Adaptations for Nutrition Flashcards
what does it mean for an organism to be single -celled?
they have a large surface area to volume ratio
what example of a protoctist uses holozoic nutrition?
amoeba
what three ways does an amoeba obtain nutrients such as oxygen and glucose through their cell membranes?
diffusion
facilitated transport
active transport
how do amoebas take in food?
they take in large food molecules such as bacteria and microscopic algae via endocytosis
the food molecules are surrounded by membranes, forming vacuoles
the food vacuoles fuse with lysosomes containing hydrolytic enzymes which digest the contents of the food vacuoles
the products of digestion are then absorbed into the cell cytoplasm
indigestible remains are egested by exocytosis
describe hydra
they are multicellular fresh water animals
they are in the same phylum as jellyfish
they are cylindrical in shape and have tentacles at the top of the body which contain stinging cells
they have an undifferentiated digestive system
label the hydra
tentacle
mouth
hollow body cavity in which digestion occurs
jelly layer
ectoderm
endoderm
how do hydra take in food?
their tentacles move paralysed prey in through the mouth and into the sac-like hollow body cavity where the prey is digested
the products of digestion are absorbed into the body cells and the indigestible remains are egested through the mouth
they therefore have only a single opening in their digestive system
what is a tube gut?
it is found in most animals and has two openings: mouth and anus
what is a sac-like body cavity?
found in hydra and only contains one opening which is the mouth
describe tube gut in animals
most animals have a distinct anterior and posterior end and a digestive system that is a tube with two openings
food is ingested at the mouth and the indigestible waste is egested at the anus
why must food be digested? give two points
food molecules are insoluble and are too large to cross membranes and be absorbed into the bloodstream
polymers must be converted to their monomers so they can be rebuilt (assimilated) into molecules needed by body cells
what are the four main functions of the human gut?
ingestion
digestion
absorption
egestion
what two types of digestion?
mechanical digestion
chemical digestion
what is the function of ingestion?
taking food into the body through the mouth
what is the function of digestion?
the breakdown of large insoluble molecules into soluble molecules that are then small enough to be absorbed into the blood
what is the function of mechanical digestion?
cutting and crushing by teeth and muscle contractions of the gut wall, increasing the surface area over which enzymes can act
what is the function of chemical digestion?
breakdown using digestive enzymes and bile and stomach acid also contribute to this
what is the function of absorption?
the passage of small soluble molecules and ions through the gut wall into the blood
what is the function of egestion?
the elimination of indigestible waste eg cellulose (dietary fibre)
describe the gut and what two functions of the human gut happen in the gut?
digestion and absorption occur in the gut
the gut is a long, hollow, muscular tube
it allows the movement of its contents in one direction only
each section is specialised and forms particular steps in the processes of mechanical and chemical digestion and absorption
what causes the food in the gut to propel along?
peristalsis
what is peristalsis and mention dietary fibres?
it is the wave of muscular contractions and relaxations of the gut wall which propel the contents along the whole length of the gut
circular muscles contract behind the bolus of food and then relax after the wave of contraction has passed
dietary fibre aids peristalsis in the intestines
give 3 steps of peristalsis
there is a longitudinal muscle and a circular muscle, longitudinal is on the outer layer and circular is on the inner
step 1 - contraction of circular muscles behind food
step 2 - contraction of longitudinal muscles ahead of food
step 3 - contraction in the circular muscle layer forces food forward
label the human digestive system (alimentary canal)
there are 14
salivary glands
mouth
epiglottis
esophagus
stomach
liver
gall bladder
pancreas
small intestine:
duodenum
ileum
large intestine (colon)
rectum
anus
what is the function of the mouth?
ingestion
mechanical digestion of food due to the crushing action of the teeth
chemical digestion of starch by salivary amylase
what is the function of the esophagus?
carriage of food to the stomach by peristalsis
what is the function of the stomach?
contraction of stomach muscles to churn up the food aka mechanical digestion
secretion of hydrochloric acid
chemical digestion of proteins by enzymes
what is the function of the duodenum?
receives pancreatic juice from the pancreas and bile from the gall bladder
chemical digestion of carbohydrates, fats and proteins by enzymes
what is the function of the ileum?
chemical digestion of carbohydrates, fats and proteins by enzymes
absorption of digested food
what is the function of the colon?
absorption of water
what is the function of the rectum?
storage of feces
what is the function of the anus?
site of egestion
label the structure of the mammalian gut wall
lumen
mucosa
sub-mucosa
muscularis - inner-circular and outer-longitudinal
serosa
describe the layers of the mammalian gut wall
the thickness varies in different regions of the digestive system eg stomach, ileum
describe serosa
it is the outermost layer containing tough connective tissue which protects the gut wall
it helps to reduce friction with other abdominal organs during peristalsis
describe muscularis
composed of two layers - inner circular and outer longitudinal
they make coordinated waves of contraction (peristalsis) pushing the bolus of food along the alimentary canal
describe submucosa
consists of connective tissues containing blood and lymph vessels which remove the absorbed products of digestion
also contains the nerves which coordinate peristalsis
describe mucosa
innermost layer
lines the gut wall
epithelium secretes mucus which lubricates and protects the mucosa
in some regions, it secretes digestive juices and in others it absorbs digested food
what makes the absorption of nutrients by gut epithelial cells possible?
if larger molecules like carbohydrates, fats and proteins are first digested into smaller molecules
different enzymes digest different food molecules and a number of enzymes are usually required to complete digestion
describe the digestion and breakdown of carbohydrates
starch -> (enzyme amylase) maltose -> (enzyme maltase) alpha glucose
lactose is also hydrolysed to glucose + galactose by lactase
sucrose is also hydrolysed to glucose + fructose by sucrase
describe the digestion and breakdown of proteins
polypeptides -> dipeptides -> amino acids
what is the difference between endopeptidases and exopeptidases?
endo: they hydrolyse peptide bonds within the protein molecule eg pepsin and trypsin
exo: they hydrolyse peptide bonds at the end of shorter polypeptide chains to make amino acids/dipeptides
describe the digestion and breakdown of fats
fats are hydrolysed by lipase and the products are fatty acids and glycerol
describe what happens in the buccal cavity
where mechanical digestion happens (in the mouth)
food is mixed with saliva by the tongue and chewed with the teeth
this increases the surface area of food for the enzymes to work on
what is saliva and what 3 things does it contain?
is a watery secretion
amylase - digests starch into maltose
bicarbonate ions - which creates an optimum pH which is slightly alkaline for amylase
mucus - lubricates the food
what happens to the bolus of food in the stomach?
it is kept there by the contraction of sphincter muscles
the swallowed food can remain in the stomach for several hours
the stomach wall muscles contract rhythmically to churn the food with gastric juice secreted from gastric glands in the mucosa of the stomach wall
what three things does gastric juice contain?
mucus - secreted by goblet cells lining the mucosa, forms a protective lining which protects the stomach wall from digestive enzymes and hydrochloric acid and helps to lubricate food
hydrochloric acid - lowers the pH of the stomach contents to pH 2 to create an optimum environment for enzymes and kills bacteria
pepsin - secreted as inactive pepsinogen., is a peptidase that works optimally in the acidic environment, activation of pepsinogen by HCl forms active pepsin
why are enzymes secreted in an inactive form?
the active form would digest the cells of the stomach/intestine wall (autolysis)
what two regions does the small intestine contain?
duodenum and ileum
how is the partially digested food transported from the stomach to the duodenum?
relaxation of the sphincter muscles at the base of the stomach releases the partially digested food, known as chyme, into the duodenum, a little at a time
describe the duodenum
the first section of the small intestine
receives secretions from the liver and pancreas
food coming from the stomach is lubricated by mucus and the hydrochloric acid is neutralised by alkaline secretions, NaHCO3, from cells in the sub mucosa
where is bile stored and made and how is it passed to the duodenum?
in the liver
stored in the gallbladder
passed through the bile duct into the duodenum
what is the role of bile?
they contain bile salts which are hydrophilic and hydrophobic
they emulsify lipids present in the partially digested food and breaking up large globules into smaller droplets, thus increasing the surface area for lipase action
it is alkaline and neutralises the acid in the food coming from the stomach creating an optimum pH environment for enzymes in the small intestine
where is pancreatic juice secreted?
secreted by specialised cells in the pancreas
enters the duodenum through the pancreatic duct
what enzymes does the pancreas secrete?
endopeptidases
trypsinogen
amylase
lipase