P1 - Bioenergetics

• What are the two essential reactions for life on Earth mentioned in the study material?

  Photosynthesis and respiration
• What happens during photosynthesis?

  Light energy is absorbed by chlorophyll to convert carbon dioxide and water into glucose and oxygen.

  
• What is the role of chlorophyll in photosynthesis?

  Chlorophyll absorbs light energy in chloroplasts.

  
• Why is photosynthesis classified as an endothermic reaction?

  Because energy is transferred from the environment to chloroplasts by light.

  
• What are the word and symbol equations for photosynthesis?

  Word equation: Carbon dioxide + Water → Glucose + Oxygen; Symbol equation: $6CO_2 +$$6H_2O \rightarrow C_6H_{12}O_6 +$$6O_2$

  
• Why is the misconception that "photosynthesis releases energy" incorrect?

  Because photosynthesis absorbs light energy to make glucose.

  
• Why is the misconception that "photosynthesis is the term given to respiration in plants" incorrect?

  Because photosynthesis and respiration are two different processes that both occur in plant cells.
• Why is the misconception that "plants photosynthesize to make oxygen" incorrect?

  Because oxygen is a by-product of photosynthesis, and the main aim is to make glucose.

  
• What does a limiting factor do in the context of photosynthesis?

  A limiting factor restricts the rate of photosynthesis if it is at low levels.

  
• How does temperature affect the rate of photosynthesis?

  As temperature increases, the rate of photosynthesis increases until an optimum temperature is reached, after which the rate decreases.

  
• What happens to enzymes controlling photosynthesis as temperature increases?

  They gain kinetic energy, which increases the rate of photosynthesis.

  
• What occurs to enzymes above the optimum temperature?

  They denature, causing the rate of photosynthesis to decrease.

  
• How does light intensity affect the rate of photosynthesis?

  As light intensity increases, the rate of photosynthesis increases until another factor becomes limiting.

  
• What happens to the rate of photosynthesis when light intensity is above a certain level?

  The rate stops increasing because another factor becomes limiting, such as temperature or CO2 concentration.

  
• How does CO2 concentration affect the rate of photosynthesis?

  As CO2 concentration increases, the rate of photosynthesis increases until another factor becomes limiting.

  
• What happens to the rate of photosynthesis when CO2 concentration is above a certain level?

  The rate stops increasing because another factor becomes limiting, such as temperature or light intensity.

  
• How does chlorophyll affect the rate of photosynthesis?

  Chlorophyll affects how much light energy can be absorbed.

  
• What law describes the relationship between distance of a light source from a plant and light intensity?

  The inverse square law.

  
• How can you identify the limiting factor from a graph of photosynthesis rate showing two or three factors?

  If increasing a particular factor increases the rate of photosynthesis, that factor is the limiting factor.

  
• How can farmers use their knowledge of limiting factors to increase profits?


  By removing limiting factors to gain maximum rates of photosynthesis, thus increasing plant yield.
• Why is the misconception that "water is a limiting factor in photosynthesis" incorrect?

  Because water is not considered a limiting factor as its volume needed is very small.

  
• What is the most likely limiting factor for photosynthesis in a greenhouse on a hot summer’s day?

  Carbon dioxide concentration.

  
• Why does the concentration of CO2 in a greenhouse increase between points X and Y?

  Because respiration occurs, releasing CO2, and there is no photosynthesis due to lack of light.

  
• Why does the concentration of CO2 in a greenhouse decrease between points Y and Z?

  Because photosynthesis occurs as there is light, and the rate of photosynthesis is greater than the rate of respiration.

  
• What temperature should a greenhouse owner keep to grow lettuces quickly and cheaply in winter?

  21.5 to 22 °C for maximum rate of photosynthesis.
• What is the method to investigate the effect of light intensity on the rate of photosynthesis using pondweed?

  1. Vary light intensity by changing the distance of the light source (e.g., 10, 20, 30, 40 cm).

  2. Control variables:

  • Use the same length/type of pondweed.
  • Maintain temperature with a water bath.
  • Use a set concentration of sodium hydrogen carbonate.

  3. Measure photosynthesis rate by counting oxygen bubbles or collecting gas in a syringe.

  4. Repeat three times at each light intensity to identify anomalies and calculate a mean.

  
• What are the independent, dependent, and control variables in the experiment investigating light intensity on the rate of photosynthesis?

  Independent: Distance from light source; Dependent: Volume of O2 released; Control: Temperature, CO2 supply, pondweed length/type, color of light.

  
• Why is sodium hydrogen carbonate used in the experiment?

  To provide carbon dioxide so that it is not a limiting factor.
• How can you test if the bubbles produced by pondweed contain oxygen?

  Add a burning splint; it will burn more brightly if oxygen is present.

  
• Why is counting bubbles not an accurate way of measuring the volume of oxygen produced?

  Because bubbles are different sizes and can be easy to miss.
• How could the method be improved to measure the rate of photosynthesis more accurately?

  By measuring the volume of O2 released in a gas syringe and increasing the length of time for measurement.

  
• What is the advantage of using an LED light source in the experiment?

  It does not emit a lot of infrared/thermal radiation, helping to control temperature.
• How could you modify the experiment to investigate the effect of CO2, temperature, or wavelength of light on the rate of photosynthesis?

  • For CO2: Use different concentrations of sodium hydrogen carbonate.
  • For temperature: Use different temperature water baths.
  • For wavelength: Use different colored filters over the bulb.
  • Control distance from light source and type/length of pondweed.

  
• What are the uses of glucose produced in photosynthesis?

  1. Used for respiration; 2. Converted into insoluble starch for storage; 3. Used to produce fats/oils; 4. Used to produce cellulose; 5. Used to produce amino acids.

  
• Why is the misconception that "glucose is used for growth" considered too vague?

  Because glucose has specific uses summarized by the acronym 'SCARF': starch, cellulose, amino acids, respiration, fats (and oils).

  
• Why did a leaf left in a cupboard with no light contain glucose but not starch?

  Because starch has been converted to glucose for respiration due to lack of light for photosynthesis.

  
• How does TMV affect plant growth?

  TMV reduces chlorophyll, leading to decreased photosynthesis, less glucose production, and ultimately less energy for growth.
• What is the relationship between glucose and respiration in plants?

  Glucose is needed for respiration to release energy for growth and other processes.

  
• How do amino acids relate to glucose in plants?

  Amino acids are produced from glucose combined with nitrate ions from the soil for protein synthesis.

  
• What is the role of cellulose in plant cells?

  Cellulose strengthens the cell wall.