Photosynthesis | Biology | Khan Academy

1.Which of the following correctly identifies ALL the reactants in the overall equation for photosynthesis? 2 pts

• Glucose and oxygen
• Carbon dioxide, water, and light energy
• ATP, NADPH, and carbon dioxide
• Oxygen and water

2.Where does photosynthesis primarily occur within a plant cell? 2 pts

• The mitochondria
• The nucleus
• The chloroplasts
• The cell membrane

3.What is the specific role of chlorophyll in photosynthesis? 2 pts

• It stores glucose produced during the Calvin cycle
• It splits water molecules to release carbon dioxide
• It absorbs light energy from the sun
• It transports ATP to the stroma

4.Which byproduct is released when water molecules are split during the light-dependent reactions? 2 pts

• Carbon dioxide
• Glucose
• ATP
• Oxygen

5.In which location within the chloroplast does the Calvin cycle take place? 2 pts

• The thylakoid membranes
• The outer chloroplast membrane
• The stroma
• The cell wall

6.Which pair of energy-carrying molecules is produced during the light-dependent reactions and then used in the Calvin cycle? 2 pts

• Glucose and oxygen
• CO₂ and H₂O
• ATP and NADPH
• Cellulose and starch

7.A student observes that increasing the light intensity beyond a certain point produces no further increase in the rate of photosynthesis. Which term best describes this threshold? 2 pts

• The Calvin limit
• The light saturation point
• The enzyme denaturation point
• The stomata threshold

8.Which of the following best explains why plants are classified as autotrophs? 2 pts

• They consume other organisms to obtain energy
• They release carbon dioxide during respiration
• They produce their own food through photosynthesis
• They depend on animals for organic molecules

9.Describe the two main stages of photosynthesis. For each stage, identify (a) where it occurs within the chloroplast, (b) the key inputs, and (c) the key outputs. 5 pts

10.Explain how the concentration of carbon dioxide affects the rate of photosynthesis, and identify what ultimately limits further increases in the rate even when CO₂ is abundant. 5 pts

11.The video describes photosynthesis as 'the foundation of nearly all food chains on Earth.' Using information from the video, explain why this statement is accurate, referencing both the products of photosynthesis and the concept of autotrophs and heterotrophs. 5 pts

12.Carbon dioxide enters a plant leaf through which structures? 2 pts

• Root hairs
• Stomata
• Thylakoid membranes
• Vascular bundles

13.Which of the following best describes the role of glucose produced during photosynthesis? 2 pts

• It is immediately released into the atmosphere as a byproduct.
• It is used only to produce oxygen for the plant.
• It provides energy and serves as a building block for molecules like cellulose and starch.
• It is transported to the thylakoid to power the light-dependent reactions.

14.Which of the following correctly distinguishes autotrophs from heterotrophs? 2 pts

• Autotrophs consume other organisms; heterotrophs make their own food.
• Autotrophs produce their own food; heterotrophs must consume other organisms for energy.
• Both autotrophs and heterotrophs rely on sunlight for energy.
• Autotrophs use only water; heterotrophs use only carbon dioxide.

15.What happens to the rate of photosynthesis as light intensity continues to increase beyond the light saturation point? 2 pts

• It continues to rise proportionally with light intensity.
• It drops sharply to zero.
• It plateaus and no longer increases.
• It decreases gradually due to chlorophyll breakdown.

16.What is the effect of excessively high temperatures on the rate of photosynthesis in most plants? 2 pts

• Photosynthesis accelerates because reactions have more thermal energy.
• Enzymes denature, reducing the rate of photosynthesis.
• The light saturation point is reached more quickly.
• Stomata open wider, allowing more CO₂ to enter.

17.According to the video, what is the optimal temperature range for photosynthesis in most plants? 2 pts

• 10–20 degrees Celsius
• 25–35 degrees Celsius
• 40–50 degrees Celsius
• 15–25 degrees Celsius

18.Why is photosynthesis considered the foundation of nearly all food chains on Earth? 2 pts

• It produces water that all organisms need to survive.
• It is the primary way energy from the sun enters the biosphere.
• It breaks down organic molecules to release energy for consumers.
• It supplies nitrogen to plants, which is then passed to animals.

19.Explain how an increase in carbon dioxide concentration affects the rate of photosynthesis, and describe what limits this effect. 4 pts

20.Describe two consequences for life on Earth if photosynthesis were to stop completely. Use evidence from the video to support each consequence. 5 pts

21.Compare the four environmental factors that affect the rate of photosynthesis. For each factor, explain how it can both increase and limit the rate of photosynthesis. 5 pts