PhotosynthesisAQA GCSE Biology: Flashcards

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Write the word equation for photosynthesis.

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Write the word equation for photosynthesis.: Carbon dioxide + water → glucose + oxygen (in the presence of light energy)
Write the balanced symbol equation for photosynthesis.: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Define photosynthesis and explain what type of reaction it is.: Photosynthesis is an endothermic reaction that converts light energy into chemical energy stored in glucose. It requires energy input (light) to proceed.
Name the three factors that limit the rate of photosynthesis.: Light intensity Carbon dioxide concentration Temperature
Explain how light intensity affects the rate of photosynthesis.: As light intensity increases, the rate of photosynthesis increases proportionally (up to a point) because more light energy is available to drive the light-dependent reactions. Beyond a certain point, another factor becomes limiting.
Explain how carbon dioxide concentration affects the rate of photosynthesis.: As carbon dioxide concentration increases, the rate of photosynthesis increases because more CO₂ is available as a substrate for the light-independent reactions. At very high concentrations, temperature or light becomes limiting instead.
Explain how temperature affects the rate of photosynthesis.: As temperature increases, the rate of photosynthesis increases because enzyme activity increases. However, above approximately 45°C, enzymes denature and the rate decreases rapidly.
State the inverse square law and explain its application to light intensity in photosynthesis.: The inverse square law states that light intensity is inversely proportional to the square of the distance from the light source (I ∝ 1/d²). As distance from a light source increases, light intensity decreases, reducing the rate of photosynthesis.
Name five uses of glucose produced during photosynthesis.: Respiration (for energy release) Making cellulose (for cell walls) Making amino acids (for proteins) Storage as starch (in plants) Storage as oils/lipids (in seeds)
Describe the location of the light-dependent reaction in the chloroplast.: The light-dependent reaction occurs in the thylakoid membranes of the chloroplast. Light energy is absorbed by chlorophyll, water is split, and energy carriers (ATP and NADPH) are produced.
Describe the location of the light-independent reaction (Calvin cycle) in the chloroplast.: The light-independent reaction occurs in the stroma of the chloroplast. It uses ATP and NADPH from the light-dependent reaction to convert carbon dioxide into glucose.
Explain what happens to glucose that is not used immediately in the plant cell.: Glucose is converted and stored as starch (in the stroma) for later use during respiration, or converted to cellulose for structural support in cell walls, or converted to oils/lipids for storage in seeds.
When investigating the effect of light intensity on photosynthesis, what is the independent variable, dependent variable, and a control variable?: Independent variable: light intensity (measured by distance from light source) Dependent variable: rate of photosynthesis (measured by oxygen production or carbon dioxide uptake) Control variable: temperature, carbon dioxide concentration, plant species, wavelength of light
When investigating the effect of carbon dioxide concentration on photosynthesis, what is the independent variable and dependent variable?: Independent variable: carbon dioxide concentration (measured in ppm or by changing concentration in a sealed system) Dependent variable: rate of photosynthesis (measured by oxygen production or glucose production)
Sketch and describe the shape of a graph showing the effect of light intensity on photosynthesis rate.: The graph is a curve that starts at the origin (0,0). It increases steeply at first, then the gradient decreases, eventually levelling off as another factor (like temperature or CO₂) becomes limiting. The curve is non-linear.