Matter & Energy in Living Systems — Problem set, Grade 10

ATP (adenosine triphosphate) is the molecule cells use to store and spend usable energy; it's called energy currency because cells spend it to pay for almost every activity.

ATP hydrolysis is favorable overall under typical cellular conditions and can be coupled to work. Its free-energy change belongs to the full reaction, not bond breaking alone.

An autotroph makes its own food (e.g., a tree); a heterotroph gets energy by eating other organisms (e.g., a human).

An autotroph, or producer, makes its own food from simple raw materials — for example, a tree, grass, or algae using sunlight to build glucose. A heterotroph, or consumer, cannot make its own food and must eat other organisms — for example, a human, a wolf, or a mushroom. Both kinds of organism still run on ATP.

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. Reactants: carbon dioxide and water. Products: glucose and oxygen.

The overall equation is 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. The reactants (starting materials) are carbon dioxide and water, and the process is powered by light energy. The products are glucose (a sugar that stores the captured energy) and oxygen (released as a byproduct).

From splitting water, during the light-dependent reactions.

In the light-dependent reactions, which occur in the thylakoid membranes, light energy is used to split water molecules apart. That splitting is what releases oxygen gas (O2). The oxygen does not come from carbon dioxide — it comes from water.

30 CO2 used and 30 O2 released.

Each glucose requires 6 CO2 and releases 6 O2. For 5 glucose molecules: 5 × 6 = 30 CO2 consumed and 5 × 6 = 30 O2 released.

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O; energy is transferred to ATP and heat.

The simplified net reactants/products correspond with those of photosynthesis, but the pathways, enzymes, and energy-transfer mechanisms differ.

Glycolysis occurs in the cytosol; pyruvate processing and the citric acid cycle occur mainly in the matrix; oxidative phosphorylation involves the inner mitochondrial membrane.

CO₂ is released during pyruvate processing and the citric acid cycle. Electron transport and ATP synthase support most ATP production. The chain does not make CO₂.

The stated aerobic yield is 15 times as large.

30 ÷ 2 = 15. Oxygen accepts electrons at the end of the respiratory chain, supporting oxidative phosphorylation. Fermentation regenerates NAD⁺ to sustain glycolysis but adds no extra ATP.

Chloroplasts use light energy in photosynthesis; mitochondria support aerobic respiration and ATP supply for many cell processes.

Chloroplasts produce ATP used in photosynthetic processes. Mitochondria contribute to ATP supply in photosynthetic and nonphotosynthetic tissues. Not every plant cell contains chloroplasts.

Carbon atoms can be reused while energy is transferred and dispersed as heat.

Photosynthesis and respiration connect carbon transfers. Usable energy must be supplied to sustain work. Gas balance, nutrients, temperature, and population changes limit real terrarium survival; cycling does not guarantee indefinite stability.

Sunlight → photosynthesis (plant makes glucose) → the runner eats the food → cellular respiration (glucose broken down to ATP) → ATP powers the muscle.

A plant's chloroplasts capture sunlight during photosynthesis and store the energy in glucose. The runner eats that plant (or an animal that ate plants), taking in the glucose. In the runner's muscle cells, cellular respiration breaks the glucose down — through glycolysis, the Krebs cycle, and the electron transport chain — transferring the energy into ATP. The muscle then spends that ATP to contract, and the leftover energy leaves as body heat. So the Sun's energy powers the run, passed along the whole chain and finally lost as heat.

Fossil fuels store energy captured by ancient photosynthesis; burning them releases that carbon as CO2 faster than photosynthesis can re-absorb it.

Millions of years ago, plants and other organisms captured sunlight through photosynthesis and stored the energy — and the carbon — in their tissues. Buried and compressed over time, they became coal and oil, locking that ancient carbon away. Burning these fuels is like a very fast version of respiration: it combines the stored carbon with oxygen and releases CO2. Because we burn them far faster than photosynthesis can pull that carbon back out of the air, CO2 builds up in the atmosphere, tipping the natural photosynthesis–respiration balance and warming the climate.

10 %

2.5 / 25 × 100 = 10 percent. The remainder is used for the herbivore's own respiration, lost as heat, or never absorbed.

Plants do not make energy; they capture it. Light energy already present is absorbed and converted into chemical energy stored in the bonds of sugars built from carbon dioxide and water. Energy is transformed from one form to another, with some lost as heat, and the total is not increased. Saying plants make food is accurate; saying they make energy is not.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Efficiency is 72/240×100 = 30%; 168 units goes to other transfers/storage under the boundary. It is not destroyed, and identifying particular outputs requires a complete measured account.

Efficiency is 72/240×100 = 30%; 168 units goes to other transfers/storage under the boundary. It is not destroyed, and identifying particular outputs requires a complete measured account.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

1 units

Increases are 10, 8, and 1 units across the three intervals, so the smallest is 1 unit between 60 and 80 percent, indicating that light has stopped being the limiting factor.

The light-dependent reactions require light to split water and generate ATP and NADPH. Without light, those products are not made, so the carbon-fixing reactions that build sugar have no energy or electron supply and stop, even though carbon dioxide and water are present. The plant continues to respire and consumes its stored sugar, and once the store is gone it cannot meet its energy needs. Carbon fixation does not require light directly, but it depends entirely on the products of the light reactions.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Net output is 14−5 = 9 units/h. The released photosynthetic O₂ is traced to water; plants also consume oxygen, and a net gas measurement alone is not gross production.

Net output is 14−5 = 9 units/h. The released photosynthetic O₂ is traced to water; plants also consume oxygen, and a net gas measurement alone is not gross production.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

150 mmol

5.0 × 30 = 150 mmol of ATP at the stated yield; quoting the yield used is part of the answer.

During the sprint, oxygen delivery could not keep pace with demand, so muscle cells relied partly on fermentation, which yields little ATP per glucose and produces lactate. After stopping, the body continues taking in oxygen at an elevated rate to process the accumulated lactate and restore its energy stores. The heavy breathing therefore reflects a repayment of the shortfall rather than a continuing need to power the activity.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

The corrected decline is 20 units, giving 2 units/min. Pathway coupling, oxygen-to-substrate relations and other demands must be specified before converting gas exchange into ATP yield.

The corrected decline is 20 units, giving 2 units/min. Pathway coupling, oxygen-to-substrate relations and other demands must be specified before converting gas exchange into ATP yield.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

4 units/hour

24 / 6 = 4 units per hour. This is the net rate; gross photosynthesis exceeds it by whatever the organisms respired.

In the dark the plant respires without photosynthesizing, so carbon dioxide accumulates and the indicator shifts toward yellow. In the light photosynthesis consumes carbon dioxide faster than respiration releases it, so the concentration falls and the indicator shifts toward blue. The experiment needs a tube with indicator and no plant, kept under each condition, to show that light and temperature alone do not change the indicator's colour.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Net daytime gain is 6×(10−3)=42 units; later loss is 18×3=54. The day’s net change is −12 units despite positive daytime release under the stated simplified conditions.

Net daytime gain is 6×(10−3)=42 units; later loss is 18×3=54. The day’s net change is −12 units despite positive daytime release under the stated simplified conditions.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.