2.4 Adaptions for Nutrition

The process by which organisms obtain energy to maintain life functions and matter to create and maintain structures. These are obtained from nutrients.

There are 8 different modes of nutrition:

1. Autotrophic (Self-feeding)

2. Photoautrophic (Light-feeding)

3. Chemoautrophic (Chemical-feeding)

4. Heterotrophic (Different-feeding)

5. Saprotrophic / Saprobiontic (Fungi)

6. Holozoic (Ingest, digest, egest)

7. Parasitic (Parasites)

8. Symbiosis / Mutualism (Live together)

Synthesis of complex organic chemicals from inorganic substances using an energy source.

Living organisms that can make their own food and provide food for all other life forms (producers). Two types:

• Photoautotrophic: oranisms use light energy to combine inorganic substances into complex organic chemicals. E.g. Green plants, alga, Protist, cyanobacteria, bacteria, etc.
• Chemoautotrophic: organisms use chemical energy, from chemicals such as hydrogen sulphide, to combine inorganic substances into complex organic chemicals. Most are Archaebacteria - extremophiles that live in conditions that are uninhabitable by most organisms. E.g. Methanogen-stomach of a cow=uses ethanoic acid as an energy source, Nitrosomonas-brackish (salty water)=use energy from ammonia.

Cannot synthesise its own complex organic chemicals - must digest organic chemicals produced by other organisms and use the products of digestion to synthesise their own organic chemicals. 

They need food sources that contain complex organic chemicals as sources of:

• Carbon - making their own organic chemicals
• Nitrogen - making proteins and nucleic acids
• Phosphate - ATP and nucleic acids
• Vitamins and Minerals - making a wide range of biochemicals
• Energy - 80 to 90% of energy in food is lost as heat

They are consumers and there are 4 different types:

• Saprotrophic / Saprobiontic
• Holozoic
• Parasitic
• Symbiosis / Mutualism

• Saprotrophic / Saprobiontic undertake 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. E.g. Fungi and bacteria grow as hyphae-microscopic fibres that may have distinct cell walls between adjacent cells, partial cell walls or none at all (coenocytium - multiple nuclei found in the same 'cell').

• Holozoic: absorption of organic matter followed by interal digestion of the organic chemicals within the organism. 
  • Single celled organisms: organic matter taken into the cell where intracellular digestion takes place; products of digestion released and used within the cell and undigested material is released to the outside. E.g. Amoeba by means of endo- and exocytosis: Amoeba senses food. Pseudopodia surrounds food. Food enclosed in a food vacuole. Enzymes from lysosomes are added into the food vacuole. Food digested and soluble materials absorbed and assimilated. Undigested waste is expelled. Example of intracellular digestion, ingested through phagocytosis and waste products expelled through exocytosis.
  • Multicellular organisms: Have a digestive system (ingested & digested extracellularly but still within) products of digestion absorbed into cells / transport system and utilised by different parts of the body. Undigested material is released to the outside as faeces during egestion. E.g. Hydra, Flatworms, Humans, etc.

Hydra: related to jellyfish and has a gastrovascular cavity which is a simple sac-like gut with only one opening to the external environment. Its digestion is a combination of extracellular and intracellular digestion, with most of it taking place in the gastrovascular cavity, through mechanical (contractions) and chemical (hydrolytic enzymes) digestion, to break down food into fragments that can then be absorbed into cells lining the gut by phagocytosis and pinocytosis. Intracellular digestion completes the breakdown of food within food vacuoles.

Flatworms are larger and have a more complex level of organisations than Hydra but still have a single gut cavity. The gastrovascular cavity is highly branched. As a result food can be digested and the products absorbed throughout the organism. Therefore, no need for a designated transport system to deliver raw materials to the tissues.

• GUT - simple pouch where food is digested and products absorbed into the bodytissue
• PHARYNX (throat) - Everted to vacuum up food that the animal crawls over
• FOOD and WASTE - enter and exit through the same opening

Tube gut has an opening for ingestion and a separate opening for egestion. Different regions are adapted for different functions: mechanical digestion by teeth (muscular action). Chemical digestion by acids, enzymes with different optimum pH = increases efficiency - quicker and continuously. Human gut is a generalised digestive system which is adapted to eating both plant and animal.

Mouth; breaks up food particles=ingestion >Salivary glands; saliva moistens & lubricates food, amylase digests polysaccharides-starch >Pharynx; swallows >Oesophagus; transports food >Stomach; stores & churns food, pepsin diges protein, HCl activates enzymes-breaks up food-kills germs, mucus protects stomach wall, limited absorption >Liver; breaks & builds many biological molecules, stores vitamins & iron, destroys old blood cells, destroys poisons, bile aids in digestion >Gallbladder; stores & concentrates bile >Pancreas; hormones regulate blood glucose levels, bicarbonates neutralise stomach acid, trypsin & chymotrypsin digest proteins, amylase digests polysaccharides, lipase digests lipids >Small intestine; completes digestion, mucus protects gut wall, absorbs nutrients, peptidase digests proteins, sucrase digest sugars, amylase digest polysaccharides >Large intestine; reabsorbs some water & ions, forms and stores faeces >Rectum; stores & expels faeces >Anus; opening for elimination of faeces, egestion.

Alimentary canal & its associated organs: The breakdown of large, insoluble molecules into small, soluble molecules that can be absorbed into the blood stream for transport to cells. There are 4 stages to this process:

• Ingestion is taking food into the alimentary canal
• Digestion is breaking food down
• Absorption is taking the soluble products of digestion into the bloodstream
• Egestion is getting rid of the undigested remain of food from the alimentary canal

BUCCAL CAVITY: Lips, tounge and teeth work together to: capture & receive food, move food about the mouth, cut, grind & chew food into smaller pieces, mix the food with saliva to lubricate food & add salivary amylase, forms food into a bolus to make swallowing easier. Neutral pH.

SALIVARY GLANDS: Secrete about 1500cm3 of saliva (6.5-7.5 pH up to 1 minute) each day which contains the enzyme salivary amylase: Starch (polysaccharide) -> Maltose (disaccharide)

OESOPHAGUS: Straight narrow tube with a muscular wall, carries food to the stomach by peristalsis. Beginning of swallowing is conscious, muscles in top part under voluntary control, lower down muscles are under involuntary control and swallowing becomes a reflex. Large amount of mucus secreted to lubricate the passage of food to the stomach.

STOMACH: Chemical (enzymes & HCl) & mechanical (muscles mix food with gastric juice) digestion. End result is semi-liquid chyme. Gastric glands contain cells that are essential for absorption: Zymogenic cells secrete pepsinogen / pepsin (digests protein into polypeptides) & in young mammals prorennin / rennin (digests milk protein). Goblet cells secrete mucus-forms a barrier between the stomach lining & the gastric juice-prevents self-digestion by pepsin & HCl. Oxyntic cells secrete HCl which provides pH (1-6.5 up to 4 hours) for enzymes, denatures proteins, softens connective tissue in food & activates pepsin & rennin. Enocrine cells secrete the hormone gastrin-promotes secretion of gastric juice-if the stomach wall is stretched the hormone is secreted, stimulating the production of enzymes.

GUT WALL: Muscle layers responsible for peristalsis. Submucosa generally carries the main arterioles & venules-it may also contain glands. Mucosa covered by layer of epithelial cells-produce mucus and responsible for final stage of digestion and absorption of nutrients.

Duodenum: first part of the small intestine & is 30cm long. Accessory organs; liver and pancreas, pass secretions into the duodenum which recieves chyme (stomach), bile (liver) & pancreatic juice (pancreas). Wall is folded into villi to increase surface area, mainly for absorption in the ileum. At the base of the villi there are intestinal glands called the crypts of Lieberhuhn. There's also Brunner's Glands that secret alkaline fluid (contains NaHCO3) and mucus (neutralise the acid chyme). pH of 7.0-8.5 for 30-60 minutes.

Ileum: Digestion completed and main site of absorption of the products of digestion. Nearly 5m long so food takes a relatively long time to pass through the ileum=increasing time available for digestion and absorption. Villi also increases the surface area and have a rich blood supply to remove the products of digestion. Most water absorbed here. pH 4-7 1-5 hours. 

Colon: Main part of the large intestine. Rest of the water and mineral salts absorbed. Vitamins produced by microorganisms in the colon are also absorbed into the blood which leaves a semi-solid mass of undigested food, dead intestinal cells and bacteria (50% of total mass)=forms faeces. pH of 4-7, 10 hours to several days.

Rectum: Last part of the large intestine, a musculartuve that temporarily stores the faeces before they are eliminated from the body.

Anus: Sphincter muscle that controls when defaecation occurs.

Glandular pocket produce large quantities of mucus by goblet cells; protects the epithelium from friction by the feacal mas.

Liver: Produces bile by breaking down haemoglobin. Bile is stored in the gall bladder and is secreted into the duodenum through the bile duct. Liver receives nearly all the products of digestion from the small intesting - carried there in the hepatic portal vein. The liver has many functions including:

• excess glucose stored as gylcogen (animals only)
• amino groups are removed from amino acids (de-amination) and converted into urea
• many vitamins are also stored in the liver

(Where they're produced) CARBOHYDRATES: 

STARCH -amylase (mouth & pancreas)-> MALTOSE -maltase (intestinal cells)-> GLUCOSE

SUCROSE -sucrase (intestinal cells)-> GLUCOSE + FRUCTOSE

LACTOSE -lactase (intestinal cells)-> GLUCOSE + GALACTOSE

PROTEINS:

PROTEIN -endopeptidases-> POLYPEPTIDES + PEPTIDE

Endopeptidases - break peptide bonds between amino acids in the middle of the molecule. Pepsin (stomach) & trypsin [secreted as inactive precursors prevent autolysis] + chymotrypsin (pancreas). PRECURSORS: Pepsinogen activated by HCl to form pepsin, trypsinogen activated by enterokinase to form trypsin. 

PEPTIDES -exopeptidase-> AMINO ACIDS + DIPEPTIDES

Exopeptidase - break peptide bonds between terminal amino acids. Carboxypeptidase (pancreas) and aminopeptidase (intestinal cells).

LIPIDS:

LIPID -lipase (pancreas)-> FATTY ACIDS +GLYCEROL

Bile  emulsifies lipids by breaking large globules of fat into small droplets, increasing surface area for action of lipases and allows very small droplets of fat to be absorbed directly into the blood stream.

Most of digestion, by hydrolysis, takes place in the lumen of the small intestine but the final stages of digestion of dipeptides and disaccharides (eg. sucrose, maltose, lactose) are intracellular or take place on the surface of the villus epithelium.

Takes place in the ileum, the surface area is greatly increased by folded wall, villi, microvilli.

• Glucose & amino acids are absorbed mainly by active transport, diffusion and co-transport into capillaries. Carried in the hepatic portal vein 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 capillaries. Glucose is absorbed from the blood by cells, for energy release in respiration, some is converted to glycogen in the liver and muscles; and any excess stored in fat cells.
• Amino acids are absorbed for protein synthesis; excess cannot be stored so are deaminated. The removed amino groups are converted to urea and the rest to carbohydrate and stored.
• Fatty acids and glycerol are absorbed seperately into the epithelial cells. Most are reassembled into triglycerides. All three are passed into the lacteal, then through the lymphatic systemto the blood stream opening at the thoraic duct. Lipids are used for membranes and hormones, excess is stored as fat.
• Most water is absorbed into the bloodstream in the ileum; excess water, mineral salts and vitamins secreted by microorganisms in the colon, are absorbed from the colon.
• Residues of undigested cellulose, bacteria & sloughed cells are egested as faeces. Cellulose fibre required to provide bulk and stimulate peristalsis.

Omnivores eat a mixture of plant and animal tissues therefore teeth are adapted for: grinding plant tissue (molars and premolars), biting (incisors), gripping (canines) and tearing flesh (incisors). Plant material is harder and less nutritious than flesh due to cellulose and other fibres that protect the cell contents. E.g. Humans and pigs.

Humans have no diastema (significant gap between teeth), pigs do. The canines have less functionality in humans, in pigs they're used for fighting. Masseter muscles (grinding) and temporalis muscles (biting) are relatively well developed as omnivores need to be able to break bones, shear meat from bodies and chew their food well.

Herbivores teeth are adapted to grind tough plant tissues to release nutrients. No need for powerful biting=small temporalis, need for grinding=large masseter. E.g. Sheep: molars and premolars are highly ridged to provide a large grinding surface for mechanical digestion of grass and other plant material. No incisors on the upper jaw and presence of diastema between the modified canine and the first premolar means that they can use their tongue to divide the buccal cavity into two, therefore they can carry on chewing food with their molars and premolars while continuing to eat with their incisors at the front of the mouth.

Carnivores: incisors and canines are adapted for biting prey. Premolars and molars are called carnassial teeth - they have single ridges and slide past each other acting like scissors to shear flesh from bones. 

E.g. Dogs: temporalis muscle is large and gives a dog a very strong and quick bite. Masseter muscle is relatively weak as dogs do not chew their food. Pieces of flesh are swallowed whole. Meat is largely protein this can be digested easily in the stomach.

Insectivore: Insects made largely of chitin and protein - easily digestible material, short gut as products of digestion easily absorbed.

Non-ruminant herbivore: Plant material with a high fibre / cellulose content - difficult to digest; bacteria / archae present in caecum which digests cellulose and produces protein. Bacterial digestion occurs after the ileum so products of bacterial digestion are not absorbed. E.g. Rabbits will eat their faeces to absorb extra nutrients. Horses do not eat faeces and therefore have less effective digestion and absorption.

Ruminant herbivore: Base of the stomach is expanded and differentiated into three chambers (not apart of the stomach) which contain bacteria and archaea tha can digest cellulose and produce fatty acids, proteins and vitamins that can be utilised by the animal. Protein digestion begins in the abdomasum (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.

Carnivore: Meat is made mostly of protein and fat - easily digestible and easily absorbed - no need for long digestive system.

Many organisms live in / on other organisms in a relationship that provides benefit to both organisms.

Buccal cavity: Initial biting of plant material (incisors) followed by grinding (molars & premolars). Food mixed with saliva to lubricate food & ease swallowing. Tongue mixes food with saliva and forms food into a bolus for swallowing. Reticulum: Large particles (stones) collect here. Vegetation passes into the rumen. Solids pass freely between the reticulum and rumen. Solids settle in the rumen and are regurgitated from the reticulum back to the buccal cavity where they are chewed again to increase surface area for action by bacteria in the rumen. Rumen: 1 cm3 of rumen fluid contains 10-50 billion microbes and over 1 million protozoa. Bacteria digest the food saprotrophically, protoza digest food particles holozoically. Microbes in the rumen digest cellulose and produce protein, fatty acids (VFA's) and B vitamins. VFA's are absorbed through the rumen wall and used as energy by the animal. Protein (digested in rumen) used to support microbial growth and functions. Bacteria break down lipids to produce VFA's and fatty acids. Fatty acids will not be absorbed by the rumen but in the small intestine. Omasum: Absorption of water and minerals. Abomasum: True, glandular stomach which secretes acid and protease enzymes. Site of digestion of bacterial protein. Also secretes lysozome (enzyme that breaks down bacterial cell walls). 

** Young ruminants that feed on milk, food passes from the base of the oesophagus directly to the abomasums - milk high in protein (only abomasum).

Organisms that live in (endoparasites) or on (ectoparasites) to obtain nourishment at the expense of the host, usually causing harm. Some are intracellular and others are extracellular.

Primary hosts organism is where the acult forms of the parasite develop.

Secondary hosts are where larval / intermediate forms of the parasite are found.

Vectors are secondary hosts which actively and directly transfer the parasite from one primary host to another primary host. E.g. Malaria.

Endoparasites e.g. pork tapeworm and beef tapeworm (smaller) lifecycles: eggs or gravid proglottids in faeces and passed into environment (diagnostic). Cattle and pigs ingest vegetation contaminated and become infected. Lavi hatch hatch, penetrate intestinal wall, and circulate to muculature. Lavi develop into cysticerci in muscle (infective). Humans infected by ingesting raw or undercooked infected meat: scolex attaches to intestine=adults in small intestine.

Scolex: embedded in the gut wall and has hooks (2 rows, backwards facing) and suckers to prevent it being dislodged by peristalsis.

Proglottids: produce from the neck and grow in size as they are pushed away from the neck. If main body removed but scolex remains, it can regenerate. Each one is hermaphrodite (both male and female reproductive organs) therefore can self-fertilise. Each contain about 50,000 eggs=increasing the chance of infecting another host. Covered in thick cuticle: resistans to the action of digestive enzymes and serete mucus and enzyme inhibitors to prevent self-digestion. pH of mucus varies to neutralise conditions.

Flat body: increases surface area for absorption of nutrients from the gut contents=smaller diffusion distance.

Microtichs: Can be covered in extensions similar to microvilli and further increase surface area.

No digestive system only needs to absorb nutrients that are already digested.

No sense organs due to living inside the gut.

Anaerobic respiration: no oxygen in the gut lumen.