Photosynthesis: What's in a Leaf? This diagram explains how leaves function as sun-catchers, detailing the inputs and outputs of photosynthesis.

Here is the complete solution to the worksheet “Photosynthesis: What’s in a Leaf?” with clear explanations for each question.

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1. List three things entering the leaf in Model 1.

✔ Answer:
- Sunlight (energy)
- Water (liquid, via the petiole/veins)
- Carbon dioxide (gas, via stomata)

Explanation:
Model 1 shows arrows pointing *into* the leaf labeled:
- “Sunlight (energy)” — enters from above.
- “Water (liquid)” — enters through the petiole (leaf stalk) and vascular tissue.
- “Carbon dioxide” — enters as a gas through tiny pores called stomata on the leaf surface.

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2. List three substances leaving the leaf.

✔ Answer:
- Oxygen (gas)
- Water (gas — via transpiration)
- Sugars (liquid — transported out via phloem)

Explanation:
Model 1 shows arrows pointing *out of* the leaf labeled:
- “Oxygen” — released as a gas through stomata (byproduct of photosynthesis).
- “Water (gas)” — evaporates from leaf cells and exits through stomata (transpiration).
- “Sugars” — produced during photosynthesis; transported out via phloem vessels to other parts of the plant.

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3. Which substance is both entering and leaving?

✔ Answer: Water

Explanation:
In Model 1, water is shown entering the leaf as a *liquid* (via xylem from roots), and also leaving as a *gas* (water vapor via transpiration through stomata). So while it’s the same chemical substance (H₂O), its physical state and purpose differ: one is for photosynthesis and transport, the other is waste/evaporation.

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4. How is the substance you identified in Question 3 changed between its entry and its exit?

✔ Answer:
Water enters the leaf as a liquid (transported via xylem for photosynthesis and cell turgor) and exits as a gas (water vapor) through stomata during transpiration.

Explanation:
This phase change from liquid to gas is part of the plant’s water cycle — helping cool the leaf and pull more water up from the roots. The water molecule itself doesn’t chemically change, but its physical state does.

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5. Use the general equation for photosynthesis and Model 1 to answer the following questions.

> General Equation:
> carbon dioxide + water → sugars + oxygen
> *(with light energy)*

a. What are the reactants for photosynthesis?
✔ Answer: Carbon dioxide and water

b. Where do these reactants enter the leaf?
✔ Answer:
- Carbon dioxide enters through the stomata (tiny pores on leaf surface).
- Water enters through the petiole/veins (xylem tissue).

c. What are the products of photosynthesis?
✔ Answer: Sugars (glucose) and oxygen

d. From where do the products leave the leaf?
✔ Answer:
- Oxygen leaves through the stomata (as a gas).
- Sugars leave through the petiole/veins (phloem tissue) to be transported to other parts of the plant.

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7. Categorize all the components involved in photosynthesis as either matter or energy.

✔ Answer:

| Component | Category |
|------------------|----------|
| Carbon dioxide | Matter |
| Water | Matter |
| Sugars | Matter |
| Oxygen | Matter |
| Sunlight | Energy |

Explanation:
Matter refers to physical substances with mass (like CO₂, H₂O, O₂, glucose). Energy refers to the ability to do work — here, sunlight provides the energy needed to drive the chemical reaction.

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8. List the layers of the leaf starting at the upper cuticle all the way to the lower cuticle.

✔ Answer (from top to bottom):

1. Upper cuticle – waxy layer protecting the leaf
2. Upper epidermis – single layer of transparent cells
3. Palisade mesophyll – tightly packed, chloroplast-rich cells for photosynthesis
4. Spongy mesophyll – loosely arranged cells with air spaces for gas exchange
5. Lower epidermis – contains stomata for gas exchange
6. Lower cuticle – protective waxy layer on bottom surface

Note: Some models include vascular bundles (veins) running through the mesophyll, but the main structural layers from top to bottom are as listed above.

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✔ Summary of Key Concepts:
- Leaves are structured to maximize light capture, gas exchange, and water transport.
- Photosynthesis converts light energy into chemical energy (sugars), using CO₂ and H₂O, releasing O₂.
- Structure-function relationship: stomata allow gas exchange, veins transport materials, mesophyll cells contain chloroplasts for photosynthesis.

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