Energy in Living Things
What is the main source of energy for almost all living things on Earth?
Sun (the Sun is primary energy source)
In which cell organelle does photosynthesis take place?
Chloroplast.
What is the purpose of cellular respiration in cells?
To release chemical energy from glucose to make ATP for cell activities.
Which process removes carbon dioxide from the atmosphere: photosynthesis or cellular respiration?
Photosynthesis removes carbon dioxide.
What is the role of producers in a food chain?
Producers make organic compounds (food) from sunlight and supply energy for the rest of the food chain.
Name the molecule that cells use for immediate energy and often abbreviate it as three letters.
ATP (adenosine triphosphate).
Write the basic idea of the photosynthesis equation in words (reactants → products).
Carbon dioxide + water (reactants) → glucose + oxygen (products). (In words: plants use carbon dioxide and water with sunlight to make sugar and oxygen.)
Which reactant is combined with glucose to produce energy in aerobic cellular respiration?
Oxygen (in aerobic respiration).
Identify one reactant that is a product of the other process (show the connection between the two processes).
Example: Oxygen is a product of photosynthesis and is a reactant in cellular respiration; glucose made in photosynthesis is used in cellular respiration.
What do we call organisms that eat both plants and animals?
Omnivores
What term describes organisms that make their own food using sunlight?
Autotrophs or producers (e.g., plants, algae)
Name the pigment that captures light energy for photosynthesis.
Chlorophyll.
Name the three main stages of aerobic cellular respiration (use common stage names).
Glycolysis, Krebs cycle (citric acid cycle), Electron transport chain (ETC).
Explain in one sentence how photosynthesis and cellular respiration form a cycle in ecosystems.
They form a cycle: photosynthesis captures energy to make glucose and releases oxygen; cellular respiration uses glucose and oxygen to release energy and produces carbon dioxide and water used again by photosynthesis.
Define what a trophic level is and give an example for level 2.
A trophic level is a position in a food chain/web based on feeding relationships; level 2 example: herbivores such as rabbits or grasshoppers (primary consumers).
Give one example of a consumer (heterotroph) and explain briefly how it gets energy.
Example: Rabbit — eats plants to get chemical energy.
Explain why plants are green in terms of light absorption and reflection.
Plants reflect green wavelengths of light and absorb red and blue; reflected green light makes leaves appear green.
Compare the amount of ATP produced by aerobic respiration versus fermentation (general comparison).
Aerobic respiration produces many more ATP (about 36–38 ATP per glucose) while fermentation produces much less (about 2 ATP per glucose).
List two ways photosynthesis and cellular respiration are different (not answers that are opposites of each other; give distinct features).
Differences: Photosynthesis occurs in chloroplasts and requires light; cellular respiration occurs in mitochondria and releases energy. Photosynthesis stores energy in glucose; respiration releases stored energy as ATP.
Explain how removing a primary consumer (level 2) might affect a food web that includes plants, insects, small birds, and hawks.
Removing a primary consumer could cause plant populations to increase and predators that rely on that consumer to decline; it can cascade and alter population sizes and interactions across the web.
Explain how energy flows through an ecosystem from producers to tertiary consumers. Include what happens to most energy at each transfer.
Energy flows from producers (convert sunlight into chemical energy) to primary consumers to secondary/tertiary consumers; at each transfer most energy is lost as heat and used for life processes, so less is available at higher trophic levels.
Describe how light intensity, carbon dioxide concentration, and temperature each affect the rate of photosynthesis (one sentence for each).
Light intensity: higher (up to a point) increases rate; Carbon dioxide: increased CO2 increases rate until another factor limits it; Temperature: low temps slow enzymes, very high temps can denature enzymes — both reduce rate outside optimal range.
Explain why mitochondria are often called the "powerhouses" of the cell, mentioning ATP and structure briefly.
Mitochondria produce most ATP via the Krebs cycle and ETC; their folded inner membrane increases surface area for ATP-producing processes.
Describe how the equations for photosynthesis and cellular respiration are related. Include the idea of energy conversion and the direction of reactants and products.
The chemical equation for photosynthesis is essentially the reverse of cellular respiration: reactants of one are products of the other; photosynthesis converts light energy into chemical energy (glucose), while respiration converts chemical energy back into usable ATP.
Create a short three-step food chain (producer → primary consumer → secondary consumer) using organisms that might live in a forest. Then explain how energy changes in amount and form as it moves along this chain.
Example chain: Oak tree (producer) → Caterpillar (primary consumer) → Songbird (secondary consumer). Energy decreases at each step (less available biomass/energy), and chemical energy in food is used for growth/movement and lost as heat; energy form stays chemical in bodies but is transformed into kinetic and heat during use.