5 Obtaining energy and
nutrients for life
• Heterotrophs include all animals, all fungi and
some bacteria.
• Autotrophs — all plants, algae and some bacteria
— differ from heterotrophs in being able to make
their own organic material from simple inorganic
substances, typically using the energy of sunlight.
• Food for a heterotroph is any organic matter that
it can obtain, break down and use as a source of
energy and organic matter.
• Photosynthesis is the process of converting
the energy of sunlight to chemical energy in
sugars.
• The raw materials of photosynthesis are
carbon dioxide and water, and the products
are sugar and oxygen.
• In plants and algae, photosynthesis occurs in
chloroplasts.
• The structures of the various parts of a plant
maximise the plant’s ability to obtain the raw
materials necessary for photosynthesis.
Plant structures in relation to photosynthesis
Food for heterotrophs
• In Australia over the last 60 years, the
consumption of different foods has changed.
• Food contains large molecules that must be
broken down into smaller parts before it can
be used by animals.
• The digestion of food involves mechanical
breakdown by structures such as teeth into
smaller pieces.
• The digestion of food also involves secretion
of enzymes that break down molecules into
smaller molecules for absorption.
The
digestive
system
The stomach & small intestine
Digestion between species
Accessing energy in organic
compounds
When you see the term ‘respiration’,
remember that it may refer to the
process of cellular respiration, but
it may also refer to the process
of breathing by a terrestrial
vertebrate.
What are the ‘inputs’ of cellular
respiration? What are the
‘outputs’?
The energy required to drive the
reactions in cells comes from ATP.
• Specialised parts of the digestive system vary in
different animals.
• Foregut-fermenters (herbivores) have very large
and complex stomachs.
• Herbivores that are hindgut-fermenters have
large caecums.
• Nectar eaters have relatively short, simple
digestive systems.
• Carnivores have relatively short alimentary canals
compared with those of herbivores.
• Chemical energy stored in organic matter is
converted to ATP by cellular respiration.