Basics for Everyone – Ingestion absorption saprophytic or saprobic heterotrophic ingestive mode of nutrition , absorptive mode of nutrition, autotrophic digestion parasitic mixotrophic prokaryotic mesokaryotic eukaryotic

/ CELL: THE UNIT OF LIFE, pre-class / By Prof. Siddharth Sanghvi

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Nutritional Modes

Ingestive Mode of Nutrition

Process	Description
Ingestion:	This is the process by which an organism takes in external food particles into its body. There are two main ways this can happen:
Macrophagy:	The organism engulfs large food particles using specialized cell structures like pseudopods or phagocytosis. Examples include amoebas and white blood cells.
Pinocytosis:	The organism takes in fluids and dissolved solutes through infolding of its cell membrane. This is common in many single-celled organisms.

Digestive Mode of Nutrition

Process	Description
Digestion:	Once food is ingested, it needs to be broken down into smaller molecules that the organism can absorb and utilize. This is achieved through:
Mechanical Digestion:	Physical breakdown of food particles into smaller pieces using teeth, muscular contractions, or grinding structures.
Chemical Digestion:	Enzymes secreted by the organism break down complex food molecules into simpler forms like sugars, amino acids, and fatty acids.

Nutritional Categories

Nutritional Type	Description
Heterotrophic Nutrition:	Organisms that obtain their food from organic compounds produced by other organisms are called heterotrophs. They can be further classified based on their mode of obtaining organic material:
Ingestive Heterotrophs:	As discussed earlier, these organisms ingest whole food particles and then digest them internally. Examples include animals and many protists.
Absorptive Heterotrophs:	These heterotrophs absorb dissolved organic matter directly from their environment. Examples include fungi and some bacteria.
Autotrophic Nutrition:	Organisms that can synthesize their own food using inorganic compounds and an external energy source (like sunlight) are called autotrophs. The two main types are:
Photosynthesis:	Autotrophs like plants and some bacteria use sunlight to convert carbon dioxide and water into organic molecules (glucose) for energy.
Chemosynthesis:	Certain bacteria utilize the chemical energy from inorganic compounds (like hydrogen sulfide or methane) to synthesize organic molecules.

Other Nutritional Terms

Nutritional Type	Description
Saprophytic/Saprobic Nutrition:	Organisms that obtain nutrients from dead and decaying organic matter are called saprobes or saprophytes. Fungi and some bacteria are common examples.
Parasitic Nutrition:	Parasites obtain nutrients from living hosts by absorbing organic matter directly from the host’s body.
Mixotrophic Nutrition:	Some organisms can exhibit both autotrophic and heterotrophic modes of nutrition depending on the conditions. Euglena, a flagellate, is a classic example.

Cellular Organization

Cellular Type	Description
Prokaryotic:	Cells that lack a true nucleus and membrane-bound organelles are prokaryotic. Bacteria and Archaea are prokaryotes.
Mesokaryotic:	This term is not widely used in modern taxonomy. It was historically used to refer to some groups of organisms with a nuclear envelope but lacking some features of a true eukaryotic nucleus.
Eukaryotic:	Eukaryotic cells have a well-defined nucleus and membrane-bound organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum. Animals, plants, fungi, and protists are all eukaryotes.

Human Digestion Process

Human Digestion Process

Step	Description
Ingestion	This is where the journey begins! We take food into our mouth through our teeth.
Mechanical Digestion	Our teeth chew the food, breaking it down into smaller pieces. This increases the surface area of the food, making it easier for enzymes to work their magic.
Salivation	As we chew, salivary glands in our mouth release saliva. Saliva contains enzymes like amylase that begin to break down carbohydrates (starches and sugars) into simpler sugars. Saliva also moistens food, making it easier to swallow.
Swallowing	Once chewed and moistened, food is formed into a bolus (a soft mass) on the tongue. The tongue pushes the bolus to the back of the throat, triggering the swallowing reflex.
Esophagus	The bolus travels down a muscular tube called the esophagus through a series of wave-like contractions (peristalsis). There’s no digestion happening here, just movement.
Stomach	The bolus reaches the muscular sac-like stomach. Here, powerful muscles churn and mix the food with gastric juices, which contain strong acids and enzymes like pepsin. These enzymes further break down proteins into smaller peptides. The acidic environment also helps kill bacteria that might be present in the food. The churned mixture of food and gastric juices is called chyme.
Small Intestine	Chyme is slowly released from the stomach into the small intestine, which is the main site for nutrient absorption. The small intestine is further divided into three sections: duodenum, jejunum, and ileum.
Duodenum	The pancreas releases digestive enzymes like trypsin (breaks down proteins), chymotrypsin (breaks down proteins), lipase (breaks down fats), and amylase (further breaks down carbohydrates). The liver also releases bile, which helps break down fats into smaller droplets for easier absorption.
Jejunum and Ileum	The walls of these sections are lined with millions of tiny finger-like projections called villi. These villi increase the surface area for absorption. Nutrients broken down by enzymes and bile are absorbed through the villi walls and transported into the bloodstream.
Large Intestine	The remaining indigestible material, mostly water, fiber, and some waste products, moves into the large intestine. Here, water is absorbed back into the body.
Elimination	The remaining waste material is stored in the rectum until it’s eliminated through the anus in the form of feces.

Steps of Digestion and Assimilation

Stage	Details
1. Ingestion	Food is taken in, chewed, and mixed with saliva. Saliva contains amylase, which begins the breakdown of carbohydrates.
2. Mechanical Digestion	Chewing breaks food into smaller pieces in the mouth. Stomach churning further breaks down food into a semi-liquid form.
3. Chemical Digestion	Mouth: Salivary amylase begins carbohydrate digestion. Stomach: Pepsin starts protein digestion. Small Intestine: Pancreatic enzymes (lipase, amylase, proteases) and bile from the liver/gallbladder continue digestion. Intestinal enzymes (maltase, lactase, sucrase) further digest carbohydrates.
4. Absorption	Small Intestine: Nutrients (amino acids, glucose, fatty acids, vitamins, minerals) are absorbed through villi and microvilli into the bloodstream. Large Intestine: Water and electrolytes are absorbed, forming feces.
5. Assimilation	Assimilation: refers to the process by which living organisms integrate nutrients from food into their tissues. It involves the transformation of absorbed substances into the biological tissues and fluids necessary for growth, repair, and maintenance. This can include processes like the conversion of nutrients into proteins, fats, and carbohydrates within the body. Bloodstream: Nutrients are transported to cells throughout the body. Cells: Amino acids are used for protein synthesis, glucose for energy or storage, and fatty acids/glycerol for energy or storage.
6. Elimination	Large Intestine: Forms and expels feces. Rectum and Anus: Control the excretion of feces.

Osmotrophs vs Saprophytes

Aspect	Osmotrophs	Saprophytes
Definition	Organisms that absorb dissolved organic compounds through their cell membranes through Osmosis, which may involve secreting enzymes to break down complex substances into simpler, absorbable forms.	Organisms that feed on dead or decaying organic matter. Specifically target dead or decaying organic matter, secreting enzymes to decompose it and then absorbing the resulting simpler compounds.
Nutrient Acquisition	By osmosis of dissolved organic compounds.	By decomposing dead or decaying organic matter.
Examples	Many bacteria, fungi, and protists.	Many fungi (molds, mushrooms) and some bacteria.
Role in Ecosystem	Play roles in nutrient cycling and decomposition.	Critical decomposers that recycle nutrients.
Environment	Commonly found in environments rich in dissolved organic matter.	Found where dead or decaying organic matter is present.
Conclusion	Similarities :Both osmotrophs and saprophytes often secrete enzymes to break down complex organic materials into simpler compounds that can be absorbed.	Differences : Osmotrophs: Emphasis on the method of nutrient absorption (osmosis). Saprophytes: Emphasis on the source of nutrients (dead or decaying matter)