Sign up to access the complete lesson and track your progress!
Unlock This CoursePlants are amazing living factories that constantly exchange gases with their environment. During the day, they take in carbon dioxide and release oxygen through photosynthesis, whilst at night they do the opposite through respiration. Understanding how to investigate these processes practically gives us real insight into how plants survive and thrive.
Key Definitions:
Practical investigations help us see gas exchange in action rather than just reading about it. We can measure actual gas production, observe real plant responses and understand how environmental factors affect these vital processes. This hands-on approach makes the science come alive!
One of the most exciting experiments in biology is watching plants produce oxygen bubbles during photosynthesis. This investigation uses aquatic plants because we can easily see and count the oxygen bubbles they release.
Elodea (Canadian pondweed) is perfect for this investigation because it produces visible oxygen bubbles when photosynthesising. Here's how to set up this classic experiment:
Fresh Elodea shoots, large beaker, funnel, test tube, bright lamp, ruler, stopwatch, thermometer and fresh pond water or tap water left to stand overnight.
Place Elodea under inverted funnel in water-filled beaker. Position test tube over funnel stem to collect gas. Shine bright light from fixed distance. Count bubbles per minute for 5-minute periods.
Light intensity (distance from lamp), light colour (coloured filters), temperature, carbon dioxide concentration (add sodium hydrogencarbonate) and number of leaves.
Always handle electrical equipment with dry hands, keep water away from electrical connections and never leave lamps unattended. Hot lamps can burn skin and crack glassware if water splashes on them. Use eye protection when handling sodium hydrogencarbonate solutions.
Plants absorb carbon dioxide during photosynthesis and we can investigate this using indicator solutions that change colour as CO₂ levels change. This gives us a clear visual way to see gas exchange happening.
Hydrogencarbonate indicator is brilliant for showing carbon dioxide changes. It's red in normal air, yellow when CO₂ increases and purple when CO₂ decreases. This makes it perfect for investigating plant gas exchange.
Place leaf discs in sealed tubes with hydrogencarbonate indicator. Set up controls with no leaves and leaves in darkness. Place some tubes in bright light and others in darkness. Watch the colour changes over 2-3 hours.
Expected Results:
Stomata are the gateways for gas exchange in plants. These microscopic pores can open and close, controlling when gases enter and leave the plant. Understanding how they work is crucial for understanding plant gas exchange.
Looking at stomata under a microscope reveals their amazing structure and shows how environmental conditions affect their opening and closing.
Peel thin epidermis from leaf underside. Mount on slide with water. View under microscope at 400x magnification. Draw and count open vs closed stomata.
Compare stomata from plants in bright light vs darkness, high humidity vs dry conditions and well-watered vs drought-stressed plants.
Count stomata in several fields of view. Calculate percentage open vs closed. Measure stomatal aperture width using eyepiece graticule.
Cacti and other desert plants have evolved special gas exchange strategies. They open their stomata at night when it's cooler and more humid, storing CO₂ as organic acids. During the hot day, stomata close to prevent water loss, but photosynthesis continues using the stored CO₂. This clever adaptation is called CAM photosynthesis (Crassulacean Acid Metabolism).
Scientists need to measure how fast gas exchange happens to understand plant efficiency and responses to environmental changes. There are several practical ways to do this in the laboratory.
Moving beyond simple observations, we can actually measure the rates of gas production and consumption. This gives us proper scientific data to analyse and compare.
Bubble Counting Method:
Gas Volume Collection:
The real skill in practical biology comes from understanding what your results mean and explaining the science behind what you observe.
Oxygen production increases with light intensity up to a maximum, then levels off. Temperature affects rates but too much heat damages plants. Adding CO₂ usually increases photosynthesis rates. These patterns help us understand limiting factors.
Successful investigations require careful control of variables. In gas exchange experiments, many factors can affect your results:
Environmental Variables:
Plant Variables:
Understanding plant gas exchange helps farmers optimise crop growth in greenhouses by controlling CO₂ levels, light intensity and temperature. It also helps us understand how forests affect atmospheric CO₂ levels and climate change. NASA even uses these principles when designing life support systems for space missions!
Even experienced scientists make mistakes in practical work. Learning from common errors helps you design better experiments and get more reliable results.
Being aware of potential problems helps you plan better investigations and interpret results more accurately.
Equipment Issues:
Method Problems: