Energy Transfers in and between Organisms

Question 1

Describe what happens during photoionisation in the light-dependent reaction

Answer 1

Light excites electrons in chlorophyll
Electrons are lost

Question 2

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.

Answer 2

Absorb different wavelengths of light for photosynthesis

Question 3

Explain why the scientists measured the rate of production of oxygen in this investigation (Photosynthesis)

Answer 3

Oxygen produced in LDR
Rate of oxygen production is proportional to rate of LDR

Question 4

In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why

Answer 4

Does not land on photosynthetic pigments
Is the wrong wavelength
Light is reflected
Temperature or CO2 are limiting factors

Question 5

Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds.

Answer 5

Reduced transfer of protons across thylakoid membrane
This means less ATP and Reduced NADP are produced
This means less light independent reaction

Question 6

Outline the steps of the Light Dependent reaction

Answer 6

Light is absorbed by pigments in photosystem II and an electron in chlorophyll is excited
Electron is transferred to a higher energy level on an electron carrier and then moves to a lower energy level, transferring its energy to a proton pump
This actively transports H+ into the thylakoid membrane and creates an electrochemical gradient for it to move back in by chemiosmosis
It moves through ATP synthase to synthesise ATP from ADP + Pi
Finally the electron and hydrogen are accepted by NADP to produce Reduced NADP
Water undergoes photolysis to be broken down into Oxygen, Protons and electrons which replace the electrons lost from chlorophyll in PSII

Question 7

Outline the steps in the Light Independent reaction

Answer 7

RuBP and CO2 react in the presence of the enzyme rubisco to form an unstable 6 carbon compound which breaks into two molecules of GP
Using 2ATP and 2NADPH, the 2 molecules of GP are reduced to form TP
5/6 of these molecules of TP are used to regenerate RuBP using ATP
1/6 of the TP is used to form useful organic products such as glucose
6 cycles are required to produce 1 hexose sugar

Question 8

Describe the process of glycolysis

Answer 8

Two phosphate from ATP are added to a molecule of glucose
This causes it to break down into two molecules of TP
A free phosphate is added to TP
TP is oxidised to Pyruvate and its hydrogen is used to reduce NAD
The phosphates are used to produce 4 molecules of ATP

Question 9

Malonate inhibits a reaction in the Krebs cycle. Explain why malonate would decrease the uptake of oxygen in a respiring cell.

Answer 9

By decreasing the rate of Krebs cycle it reduces the amount of Reduced NAD and FAD produced
So fewer electrons passed through electron transfer chain
Oxygen is the terminal electron acceptor

Question 10

In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production
of ATP by anaerobic respiration

Answer 10

Converting pyruvate to lactate oxidises reduced NAD
So glycolysis continues

Question 11

For the first 10 minutes, the tap attached to tube A was left open and the syringe from tube B was removed.
Suggest three reasons why the apparatus was left for 10 minutes.

Answer 11

To reach a constant rate of respiration
Allow for pressure changes in apparatus
Equilibrium reached

Question 12

During the experiment, the coloured liquid in the tubing moved towards tube B.
Explain what caused this

Answer 12

The seeds were aerobically respiring so absorb oxygen
They release an equal amount of CO2 but this is absorbed by KOH solution
This causes a decrease in gas volume and pressure so the bead moves towards tube B

Question 13

Describe the advantage of the Bohr effect during intense exercise

Answer 13

Increases dissociation of oxygen
For increased aerobic respiration

Question 14

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

Answer 14

An increase in temperature results in an increase in enzyme controlled reaction
This means the rate of Krebs cycle is increased so rate of CO2 released is higher
So spiracles remain open for longer

Question 15

Outline the process of the Link reaction

Answer 15

Pyruvate is actively transported into the Mitochondrial matrix
Pyruvate is decarboxylated and oxidised
This produces a molecule of Reduced NAD
It then combines with Coenzyme A to form Acetyl CoA

Question 16

Outline the process of the Krebs cycle

Answer 16

Oxaloacetate reacts with Acetyl CoA in the presence of enzyme citrate synthase to produce a molecule of Citrate
This is then decarboxylated and oxidised to give one molecule of Ketoglutarate and reduces NAD
This is then decarboxylated and oxidised again to reform Oxaloacetate and reduces two molecules of NAD and one molecule of FAD as well as one molecule of ATP

Question 17

Outline the process of Oxidative Phosphorylation

Answer 17

Reduced NAD/FAD donate their electron to an electron carrier
They move through the electron transfer chain and transfer their energy to proton pumps which actively transport H+ from reduced NAD/FAD into the intermembrane space
This creates a concentration gradient where the protons move by back into the matrix by facilitated diffusion through the channel protein ATP synthase
This provides energy for ATP synthesis
Oxygen acts as the terminal electron acceptor and accepts the H+ and electrons to form water

Question 18

Freshwater marsh soils are normally waterlogged. This creates anaerobic
conditions.
Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions

Answer 18

In anaerobic conditions, denitrifying bacteria thrive so break down nitrates and nitrites into N2 gas
Nitrifying bacteria also cannot survive to turn Ammonium into nitrites/nitrates

Question 19

Explain why an increase in shoot biomass can be taken as a measurement
of net primary productivity

Answer 19

Represents dry mass
Represents GPP- respiratory losses

Question 20

Describe the role of saprobionts in the nitrogen cycle

Answer 20

Use enzymes to break down proteins/DNA/RNA/urea
Releasing ammonium into the soil

Question 21

One environmental issue arising from the use of fertilisers is eutrophication.
Eutrophication can cause water to become cloudy. You are given samples of water from three different rivers.
Describe how you would obtain a quantitative measurement of their
cloudiness

Answer 21

First place a sample of clean water into a cuvette and use this to calibrate for 0 absorption
Then place a sample of each of the river waters into a cuvette and use a colorimeter to measure absorbance

Question 22

Give two examples of biological molecules containing nitrogen that would
be removed when a crop is harvested.

Answer 22

Proteins
DNA
RNA