Quaestio: How do other
organisms obtain and process
nutrients?
Nunc Agenda:
Digestion and Absorption.

Nutrition includes ingestion, digestion and
absorption (in that order).

Ingestion: The process of taking-in food.

Digestion: The chemical process in which food
molecules are broken down into simpler, smaller
forms.

Absorption: The process of transporting
nutrients across the cell membrane.
More on Digestion.

Many times, digestion is preceded by the
mechanical breakdown of food.
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
Food is cut, crushed, or broken before any chemical
reaction takes place.
Mechanical Digestion: The process of
physically breaking down food


(increases surface area).
Mechanical breakdown of food increases the
surface area of the food particles

allows digestion to happen more quickly.
Digestion Happens in Stages.

The chemical breakdown of food occurs in
stages.


Large molecules are broken into progressively
smaller molecules that can eventually be absorbed.
Chemical Digestion: The process of breaking
big molecules into smaller ones.
Q: What kind of chemical process do you think this is?
A: Hydrolysis! Hydrolysis is the chemical breakdown
of bonds (through the addition of water). Hydrolytic
enzymes are involved.
Intracellular Vs. Extracellular
Digestion

Intracellular Digestion: takes place within the
cell environment.


Single-celled organisms perform intracellular
digestion on food vacuoles by using lysosomes.
Extracellular Digestion: takes place outside
the cell environment.

Many multicellular organisms carry out extracellular
digestion. Humans do as food passes through the
gastrointestinal system. (i.e. mouth, stomach, small
intestine). They then carry out intracellular digestion
once food molecules enter cells.
Digestion in Protists.

Protists have intracellular digestion.


(unicellular, eukaryotic organisms)
2 example organisms (protozoans):


1. Amoebas
2. Paramecia
The Ameba.

Amebas have pseudopods, or “false feet,”
that are used for locomotion and digestion.




These projections of the cell move and shift by
filling with cytoplasm.
they engulf food particles through phagocytosis.
The particle is enclosed in a food vacuole
Lysosomes fuse with the vacuole and digestive
enzymes break down the food.
Digestion taking place: note number of food vacuoles.
Amoeba proteus engulfing cells of Paramecium sp. by phagocytosis.
LM. [Robert Brons/BPS]
Paramecium Digestion.

Cilia: Tiny hairlike organelles at the surface of
the cell.


Ciliates (I.e. paramecia) are the most complex
protozoans. Their form of locomotion is considered
more evolved than that of the flagellates or
amoeboids.
Uses of cilia:
 Locomotion
 Nutrition

The cilia sweep food particles down the oral groove into the
organism’s gullet.
More on Paramecium Digestion.

When food collects at the end of the
paramecium’s gullet, the cell membrane bulges
inward and pinches off, forming a food vacuole.

As with the amoeba, a lysosome fuses with the
food vacuole. Digestion occurs within the food
vacuole when the lysosome’s enzymes enter it.

Indigestible material leaves the paramecium
through the anal pore.
Paramecium Movies

See Web Movies.

Watch Paramecium Locomotion
Watch Paramecium Up-Close (Cyclosis
and Oral Groove Cilia Action)

http://www.microscopyu.com/moviegallery/pondscum/paramecium/
The Hydra.

Hydras are coelenterates in the animal kingdom.
(Phylum = Cnidaria). Hydras are about five
millimeters long and live in fresh water.

They are in the same phylum as jellyfish and coral.

Hydras normally attach themselves to
underwater objects.

Hydras have a tubelike body with only one
opening: a mouth. The mouth leads to an
internal cavity.
The jellyfish Medusa (Phylum: Cnidaria, Class: Scyphozoa)
captures a shrimp (Phylum: Arthropoda, Subphylum: Crustacea).
Jellyfish are relatives of hydra.
The Real
Medusa
The Hydra

Hydras are only two
cell layers thick.
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Outer Layer:
Ectoderm.
Inner Layer:
Endoderm.
Forms a
gastrovascular cavity
The hydra’s namesake.
The green hydras we saw in our pond lab have a symbiotic
relationship with algae. The algae receive protection within
the body of the hydra while the hydra receives a food supply
(Algae are phototrophs). Algae contain the photosynthetic
pigment chlorophyll.
Chlorohydra viridissima
Hydra in Action.

See Web Movies.
http://www.microscopyu.com/moviegallery/pondscum/hydra/
Digestion in Hydra.

The tentacles bring food to the mouth

Digestion is intracellular and extracellular.

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Endoderm cells secrete enzymes into the
gastrovascular cavity(Extracellular digestion)
when dissolved, endoderm cells engulf food and
intracellular digestion takes place
Once broken down, food molecules diffuse quickly
across the cell layers of the hydra.
Key Idea: The Hydra has a two-way digestive
tract. The mouth is both an entrance for food and
an exit for wastes
Question


Compare digestion in the amoeba and
paramecium
How is digestion in the hydra similar to
protozoans?
The Earthworm.

Classification: phylum Annelida (the segmented
worms) in the Animal kingdom.

The earthworm, like the hydra, is multicellular.

Its body system is more complex than that of the
hydra.
Nutrition in the Earthworm.

Earthworm anatomy:

The earthworm consists of a “tube-within-atube” body design.
Outer tube: body wall.
 Inner tube: digestive system (aka the alimentary
canal).

Digestion in the Earthworm.

one-way digestive path.


Food enters through the mouth, proceeds
through the body, and leaves through the
anus.
Food is broken down mechanically and
chemically in the earthworm.
Advantages to One-Way
Digestion.

Can you think of some advantages the
earthworm’s form of digestion has over the
hydra’s form of digestion?
Advantages.

The earthworm doesn’t have outgoing
waste passing through the same opening
as its incoming food.

The earthworm can still eat while digestion
is taking place. The hydra can only ingest
food after digestion is completed.

Allows for specialization of different parts
of the digestive system.
What Does an Earthworm Eat?

An earthworm eats large quantities of soil,
as well as leaf litter and other decaying
plant matter.
Earthworms process the soil, obtaining nutrients from organic matter with it. [Richard
Humbert/BPS]
The Details.

Earthworm Digestive Anatomy.




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Mouth: Where food enters.
Pharynx: Pulls food into the mouth with a
sucking action.
Esophagus: pushes the food through to the
rest of the digestive tract through peristalsis.
Crop: temporarily stores food and gradually
releases it into the gizzard.
Gizzard: A thick-walled grinding organ that
crushes food (mechanical breakdown).
More Details.

Earthworm Digestive Anatomy.



Intestine: site of chemical digestion and
absorption of nutrients
Typhlosole: A fold in the intestinal wall that
increases the surface area for more
absorption to take place.
Anus: Where the undigested materials are
egested and the digested wastes are
excreted.
Earthworm Digestion Animation.

See Web Animation.
http://www.tvdsb.on.ca/westmin/science/snc2g1/wormdig.htm
The Grasshopper.

Grasshoppers are arthropods (kingdom
Animalia, phylum Arthropoda). They are
in the Insecta class.

What else is in the Arthropod phylum?

Arthropods are identified by their hard
exoskeleton (made of chitin!).
Nutrition in the Grasshopper.


Digestive Anatomy of the Grasshopper
Similar to the earthworm, with the addition of:


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Mouthparts (jaws): Adapted for chewing
Salivary Glands: Add saliva to food  enzymes
break down food.
Rectum: Water is absorbed here.
Broad-winged katydid, a herbivore, feeding. [Peter J. Bryant/BPS]

How is earthworm digestion similar to
grasshopper digestion? How are they
different?

Compare and contrast digestion in
unicellular and multicellular organisms.