Focus Question: What do yeast Focus Question: What do yeast need to become active?need to become active?

Living SystemsLiving Systems

Investigation 3 - Part 1Investigation 3 - Part 1

Living Organisms• Help investigate food

• Yeast - single-celled organisms– Dormant

• What do you think the yeast will need to break out of resting, dormant state and become active?– Water– Food– Warmth

Activating Yeast• Warm water - provide warmth & water

• Food - cookies

• Measuring tools, containers, zip-lock bags

• Plan for finding out what yeast need to break its dormancy

• How will you find out what conditions are needed to activate the yeast?

Activating Yeast• If warmth, water, and food activate

yeast, how will you know if yeast needs all three variables to become active, or if only food, or only water, or only warmth will activate the yeast?

• Need to test all the variables in order to determine which ones result in yeast activation.

Experimental Process• All living organisms need water. So

yeast probably needs water to become active.– Just to be sure, one experiment with no

water, only food and yeast.

• Does yeast need water and food to become active or does it just need water to become active?

Procedure• Two zip bags, label one “cookie”• Add two level 5-ml spoons yeast to

each bag• Add 50-ml hot water to bag. Wet all of

yeast.• Add two animal cookies to “cookie”

bag, soak, then crush• Seal bags shut, pushing air out.• Place sealed bags in hot water bath.

Procedure• Keep hot water between 40 - 50

degrees Celcius

• Yeast lab sheet procedure

• Place in hot water bath for 10 minutes

• Analyze Cookie Ingredients - Answer questions on bottom of worksheet

• Ingredients ordered from most to least.

• After 10 minutes, remove bags and lay flat - what do you see?– Bubbles and gas are evidence yeast is

alive and active– Yeast getting energy from food

• Cookie provides food for yeast• Plain water does not

• What are two most abundant ingredients on cookie labels?– Flour– Sugar

• Something in cookie is food for yeast.

• Think of a way to find out what is in the cookie that is food for yeast.

• Is one of the ingredients the food that activated the yeast?