Topic 5-energy transfers Flashcards
what are two stages of photosynthesis?
Light dependant and light independant
what are the 3 factors that can affect rate of photosynthesis?
carbon dioxide concentration, light intensity and temperature
what organelles are the site of photosynthesis?
chloroplasts
what is the grana in a chloroplast and what is the purpose?
Stacks of thykaloid membranes, provide a large surface area for the attachment of chlorophyll electrons and enzymes
what is inside thykaloid membranes?
photosynthetic pigments
what structures make leaves adapted for photosynthesis?
- Large surface area
- Thin, short diffusion pathway
-Transparent cuticle and upper epidermis - Palisade cells contain lots of chloroplasts
- Lots of stomata for gas exchange, which open and close in response to light intensity
- xylem to transport water to leaf cells
What is in a thylakoid membranes
Photosynthetic proteins, electron carrier proteins embedded within these
what do the inner and outer chloroplast membranes do?
Controls what enters and exits the organelle
what is the stroma in a chloroplast?
fluid centre containing enzymes
what are chlorophylls?
a group of 5 closely related pigments
what is a pigment
a molecule that can absorb light
why are there different chlorophylls?
to absorb different wavelengths of light
what is the most abundant chlorophyll?
chlorophyll A
What is a photosystem?
A complex containing chlorophyll, pigments and proteins
where are photosystems located?
Thylakoid membrane
what is the mobile phase in a chromatogram?
when the pigments are moving
how are the pigments within a photosystem separated?
Chromatogram,
what is the stationary phase in a chromatogram?
when the pigments have finished moving and are stationary
how to calculate RF value
distance travelled by the pigment/ distance travelled by solvent (water)
What are the adaptations of the thylakoid membranes?
- Folded membranes so they have a larger surface area, so:
- more chlorophyll on the surface
- more carrier proteins embedded on the surface
- can absorb more light
- increases the rate of photosynthesis
what is the light independent reactions also known as?
calvin cycle
which stage comes first in photosynthesis?
Light dependant
what are the 5 chlorophyll pigments?
chlorophyll A, chlorophyll B, carotene, xanthophyll, phaeophytin
why is it an advantage to have a greater variety of chlorophyll pigments?
Wider range of light lengths can be absorbed, more light energy absorbed means the rate of light dependant reactions are increased, more carbohydrates can be made
(Chromatogram) Explain why the student marked the origin using a pencil rather than using
ink (1)
Ink and leaf pigments would mix
(chromatogram) Describe the method the student used to separate the pigments after the
solution of pigments had been applied to the origin (2)
Level of solvent below origin line, (1)
remove before the solvent reaches the top (2)
The pigments in leaves are different colours. Suggest and explain the
advantage of having different coloured pigments in leaves. The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves. (1)
Absorbs different wavelengths of light for photosynthesis
Why should you draw the line where the solvent reached immediately?
The solvent may continue moving after the paper is removed from it, so it is important to draw a pencil line immediately.
Why does chromatography paper need to be straight and vertical?
to ensure pigments move in a straightline upwards and dont run off the sides
where does the light dependant reaction occur in the chloroplast?
On the thylakoid membrane
Where does the light independant reaction occur in the chloroplast?
In the stroma
what is oxidation and reduction?
Oxidation is loss of electrons, loss hydrogen or the gain of oxygen. Reduction is gain of electrons, gain of hydrogen or loss of oxygen. OIL RIG. When one substance is oxidised, another has to be reduced
what does oxidation do in terms of energy?
releases energy
what does reduction do in terms of energy?
absorbs energy
what is produced in the light dependent stage of photosynthesis?
ATP and reduced NADP
what are the 3 reactions in the light dependent stage of photosynthesis?
- Photoionisation of chlorophyll
- Photolysis
- Chemiosmosis
does photolysis or chemiosmosis come first?
photolysis
describe the process of photionisation
- light hits chlorophyll on the thylakoid membrane, which absorbs the light energy via electrons
- the energy absorbtion is so great the electron jumps so far away from the nucleus it is released by the chlorophyll
- because the chlorophyll has lost electrons it becomes an ion
(photoionisation meaning light (photo) is used to create an ion (ionisation)
Describe what happens during photoionisation in the light-dependent
reaction (2)
Electrons are lost
what happens during photolysis?
the light energy absorbed by chlorophyll splits water into oxygen, hydrogen is split into 2 protons and 2 electrons
where do the hydrogen ions go after photolysis?
they reduce NADP, then diffuse into the lumen of the thylakoid, creating a gradient
what happens in chemiosmosis (photosynthesis)?
- The electrons lost by chlorophyll (in photoionisation) are captured by carrier proteins in an electron transport chain on the thylakoid membrane
- As the electrons move from one carrier protein to the next, they release energy.
- The energy is used to phosphorylate ADP into ATP. The final electron acceptor is NADP+ which becomes reduced NADP
what happens to the energy released in the electron transport chain in chemiosmosis (photosynthesis)?
it is used to actively transport hydrogen protons from the stroma into the thylakoid lumen, creating a concentration gradient.
They diffuse back through ATP synthase.
In photosynthesis, which chemicals are needed for the light-dependent
reaction?
NADP, ADP, Pi and water
what is the purpose of the light dependant reaction in photosynthesis?
to convert ADP into ATP, and to use water to reduce NADP
what is needed to create ATP and reduced NADP?
Light energy and water
Where does the calvin cycle occur?
in the stroma of the chloroplast
The light absorbed by chlorophyll is used in the light-dependent reaction.
Name the two products of the light-dependent reaction that are required for the light-independent reaction. (2)
-ATP
-Reduced NADP
is the calvin cycle temperature sensitive?
yes because rubisco is an enzyme
where is the enzyme rubisco found?
stroma of the chloroplast
what is needed for the light independent reaction to occur?
carbon dioxide, ATP and reduced NADP
is light energy required for the calvin cycle to occur?
No
what type of sugar is formed in the calvin cycle
hexose sugar
what is RuBP?
Ribulose biphosphate, a 5 carbon compound
Describe calvin cycle
- Carbon dioxide (1C) reacts with RuBP (5C), creating a 6 carbon molecule but it is unstable and splits into 2, 3 carbon molcules called GP. This fixation is catalysed by rubisco
- The 2 GP molecules are reduced to form Triose phosphate, using energy from ATP produced earlier, and the H from the NADPH that was made in photolysis
- A carbon is removed from the 2 TP molecules to go towards a hexose sugar, and the other 5 make another RuBP
- Calvin cycle repeats 6x to make 5 more carbons to form a hexose sugar (e.g. glucose or sucrose)
What happens to the H+ in photolysis of water?
picked up by NADP to form NADPH, used in calvin cycle later
what enzyme catalyses the formation of 2 GP molecules from RuBP+CO₂ ?
Rubisco
Heat stress decreases the light-dependent reaction of photosynthesis, explain why this leads to a decrease in the light independant reaction (2)
- Less ATP and less reduced NADP formed
A decrease in the activity of the enzyme rubisco would limit the rate of
photosynthesis.
Explain why. (2)
Less carbon dioxide would react with RuBP, so less GP would be formed
Where precisely is rubisco found in a cell? (1)
In the stroma
In natural ecosystems, most of the light falling on producers is not used in
photosynthesis.
Suggest two reasons why (2)
Light is reflected
Light is the wrong wavelength
what is a factor called that limits the rate of photosynthesis?
a limiting factor
what are limiting factors of photosynthesis?
Carbon dioxide, light intensity and temperature
what is a limiting factor of photosynthesis
anything that reduces the rate of photosynthesis
what are the two types of respiration?
-aerobic
-anaerobic
what are the 4 stages of aerobic respiration?
-Glycolysis
-Link reaction
-Krebs cycle
-Oxidative phosphorylation
where does glycolysis happen?
cytoplasm
where does link reaction happen?
mitochondrial matrix
where does krebs cycle happen?
mitochondrial matrix
what is the first stage of both aerobic and anaerobic respiration?
glycolysis
what are the 3 steps of glycolysis
- Glucose (6C) is phosphorylated into glucose phosphate, using ATP
- Glucose phosphate (6C) is hydrolysed into 2 triose phosphate molecules (2x3C)
- Triose phosphate molecules are oxidised to produce pyruvate, with a net gain of 4 ATP and 2 reduced NAD
what is the purpose of glycolysis
to split glucose (a 6 carbon molecule and hexose sugar) into 2 3 carbon molecules
What is the process called of glucose becoming glucose phosphate
phosphorylation
what are the products of glycolysis?
2 ATP, 2 reduced NAD, and 2 pyruvate which are transported into the mitochondrial matrix
How do triose phosphate molecules become pyruvate in the final stage of glycolysis?
Both triose phosphate molecules are oxidised
Simultaneously, because 2 molecules are being oxidised, 2 NAD molecules are reduced, one for each pyruvate.
what happens to reduced NAD and pyruvate after glycolysis?
Actively transported into the cytoplasm and mitochondrial matrix
what happens in the link reaction? (looking at 1 pyruvate)
- The pyruvate is oxidised into a 2 carbon molecule of acetate, releasing CO2
-NAD gets reduced simultaneously, it picks up the hydrogen lost during oxidation and becomes reduced NAD - This acetate molecule then combines with co-enzyme A, to produce acetylcoenzyme A.
-The molecule of acetylcoenzyme A enters the Krebs cycle
What are the products of the link reaction from 1 total glucose molecule?
-2 acetyl CoA
-2 reduced NAD
-2 CO2 released
What happens in the krebs cycle?
- The acetyl CoA reacts with a 4 carbon molecule, releasing the coenzyme A to be reused
- This creates a 6 carbon molecule, (2 from acetyl CoA and 4 from this new molecule)
- The 6 carbon molecule enters the Krebs cycle
- In a series of redox reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate level phosphorylation, CO2 is lost in this process.
