Modes of Nutrition

What is nutrition?

The process by which organisms obtain energy to maintain life functions and matter to create and maintain structure.

What are the 2 main types of nutrition?

• Autotrophic.

• Heterotrophic.

What is autotrophic nutrition?

Synthesise of complex organic compounds from simple inorganic molecules using an energy source.

Give examples of simple inorganic molecules.

• Carbon dioxide

• Water

Give an example of an autotrophic organism.

Plants are autotrophic.

Photosynthesis is a process which takes place in the chloroplasts of green plants and algae.

Simple inorganic compounds (water and carbon dioxide) form complex organic compounds such as glucose and starch.

What is photoautotrophism?

Uses light energy to combine simple inorganic molecules into complex organic compounds.

What is chemoautotrophism?

Uses chemical energy, from chemicals such as hydrogen sulphide, to combine simple inorganic molecules into complex organic compounds.

What is heterotrophic nutrition?

Cannot synthesise its own complex organic compounds:

It must digest organic chemicals produced by other organisms and use the products of digestion to synthesise their own organic chemicals.

State the types of heterotrophic nutrition.

• Holozoic

• Saprobiant

• Parasites

• Symbiosis / mutualism

What is a saprobiant?

Feed on dead or decaying matter by secreting enzymes extracellularly; the products of digestion are then absorbed.

What does extracellular mean?

Outside the cell.

What is holozoic nutrition?

Absorption of organic matter followed by internal digestion of the organic chemicals within the organism.

This form of nutrition is used by most animals and they have a specialised digestive system.

What is a parasite?

Lives in or on another living organism, obtains nourishment from the host and causes harm to the host.

The host usually derives no benefit.

What are ectoparasites and endoparasites?

Ectoparasites live on the outside of a host organism.

Endoparasites live inside a host organism.

What is mutualism / symbiosis?

When organisms live in / on other organisms in a relationship that provides benefit to both organisms.

How do unicellular organisms such as amoeba get their nutrition?

• Unicellular organisms, such as amoeba, have no gut.

Amoeba senses the food → Pseudopodia surrounds the food → Food is enclosed in a food vacuole → Enzymes from the lysosomes are secreted into the food vacuole → Food is digested and soluble materials are absorbed and up → Undigested material is expelled via exocytosis.

How does Hydra gain its nutrition?

• Has a simple, sac-like gut.

• There is a single opening to the external environment.

• Digestive enzymes are secreted into the lumen of the gut; digested food is absorbed by the gut wall.

• Undigested food is egested via the mouth.

How does an earthworm get its nutrition?

• Earthworms have a tube-like gut with an opening at both ends; a mouth for ingestion and an anus for egestion.

• The gut has different regions e.g. an oesophagus, and intestine, each with a specific function.

Why is the tube-like gut of an earthworm more efficient for digestion than the sac-like gut of a hydra?

Different regions of the gut are adapted for different functions:

• mechanical digestion by teeth, muscular action

• chemical digestion by acids

• chemical digestion by enzymes with different optimum pH.

This type of gut increases the efficiency of digestion and also enables an organism to eat and digest a wider range of foods.