Biology 103

PCC, Cascade

Pre-lab homework Lab 7: Nutrition & Digestion Lab Section:

Name:

1. In Biology 101 you learned about the four different types of macromolecules that organisms use to build themselves. For each of the four types give a short description of the role these molecules play and an example of 2-3 molecules of each type. Molecule

Role

Example

Carbohydrates

Nucleic Acids

Proteins

Lipids

2. Fill out the table on the back of this page!

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Biology 103

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Use the following table to list the enzymes responsible for digestion of each class of molecule and where they are produced and where they are active. Hint: Table 30-5 (Audesirk) in your text has all the information you need to fill this table out – be careful though because these tables are organized very differently! If you have the Cain textbook check out a copy of Audesirk from the library (its on reserve) or find another source to complete this table.

Food Molecule

Enzymes

Source of enzyme &

Substance that aids in

location of action

digestion of this class of molecule

Carbohydrates

Proteins

Lipids

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Biology 103

PCC, Cascade

Lab 7: Nutrition & Digestion Lab section

Name:

Objectives: Upon completion of this activity, you should be able to: •

Describe the pattern of food processing in humans

•

Describe the structure and function of the main parts of the human digestive system.

•

Explain the differences in digestive strategies between fungi and animals

•

Discuss the strategy that plants use to maintain nutrient requirements.

Exercise 1: Digestive enzyme specificity: In this activity we will examine the ability of different digestive enzymes to catalyze the hydrolysis of various substrates. The two enzymes we will work with, amylase and trypsin, both hydrolyze polymers into monomers. Amylase hydrolyzes starch (a polysaccharide) while trypsin hydrolyzes proteins. Your digestive system uses dozens of different enzymes to hydrolyze the foods that you eat into useful subunits that are then used to build complex macromolecules or are further broken down and used as an energy source. In this experiment we will test the ability of these enzymes to hydrolyze their favored substrate and an alternate substrate. To set up the experiment follow this procedure: 1. Collect 9 test tubes and label them 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 3c 2. In test tube 1a, 1b, and 1c put 2 droppers full (not 2 drops – 2 droppers!) of amylase. 3. In test tube 2a, 2b, and 2c put 2 droppers full (not 2 drops – 2 droppers!) of trypsin. 4. In test tube 3a, 3b, and 3c put 2 droppers full (not 2 drops – 2 droppers!) of water. 5. Now you need to add the substrate molecules to the enzymes already in your test tubes o In test tubes 1a, 2a and 3a put 2 droppers full of starch (a polysaccharide) o In test tubes 1b, 2b, and 3b add a strip of photographic film (the dark color is held to the film by a bond similar to a peptide bond that holds proteins together) o In test tubes 1c, 2c, and 3c put 2 droppers full of sucrose (a disaccharide) 6. Leave the tubes to incubate for 45 minutes while you work on the rest of the lab.

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Biology 103

PCC, Cascade

After the 45 minutes of incubation we will test for the presence of each of the three substrates: 1. To test for starch in tubes 1a, 2a, and 3a add a drop of Lugol’s iodine solution to 4 spots on a spot plate and then add starch to spot one and the fluid in the tubes to each of the other spots. In the presence of starch the iodine will turn a dark purple/black color. a. Why do we need the first spot with starch and iodine?

2. To test for the activity of the enzyme trypsin on its preferred substrate simply lift the strip of photographic film from the tube (for each of tube 1b, 2b, and 3b). Active trypsin should remove the dark coloring resulting in a mostly transparent region of the strip. 3. Finally we must test for the activity of trypsin and amylase on sucrose – a substrate that is not the primary substrate for either enzyme. To do this we will test for the subunits of sucrose. Recall that sucrose is a disaccharide made up of two monosaccharides joined together (the two are fructose and glucose). We will use the Bennedict’s test for the presence of fructose and glucose. To perform this test you will need to do the following: a. place a 400ml (or larger) beaker half full of water on a hot plate, add a few boiling chips and begin to heat the water. b. add 2 droppers full (not 2 drops – 2 droppers!) of glucose to a test tube and label it ‘G’. i. Why do we need this tube?

c. Take tubes 1c, 2c, 3c, and G and add 1 dropperful of Bennedict’s solution. d. place the test tubes into the beaker of now boiling water and wait 3-4 minutes. e. Carefully remove the test tubes using a test tube holder and place them in a test tube rack. ***Take Care – Test Tubes will be HOT!*** f. Compare the solutions in the tubes. In the presence of a sugar like glucose the solution will turn a orange/red color. In the presence of sucrose the solution should remain a light blue color. 4. Now fill out the data table and answer the questions on the next page.

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Biology 103

PCC, Cascade

Tube #

Ingredients

1a

Amylase + Starch

1b

Amylase + Film

1c

Amylase + Sucrose

2a

Trypsin + Starch

2b

Trypsin + Film

2c

Trypsin + Sucrose

3a

Water + Starch

3b

Water + Film

3c

Water + Sucrose

Prediction

Result

Questions on Digestive enzyme specificity: 1. Why do we need to include tubes 3a, 3b, and 3c? What are they telling us?

2. Which of the substrates can amylase act on? Which is it unable to act on? Why do you think this is?

3. Which of the substrates can trypsin act on? Which is it unable to act on?

4. Compare your results from tube 1 and 2. What do these results tell you about how specific enzymes are?

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Biology 103

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5. Amylase is a digestive enzyme secreted in your saliva and starch digestion begins almost as soon as you put a starchy food in your mouth. But amylase is also produced in the pancreas and secreted into the small intestine. Why do you think your body produces amylase in two different places? (Hint: Why does the amylase from your mouth stop working?)

6. There are hundreds of different proteins in the foods you consume and yet your stomach produces only a single protein digesting enzyme. Your small intestine produces a few more but there are less than 10 different enzymes that can hydrolyze peptide bonds. If enzymes are so specific how can your body get away with so few protein digesting enzymes?

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Biology 103

PCC, Cascade

Exercise 2 Animal Digestive systems: On the following diagram label these structures: anus, appendix, cecum, esophagus, gallbladder, large intestine, liver, mouth, pancreas, pharynx, rectum, small intestine, stomach, salivary glands,

In the space below draw a picture of a slide of the small intestine at 5x (a dissection scope) and at 100x (using your microscope). Think about how the structure aids the function of the intestine.

Small Intestine (5x)

Small Intestine (100x)

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Biology 103

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Specialization of the digestive system: The following represents two ways that digestive systems show specialization. First are specialized digestive tracts (a carnivore on the left and an herbivore on the right) after you compare them look over the skulls of a carnivore, an herbivore, and an omnivore and describe specializations you can see. Look at the diagram to the left – what difference can you see in the digestive systems of these two organisms?

Why do you think this difference is so pronounced in these organisms?

Compare the skulls provided what are three differences that you see in these skulls that you think are related to the food source that they consume. (Hint: pay close attention to the teeth!)

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Biology 103

PCC, Cascade

Exercise 3 Nutrition in Plants: In a classic experiment Jean-Baptiste van Helmont grew a willow tree for 5 years adding only water and measured the amount of weight gain for the tree and weight loss from the soil. At start of experiment

At end of experiment

Weight change

Weight of Soil

90.9 kg

90.84 kg

- 0.06 kg

Weight of Tree

2.5 kg

76.8 kg

+ 74 kg

Weight gain not from

+ 73.94 kg

soil

1. What is the basic equation of photosynthesis?

2. Where did the additional plant weight come from? (Hint: it isn’t all from the ground and water!)

3. What do you think is being taken out of the soil? Where is the plant using these nutrients?

4. Since the amount of material being taken out of the soil is so small then how important can it be?

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Biology 103

PCC, Cascade

Plant root structure: Plant roots are the main plant organs responsible for the uptake of nutrients other than CO2. Because of this they have needs that are in some ways similar to the needs of animal digestive systems. In the space below sketch a root tip, be sure to notice the fine root hairs that are abundant a short distance from the growing tip of the root.

longitudinal section of root tip showing root hairs (400x)

The root hairs are an adaptation that increases surface area in plant roots. Why would this be an advantage to the plant?

Look back at your sketches of the cross section through the human intestine. How is your digestive system adapted to increase its surface area?

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