Page 2: Gas Exchange and Photosynthesis

This page illustrates the relationship between photosynthesis, respiration, and gas exchange in plants under different conditions. It covers scenarios from nighttime to bright sunlight, demonstrating how the balance between photosynthesis and respiration affects carbon dioxide and oxygen levels.

The concept of the compensation point is introduced, showing when photosynthesis and respiration rates are equal, resulting in no net gas exchange. The page also touches on the use of hydrogen carbonate indicators to visually represent these processes.

Definition: Compensation point - The light intensity at which the rate of photosynthesis exactly matches the rate of respiration, resulting in no net gas exchange.

Highlight: In bright sunlight, photosynthesis rates are much higher than respiration rates, leading to net oxygen production and carbon dioxide consumption.

Example: The color change of hydrogen carbonate indicator from yellow to purple demonstrates the shift from respiration-dominated to photosynthesis-dominated conditions.

Page 4: Leaf Structure and Testing for Starch

The final page focuses on leaf anatomy and the practical aspect of testing for starch in leaves GCSE biology. It details the various parts of a leaf and their functions in facilitating photosynthesis, including the waxy cuticle, stomata, and different types of cells.

The page concludes with a step-by-step guide on how to test for the presence of starch in leaves, a key experiment in CCEA GCSE Biology food tests. This practical demonstration provides evidence for photosynthesis occurring in leaves.

Vocabulary:

• Stoma (plural: stomata) - Tiny pores in leaves that allow gas exchange.
• Palisade mesophyll - The main site of photosynthesis in leaves, containing many chloroplasts.

Example: The iodine test for starch in leaves involves first destarching the plant, then exposing it to light, and finally testing for starch production. A color change from yellow-brown to blue-black indicates the presence of starch.

Highlight: The process of testing for starch includes killing the leaf, removing chlorophyll, and then applying iodine. This method is crucial for demonstrating that photosynthesis has occurred.