1. explain why the chesapeake bay is particularly vulnerable to pollution from multiple states. include the concept of watershed in your answer.
2. describe the role of sav (submerged aquatic vegetation) in the chesapeake bay ecosystem and explain what happens when sav beds decline.
3. compare the light - dependent and light - independent reactions of photosynthesis in terms of location, inputs, and outputs.
4. explain why animals depend on plants for survival, but plants do not depend on animals. use the terms autotroph and heterotroph in your response.
5. describe the three stages of aerobic cellular respiration and identify where each occurs in the cell.
6. a student claims that mitochondria are not needed for cells to produce atp because glycolysis occurs in the cytoplasm. evaluate this claim and explain why it is incorrect.
7. explain what happens at the molecular level when a person holds their breath for too long. include discussion of $\ce{co_{2}}$, chemoreceptors, and the medulla oblongata.
8. compare negative feedback and positive feedback loops. give one example of each and explain why negative feedback is more common in the body.

Question

Accepted Answer

### Question 1
# Brief Explanations:
The Chesapeake Bay watershed spans multiple states (e.g., VA, MD, PA, WV, DE, NY, DC). A watershed is an area where all water drains to a common body. Pollution (e.g., runoff with nutrients, sediment) from these states’ urban, agricultural, or industrial areas flows via rivers/streams into the Bay. The Bay’s semi - enclosed nature (shallow, slow - flowing) limits water exchange, so pollution accumulates, making it vulnerable to multi - state pollution.
# Answer:
The Chesapeake Bay is vulnerable to multi - state pollution because its watershed covers multiple states (VA, MD, PA, WV, DE, NY, DC). A watershed is a land area where all water drains to a common body (the Bay here). Pollution (nutrient - rich runoff, sediment, etc.) from urban, agricultural, or industrial areas in these states flows via rivers/streams into the Bay. The Bay’s semi - enclosed, shallow, and slow - flowing nature restricts water exchange, causing pollution to accumulate.

### Question 2
# Brief Explanations:
**Role of SAV in Chesapeake Bay Ecosystem**: SAV (e.g., eelgrass, widgeongrass) provides habitat for fish, shellfish, and invertebrates. It stabilizes sediments (reducing turbidity), absorbs nutrients (reducing eutrophication), and produces oxygen. It also serves as a food source (directly or via detritus).
**When SAV Beds Decline**: Sediment resuspension increases turbidity, blocking light and further reducing SAV. Nutrient levels rise (less uptake), causing algal blooms. Algae deplete oxygen (hypoxia), harming aquatic life. Habitat loss occurs, reducing biodiversity and fish/shellfish populations.
# Answer:
- **Role of SAV**: SAV provides habitat for aquatic species, stabilizes sediments (reducing turbidity), absorbs nutrients (combating eutrophication), produces oxygen, and is a food source (directly or via detritus).
- **SAV Decline Consequences**: Turbidity rises (sediment resuspension), blocking light and worsening SAV loss. Nutrient levels increase (less uptake), fueling algal blooms. Algae cause hypoxia (oxygen depletion), harming aquatic life. Habitat loss reduces biodiversity and fish/shellfish populations.

### Question 3
# Brief Explanations:
| Reaction Type | Location | Inputs | Outputs |
| --- | --- | --- | --- |
| Light - Dependent | Thylakoid membranes (chloroplasts) | Light energy, $H_2O$, ADP, $P_i$, $NADP^+$ | $O_2$, ATP, $NADPH$ |
| Light - Independent (Calvin Cycle) | Stroma (chloroplasts) | $CO_2$, ATP, $NADPH$ | Glucose (or other sugars), ADP, $P_i$, $NADP^+$ |

Light - dependent reactions use light to split $H_2O$, make ATP (via photophosphorylation) and $NADPH$ (electron transport), releasing $O_2$. Light - independent reactions (Calvin Cycle) use ATP and $NADPH$ to fix $CO_2$ into glucose, regenerating ADP, $P_i$, and $NADP^+$.
# Answer:
| Reaction | Location | Inputs | Outputs |
| --- | --- | --- | --- |
| Light - Dependent | Thylakoid membranes (chloroplasts) | Light, $H_2O$, ADP, $P_i$, $NADP^+$ | $O_2$, ATP, $NADPH$ |
| Light - Independent | Stroma (chloroplasts) | $CO_2$, ATP, $NADPH$ | Glucose, ADP, $P_i$, $NADP^+$ |

Light - dependent reactions occur in thylakoid membranes, use light, $H_2O$, ADP, $P_i$, $NADP^+$ to make $O_2$, ATP, $NADPH$. Light - independent (Calvin Cycle) occurs in stroma, uses $CO_2$, ATP, $NADPH$ to make glucose, regenerating ADP, $P_i$, $NADP^+$.

### Question 4
# Brief Explanations:
- **Animals Depend on Plants**: Animals are heterotrophs (can’t make their own food). They rely on plants (autotrophs, make food via photosynthesis) for organic molecules (food, energy), $O_2$ (from photosynthesis for respiration), and $CO_2$ removal (plants take in $CO_2$).
- **Plants Do Not Depend on Animals (Largely)**: Plants are autotrophs (produce food via photosynthesis, $CO_2 + H_2O + light
ightarrow glucose + O_2$). They can reproduce (e.g., wind - pollinated, self - pollinated) and get nutrients from soil. While animals can aid in pollination/dispersal, most plants can survive without animal - mediated pollination/dispersal (e.g., grasses, conifers).
# Answer:
Animals (heterotrophs) depend on plants (autotrophs) because plants produce organic molecules (food) via photosynthesis, release $O_2$ (for animal respiration), and absorb $CO_2$ (regulating the atmosphere). Plants (autotrophs) do not depend on animals as they make their own food ($CO_2 + H_2O + light
ightarrow glucose + O_2$), get nutrients from soil, and can reproduce via non - animal means (e.g., wind pollination, self - pollination). Though animals can aid in pollination/dispersal, most plants can survive without them.

### Question 5
# Brief Explanations:
1. **Glycolysis**: Occurs in the cytoplasm. Inputs: Glucose, 2 ATP, 2 $NAD^+$, 4 ADP + 4 $P_i$. Outputs: 2 Pyruvate, 2 NADH, 4 ATP (net 2 ATP), 2 $H_2O$.
2. **Citric Acid Cycle (Krebs Cycle)**: Occurs in the mitochondrial matrix. Inputs: 2 Pyruvate (converted to 2 Acetyl - CoA), 6 $NAD^+$, 2 $FAD$, 2 ADP + 2 $P_i$, 6 $H_2O$, 4 $CO_2$ (from prior decarboxylation). Outputs: 6 NADH, 2 FADH₂, 2 ATP, 4 $CO_2$, 6 $H_2O$.
3. **Electron Transport Chain (ETC)**: Occurs in the inner mitochondrial membrane. Inputs: 10 NADH, 2 FADH₂, $O_2$, ADP + $P_i$. Outputs: ~30 - 34 ATP, $H_2O$ (from $O_2$ + electrons + protons).
# Answer:
1. **Glycolysis**: Location - Cytoplasm. Inputs - Glucose, 2 ATP, 2 $NAD^+$, 4 ADP + 4 $P_i$. Outputs - 2 Pyruvate, 2 NADH, 2 net ATP, 2 $H_2O$.
2. **Citric Acid Cycle (Krebs Cycle)**: Location - Mitochondrial Matrix. Inputs - 2 Acetyl - CoA (from pyruvate), 6 $NAD^+$, 2 $FAD$, 2 ADP + 2 $P_i$, 6 $H_2O$, 4 $CO_2$ (from pyruvate decarboxylation). Outputs - 6 NADH, 2 FADH₂, 2 ATP, 4 $CO_2$, 6 $H_2O$.
3. **Electron Transport Chain (ETC)**: Location - Inner Mitochondrial Membrane. Inputs - 10 NADH, 2 FADH₂, $O_2$, ADP + $P_i$. Outputs - ~30 - 34 ATP, $H_2O$.

### Question 6
# Brief Explanations:
The claim is incorrect. Glycolysis (in cytoplasm) produces a net of 2 ATP. For most eukaryotic cells, aerobic respiration (needing mitochondria) is the main ATP - producing pathway. The Citric Acid Cycle (in mitochondrial matrix) and ETC (in inner mitochondrial membrane) produce ~30 - 34 ATP. Mitochondria are needed for efficient ATP production (aerobic respiration) as glycolysis alone provides little ATP. Some cells (e.g., anaerobic bacteria) rely only on glycolysis, but eukaryotic cells (like human cells) need mitochondria for sufficient ATP to power cellular processes (e.g., muscle contraction, active transport).
# Answer:
The claim is incorrect. Glycolysis (in cytoplasm) produces only 2 net ATP. Mitochondria are needed for aerobic respiration (Citric Acid Cycle in matrix, ETC in inner membrane), which produces ~30 - 34 ATP. Eukaryotic cells (e.g., human cells) require mitochondria - mediated aerobic respiration to generate enough ATP for energy - intensive processes (e.g., muscle contraction, active transport). Only anaerobic organisms (e.g., some bacteria) rely solely on glycolysis, but most eukaryotic cells need mitochondria for efficient ATP production.

### Question 7
# Brief Explanations:
When a person holds their breath, $CO_2$ accumulates in the blood (from cellular respiration, $C_6H_{12}O_6 + 6O_2
ightarrow 6CO_2 + 6H_2O + ATP$). Blood $CO_2$ levels rise, forming $H_2CO_3$ (carbonic acid, $CO_2 + H_2O
ightleftharpoons H_2CO_3$), which dissociates into $H^+$ and $HCO_3^-$. Chemoreceptors (in carotid/aortic bodies, and medulla oblongata) detect increased $CO_2$ (or $H^+$). The medulla oblongata (respiratory control center) sends signals to increase breathing rate/depth to expel $CO_2$, restore blood gas balance, and prevent acidosis.
# Answer:
When holding breath, $CO_2$ accumulates (from cellular respiration: $C_6H_{12}O_6 + 6O_2
ightarrow 6CO_2 + 6H_2O + ATP$). Blood $CO_2$ forms $H_2CO_3$ ($CO_2 + H_2O
ightleftharpoons H_2CO_3$), increasing $H^+$ (acidosis). Chemoreceptors (carotid/aortic bodies, medulla) detect $CO_2$/$H^+$ increases. The medulla oblongata (respiratory center) triggers increased breathing to expel $CO_2$, restoring blood gas and pH balance.

### Question 8
# Brief Explanations:
- **Negative Feedback Loop**: A process that reverses a change to maintain homeostasis. Example: Blood glucose regulation. High glucose → pancreas releases insulin → cells take up glucose → glucose levels drop. Low glucose → pancreas releases glucagon → liver releases glucose → glucose levels rise.
- **Positive Feedback Loop**: A process that amplifies a change. Example: Childbirth. Uterine contractions → oxytocin release → more contractions → until birth.
- **Why Negative Feedback is More Common in the Body**: Negative feedback maintains homeostasis (stable internal environment), which is essential for cell/organ function. Most bodily parameters (e.g., temperature, pH, glucose) need to be stable. Positive feedback is rare as it amplifies changes, which can be harmful unless limited (e.g., childbirth has a defined end).
# Answer:
- **Negative Feedback Loop**: Reverses a change to maintain homeostasis. Example: Blood glucose - High glucose → insulin release (pancreas) → cells take up glucose → glucose drops. Low glucose → glucagon release (pancreas) → liver releases glucose → glucose rises.
- **Positive Feedback Loop**: Amplifies a change. Example: Childbirth - Uterine contractions → oxytocin release → more contractions → until birth.
- **Why Negative Feedback is More Common**: It maintains homeostasis (stable internal environment) essential for cell/organ function (e.g., stable temperature, pH, glucose). Positive feedback amplifies changes, which is harmful unless limited (e.g., childbirth ends with birth), so negative feedback is more common to sustain a stable internal state.

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