WJEC AS Biology Unit 2.4 - Adaptations for Nutrition

Heterotrophs

• Organism that requires a source of orgaic molecules produced by autotrophs for their nutrition

• Examples; animals, fungi, some Protoctista and some bacteria

Saprotrophs

• Organism that feeds on dead and decaying matter by extracellular digestion

• secrete distive enzymes out of the body then absorb the soluble products across the cell membranes

• Example of heterotrophs

• Examples; all fungi, some bacteria and the mould Rhizopus

Process of saprotrophic nutrition in fungi

• secretion of digestive enzymes from hyphae

• extracellular digestion of dead organic matter

• enzymes digest the substrate (the matter on which the fungus grows and feeds)

• absorption of small soluble products of digestion

• products transported through mycelium

Autotrophs

• Organisms that use simple organic molcules to synthesise complex organic compunds for their nutrition

• Examples; green plants/autotrophic bacteria

• Two types; chemoautotrophs and photoautotrophs

Photoautotrophs

• form of autotroph

• use light energy as a soure of energy to synthesise complex organic food materials

Chemoautotrophs

• form of autotroph

• organism that use chemical energy from inorganic molecules to synthesise complex organic food materials

• examples; prokaryotes

Holozoic

• example of heterotrophic nutrition

• organism which feed on solid organic material synthesised by autotrophs which is then digested internally to form smaller soluble molecules for absorption

• method of most animals

• internal digestion of food substances

• examples; herbivores, carnivores, omnivores, detritivores

process of holozoic nutrition

1. ingestion; food is taken into the body, usually through the mouth

2. digestion; the breakdown of small, insoluble food molecules into small, soluble food molecules

3. absorption; the uptake/passage of soluble food molecules and ions across cell membanes through the gut wall into the capillaries or lacteals

4. assimilation; the uptake and use of soluble food molecules by cells in the body

Herbivores

animals that feed solely on plant materials

Carnivores

animals that feed on other animals

Omnivores

animals which feed on both animals and plant materials

Detritiovores

animals which feed on dead and decaying materials

Mutualism

• a close association/interaction of/between organisms from more than one species, in which they both benefit from the relationship

• example; digestion of cellulose by microroganisms in the gut of a herbivore

Parasite

an organism which lives on or in another organism, the host, obtaining nutritents from it, at the expense of the host, causing the host harm

includes the headlouse and the tapeworm

similiarities between the adaptations of amoeba and hydra for obtaining their nutrition

• both are holozoic

• both carry out internal digestion

• both ingest food

differences between the adaptations of Amoeba and Hydra for obtaining their nutrition

• Amoeba;

  • engulfs food using membrane/phagocytosis/endocytosis

  • food taken into a vacuole

  • intracellular enzymes

• Hydra;

  • captures prey with tentacles

  • food taken into a gut/mouth

  • extracellular enzymes

Nutrition in unicellular organism

• animal-like single-celled Protoctista, e.eg. Amoeba, use holozoic nutrition

• simplest form of holozoic nutrition

• obtain all necessary nutrients by diffusion, facilitated diffusion and active transport across cell membranes

Process of nutrition in unicellular organisms (Amoebas)

1. Amoeba senses food

2. Pseudopodia surround the food

3. Engulf large food molecules by phagocytosis and smaller molecules by pinocytosis, forming vesicles/food vacuoles

4. Food vacuoles fuse with lysosomes

5. Contents digested by digestive enzymes secreted into the food vacuoles

6. Food is digested and soluble product materials are absorbed into the cytoplasm and assimilated

7. Undigested waste and indigestible remains are egested by exocytosis

Hydra

• Hydra; simple multicellular organisms - more complex then Amoeba - with a simple, undifferentiated, sac-like gut with a single opening

• Heterotrophic

• Holozoic

• Stinging cells on tentacles immobilise prey

• Contain photosynthetic Protoctista

• Mutualism as both organisms benefit; Protoctista pass sugars to Hydra

Process of nutrition in multicellular organisms (Hydra)

1. Ingestion; tentacles around their ‘mouth’ draw prey through mouth to a hollow body cavity which can extend depending on size of prey

2. Digestion; endodermal cells secrete protease + lipase (digestive enzymes). Other endodermal cells are phagocytic and engulf food particles by phagocytosis which they then digest in food vacuoles. Prey is digested extracellularly

3. Absorption; products of digestion absorbed into the cells

4. Gratin; indigestible remains and waste egested through the mouth

Structural adaptations of Hydra for nutrition

• One body opening - the mouth

• Tentacles with stinging cells to paralyse the pray and move it into hollow body cavity

• Contain photosynthetic Protoctista that produce sugars that Hydra use

• For relatively undifferentiated; no specialised areas to undertake different parts of digestion and absorption

Nutrition in more complex organisms

• adaptation from simple, undifferentiated sac-like gut with single opening to a tube fit with different openings for ingestion and digestion + specialised regions for the digestion of different food substances

• More advanced organisms with a varied diet, have evolved a tube gut that is divided into various parts along its length and each part is specialised to carry out particular functions

Human digestive system

• adapted to a mixed omnivorous diet that includes both plant and animal material

• Each section is specialised and performs particular steps in the processes of mechanical and chemical digestion + absorption

• Food is propelled along the gut by peristalsis

Peristalsis

Rhythmic wave of coordinated muscular contractions in the circular and longitudinal muscle of the gut wall, passing food along the gut in one direction only

2 types of digestion

• mechanical digestion

• Chemical digestion

Mechanical Digestion

• breaks down food into smaller pieces, increasing its total surface area for enzyme action

• Physical process

• Includes; chewing, churning and mixing

• Carried out by mouth and stomach

Chemical digestion

• involved hydrolysis via the use of enzymes to break down large insoluble molecules into smaller, soluble molecules

Functions of the Gut

• Ingestion

• Digestion

• Absorption

• Egestion

Ingestion

Taking food into the body via the buccal cavity

Digestion

The breakdown of large insoluble food molecules into smaller soluble molecules that are small enough to be absorbed into the blood

Absorption

The passage of molecules and ions through the gut wall into the blood

Egestion

The elimination of waste not made by the body, including food that cannot be digested

Structures with the Human Digestive System

• Mouth

• Oesophagus

• Stomach

• Duodenum

• Ileum

• Colon

• Rectangle

• Anus

Function of Mouth/Buccal Cavity

• Ingestion

• Mechanical digestion

• Chemical digestion of starch and glycogen

Function of Oesophagus

Carriage of food to the stomach via peristalsis

Function of Stomach

Digestion of proteins

Function of Duodenum

Digestion of carbohydrates, fats and proteins

Function of Ileum

• Digestion of carbohydrates, fats and proteins

• Absorption of food and water

Function of Colon

Absorption of Colon

Function of Rectum

Storage of faeces

Function of Anus

Egestion

Structure of the gut wall (diagram)

Structure of the gut wall

• 4 tissue layers surrounding the lumen

• Muscle; 2 layers in different directions;

  • Circular muscles

  • Longitudinal muscles

• Submucosa

• Mucosa

• Lumen

Structure and function of the lumen

Cavity of the gut

Structure and function of the Serosa in the gut wall

• Tough, connective tissue protecting the gut wall

• Reduces friction with other organs as gut moves while processing food

Structure and function of the Muscle in the gut wall

• 2 layers of muscle in different directions

• Longitudinal muscles;

  • Relax, pushing the food along

• Circular muscles;

  • Contract behind ball of food

Structure and function of Submucosa

• Connective tissue containing blood and lymph vessels

  • Which remove absorbed products of digestion

• Nerves coordinate peristalsis

Structure and function of Mucosa in the gut wall

• Innermost layer

• Lines the gut wall

• Its epithelium secretes mucus

  • Lubricating and proctecting the mucosa

• In some regions of the gut, it secretes digestive juices and in other absorbs digested food

Buccal cavity

• Salivary glands secrete saliva which contains;

  • Amylase, beginning digestion of starch and glycogen to maltose which is hydrolysed further by maltase to alpha glucose

  • HCO3- and CO3- ions which neutralise pH and provide optimal. pH of saliva varies from 6.2-7.4. Optimum ~ 7.0

  • Mucus lubricates the food’s passage down the oesophagus

• Tongue;

  • Has taste his

  • Helps manipulate the food in the mouth

  • Assists with swallowing

• Teeth;

  • Break down food via mechanical digestion. Digestion into smaller pieces which increases surface area for substrate to come into contact with enzymes

Oesophagus

• No role in digestion

• Carries food to the stomach

• Food passes through for a short period of time before reaching the stomach

• No enzymes secreted

Wall of the Oesophagus

Stomach

• food is churned (mechanical digestion) with gastric juice

• Salivary amylase is denatured due to acidic pH

• Bacteria consumed are killed by the acidic pH

• Oblique muscle = extra muscle layer of muscle to help churn the contents of the stomach (chyme)

• Gastric juice is secreted by from gastric pits

• Very little absorption occurs but main site of alcohol absorption

• Pepsinogen —(HCl)—> Pepsin

• Proteins —(Pepsin)—> polypeptides/peptides

Stomach wall

Oblique layer of muscle

Extra muscle layer within the stomach wall that helps to churn the contents of the stomach

Gastric Pit structure

Gastric Juice

• Zymogen/chief cells secrete the inactive enzyme pepsinogen. Pepsinogen is activated by H+ ions —> pepsin, an active endopeptidase which hydrolyses proteins into polypeptides

• Oxyntic cells secrete the hydrochloric acid (HCl). Lowers pH of stomach contents —> 2; optimum pH for the enzymes and kills most bacteria in food

• Goblet cells secrete mucus. Forms a lining which protects the stomach wall from the enzymes and lubricates the food

Proteases

• Hydrolyses proteins into polypeptides, dipeptides and amino acids

• Two types;

  • Endopeptidase

  • Exopeptidase

Endopeptidases

hydrolyse non-terminal peptide bonds within the protein/polypeptide molecules, adjacent to specific amino acids and form peptides

Exopeptidases

• Can act after endos

• Hydrolyse the terminal peptide bonds of the peptides, from the free amino end or the free carboxyl end

Small intestine

• Duodenum

• Ileum

Duodenum

• first c shaped part of the si

• Receives secretions from the pancreas and liver

• Main role=digestion but also involved in absorbing nutrients

• Pancreas empties pancreatic juice into the duodenum

• Bile is made in the liver, stored in the gall bladder and emptied into the duodenum via the bile duct

Pancreatic juice

• secreted by islet cells (exocrine glands in the pancreas)

• Enters duodenum via pancreatic duct

• Secretes at least one type of each digestive enzyme;

  • Pancreatic amylase; digests any remaining starch → maltose

  • Lipase; hydrolyses lipids → fatty acids and monoglycerides

  • Endopeptidases; hydrolyse proteins and polypeptides → peptides

• Also contains trypsinogen;

  • Inactive precursors and endopeptidase

  • Activated by enterokinase (in pancreatic juice to activate trypsinogen)

  • Trypsinogen → trypsin

  • Trypsinogen -enterokinase→ trypsin

  • Polypeptides -trypsin→ shorter peptides

• Also contains sodium hydrogen carbonate ions;

  • Raise the pH to make pancreatic juice and contributes to;

    • Neutralising acid from the stomach

    • Providing an appropriate pH for the pancreatic enzymes to work efficiently

• optimum pH for all pancreatic enzymes ~ pH8

Trypsinogen

Inactive precursor of trypsin. Activated by enterokinase. Inactive otherwise it could digest the proteins of the cells which secrete it/the duodenum

Sodium hydrogen carbonate ions

• raise the pH to make pancreatic juice and contribute to;

  • Neutralising acid from the stomach

  • Providing an appropriate pH for the pancreatic enzymes to work efficiently

Bile

• Made in liver, stored in gall bladder and emptied into the duodenum via the bile duct

• Contains no enzymes

• Contains bile salts; Emulsify lipid globules by lowering surface tension and breaking up large globules into smaller globules therefore increasing S.A. and make digestion more effective by lipase

• More hydrogen carbonate ions

• Have hydrophobic and hydrophilic parts

Ileum

• digestion that arts in the duodenum carries on into the ileum

• Main role = absorption of products of digestion

Structure of Ileum

Has all layers in common with rest of gut but is adapted for efficient absorption of products of digestion

Adaptations of ileum for efficient absorption of products of digestion

• Circular folds; finger-like projections = villi and infoldings of epithelial cell membranes = micro villi → large SA for absorption of nutrients and secretion of enzymes and increase SA for digestion of disaccharides and dipeptides as enzymes can embedded in the cell surface membranes

• Good blood supply for transporting amino acids and glucose away and lacteals for transporting products of lipid digestion away → maintain concentration gradients

• Walls of villi = 1 cell thick and network of capillaries → short diffusion pathway

• Cells have many mitochondria → ATP synthesis for active transport

• Many transport proteins within cell membranes

• Circular and longitudinal muscles propel food by peristalsis and mix the contents, improving absorption

• Goblet cells secrete muscle for lubrication of food

• Brunner’s glands/intestinal glands/crypts of Lieberkuhn secrete alkaline intestinal juice which contains digestive enzymes

Epithelial cells of the small intestine

Secretions of the small intestine epithelial cells

• Endo + exopeptidases;

  • Peptides secreted by villus epithelial cells and digestion continues on the gut lumen

  • Dipeptidases in the cell surface membranes digestion dipeptidases → amino acids

• Carbohydrases;

  • Secreted and digestion continues in the gut lumen

  • Carbohydrases in the cell surface membranes digest disaccharides and monosaccharides

  • Some disaccharides are absorbed so their digestion = intracellular

  • often embedded in the epithelial cells which secrete surface membranes but can be secreted in intestinal juices from intestinal glands

  • Dipeptidases act in a similar way but on dipeptides

• Trypsin, lipase and pancreatic amylase continue to act

Main mechanisms of absorption in the ileum

Diffusion, facilitated diffusion and active transport

The large intestine

• Comprises the caecum, the appendix, the colon and the rectum

Colon

• undigested food, mucus, bacteria and dead cells pass into the colon

• Colon wall has fewer villi than the ileum

• These villi have a major role in water absorption

• Vitamin K and folic acid = secreted by mutualistic microorganisms living in the colon

• Minerals absorbed from the colon

• As material passes along the colon, water is absorbed

Structure of the wall of the colon

Substances absorbed in the ileum

• glucose and other monosaccharides

• Amino acids

• Fats

• Cholesterol and fat-soluble vitamins

• Water-soluble vitamins

• Mineral ions

• Water

Absorption of glucose

Absorption of monosaccharides

Absorption of amino acids

Assimilation after absorption

Absorption of fats

Absorption of vitamins, water soluble vitamins,

Absorption in the large intestine

Egestion

Summary of absorption

Describe the process of glucose transport from the lumen of the small intestine into and then out of epithelial cells

Carnivore

Herbivore

Dentition of Herbivores

Dentition of Carnivores

Incisors in Herbivores

Canines in Herbivores

Diastema

Molars and premolars of Herbivores

Jaw of Herbivores

Muscles of Herbivores

Skull of Herbivores

Incisors of Herbivores

Canines of Herbivores

Carnassials

Jaw of Carnivores