Topic1.4 - Enzymes & Digestion

Question 1

The digestive system is often referred to as…

Answer 1

The digestive tract or the alimentary canal

Question 2

The steps of digestion

Answer 2

Ingestion
Digestion 
Absorption 
Assimilation 
Egestion

Question 3

Ingestion

Answer 3

Food is taken into the alimentary canal

Question 4

Digestion

Answer 4

Large, insoluble molecules of food are broken down to small molecules

Question 5

Absorption

Answer 5

The small molecules are absorbed into the blood

Question 6

Assimilation

Answer 6

The use of the molecules inside the cells

Question 7

Egestion

Answer 7

Food which could not be digested or absorbed is removed from the body

Question 8

Some molecules are already small enough to enter the blood e.g. …

Answer 8

Vitamins, minerals and simple sugars such as glucose

Question 9

Humans cannot digest ……… at all so it passes through the system relatively …………

Answer 9

Cellulose

Unchanged

Question 10

Large molecules must be digested e.g. …

Answer 10

Starch, proteins and fats

Question 11

Types of digestion

Answer 11

Mechanical

Chemical

Question 12

The 2 major sites of mechanical digestion

Answer 12

• the mouth where teeth break the food into smaller chunks

- the action of bile which emulsifies fats creating a greater surface area for enzymes to work on

Question 13

Chemical digestion results in…

Answer 13

The breakage of bonds holding large molecules together. The results are smaller, more soluble compounds that can enter the blood

Question 14

……… are responsible for controlling these reactions during digestion

Answer 14

Enzymes

Question 15

How are fats (lipids) digested?

What are the products?

Answer 15

Mechanical digestion by the action of teeth and bile
Chemical digestion by the action of lipase

Products = glycerol molecules
fatty acid molecules

Question 16

How are proteins digested?

What are the products?

Answer 16

Mechanical digestion by the action of teeth and water
Chemical digestion by the action of proteases and peptidases

Products = amino acid molecules

Question 17

How are carbohydrates (starch) digested?

What are the products?

Answer 17

Chemical digestion by the action of amylase

Products = maltose molecules

Question 18

How are carbohydrates (maltose) digested?

What are the products?

Answer 18

Chemical digestion by the action of maltase

Products = glucose molecules

Question 19

Process of digestion in the mouth/buccal cavity

Answer 19

• food is ingested at the mouth
• food is broken down mechanically by the teeth (cutting, piercing, grinding)
• the action of salivary amylase chemically digests starch into maltose
• the saliva moistens the food to allow it to pass down the oesophagus
• the tongue moves the food to the back of the mouth so it can be swallowed

Question 20

Process of digestion in the oesophagus

Answer 20

• a muscular tube leading from the mouth to the stomach
• the muscles help move the chewed food along by a process called peristalsis - this is how food is moved throughout the alimentary canal

Question 21

Process of digestion in the stomach

Answer 21

• considered a J shaped muscular bag
• the inner lining of the stomach is folded and within these folds are the gastric pits (that are lined with cells that produce gastric juice)
• the stomach digests food in 2 major ways:
  
  • chemical digestion through the use of enzymes (e.g. pepsin)
  • mechanical digestion via the churning of the muscular walls - this makes sure that the food and the gastric juice are well mixed

Question 22

Process of digestion in the small intestine

Answer 22

• 2 major roles = digestion and absorption
• digestion in the small intestine takes place in the duodenum (the upper region close to the stomach)
• the digestive secretions involved include:
  
  • bile
  • intestinal juice
  • pancreatic juice

Question 23

Process of digestion in the ileum

Answer 23

• when food reaches the lower part of the small intestine (the ileum) the complex food molecules have been completely digested into simple molecules that can cross the gut wall and enter the blood stream
• has a number of features to allow efficient absorption of the amino acids, fatty acids, glycerol, vitamins, minerals and glucose
• it’s long, highly folded and lined with many structures called villi - all of these features increase the surface area for the absorption of the simple food molecules

Question 24

Bile (where it’s produced, what it contains)

Answer 24

• produced in the liver, stored in the gall bladder
• doesn’t contain enzymes
• contains:
  
  • mineral salts- have an alkaline pH and are involved in neutralising the acid chyme. The enzymes of the small intestine can only work efficiently at a neutral pH.
  • bile salts- these emulsify lipids, involves breaking large fat globules into much smaller droplets with an increased surface area

Question 25

Intestinal juice (where it’s produced, what it contains)

Answer 25

• made by the walls of the duodenum
• contains:
  
  • mineral salts- used to create a neutral environment allowing enzymes to work
  • mucus- lubricates intestinal walls allowing easier movement and also protects the intestinal wall from self digestion
  • enzymes- proteases, amylase, maltase, lactase, sucrase

Question 26

Pancreatic juice (what it contains)

Answer 26

Contains

• mineral salts: to neutralise acids
• protease enzymes: -some break down proteins into polypeptides
  - others break down polypeptides into amino acids
• pancreatic amylase: completes the digestion of starch begun in the mouth
• lipase enzymes: involved in the chemical breakdown of the lipid droplets produced by the action of bile

Question 27

Process of digestion in the large intestine (colon)

Answer 27

Responsible for the reabsorption of water- w/o this process we’d become rapidly dehydrated

All of the digestive juices contain high levels of water - some of this is absorbed in the small intestine but much passes into the large intestine w/ the undigested food and fibre

The reabsorption process turns the liquid undigested food into semi-solid faeces

The colon has a large SA in order to facilitate a higher rate of reabsorption

Question 28

Process of egestion

Answer 28

The exit of faeces from the body

After reabsorption, food passes through the colon into the rectum

The rectum stores the faeces until we’re ready to go to the toilet - upon relaxation of the anus faeces will exit the body

Question 29

Content of faeces

Answer 29

1- indigestible food
2- dead cells from the lining of the intestine
3- bile pigments

Question 30

Features of the ileum to allow efficient absorption of the fatty acids, amino acids, glycerol, vitamins, minerals and glucose:

Answer 30

1- very long (6m) : food will spend a lot of time passing through
2- highly folded : greatly increases SA
3- has an excellent blood supply to maintain concentration gradients into the blood stream
4- covered in structures called villi that greatly increase the SA and also have thin, permeable walls

Question 31

Most of the digested substances are absorbed by the process of ………
Steps involved:

Answer 31

Diffusion

(i) the substances enter capillaries found within the villi - fatty acids and glycerol enter lacteals which carry lymph, these fatty substances will enter the blood in a vein
(ii) having entered the blood stream the substances are carried to the liver where they’ll either be stored or used up in other parts of the body

Question 32

Structure of a villus:
Goblet cell-
Lacteal-
Blood capillaries-
Artery-
Vein-

Answer 32

Goblet cell- makes mucus
Lacteal- absorbs digested fats
Blood capillaries- absorb amino acids and sugars
Artery- bringing blood from the heart
Vein- returning blood to liver

Question 33

What are enzymes?

Answer 33

Enzymes are protein molecules that act as biological catalysts, increasing the rate of biological reactions.

Question 34

Lock and key model

Answer 34

Each enzyme is specific to 1 particular substrate. Each substrate has an active site which is a uniquely shaped pocket. Substrate and enzyme fit tightly together in the active site. Substrate gets broken down into 2 product molecules (some enzymes build smaller molecules up into larger ones).

Question 35

Factors affecting rate

Answer 35

Temperature
pH
Enzyme concentration

Question 36

Factors affecting rate: at lower temperatures

Answer 36

At lower temperatures the enzymes and substrates move very slowly (low kinetic energy) so there are fewer collisions and therefore activity is low

Question 37

Factors affecting rate: at optimum temperature

Answer 37

Maximum enzyme activity occurs at the optimum temperature of 35-40^C

Question 38

Factors affecting rate: at higher temperatures

Answer 38

At higher temperatures (around 60^C) the enzymes are denatured - the heat changes their shape and the active site no longer fits the substrate - this is an irreversible change and stops the enzyme from working.

Question 39

Factors affecting rate: pH

Answer 39

Each enzymes has an optimum pH - at either side of the optimum pH they work less well bc the incorrect pH changes the shape of the enzymes active site and will result in the substrate not binding as well and so a decrease in the rate of reaction.

Question 40

Factors affecting rate: enzyme concentration

Answer 40

As enzyme concentration increases so does the rate of reaction - this is bc there is a greater chance of collision between the enzyme and the substrate. Eventually the rate will level off as substrate gets used up.

Question 41

Commercial uses of enzymes

Answer 41

Manufacture of biological washing powders - the enzymes digest the stains on the clothes. They’ll contain protease, carbohydrase and lipase enzymes. The enzymes used are chosen as they work over a range of temperatures (thermostable)