Module 5 - photosynthesis Flashcards
what is photosynthesis?
It is the process whereby light energy from the sun is transformed into chemical energy and used to synthesise large organic molecules from smaller, inorganic substances
What does photo mean?
light
what does synthesis mean?
Making something
what is the chemical equation for photosynthesis ?
6C02 + 6H2O -> C6H12O6 + 6O2
what is the equation for photosynthesis ?
Carbon dioxide + water -> glucose + oxygen
What is Van Helmont’s experiment ?
- He grew a willow tree in a tub for 5 years
- weighted the mass of the tree and the soil in the beginning and end of the experiment
- this demonstrated that something is being incorporated into the biomass of the tree causing it to increase its mass
- the substance is not being derived from soil
What did Van Helmont conclude?
- That the increase in mass was the mass of the added water.
- This is partly true but later it was shown that carbon dioxide was also contributing to the increase in mass
So why did some of the soil gain mass in Van Helmont’s experiment?
- in order to make proteins it is necessary for the plant to accquire nitrogen in the form of nitrates.
- these are obtained from the soil along with other minerals which accounts for the slight loss of mass from the soil noted after 5 years
Is a willow tree a hetertroph or autotroph? Why?
- heterotroph
- energy was required for the conversions of small in organic molecules into larger organic molecules.
- energy was in the form of light
What are autrophs?
- They are organisms that are capable of synthesising their own complex organic food molecules from simpler inorganic ones
- they are self -feeding and organisms in this group make use of an external, non-living supply of energy to drive their self-feeding way of life/
What are photoautrophs?
This captures the sun’s energy and use it to convert simple inorganic molecules such as carbon dioxide and water, into complex, energy-rich organic food
what are chemoautrophs?
They obtains the energy they need for food manufacture by oxidising inorganic molecules such as ammonia and hydrogen sulphide.
- they do not use light
what are species of chemoautrophs known as?
Known as Nitrifying bacteria
- plays an essential part in the nitrogen cycle
- nitrifying bacteria oxidises ammonium and nitrate ions
what happens to energy releases by the oxidation reactions?
It is used by the bacteria to manufacture their own food
what happens to the nitrates absorbed by green plants?
- Nitrogen is incorporated by green plants and nitrogen is incorporated into nitrogen-containing organic compounds
What are primary producers?
organisms can produce their own food through photosynthesis
what type of molecules do aututrophs synthesise?
lipids, proteins, nucleic acids and vitamins
what does auto mean?
self
what does troph mean?
nutrition
what does hetero mean?
another
what does troph mean?
nutrition
what are heterotrophs?
These organisms cannot make their own food. They ingest and digest complex organic molecules releasing the chemical potential energy stored in them.
- these molecules then can be converted into molecules such as glycogen, lipids, proteins and nucleic acids
examples of heterophs?
- animals
- fungi
- some bacteria
Do autotrophs respire?
yes
Can autotrophs synthesise complex organic molecules from simple inorganic molecules?
yes
do autotrophs use light energy?
photoautotrophs - yes
chemoautotrophs - no
do autotrophs hydrolyse complex organic molecules?
yes
examples of autotrophs ?
- plants
- algae
- some bacteria
do heterotrophs respire?
yes
Can heterotrophs synthesise complex organic molecules from simple inorganic molecules?
No
do heterotrophs use light energy?
no
do heterotrophs hydrolyse complex organic molecules?
yes
what is a compensation point?
when photosynthesis and respiration proceed at the same rate, so that there is no net gain or loss of carbohydrates, the plant is then at compensation point
what is a compensation period?
the time a plant takes to reach its compensation point
where in the cell does photosynthesis occur?
Inside the chloroplasts
what do the inner membrane and outer membrane of the chloroplast make up?
They make up the chloroplasts envelope
Structure of the thylakoid membrane?
- They are arranged in stacks which contain pigments including chlorophyll.
- these stacks of membrane are called grana
where does the light dependent reaction occur?
Thylakoid membrane
where does the light Independent reaction occur?
Stroma
where are the photosynthetic pigments found?
- Found within the photosystems which are embedded in the thylakoid membrane of the grana
what happens to the products of the light dependent reaction?
They move from the thylakoid membrane into the stroma for the light dependent reaction. The ATP is used to fix the CO2 into glucose.
what is the circular DNA?
- Independent of DNA in plant cell nucleus.
- This gene codes for proteins required for photosynthesis.
Is circular DNA similar to mitochondrion?
yes, similar to mitochondrion and photosynthetic bacteria
what is the thylakoid membrane?
- series of flattened sacs allowing compartmentalisation so that different enzyme - driven reactions can occur at the same time
- the site of photosystems (light harvesting units), electron carriers and ATP synthase
What is Granum/Grana?
In some places the membrane are arranged into stacks creating a larger surface area for photosystems.
- This increases the light absorbing capacity
How is Grana similar to mitochondrion?
Similar to infolding of cell membrane for photosynthetic pigments in some bacteria
what is lamellae?
Membrane which join the grana to one another
what is the stroma?
- equivalent to cytoplasm
- contains photosynthetic enzymes for the light independent reaction
is the stroma similar mitochondrian?
yes, similar to mitochondria and photosynthetic bacteria
What are 70S Ribosomes?
- Suspended in the stroma; not in the endoplasmic recticulum
synthesise enzymes needed in photosynthetic reactions and enzymes for starch build up and breakdown (amylase)
is 70S Ribosomes similar to mitochondrian?
same smaller size ribosomes as found in photosynthetic bacteria (smaller than 80S ribosomes found in eukaryotes)
What are starch grains and lipid droplets?
Glucose is produced directly from the photosynthesis but chemical energy cannot be stored in this form (would affect water potential) so converted into osmotic effect lipid can be utlised in phospholipid synthesis.
Are starch grains similar to mitochondrian?
found in photosynthetic bacteria
what are photosynthetic pigments?
-photosynthetic pigments absorb light energy
- each pigment absorbs a range of wavelengths in visible region of the electromagnetic spectrum and has its own distinct peak of absorption.
- other wavelengths are reflected
what are primary pigments?
- the most abundant pigment chlorophyll which exists in 3 forms
what are the 3 forms of the pigments?
- chlorophyll a (2 types)
- chlorophyll b
what colour light does chlorophyll absorb and reflect?
- absorbs red light and blue light
- it reflects green light
what does it mean if the chlorophyll is the most abundant?
- That the leaves appear green
what does the primary pigment molecule consist of?
a porphyrin group- similar to haem found in haemoglobin only with a magnesium atom at it centre instead of iron
- a long phytol chain
what are accessory pigments?
- they do not contain a porphyrin group
- these pigments absorb wavelengths of light which poorly absorbed by chlorophyll
- they absorb green light
- this means that the light energy which would otherwise be reflected can also be harvested
example of accessory pigments?
carotene (orange)
xanthophyll (yellow)
what are photosystems?
proteins with pigments attached, embedded into the thylakoid membrane
what are 2 types of photosystems?
Photosystem 1 and Photosystem 2
what type of chlorophyll does photsystem 1 have?
- Chlorophyll a
- P700
- absorbs red light
what type of chlorophyll does photsystem 2 have
- Chlorophyll b
- P680
- absorbs red light
what are the steps of cyclic phsophorylation?
- Photosythetic pigemnets e.g. chlorophyll a absorbs light energy into photosystem 1
- excites an electron to a higher energy level
- electron flows through an electron transport chain releasing its energy
- energy used to create a proton gradient
- hydrogen ions flow back into the stroma through ATP synthase
- this provides the energy for ADP + Pi -> ATP
what are the two types of phosphorylation?
cyclic and non-cyclic
Summary of cyclic phosphorylation?
- Photosystem 1 only
- ATP only made
- electrons are recycled
- uses electron transport chain
- photosystem 1 - obtains electrons from itself
Summary of non - cyclic phosphorylation?
- Photosystem 1 and 2
- reduced NADP and ATP made
- oxygen
- electron leaves Photosytem 1 to reduce NADP
- electrons replaced
photolsysis of water - uses electron transport chain
-photosystem 1 obtains electrons from photosystem 2 - electrons obtain electrons from photolysis from water
what is chemiosmosis?
- electron transport chain -> electrons lose energy along the electron transport chain
- this energy is used to pump protons (H+) across a membrane
- this creates a proton gradient
- protons diffuse through ATP synthase - chemiosmosis
- this provides the energy for ADP + pi -> ATP
what is an electron transport chain?
electrons flowing through proteins in a membrane
give the 3 limiting factors of photosynthesis?
- light intensity
- Carbon dioxide concentration
- temperature
how does light intensity affect the rate of photosynthesis?
- the higher the light intensity, the more energy there is for the light dependent reaction
- faster the rate of photosynthesis
- light needs to be the right wavelengths
- so they look green because they reflect green light
- they absorb red and blue
- different pigments absorbs different wavelengths
how does carbon dioxide affect the rate of photosynthesis?
- carbon dioxide needed for the light independent reaction
- carbon dioxide is continuously the limiting factor (day twice)
- carbon dioxide is about 0.04% of the atmosphere
- optimum carbon dioxide concentration is 0.4%
- above 0.4% - carbon dioxide has a negative effect on the rate of photosynthesis
how does temperature affect the rate of photosynthesis?
- photosynthesis is controlled by enzymes
- if you increase temperature, you increase the rate of reaction up to the optimum temperature
- beyond the optimum temperature, the temperature decreases
- high temp can cause the stomata to close -> carbon dioxide decreases
therefore decreases the calvin cycle
how could someone increase light intensity?
- use lighting at night (correct wavelength)
- absorbs light to pass in
how could someone increase carbon dioxide?
- burns fossil fuel in a greenhouse
- increase carbon dioxide concentraation
e.g. propane
how could someone increase temperature?
- burner increases temperature
greenhouse traps warm air - heating/ cooling to maintain optimum temperature (thermostat)
What are the stages of the light Dependent reaction?
There are photosystems all over the thylakoid membranes, absorbing light energy
• They are arranged in pairs; PSIl comes first, then PSI
• In non-cyclic photophosphorylation, the following happens;
• When the chl-a in the reaction centre of PSII absorbs light, e are “excited” to a higher energy level, where they are passed along an electron transport chain (ETC)
• The carriers are iron-containing proteins attached to the thylakoids
• When they accept e, they are REDUCED & when they pass them on, they are
OXIDISED
• The energy released as the e pass along is used to phosphorylate ADP
ADP + Pi -> ATP. This is photophosphorylation
• The e that left PSIl are replaced by the splitting of nearby water molecules
(PHOTOLYSIS)
PSI is also absorbing light, and e are being excited (replaced by the ones arriving from PSIl)
•.
Again, these e- pass along an ETC
At the end, a substance called ferredoxin (iron protein complex) passes the e, along with the Ht from the water, to a substance called NADP
• This causes the NADP to become reduced (“Reduced NADP”/NADPH/NADPH2)
What are the stages of the light independent reaction? (Calvin cycle)
The Calvin cycle occurs in the STROMA
• This is where carbon is “fixed”/incorporated into organic molecules using COz as the raw material
• CO2 diffuses into the leaf via the stomata, across the spaces of the spongy mesophyll, into the mesophyll cells, then into the chloroplast stroma
: The co lapsed eternepto freule alad pup filose bishosphate)
• An unstable 6C molecule is formed
• This immediately splits into 2 X GP (Glycerate-3-phosphate)
• Then, the useful products from the light dependent stage are needed for the next
step
• The GP is converted into 2 X TP (triose phosphate)
The reduced NADP acts as a “reducing agent” & donates hydrogen atoms
The ATP acts as an energy source
• TP is a 3C sugar (the whole point of PHS is to make sugars!!)
• 5/6 of the TP has to be used to regenerate the RUBP, to keep the cycle going
• 1/6 of the TP can be used to make other carbohydrates e.g. glucose, sucrose (disacc), starch & cellulose (polysacc’s)
• TP is also used to make glycerol, fatty acids and amino acids - lots of crucial substances for the plant.
What are the 3 main stages of the Calvin cycle?
Fixation - carbon dioxide is fixed (incorporated into an organic molecule) in the first step.
• Reduction - GP is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP.
• Regeneration - RuBP is regenerated from the recycled TP.
What is chemiosmosis?
The process of ATP prduction
How is the high production of ATP achieved?
high energy e provide the energy to create the H* gradient, which leads to the production of ATP
