Photosynthesis in a Leaf - Illustration of leaf anatomy and the photosynthetic process.

Based on the provided image of the worksheet "Photosynthesis: What's in a Leaf?", I can now solve the problem by answering the questions based on the diagram and general biological knowledge.

Here is a step-by-step solution to the worksheet:

Question 1: List three things entering the leaf as reactants.
Based on the arrows pointing *into* the leaf in the diagram, the three main things entering the leaf for photosynthesis are:
- Carbon Dioxide (CO₂): Enters through the stomata.
- Water (H₂O): Transported from the roots through the xylem to the leaf.
- Sunlight: Provides the energy required to power the chemical reactions of photosynthesis.

Question 2: List three substances leaving the leaf.
Based on the arrows pointing *out of* the leaf in the diagram, the three main substances leaving the leaf are:
- Oxygen (O₂): A waste product of photosynthesis, released through the stomata.
- Glucose (C₆H₁₂O₆): The primary sugar produced by photosynthesis, which is transported to other parts of the plant via the phloem.
- Water Vapor (H₂O): Released into the atmosphere through the process of transpiration, also via the stomata.

Question 3: What are the products of photosynthesis?
The products of photosynthesis are:
- Glucose (C₆H₁₂O₆): This is the main food source for the plant, used for energy and growth.
- Oxygen (O₂): This is released as a byproduct.

Question 4: Where does this reaction take place?
The reaction of photosynthesis primarily takes place in the chloroplasts, which are organelles found within the cells of the leaf, particularly in the mesophyll tissue (the spongy and palisade layers). The chloroplasts contain the green pigment chlorophyll, which captures sunlight.

Question 5: What are the reactants of photosynthesis?
The reactants (or raw materials) for photosynthesis are:
- Carbon Dioxide (CO₂)
- Water (H₂O)

Question 6: From where do the products leave the leaf?
- Glucose leaves the leaf through the phloem, which is part of the vascular bundle (vein) shown in the diagram.
- Oxygen and water vapor leave the leaf through the stomata, which are small pores on the surface of the leaf, typically on the underside.

In summary, the leaf is a highly specialized organ designed for photosynthesis. It takes in carbon dioxide and water, uses sunlight as an energy source, and produces glucose and oxygen. The structure of the leaf, with its large surface area, stomata for gas exchange, and vascular bundles for transport, is perfectly adapted to carry out this vital process.