Parasites and mutualists

LO: To explain how the survival of one organism may depend on the

presence of another species through:

a)parasitism

b)mutualism

You have two minutes in pairs to write down what you think a parasite and a mutualist is.

Hink: For the mutualist think about the word mutual!

In most feeding relationships a predator kills and eats a prey and then moves on to find a more prey.

Parasites

Parasitism is a feeding relationship in which two organisms live together with one feeding off the other.

The organism doing the feeding is a parasite and the organism it feeds on is its host. Parasites usually harm their host but do not kill it.

Can you think why this is?

Headlice and fleas

Headlice and fleas are parasites. They bite other animals (hosts) such as humans so they can feed off their blood.

Tapeworms

Other parasites, such as the tapeworm, live inside their hosts. Tapeworms live inside vertebrate intestines. Their eggs leave the host in its faeces. Eggs swallowed by other animals hatch and grow inside their bodies.

Tapeworms absorb nutrients from the host’s gut which can cause the host to lose weight.

The worm can also grow large enough to block the host’s intestines.

Add the following point to your handout:

The scolex- head of the tapeworm

• The head has hooks and suckers to attach it to the small intestine wall.

• It has no eyes.

• The flat body gives it a large surface area for food absorption

• It has no circulatory system, intestines or much of a nervous system.

• The outside of the worm contain substances that stop it being digested by enzymes in the small intestine.

• Each segment contains male and female reproductive organs so the worm can self fertilise its eggs if other tapeworms are not nearby.

The world's longest parasite is the tapeworm so the next question is 'What is the world's longest tapeworm?'The longest tapeworm ever removed from a human came out of Sally Mae Wallace on September 05, 1991.In all, doctors pulled 37 feet of tapeworm out of Sally Mae Wallace's body through her mouth.If you find all of this disgusting, be glad you're not a whale as tapeworms in whales can grow up to 120 feet long.

European mistletoe

Believe it or not mistletoes is also a parasiste.

It has leaves that can photosynthesise but its roots grow into the veins of the host tree and absorb water and mineral salts.

Mutualists

Some organisms live in close relationships where both organisms benefit. This is called mutualism.

What do you think is happening here?

Oxpeckers

Oxpeckers have a mutualistic relationship with large herbivores in Africa.

Both the oxpecker and the herbivore benefit from the relationship. The oxpecker eats parasitic insects that live on the skin of the herbivore.

Cleaner fish

Cleaner fish eat dead skin and parasites from the skin of larger fish, such as sharks.

You could say a fish pedicure is a mutualistic behaviour!!- why?

Nitrogen –fixing bacteria

Some organisms live in mutualistic relationships inside other organisms.

Bacteria that turn nitrogen in the air into nitrogen compounds are called nitrogen-fixing bacteria. Some live inside the roots of legumes (plants like peas that produce pods).

What do the bacteria gain?

they are protected from the environment

They gain chemical substances from the plant they use as food.

What do the legumes gain?

It gets nitrogen compounds which it needs to grow well from the bacteria.

You may remember these from the work on deep sea volcanic vents in topic 1- what are they?

They are giant tubeworms.

Chemosynthetic bacteria

Chemosynthetic bacteria are producers that get their energy from chemical substances and not from light.

There are chemosynthetic bacteria inside giant tube worms.

The tubeworms gather the chemical substances that the bacteria need for chemosynthesis.

The tubeworms feed on

substances made by the bacteria.

Questions1. In the human-headlouse feeding relationship,

name

i) the parasite

ii) the host

2. Explain fully the difference between parasitic relationships and mutualistic relationships.

3. The tubeworm-bacteria relationship is mutualistic. Explain why each organism needs the other.

4. With the mutualistic relationship of the nitrogen-fixing bacteria and the legume what do both organisms gain?

Plenary

‘What am I?’ game!

Write down on your mini whiteboard what the

description is describing

I am an organism that feeds off

another

I am a parasite!

I am the organism that the parasite

feed off

I am the host!

I am the worm that absorbs nutrients from

my host’s intestine

I am a tapeworm

I am the parasite that takes blood from it’s

host

I am a flea or headlouse

I am the relationship where both

organisms benefit

I am mutualism

I am the bacteria that helps legumes

to gain nitrates

I am nitrogen-fixing bacteria

I am the bacteria in tubeworms that allow

them feed on substances I make

I am chemosynthetic

bacteria