In order to survive, organisms must maintain constant interior conditions in a changing environment

In order to survive, organisms must maintain constant interior conditions in a changing environment.

• The interior environment that cells must maintain includes:– Water volume– Salt concentration– Oxygen, carbon dioxide levels– Toxic metabolic waste levels– Essential nutrients

• Organisms must respond to their environment to avoid harm and to seek beneficial conditions

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• Organisms must reproduce to ensure survival of the species.

• Simple unicellular organisms like prokaryotes and protists have simple ways to meet their survival needs.

• Multicellular organisms have evolved more complex body plans that provide a variety of solutions to survival challenges that all organisms face.

• As multicellular organisms have evolved into larger more complex forms over time, their cells have become more removed from the external environment.

• These cells have become more specialized to one specific function.

• Specialized cells with a common function form tissues

• Different tissues come together to form large anatomical structures - organs.

• Organs are part of organ systems.

• Organ systems include– Reproductive– Digestion– Respiration– Circulatory

–Immune–Excretory–Endocrine–Nervous

• Intracellular using enzymes• Extracellular using enzymatic secretions in

gut cavities and then absorbed into cells in the lining of the gut

• The simplest example of digestion is that of a single celled organism.

• Protists utilize intracellular digestion. In Amoeba, pseudopods surround and engulf food through phagocytosis.

• Phagocytosis– Involves larger particles– Cell membrane expands around a particle– Lysosomes containing digestive enzymes break

down food.– Resulting molecules duffuse into cytosol– Undigestable particles are released from the

vacuoles.

• Pinocytosis– Another form of endocytosis– Smaller particles/liquids– Vesicle fuses with a lysosome

Pinocytosis/Phagocytosis

• In the paramecium, cilia sweep microscopic food such as yeast cells into its oral groove.

• A food vacuole forms around the particles and breaks off into the cytoplasm

• Waste is eliminated through an anal pore.

Paramecium

• Oral groove: cilia sweeps food in body like a mouth

• Gullet: encloses food like a stomach, forms a food vacuole

• Anal pore: opening where wastes are removed

• Trichocysts: structures used for defense



• Animals are multicellular heterotrophic organisms that must acquire energy from the consumption of food.

• Food must be digested and or absorbed to be used by cells.

• Mechanical - cutting & grinding in the mouth and churning in the stomach and small intestines. Molecular structure is unchanged

• Chemical - enzymatic hydrolysis of food particles (proteins, lipids, carbs, nucleic acids, minerals, vitamins like Niacin for NADH)

• Absorption - glucose, fatty acids, amino acids…)

DIGESTION IN EARTHWORMS

• Earthworms have a complete one way two-opening digestive tract.

• The digestive tract is a tube that moves food through in one direction.

DIGESTION IN EARTHWORMS



Digestion in Earthworms

• Mouth - beginning of the digestive tract. The earthworm takes in soil and organic matter

• Pharnyx - the mixture enters the pharnyx which which is the opening between segments 1-6 of the worm.

• Esophugus - is the passageway between the pharnyx and the crop.

Digestion in Earthworms

• Crop - stores food temporarily

• Gizzard - churns and grinds food

• Intestines - takes up 2/3 of the worms body. Digestion and absorption takes place

• Anus - Soil and indigestible matter leaves through the anus

Digestion in HumansDigestion of large food molecules is essential.

• large food molecules are usually polymers, such as polysaccharides, proteins and lipids, which are too large to be absorbed from the digestive tract into the circulatory system for transport because they are simply too large to move across the membranes of small intestine epithelial cells.

• after digestion, polysaccharides are broken down into monosaccharides, polypeptides are broken down into amino acids, and lipids are broken down into glycerol and fatty acid

• monomers, such as monosaccharides, amino acids, glycerol, and fatty acids are small enough to be absorbed by small intestine epithelial cells, moving these substances by either diffusion, facilitated diffusion, or active transport through membrane proteins

Enzymes are needed in digestion.

• at body temperature (37 ｡ C in mammals), reaction rates are too slow to be efficient at hydrolysis reactions of large food molecules

• hydrolytic reactions in the digestion of large food molecules, such as polysaccharides, proteins and lipids into their monomers, are exothermic, but occur very slowly due to considerable activation energy

• enzymes lower activation energy, catalyzing hydrolysis reactions of large food molecules into their monomers

Amylase, protease, and lipase are important enzymes in digestion

Enzyme amylase pepsin phospholipase

Source Salivary glands

stomach pancreas

Substrate starch proteins phospholipids

Products maltose polypeptide Glycerol phosphate, fa’s

Optimum

pH

7-8 2-3 8

Digestive System

A. MouthB. PharnyxC. EsophagusD. StomachE. Small IntestineF. Large IntestineG. RectumH. AnusI. Salivary glandsJ. LiverK. GallbladderL. pancreas

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Function of the Stomach;

• a large, expandable, muscular and glandular organ

• stores and mixes food, aiding in both physical and chemical digestion



Gastric Pits Secrete: a) HCl - producing a stomach pH of about 2, facilitating

pepsin activity, and killing foreign pathogens, such as bacteria

b) pepsinogen - converted to pepsin under acidic conditions

c) pepsin - catalyzes the hydrolysis of large proteins and polypeptides into smaller polypeptides

d) mucus - which protects stomach cells from acidic conditions

e) chyme - product of stomach digestion, an acid fluid released from stomach into small intestine via pyloric sphincter

Function of the small intestine:I. Digestion

a) pancreas releases bicarbonate = NaHCO3-, which neutralizes acidic chyme, producing a pH = 8

b) enzymes from pancreas, and small intestine epithelial cells hydrolyze large molecules into smaller molecules

c) polypeptides & oligopeptides digested into amino acids

d) polysaccharides & disaccharides digested into monosaccharides

e) triglycerides digested into fatty acids and glycerol

f) bile produced in liver, stored in gall bladder, released through pancreatic duct

h) emulsifying fat droplets into smaller particles on which pancreatic lipase can act more efficiently

II. Motility - by peristalsis: rhythmic contractions of circular and longitudinal smooth muscles lining small intestine slowly force chyme down intestinal tract

III. Absorption - lining of small intestine is folded, increasing surface area for absorption, and each fold is folded again into villi, with each villus acting as an absorptive unit.



Function of large intestine:a) Absorption of vitamin K produced by mutualistic

bacteria

b) Reabsorption of water, Na+, K+ from intestinal lumen to capillaries

c) Motility by peristalsis: rhythmic contractions of smooth muscles lining large intestine slowly force fecal matter down intestinal tract

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In order to survive, organisms must maintain constant interior conditions in a changing environment