Chapter 5- Energy transfers in between organisms Flashcards
What are the products of photosynthesis
Glucose and oxygen
Write out the word equation for photosynthesis
Water + carbon dioxide= glucose + oxygen
What are the two stages of photosynthesis
Light independent stage, and light dependent stage
What is the rate of photosynthesis determined by
Carbon dioxide, concentration, light intensity, and temperature
How is chloroplast adapted for photosynthesis
- Contains stacks of thylakoid membranes called grana, which provides a large surface area for the attachment of chlorophyll, electrons and enzymes
- A network of proteins in the grana hold the chlorophyll in a very specific manner to absorb the maximum amount of light
- The granal membrane has ATP synthase channels embedded which allows ATP to be synthesised
- Chloroplast contain DNA and ribosomes allowing them to synthesise proteins needed in the light dependent reaction
Describe the light dependent reaction
- Light hits the chlorophyll molecule at PSII causing the electrons to become excited. This is called photoionisation
- Photolysis is the splitting of water with light. One molecule of water requires 4 photons of light to split. When water splits it produces one molecule of oxygen, 4 protons and 4 electrons.
- The excited electron then moves down the electron transfer chain, at each electron channel the electron loses energy. The energy from the electron is used to pump 4 protons from the stroma to the thylakoid space
- The electron then moves down the chain further to PSI. Here more photons of light are
absorbed causing the electron to move back up to a high energy level - The electron then moves along the chain to another complex where the electron combines
with a proton to form a hydrogen atom. This is then used to reduce NADP, forming reduced
NADP - The pumping of protons across the membrane means that there is now a greater
concentration of protons in the thylakoid space than the stroma. As a result a proton gradient
forms with a high concentration in the thylakoid space and a low concentration in the
stroma. The protons move across the membrane by diffusion through a protein known as a
stalked particle. The movement of these protons drives the process of
photophosphorylation. The enzyme ATP synthase phosphorylates ATP from ADP and Pi.
Describe the light independent reaction
- . CARBON DIOXIDE FIXATION - carbon dioxide that has diffused in through the stomata is fixed
with ribulose bisphosphate (RuBP) in a process known as carboxylation. The enzyme
Rubisco is needed in order to do this. A 6 carbon sugar is formed first, however this is very
unstable and therefore forms 2 molecules of glycerate-3-phosphate. - REDUCTION PHASE - The 2 molecules of glycerate-3-phosphate contain a -COOH group and
is therefore an acid. The reducing power of reduced NADP therefore reduces the
glycerate-3-phosphate, with energy being provided by ATP. This therefore forms 2 molecule
of triose phosphate. All of the NADP from the light dependent reaction has now been used
with only some of the ATP being used - REGENERATION OF RuBP - 5 molecules of triose phosphate are used in order to regenerate
3 molecules of ribulose bisphosphate. The remaining amount of ATP from the light
dependent stage is now used. - ORGANIC MOLECULE PRODUCTION - 2 molecules of triose phosphate can combine to form
the intermediate hexose sugar fructose 1,6 bisphosphate where after it forms molecules of
glucose
(6 turns of the calvin cycle are required to produce 1 molecule of glucose per molecule of carbon dioxide)
What is aerobic respiration
It is the splitting of a respiratory substrate, to release carbon dioxide as a waste product
What is anaerobic respiration
Anaerobic respiration occurs in the absence of oxygen
Describe the first stage of respiration, glycolysis
Glycolysis takes place in the cytoplasm of the cell. Glucose is phosphorylated to produce 2 molecules of pyruvate, 2 molecules of ATP and 2 molecules of NADH
( In anaerobic respiration the pyruvate is further converted into lactate with the help of NADH. Lactate is then converted back to pyruvate in the liver.
(From one molecule of glucose, 2 molecules of ATP, 2 molecules of reduced NAD (NADH) and 2 molecules of pyruvate are formed)
Describe the link reaction in aerobic respiration
- In the link reaction 2 mlecules of pyruvate are actively transported into the mitochondria
- The enzyme decarboxylase then removes a molecule of CO2 with a hydrogen also being lost, going on to reduce NAD (forming NADH)
- The acetate formed then combines with coenzyme A to form a molecule of acetyl co-enzyme A.
(per glucose molecule 2 molecules of acetyl coenzyme A are formed and 0 ATP)
Describe the krebs cycle
The krebs cycle occurs in the matrix of the mitochondria
1. Acetyl co-enzyme A gives the 2 carbon acetate to a 4 carbon molecule already present.
2. The 6 carbon molecule that is formed then undergoes a series of reactions
3. Eventually, the 4 carbon molecule is regenerated to accept another acetate molecule
What are the products of the krebs cycle
Product per glucose molecule:
- 4 carbon dioxide molecules
- 2 reduced FAD
- 2 ATP
- 6 reduced NAD
Describe oxidative phosphorlyation
- Reduced NAD from the krebs cycle binds to protein complex 1, which releases its hydrogen atoms as protons and electrons
- Electrons are transported along the electron transfer chain, at each protein they release more energy
- The energy released is used to actively transport protons into the inner membrane space from the mitochondrial matrix
- This creates an electrochemical gradient, so protons move through ATP synthase by facilitated diffusion
- ATP synthase phosphorlyates ADP and Pi and to create ATP
- At the end of the electron transfer chain, electrons along with protons are picked up by oxygen, which then forms water
Describe glycolysis
- Glucose is phosphorylayted to glucose phosphate using ATP
- Glucose phosphate splits into 2 triose phosphate (TP)
- 2x TP is oxidised to 2x pyruvate, and reduced NADH is formed as well as 2 molecules of ATP
Draw a flowchart to represent what happens during glycolysis
-
How do the products from glycolysis enter the mitochondria
Via active transport
What happens in the electron transfer chain
- Electrons released from reduced NAD and FAD undergo a series of redox reactions
- The energy released from the electrons is used to create a proton gradient
- Oxygen acts as the final electron acceptor
How is a proton gradient established during chemiosmosis in respiration
- Energy released from the electron transfer chain is coupled to the active transport of H+ ions from the mitochondrial matrix into the intermembrane space
How does chemiosmosis produce ATP during aerobic respiration
- Protons move down their concentration gradient from the intermembrane space into the mitochondrial matrix via the channel protein ATP synthase
- ATP synthase catalyses ADP + Pi to ATP
State the role of oxygen in aerobic respiration
Oxygen is the final electron acceptor in the electron transfer chain
(produces water as a byproduct)
What is the benefit of an electron transfer chain rather than a single reaction
- Energy is released gradually
- Less energy is released as heat
Name 2 types of molecule that can be used as alternative respiratory substrate
( Amino acids) from proteins
(glucerol and fatty acids from) lipids
How can lipids act as an alternative respiratory substrate
- Phosphorylation of glycerol —> TP for glycolysis
- Fatty acid –> acetate
- Acetate enters the link reaction
- H atoms produced for oxidative phosphorylation
