Photosynthesis Flashcards
What is a chloroplast?
are the organelles in plant cells where photosynthesis occurs
What are each chloroplast surrounded by?
a double-membrane envelope
Each of the envelope membranes is a phospholipid bilayer
What are chloroplast filled with?
fluid known as the stroma
What is the stroma the site of?
the light-independent stage of photosynthesis
A separate system of membranes is found in the stroma.
What is it called?
- what is the membrane system the site of?
Thylakoids
the light-dependent stage of photosynthesis
What does the thylakoid membrane contain?
the pigments, enzymes and electron carriers required for the light-dependent reactions
thylakoid
membrane system consists of a series of flattened fluid-filled sacs
when thylakoids stack up what structure do they form?
grana (singular – granum)
What are grana connected by?
membranous channels called stroma lamellae, which ensure the stacks of sacs are connected but distanced from each other
What does the membrane of the grana create?
a large surface area to increase the number of light-dependent reactions that can occur
What does the membrane system (thylakoid) provide?
a large number of pigment molecules in an arrangement that ensures as much light as necessary is absorbed
What does the stroma contain?
small (70S) ribosomes, a loop of DNA and starch grains
What does the loop of DNA code for in the stroma?
The loop of DNA codes for some of the chloroplast proteins (other chloroplast proteins are coded for by the DNA in the plant cell nucleus)
the protiens coded for by the loop of DNA in the stroma of chloroplast DNA are produced where?
at the 70S ribosomes
Stroma
What are sugars formed during photosynthesis stored as?
starch inside starch grains
Photosynthesis occurs in 2 stages. What are they and where do they take place?
- the light-dependent stage, which takes place in the thylakoid membranes and the thylakoid spaces (the spaces inside the thylakoids)
- the light-independent stage, which takes place in the stroma
What happens during the light- dependent stage of photosynthesis (overview) ?
- Reduced NADP is produced when hydrogen ions combine with the carrier molecule NADP using electrons from the photolysis of water
- ATP is produced (from ADP and Pi by ATP synthase in a process called photophosphorylation (ADP + Pi → ATP)
- Photophosphorylation uses the proton (H+) gradient generated by the photolysis of water
- Energy from ATP and hydrogen from reduced NADP are passed from the light-dependent stage to the light-independent stage of photosynthesis
light-dependent stage of photosynthesis
the energy and hydrogen are used during…?
the light-independent reactions (known collectively as the Calvin cycle) to produce complex organic molecules, including (but not limited to) carbohydrates, such as:
- Starch (for storage)
- Sucrose (for translocation around the plant)
- Cellulose (for making cell walls)
What is the site of photosynthesis?
chloroplast
Define photosystem
The pigment molecules are arranged in light-harvesting clusters
grana provides a large number of pigment systems.
In a photosystem, the different pigment molecules are arranged in?
funnel-like structures the thylakoid membrane (each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre)
What are dissolved in the stroma?
CO2, sugars, enzymes and other molecules
What is the stroma ?
The stroma is the fluid that fills the chloroplasts and surrounds thylakoids
What do Chloroplasts contain several different of ?
photosynthetic pigments within the thylakoids, which absorb different wavelengths of light
What are the 2 group of pigments?
-
Chlorophylls:
Chlorophyll a and b -
Carotenoids:
Carotene and xanthophyll
Chlorophylls:
What are the pigment colours of Chlorophyll a and Chlorophyl b ?
Chlorophyll a -> yellow-green
Chlorophyll b -> blue-green
Carotenoids:
What are the pigment colours of carotene and Xanthophyll?
carotene -> orange
Xanthophyll -> yellow
What do Chlorphylls absorbe wavelengths in?
What do they reflect?
the blue-violet and red regions of the light spectrum
They reflect green light, causing plants to appear green
What wavelengths of light mainly do Carotenoids absorb ?
mainly in the blue-violet region of the spectrum
What is an absorption spectrum?
is a graph that shows the absorbance of different wavelengths of light by a particular pigment
What is an action spectrum?
is a graph that shows the rate of photosynthesis at different wavelengths of light
When is the rate of photosynthesis th highest according to spectrums?
The rate of photosynthesis is highest at the blue-violet and red regions of the light spectrum, as these are the wavelengths of light that plants can absorb (ie. the wavelengths of light that chlorophylls and carotenoids can absorb)
There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum:
Explain
- Both graphs have two main peaks – at the blue-violet region and the red region of the light spectrum
- Both graphs have a trough in the green-yellow region of the light spectrum
What is Chromatography?
is an experimental technique that is used to separate mixtures:
- The mixture is dissolved in a fluid/solvent (called the mobile phase) and the dissolved mixture then passes through a static material (called the stationary phase)
- Different components within the mixture travel through the material at different speeds
- This causes the different components to separate
- A retardation factor (Rf) can be calculated for each component of the mixture
Rf value =
Rf value = distance travelled by component ÷ distance travelled by solvent
What are the two of the most common techniques for separating these photosynthetic pigments ?
- Paper chromatography – the mixture of pigments is passed through paper (cellulose)
- Thin-layer chromatography – the mixture of pigments is passed through a thin layer of adsorbent (eg. silica gel), through which the mixture travels faster and separates more distinctly