💡 7th Grade Life Science: Photosynthesis Practice Questions

The correct answer is B.

• 💡 Understanding Photosynthesis: Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.
• 👉 Key Purpose: The main goal for a plant performing photosynthesis is to create its own food, specifically glucose (a type of sugar). This sugar provides the energy the plant needs to grow, develop, and carry out all its life functions.
• ❌ Why other options are incorrect:
  • A: Plants absorb carbon dioxide, they don't primarily release it during photosynthesis.
  • C: Plants release oxygen as a byproduct of photosynthesis, they don't absorb it for this process.
  • D: While transpiration (related to water movement) can have a cooling effect, it's not the primary purpose of photosynthesis itself.
• ✅ Therefore, producing food for energy and growth is the fundamental reason plants undergo photosynthesis.

The correct answer is C.

• 💡 Reactants of Photosynthesis: Photosynthesis requires specific ingredients, often called reactants, to begin the process.
• 👉 From the Environment: Plants absorb water from the soil through their roots and take in carbon dioxide gas from the air through tiny pores on their leaves called stomata.
• 📌 Energy Source: While sunlight is absolutely crucial, it's an energy source that powers the reaction, not a raw material that is chemically incorporated like water and carbon dioxide.
• ❌ Why other options are incorrect:
  • A: Glucose is a product, and oxygen is a byproduct.
  • B: Oxygen is a byproduct, not a primary raw material.
  • D: Sunlight is energy, and nitrogen is important for plant growth but not a direct reactant in the photosynthesis equation itself.
• ✅ So, carbon dioxide and water are the two main raw materials.

The correct answer is C.

• 💡 Photosynthesis Equation: The overall process of photosynthesis can be represented by a simple equation.
• 👉 Energy Input: For carbon dioxide and water to react and form glucose and oxygen, a significant amount of energy is required. This energy comes directly from the sunlight. Without sunlight, the chemical reaction cannot occur.
• 📌 Role of Chlorophyll: While chlorophyll is essential because it absorbs the sunlight energy, it acts as a catalyst and pigment within the plant, not a reactant in the equation itself.
• ❌ Why other options are incorrect:
  • A: Heat is not the primary energy source for photosynthesis; sunlight is.
  • B: Chlorophyll is a pigment that helps capture sunlight, but it's not a reactant that gets transformed into products.
  • D: Minerals are nutrients for the plant but not direct inputs for the chemical reaction of photosynthesis.
• ✅ Therefore, Sunlight Energy is the missing component that powers the reaction.

• 💡 Photosynthesis Requirements: Photosynthesis needs three main things: carbon dioxide, water, and sunlight energy.
• 👉 The Role of Light: Sunlight provides the energy needed to power the chemical reaction that converts carbon dioxide and water into glucose and oxygen. It's like the fuel for the plant's food-making factory.
• ❌ No Light, No Photosynthesis: Without any light source, even if there's enough water and carbon dioxide, the plant cannot capture the energy required to start and complete the photosynthesis process.
• ✅ Conclusion: No, the plant will not be able to perform photosynthesis effectively without a light source. It needs light energy to convert the raw materials (carbon dioxide and water) into food (glucose). Over time, the plant would eventually run out of stored energy and die.

• 💡 Limiting Factors: In photosynthesis, if any of the essential ingredients (carbon dioxide, water, or sunlight) are in short supply, they can become a "limiting factor" that slows down the entire process.
• 👉 Carbon Dioxide as a Reactant: Carbon dioxide \( (CO_2) \) is one of the key raw materials that plants take in from the atmosphere to build glucose (sugar). The chemical equation for photosynthesis is:
  \[ 6CO_2 + 6H_2O + \text{Sunlight Energy} \rightarrow C_6H_{12}O_6 + 6O_2 \]
• 📌 Impact on Growth: If there isn't enough carbon dioxide available, the plant can't produce enough glucose, its primary food source. Less food means less energy for growth, leading to a slower growth rate.
• ✅ Conclusion: The scientist's observation is consistent because carbon dioxide is a crucial reactant for photosynthesis. When its levels are low, it limits the rate at which the plant can produce food, directly impacting its ability to grow and thrive, even if other conditions (like sunlight and water) are ideal.

• 💡 Interconnectedness of Life: Photosynthesis is a foundational process that supports almost all life on Earth, creating a vital link between plants, animals, and humans.
• 👉 Production of Oxygen: One of the most direct benefits is the production of oxygen \( (O_2) \). Oxygen is released into the atmosphere as a byproduct of photosynthesis. Animals and humans need oxygen for cellular respiration, the process that releases energy from food, allowing us to live and function. Without plants producing oxygen, the air would not be breathable.
• 👉 Creation of Food: Plants produce glucose (sugar) as their food, which forms the base of almost all food chains.
  • Herbivores (plant-eating animals) directly consume plants for energy.
  • Carnivores (meat-eating animals) eat herbivores, indirectly getting energy that originated from plants.
  • Humans consume both plants (fruits, vegetables, grains) and animals that eat plants, making photosynthesis the ultimate source of our food and energy.
• ✅ Summary: Photosynthesis provides two essential things for animals and humans: the oxygen we breathe and the food (energy) that sustains us, either directly from plants or indirectly through animals that eat plants.

• 💡 Role of Trees in Ecosystems: Trees are prime examples of photosynthetic organisms. They play a massive role in regulating Earth's atmosphere.
• 👉 Carbon Dioxide Absorption: During photosynthesis, trees absorb large amounts of carbon dioxide from the atmosphere. Carbon dioxide is a major greenhouse gas that contributes to climate change by trapping heat. By absorbing \( CO_2 \), trees help to reduce its concentration in the air.
• 👉 Oxygen Production: As a byproduct of photosynthesis, trees release oxygen into the atmosphere. This improves air quality, making the air fresher and healthier for living beings, especially in urban areas where pollution can be high.
• 👉 Other Benefits: Beyond photosynthesis, trees also:
  • Provide shade, reducing energy consumption for cooling.
  • Filter pollutants from the air.
  • Help manage stormwater.
  • Support biodiversity.
• ✅ Conclusion: Planting trees is promoted because their photosynthetic activity helps to remove excess carbon dioxide (a greenhouse gas) from the atmosphere, mitigating climate change, and simultaneously releases oxygen, improving the overall air quality.

• 💡 Artificial Light for Photosynthesis: Grow lights are designed to mimic the spectrum and intensity of natural sunlight, providing the necessary energy for plants to thrive indoors.
• 👉 Energy for Food Production: Just like outdoor plants, your indoor herbs need energy to perform photosynthesis. Photosynthesis is the process where they convert carbon dioxide and water into glucose (their food) and oxygen.
• 📌 Role of Light in Photosynthesis: Light is the critical energy source that powers this conversion. Without sufficient light, the photosynthetic process slows down or stops entirely.
• ❌ Consequences of Insufficient Light: If your herbs don't receive enough light, they can't produce enough food. This will lead to:
  • Stunted Growth: They won't have the energy to grow larger or produce new leaves.
  • Yellowing Leaves: A sign of insufficient chlorophyll production or breakdown due to lack of light.
  • Weak Stems: The plant may become "leggy" as it stretches to find light, resulting in weak, elongated stems.
  • Eventual Death: Without food, the plant will eventually die.
• ✅ Conclusion: The grow light is important because it provides the essential light energy that your herbs need to carry out photosynthesis. This process creates the food (glucose) necessary for their survival, healthy growth, and the production of delicious leaves for your kitchen!