B3: Organisation and the digestive system

Cells

Basic building blocks of all living organisms

Tissue

Group of cells with similar structure + function

Organs

Group of tissues working tog for a specific function

Organ systems

Groups of organs working tog to perform a specific function

Organisms

A number of organ systems working tog

Put into order of size

• Organ systems

• Cells

• Organs

• Organisms

• Tissues

1. Cells

2. Tissues

3. Organs

4. Organ systems

5. Organisms

Types of tissue in the stomach involved in the digestion of food

1. Muscular

2. Glandular

3. Epithelial

Role of tissues in the stomach

1. Muscular- churns food

2. Glandular- releases enzymes

Role of the 3 types of tissue

What do specialised cells have?

Adaptations to help them carry out their functions

Adaptations of muscle cells

1. Can contract (get shorter)

   • Contain special protein fibres that can change their length

2. Have lots of mitochondria

   • Provide energy needed for contraction

Main nutrients in food

1. Carbohydrates (starch)

2. Protein

3. Lipids (fats)

Why do the 3 main nutrients in food need to be digested?

Too large to be absorbed into the BS

What happens during digestion?

• Large food molecules broken down into small molecules by enzymes

• SM can be absorbed into the BS

What acid does stomach contain and what is its function?

HCl

• Helps enzymes digest proteins

How does the churning action of stomach muscles turn food into a fluid to aid digestion?

Increases SA for enzymes to digest

What chemicals are released from the pancreas into the SI?

Enzymes

• Continue digestion of starch + protein

• Start digestion of lipids

What chemicals are released from the liver into the SI?

Bile

• Speeds up digestion of lipids

• Neutralises stomach acid released from stomach

Digestive system

Organ system in which several organs work tog to digest + absorb food

How are the products of digestion used by the body?

To build new carbohydrates, lipids, proteins

What is the glucose produced from digestion used in?

Respiration

What do enzymes do?

Catalyse chemical reactions

Enzymes

Large protein molecules with an active site

• Biological catalysts that catalyse specific reactions in living organisms

How are enzymes able to catalyse specific reactions in living organisms?

Due to the specific shape of their active site

Active site

Where substrate attaches to

Substrate

Molecule enzyme breaks down

• Specific to 1 enzyme

For an enzyme to catalyse a reaction, the substrate must…

Fit perfectly into the active site

How does an enzyme catalyse a reaction?

1. Substrate binds to specific AS

2. Enzyme breaks down substrate into products

Catalyst

Increase the rate of chemical reactions w/o being used up / chemically changed

What happens if a substrate doesn’t fit into an active site

Enzyme can’t break down the substrate

Enzymes are…

Specific

What is meant by ‘enzymes are specific‘?

Substrate must fit perfectly into the AS (for reaction to be catalysed)

• Lock and key theory

Enzymes in the digestive system + what they help break down

1. Protease- proteins

2. Lipase- lipids

3. Carbohydrase- carbohydrates

4. Amylase- starch

Where is protease found?

1. Stomach

2. Pancreatic fluid

3. SI

What do digestive enzymes do?

Convert food into small soluble molecules that can be absorbed into the BS

Proteins

Long chains of AA

What happens when we digest proteins?

1. Protease enzymes convert protein back to individual AA

2. AA absorbed into BS + body cells

3. AA joined in a diff order to make human proteins

What is starch?

Carbohydrate

What is starch made up of?

Chain of glucose molecules

What is produced when carbohydrates like starch are digested?

Simple sugars

Where is amylase found?

1. Saliva

2. Pancreatic fluid

Structure of lipids

1 molecule of glycerol attached to 3 molecules fatty acids

What does lipase break down / digest lipid molecules into?

• Glycerol

• Fatty acids

Where is lipase found?

• Pancreatic fluid

• SI

What do these enzymes break down these molecules into?

1. Carbohydrase

2. Amylase

3. Protease

4. Lipase

1. Carbohydrase- carbohydrates- simple sugars

2. Amylase- starch

3. Protease- proteins- AA

4. Lipase- lipids- glycerol + fatty acids

Amylase

Carbohydrase which breaks down starch

Where is bile made + stored?

• Made in liver

• Stored in gall bladder

Bile

What does bile help?

Speed up digestion of lipids

Is bile an enzyme?

No

What does bile do to lipids?

Bile emulsifies lipids

How does bile speed up the digestion of lipids?

• It converts large lipid droplets into smaller ones

• Increases SA of lipid droplets

• Which increases rate of lipid break down by lipase

What does bile emulsifying lipids do?

• Increases SA of lipid droplets

• Which increases rate of lipid break down by lipase

Is bile acid or alkaline?

Alkaline

Bile is alkaline- what does this allow it to do?

Can neutralise stomach acid, creating alkaline conditions in SI

What does bile emulsify fats to form?

Small droplets which increases the SA

What helps increase the rate of fat breakdown by lipase?

• Alkaline conditions

• Large SA

Factors that affect enzyme action

• Temp

• pH

What happens to enzyme activity as temp increases (not exceeding optimum)?

Increases (reaction gets faster)

Why does enzyme activity increase as temp increases (not exceeding optimum)?

• Enzyme + substrate moving faster

• → more collisions per s betw substrate + AS

Optimum temperature

Temp at which the enzyme is working at the fastest possible rate

What happens at the optimum temperature

Max frequency of successful collisions between the substrate + AS

Optimum temp for human enzymes

37 °C

What happens to enzyme activity as temp increases beyond the optimum?

Decreases to 0

Why does enzyme activity become 0 after temp has been increased past the optimum?

• At high temps, enzyme molecule vibrates + shape of AS changes

• Substrate no longer fits perfectly into AS

• AS has denatured

What is meant by the active site has denatured?

• Substrate no longer fits perfectly into AS

• Enzyme can’t catalyse the reaction

What happens when an enzyme is denatured?

Shape of AS changes

Optimum pH

Enzyme activity is maximum

What happens to enzyme activity if PH is made more acidic or alkaline and why?

Drops to 0

• AS denatures if conditions are too acidic or alkaline

Each enzyme has a?

Specific optimum pH

What conditions to enzymes in the stomach work best at?

Acidic pH

• Eg protease

What conditions to enzymes in the small intestine work best at?

Alkaline pH

• Eg enzyme released fm pancreas into SI (lipase)

Are there different protease enzymes in the stomach and SI, and why?

Yes

• Stomach- acidic

• SI- alkaline

What are buffer solutions used for?

To control pH

Examples of carbohydrates

• Starch

• Sugars (glucose)

How to test for food groups + positive results

1. Starch

2. Glucose

3. Proteins

4. Lipids

1. Starch- iodine solution- blue-black

2. Glucose- benedict’s solution

3. Protein- biuret solution- purple/ lilac

4. Lipids- ethanol- white, cloudy emulsion

Positive + negative results to test for starch with iodine solution

1. Positive- orange changes to blue-black

2. Negative- no color change, IS remains orange

If glucose is present, what does the color of benedict’s solution tell us?

Approx amount of sugar present

• Not exact amount

Positive + negative results to test for sugars (glucose) with benedict’s solution

• Green (small amt)

• Yellow (more)

• Brick red (lots)

What sugars does the benedict’s test work for?

Reducing sugars (eg glucose)

Examples of non-reducing sugars

Sucrose

Positive + negative results to test for proteins with biurets solution

Biuret solution (blue) changes to purple/ lilac

Positive results to test for lipids with ethanol

Cloudy, white emulsion

When testing for flames with ethanol, why is it imp that no naked flames are present?

Ethanol is v flammable

What are digestive enzymes produced by?

Specialised cells in glands + lining of digestive system

What happens in the SI?

Products of digestion absorbed into the BS

How is the small intestine adapted for absorbing products of digestion?

Villi is / has:

1. V long

2. Lots of villi inside the SI

3. Microvilli on the surface of villi

4. V good blood supply (capillaries)

5. A thin membrane

What do the adaptations of the small intestine mean there is?

Rapid rate of diffusion

If a molecule can’t be absorbed by diffusion, how is it absorbed?

AT

In what conditions do protease enzymes in the stomach work best at?

Acidic

How does the stomach maintain a low pH for protease enzymes?

Releases HCl

In what conditions do enzymes in the pancreas + SI work best at?

Alkaline

• Alkaline conditions provided by bile

Role of bile

• Neutralises acid

• Emulsifies fats

Purpose of HCl in the stomach

• Provides optimum acidic pH for protease

• Kills bacteria in the stomach

What does the thick layer of mucus produced by the stomach do?

Coats stomach walls- protects them from being digested by the acid + enzymes

What happens if someone develops a stomach ulcer?

• Protective mucus is lost

• Acid production may increase

• Lining of stomach is attacked by acid + enzymes → painful

Why is bile not an enzyme?

Doesn’t break down fat molecules

• It emulsifies fats into tiny droplets

What happens in the small vs large intestine?

1. Small- products of digestion absorbed into BS

2. Large- water absorbed into BS

Pancreas

Releases enzymes into SI

Does digestion take place in the pancreas?

No