Page 192 - Big Ideas Year 9 sciPAD 2025

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192 SCIPAD - BIG IDEAS - BOOK 1
LIFE OF ANIMALS
Herbivore Digestive Systems
Animals that rely on plants for nutrition are called herbivores. Plant material is high in cellulose -
a tough fibrous molecule that is very hard to digest. Cellulose cannot be digested without the
enzyme cellulase. Some micro-organisms are able to produce this enzyme, but mammals cannot.
This means that in order to digest cellulose, herbivores need to hold large communities of micro-
organisms in their gut. Because of this, herbivores can often have several stomach chambers and
a much longer digestive tract. Herbivores with multiple stomach chambers - such as camels, deer,
sheep, giraffes and cattle — are called ruminants.
The Four-Chambered Stomach of a Ruminant
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3
4
Abomasum
Enzymes and acids are secreted to
further digest nutrients.
Reticulum
Partially digested material from the
rumen is regurgitated into the mouth
for further chewing.
Rumen
A very large, elastic sac containing
billions of microorganisms that
begin to digest cellulose.
Mouth
Plant material is cut by the action of
incisors and quickly swallowed. Upon
regurgitation, the food is thoroughly
chewed with the large, flat molars.
Omasum
Water and some nutrients
begin to be absorbed.
1. Describe why plant material is hard to digest. 

2. Outline how the teeth of a ruminant are adapted for cutting grass (you might want to look
back at the page titled ‘Dentition’). 


3. (a) Name the enzyme that digests cellulose. 
(b) State how this enzyme is produced. 


4. Describe the key difference between the stomach of a ruminant and the stomach of a
human. 


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