Define the term photosynthesis
A method of autotrophic nutition by which green plants (and some other organisms) use sunlight to synthesise glucose and
... [Show More] other organic molecules from carbon dioxide and water
Name 8 nutrients needed by plants in large quantities (macronutrients)
Potassium ions, Sodium ions, Magnesium ion, Calcium ions, Nitrates, Phosphates, Sulphates and Iron ions
Name 5 nutrients needed by plants in only small amounts (micronutrients)
Copper, Manganese, Molybdenum, Boron and Zinc - ions
Where does photosynthesis take place?
On the thylakoid membranes inside chloroplasts
Name some adaptations of leaves for photosynthesis
Leaves are arranged in a mosaic to allow light to hit lower leaves
Leaves have large SA to absorb as much light as possible
Thin leaves provide short diffusion pathways for gases and allow all layers of leaves to receive light
Cuticle and epidermis transparent
Palisade cells packed close and have long axis at 90 degrees to the sun
Xylem and Phloem to transport products
Stomatal pores can be controlled to allow in more CO2/control rate of transpiration
Air spaces in spongy mesophyll allows easy diffusion of gases through the leaf
How is a chloroplast adapted for photosynthesis?
Chloroplasts can move for best positions
Contains several photosynthetic pigments to absorb many different wavelengths of light
Thylakoids in stacks to maximise absorption of light
Thylakoids have large SA
Thylakoids are thin providng a short diffusion pathway
Describe Englemann's experiment to find what wavelengths of light are most effective for photosynthesis
Used a prism to slit white light into a spectrum
Shone spectrum on Spirogyra ( with spiral chloroplasts)
Added aerobic bacteria to Spirogyra sample
Aerobic bacteria clustered at points on the Spirogyra which produced the most oxygen
These with the greatest rate of photosynthesis
Therefore the wavelengths shone on these areas of the Spirogyra are most efficient for photosynthesis
What is the function of photosynthetic pigments?
To absorb light energy/ photons of light
What is a pigment?
The natural colouring matter of animal or plant tissue
Where does chlorophyll b have absorption peaks on its absorption spectrum?
470nm and 640nm
Where does chlorophyll a have absorption peaks on its absorption spectrum?
450nm and 670nm
Where do carotenoids have absorption peaks on its absorption spectrum?
450nm and 500nm
Name 4 photosynthetic pigments
Chlorophyll a, chlorophyll b, carotene, xanthophyll
Name two carotenoids
Carotene and xanthophyll
Why is it advantageous for a plant to have many different photosynthetic pigments?
Pigments absorb limited parts of the spectrum/limited range of wavelengths of light
More pigments increases the range of wavelengths that can be absorbed
Increases the efficiency of photosynthesis
Why do leaves of flowering trees go red/brown in the winter?
Chlorophyll is retracted from the leaves (to conserve the pigment and save energy by not having to make more of it) leaving just the carotenoids which reflect red/brown light/ are red/brown coloured
How are the photosynthetic pigments arranged in chloroplasts?
Arranged in antenna complexes with special proteins to help funnel light (energy) down towards the reactions centre (chlorophyll a - the primary pigment)
Where are the photosynthetic pigments found in chloroplasts?
Photosystems are found on Thylakoid membranes
What is the name given to the combination of an antenna complex and a reaction centre?
Photosystem
What are the components of a photosystem
An antenna complex made of special proteins and photosynthetic pigments
A primary pigment - called the reaction centre
What technique can be use to separate out photosynthetic pigments from a cluster of pigments found in a photsystem and identify them?
Chromatography
How is the action spectrum of photosynthesis related to the absorption spectra of the photosynthetic pigments?
Close correlation (same shape/trend)
Suggests that the wavelengths used in light absorption are used in photosynthesis
What does an absorption spectrum show?
The wavelengths of light absorbed by a specific substance
What does an action spectrum of photosynthesis show?
The rate of photosynthesis at different wavelengths of light
Where does the LDS occur?
Thylakoid membranes
Name two reactions that take place in the LDS?
Photolysis of water
Photophosphorylation of ADP
What is another name for non-cyclic photophosphorylation?
The Z scheme
Describe the sequence of steps and reactions that occur in the Z scheme
Photons of light/light energy absorbed by PS2 are channelled to a reaction centre (chlorophyll a)
This causes excitation of two electrons which are accepted by the primary electron acceptor which passes them to an ETC on the membrane
The electrons pass through a pump between PS2 and PS1 at which energy from the electrons is used to pump protons into the thylakoid interior space creating an ECG used to synthesise ATP
Photons are absorbed by PS1, 2 electrons excited and passed to 2nd electron acceptor which passes electrons to NADP+
Photolysis of water produces electrons to replace those lost by PS2 and protons which combine with electrons from PS1 to reduce NADP+in the stroma
PS1's electrons replaced by those coming from PS2
How many electrons are excited at a time from a photosystem when it absorbs photons of light?
2
What is photophosphorylation?
When energy lost by electrons (excited by photons striking a photosystem) on the ETC is captured and used for pumping protons into the interior space thus creating an ECG by which ATP is phosphorylated via chemiosmosis
What are the products of photolysis of water?
Oxygen, protons and electrons
Where does the photolysis of water occur?
Thylakoid interior space
How is the concentration of protons in the stroma decreased?
Reduction of NADP+
How is the concentration of protons in the thylakoid interior space increased?
Photolysis of water
How is an ECG established across a thylakoid membrane?
Pumps on membrane pump protons from stroma into interior space. Photolysis of water produces more protons in the interior space and reduction of NADP+ decreases the concentration of protons in the stroma
What is chemiosmosis?
The theory that the electrochemical gradient made from the pumping of protons to only one side of a membrane provides the energy for ATP production by generating a flow of hydrogen ions through a channel protein with ATPsynthase attached
Name the two stages of photosynthesis
Light Dependent Stages
Light Independent Stage (Calvin Cycle)
Where does the Calvin cycle take place?
In the stroma
Describe the process of cyclic photophosphorylation
PS1 absorbs photons of light/light energy which are channeled to a reaction centre (chlorophyll a) and used to excite two electrons
These electrons are accepted by an acceptor and those electrons not used for reduction of NADP+ are passed down an ETC
Electrons de-excite down the ETC and their energy is used to pump protons into the thylakoid interior space creating an ECG
The electrons are re-accepted by PS1
What are the product(s) of cyclic photophosphorylation?
ATP
What are the product(s) of non-cyclic photophosphorylation?
ATP, Oxygen, NADPH2
What is the terminal electron acceptor in cyclic photophosphorylation?
Chlorophyll
What is the terminal electron acceptor in non-cyclic photophosphorylation?
NADP+
Which photosystem is involved in cyclic photophosphorylation?
PS1
Why can the Calvin cycle not take place without the LDS?
The LDS produces ATP and NADPH2 which are needed to convert glycerate-3-phosphate to triose-phosphate in the Calvin cycle
Describe the sequence of events that occur in the Calvin cycle
CO2 that has diffused in through stomata is combined with RuBP using the enzyme RUBISCO (carboxylation)
This forms a short lived 6C sugar that decays into two molecules of G3P
G3P is reduced by NADPH2 (requiring phosphate from a molecule of ATP) to form triose phosphate
For every 6 molecules of triose phosphate formed 5 are used to regenerate RuBP and one is used to build up glucose phosphate
The regenerations of RuBP uses ATP from the LDS
Why does ribulose bisphosphate need to be regenerated?
To allow the Calvin cycle to start again/continue turning
How many turns of the Calvin cycle is needed to make one molecule of glucose?
6
What is the general equation for photosynthesis?
6CO2 + 6H20 -> C6H12O6 + 6O2
How do plants synthesise glucose from triose phosphate?
The reversal of glycolysis
How is starch formed by plants?
By the polymerisation of glucose via condensation reactions
How do plants produce lipids?
G3P from the Calvin cycle can be converted into Acetyl CoA which is used to synthesise fatty acids
Triose phosphate can be converted into glycerol
Glycerol is combined with fatty acids via condensation reactions to produce lipids
How do plants produce proteins?
G3P from the Calvin cycle is converted to Acetyl CoA which eneters the Krebs cycle. Intermediate molecules of the Kreb's cycle can be made into amino acids by combining with nitrogen
How do plants obtain nitrogen?
Take up through the roots as nitrates and ammonium ions
What are the symptoms of nitrogen deficiency in plants?
Stunted growth as there is a lack of nucleic acids thus inhibiting cell division
What are the uses of magnesium in a plant?
Mg ions are required constituents of chlorophyll and used for the activation of ATPase
What are the symptoms of magnesium deficiency in plants?
Chlorosis (yellowing of leaves as not enough chlorophyll is made)
Death
Name 3 limiting factors of photosynthesis
Temperature
CO2 concentration
Light intensity
Describe how the rate of photosynthesis varies with temperature
For normal plants photosynthesis can only occur if temperature is above 0 degrees Celsius
Rate increases as temperature increases up to an optimum temp (roughly 25 degrees Celsius)
Passed optimum the rate levels off before then decreasing
Describe how the rate of photosynthesis varies with light intensity/CO2 concentration
Rate increases as intensity/concentration increases up to a point and then plateaus/tails off
Another factor is the limiting factor after the rate tails off
Give 3 examples of minerals taken up from the soil, by plants, that are combined with products of the LDS and what they are used to form
Nitrates: Form amino acids which join to form proteins
Phosphates: Used to produce phospholipids and are found in ATP/ADP
Magnesium: Constituent of chlorophyll
Nitrates and phosphates: from nucleotides
What does NADP+ stand for?
Nicotinamide adenine dinucleotide phosphate
Where is NADPH2 produced?
Thyalkoids (stroma right next to it though!)
Why is photosynthesis essential for the survival of all animals?
Produces oxygen needed by animals for aerobic respiration
During PS carbon is fixed during formation of organic compounds such as glucose which animals require [Show Less]