Cellular Respiration

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Agri-science Resources for High School Sciences

Science

Grade 10-12

Seed Respiration
Biology

Biology Lab

Individual or teams of 2

DESCRIPTION
Plants generate Oxygen, which is essential for humans to survive. However, plants also consume Oxygen during respiration. It is acutally possible to measure the amount of Oxygen used by plants with a device called a repirometer. Germinating seeds will be used to demonstrate Plant Respiration.

LEARNING OUTCOMES
Students will: • examine oxygen consumption by seeds • understand the importance of respiration to life on Earth

MATERIALS
• large test tube • metric ruler • germinating seeds of any kind (1g) • one-hole stopper • limewater • pipette • wad of cotton • marking crayon • liquid detergent • balance • paper towels • spatula • scotch tape • support stand and clamp • rigid polyethylene tubing or hollow glass tubing, 20 cm long and bent at right angle

READINESS ACTIVITIES
Students should: • review the life cycle of a plant, especially during germination • examine respiration in other organisms, such as humans

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Seed Respiration

Agri-science Resources for High School Sciences

Biology

Introduction
Plants are known for their ability to convert Carbon dioxide into Oxygen. However, all aerobic organisms take in Oxygen and give off Carbon dioxide as long as they are alive. This is true for plants as well as animals. During germination, seeds use sugars and other molecules as a substrate for respiration.

Germination
Germination of a seed begins with water uptake by the seed. This process is called imbibition. The uptake of water by a seed is an essential step in order for the seed to germinate. The total amount of water taken up is about 2-3 times the weight of the seed. Whether or not a viable seed will germinate depends on a number of factors. The chemical environment of the seed must be right. Water must be available, Oxygen has to be present since the seed must repire and no dangerous chemicals should be present. The physical environment must also be favourable. The temperature must be suitable as well as the light quality and quantity. A person may wonder why seeds are often buried underground. The reason is that this helps guarantee the seeds receive the correct amount of light for germination. Full sunlight can often prevent a seed from germinating. The extent to which germination has progressed can be determined by measuring water uptake or respiration.

Oxygen Consumption
If you place a living organism in a closed system, it is possible to measure its consumption of Oxygen. In this exercise, a respirometer will be used to measure oxygen consumption. The instrument contains limewater and germinating seeds. As the seeds consume oxygen, carbon dioxide is excreted. The carbon dioxide is then absorbed by the limewater, creating a slight vacuum in the respirometer. This vacuum will draw a drop of liquid detergent in the glass tubing inward. This movement will be measured in millimeters using a metric ruler taped to the glass tubing. This will give an idea of how much oxygen the germinating seeds consume. 50

Seed Respiration

Agri-science Resources for High School Sciences

Biology

Figure 1. The device that will be used to measure the oxygen consumption of the germinating seeds: a respirometer.

Procedure
1. Prior to the lab, obtain some small plant seeds. Try and use a different variety than your classmates. The seeds need to be germinating for the experiment. You can do this by spreading them on wet paper towel a day or two before the lab. 2. Begin by inserting the short end of the tube into the hole of the stopper. BE VERY CAREFUL if you are using GLASS. It could break easily. The long end of the tube should be sticking out at a right angle as in the diagram. 3. Draw a line 0.5 cm above the bottom of the test tube with the marking crayon. Add limewater to the tube up to this mark. 4. Moisten a small wad of loose cotton...
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