Energy transfer in and between organisms

What is aerobic respiration?

Respiration that requires oxygen, produces CO2 and a lot of ATP

What is anaerobic respiration?

Respiration that does not require oxygen, makes little ATP

What does anaerobic respiration in plants produce?

Ethanol and Carbon Dioxide

What does Anaerobic respiration in animals produce?

Lactate (lactic acid)

Stages of Aerobic respiration

Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation

Which reaction do both aerobic and anaerobic respiration have?

Glycolysis

Which produces more ATP? Aerobic or anaerobic respiration

Aerobic respiration

How many molecules of ATP are produced per molecule of glucose?

38

What is glycolysis?

The splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules

Why is glucose converted into pyruvate?

Because glucose is too big to pass through the membrane but pyruvate is smaller.

Where does glycolysis occur?

In the cytoplasm

What do you get when you combine acetate and coenzyme A?

Acetylcoenzyme A

How many carbons does acetylcoenzyme A have?

2

What is the Krebs cycle?

The introduction of acetylcoenzyme A into a cycle of oxidation- reduction reactions that yield some ATP and a large quantity of NADH and FADH2

At what stage of aerobic respiration is water produced?

Oxidative phosphorylation

Reduced NAD in animals

NADH

Reduced NAD in plants

NADPH

Another name for the 6-Carbon molecule in the Krebs cycle

Citrate

Phosphorylation of glucose to glucose phosphate

Glucose is made reactive (so it can be later split into two) by adding two phosphate molecules. This lowers the activation energy for the enzyme-controlled reactions that follow.

Where does the glucose get the phosphate to be converted into glucose phosphate?

From 2 ATP molecules that then become ADP

Splitting of phosphorylated glucose

Each glucose molecule is split into two 3-Carbon molecules known as triose phosphate

Oxidation of triose phosphate

Hydrogen is removed from each of the triose phosphate molecules and transferred to a hydrogen carrier molecule known as NAD to form NADH

How is ATP produced from triose phosphate?

Enzyme controlled reactions convert triose phosphate into pyruvate. In the process two molecules of ADP are converted into ATP

How many carbons does pyruvate have

3

Yield of ATP from one glucose undergoing glycolysis

4 produced but 2 are reused

Yield of NADH from one glucose molecule undergoing glycolysis

2

How many pyruvate are produced from One glucose

2

Stages of links reaction

Pyruvate is oxidised to acetate
2-carbon acetate combines with a molecules of CoA to produce acetylcoenzyme A

How is pyruvate oxidised to acetate?

The 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens. These hydrogens are accepted by NAD to form NADH

What is oxidative phosphorylation?

The mechanism by which some of the energy of the electrons within the hydrogen atoms is conserved in the formation of ATP

Where does oxidative phosphorylation occur?

Mitochondria (matrix)

Synthesis of ATP by oxidative phosphorylation

Transfer of electrons down a series of electron carriers (electron transfer chain)

Steps in the synthesis of ATP (oxidative phosphorylation)

Hydrogen atoms produced in glycolysis and Kerbs combine with NAD and FAD.
NADH and FADH2 donate electrons from the hydrogen they are carrying to the first molecule in the ETC
Electrons pass down ETC is a series of oxidation- reduction reactions. The energy released causes active transport of protons across the inner mitrochondrial membrane into the inter-membrane space
Protons accumulate in the intermembrane space before they diffuse back into the mitrochondrial matrix through ATP synthase
At the end of the ETC the electrons combine with these protons and oxygen to form water. Therefore water is the final acceptor of electrons in the ETC

What is the last electron acceptor in the ETC (oxidative phosphorylation)?

Oxygen

Chemiosmosis

The synthesis of ATP

Why is it better that energy is released a little at a time rather than in one go?

Because the greater the energy released in one step the more wasted as heat, so less is available for more useful purposes

In what organisms does anaerobic respiration lead to the production of ethanol?

Certain bacteria and fungi (e.g. Yeast) as well as plants (e.g. Root cells underwaterlogged conditions)

How is ethanol produced?

The pyruvate molecule formed at the end of glycolysis loses a molecule of carbon dioxide and accepts hydrogen from Reduced NAD

Why does anaerobic respiration occur in animals?

A means of overcoming a temporary oxygen shortage

Where does lactate production most commonly occur?

In muscles

What happens to the lactate?

Oxidised back to pyruvate when oxygen is available again

What effect does lactate have on enzymes?

It is an acid so it can harm enzymes so it is important that it is removed

How is lactate removed?

Carried by the blood to the liver to be converted to glycogen

What stage is ATP produced in anaerobic respiration?

Glycolysis

Why does the Krebs cycle not occur in anaerobic respiration?

Because the pyruvate is converted into lactate or ethanol so is not available for the Krebs cycle.

How are leaves adapted for photosynthesis?

Large surface area.
Leaves are arranged so they avoid overlapping.
Thin as most of the light will be absorbed in the very top of the leaf.
Transparent cuticle and epidermis to let light through.
Long, narrow upper mesophyll cells packed with chloroplasts.
Numerous stomata for gas exchange so all mesophyll cells are only a short diffusion pathway from one.
Stomata that respond to light intensity.
Many air spaces in the lower mesophyll layer to allow rapid diffusion.
A network of xylem that bring water to the leaf cells and phloem that carrier away the sugars produced during photosynthesis.

What is the equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆+ 6O₂

Leaf cross section.

What are the three main stages of photosynthesis?

Capturing of light energy.
The light-dependent reaction.
The light-independent reaction.

In photosynthesis, which comes first, the light-dependent or the light-independent reaction?

The light-dependent reaction comes first.

In what organelle does photosynthesis take place?

Chloroplasts.

What are the two main parts of chloroplasts?

The grana (stacks of thylakoids) and the stroma which is a fluid-filled matrix.

Which stage of photosynthesis takes place in the grana?

The light-dependent stage.

Which stage of photosynthesis takes place in the stroma?

The light-independent stage.

List two molecules that are the raw materials of photosynthesis.

Carbon dioxide and water.

Name two molecules that are the products of photosynthesis.

Glucose and Oxygen.

Name the products of the light-dependent reaction.

Reduced NADP, ATP and oxygen.

Name the products of the light-independent reaction.

Sugars and other organic molecules.

What is oxidation?

When a substance gains oxygen or loses hydrogen. When a substance is oxidised it loses electrons.

What is reduction?

When a substance loses oxgen or gains hydrogen. If something is reduced it gains electrons.

What is photoionisation?

When a chlorophyll molecule becomes ionised.

In the light-dependent reaction the chlorophyll molecule has been oxidised (lost electrons) so what has been reduced?

The electron carrier because it has gained the electrons lost by the chlorophyll molecule.

How is ATP made in the light-dependent reaction of photosynthesis?

When a chrolophyll molecule absorns light energy it boosts the energy of a pair of electrons within the molecule, this raises them to a higher energy level.
These electrons are said to be in an excited state, they have so much energy that they leave the chlorophyll molecule all together.
This chlorophyll molecule becomes ionised (photoionisation).
The electrons that lost are taken up by an electron carrier (it has been reduced).
The electrons now pass down a number of electron carrier in a series of oxidative-reduction reactions.
These electron carrier form a transfer chain that is located in the membranes of the thylakoids.
Each new carrier is at a slightly lower energy level than the previous one so the electron loses energy at each stage.
Some of this energy is used to combine an inorganic phosphate molecule with an ADP molecule in order to make ATP.

What is the chemiosmotic theory?

It is used to describe the mechanism by which ATP is produced. It will usually only be mentioned in the light-dependent section of photosynthesis.

Describe the chemiosmotic theory. (Light-dependent reaction of photosynthesis).

Each thylakoid in an enclosed chamber into which protons (H+) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps.
The energy used to drive this process comes from electrons released when water molecules are split by light (photolysis).
The photolysis of water also produces protons which further increases their concentration inside the thylakoid space.
Overall, this creates and maintains a concentration gradient of protons across the thylakoid membrane with a high concentration inside the thylakoid space and a low concentration in the stroma.
The protons can only cross the thylakoid membrane through ATP synthase channel proteins - the rest of the membrane is the membrane surface are so are known as stalked granules.
As the protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with an inorganic phosphate to form ATP.

What is the equation for photolysis?

2H₂O→ 4H+ + 4e- + O₂

Why is it important that the photolysis of water takes place in photosynthesis?

When the light strikes the chlorophyll molecule it loses electrons and if the chlorophyll is to continue absorbing light energy these electrons must be replaced. The replacement electrons are provided from water molecules that are spilt using light energy. This photolysis of water also yields protons.

In photosynthesis what is the electron carrier?

NADP

What role does NADP play in photosynthesis?

It acts as an electron carrier to take up the protons released from photolysis.

What is the other name for NADPH?

Reduced NADP.

Is NADP in plants or animals?

Plants.

What is the main product of the light-dependent stage of photosynthesis?

Reduced NADP/NADPH.

What product from the light-dependent stage of photosynthesis enters the light-independent stage?

Reduced NADP/NADPH and the electrons it is carrying from the chlorophyll molecule. Also ATP.

What is the by-product of photolysis that is either used in respiration or diffuses out of the leaf as a waste product?

Oxygen.

Light-dependent stage of photosynthesis.

Does the light-independent reaction require light?

It doesn't require light directly, it can occur without light but it uses products from the light-dependent reaction.

Describe what happens in the photolysis of water?

Water molecules are split to form electrons, protons and oxygen as a result of light exciting electrons/raising them to a higher energy level.

Is oxygen being lost from carbon dioxide an oxidation or reduction reaction?

Reduction.

Is an unsaturated fat molecule gaining a hydrogen atom an oxidation or reduction reaction?

Reduction.

Is light causing an electron to leave a chlorophyll molecule an oxidation or reduction reaction?

Oxidation.

Name 4 ways that chloroplasts are structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis.

The thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light-dependent reaction.
There is a network of proteins in the grana that hold the chlorophyll in a very precise manner that allows the maximum absorption of light.
The granal membranes have ATP synthase channels which catalyse the production of ATP. They are also selectively permeable which allows establishment of a proton gradient.
Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light-dependent reaction.

Where does the light-independent stage take place?

The stroma of chloroplasts.

What is the Calvin cycle?

It is the light-independent stage of photosynthesis.

Describe the steps in the Calvin cycle.

CO2 (from the atmosphere) diffuses into the leaf through stomata and dissolves in the water around the walls of the mesophyll cells. It then diffuses through the cell-surface membrane, cytoplast membranes and into the stroma of the chloroplast.
In the stroma the CO2 reacts with RuBP a reaction that is catalysed by rubisco.
This produces two molecules of 3-carbon glycerate 3-phosphate.
Reduced NADP from the light-dependent reaction is used to reduce glycerate 3-phosphate to triose phosphate using energy supplied from ATP.
The NADP is re-formed and goes back to the light-dependent reaction to be reduced again by accepting more protons.
Some triose phosphate molecules are converted to organic substances that the plant requires e.g. starch, cellulose, lipids, glucose, amino acids and nucleotides.
Most triose phosphate molecules are used to regenerate RuBP using ATP from the light-dependent reaction.

What is Rubisco?

Ribulose Bisphosphate carboxylate which is an enzyme that catalyses the reaction between CO2 and RuBP in the light-independent reaction of photosynthesis (Calvin cycle).

What is RuBP?

It is Ribulose Bisphosphate that is a 5-carbon compound. It reacts with CO2 in the Calvin cycle.

Describe the role of ribulose bisphosphate (RuBP) in the Calvin cycle.

It accepts/combines with a molecule of CO2 to produce 2 molecules of glycerate-3-phosphate.

Sate how the reduced NADP from the light-dependent reaction is used in the light-independent reaction.

It is used to reduce (donate hydrogen) glycerate-3-phosphate to triose phosphate.

Apart from NADP, which other product of the light-dependent reaction is used in the light-independent reaction?

ATP.

State precisely where in a plant cell the enzymes involved in the Calvin cycle are found.

Stroma of the chloroplast.

How are chloroplasts adapted to carrying out the light-independent reaction of photosynthesis?

Thf luid of the stroma contains all the enzymes needed.
Stroma fluid is membrane-bound in the chloroplast which means a chemical environment which has a high concentration of enzymes and substrates can be maintained within it.
The stroma fluid surrounds the grana and so the products of the light-dependent reaction in the grana can readily diffuse into the stroma.
It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light-independent reaction.

What is the compensation point?

Where there is no net exchange of gases into and out of the plant.

Name 3 things that could be limiting factors for the rate of photosynthesis.

Light intensity
CO2 levels
Water

Glycolysis.

Link reaction.

Krebs cycle.

Describe glycolysis.

Glucose is made more reactive by adding two phosphate molecules (phosphorylation). The phosphate molecules come from the hydrolysis of two ATP molecules to ADP. This provides the energy to activate glucose and lowers the activation energy as well.
Each glucose molecule is split into two 3-carbon molecules known as triose phosphate.
Hydrogen is the removed from each of the two molecules of triose phosphate and transferred to a hydrogen-carrier molecule (NAD) to form reduced NAD.
Enzyme-controlled reactions convert each triose phosphate into another 3-carbon molecule called pyruvate and in the process two ATP molecules are regenerated from ADP.

What is the overall equation for the link reaction?

Pyruvate + NAD +CoA --> acetyl CoA + reduced NAD + CO2

What are coenzymes?

They are molecules that some enzymes require in order to function. Coenzymes play a major role in photosynthesis and respiration where they carry hydrogen atoms from one molecule to another.

Name three coenzymes.

NAD - important throughout respiration.
FAD - important in the Krebs cycle.
NADP - important in photosynthesis.