Nutrition and Food Processing in Animals and Plants

• In less complex animals, digestion is simple due to the absence of a digestive tube with accessory glands
• In cnidarians, like hydras which have a gastrovascular cavity, extracellular digestion occurs throughout the cavity

  • They have a single opening that acts as a mouth and anus
• The most primitive type of gut or digestive tract is found in nematodes
• Parasitic roundworms like pinworms (Enterobius vermicularis) and Ascaris lumbricoides (Giant roundworm) feed on the nutrients from the host’s partially digested food. The food passes through the esophagus into the intestine, where it is further digested by enzymes secreted by the worm. Nutrients are absorbed through the intestine's lining and utilized by the worm for energy, growth, and reproduction
• Some parasitic roundworms like hookworms (Ancylostoma duodenale and Necator americanus) feed on blood sucked from the host through their hooks.
• Pathway of Food

  Food is ingested through the mouth, chewed/ground into smaller pieces with the help of the teeth, mixed with saliva, and pushed backwards by the tongue->bolus is swallowed and moved to the oropharynx (meanwhile, the epiglottis closes)->from the oropharynx (the portion of the pharynx situated behind the oral cavity), the bolus now enters the esophagus and passes down by peristalsis->cardiac sphincter->the stomach holds the food for about 3 to 4 hours to mix it with gastric juices and digestive enzymes->pyloric sphincter->
• Pathway of Food (cont.)

  then, the chyme enters the duodenum where various enzymes completely breakdown the carbs, proteins, and fats->the food molecules are now small enough to be absorbed by the jejunum and ileum->undigested food is channeled into the large intestine or colon where water and ions are reabsorbed and the bulk that remains is now called stool->stool is stored for a while in the rectum until movements into the anus occur and the defecation reflex is initiated (this involves the relaxation of the internal and external anal sphincters)->stool exits through the anus
• In the stomach, pH is maintained at a very acidic level (pH 1 to 2) by hydrochloric acid.
• Enzymes And Secretions

  1. Salivary amylase, oral cavity
  2. Lingual lipase, oral cavity
  3. Hydrochloric acid (HCl), stomach
  4. Pepsinogen, stomach
  5. Pepsin, stomach
  6. Intrinsic factor (a protein), stomach
  7. Trypsinogen, small intestine, duodenum (produced by the pancreas)
  8. Trypsin, small intestine, duodenum (produced by the pancreas)
  9. Chymotrypsinogen (produced by the pancreas)
  10. Pancreatic lipase (produced by the pancreas)
  11. Nucleases (produced by the pancreas)
  12. Pancreatic amylase (produced by the pancreas)
  13. Sucrase
  14. Lactase
  15. Maltase
• Salivary amylase

  • Initiates carb breakdown
• Lingual lipase, oral cavity

  Starts fat digestion
• Hydrochloric acid (HCl), stomach

  • Secreted by parietal cells
• Pepsinogen, stomach

  • Secreted by chief cells, transformed by HCl into its active form
• Pepsin, stomach

  • Active form of pepsinogen
• Intrinsic factor (a protein), stomach

  • Secreted by parietal cells, protects vitamin B12 from digestion
• Trypsinogen, small intestine, duodenum (produced by the pancreas)

  • Converted by enterokinase to its active form
• Trypsin, small intestine, duodenum (produced by the pancreas)

  • Breaks down proteins into amino acids
• Chymotrypsinogen (produced by the pancreas)

  •  Breaks down proteins into their aromatic amino acids
• Pancreatic lipase (produced by the pancreas)

  • Breaks down triglycerides into fatty acids and glycerol
• Nucleases (produced by the pancreas)

  • Breaks down nucleic acids into nucleotides
• Pancreatic amylase (produced by the pancreas)

  • Breaks down starch, glycogen, and most carbs except cellulose into monosaccharides
• Sucrase, Lactase and Maltase

  Brush border” enzymes (secreted and found along the entire lining of the small intestine) break down disaccharides
• The Accessory Glands

  • Liver
  • Gallbladder
  • Pancreas
• Liver

  • Consists of only 4 major cells: hepatocytes (main functional cells of the liver), hepatic stellate cells, Kupffer cells, and sinusoidal endothelial cells
  • Consists of four lobes: right, left, quadrate, and caudate
  • Blood circulates through the liver by the portal vein and the hepatic vein
  • Neutralizes and eliminates toxic substances from the blood
  • Stores vitamins, iron, and glucose
• Liver (cont.)

  • Synthesizes proteins such as albumin and fibrinogen (form blood clots)
  • Coverts highly toxic ammonia (accumulates during protein breakdown) into urea, a more tolerable form
  • Produces bile, a fluid that contains cholesterol, bile acids, and bilirubin which aid in lipid digestion (Stored in the gall bladder)
• Gallbladder (cont.)

  Bile may flow into the gall bladder via the cystic duct to be stored, concentrated, and used later, OR it may go directly into the CBD, to the ampulla of Vater, and then to the duodenum. It is through the cystic duct that bile enters and exits the gall bladder.
• Gallbladder

  The pathway of bile or the biliary tree:

  Canaliculi in the liver merge to form bile ducts or intrahepatic ducts->the bile ducts drain into the right and left hepatic ducts->the right and left HDs then merge to form the common hepatic duct->the CHD and the cystic duct (of the gall bladder) join to form the common bile duct (CBD)->the CBD and the pancreatic duct (from the pancreas) or the duct of wirsung then merge to form the ampulla of vater, which finally drains into the duodenum
• Pancreas

  • Both an endocrine and an exocrine gland
  • An endocrine gland secretes directly into the blood, while an exocrine gland releases secretions through ducts that lead to the outside of the body or into a body cavity
  • The islets of Langerhans are responsible for the secretion of insulin (lowers blood sugar/glucose levels) and glucagon (raises sugar/glucose levels), which is an endocrine function
  • For its exocrine functions, digestive enzymes such as trypsinogen, chymotrypsinogen, and carboxypeptidase are secreted into the duodenum by the pancreatic duct and the ampulla of vater
• What nutrients are obtained from the soil?

  • Soil is a mixture of many ingredients which may include organic compost, minerals, water, air, and microorganisms
  • Mineral composition varies depending on the composition of the preexisting/parent rocks
  • Microorganisms are very important in recycling nutrients
• Macro and Micronutrients

  • Macronutrients are molecules that plants need in relatively large amounts
  • Essential macros are C, H, O, N, K, Ca, Mg, P, and S
  • Micronutrients are those required in relatively small quantities
  • The micronutrients are Cl, Fe, Mn, B, Zn, Mo, and Cu
  • A deficiency in any of these micros can generate severe effects on plant growth and development
• Photosynthesis

  • The essential nutrients are indispensable in the life of plants and in the process of photosynthesis
  • Magnesium for example, is a micronutrient that serves as a component of the chlorophyll pigment, which if deficient may lead to chlorosis (a condition in which leaves produce insufficient chlorophyll)
• The Light-Dependent Reactions

  • The first phase of photosynthesis, occurs in the thylakoid membrane
  • Water is split into hydrogen ions and oxygen
  • There are two rxn centers: photosystem (PS) II and PS I
  • When chlorophyll absorbs a photon (the particle of light energy), one of the electrons in chlorophyll is boosted to a higher energy level where it becomes reactive or unstable
  • The energy is converted to ATP and an electron carrier called NADPH
  • Each photosystem has only one chlorophyll a, hundreds of chlorophyll b, and carotenoids that help collect light energy
• The Light-Independent Rxns (AKA the Calvin Cycle)

  • The products of light-dependent rxns, ATP and NADPH, are used in this phase
  • CO2 is reduced to glucose through redox reactions
  • These reactions occur in the stroma, the fluid-filled part of a chloroplast, outside of the thylakoid membrane
  • Note: plant cells also utilize the sugar from photosynthesis by carrying out cellular respiration
• Light-Dependent Reactions (vs Calvin)

  • Requires sunlight
  • Thylakoid membranes within chloroplasts
  • Capture light energy and convert it into chemical energy (ATP & NADPH)
  • Water & Sunlight
  • ATP, NADPH, & Oxygen (O2)
• Calvin Cycle (vs Light-Dependent Reactions)

  • Does not require sunlight (can occur in the dark or at night)
  • Stroma within chloroplasts
  • Uses ATP & NADPH from light-dependent reactions to fix carbon dioxide and build sugars
  • Carbon dioxide (CO2), ATP & NADPH
  • Glucose (and other sugars)
• Special Nutritional Strategies of Plants

  • Some bacteria live symbiotically with the roots of plants by helping the plants fix nitrogen
  • These bacteria, called Rhizobium, move into the cortex of the root and take control of cell division in the cortex and the pericycle cells
  • The bacteria change shape and are transformed into bacteroids.
  • They produce nitrogenase enzymes and fix atmospheric nitrogen into usable forms that plants can use
• • Mycorrhizal fungi are found in nearly 90% of vascular plants
  • These fungi play an important role in the transfer of phosphorus and in the uptake of some micronutrients
  • These fungi also increase the surface area of roots available for nutrient uptake
• There are also carnivorous plants that grow in nitrogen-poor soils

  • By catching insects and small animals, they obtain and adequate supply of nitrogen
  • Many species of plants tap the resources of other plants by growing close with the host plant
  • These parasitic plants siphon the nutrients through the sap of their host
• A bile canaliculus (plural: canaliculi; also called bile capillaries) is a thin tube that collects bile secreted by hepatocytes.
• Mycorrhizal fungi are found in nearly 90% of vascular plants

  These fungi play an important role in the transfer of phosphorus and in the uptake of some micronutrients

  These fungi also increase the surface area of roots available for nutrient uptake