UNIT

2 The nutrition function

Natural Science 2. Secondary Education

DIGESTION IN DIFFERENT ANIMALS

UNIT

2 Digestion in different animals

DIGESTION

ANIMALS WITH NO DIGESTIVE

SYSTEM

ANIMALS WITH A DIGESTIVE

SYSTEM

WITH GASTROVASCULAR CAVITIES

RUMINANTSSNAILSClick on each box to find out more

BIRDS

like

WITH DIGESTIVE TRACTS

Natural Science 2. Secondary Education

• Digestion is the process by which animals transform food into smaller components to obtain nutrients from it.

What is digestion?

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2 Digestion in different animals

Natural Science. Secondary Education, Year 2Natural Science 2. Secondary Education

• Sponges do not have a digestive system.• They absorb water through their pores.• Inside their bodies, specialised cells catch the food particles in the water, and digest them in the cytoplasm.

Animals with no digestive system

How watermoves througha sponge

A cell specialised to catch nutrients from the water

UNIT

2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education

• In almost all animals (with the exception of sponges), digestion is carried out by a digestive system.• It is separated into three stages:

• Food is crushed by mechanical means. The molecules of nutrients are broken down through chemical processes.• Nutrients are absorbed and carried to the cells.• The materials that cannot be used are eliminated.

Animals with digestive systems

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2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education

• Cnidarians and platyhelminthes. • Their gastrovascular cavities are bag-shaped and are sometimes branched.• They have only one opening, which is used both to ingest food and to eliminate waste. • Digestion takes place inside the cavity. The cells lining the cavity walls absorb nutrients.

Animals with gastrovascular cavities

Gastrovascular cavity

Opening

The gastrovascularcavity of a jellyfish

UNIT

2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education

• A digestive tract is a long tube with an opening for food to go in (mouth) and another opening for indigestible material to go out (anus).• The simplest digestive tracts, like those found in annelids, have parts that specialise in grinding food, but they do not have digestive glands.

Animals with digestive tracts

The digestive tractof an annelid

Anus

Mouth

Gizzard (this grinds up food)

UNIT

2 Digestion in different animals

Natural Science 2. Secondary Education

• The most complex digestive tracts, like those found in molluscs, arthropods and vertebrates, have specialised parts and digestive glands that produce substances which break down the molecules of nutrients.

The digestive tractof a ruminantMouth

Oesophagus

Stomach:Ru: rumenRe: reticulumO: omasumA: abomasum

Small intestine

Largeintestine

Anus

Digestiveglands:PancreasLiver

RuRe O

A

Animals with digestive tracts

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2 Digestion in different animals

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Natural Science 2. Secondary Education

1) Digestion begins with the snail ingesting food with a sort of toothed tongue called the radula.

2) Food then passes to the mouth, where it mixes with saliva.3) The short oesophagus transports the food to the stomach. Although the

salivary glands surround the stomach, the saliva is released in the mouth.4) From the stomach, food passes to the spiral-shaped intestine, and is

expelled through the anus which is surprisingly close to the snail’s head.

Digestion in a snail

Anus

Salivaryglands

Stomach

IntestineMouth

Radula

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2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education

1) The animal ingests food without chewing and it passes to the rumen.2) Inside the rumen, microorganisms begin to digest the food.3) Parts of the food get sent back to the animal’s mouth to be chewed. This

is calling chewing cud, or ruminating.4) The chewed food is swallowed again, but this time it passes to the

reticulum, the omasum and the abomasum, where digestion is completed.5) The food passes to the intestine, where nutrients are absorbed and

faeces is formed.

Digestion in a ruminant

1

2

3

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2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education

Digestion in a bird

Crop

Gizzard

Cloaca

Proventriculus

1) Food passes from the mouth to the oesophagus, where there is a pouch called a crop. This is where food is moistened and softened to facilitate digestion. Sometimes birds regurgitate this softened food for their young.

2) Food then passes to the stomach, which is made up of a proventriculus, which separates digestive fluids, and a gizzard, which has a very muscular wall to finish grinding the food.

3) From there, the food goes to the intestine, where it is mixed with fluids in the liver and the pancreas.

4) The intestine ends in the cloaca.

UNIT

2 Digestion in different animals

Go back to the Start menuNatural Science 2. Secondary Education