Energy Transfers In and Between Organisms

What are the two stages of photosynthesis?

The light dependent stage and the light independent stage

What is the rate of photosynthesis determined by?

The rate of photosynthesis is determined by carbon dioxide concentration, light intensity and temperature

How are chloroplasts adapted to photosynthesis?

A) they contain stacks of thylakoid membranes called grana which provides a large surface area for the attachment of chlorophyll, electrons and enzymes. B) there is a network of proteins in the grana that hold the chlorophyll in a very specific manner to absorb the maximum amount of light. C) the granal membrane has ATP synthase channels embedded allowing ATP to be synthesised as well as being selectively permeable allowing the establishment of a proton gradient. D) chloroplasts contain DNA and ribosomes allowing them to synthesise proteins needed in the light dependent reaction

What happens in the light dependent reaction of photosynthesis?

A) Photons of light hit chlorophyll molecules in PSII causing the electrons to become excited. This is called photoionisation. The charge separation from this drives the process of photolysis. B) Photolysis is the splitting of water with light. One molecule of water requires 4 photons of light to split. When water is split it produces 1 molecule of oxygen, 4 protons and 4 electrons. The oxygen either naturally diffuses out through the stomata or is used in respiration. The 4 electrons replace those lost from the chlorophyll, whilst the protons move into the stroma, later creating a proton gradient. C) The excited electron then moves down a series of protein complexes. At one of the complexes the energy from the electron is used to pump 4 protons from the stroma to the thylakoid space. D) 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. E) 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. F) 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.

What happens in the light independent reaction of photosynthesis?

A) 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. B) 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 molecules of triose phosphate. All of the NADP from the light dependent reaction has now been used with only some of the ATP being used. C) 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. D) 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.

How many turns of the Calvin cycle are needed to produce one molecule of glucose?

6 turns of the Calvin cycle are required to produce 1 molecule of glucose per molecule of CO2

In photosynthesis which chemicals are needed for the light dependent reaction?

NADP, ADP, Pi and water

Describe what happens during photoionization in the light-dependent reaction

The chlorophyll absorbs the light which excites the electrons in the chlorophyll. This causes the electrons to be lost and the chlorophyll becomes positively charged

Why is pencil used instead of ink, as a base line, in chromatography?

This is because the ink would cause the original line to move to a different position

How would you separate pigments after the solution of pigments had been put on the origin line, in chromatography?

Ensure that the level of solvent is below the origin line and then watch the pigments go up the chromatography paper. Remove the paper before the solvent reaches the top

What is the advantage of having different colored pigments in leaves?

To absorb different and more wavelengths of light for photosynthesis.

How does a decrease in the light-dependent reaction of photosynthesis lead to a decrease in the light-independent reaction?

It is because there is less ATP and reduced NADPH.

How would a decrease in the activity of the enzyme Rubisco limit the rate of photosynthesis?

Less carbon dioxide reacts with RuBP, so there is less GP.

Where is Rubisco found in a cell, precisely?

In the stroma.

Why is it important that water potentials are the same when experimenting with chloroplasts?

So that osmosis would not occur, as that may cause the chloroplast to swell or shrivel.

How does reducing the transfer of electrons down the chain reduce the rate of photosynthesis?

Reduced transfer of protons across the thylakoid membrane, so less ATP is produced. Less NADPH is produced, so the light-independent reaction slows or stops.

What is aerobic respiration?

The splitting of a respiratory substrate to release carbon dioxide as a waste product.

Describe the process of glycolysis.

Glycolysis is the first process of both aerobic and anaerobic respiration. It takes place in the cytoplasm of the cell. Glucose is phosphorylated into glucose phosphate using ATP. This is then converted into triose phosphate as the glucose phosphate is not stable. The triose phosphate is then oxidized to produce pyruvate with a net gain of ATP and reduced NAD.

Why does inhibiting a reaction in the Krebs cycle decrease the uptake of oxygen in a respiring cell?

Less NAD/coenzymes are available, so fewer electrons are removed and passed to the electron transfer chain. Oxygen is the final electron acceptor.

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

Regenerates NAD, so glycolysis continues.

Why do lots of yeast cells die during the death phase?

Increase in ethanol, carbon dioxide, or acidity.

Why is it good that fatty acids are transported into the mitochondria during exercise?

Oxidation of fatty acids provides ATP.

Describe the advantage of the Bohr effect during intense exercise.

It increases the dissociation of oxygen, which is useful for aerobic respiration in the tissues. This leads to a delay in anaerobic respiration in the tissues, which would cause lactate buildup, which is harmful.

Suggest and explain one physiological change that would allow for the removal of the increased volume of carbon dioxide produced during intense exercise.

Increased breathing rate leads to increased PCO₂ per breath but more breaths.

Suggest an explanation for the effect of temperature on the rate of carbon dioxide release.

At higher temperatures, up to the optimum, enzymes work faster, increasing metabolism. This means there is a higher rate of respiration and carbon dioxide release. The spiracles also open more often and are able to get rid of the carbon dioxide.

What are the four steps of aerobic respiration?

Glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation.

Describe the process of the link reaction.

In the link reaction, the 2 molecules of pyruvate are actively transported into the mitochondria. The enzyme decarboxylase removes a molecule of CO₂, and a hydrogen is lost, which reduces NAD. The resulting acetate combines with coenzyme A to form acetylcoenzyme A, a 2-carbon molecule. Per glucose molecule, 2 molecules of acetyl coenzyme A are formed, along with 2 CO₂ and 2 reduced NAD.

Describe the process of the Krebs cycle.

The Krebs cycle occurs in the mitochondrial matrix. Acetyl coenzyme A combines with a 4-carbon molecule to make a 6-carbon compound. Coenzyme A is released and reused. The 6-carbon molecule then undergoes decarboxylation (releasing 2 CO₂), produces 1 ATP via substrate-level phosphorylation, 1 reduced FAD, and 3 reduced NAD. The molecule is then recycled back into the 4-carbon compound to continue the cycle.

What are the products of one Krebs cycle?

3 reduced NAD, 1 reduced FAD, 1 ATP, and 2 CO₂.

What are the products of one molecule of glucose in the Krebs cycle?

6 reduced NAD, 2 reduced FAD, 2 ATP, and 4 CO₂.

Describe the process of oxidative phosphorylation.

In the mitochondrial matrix, reduced NAD and FAD release hydrogen atoms, which split into protons and electrons. Electrons move along the electron transport chain, releasing energy used to actively transport protons into the intermembrane space, forming an electrochemical gradient. Protons diffuse back through ATP synthase, driving the phosphorylation of ADP to ATP (producing 34 ATP molecules). At the end, oxygen accepts electrons and protons to form water—making oxygen the final electron acceptor.

What is an ecosystem?

An ecosystem is a community together with the non-living components of its environment.

What is a community?

Populations of different species living in a particular area.

What is the distribution and abundance of organisms in a habitat controlled by?

Both biotic and abiotic factors.

What is a niche?

A species' particular role in its habitat.

What is the role of the sun in ecosystems?

The sun is the source of all energy in ecosystems; photosynthetic organisms use this energy to produce their own food.

What is an autotroph?

An organism that can produce its own food using light, water, carbon dioxide, and other chemicals.

What are heterotrophs?

Organisms that cannot synthesize their own food.

How much chemical food energy is passed on between organisms in the food chain?

10%.

What is energy in the food chain lost to the surroundings as?

Energy is lost through uneaten parts (e.g., bones), decay of dead material, excretion (e.g., in faeces), and as heat from exothermic reactions like respiration.

What is the formula for the efficiency of energy transfer between the trophic levels?

How can biomass be measured?

The biomass can be measured in terms of mass of carbon or dry mass of tissue per given area per given time

Why is dry mass used?

The dry mass is used as the wet mass can vary too much

How can the chemical energy stored in dry mass be estimated?

The chemical energy stored in dry biomass can be estimated using calorimetry - bomb calories

What is bomb calorimetry?

Bomb calorimetry is where a sample of known mass is burnt in pure oxygen and the change in temperature of the water surrounding it is measured to calculate the energy in the sample

What is net primary productivity (NPP)?

The rate at which energy is transferred into the organic molecules that make up new plant biomass, after respiratory losses to the environment have been taken into account

What is gross primary productivity (GPP)?

The rate at which energy is incorporated into organic molecule in the plants in photosynthesis, in a given area or volume in a given time

What are the four stages of the nitrogen cycle?

Ammonification, nitrification, denitrification and nitrogen fixation

What is ammonification?

Where microbes known as saprobionts break down organic matter to ammonia in a two-stage process. Saprobionts then use the products of decomposition for respiration.

What is nitrification?

Where nitrifying bacteria convert ammonia to nitrate ions, in an oxidation reaction, with a nitrate ion intermediate

What is denitrification?

Where nitrate ion are converted to nitrogen gas

What is nitrogen fixation?

Where nitrogen gas is fixed into other compounds by bacteria with nitrogen fixing ability. They do so by reducing nitrogen gas to ammonia which subsequently dissolves to form ammonia

What form do most plants take nitrogen up?

Most plants can take in nitrate ions through their roots

How is phosphorus released?

phosphate is released from sedimentary rock as a result of weathering, as well as through the decay of bones, shells and the excreta of some birds

How are mycorrhizae important?

they are important in facilitating the uptake of water and inorganic ions by plants.

What are fertilisers used for?

Natural and artificial fertilizers are used to replace the nitrate and phosphates lost by harvesting plants and removing livestock

How are nitrogen fertilisers useful?

they greatly increase crop yields and therefore can help to deal with the demands of a growing human population.

How are nitrogen fertilisers negative?

They can reduce biodiversity, leaching and eutrophication

What is leaching?

The process by which mineral ions, such as nitrate, dissolve in rainwater are carried from the soil to end up in rivers and lakes.

What is eutrophication?

When the mineral ions from excess fertiliser leach from farmlands into waterways, causing the rapid growth of algae

How can leaching lead to the death of an ecosystem?

Leaching causes eutrophication to occur. This provides algae in waterways with enough nitrate ions to grow more rapidly than it otherwise would do. As a result, this can block out light from other plant, causing decay and the use of oxygen by decomposers. The use of oxygen by decomposers causes other organisms to die due to asphyxiation