• Two organisms in close association.
• Both contribute to and benefit from relationship.

For example,

Rhizobium and Papilionaceae

• Rhizobium – nitrogen fixing bacteria
• Papilionaceae – a flowering plant, leguminous
• Nitrogen fixation
  - Requires anaerobic conditions
  - Catalysed by enzyme nitrogenise
  - Uses energy in the form of ATP

Relationship

• Roots of Papilionaceae release hormones.
• Hormones attract Rhizobium.
• Rhizobium penetrates roots.
• Moves to cortex of root.
• Stimulates production of plant hormones such as auxin.
• Causes nodule of tissuse to from (composed of large amounts of Rhizobium).
• Rhizobium in nodule become Y-shaped (now called bacteroids).
• Leghaemoglobin surrounds bacteroids and absorbs any oxygen present.
• Provides anaerobic conditions needed for nitrogen fixation.

Benefits of relationship

• Rhizobium obtains supplies of carbohydrate from photosynthetic activity of Papilionaceae.
• Papilionaceae receive supply of ammonia from Rhizobium (process of nitrogen fixation) allows it to grow in nitrogen deficient soil.

• A parasite is an organism which lives in close association with another living organism, the host.
• The parasite is dependent upon the host for food and can cause the host harm.
• Endoparasites live inside their host while Ectoparasites live on the outside of their host.

For example,

Taenia Solium

• Pork tapeworm
• Endoparasite
• Primary host - man - adult stage attached to wall of small intestine.
• Secondary host - pig - larvae develop in muscular tissue of a pig.

Adaptations

• No mouth or alimentary canal.
• It absorbs digested food of host from all over body.
• It has tegument, thick outer covering made of protein and chitin to protect from acidic condition and action of digestive enzymes.
• It can live in low oxygen concentrations.
• It reduced nervous system and lack of sense organs.
• It produces large amounts of offspring
• It has suckers and hooks to attach to gut wall of host (scolex-head).
• Proglittides containing self fertilised eggs are excreted from host body in faeces and can be taken in by pigs.

Damage to humans

• Very little effect on healthy hosts except deprivation of food.
• In unhealthy hosts can causes abdominal pain, vomiting, constipation, loss of appetite and may become less resistant to other diseases.

• Upper incisors replaced by horny pad.
• Sideways movement of jaw allows grass to be cut by lower incisors and canines against horny pad.
• Roots of teeth open so can grow continually.
• Diastema, toothless gap between incisors and premolars for forming bolus.
• Premolars and molars all same height and flat allowing sideways movement of jaw.

Digestive System

• Four chambered stomach
  - Grass fermented in rumen and reticulum by bacteria
  - Food is regurgitated and rechewed- rumination
  - Passes onto omasum and the abomasums

• Large pointed canine teeth which enables them to pierce the skin of and kill their prey.
• Their incisors are small that that of a ruminant and are used for nibbling meat of the bone.
• Their molars and premolars are sharp and act like scissor blades.
• Their jaws move up and down and not side to side they bite, cut and swallow food quickly so that another animal does not take it.
• They have carnassials teeth adapted for slicing.
• They have sharp hearing and eyesight and are fast and agile allowing them to hunt effectively for food.

That's the end of the topic!

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