PHOTOSYNTHESIS
What is the role of rubisco in Photosynthesis
Answer: Fixes carbon dioxide for the light independent stage
Identify the 3 stages of cellular respiration?
Glycolysis
Krebs Cycle
Electron Transport Chain
What is an enzyme?
a biological catalyst, usually a protein, that speeds up chemical reactions in living organisms
What is the enzyme used to fix carbon dioxide from air in CAM plants?
PEP carboxylase
What is the use of crisper cas 9 in photosynthesis?
Edit the genome of crops potentially improving photosynthesis and crop yields.
The light-dependent and light-independent stages of photosynthesis are often described as linked processes. Explain this.
The stages are often described as linked because the light-independent reaction needs the products of the light-dependent reaction in order to proceed
What role do enzymes play in cellular respiration?
Enzymes are essential to cellular respiration because they act as biological catalysts that speed up the chemical reactions of this process. They do this by lowering the activation energy required for each reaction to occur.
Compare catabolic and anabolic reactions
Catabolic: breakdown of a larger molecule into smaller components, with the release of energy (exergonic)
Anabolic: smaller molecules are joined to form larger ones. They require the input of energy.
Explain why it is beneficial for a plant to have a high level of carbon dioxide in its leaves
increases the rate of photosynthesis → therefore increasing production of glucose/growth or reducing the production of hydrogen peroxide and ammonia → which are toxic and harmful to plants)
- What are biofuels?
Fuels made from biomass and offer an alternative to traditional fossils fuels.
What is the relationship between light dependent and light independent stages of photosynthesis?
The outputs of light dependent stage (co-enzymes) are used as inputs in the light independent stage to provide energy, and protons and electrons for the calvin stage.
Identify and describe 3 factors that affect the rate of cellular respiration
Glucose Availability: Increased glucose concentration → increases cellular respiration until a certain point. The rate plateaus as all enzyme active sites are occupied by substrate or there is another limiting factor.
Temperature: As temperature increases → the rate of cellular respiration increases. After optimal temperature the enzymes denature lowering the rate of cellular respiration.
Oxygen Concentration: As oxygen levels increase → the rate of cellular respiration increases until a certain point then plateaus due to another limiting factor.
pH: As pH is at optimal level → the rate of cellular respiration increases. Above or below optimal pH causes the enzymes to denature and slows the rate of cellular respiration.
Explain how an increase in temperature affects the activity of enzymes
A rise in temperature gives both the enzyme and substrate molecules more kinetic energy, this results in more frequent and energetic collisions between the enzyme and the substrate molecules. Consequently, more enzyme-substrate complexes are formed per unit of time. If the temperature exceeds the optimal temperature, the enzyme is denatured and the rate of reaction decreases.
Describe three distinct differences between C3 and C4 plants.
C3 plants use Rubisco to fix carbon dioxide, whereas C4 plants use PEP carboxylase.
C3 plants are prone to photorespiration where Rubisco binds to oxygen, whereas this is less of an issue in C4 plants, which have adaptations to avoid this.
In C3 plants the Calvin cycle is in the mesophyll cell, whereas in C4 plants the Calvin cycle is in the bundle sheath cells.
- Compare strengths and weaknesses of biofuels
strength= good climate impact, energy security, localised energy
weaknesses= food vs. fuel, cost,
What is the location, input and output of light Dependent Stage
Location: Thylakoid/gramums
Inputs: Water (H2O), NADP+, ADP+Pi
Outputs: Oxygen, NADPH, ATP
Compare anaerobic respiration and aerobic respiration, including stages, advantages and disadvantages and ATP yield.
Anaerobic Respiration
No oxygen
Stages:
Glycolysis
Fermentation
Advantages:
- Fast ATP production
Disadvantages:
- Low ATP yield
- Too much lactic acid → toxic
ATP Yield: 2 ATP per glucose molecule
Aerobic Respiration
Oxygen
Stages:
Glycolysis
Krebs Cycle
Electron Transport Chain
Advantages
- High ATP yield
Disadvantages:
- Slow ATP production
ATP Yield: 26-28 ATP per glucose molecule
What are the four factors that affect enzyme activity?
Increasing the temperature
pH activity
Substrate concentration
Enzyme concentration
Explain the process of CO2 fixation and storage in CAM plants at night
At night, CAM plants open their stomata, allowing CO₂ to enter the leaf mesophyll cells. The enzyme PEP carboxylase then fixes this CO₂ with phosphoenolpyruvate (PEP), forming a four-carbon organic acid like malate. This malic acid is then stored in the plant's central vacuole until the next day. During photosynthesis, the malate is converted back into carbon dioxide which then enters into the Calvin cycle
- List 3 applications of biofuels
transportation fuels, generate electricity, reduce impact on climate
Explain the role of chlorophyll in photosynthesis and describe how it contributes to the production of glucose.
Chlorophyll is a pigment found in the chloroplasts of plant cells that absorbs light energy. This light energy is used to convert carbon dioxide and water into glucose and oxygen during photosynthesis. Without chlorophyll, plants would not be able to capture the energy needed to drive the chemical reactions that produce glucose.
Explain the location, inputs, outputs and function of each stage of Aerobic respiration
Glycolysis
Location: Cytosol
Function: breakdown of glucose into 2 molecules of pyruvate.
Inputs:
Glucose
NAD+ (x2)
ADP + Pi (x2)
Outputs:
Pyruvate (x2)
NADH (x2)
ATP
Krebs Cycle
Location: Mitochondrial matrix
Function: produces high energy co-enzymes.
Inputs:
Acetyl CoA
NAD+
FAD
ADP + Pi (x2)
Outputs:
Carbon dioxide
NADH
FADH2
ATP (x2)
Electron Transport Chain
Location: Cristae
Function: produces ATP
Inputs:
Oxygen
NADH
FADH
ADP + Pi
Outputs:
Water
NAD+
FAD
ATP (26-28)
What is the process of competitive inhibition and non-competitive inhibition?
Competitive inhibition: The inhibitor binds to the active site of the enzyme - forming an enzyme-inhibitor complex. This directly blocks the active site - no reaction occurs.
Non-competitive inhibition: The inhibitor binds to the allosteric site of the enzyme - forming an enzyme-inhibitor complex. This changes the shape of the active site - no reaction occurs
Explain how C4 plants minimise photorespiration and why this provides an advantage over C3 plants in hot environments.
C4 plants minimise photorespiration by initially fixing carbon dioxide in mesophyll cells using the enzyme PEP carboxylase, which does not bind to oxygen (1 mark). The CO₂ is converted into a 4-carbon compound such as malate, which is transported to bundle sheath cells (1 mark). In bundle sheath cells, the CO₂ is released at high concentration around RuBisCO, reducing the chance of RuBisCO binding to oxygen (1 mark). This adaptation decreases photorespiration and allows more efficient photosynthesis under conditions of high temperature and light (1 mark). As a result, C4 plants have an advantage over C3 plants in hot environments because they conserve energy and resources while maintaining higher rates of photosynthesis (1 mark).
OR
PEP carboxylase in mesophyll cells.
Formation of 4-carbon compounds.
CO₂ released in bundle sheath cells around RuBisCO.
Reduces photorespiration, increases efficiency.
Advantage in hot environments (energy and productivity).
What are some examples of crisper cas 9 potential changes to crops?
modifying RUBISCO's activity. Change C3 plants to C4 or CAM, having physical tolerance to heat or drought, immunity against bacteria and viruses