B3 - Digestion

Question 1

What is a tissue?

Answer 1

A group of cells with similar structure/function

Question 2

What is an organ?

Answer 2

A group of tissues that perform a specific function together

Question 3

What are enzymes?

Answer 3

Biological catalysts with a specific active site that speed up reactions

Question 4

What is the first organ in the digestive system and what is its role?

Answer 4

• Food chewed in mouth
• Mouth enzymes in saliva begin to digest starch and break it down into smaller sugar molecules

Question 5

How does the food travel from the mouth into the stomach? What happens in there?

Answer 5

• food passes down oesophagus to stomach
• enzymes begin digestion of protein
• stomach has hydrochloric acid that helps digest proteins
• stomach muscles churn the food and turn it into a liquid, increasing surface area for enzymes to digest

Question 6

What happens after food has left the stomach?

Answer 6

• fluid passes to small intestine
• pancreas releases enzymes into intestine, continue digestion of starch and proteins and lipids
• liver releases bile into intestine to speed up digestion of lipids, bile neutralises acid from the stomach
• small molecules are absorbed into the bloodstream by diffusion/active transport

Question 7

What are the substances that can diffuse through the cell membrane?

Answer 7

Glucose, water, oxygen and amino acids ( acids that form together to make proteins)

Question 8

What substances cant diffuse through cell membranes?

Answer 8

Proteins and starch molecules, too big

Question 9

Where does the food go after the small intestine?

Answer 9

Food ends up in large intestine where water is absorbed into the bloodstream, the faeces are released from the body through the anus

Question 10

How does an enzyme work?

Answer 10

• Lock and key model - each substrate fits into the active site of the enzyme, substrate binds together as they fit together
• The enzyme breaks down the substrate into products
  The reaction can continue to happen in it, until the enzyme becomes denatured- it changes shape.

Question 11

What effect does temperature have on enzyme activity?

Answer 11

Temperature increases=rate of reaction increases
Optimum temperature - reaction works as fast as possible
After optimum temperature enzyme begins to denature and stops working

Question 12

How are enzymes denatured by temperature?

Answer 12

• the high temperature causes the protein chains to unravel
• changes shape of active site

Question 13

Why do enzymes have an optimum pH?

Answer 13

• Forces holding the protein chains in position are affected by pH
• A change in pH can change the shape of the active site

Question 14

What 3 places is amylase made in? Its function?

Answer 14

• Made in: salivary glands, pancreas, small intestine
• Function: breaking down starch into glucose

Question 15

What 3 places is protease made in? Its function?

Answer 15

• Made in: stomach, pancreas, small intestine
• Function: breaking down proteins into amino acids

Question 16

What 2 places is lipase made in? Its function?

Answer 16

• Made in: pancreas, small intestine
• Function: breaking down lipids into fatty acids and glycerol

Question 17

What is the general function of digestive enzymes?

Answer 17

To food into small soluble molecules that can be absorbed into the bloodstream

Question 18

What are products of digestion used for?

Answer 18

Used to build new carbohydrates, lipids and proteins

Question 19

What enzyme breaks down carbohydrates?

Answer 19

Carbohydrases break down into simple sugars

Question 20

What 2 places is starch digested in the body?

Answer 20

Mouth
Small intestine

Question 21

What 2 places is protein digested in the body?

Answer 21

Stomach
Small intestine

Question 22

What place is fat digested in the body?

Answer 22

Small intestine

Question 23

Why is starch not digested in the stomach?

Answer 23

Stomach has no amylase
Conditions are too acidic for amylase to work

Question 24

How can the mouth break down starchy foods?

Answer 24

Teeth break down food
Saliva has amylase

Question 25

Where is bile made?

Answer 25

Liver

Question 26

Where is bile stored?

Answer 26

Gall bladder

Question 27

What is bile? How does it help in digestion?

Answer 27

- Alkaline to neutralise hydrochloric acid in the stomach - Emulsifies fat into small droplets, increases surface area increasing breakdown of fat by lipase

Question 28

Explain how protein is digested

Answer 28

1) First broken down mechanically into smaller pieces by chewing in the mouth 2) Protease enzymes break down protein in the stomach and small intestine 3) Protease broken down into amino acids

Question 29

Food test 1 - what is the test for starch?

Answer 29

1. solid food groud up using pestle and mortar and add to water 2. add iodine to sample 3. iodine present = yellow-->blue/black

Question 30

Food test 2 - what is the test for sugar?

Answer 30

-make food solution -place 2cm^3 of solution in test tube - 10 drops of benedicts solution (blue) - warm solution with hot water bath - green= small amount of sugar -yellow= some amount of sugar -brick red = a large amount of sugar

Question 31

Food test 3 - what is the test for proteins?

Answer 31

-make food solution -place 2cm^3 of solution in a test tube -add 2cm^3 of biuret solution (blue) - change from blue to purple /lilac

Question 32

Food test 4 - what is the test for lipids?

Answer 32

- grind food with mortar and pestle and add distilled water, but don't filter as lipid molecules can stick to filter paper - put 2cm^3 of food solution into test tub - add few drops of distilled water and few drops of ethanol - gently shake solution - if present, solution will turn cloudy

Question 33

Required Practical 5: investigate the effect of pH on the rate of reaction of amylase enzyme

Question 34

How is the small intestine adapted for absorption?

Answer 34

Walls covered in villi and each villus is covered in microvilli. These increase the surface area for absorption The wall of the small intestine is very thin which shortens the diffusion path Villi have a very rich blood supply which maintains a steep concentration gradient for diffusion to occur rapidly

Question 35

What is the role of the liver in digestion?

Answer 35

The liver produces bile, which emulsifies lipids and breaks lipids into small droplets, aiding their absorption

Question 36

What is the role of the pancreas in digestion?

Answer 36

The pancreas produces digestive juices, including enzymes used in chemical digestion of proteins, lipids and carbohydrates

Question 37

Food test 2 - what is the test for glucose?

Answer 37

1. solid ground up using pestle and mortar and added to water 2. add benedicts reagent to food sample 3. heat with bunsen burner/hot water bath 4. glucose present = red, orange, green or yellow

Question 38

Food test 3 - what is the test for protein?

Answer 38

1. solid ground up using pestle and mortar and add to water 2. add birute reagent to food sample 3. protein present = blue-->purple/lilac

Question 39

Food test 4 - what is the test for lipids?

Answer 39

1. solid ground up using pestle and mortar and add water - don't filter as lipid molecules can stick to paper 2. add a few drops of water and ethanol to solution 3. gently shake solution 4. lipids present=colourless--->cloudy

Question 40

Required practical 5 - investigating enzymes

Answer 40

1. Add iodine solution to each well in spotting tile 2. In water bath at set temperature, add 2cm^3 of starch, amylase and pH buffer solution(5) and leave for 5 minutes 3. Mix all 3 solutions together and stir 4. Return to water bath and start stopwatch 4. Every 30 seconds add a few drops to spotting tile using pipette 5. Repeat using different pH buffers

Question 41

Why would you expect it to take longer for starch to disappear at lower temperatures?

Answer 41

- Molecules have low kinetic energy so fewer collisions between starch and amylase

Question 42

How could you use this experiment to determine the pH amylase works best in?

Answer 42

- look for quickest time iodine stopped turning blue/black