9.4.4

Limiting Factors

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The Rate of Photosynthesis

The four key factors affecting the rate of photosynthesis are:

Temperature

Temperature

  • Initially, the rate of photosynthesis increases as the temperature increase. Above about 45°C, the rate starts to fall.
  • Enzymes such as rubisco play an important role in photosynthesis.
  • At low temperatures, enzymes have less kinetic energy and are less likely to successfully collide with the substrate. This means fewer enzyme-substrate complexes are formed.
  • Above the optimum temperature, enzymes will denature and the rate of photosynthesis will fall.
Light intensity

Light intensity

  • Increasing light intensity increases the rate of photosynthesis because more energy is provided.
  • In low light intensities the light-dependent reaction cannot take place. This causes levels of reduced NADP and ATP to fall.
  • Reduced NADP and ATP are necessary to convert GP to TP and to regenerate RuBP.
  • Without reduced NADP and ATP the Calvin cycle cannot take place and rate of photosynthesis declines.
Carbon dioxide (CO<sub>2</sub>) concentration

Carbon dioxide (CO2) concentration

  • Increasing the CO2 concentration increases the rate of photosynthesis.
  • At high CO2 concentrations, there is more carbon available for fixation in the Calvin cycle.
  • If the rate of the Calvin cycle increases, more GP and TP is produced and more RuBP is regenerated.
  • Very high CO2 concentrations can cause stomata to open wider causing more water to be lost.
  • Too much water loss will then cause the stomata to close and the rate of photosynthesis to slow again.
Chlorophyll concentration

Chlorophyll concentration

  • High chlorophyll concentration gives a high rate of photosynthesis.
  • If there is more chlorophyll, light can be absorbed at a faster rate. This will cause the light-dependent reaction rate to increase.

Agricultural Practices

Commercial growers need to understand limiting factors of photosynthesis to try and maximise yields. This is done by preventing low light intensity, low temperatures and low CO2 levels.

Light intensity

Light intensity

  • A high light intensity is optimum for maximising yield.
    • This is achieved by providing lamps and a lit environment at night time.
Temperature

Temperature

  • The optimum temperature for plant enzymes is approximately 25oC.
    • A temperature below 10oC or above 40oC would decrease the rate of photosynthesis and reduce yields.
    • In order to achieve an optimum temperature, glasshouses are used to trap heat energy from sunlight.
    • Heating and cooling systems can also be used.
Carbon dioxide

Carbon dioxide

  • The atmospheric concentration of CO2 is 0.04% but increasing this to 0.4% increases rate of photosynthesis.
    • This can be done by adding CO2 into the air.
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1

Unity & Diversity - Molecules

1.1

Water

1.1.1Water & Hydrogen Bonding1.1.2IB Multiple Choice - Water & Hydrogen Bonding1.1.3Extended Response - Water
1.2

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1.4

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2

Unity & Diversity - Cells

2.1

The Origin of Cells

2.1.1Origins - Endosymbiosis
2.2

Introduction to Cells

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Ultrastructure of Cells

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2.4

Cell Division

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Structure of DNA & RNA

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2.6

DNA Replication, Transcription & Translation

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2.7

Cell Respiration

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2.8

Photosynthesis

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2.9

Viruses

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3

Unity & Diversity - Organisms

3.1

Diversity of Organisms

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3.2

Evidence for Evolution

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Natural Selection

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4

Unity & Diversity - Ecosystems

4.1

Classification

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Cladistics

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4.3

Evolution & Speciation

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Conservation of Biodiversity

4.4.1Coming Soon!
5

Form & Function - Molecules

5.1

Carbohydrates & Lipids

5.1.1Monosaccharides5.1.2Disaccharides & Polysaccharides5.1.3Triglycerides & Phospholipids5.1.4Cellulose5.1.5Starch & Glycogen
5.2

Proteins

5.2.1Structure & Functions of Proteins
6

Form & Function - Cells

6.1

Membranes & Membrane Transport

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6.2

Organelles & Compartmentalization

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6.3

Cell Specialization

6.3.1Cell Specialization
7

Form & Function - Organisms

7.1

Gas Exchange

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7.2

Transport

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7.3

Muscle & Motility

7.3.1Skeletal Muscle7.3.2Sliding Filament Theory7.3.3Contraction
8

Form & Function - Ecosystems

8.1

Species, Communities & Ecosytems

8.1.1Population Dynamics8.1.2Communities & Measuring Diversity8.1.3Relationships Between Populations8.1.4Overview of Ecosystems8.1.5Nutrient Cycles8.1.6Fertilisers8.1.7Eutrophication8.1.8Chi-Squared Test
8.2

Energy Flow

8.2.1Energy8.2.2Energy Flow8.2.3Biomass & Food Chains8.2.4Heterotrophs & Autotrophs
8.3

Carbon Cycle

8.3.1Carbon Cycle
8.4

Climate Change

8.4.1Carbon Dioxide8.4.2The Greenhouse Effect8.4.3Global Warming8.4.4Maintaining Biodiversity
9

Interaction & Interdependence - Molecules

9.1

Enzymes

9.1.1Enzymes9.1.2Factors Affecting Enzyme Activity9.1.3Enzyme-Controlled Reactions9.1.4End of Topic Test - Enzymes
9.2

Metabolism

9.2.1Molecules to Metabolism
9.3

Cell Respiration

9.3.1Glycolysis9.3.2Aerobic Respiration
9.4

Photosynthesis

9.4.1Light-Dependent Reaction9.4.2Light-Independent Reaction9.4.3End of Topic Test - Photosynthesis Reactions9.4.4Limiting Factors9.4.5Photosynthesis Experiments9.4.6End of Topic Test - Photosynthesis9.4.7End of Topic Test - Photosynthesis
10

Interaction & Interdependence - Cells

10.1

Chemical Signalling

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Neural Signalling

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Adaptation to Environment

10.3.1Coming Soon!
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Ecological Niches

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11

Interaction & Interdependence - Organisms

11.1

Integration of Body Systems

11.1.1Plant Tropisms
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Defence Against Disease

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12

Interaction & Interdependence - Ecosystems

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Transfers of Energy & Matter

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13

Continuity & Change - Molecules

13.1

DNA Replication

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Protein Synthesis

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Mutation & Gene Editing

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14

Continuity & Change - Cells

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Water Potential

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15

Continuity & Change - Organisms

15.1

Inheritance

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15.2

Homeostasis

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16

Continuity & Change - Ecosystems

16.1

Natural Selection

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16.2

Stability & Change

16.2.1Coming Soon!
16.3

Climate Change

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Practice questions on Limiting Factors

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What are the key factors affecting the rate of photosynthesis?Fill in the list
  2. 2
    What effect does increasing light intensity have on rate of photosynthesis?Multiple choice
  3. 3
    Which of the following statements about carbon dioxide are true?True / false
  4. 4
    What three factors can farmers control to maximise yields?Fill in the list
  5. 5
    What is the approximate optimum temperature range to maximise plant yields?Multiple choice
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End of Topic Test - Photosynthesis Reactions

Photosynthesis Experiments