Adaptations For Nutrition

• Animal-like Protista such as amoeba use holozoic nutrition. 
• They are single-celled and have a large SA: V 
• They absorb nutrients such as oxygen and glucose through their cell membrane via diffusion facilitated diffusion and active transport. 
• They take large food molecules such as bacteria and microscopic algae via endocytosis. 
• The food molecules are surrounded by membranes and form food vacuoles. 
• The vacuoles fuse with hydrolytic enzymes which digest the contents of the food vacuoles. 
• The products of digestion are then absorbed into the cell cytoplasm. 
• The indigestible remains are then excreted via exocytosis.

• Hydra are multicellular, freshwater animals that are in the same family as jellyfish. 
• They are cylindrical and have tentacles on top of their body with stinging cells. They also have an undifferentiated digestive system. 
• The tentacles move the paralysed prey in through the mouth into the sac-like body cavity where prey is digested. 
• The products of digestion are absorbed into body cells and undigested remains are egested from the mouth 

• Humans have their digestive system split into various sections with specific roles. 
• Food must be digested to make them soluble and small enough to cross membranes to be absorbed into the bloodstream. 
• When food is digested polymers must be converted to their monomers so they can be assimilated into molecules needed by body cells

• The human gut performs 4 main functions:
  • Ingestion - Taking food into the body from the mouth
  • Digestion - The breakdown of large insoluble molecules into soluble molecules which are then small enough to be absorbed into the blood.
  • There are 2 types of Digestion
    • Mechanical- Cutting and crushing by teeth and muscle contractions of the gut wall. It increases the SA over which enzymes act. 
    • Chemical- Digestion via the secretion of enzymes. Bile and stomach acid contribute to chemical digestion.
• Absorption - The passage of small soluble molecules and ions through the gut wall into the blood
• Egestion - The elimination of indigestible waste. 
• Digestion and absorption take place in the gut. The gut is a long hollow tube which allows  movement of its contents in one direction only. 
• Each section is specialised and performs particular steps in the process of mechanical and chemical digestion and absorption.
• The food is propelled down the gut via peristalsis

• Peristalsis 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 fibres aid peristalsis in the intestines

• The gut wall consists of 4 layers surrounding a cavity (the lumen of the gut). 
• The proportions of the layers depend on the functions of that part of the gut
• The serosa contains thick connective tissue which protects the gut walls. It helps reduce friction with other abdominal organs during peristalsis. 
• The muscular comprises of the outer and inner circular muscles. They make coordinated waves of contraction pushing food along the alimentary canal. 
• The submucosa consists of connective tissue containing blood and lymph vessels that remove the absorbed products of digestion. This layer contains the nerves that coordinate peristalsis. 
• Mucosa lines the gut wall and is the innermost layer. The epithelium secretes mucus which lubricates and protects the mucosa. In some regions of the gut, it secretes digestive juices and in others, it absorbs digested food.

• Absorption of nutrients by gut epithelial cells is only possible if macromolecules are first digested into smaller molecules. 
• Different enzymes digest different food molecules and usually, several enzymes are required to complete digestion. 

Carbohydrates

• Starch + Amylase -> Maltose + Maltase -> Alpha glucose
• Lactose is hydrolysed to glucose and galactose by lactase. 
• Sucrose is hydrolysed to glucose and fructose by sucrase

Carbohydrates

• Polypeptides ->  Dipeptides -> Amino Acids
• Endopeptidase hydrolyse peptide bonds with the protein molecules (pepsin and trypsin)
• Exopeptidase hydrolyses peptide bonds at the end of short polypeptide chains.

Fats

• Fats are hydrolysed by lipase the products are fatty acids and glycerol.

• Mechanical digestion occurs in the mouth. Food is mixed with saliva by the tongue and chewed by the teeth. This increases the SA of food for enzymes to work on. 
• Saliva contains = Amylase to convert starch to maltose 
• Bicarbonate ions create an optimum alkaline ph for amylase
• Mucus lubricates the food. 
• The Oesophagus has no specific role in digestion however it connects the mouth to the stomach.

• A bolus of food enters the stomach and Is kept there by the contraction of 2 sphincters. 
• The swallowed food can remain in the stomach for several hours. 
• The stomach walls muscles contract rhythmically to churn the food with the gastric juice secreted by glands in the stomach wall. 
• Gastric juice is secreted by gastric glands in the mucosa it contains mucus secreted by goblet cells in the mucosa. 
• Mucus forms an effective lining to protect the wall from digestive enzymes.
• The HCL helps to lubricate the food. It also lowers the PH of the stomach to PH2 to create an optimum environment for enzymes and kills bacteria. 
• It also contains pepsin which is a peptide that works optimally in the acidic environment of the stomach. Activation of HCl and pepsinogen form pepsin. 

• The small intestine is made up of 2 regions the duodenum and the ileum. 
• Relaxation of the sphincter muscles at the base of the stomach releases the partially digested food into the duodenum a little at a time. 

Duodenum

• This is the first section of the small intestine and receives secretions from the liver and pancreas. The food coming from the stomach contains lubrication by mucus and the HCl is neutralised by alkaline secretions in the submucosa. 
• Bile is made in the liver, stored in the gall bladder and passed through the bile duct into the duodenum. 
• Bile is alkaline and neutralises the acid in the food in the stomach creating an optimum ph environment for the enzymes in the small intestine to work. 
• Pancreatic juice is secreted by islet cells found in thee oancreas. It enters the duodenum through the pancreatic duct

Enzymes

• Endopeptidase hydrolysyes proteins to peptides
• Trypsinogen is an inactive enzyme which is converted into the endopeptidase trypsin by enterokinase
• Amylase chemically digests any remaining starch to maltose
• Lipase hydrolysis lipids into fatty acids. 
• Sodium Hydrogen Carbonate raises the ph to make pancreatic juice more alkaline
• Enterokinase converts trypsinogen to trypsin. 

• The ileum is adapted for absorption as it is
• very long
• its lining is folded
• on the folds are villi and epithelial cells 
• lining the villi are microvilli which help increase the SA

Columnar Epithelial Cells

• Microvilli provide a large SA for absorption
• Large numbers of mitochondria produce ATP energy for active transport.  

Goblet Cells

• These cells secrete mucus which lubricates and protects the lining of the intestine. 
• In the ileum, there are also enzymes associated with epithelial cells at the tips of the villi. 

Proteins

•  Endopeptidase and exopeptidase are secreted by cells at the tips of the villi into the gut lumen and continue the digestion of polypeptides. 
• Dipeptides are hydrolysed to amino acids by enzymes on the cell membranes of epithelial cells. 

Proteins

•  Carbohydrase on epithelial cell membranes hydrolysed disaccharides into monosaccharides which are then absorbed into the epithelial cells. 
• GLUCOSE + Maltose = Alpha Glucose
• Glucose + Sucrose = Fructose
• Glucose + Lactose = Galactose

Fatty Acids and Glycerol

• From the lumen to the epithelial cell diffusion takes place then they are reassembled into triglycerides
• From the epithelial cell to the capillary diffusion takes place and then they are carried to the blood via the lymphatic system. 

Glucose and Galactose

• From the lumen to the epithelial cell co-transport occurs with Na+
• From the epithelial cell to the capillary facilitated diffusion takes place. 

Na+

• From the lumen to the epithelial cell Na+ requires Co-transport with glucose 
• From the epithelial cell to the capillary facilitated diffusion takes place. 

Amino Acids

• From the lumen to the epithelial cell active transport is required
• From the epithelial cell to the capillary facilitated diffusion takes place. 

Water

• From the lumen to the epithelial cell water requires osmosis
• From the epithelial cell to the capillary osmosis is also required. 

• Glucose is required for aerobic respiration, any excess is formed stored as glycogen. 
• Amino acids are used for protein synthesis. Any excess is deaminated in the liver. 
• Lipids are used as energy storage and protection for vital organisms. They are also used as insulation under the skin.

• The large intestine is divided into the caecum, appendix, colon and rectum. By the time it reaches the rectum food cells bacteria and cellulose have become faeces. 
• The faeces then gets egested. 
• In the large intestine water mineral ions and vitamins produced by symbiotic bacteria in the gut are absorbed. 

• Autotrophic organisms can synthesise their own complex organic molecules from simpler organic molecules using either light energy or chemical energy. 
• Photoautotrophic organisms use light energy to synthesise their own organic molecules through photosynthesis
• Chemoautotrophic organisms use energy from chemical reactions to synthesise organic molecules. 

• Heterotrophic organisms cannot produce their own food or organic molecules so they consume organic molecules from other organisms
• They then break down the complex molecules into smaller soluble molecules which they then absorb and assimilate. 
• Heterotrophs include animals fungi some protactist and some bacteria. 

• Involves ingestion digestion and egestion. 
• Carnivores eat animals herbivores eat plants omnivores eat both. Detritivores feed on dead and decaying matter. 
• Holozoic nutrition includes ingestion digestion and absorption into the bloodstream assimilation and then ejection and excretion. 
• Excretion is the removal of any indigestible remains, for example cellulose in humans.

• Fungi feed on dead and decaying matter.
• Carry out extracellular digestion. This means enzymes are secreted onto the food material outside the body. 
• They then absorb the soluble products of digestion into their cells by diffusion or active transport. 
• Decomposers are microscopic saprotrophs that play a part in decaying leaf litter and recycling nutrients such as nitrogen. eg. Rhizobium

• The Tapeworm is ribbon like and 10 metres long. 
• It has a head made of muscle with suckers and hookers. 
• Its body is a linear series of sections called proglotids
• It has 2 hosts the primary is the human and the secondary is the pig. 
• The larval form is found in pigs. The pig becomes infected if it feeds on drainage channels with human faeces. 
• Humans become infected by eating undercooked pork. 

• Parasites are organisms that live on or in other organism called the host. They obtain nurishment at the expense of the host so they cause harm or death. 
• Endoparasites live inside the host.
• Ectoparasites live on top of the host. 
• Many organisms are parasites for at least a part of their lives. Plants and animals are parasites by bacteria fungi viruses nematodes and insects. 
• Bacteria can be parasites by viruses called bacteriophages.

Gut is constantly in motion - Suckers and hooks to attach the tapeworm to the gut wall. 

Extreme Ph Digestive enzymes and immunity - A thick cuticle and the production of inhibitory substances on the surface to prevent digestion by the host enzymes. Body covering protects them from the host immune response. 

Reproductive problems (No mates high offspring mortality) -  Tapeworms have both male and female organs so they can self fertilise. Large numbers of eggs are produces and each mature segment can produce 40,000 eggs. Eggs also have shells to protect them when moving to another host. 

Host Death - If the host dies then the tapeworm also dies. Adult tapeworms cause little discomfort to the host so there is no immune response. 

Tapeworm has no digestive system- The tapeworm is long and flat so it has a large SA:V. It lives in the small intestine and is surrounded by the hosts food that has already been digested and can be reabsorbed over the entire body surface of the tapeworm via diffusion.  

• These animals have teeth adapted for catching prey, crushing bones and tearing meath. 
• Small Sharp Incisors- To grip and tear flesh from the bone
• Curved Canines - Seize and Hold on to prey.
• Molars and Premolars- Cutting and Crushing food, 
• Carnassials- Slide past each other like blades and crush bones. 
• Vertical Jaw Movement - So kaw can open widely and doesn't dislocate when a prey struggles in its grip.

• Lice are wingless insects that are unable to flyand their legs are poolt adapted to jumping and walking. They can only survive on their host. 
• Humans can be infected by body or hair lice. 
• Adult lice lay eggs which hatch after 1-2 weeks. 
• An egg hatches into a nymph which after a series of moults becomes an adult. The adults and nymph feed on blood which in the case of head live is sucked from the scalp of the hair. 

• Teeth are important in the mechanical digestion of food, Chewing increases the SA for enzymes to act on and also makes it easier to swallow food. Human teeth are unspecialised as they are omnivores but there are 4 main types of teeth

• Incisors - Biting and cutting food. 

• Canines- Tearing and ripping meat apart

• Molars and Premolars - Grinding and chewing food

• The diet is mostly of cellulose which is difficult to digest. Herbivore teeth are adapted for grinding to increase SA for the cellulose enzyme to work on. 

• Loose Jaws- Lower jaw moves side to side to produce circular grinding mechanism. 

• Horny Pad - Animal wraps tongue around grass and pulls across the horny pad on the upper jaw. 

• Incisors - Slice through the plant material.

• Diastema - Gap between the front teeth and cheek. Tongue moves cut grass to the large grinding surface of cheek teeth.

• Molars and Premolars- .Interlocking like M and W to grind food.

• Ruminants mainly eat grass and forage which contain a large amount of cellulose cell walls which they are unable to digest as they don't produce the cellulase enzyme.
• So they rely on mutualistic bacteria which live in the gut to secrete the cellulase. 
• The bacteria live in one of the chambers of the stomach called the rumen. 

• The grass is chewed, mixed with saliva and swallowed.
• The grass then passes to the rumen and is churned and mixed with bacteria that secrete cellulase to digest cellulose to glucose. The glucose is absorbed into the blood providing energy to the animal. 
• The bacteria produce waste co2 and methane which is released by the animal. 
• Any undigested grass is passed to the reticulum chamber and is formed into cud. The cud is regurgitated into the mouth for further chewing and is repeated several times. 
• The cud is then passed to the omasum where water is absorbed into the blood. 
• In the abomasum, bacteria are killed and digested, they provide an important source of protein to the animal. 

• In the rabbit, the caecum is enlarged to accommodate cellulose digesting bacteria. The bacteria are near the end of the gut so regurgitation is not possible. 
• Instead, refection occurs where the rabbit ingests faeces so that the material passes through the gut twice to increase the efficiency of digestion. 

• The carnivore gut is relatively short compared to the length of its body due to the diet being mainly protein which is easy to digest. 
• The gut of a herbivore is longer in relation to its body as its diet is high in cellulose which is much harder to digest.