 How Calvin won the Nobel
Prize
• What was the aim
of the experiment?
• What is Chlorella?
• Why was radioactive C added?
Can be visualized using photographic film
Activity 5.6 How Calvin won the Nobel
Prize
• How did he identify what had been
produced? Chromatography
Complete # 1-5.
Simplified Calvin Cycle
Chloroplasts
• Animal cell ultrastructure
– sER, rER, golgi, nucleus, nucleolus, ribosomes, lysosomes,
mitochondria, membrane, centrioles
• What are the differences between plant and animal cells?
– Cell wall, vacuole, amyloplasts, no centrioles, chloroplasts,
pits, plasmodesmata
• Box on page 24
Lumen
Limiting Factors
– Define limiting factors• the factor which limits the rate of
photosynthesis, as this factor
increases the rate of photosynthesis
increases and vice versa, this factor is
furthest from its optimum.
– List some factors which COULD be
limiting in photosynthesis?
• CO2 conc, light intensity,
temperature, water supply
Limiting Factors
• For each of the factors below
sketch a graph of its affect on
the rate of photosynthesis
– Light intensity
– Carbon dioxide
concentration
– Temperature
– Light wavelength
– Water availability- too
complex to graph as water is
involved in many processes
Do you think that there is a link
between productivity and
biodiversity?
Biodiversity hotspots around the world.