practice test questions

coenzyme vs co factor

A coenzyme is an organic molecule that aids in the functioning of an enzyme by donating energy or molecules which are then recycled whereas a cofactor is an inorganic molecule that increases the affinity of the active site and the substrate. NADP is a coenzyme as it is organic and carries protons and electrons between stages of photosynthesis. Metallic ions such as zinc are cofactors as they increase the affinity of the substrate to the active site

With explicit reference to the stages of photosynthesis, describe how NADP+ is a co-enzyme.

NADP bonds to H+ ions from the splitting of water in the light dependent stage of photosynthesis (1) and transports them in the loaded form of NADPH to the light independent stage of photosynthesis (1). Whilst not an enzyme, the reaction could not proceed without NADP (1)

With explicit reference to the stages of photosynthesis, describe how NADPH is a co-enzyme.

NADPH carries high-energy electrons and H⁺ ions from the light-dependent stage of photosynthesis (1). It transports them to the Calvin cycle in the light-independent stage, where they are used to reduce carbon molecules and produce glucose (1). Whilst not an enzyme, the reaction could not proceed without NADPH (1).

With explicit reference to the stages of aerobic cellular respiration, describe how NADH is a co-enzyme.

NADH carries high-energy electrons and hydrogen ions produced during glycolysis and the Krebs cycle (1). It transports these electrons to the electron transport chain, where they are used to produce ATP (1). While not an enzyme, NADH is crucial for facilitating electron transfer and energy production (1).

With explicit reference to the stages of aerobic cellular respiration, describe how NAD+ is a co-enzyme.

NAD⁺ acts as an electron acceptor during glycolysis and the Krebs cycle, where it becomes reduced to NADH (1). This allows it to transport high-energy electrons to the electron transport chain (1). While not an enzyme, NAD⁺ is essential for maintaining the flow of electrons and enabling cellular respiration to continue (1)

With explicit reference to the stages of aerobic cellular respiration and photosynthesis, describe how ATP is a co-enzyme.

ATP acts as an energy carrier by storing and transporting chemical energy within cells (1). In aerobic cellular respiration, ATP is produced during glycolysis, the Krebs cycle, and primarily in the electron transport chain (1). It provides energy for energy-requiring reactions, such as the phosphorylation of glucose in glycolysis or the active transport of molecules across mitochondrial membranes (1).

Additionally, ATP provides the energy needed for reactions in the Calvin cycle during the light-independent stage of photosynthesis, enabling the conversion of carbon dioxide into glucose (1). While not an enzyme, ATP is essential for driving these critical cellular processes (1).

C3 plants contain no what….

C3 plants contain no mechanism to minimise photorespiration.

Why is photorespiration harmful to plants?

Undertaking photorespiration stops carbon dioxide from binding with Rubisco and fulfilling the light-independent stage of photosynthesis to produce glucose.

Explain how C4 plants have evolved adaptations to maximise photosynthesis.

C4 plants separate the initial carbon fixation from the remainder of the Calvin cycle in photosynthesis between cells. Initial carbon fixation occurs in a mesophyll cell whilst the remainder of the Calvin cycle takes place in a bundle-sheath cell.This separation allows for a high concentration of co2 around Rubisco, encouraging it to bind co2 rather than o2 which decreases photorespiration and increases photosynthesis.

Explain the differences between C4 and CAM photosynthesis.

C4 photosynthesis separates initial carbon fixation from the remainder of the Calvin cycle over space, between a mesophyll cell and a bundle-sheath cell.Conversely, CAM photosynthesis separates these two steps over time, between day and night with the use of a vacuole.

The sugarcane farming industry is large in Australia. However, all of the farming occurs in Queensland and far north New South Wales. Sugarcane is a C4 plant.

Cereal crops like wheat and barley grow well in Victoria. Explain why sugarcane would likely be outcompeted by other cereal crops if it were introduced into a similar Victorian environment.

As sugarcane undertakes C4 photosynthesis to cope with hot environments, it expends more energy compared to the standard C3 photosynthesis.Whilst this payoff is advantageous in hot environments, in colder environments such as Victoria, the sugarcane is now expending significantly more energy than other C3 plants to undertake photosynthesis.This likely means the other cereals would outcompete sugarcane as it costs them less energy to photosynthesise.

If Substrate Saturation Occurred – What Happens if Enzyme Concentration Increases:

Increasing the enzyme concentration would initially increase the rate of reaction (1) as more active sites become available for substrate binding (1). However, the reaction rate would eventually plateau again once all substrate molecules are bound to enzymes (1). The total amount of product produced would remain the same unless more substrate is added (1).

If Enzyme Saturation Occurred – What Happens if Substrate Concentration Increases:

Increasing the substrate concentration would initially increase the rate of reaction (1) as more substrate molecules collide with available enzyme active sites (1). However, the reaction rate would plateau once all enzyme active sites are occupied, and no further increase in rate could occur (1). The total amount of product produced would depend on the availability of active enzymes (1).

If Enzyme Saturation Occurred – What Happens if the Concentration of Enzymes Increases:

If enzyme saturation has occurred, increasing the enzyme concentration will not increase the rate of reaction (1) because all the substrate molecules are already bound to the available enzyme active sites (1). The reaction rate will remain constant, as adding more enzymes cannot process more substrate without an increase in substrate concentration (1).

If Substrate Saturation Occurred – What Happens if the Concentration of Substrate Increases:

If substrate saturation has occurred, increasing the substrate concentration would not significantly affect the rate of reaction (1) because all enzyme active sites are already occupied (1). The reaction rate would remain constant, as adding more substrate would not increase the number of enzyme-substrate complexes formed (1). The total amount of product produced could still increase if more enzymes are available to process the extra substrate (1).

If the addition of substrate increases the rate of reaction whats happening

The inhibitor is competitive as the substrate is able to outcompete the inhibitor for the active site

Increasing the substrate concentration can limit the effect of a competitive inhibitor as it can out compete the inhibitor for the active site

What happens in a chain of reactions if enzyme 3 becomes non-functional?

There will be a build-up of the second intermediate substrate because enzyme 3 cannot break it down.

The production of the end product will decrease since the chain of reactions is disrupted.

y is repeating an experiment good

Repetition increases the accuracy (1) and validity (1) of the data.

Green organisms growing in the sunlight

will be undergoing photosynthesis at a higher rate than cellular respiration

Green light reflected/not absorbed by chlorophyll

Explain the role of ATP in cells, where it is produced and where it is used.

ATP is a form of usable energy for cells. ATP is manufactured in the cytosol (2 molecules) and in the mitochondria (34 or 36 molecules). ATP is used within the cell in which it is manufactured.

benefits of greenhouse

You can can control the temperature

You can can control the light intensity.

You can can control the wavelength of light.

You can can control the carbon dioxide concentration.

Explain why extra carbon dioxide added to the air in a greenhouse increases the tomato crop.

Carbon dioxide is an input for photosynthesis, therefore increasing the amount of carbon dioxide present increases the photosynthetic rate and so more tomatoes can be produced.

A tuna fish is a very active hunter. Although fish are described as cold-blooded, the tuna fish’s body

temperature is usually a few degrees higher than the water around it.

Provide an explanation for this phenomenon.

Heat is a by-product of metabolic activity. As tuna are active hunters, they require lots of energy and therefore undergo many reactions of aerobic cellular respiration and producing lots of heat.

Compare the photosynthesis in C3 and C4 plants account for the difference in the rate of photosynthesis at varying carbon dioxide concentrations between the two types of plant.

C4 plants maintain a higher rate of photosynthesis compared to C3 plants because they create and sustain a concentration gradient of CO₂. In C4 plants, CO₂ is converted into a 4-carbon compound like malate using the enzyme PEP carboxylase in the mesophyll cells. This process ensures a continuous flow of CO₂ into the cells by maintaining a high concentration gradient. The malate is then transported to bundle-sheath cells, where CO₂ is released and efficiently fixed by Rubisco. This mechanism allows C4 plants to perform well even at low CO₂ concentrations, as reflected in the graph.

In contrast, C3 plants rely solely on Rubisco for carbon fixation. Rubisco cannot maintain a CO₂ concentration gradient and is inefficient at low CO₂ levels, as it often binds oxygen instead of CO₂, leading to photorespiration. This explains why the rate of photosynthesis for C3 plants is much lower at low CO₂ concentrations compared to C4 plants. At higher CO₂ concentrations, the difference diminishes because C3 plants have sufficient CO₂ to reduce photorespiration, narrowing the gap in photosynthesis rates.

what happens when enzymes denature

enzymes denature – structure permanently breaks, active site alters/changes shape- substate no longer complementary

how does high co2 levels affect nadh+ cycle

high CO₂ levels accelerate glucose production in the Calvin cycle, which increases the demand for NADPH. This leads to faster regeneration of NADP⁺, driving the light-dependent reactions at a higher rate, including water splitting.

how does high co2 levels affect atp cycle

When CO₂ levels are high, the Calvin cycle consumes ATP more rapidly. This increases the demand for ATP production in the light-dependent reactions. To sustain this, more water is split, ensuring a continuous supply of electrons and protons and so H+ accumulates more rapidly creating a concentration gradient faster increasing the production of ATP.

The purpose of a control

A control is used as a baseline to compare the results of an experiment. It does not receive the independent variable, so it helps show what changes are caused by that variable. This makes it easier to spot any effects from other factors (extraneous variables).

why do we increase the number of trials

Add more trials/increasing replication increases the accuracy and validity of results by minimizing the effect of outliers (1)

-Averaging data

Improving accuracy brings results closer to the true values [1]. Averaging data collected by multiple repeats of

the same experiment decreases the effect that errors such as random errors have on the results [1]. An example

of a random error is reading the meniscus wrong when measuring the amount of filtrate produced [1].

why is a decreased likelihood of photorespiration good

less energy is lost and MORE GLUCOSE IS PRODUCED THUS INCREASING YIELD

Why does increasing the rate of aerobic respiration also improve crop yields?

Higher aerobic respiration higher yield/production ATP [1]

More energy (ATP) available for growth/bigger/mass/production [1]

Why does increasing the rate of photosynthesis also improve crop yields?

MORE GLUCOSE IS PRODUCED THUS INCREASING YIELD

Outline how pyruvate is utilised in aerobic respiration.

Pyruvate is transported to the fluid matrix of the mitochondrial via active transport [1] and converted to Acetyl CoA with the help of coenzyme A [1]. Acetyl CoA is an input for the Krebs cycle [1].

y is nadh not an enzyme

its altered in the reaction

what happens if an individuals electron transport chain doesnt work

The person would die (1) as the electron transport chain is where most ATP is produced (1).

They would not have sufficient energy to sustain life (1)

what would happen to the rate of aerobic respiration if ATP synthase was denatured.

The rate of aerobic respiration would decrease (1) as the active site would alter shape (1) and the substrate cannot bind (1) to convert ADP + Pi to ATP (1). A decrease in the amount at ATP produced means a decrease in the rate of aerobic respiration since less output/product is produced.

Competitive inhibition vs non competitive enzyme activity

Competitive inhibition has a higher rate of enzyme activity as the substrate competes for the active site compared to non-competitive inhibiton

Competitive inhibitors have a similar shape to the specific substrate on which an enzyme acts.

Is energy used by living organisms?

Energy is never used. In doing work, energy is converted from one form to another and at the end of the process may be unusable. Most organisms store energy in chemicals such as fat or starch. The energy is made available to do cellular work during cellular respiration.

What is the ‘lock-and-key’ model and how does it differ from the induced fit?

Only the correct enzyme with the correct molecular shape will bind to the substrate molecule, in the same way that a particular key will open a particular lock. The induced fit model states that there can be some change in the active site. The flexibility allows for closer fit between the substrate and the enzyme.

What is ATP (adenosine triphosphate)? Explain its role in cells.

ATP is a molecule containing adenosine attached to ribose, which is bound to a chain of three phosphate groups. Energy is released for cellular reactions when the terminal phosphate group is removed to form ADP. ATP is the immediate source of energy for cells. When energy is released by cellular reactions, it is stored in ATP.

What is the major difference between heterotrophic and autotrophic organisms?

Autotrophic organisms make their own organic materials through processes such as photosynthesis or chemosynthesis. Heterotrophs rely on an external source of ready-made organic material. For example, you are a heterotroph and use organic materials found in animal or plant material that you eat.

What is the role of pigments in photosynthetic organisms and why is there a range of different pigments?

igments trap the light energy required for the photosynthetic process. Different pigments trap different wavelengths (colours) of light. Green pigments are effective at absorbing red and blue light. A range of pigments means that a plant can trap a wider range of light. The pigments a photosynthetic organism has will enable it to photosynthesise efficiently in a particular environment.

Aerobic respiration is said to be more efficient than anaerobic respiration. Explain this statement.

Aerobic respiration is more efficient as the glucose molecule is broken down to simple inorganic materials, carbon dioxide and water, and the maximum amount of energy is extracted – enough to make 36 molecules of ATP. Anaerobic respiration represents the partial breakdown of a glucose molecule to alcohol and lactic acid (still large molecules) and releases only enough energy to make 2 molecules of ATP.

how does temp affect enzymes

As temperature increases above optimal, the enzyme begins to denature, creating a conformational change in the active site and decreasing the rate of reaction.¹As temperature decreases below optimal, there is not enough kinetic energy for the enzyme to function efficiently, thereby decreasing the rate of reaction.²

limitations of an experiment

no control

if the independent variable does not have a wide enough range to test the hypothesis

what wave length is best

red and blue

Describe the role played by each of the coenzymes NADPH and ATP in photosynthesis. 

NADPH: The hydrogen produced in the light dependent stage binds with NADP⁺ to form NADPH. The NADPH moves into the stroma and delivers hydrogen for the light independent reaction/Calvin cycle.

ATP: is produced as a result of light absorption and the splitting of water in the light dependent stage of photosynthesis. It then diffuses into the stroma where it breaks down to ADP and Pi. The energy released is used in the light independent stage/Calvin cycle to join hydrogen to carbon dioxide to make triose/glucose.

Outline three additional steps that could be carried out to extend the investigation and assist with identifying the unknown plant.

• Test for the presence or absence of malate. If present, the plant is not a C3 plant.

•  Section leaves to look for the presence of bundle-sheath cells. If present, the plant is a C4 plant.

•  Test for the presence or absence of PEP carboxylase. If absent, the plant is not a C3 plant.

•  Compare the plant's structure with other known C3, C4 and CAM plants.

•  Compare the plant's genome with other known C3, C4 and CAM plants.

metabolic activity

mention atp production and how it requires atp

The scientists repeated the experiment. They kept all conditions the same as for the first experiment, except that the cells were kept in low-oxygen conditions.

Would the uptake of glucose into the cells be expected to be higher, lower or the same as for the first experiment? Justify your response.

The uptake of glucose will be higher in low-oxygen conditions as less ATP is produced in aerobic respiration per glucose molecule; therefore, to produce the same amount of ATP, more glucose will be required.

Or

Glucose uptake will be lower in low-oxygen conditions as the cell will respire anaerobically, resulting in less ATP produced per glucose molecule and less energy available for cellular activities. Cellular activities would reduce, and less glucose would be required.

when chloryphyll cannot absorb any more light is it

SATURATED

when describing trend

mention anincrease and decreate with data points. and the rate of increase

when explaining a control variable in this incase the control was o2 and co2 concetrationa dn the temp was constatnly changing

All other factors were kept constant therefore any change in carbon dioxide levels or oxygen levels must be due to temperature alone.

Explain the role played by chlorophyll in the light dependent reaction

Chlorophyll absorbs the light energy (captures light energy) needed to initiate the light dependent reactions (1 mark)

Chlorophyll facilitates the splitting of the water molecule or any other reasonable answer (1 mark)

Experiment 1: Leaf in Bottle with CO₂ Sensor and Heat Lamp (Photosynthesis)

Independent Variable

• Presence of light (via heat lamp)

Dependent Variable

• Change in carbon dioxide concentration (measured by CO₂ sensor)

Controlled Variables

1. Type and volume of the bottle

2. Duration of exposure to light

3. Type of plant/leaf used

Random Errors & Improvements

1. Size of the leaf

   • 🔧 Improvement: Use a leaf punch to standardize leaf area (e.g., same diameter circle).

2. Natural differences in stomata density

   • 🔧 Improvement: Use leaves from the same species, age, and position on the plant (e.g., all upper canopy leaves).

3. Ambient CO₂ fluctuations

   • 🔧 Improvement: Conduct the experiment in a sealed or controlled-air environment (like a lab with limited air circulation).

Systematic Errors & Improvements

1. CO₂ sensor calibration issues

   • 🔧 Improvement: Calibrate the sensor before each trial using a known gas concentration standard.

2. Heat lamp distance inconsistency

   • 🔧 Improvement: Fix the lamp at a set distance using a stand or ruler, and use the same setup each time.

3. Glass filtering out some light wavelengths

   • 🔧 Improvement: Use a glass that allows full-spectrum light or use a plastic dome specifically designed for plant growth experiments.

Experiment 2: Yeast Respiration in Tubes with Balloons

Independent Variable

• Type of condition or substance added (e.g., sugar vs. sweetener, water temp, shampoo presence)

Dependent Variable

• Size of the balloon (indirect measure of CO₂ production from yeast respiration)

Controlled Variables

1. Amount of yeast (1.2 g in all tubes)

2. Volume of liquid added (10 mL total for tubes 1, 2, 4; 10 mL in tube 3 from 8 mL water + 2 mL shampoo)

3. Time of incubation (1 hour)

Random Errors & Improvements

1. Balloon elasticity differences

   • 🔧 Improvement: Pre-stretch all balloons or use lab-grade balloons tested for uniform elasticity.

2. Room temperature changes

   • 🔧 Improvement: Conduct all trials in a temperature-controlled room or put all tubes in the same environment.

3. Yeast granule inconsistency

   • 🔧 Improvement: Dissolve yeast in water and mix thoroughly before adding to each tube to ensure even distribution.

Systematic Errors & Improvements

1. Faulty pipette/scale

   • 🔧 Improvement: Regularly calibrate lab equipment and check for accuracy using reference weights or volumes.

2. Water bath not at true 32 °C

   • 🔧 Improvement: Use a thermometer to check the water bath’s actual temperature, and adjust it or use a thermostatically controlled bath.

3. Balloon leakage

   • 🔧 Improvement: Test balloon seals beforehand with water or air, and use rubber bands or clamps for a tight seal.

how can CRISPR-Cas 9 could be used to:

●modify Rubisco to increase its affinity to CO2/decrease its affinity to O2

increasing the efficiency of photosynthesis.

●alter C3 plants so they function as C4 or CAM plants, resulting in

greater efficiency of photosynthesis in warm, dry climates.

●increase drought tolerance of plants, so photosynthesis can proceed

with smaller quantities of water.

●modify chloroplast so they can capture more light, increasing the

efficiency of photosynthesis.

●modify stomata, so they stay open for longer to increase CO2 uptake,

increasing the efficiency of photosynthesis.

●modify stomata, so they stay closed during the day to reduce water

loss, increasing the efficiency of photosynthesis.

C4 plant Adaptation + advantage

Adapatation

• Carbon fixation occurs in mesophyll cells, while the Calvin cycle occurs in bundle sheath cells.

Advantage

• A CO₂ rich environment is created around Rubisco, reducing photorespiration (reducing wasteful energy loss).

CAM plant

Adaptation

• Carbon dioxide is fixed into organic acids at night when stomata are open.

Advantage

• CO₂ is constantly available for the Calvin cycle, reducing photorespiration (reducing wasteful energy loss).
  OR

• Storage of CO₂ at night means that photosynthesis can still occur during the day when stomata are closed.

Adaptation

• Stomata do not open during the day.

Advantage

• Stomata are closed during the day which minimises water loss.

Describe the process by which this input (chemical reactant) enters a chloroplast. (2

marks)

• process is osmosis (1);

• water molecules able to diffuse across semi-permeable membrane from a from area of high water concentration

to low water concentration (1)

whats a limiting factor

A limiting factor is preventing any further increase in the rate of photosynthesis and oxygen production.

The limiting factor is the 'weakest link' that restricts the rate from increasing.

Explain why the rate of photosynthesis fastest in the all light condition and slowest in the

green light condition? (2 marks)

ALL: all wavelengths of light absorbed, more energy, faster rate of photosynthesis. (1 mark)

GREEN: most green light is reflected, therefore less light is absorbed leading to lower rate of

photosynthesis (1 mark)

what happens if stomata closes

Stomata close so no CO2 can be absorbed/enter the plant (1 mark)

Light independent reaction cannot proceed so no glucose is produced. OR CO2 is an input of

the light independent reaction so rate of reaction decreases. (1 mark)