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Intracellular and Extracellular Digestion, Study notes of Zoology

Both intracellular and extracellular digestion are ancient mechanisms of acquiring nutrients. Intracellular digestion is crucial at the cellular level (even in complicated organisms for excretion and protection), whereas extracellular digestion permits larger organisms to efficiently utilize a broader variety of food sources with specialized systems.

Typology: Study notes

2024/2025

Available from 05/07/2025

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Topic: Intracellular and Extracellular
Digestion
Introduction: What is Digestion?
food molecules into simpler, smaller
molecules that are absorbed and used by an
organism in order to gain energy, grow, and
There are two general strategies organisms
Digestion within
Digestion
outside cells, usually within special
Intracellular
Digestion of Substance in the Cytoplasm or
Special Organelles (e.g., Lysosomes) of a
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Topic: Intracellular and Extracellular

Digestion

Introduction: What is Digestion?

food molecules into simpler, smaller molecules that are absorbed and used by an organism in order to gain energy, grow, and There are two general strategies organisms Digestion within

Digestion

outside cells, usually within special

2. Intracellular Digestion: Intracellular

Digestion of Substance in the Cytoplasm or Special Organelles (e.g., Lysosomes) of a

Definition: Intracellular digestion of

substance in the cytoplasm or special

Intake: The food particles or large molecules

Phagocytosis:

solid particles (e.g., bacteria, waste food) into

Pinocytosis:

and dissolved solutes into very small vesicles known as pinosomes.

Fusion: The vesicle containing food

(phagosome) merges with a lysosome. Lysosomes are vesicles filled with very active

Digestion: These enzymes of resultant

phagolysosome (secondary lysosome), dismantle all these intricate protein particles,

Sponges (Porifera): Multicellular but a

simple animal where specialized cells (amoebocytes and choanocytes) carry out

Immune Cells: Immune cells such as

macrophages in multicellular animals (human beings) employ intracellular digestion to kill infecting microorganisms (viruses, bacteria)

Key Organelle: At the center is the

Lysosome. Most recent studies have continued to uncover lysosomal functionality, its connection to nutrient perception (e.g., through interactions of the mTOR pathway) and its correlation with disease processes

Weaknesses: Restricted by the size of the

particle the cell can engulf and the effectiveness of individual lysosomes. Ineffective for breaking down very large

Bacteria: The majority of bacteria spit

enzymes (exoenzymes) to break down complex organic material within their

Most Animals (including Humans):

Possess specialized digestive compartments (mouth, stomach, intestines). Food is broken down in these compartments (e.g., pepsin in stomach, amylase in saliva and intestine, lipase in intestine) before nutrient absorption

Benefits:

Permits organism to consume and digest food

Enzyme Location Inside lysosomes Secreted outside the cell Process Enzyme^ secretion Common In Protozoa, Sponges, Immune cells Fungi, Bacteria, Most Animals Both intracellular and extracellular digestion are ancient mechanisms of acquiring nutrients. Intracellular digestion is crucial at the cellular level (even in complicated organisms for excretion and protection), whereas extracellular digestion permits broader variety of food sources with specialized systems. Knowledge of these processes is important to understanding metabolism, cell biology, and organismal