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.