Lesson Plan

4. Explain how plants maintain gas levels in the atmosphere

KS3-16-04

Intent

Lesson Intention

  • Explain how plants help maintain levels of oxygen and carbon dioxide in the atmosphere

National Curriculum

  • The dependence of almost all life on Earth on the ability of photosynthetic organisms, such as plants and algae, to use sunlight in photosynthesis to build organic molecules that are an essential energy store and to maintain levels of oxygen and carbon dioxide in the atmosphere

Working Scientifically

  • Use appropriate techniques, apparatus, and materials during fieldwork and laboratory work, paying attention to health and safety
  • Make and record observations and measurements using a range of methods for different investigations; and evaluate the reliability of methods and suggest possible improvements

Learning Outcomes

  • Recall the equation for photosynthesis
  • Explain how plants help maintain levels of oxygen and carbon dioxide in the atmosphere
  • Make and record scientific observations

Resources

Resources: Pond weed – elodea or cabomba, scalpel/knife, clear funnel, test tube, beaker, stopwatch and sodium hydrogen carbonate.

Handout: An investigation sheet for the students to complete.

Rocket words

  • atmosphere
  • oxygen
  • composition
  • gas
  • nitrogen

Implementation

Prior Learning: 

Use lessons 1-3 to recap on photosynthesis, atmosphere gases and the importance of plant life. In order to complete the mission assignment, you may wish to remind the students of the test for oxygen (placing a glowing splint into a tube). 

Starter

What gases are essential for life? The students should discuss their ideas with their talk partners.

Main Teaching

Use the beginning of the presentation to explore the atmospheric make-up of different planets, emphasising that Earth is the only planet with an atmosphere that is known to support life. Then, outline how plants are crucial to maintaining oxygen levels in the atmosphere. Answer questions and take part in activities during the presentation and then carry out the experiment.

Career Film: Mark Tuson works as a Team Leader at the RHS.

Expert Film: This is Mark Tuson, who works as a Community Outreach Advisor at the RHS. Mark talks about how plants maintain gas levels in the atmosphere. 

Mission Assignment

Carrying out an experiment to collect gas produced from photosynthesis

In this experiment, the students will be comparing the amount of gas produced through photosynthesis between two plants - one that has been left in the light and one that has been in darkness.

Method:

  1. Fill a large beaker with water and add a spatula of sodium hydrogen carbonate.
  2. Take a sprig of pond weed and submerge it in the beaker of water. Use scissors to cut the stem at an angle, keeping it underwater at all times.
  3. Place a clear funnel over the pond weed.
  4. Top up the beaker with more water until the water level covers the tip of the funnel.
  5. Fill the test tube to the brim with water. Place your thumb over the end of the tube, invert the tube and place the top of the test tube underwater before removing your thumb.
  6. Then, place the test tube over the tip of the funnel.
  7. Repeat this for another beaker.
  8. Place one beaker in direct sunlight and the other in a darkened space for 15 minutes. Then, compare how much gas has been collected in the two test tubes.

You can test the gas collected to see if it is oxygen by placing a glowing splint into the tube to see if it relights.

Note: We left our experiment for a full day to achieve a more exaggerated result.

Differentiated tasks (Support/Challenge)

Support: Ask the students to identify the independent, dependent and control variables in this experiment. Can they make some changes to make their results more accurate? If they compare their results with another group, can they explain the differences?

Challenge: What changes could be made to this experiment to make the pondweed produce more oxygen? Ask the students to explain their changes. How would they achieve them and what effect would they have? 

Impact & Assessment Opportunities

Plenary

Discuss ways in which the Mission Assignment could be replicated or altered. What other variables could be examined? The students can also review the keywords and add them to the keywords sheet provided.

Teacher Mastery

To maintain enough oxygen levels, plants and algae must continue to carry out photosynthesis. Photosynthesis is the process in which plants utilise the Sun's energy to convert carbon dioxide and water into food. Carbon dioxide is taken from the atmosphere and combined with water and sunlight to produce both glucose and oxygen. Carbon dioxide is taken from the atmosphere and oxygen is released into the atmosphere. This gaseous exchange is required to maintain adequate levels of both gases. Molecules enter and leave via diffusion. Photosynthesis takes place in the chloroplasts in the leaves of the plant. We need oxygen to breathe and we rely on plants to sustain that supply. Respiration is the opposite to photosynthesis and uses oxygen and glucose to produce carbon dioxide, energy and water. 

Respiration takes place in the mitochondria. We need carbon dioxide as it is one of the greenhouse gases that sustains the atmosphere. Because of respiration, stored energy can be released and used. Plant cells need this energy to stay alive.