Effect of substrate concentration on enzyme function

• Read through the introductory materials below.
• Open the Unit 2 Experiment Answer Sheet and complete the following Experiment exercises this unit:
  • Experiment 2 Exercise 1A – Effect of substrate concentration on enzyme function (~30 min)
  • Experiment 2 Exercise 1B – Effect of pH on enzyme function (~30 min)
  • Experiment 2 Exercise 2 – Cellular Respiration and Photosynthesis (~1.5 hrs)
• Save your completed Unit 2 Experiment Answer Sheet and submit it by Midnight Sunday (CT).

Enzymes – Introduction

This unit we will examine enzyme function using a virtual simulation. Be sure to review our online lecture on Energetics and pp 80 – 82 in your book. As we have learned this unit, enzymes are biological catalysts that can lower the activation energy required to allow reactions to proceed. Enzymes are very sensitive to the environment in which they work, meaning changes in substrate concentration, temperature, pH, salts and other chemicals can drastically alter their function. This is one of the reasons the buffers we learned about last unit are so important!

When you are ready to begin these two exercises, go to:

Bioman. No date. Enzymatic (Links to an external site.)

Procedure

1. Click on “Start a New Game” and follow the on-screen instructions.
2. When you get to the “Main Menu”, click on “Experiments”.  You will have to click twice.
3. Click “OK” and follow the on-screen instructions.  Please note that you do not need to submit the answers from the quiz.

You will need an understanding of the different types of experimental variables in order to correctly graph your results. There are three different types of variables:

Independent Variable: This is the variable that the experimenter manipulates and is expected to affect the dependent variable. For example, if you think the amount of sunlight affects plant growth, you would vary the amount of light a plant receives (e.g., 2 hrs/day, 4hrs/day, 6 hrs/day). The amount of sunlight would be the independent variable.

Dependent Variable: This variable is expected to vary depending on the independent variable. In the example above, plant growth would be the dependent variable, because it is dependent on the amount of sunlight it receives.

Control Variable: This type of variable includes factors (there may be many) that could affect the outcome of your experiment. By holding these variables constant in all treatments, the experimenter knows that only the independent variable is affecting the outcome. In the example above, the variables you would want to hold constant would be things such as temperature, water and nutrients.

When graphing your results, the two variables of interest are the independent and dependent variables. The independent variable is always graphed on the x-axis and the dependent variable is always graphed on the y-axis. When you generate a graph, you must also always label each axis and include any units of measure.

When you are ready to begin, use the instructions in the Unit 2 Experiment Answer Sheet to complete these exercises.

Cellular Respiration and Photosynthesis – Introduction

In this exercise, you will have the opportunity to explore the relationship between the air we breathe and the plants around us. Be sure to review our online lecture on Energetics and Chapters 6 and 7 in your book; particularly pp 92-93.

Cellular respiration is the metabolic pathway in which all plants and animals extract usable energy (ATP) from foods either eaten (animals) or synthesized (plants). Yes, plants perform cellular respiration! This is because the energy they generate via photosynthesis is used to produce sugars. It is these sugars that are then broken down by cellular respiration to provide the energy to carry out plant cellular functions, just like in animal cells!

Cellular respiration and photosynthesis are linked by their reactants and products. Here is a chemical summary of the two reactions:

Cellular Respiration:     Oxygen + Glucose » Energy + Carbon dioxide + Water

Photosynthesis:             Energy + Water + Carbon dioxide » Glucose + Oxygen

What do you notice about the reactants and products of these two processes? RIGHT! The reactants of cellular respiration are the products of photosynthesis and the products of cellular respiration are the reactants of photosynthesis. Without photosynthesis and the production of oxygen, aerobic cellular respiration could not occur. And, carbon dioxide levels would increase significantly!

In this exercise, you will demonstrate this relationship between these two important processes using snails and Elodea, a water plant. When you are ready to start this exercise, go to:

Virtual Labs Simulation
http://www.classzone.com/cz/books/bio_09/resources/htmls/virtual_labs/virtualLabs.html (Links to an external site.)

If a link to Carbon Transfer through Snails and Elodea is not directly available, then follow these instructions:

• Select Missouri as your location and click Go
• Click on the Go beneath Biology 2010
• Under the Labs heading, click on Virtual Labs
• Click on Carbon Transfer through Snails and Elodea

You will need to open the Unit 2 Experiment Answer Sheet and follow the instructions carefully. The simulation is a little clunky to use and if you don’t do things right, you will have to start over. You must complete certain steps before you can proceed.

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