When it comes to AS/A-level Biology, do you remember what is autotrophic and heterotrophic nutrition?

• Use external sources of energy (energy from sun or chemical reactions) in the synthesis of organic food materials.
• Autotrophs are the producers in the ecosystem.

(a) Photosynthetic autotrophs - obtain energy from suns radiation which is used to build essential organic compounds from inorganic molecules by the process of photosynthesis.

• They contain pigment, chlorophyll, to absorb light energy.
• E.g. algae, green plants

6CO2 + 6H2O → C6H12O6 + 6O2

(b) Chemosynthetic autotrophs - use energy from certain chemical reactions to synthesise organic molecules from inorganic molecules.

• E.g. nitrifying bacteria – Nitrosomonas and Nitrobacter

• Heterotrophs must be supplied with readymade organic compound from which to derive their energy.
• Heterotrophs are the consumers.

Types of heterotrophic nutrition

1. Holozoic nutrition
2. Saprobiontic nutrition - feed on dead material
3. Mutualistic nutrition - 2 or more organisms associated with each other. Both contribute and benefit from relationship.
4. Parasitic nutrition - feed on living host

• Characteristic of higher animals including humans.
• It involves feeding on organic matter from the bodies of other organisms.
• There are 5 stages to holozoic nutrition:

1. Ingestion - taking food into the mouth
2. Digestion - mechanical and chemical breakdown of food (chewing and mixing with enzymes)
3. Absorption - small, soluble molecules taken into the bloodstream
4. Assimilation - use of absorbed products
5. Egestion - getting rid of undigested parts of food

• Organisms feed on dead/ decayed matter.
• Do this by secreting enzymes to digest the material (lipase, protease, and carbohydrase etc.) and then absorbs nutrients from the digested organic matter.
• Digestion is classed as extracellular.
• Saprobionts have no digestive system of their own.
• E.g. Bacteria and fungi

For example,

Rhizopus Stolonifera

• Also known as pin mould.
• Found on bread.
• Immature stage - cotton-like structures.
• Mature stage - produces stalks with heads used to spread spores.
• Rhizoids- ‘roots’ penetrate organic matter and secretes digestive enzymes and absorbs nutrients. (Also known as rhizoid hyphae)
• Hyphae - ‘stalks’ of a mould or fungus. Joined by stolon.
• Sporangia - mature hyphae topped by spores.
• Aseptae - hyphae unjoined by cross walls
• Septae - hyphae joined by cross walls.
• Stolon - external hyphae connecting other hyphae.

In part 2, you will know more about mutualistic and parasitic nutrition.

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Drafted by Bonnie (Biology)