Gas Exchange in Plants Practical Study

Gas Exchange in Plants

• Green plants carry out photosynthesis to create their own food.
• Photosynthesis uses carbon dioxide and produces oxygen.
• Respiration releases energy from food, using oxygen and producing carbon dioxide.
• Gas exchange is important throughout the day.

Practical 7.9 Study

• Aim: To determine how carbon dioxide levels change in tubes containing leaves, under light and dark conditions.
• Apparatus: Boiling tubes, cotton thread, fresh green leaves, test tube rack, measuring cylinder (10cm³), hydrogencarbonate indicator, table lamp, aluminium foil.
• Procedure:
  • Add hydrogencarbonate indicator to tubes. Note the colour.
  • Place leaves in some tubes (A & C).
  • Seal tubes and avoid air leaks.
  • Expose one set of tubes (A & C) to light, and the other set (B & D) to darkness.
  • Observe the colour change after 5 hours

Hydrogencarbonate Indicator

• Different colors correspond to different carbon dioxide levels.
• Purple = lower than normal level
• Red = normal level (about 0.04%)
• Yellow = higher than normal level

Results and Discussion

• • Tube A (light): The indicator colour changes to a vibrant purple, suggesting that the plant actively absorbed carbon dioxide from the surrounding environment as part of the process of photosynthesis. This change signifies the plant's ability to convert light energy into chemical energy, synthesizing glucose while releasing oxygen as a byproduct.
  • Tube B (dark): In this tube, there is no noticeable change in the colour of the indicator, which remains red. This outcome indicates that the plant is not altering the levels of carbon dioxide present in its surroundings, likely due to the lack of light necessary for photosynthesis. The dark condition restricts the plant's ability to absorb carbon dioxide, thereby demonstrating the important role of light in the photosynthetic process.
  • Tube C (light): Here, the indicator colour shifts to yellow, which reveals that the plant is releasing carbon dioxide as a result of respiration. This process typically occurs when plants convert glucose into energy for growth and metabolism, resulting in the production of carbon dioxide as a waste byproduct. It highlights the dual role of plants in both using and releasing carbon dioxide during different metabolic activities.
  • Tube D (dark): In this instance, the indicator remains unchanged, retaining its red colour. This suggests that the plant does not alter the carbon dioxide levels, reinforcing the idea that, even in darkness, without the necessary light energy for photosynthesis, the plant cannot perform gas exchange efficiently. This showcases the metabolic limitations faced by plants during periods without light.
  • The variations in colour changes across these tubes effectively illustrate the contrasting physiological responses of the plant to light and darkness. Such differences underscore the vital interplay between photosynthesis, which occurs in light, and respiration, which can occur both in light and dark conditions. Consequently, these observations help us understand the intricate balance of gas exchange in plants and how it affects the carbon dioxide concentration in the environment.

  Gas Exchange in Plants Under Light Conditions

• Plants carry out both photosynthesis and respiration..

• The rate of photosynthesis is usually greater than respiration.

• This leads to a net uptake of carbon dioxide and release of oxygen.

Gas Exchange in Plants Under Dark Conditions

• Plants only carry out respiration, not photosynthesis
• This results in a net release of carbon dioxide and uptake of oxygen.

Gas Exchange Through Stomata

• Gases like carbon dioxide and oxygen are exchanged through pores called stomata.
• These pores are located on leaves.