2.4 adaptations for nutrition Flashcards
mode of nutrition: autotrophic definition
- an organism that produces its own food
synthesis of complex organic chemicals from simpler inorganic substances using an energy source
mode of nutrition: photoautotrophic definition
uses LIGHT ENERGY to combine inorganic substances into complex organic chemicals
- an organism which obtains its nutrition through photosynthesis
mode of nutrition: chemoautotrophic definition
uses CHEMICAL ENERGY, from chemicals such as hydrogen sulphide, to combine inorganic substances into complex organic chemicals
- an organism which obtains its nutrition through inorganic molecules, e.g sulfur, in the absence of light
mode of nutrition: heterotrophic definition
- an organism that cannot produce its own food
- it obtains energy by feeding on organic compounds produced by other organisms
- cannot synthesise its own complex organic chemicals
- it must digest organic chemicals produces by other organisms and use the products of digestion to synthesise their own organic chemicals
mode of nutrition: saprotrophic/saprobiontic definition
- an organism that feeds by extracellular digestion e.g fungi
- extracellular digestion of dead or decayed organic matter
- enzymes are secreted by an organism which then digest the organic chemicals of the substrate on which they live
- the products of digestion are then absorbed by the saprotroph
mode of nutrition: holozoic definition
- absorption of organic matter followed by internal digestion of the organic chemicals within the organism
mode of nutrition: parasitic definition
- living in or on another host organism, whereby nourishment is obtained from a host organism, usually to the detriment/harm of the host
(ectoparasites live on the outside of a host organisms, while endoparasites live inside a host organism, some are intracellular, and others are extracellular)
mode of nutrition: symbiosis/mutualism definition
- many organisms live in/on other organisms in a relationship that provides benefit to both organisms
where do ectoparasites live?
where do endoparasites live?
- ectoparasites = live on the outside of a host organisms
- endoparasites = live inside a host organism, some intracellular, and others extracellular
all photoautotrophic organisms carry out ____?
photosynthesis
- combining CO2 and water to produce their own organic compounds
- this process uses energy from photons of light and transfers light energy into chemical energy
what does the process of photosynthesis turn energy from and into?
transfers light energy into chemical energy
what is the equation of photosynthesis?
carbon dioxide + water —> glucose + oxygen
many chemoautotrophs are members of the Archaebacteria, extremophiles that live in conditions that are uninhabitable by most organisms
e.g.
- pyrolobus - extreme thermophile living in temps of >100°C
- methanococcus - lives in stomach of a cow and uses ethanoic acid as energy source
some bacteria are also chemoautotrophs e.g
- nitrosomanas - obtain their energy from ammonia
all animals and fungi and many bacteria and archaea are ____?
heterotrophic
- they obtain their energy and organic compounds by digesting the organic compounds produced by other organisms
- they then use the products of digestion to synthesis their own organic compounds
heterotrophic organisms need food sources that contain complex organic chemicals as sources of:
- carbon = for making their own organic chemicals
- nitrogen = for making proteins and nucleic acids
- phosphate = for ATP, phospholipids and nucleic acids
- vitamins and minerals = for making a wide range of biochemicals
- energy
what are the several different forms of heterotrophic nutrition?
- saprophytic nutrition
- parasitic nutrition
- holozoic nutrition
what happens in saprotrophic nutrition?
- extracellular enzymes are secreted from the organism which then digest whatever the organisms are growing on
- the products of digestion are then absorbed and used by the organisms as their sources of energy and raw materials
e.g fungi and many bacteria
how do fungi describe saprotrophic nutrition?
- fungi, and moulds, are responsible for the breakdown of large volumes of dead organic matter, including food
- they grow as hyphae, microscopic fibres that may have distinct cell walls between adjacent cells, partial cell walls or none at all
- fungal hyphae grow on e.g bread
- extracellular enzymes from growing tips
- digestion takes place outside the body
- nutrients are absorbed from all over the hyphae
- this is an example of heterotrophic nutrition, as the fungus is unable to synthesis complex organic chemicals from inorganic chemicals and cannot utilise energy from sources other than organic chemicals
what are parasites?
- organisms that live in (endoparasites) or on (ectoparasites) another organsim
- and they obtain nourishment from it
- at the expense of/ causing harm to the host
animas which are parasites are usually highly specialised to be able to survive, obtain nutrition and reproduce in or on their host organism
what is the primary host organism in parasitic nutrition?
primary host organism = where the adult forms of the parasite develops
what is the secondary host in parasitic nutrition?
secondary hosts = where larval/intermediate forms of the parasite are found
what are the vectors in parasitic nutrition?
vectors = secondary hosts which actively and directly transfer the parasite from one primary host to another primary host
e.g malaria
what are examples of endoparasites?
- pork tapeworm (Taenia solium)
- beef tapeworm (Taenia saginata)
what are examples of the structural adaptations of tapeworms to enable them to live in the digestive system of an animal?
- the head of the tapeworm is called the scolex. this is embedded in the gut walk and has hooks and suckers to prevent it being dislodged by peristalsis
- there is no digestive system or mouth as the tapeworm only needs to absorb nutrients that have already been digested (through its body surface)
- the body is flat to increase surface area for absorption of nutrients from the gut contents
- each proglottid is covered in a thick cuticle which is resistant to the action of the digestive enzymes. they also secrete mucus and enzyme inhibitors to reduce the risk of digestion
- respiration is anaerobic as there is no oxygen in the gut lumen
- has a low metabolic rate and so doesn’t require aerobic respiration
- each proglottid is hermaphrodite containing both male and female reproductive organs. ∴ it doenst need to find a mate as it can self-fertilise. each proglottid can contain about 50,000 eggs, this increases the chance of infecting another host
- thick cuticle
- secretes anti-enzymes that prevent its digestion by host enzymes
- scolex has suckers and hooks for attachment to gut wall
- long, thin body proves large surface-area-to-volume ratio for absorption
what is an example of an ectoparasite? + info
- headlouse (Pediculus humanus capitis)
- it lives on the head where it clings to hairs using strong claws
- eggs are laid and glued to the base of hairs
- when empty they are white, these are called nits
- both adult and larval stages of headlice feed on blood
- head lice are obligate parasites and can only live in human hair
- they have no vectors or secondary hosts and transmission is by direct head-to-head contact when adults, larvae or eggs can be transferred from one host to another
can plants also be parasitic?
+ info
yes
- some such as dodder, have no leaves or roots
- dodder has many suckers which penetrate the xylem (to obtain water and minerals) and the phloem (to obtain sugars and amino acids)
- dodder cannot carry out photosynthesis so is called an obligate parasite: it has to live on a host plant to survive
- mistletoe is semi-parasitic
- its roots penetrate the xylem and phloem of the host plant, but it also has leaves which can carry out photosynthesis
what does holozoic nutrition involve?
- the ingestion and then digestion of a food source
- this means that an organism does not have to remain attached to its food source in order to digest the food, it can ingest its food and then digest the food elsewhere
- the products of digestion are the absorbed and assimilated and waste is egested
what is an example of a single-celled holozoic organism?
+ info
- amoeba
- amoeba senses food
- pseudopodia surround the food
- the food is enclosed in a food vacuole (food + water)
- enzymes from the lysosomes are secreted into the food vacuole
- food is digested and soluble materials are absorbed and assimilated (used up)
- undigested waste is expelled (egestion)
EXAMPLE OF INTRACELLULAR DIGESTION - food particles are ingested through endocytosis/phagocytosis and undigested food/waste products are expelled through exocytosis
multi-cellular organisms show increasing levels of organisation that enable them to digest a wider range of foods and to digest them more efficiently
- they have digestive systems that carry out extracellular digestion, but still within the organisms
- the products of digestion are then absorbed, and undigested food egested
- however, they still have to ingest and then digest their food sources
what is the digestion like in the multi-cellular organism: hydra?
- hydrolytic enzymes secreted into the enteron by the endodermis
- extracellular digestion partially digests food molecules
- partially digested food transported, via phagocytosis, into endodermal cells where intracellular digestion takes place
- undigested material egested from the enteron via the single opening
what is the digestion like in the multi-cellular organism: flatworms?
- flatworms are larger and have a more complex level of organisation that Hydra, but still have a single gut cavity for digestion of food
- the gastrovascular cavity is highly branched. as a result, food can be digested, and the products of digestion can be absorbed throughout the organism
- thereofre, there is no need for a designated transport system to deliver raw materials to the tissues
(- gut = simple pouch in which the food is digested and the products absorbed into the body tissue
- pharynx (throat) = is everted to suck up food that the animal crawls over
- food and waste enter and exit through the same opening)
more complex animals have developed a tube gut which has an opening for ingestion and a separate opening for egestion
this type of gut increases the efficiency of digestion and also enables an organism to eat and digest a wider range of foods
what ate examples of how different regions of the gut is adapted for different functions:
- mechanical digestion by teeth, muscular action
- chemical digestion by acids
- chemical digestion by enzymes with different optimum pH
what does the human gut consist of?
- buccal cavity
- epiglottis
- oesophagus
- stomach
- liver
- gall bladder
- small intestine
- colon
- pancreas
- appendix
- rectum
what happens in the buccal cavity in the human digestive system?
- in the buccal cavity/mouth, a mixture of mechanical and chemical digestion takes place:
- lips, tongue and teeth work together to:
• capture and receive food
• move food about the mouth
• cut, grind and chew food into smaller pieces
• mix the food with saliva to lubricate food
• forms food into a bolus to make swallowing easier - salivary glands secrete about 1500cm^3 of saliva every day
• saliva has a slightly acidic pH
• it contains the enzyme salivary amylase
STARCH —> MALTOSE
what happens in the oesophagus in the human digestive system?
- the oesophagus is a straight narrow tube with a muscular wall which carries food to the stomach by the process of peristalsis
- this is due to waves of contraction of muscles in the gut wall which pushes the food forwards through the whole gut
when you start to swallow, the ____ closes to prevent food from entering the trachea and lungs
epiglottis
what happens in the stomach in the human digestive system?
- the stomach also carries out chemical and mechanical digestion
• chemical: through the action of enzymes and hydrochloric acid
• mechanical : through the action of the muscles in the stomach that contract and relax to mix food with gastric juice and to further breakdown large particles of food into smaller particles with a larger surface area for chemical action
what is the end result of digestion in the stomach?
- a semi-liquid called chyme
the stomach wall contains a large number of gastric glands/pits which produce a mixture of chemicals called gastric juice.
these chemicals are produced by what cells?
- zymogenic/chief cells - secrete pepsinogen (precursor of pepsin) - digestion of protein into polypeptides; digestion of milk protein
- oxyntic cells - secrete hydrochloric acid - provides optimum pH for enzymes; denatures proteins and softens connective tissue in food; activates pepsin
- goblet/neck cell - secretes mucus - forms a barrier between the stomach lining and the gastric juice; protects the stomach wall and glands from self-digestion by pepsin and hydrochloric acid
what is the small intestine comprised of?
- duodenum
- ileum
- (sometimes see reference to the jejunum which is the part of the duodenum between the duodenum and the ileum - but dont need to know)
what is the duodenum
- the first section of the small intestine
- where proteins and lipids are hydrolysed
what happens in the ileum in the human digestive system?
- the second section of the small intestine that serves as the main site of absorption of the products of digestion
- nearly 5cm long
- where digestion is completed and is the main site of absorption of the products of digestion
- bc of its length, food takes a relatively long time to pass through ileum, thus increasing the time available for digestion and absorption
- the villi also increase the s.a greatly
- and have a rich blood supply to remove the products of digstion
- most of the water in our food is absorbed in the ileum
what happens in the large intestine in the human digestive system?
- the ileum opens into the first part of the large intestine called the caecum
- this has no role in the human digestive system
- but in some animals, this is the site of cellulose digestion
- the appendix is a blind-ended sac which opens from the caecum
- the undigested food and remaining water and minerals first pass into the colon
what happens in the colon in the human digestive system?
- the main part of the large intestine
- where the rest of the water and mineral salts are absorbed
- vitamins produced by microorganisms in the colon are also absorbed into the blood
- this leaves a semi-solid mass of undigested food, dead intestinal cells and bacteria (about 50% of the total mass)
- this forms the faeces
what happens in the rectum in the human digestive system?
- last part of the large intestine
- muscular tube that temporarily stores the faeces before they are eliminated from the body
what happens in the anus in the human digestive system?
- made from sphincter muscles that control when defaecation occurs
what happens in the (accessory organ) liver in the human digestive system?
- produces bile by breaking down haemoglobin
- bile is stored in gall bladder and secreted into the duodenum through the bile duct
- the liver receives nearly all the products of digestion from the small intestine, carried there by the hepatic portal vein
- liver has many functions, including:
• excess glucose is stored as glycogen
• amino groups are removed from amino acids (de-amination) and converted into urea
• manu vitamins are also stored in the liver
what happens in the (accessory organ) pancreas in the human digestive system?
- has 2 main secretory functions:
• ENDOCRINE : it secretes the hormones insulin and glucagon for control of blood glucose levels. blood carries secretions to site of action
• EXOCRINE : it secretes pancreatic juice, a mixture of: enzymes, enzyme precursors and sodium hydrogen carbonate - these secretions are carried by the pancreatic duct to their site of action in the duodenum
what is the pancreas’ 2 main secretory functions?
- endocrine
- exocrine
how are the duodenum and ileum adapted to increasing the efficiency of digestion and absorption by?
- having folds in the wall to increase surface area
- the inner surface is further folded to form millions of structures called villi
- the surface of the epithelial cells covering the villi is further folded to form many microvilli
how is each villus further adapted to increase the efficiency of digestion and absorption?
- rich capillary network to absorb and remove products of digestion and maintain a concentration gradient
- lacteals to absorb the products of fat digestion and maintain a concentration gradient
- they are thin to reduce diffusion distance
- microvilli increase surface area
- epithelial cells contain large numbers of mitochondria to provide the ATP for active transport
name the 2 types of digestion
- mechanical
- chemical
what is mechanical digestion
- type of digestion that involves physically breaking down food material into smaller pieces
- increases total surface area for chemical digestion
- the teeth and muscle contractions break large pieces of food into smaller pieces
what is chemical digestion?
- a type of digestion that involves breaking down large, insoluble molecules into smaller, soluble molecules using enzymes
- involves many different enzymes which carry out specific functions to digest a wide range of different biochemicals
- each enzyme has its own temperature (around the body temperature of the organisms) and pH
in mammals, different regions of the gut have a different pH, providing different conditions for enzymes
as enzymes pass from one region of the gut to another, they are deactivated
(- the time spent in different parts of the gut can reflect the diet of an animal)
- due to the pH being differebt in different parts of the gut, the enzymes present will have different pH optima, and even if they are digesting the same food, can work on bonds between different amino acids or monosaccharides
what is the main polysaccharide found in the human diet that we can digest?
starch
where does digestion of starch occur?
- mouth
- duodenum
- through action of salivary and pancreatic amylase
STARCH —amylase—> MALTOSE
where does the digestion of maltose and other disaccharides e.g sucrose and lactose, into monosaccharides takes place?
- on the surface of the epithelial cells covering the villi
- the enzyme is embedded in the cell membranes, and the monosaccharides are then absorbed
what does the digestion of protein involve?
- breaking long polypeptide chains into amino acids and dipeptides that can be absorbed into the blood
some protease enzymes are secreted as inactive precursors to prevent autolysis (self-digestion)
where is protein digested in the digestive system?
- begins in stomach
- duodenum
- ileum
digestion of protein in the stomach:
- pepsinogen is also secreted in the stomacch
- it is activated by hydrochloric acid to form the endopeptidase enzyme, pepsin (optimal pH ~2.0)
- endopeptidase enzymes hydrolyse peptide bonds between amino acids in the middle of a polypeptide chain (non-termial peptide bonds)
PROTEIN —> POLYPEPTIDES + PEPTIDES
what do endopeptidase enzymes hydrolyse?
peptide bonds between amino acids in the middle of a polypeptide chain (non-terminal peptide bonds)
digestion of protein in the duodenum:
- the precursor trypsinogen (secreted by the pancreas) is activated by the enzyme enterokinase to form the enzyme trypsin
- trypsin is also an endopeptidase (optimum pH ~8.0)
- the pancreas and intestinal glands secrete exopeptidase enzymes which break peptide bonds between amino acids at the end of peptide/polypeptide chains (terminal peptide bonds)
- exopeptidases digest peptides into amino acids and dipeptides
PEPTIDES —> AMINO ACIDS + DIPEPTIDES
what do exopeptidase enzymes hydrolyse?
they break peptide bonds between amino acids at the end of peptide/polypeptide chains (terminal peptide bonds)
digestion of protein in the ileum:
- the final digestion of dipeptides into amino acids takes places through enzymes embedded in the cell membranes of the epithelial cells in the ileum
- the combined action of endo and exopeptidases increases the rate of protein digestion
digestion by an endopeptidase before digestion by an exopeptidase increases the rate of digestion of proteins
lipids are digested by enzymes called ___?
lipases
LIPID —lipase—> FATTY ACIDS + GLYCEROL
by what are lipases produced?
mostly by the pancreas
bile ____ lipids by breaking large globules of fat into small droplets
emulsifies
- this increases the s.a for the action of lipases
- emulsification also allows very small droplets of fat to be absorbed directly into the blood stream
where does absorption mainly take place?
- ileum by the villi
- glucose and amino acids are absorbed mainly by ____________ into capillaries
- they are then carried in the _____ to the liver
- some disaccharides and dipeptides are absorbed into the epithelial cells where they are digested intracellularly; the monosaccharides and amino acids then pass into the ____?
- glucose is absorbed from the blood by cells, for energy release in respiration. some is converted to _____ in the liver and muscles and any excess is stored in fat cells
- active transport, diffusion and co-transport
- hepatic portal vein
- capillaries
- glycogen
amino acids are absorbed for ____ ; excess cannot be stored so are deaminated whereby the removed amino groups are converted to ____, and the remainder are converted to carbohydrate and stored
- protein synthesis
- urea
fatty acids and glycerol are absorbed separately into the epithelial cells. most are reassembled into triglycerides
- most triglycerides, fatty acids and glycerol pass into the lacteal, then through the lymphatic system to the blood stream opening at the thoracic duct
- some short-chain fatty acids diffuse directly into the blood in the capillaries
- lipids are used to produce cell
membranes and hormones, and excess is stored as fat
most water is absorbed into the bloodstream in the ____; the remainder of the water, together with mineral salts along with vitamins secreted by microorganisms in the colon, are reabsorbed from the colon
- ileum
herbivores definition:
- plant-based diet which is difficult to digest due to the high cellulose content
- animals that only eat plants
carnivores definition:
eat mainly animal tissues which are rich in protein and fat and easier to digest
omnivores defintion:
eat a mixed diet and need to be able to digest a wide range of foods
different teeth have different functions that reflect the diet of the animal.
what are the different kinds of teeth and their functions?
- incisors = involved in biting and tearing flesh
- canines = for gripping prey
- molars and premolars = adapted for grinding plant tissue (herbivores and omnivores) or shearing flesh from bones (carnivores)
herbivore examples
- sheep
- cows
how have herbivores’ teeth adapted to grind tough plant tissues to release nutrients?
- small, flat incisors on lower jaw for cutting grass against upper horny pad
- diastema between incisors and premolars - separates fresh grass from the cud and enables manipulation of food by the tongue (space where tongue can push food to the grinding cheek teeth)
- premolars and molars have a large surface area and sharply ridged biting surfaces for grinding plant material
- no/very small canines
- jaw moves in (horizontal/circular) plane
how have carnivors’ teeth (incisors and canines especially) adapted for biting and gripping prey?
- sharp incisors to remove flesh from bone
- large, pointed canines required to grip and kill prey
- sharp carnassials (modified premolars and molars) to slice and shear meat
- molars with sharp, flattened edges to crush bone
the length, relative size and function of different regions of the digestive system varies depending on ____?
diet
description of digestive system of an insectivore?
- insects made largely of chitin and protein:
- easily digestible material, short gut as products of digestion easily absorbed
description of digestive system of a non-ruminant herbivore?
- plant material with a high fibre/cellulose content :
- difficult to digest;
- bacteria/archaea present in caecum which can digest cellulose and produce protein
- bacterial digestion occurs AFTER the ileum, so products of bacterial digestion not absorbed
- some e.g rabbits, will eat their faeces so they absorb the extra nutrients while others e.g horses, dont so therefore have less effective digestion and absorption
description of digestive system of a ruminant herbivore?
- the base of the oesophagus is expanded and differentiated into 3 chambres
- these chambers contain bacteria and archaea that can digest cellulose and produce fatty acids, proteins and vitamins that can then be utilised by the animals
- protein digestion begins in the abomasum (true stomach)
- absorption occurs AFTER the site of bacterial digestion, so digestion is more efficient
- most ruminants regurgitate their food following bacterial digestion in the rumen; this is then chewed a second time to further breakdown the tough fibres and release more nutrients
description of digestive system of a carnivore?
- meat is made mostly of protein and fat:
- easily digestible and easily absorbed, no need for long digestive system
- the stomach is relatively larger to enable increased digestion of protein
the ruminant ‘stomach’ is well adapted to eating an almost completely plant diet.
- 4 chambered ‘stomach’ of a ruminant
what is the path taken by food as it passes through?
- RETICULUM (large objects e.g stones, collect here, liquids pass into the OMASUM, while solids pass into the RUMEN
- solids pass between the rumen and reticulum and are regurgitated and chewed again
- in the rumen, bacteria, archaea and protoctista begin to digest the cellulose cell walls which releases cell contents
- the microbes produce small fatty acids and B vitamins which provide additional nutrition to the animal. microbes use protein released from the cells for their own growth
- the contents of the rumen eventually pass into the omasum where water and minerals are absorbed before the contents pass into the true stomach (the ABOMASUM). this is where bacterial and remaining dietary protein begins to be digested
in young ruminants that feed in milk, food passes from the base of the oesophagus directly to the abomasum; milk is high in protein and only the abomasum is needed to digest protein
- there is no milk intake in adults - their diet is high in cellulose and low in protein
- in adults, the rumen becomes the largest part of the stomach as most of the food that needs to be digested is cellulose
name the two types of autotrophic organisms:
- photoautotrophic
- chemoautotrophic
describe extracellular digestion by saprotrophs:
- release enzymes which catalyse the breakdown of dead plant and animal material into simpler organic matter / feeds by extracellular digestion
- absorb the products of digestion
what is meant by the term ‘ holozoic’?
describe a heterotrophic organism that internally digests food substances
what processes does holozoic nutrition involve?
- ingestion
- digestion
- absorption
- assimilation
- egestion
define ingestion
the process by which organisms take food into their body
define digestion
the process by which large, insoluble molecules are broken down into smaller, soluble molecules that can be absorbed across cell membranes
what is assimilation?
the synthesis of biological compounds from absorbed simpler molecules
define absorption
the movement of useful substances into the bloodstream
define egestion
the removal of undigested waste material from the body
describe how unicellular organisms obtain nutrients
- ingestion via phagocytosis
- intracellular digestion (using hydrolytic enzymes) breaks down large, insoluble molecules into smaller, soluble molecules
- products of digestion pass into the cytoplasm by diffusion and active transport
- undigested material removed by exocytosis
describe the structure of Hydra
- is a small, multicellular, freshwater organisms
- basic, undifferentiated sac-like gut
- single opening, surrounded by tentacles that serve as a mouth and an anus
- single gut cavity (known as the enteron)
describe the shape of the gut in more complex organisms
- tube-like with two openings, a mouth for ingestion and anus for egestion
state the names of the different layers of the gut wall:
- epithelium
- mucosa
- submucosa
- muscle layer
- serosa
what is the epithelium in the gut wall?
- a single layer of cells that line the gut wall
- layer of cells in contact with food
describe the structure of the mucosa layer of the gut wall:
- mucous membrane lining the gut wall
- contains glands that secrete digestive enzymes, mucus and an acid or alkaline liquid that provides an optimum pH
- inner layer that secretes mucus for lubrication
- in some areas it secretes digestive juices, in others it absorbs products
describe the structure of the sub-mucosa layer of the gut wall:
- layer of connective tissue below the mucous membrane
- contains blood and lymph vessels for the transport of digestion product (to remove) and glands that secrete an alkaline fluid
describe the muscle layer of the gut wall:
- a layer of circular and longitudinal muscles beneath the submucosa
- longitudinal muscle contracts to shorten the gut and circular muscle contracts to reduce diameter
- these waves of contraction called peristalsis force food along the gut
explain the action of circular and longitudinal muscles in peristalsis
- the contraction of the circular muscle behind the bolus of food and the relaxation of the longitudinal muscle in front forces food down the gut
what is the serosa?
- the tough, protective layer that surrounds the gut
- tough outer coat of connective tissue
what types of digestion take place in the buccal cavity?
- mechanical digestion and chemical digestion of starch
what is the normal pH range of the buccal cavity?
pH 6.5-7.5
what is the buccal cavity?
- the oral cavity through which food enters the body
what is the function of the teeth?
- crush and grind food into smaller pieces, increasing its surface area
describe the function of salivary glands:
- secrete amylase, mineral ions and mucus into the buccal cavity
what is the function of the oesophagus?
carries food from the buccal cavity to the stomach by peristalsis
describe the processes that take place in the stomach
- mechanical digestion (mixing and grinding) and chemical digestion of protein
what type of glands are found in the stomach?
gastric glands
describe the function of gastric glands
- secrete endopeptidases, hydrochloric acid and an alkaline mucus into the stomach
what is the normal pH of the stomach?
pH 2
what is the role of the liver?
- secretes bile into the small intestine via the gallbladder and bile duct
describe the composition and function of bile
- consists of bile salts and an alkaline fluid
- neutralises stomach acid, providing an ideal pH for lipases
what is the normal pH range of the small intestine?
pH 7 to 8
describe the role of the pancreas
- it secretes enzymes and an alkaline fluid into the duodenum via the pancreatic duct
what is the large intestine also called?
colon
describe the function of the colon
reabsorbs water and minerals from the waste material
what is the rectum?
- the segment of the larger intestine that stores faeces prior to egestion
which enzymes are involved in carbohydrate digestion?
where are they found?
- amylase in saliva and pancreatic juice
- maltase, sucrase, lactase on the membrane of the epithelial cells of the small intestine
what are the substrates and products of the carbohydrases?
- amylase hydrolyses starch to maltose
- maltase hydrolyses maltose to alpha-glucose
- sucrase hydrolyses sucrose to glucose and fructose
- lactase hydrolyses lactose to glucose and galactose
what is the optimum pH of amylase?
pH8
which enzymes are involved in protein digestion?
what are their roles?
- endopeptidases - hydrolyse non-terminal peptide bonds within a protein to form smaller peptides
- exopeptidases - hydrolyse the terminal peptide bonds of a protein to form dipeptides and amino acids
what are some examples of endopeptidases?
- trypsin
- pepsin
describe how trypsin is produced
- secreted by the pancreas as inactive trypsinogen
- enterokinase converts inactive trypsinogen into active trypsin in duodenum
what is the name of the inactive form of pepsin?
pepsinogen
where is pepsinogen secreted from?
gastric glands
describe how inactive pepsinogen is converted into its active form, pepsin
hydrochloric acid converts inactive pepsinogen into active pepsin
where are lipids digested?
small intestine
what must happen before lipids can be digested?
- must be emulsified by bile salts produced by the liver
- this breaks down large fat molecules into smaller, soluble molecules called micelles, increasing the surface area
how are lipids digested?
- lipases hydrolyse lipids into monoglycerides, fatty acids and glycerol
where are lipases found?
in pancreatic juice
state the processes by which absorption takes place in the ileum
- simple diffusion
- facilitated diffusion
- active transport
- osmosis
which molecules are absorbed by simple diffusion in the ileum?
- monoglycerides, fatty acids and glycerol
why can monoglycerides, fatty acids and glycerol be absorbed via simple diffusion?
- they are non-polar molecules so can easily diffuse across the membrane of the epithelial cells
what happens to monoglycerides, fatty acids and glycerol once they are absorbed into cells?
- reformed into triglycerides, absorbed into the lacteals and transported via the lymphatic system into the blood
how are amino acids absorbed from the lumen of the gut?
via active transport into epithelium cells and then into the bloodstream by facilitated diffusion
which molecules rely on co-transport from the lumen of the gut into the cytoplasm of the epithelial cells?
glucose and other monosaccharides
explain how sodium ions are involved in co-transport
- sodium ions (Na+) are actively transported out of the cell into the lumen, creating a diffusion gradient
- nutrients are then taken up into the cells along with Na+ ions
how do monosaccharides pass from the epithelial cells into the blood stream?
via facilitated diffusion
describe the adaptations of herbivores to a high cellulose diet
- long gut
- loose articulation of the lower jaw
- horny pad on the upper jaw
- specialised dentition for grinding tough plant material
what are ruminants?
- mammals that digest plant material slowly in a specialised four-chambered stomach and regurgitate it to chew it again, enabling the efficient breakdown of fibre
name the 4 chambres of the ruminant stomach:
- rumen
- reticulum
- omasum
- abomasum
describe the rumen
- the first stomach of a ruminant
- it contains mutualistic bacteria that are able to hydrolyse cellulose into glucose
describe the adaptations of carnivores to a high protein diet:
- short gut
- powerful jaw muscles
- specialised dentition for cutting and tearing meat
- usually large stomach for digestion of mostly protein diet
name the two types of parasites
- ectoparasites
- endoparasites
how can humans and pigs become infected by the pork tapeworm?
- humans become infected by consuming undercooked pork (containing larval forms of the tapeworm)
- pigs may become infected by ingesting contaminated faeces
how does the pork tapeworm feed?
- absorbs pre-digested nutrients in the gut through its cuticle
mechanical digestion in the mouth mixes salivary amylase with food, and the teeth break large pieces of food into smaller pieces NOT smaller molecules
what’s the difference between egestion and excretion?
egestion = getting rid of undigested food via faeces
excretion = eliminating waste made within the body e.g urea, and carbon dioxide
what does digestion result in?
large biological molecules being HYDROLYSED to smaller molecules that can be absorbed across cell membranes
what should you say instead of cellulose cannot be digested by herbivores?
herbivores are less efficient at digesting cellulose
how is a cows digestive system adapted to its diet? [2]
- cows have a FOUR CHAMBERED STOMACH
- that contains CELLULOSE DIGESTING BACTERIA
- the LONG GUT allows MORE TIME for the cellulose to be broken down
- cows also CHEW THE CUD which means they REGURGITATE some of the contents so that it can be CHEWED AGAIN to aid further digestion
what is the function of bile in the digestive system? [2]
- emulsification
- which is when large droplets of fat are broken down into smaller droplets of fat
- this is because a larger surface area means that the enzyme lipase can digest the fat more quickly
- also used in neutralising acid
- this is because the contents of the stomach is acidic and must be neutralised so that the enzyme in the small intestine work efficiently
order and process of food in ruminants:
- grass is mixed with saliva and then chewed (forming cud) before being swallowed
- cud enters the first chamber of the stomach - RUMEN. cellulose digesting bacteria produce cellulase, breaking down cellulose in the grass into glucose. this ferments into organic acids which are absorbed into the blood stream. the process produces a lot of carbon dioxide and methane which is expelled
- fermented cud from the rumen enters the second stomach chamber - RETICULUM. the cud is regurgitated from here and the rumen back into the mouth to be rechewed
- rechewed cud is swallowed and enters the third chamber of the stomach - OMASUM. water absorption occurs here
- from the omasum food enters the fourth and final chamber of the stomach - ABOMASUM. protein digestion occurs here
- the products of digestion are absorbed into the blood in the small intestine
body wall cells of a tape worm have been observed to contain transmembrane proteins involved in active transport mechanisms.
suggest how these mechanisms aid the survival of the parasite within its host [2]
- enable the worm to absorb ions/amino acids/glucose
- against concentration gradient
humans are the primary host of the pork tapeworm. where would the adult tapeworm would be located in a human?
small intestine
- as the tapeworm lacks a digestive system
- the small intestine contains the (products of digestion/digested nutrients/soluble nutrients) / nutrients can simply be (absorbed/diffuse) across the tapeworm’s BODY SURFACE/MEMBRANE
some protease enzymes are added to the stomach in the form of inactive precursors.
explain why these enzymes are not secreted in their active form [1]
- to prevent (autolysis / self-digestion)
coeliac disease in human is caused by a protein, gluten, found in wheat, barley, and rye.
it leads to a loss of villus height and a breakdown of microvilli.
explain why people with coeliac disease sometimes suffer from deficiency disease [2]
- surface area reduced
- do not absorb substances so efficiently/reduced uptake
coeliac disease in human is caused by a protein, gluten, found in wheat, barley, and rye
explain the reduced efficiency of digestive enzymes, such as those involved with the final breakdown of dipeptides, in people with coeliac disease [1]
- no or fewer microvilli / surface areas reduced for enzyme action / catalytic surface reduced / enzymes absorbed onto membranes
pepsin and trypsin are enzymes involved in the digestion of proteins. both are secreted as inactive precursors (pepsinogen and trypsinogen). give the names of the substances responsible for their activation
-enzyme: pepsin
-precursor: pepsinogen
-activated by: hydrochloric acid
-enzyme: trypsin
-precursor: trypsinogen
-activated by: enterokinase
name the part of the alimentary canal where villi would be found
ileum (+ duodenum)
name the blood vessel that transports amino acids to the liver [1]
hepatic portal vein
what is the name of the layer that contains glands that release secretions?
mucosa
what is the name of the layer that contains vessels to transport products of digestion?
submucosa
what is the name of the layer that undergoes peristalsis?
muscle layer
what absorbs lipids following digestion?
lacteal / lymph vessel / lymphatic vessel
what connects with the bile duct?
- duodenum
suggest why infecting yourself with tapeworms could lead to weight loss but also cause serious health problems [2]
- tapeworm (absorbs nutrients from gut contents / causes malnutrition)
- block gut lumen
- (larval forms) can form cysts in vital organs
