digestive system

Question 1

what does digestion do

Answer 1

food is broken down into small simple and soluble substances that can be absorbed and used by our body cells through digestion

Question 2

processes of human nutrition

Answer 2

• ingestion (happens in mouth)
food is taken into the alimentary canal
• digestion (starts in mouth)
food is broken down into simple + soluble molecules
• absorption (large + small intestines)
absorbed food molecules enter the circulatory system (eg. glucose is absorbed into the bloodstream)
• assimilation
absorbed food molecules are taken up by body cells for metabolism (eg. glucose converts into glycogen stored in muscle cells)
• egestion
undigested + in absorbed materials are removed

Question 3

if nitrogen is used as an index of proteins, express the following in terms of nitrogen intake (i) nitrogen in faeces (f) and nitrogen in urine (u)
• amount of proteins digested and absorbed:
• amount of proteins used in growth:

Answer 3

• amount of proteins digested and absorbed: i - p [urine is the amino groups from excess proteins hence is not absorbed]
• amount of proteins used in growth: i - p - u

Question 4

what does the pancreas do

Answer 4

produces pancreatic juice containing enzymes to help digest food
produces insulin

Question 5

what does the liver do

Answer 5

produces bile, helps to physically break down fat

Question 6

what does the gallbladder do

Answer 6

stores bile from liver temporarily, doesn’t produce anything

Question 7

what does the small intestine do

Answer 7

absorb digested foods

Question 8

why is the small intestine so long

Answer 8

the length of the small intestine increases the surface area and time for the nutrients in the food to be digested and absorbed

Question 9

2 types of digestion

Answer 9

physical and chemical digestion

Question 10

swallowing procedure

Answer 10

the tongue rolls the food into a soft mass called bolus
1. the tongue rises to push the bolus towards the pharynx
2. the soft palate moves up to prevent the bolus from entering the nasal cavity
3. the larynx rises, and the epiglottis covers the opening to the trachea (to prevent it from entering)
4. the bolus enters the oesophagus
the food is moved along the alimentary canal from the oesophagus to the rectum through peristalsis

Question 11

function of the epiglottis

Answer 11

prevents food from entering the lungs and obstructing the airway

Question 12

what is physical digestion and the purpose of it

Answer 12

breaks down food into smaller pieces by physical actions (no change in the nature of the molecule)
helps to increase the total surface area of the food so as to promote chemical digestion (will later be further broken down into small molecules by chemical digestion)

Question 13

where does physical digestion mainly occur

Answer 13

mainly occurs in mouth cavity (mastication) alimentary canal (churning and peristalsis) small intestine (emulsification by bile)

Question 14

what is chemical digestion and what does it require

Answer 14

complex food substances are broken down into simple food substances by chemical reactions (requires digestive enzymes to break chemical bonds)

Question 15

what is food mixed with in the mouth cavity

Answer 15

saliva

Question 16

what does saliva contain and what are the function of such substances

Answer 16

saliva contains salivary amylase (catalyses the hydrolysis of starch and water into maltose) mucus (helps to moisten and lubricate food to facilitate chewing and swallowing) water (dissolves soluble substances in food so we can taste it)

Question 17

what do glands in the stomach secrete

Answer 17

gastric glands in the stomach secrete gastric juice

Question 18

what does gastric juice contain and what are the functions of its substances

Answer 18

contains pepsin (protease that works best in acidic mediums, catalyses the hydrolysis of proteins into peptides)
hydrochloric acid (provides acidic medium for action of pepsin + kills most bacteria in food)
mucus (protects stomach wall from being digested by proteases + damaged by hydrochloric acid / food particles)

Question 19

how does physical digestion occur in the stomach and what is the resulting substance + functions

Answer 19

the churning action of the stomach physically digests food into smaller pieces to increase the surface area for the action of digestive enzymes + mix the food w digestive enzymes
food is churned into a creamy liquid called chyme which is then released into the duodenum

Question 20

what substances are involved in digestion in the small intestine

Answer 20

bile, pancreatic juice, intestinal juice

Question 21

what is bile

Answer 21

(green alkaline fluid produced by liver and released thru the bile duct (can be temporarily stored in gallbladder))

Question 22

what substances do bile contain and what are its functions

Answer 22

bile salts
emulsify lipids into small droplets (facilitates chem digestion by increasing the total surface area for lipase to act on)

sodium hydrogencarbonate
(alkaline, neutralises chyme as acids are unfavourable for the action of enzymes in the small intestine, and provides an alkaline medium instead)

Question 23

where is pancreatic juice released

Answer 23

produced by pancreas, released through pancreatic duct into duodenum

Question 24

what does pancreatic juice contain and what are the functions of its substances

Answer 24

pancreatic amylase,
proteases (trypsin for proteins; needs diff types due to diffs in active sites of proteins / peptides),
pancreatic lipase,
sodium hydrogencarbonate (neutralises acidic chyme + provides an alkaline medium for the action of enzymes in the small intestine)

Question 25

where is intestinal juice produced and what are its properties

Answer 25

secreted by intestinal glands in the walls of small intestine, slightly alkaline

Question 26

what does intestinal juice contain

Answer 26

contains mainly water / mucus / sodium hydrogencarbonate

Question 27

what doesn’t intestinal juice contain

Answer 27

enzymes

Question 28

where can enzymes be found in the small intestine (apart from chyme / digestive juices)

Answer 28

there are also enzymes embedded in the epithelium of the small intestine they are on the cell membrane of the epithelial cells lining the inner wall of the small intestine (contains carbohydrases, eg. maltase / sucrase / lactase and proteases)

Question 29

what are gallstones’ effect on fat digestion

Answer 29

• decrease in secretion of bile salts from the liver -> decrease in rate of emulsification of fats • decrease in secretion of pancreatic lipase from the pancreas -> decrease in rate of hydrolysis of fats • decrease in secretion of hydrogencarbonate (as both bile and pancreatic juice contain it) -> less able to provide an optimum pH for enzymes to function / they can’t really function (as proteins denature in acidic / hot conditions) • leads to poor digestion of lipids (as some lipids may be left undigested / unabsorbed bc of the decrease in rate of hydrolysis of fats) which are then passed out of the body through egestion -> oily faeces

Question 30

what food substance are enzymes

Answer 30

protein

Question 31

how do enzymes aid digestion

Answer 31

act as a biological catalyst which speeds up metabolic reactions taking place inside or outside living cells

Question 32

action of enzymes process

Answer 32

substrate molecule binds to active site to form a enzyme-substrate complex substrate molecule is converted into its products products leave active site, enzyme is released in its original form (can be reused and can bind to another substrate molecule)

Question 33

3 main types of enzymes

Answer 33

carbohydrases (helps to catalyse the breakdown / hydrolysis of poly/disaccharides by breaking glycosidic bonds) proteases (catalyse hydrolysis of proteins / polypeptides into peptides by breaking down / hydrolysing the peptide bonds // breakdown of peptides into amino acids by breaking peptide bonds) [some proteins cannot be hydrolysed into amino acids] lipase (catalyse the hydrolysis of lipids into fatty acids + glycerol by breaking / hydrolysing ester bonds)

Question 34

control setup for action of bile experiment

Answer 34

set up another test tube w/ identical volume of vegetable oil and distilled water, and add x drops of distilled water instead of bile proves that the result in the test tube is actually caused by the bile

Question 35

how are enzymes formed

Answer 35

through the assimilation of amino acids in our bodies to become different types of proteins, one of which are enzymes

Question 36

the shape of an active site is ?? to the shape of the ???

Answer 36

complementary, substrate

Question 37

what is an example of a food that cannot be digested

Answer 37

dietary fibre

Question 38

how does absorption occur

Answer 38

food substances / minerals / vitamins / water can pass through the wall of the small intestine and enter the blood capillaries

Question 39

where does absorption take place

Answer 39

in the small / large intestine (mostly in the small intestine)

Question 40

what happens to the absorbed food substances

Answer 40

they are then carried to all parts of the body via the transport system

Question 41

what systems are the transport system made out of

Answer 41

circulatory (for proteins / carbs) lymphatic (for lipids)

Question 42

what is the large intestine responsible for

Answer 42

to absorb minerals and most of the remaining water

Question 43

what is produced in the large intestine and where is it stored

Answer 43

faeces are produced (a semi-solid waste) it is temporarily stored in the large intestine until they are passed out through the anus

Question 44

how is the bolus transported to the stomach

Answer 44

through peristalsis along the pharynx and the oesophagus

Question 45

how monosaccharides can be released from white rice (w reference to chemical digestion):

Answer 45

white rice contains starch (1). salivary amylase in saliva catalyses the hydrolysis of starch into maltose (1). pancreatic amylase in pancreatic juice catalyses the hydrolysis of remaining starch into maltose (1). the maltase embedded in the cell membrane of epithelial cells lining the inner wall of the small intestine (1) catalyses the hydrolysis of maltose into glucose, which is a monosaccharide (1).