Notes
ATP
ATP stores energy in its phosphate bonds. Removing the third phosphate releases energy and forms ADP. Cells recharge ADP to ATP using energy from food.
Photosynthesis
$6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$
- Happens in chloroplasts. Chlorophyll absorbs red and blue light.
- Light reactions (thylakoids): split water, release $\text{O}_2$, make ATP and NADPH.
- Calvin cycle (stroma): uses $\text{CO}_2$, ATP and NADPH to make sugar.
Cellular respiration
$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$
| Stage | Location | Result |
|---|---|---|
| Glycolysis | Cytoplasm | 2 pyruvate, 2 ATP |
| Krebs cycle | Mitochondrial matrix | Releases $\text{CO}_2$, energy carriers |
| Electron transport chain | Inner mitochondrial membrane | Most ATP; $\text{O}_2$ forms water |
Fermentation
Without oxygen, cells use glycolysis plus fermentation (2 ATP). Muscles make lactic acid; yeast make ethanol and $\text{CO}_2$.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Respiration uses glucose and oxygen and releases carbon dioxide, water and ATP.
Plants respire day and night; photosynthesis needs light.
Roots are underground with no light, so they have few or no chloroplasts.
Fermentation keeps glycolysis running, which still makes 2 ATP.
Without oxygen as the final acceptor, the chain stops.
ATP and NADPH from the light reactions power sugar building.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student places an aquatic plant in water at different distances from a lamp: 10 cm, 20 cm, 30 cm and 40 cm. She counts the oxygen bubbles released per minute: 40, 25, 12 and 5.
(a) State a hypothesis this experiment tests and identify the independent variable.
Show the answer and scoring guide
Hypothesis: If the plant is closer to the light, then it will give off more oxygen bubbles, because more light speeds up photosynthesis. The independent variable is the distance from the lamp (light intensity).
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(b) Explain what the bubbles are and where in the chloroplast they come from.
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The bubbles are oxygen gas. They come from water molecules split during the light-dependent reactions in the thylakoid membranes.
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(c) The student notices bubbles stop increasing when the lamp is closer than 10 cm. Give one reason why.
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Another factor has become limiting, such as the amount of carbon dioxide in the water or the temperature. The enzymes of the Calvin cycle can only work so fast, so more light no longer raises the rate.
Check off the points you earned: