Quick Quiz Recap1. What is the definition of osmosis?2. What is the difference between

osmosis and diffusion?3. How is a red blood cell adapted for

its job?4. Where does protein synthesis occur?5. Where does respiration occur?6. What is respiration?7. What is the job of the cell wall?8. Name 3 organelles you find in a

plant cell but not an animal cell

Enzymes

Respiration • Summarise respiration

– What is it?– Where does it occur?– Why is it needed?

Enzymes• What are they?

Amylase and Starch• How do you test for STARCH?

• How do you test for GLUCOSE?

Amylase and Starch• EQUIPMENT- for 30 students• Boiling tubes• Thermometers• Iodine• Benedict’s Solution• Starch solution• Amylase

Amylase and Starch1. Set up 2 water baths. One will be for the

Benedict’s test, the other should be maintained at roughly 350.

2. Add some amylase to starch. Wait 5 minutes. 3. Split the solution between 2 test tubes. Test one

for starch and test one for glucose. Write your results for room temperature.

4. Next, place a volume of amylase in a test tube and put it in a water bath at 350. Do the same for a small volume of starch.

5. After 10 minutes of being in the water bath, mix the two solutions together. Place back in the 350 water for 10 minutes.

6. After 10 minutes test the solution for starch and for glucose like you did before.

7. Write up the experiment

Amylase and Starch• Results and conclusion –What should

have happened and why?

• Evaluation

IODINE TEST BENEDICT’s TEST

ROOM TEMP40 Degrees

Enzymes

What is an enzyme?What type of molecules are enzymes?

How do enzymes work?

Enzymes as CatalystsA catalyst causes reactions to occur more easily and more quickly

by reducing the activation energy needed to start the reaction. They also allow reactions to occur at lower temperatures.

Energy

Progress of reaction

Substrates

Products

High energy intermediate

Activation energy

Substratemolecules

(complementaryshape to active site)

Productmolecules

diffuse awayfrom the

active site

This is the ‘lock and key model’ of enzyme activity.

Enzyme remainsunchanged

Enzymemolecule

Activesite

Reactionoccurs

The Active Site - The Lock and Key ModelSubstrate and enzyme molecules react together...Substrate molecules bind with enzyme molecules at the activesite because of their complementary shapes.

The enzyme converts the substrate into products.

Enzymemolecule

Enzymes have a special site on their surface called an active site into which the reacting substrate molecules fit.

Active Sites

An amylase enzyme will accept starch molecules but not the molecules of other carbohydrates, proteins or lipids.

Substratemolecule inthe active site

Amylase, although a relatively simpleenzyme is still a complex molecule

Enzymes are highly specific and each enzyme has a different shaped active site.

Conditions effecting enzyme activity

What effects an enzyme?Name 2 things that will effect how well

an enzyme works?

Think about human digestion and thermoregulation

Conditions effecting enzyme activity practical

• EQUIPMENT• Hydrogen Peroxide• Potatoes• Knives• Potato borers• Boiling tube and bungs• Ice• Thermometers

The Effect of Temperature on the volume of oxygen produced by the enzyme catalase when reacted with

Hydrogen Peroxide• Variables• Dependent=

• Independent=

• Control=

• Results TableTemperature

Volume of Oxygen

METHOD1. Measure out a 4cm strip of potato. Place in a

boiling tube.2. Measure out 30 cm3 of Hydrogen Peroxide using

a measuring cylinder and then transfer to a boiling tube

3. Place the boiling tubes in the water bath/ice, depending on the temperature you are measuring.

4. Leave them in the water bath/ ice until the Hydrogen Peroxide has reached the correct temperature

5. When your hydrogen peroxide solution has reached the temperature you are investigating, transfer it to the boiling tube with the potato in and place the bung on as quickly as possible.

6. Record the volume of oxygen produced in 5 minutes

7. Repeat the experiment for different temperatures

Results and ConclusionsTemperature 0 Volume of

Oxygen Produced cm3

0 410 820 1630 3740 8050 2060 0

•Draw a graph of the results•Describe and explain for 5 marks the graph

•Include the term kinetic energy•Include collisions•Include denature•Include active site

The Effect of Temperature on Enzyme ActivityAt low temperatures the reacting molecules do not have much kinetic energy, so the collisions are fewer and the rate of reaction is slow.

As the temperature rises, the reacting molecules gain kinetic energy, so the number of substrate/enzyme collisions increases, and consequently the rate of reaction is much higher.

However, as the temperature is increased beyond the optimum temperature, special bonds that stabilise the enzyme’s three dimensional structure are broken, and the physical shape of the enzyme’s active site starts to change.

The Effect of Temperature on Enzyme ActivityEventually a temperature is reached where the rate of reaction is greatest - this is called the optimum temperature.

Special bonds stabilise an enzyme’s 3D shape

Special Bonds

If the special bonds are broken the 3D shape is lost

The Effect of Temperature on Enzyme Activity

Denatured enzymes will not be able to catalyse a reaction and hence the products are not formed.

Denaturing is permanent and reducing the temperature will not undo the damage to the active sites.

Substrate molecules no longer fit properly, and at a critical temperature, the substrate will not fit into the active site at all - at this point the enzyme is said to have been denatured.

Substrate moleculeno longer fits in the active site

Enzymemolecule

The reaction rate doubles for every 10°C rise in temperature.

The enzyme has been denatured.

Temperature and Enzyme Activity

For many enzymes, the maximum rate of reaction is reached at atemperature between 37°C to 40°C.This is the optimum temperature.

As the temperature increases, molecules move more quickly and collide more often - the reaction rate increases.

Rapid increasein reaction rate.

The Effect of pH on Enzyme ActivityEach enzyme has an optimum pH (fastest reaction rate) and pH can alter the shape of the active site. The shape change may be temporary or permanent, in which case the enzyme is denatured.

Summary• What is the job of an enzyme?• Explain 2 conditions that effect

enzyme activity• Name 3 places where enzymes are

required in the human body.