Chapter Five: Photosynthesis Flashcards
What is photosynthesis?
Process by which light/solar energy is used to make glucose, by converting it to chemical energy stored in chemical bonds
What is the general formula for photosynthesis?
6CO2 + 6H2O –> C6H12O6 + 6O2
Reverse of respiration
Why is photosynthesis a reduction reaction?
Because carbon dioxide (energy poor) is gaining electrons from hydrogen to become energy rich sugar
What are organisms that make their own food called?
Autotrophs
State the structure of a chloroplast
Enclosed by a double membrane
Has grana, which are layers of membranes called thylakoids
And stroma, colourless proteinaceous matrix in which grana are embedded
Where in a chloroplast do light dependant reactions occur?
Grana
Where does the Calvin cycle/light-independant reactions occur?
Stroma
Why will a plant die if only exposed to green light?
It reflects green light and absorbs all others. So due to lack of energy would not make food
What are pigments?
Substances that absorb light in the visible spectrum
Which pigment can directly participate in light dependant reactions?
Chlorophyll a
Different pigments can absorb…
Different wavelengths of light
What do other accessory pigments do?
Assist in photosynthesis by capturing and passing on photons of light to chlorophyll a, and thus expanding range of light which can be used to make sugar
Name 3 accessory pigments
Chlorophyll b
Cartenoids
Phycobilins
Differentiate the accessory pigments in terns of colours
Chlorophyll b - reflects green light
Cartenoid - yellow orange red
Phycobilin - red found in red algae
What is the condition relating light being used as energy to create sugar?
ONLY light ABSORBED can be used
What is the function of light dependant reactions?
Produce energy (ATP) and protons for the light-independent reactions
What is the function of light independant reactions?
Making sugar (PGAL)
Grana is made of stacks of thylakoids, what’s inside of these?
Hundred of light-absorbing complexes called photo systems which house chlorophyll a, b and cartenoids
In a simple equation state how ATP is made in chloroplasts (as in mitochondria) and state the one difference
Light -> chlorophyll -> excited electrons -> ETC -> proton gradient -> ATP synthetase -> ATP
However, water is not the by-product it is instead the source of electrons and protons!!
What is the name of the process which breaks down water, and what are the products?
Photolysis
Electrons, protons, oxygen
What is the role of each product from photolysis in sugar making?
Electrons - replace those lost by chlorophyll
Protons - go through ATP synthetase channels and get carried by NADP to stroma for Calvin cycle/light-independent reactions
Oxygen - waste released to atmosphere. This is how we get our oxygen!!
What is the function of the Calvin cycle?
Sugar / PGAL production
Briefly, what happens during the light-independent reactions ?
CO2, which the plant takes in through it’s veins, combines with protons and electrons from the light reactions carried by NADP to produce sugar
Give the simplified equation for the light-independent reactions
CO2 + H+ + electrons -> PGAL
What is carbon fixation and when does it occur?
Incorporation of CO2 into a sugar molecule
In the Calvin cycle
What is the full form of PGAL?
Phosphoglyceraldehyde
What is the all important enzyme in the Calvin cycle? (short and formal names)
Rubisco - Ribulose bipphosphate carboxylase
State the (4) essence of the light independent reactions
- take place in stroma of chloroplasts
- PGAL is produced
- Rubisco enzyme is required
- large amounts of ATP needed (come from light dependant reactions)
How many carbons in one PGAL?
Its a 3 carbon sugar
What is another way to say PGAL?
G3P
Glyceraldehyde-3-phosphate
Differentiate when CR and P occur
CR - all the time
P - only in light
Differentiate reactions of CR and P overall
CR - oxidation
P - reduction
What are 2 similarities between CR and P?
- rely on ETC to make a proton gradient
* ATP produced by ATP synthetase
Differentiate molecule requirements and released between CR and P
CR - O2 needed, CO2 released
P - CO2 needed, O2 released
Differentiate the proton carriers in CR and P
CR - NAD
P - NADP
Differentiate the cyclical processes contained by CR and P
CR - Krebs
P - Calvin
Why does majority of photosynthesis take place in the palisade layer?
Has many tightly packed cells that contain chloroplasts
The spongy mesophyll layer also has cells of chloroplasts but loosely packed with many AIR SPACES. What does this allow?
Exchange of oxygen, water vapor, and carbon dioxide
What does the clear epidermis do?
It does not photosynthesise
It protects the delicate underlying cells
It allows light to pass into the leaf
What is the layer above epidermis called and what’s of made of?
Cuticle
Cutin
What is the use of the cuticle?
It is waterproof so it minimises excessive water loss
What controls the opening and closing of stomates?
Guard cells
What is the use of stomata?
Allow for gas exchange with minimum water loss
Do light independent reactions occur at night?
No. They may not need light but do need H+, ATP, and NADP from the light dependant reactions
