Phylum Platyhelminthes | Animal kingdom | Biology | Khan Academy

Summary

The transcript explores the characteristics and adaptations of platyhelminths (flatworms), with a focus on tapeworms. It explains their flat, dorso-ventrally flattened bodies, parasitic nature, and specialized features like hooks and suckers that help them cling to the walls of their host's small intestine. The video also covers the unique excretory system, involving flame cells for osmoregulation, and the hermaphroditic reproductive process. Additionally, it touches on the regenerative abilities of some flatworms, such as planaria, which can regenerate from broken body parts. The life cycle of tapeworms involves multiple hosts and larval stages, emphasizing their complex nature as parasites.

Takeaways

• 😀 Tapeworms belong to the phylum Platyhelminthes, which is known for its dorsoventrally flattened body structure.
• 😀 The term 'Platyhelminthes' comes from 'platy' meaning flat and 'helminth' meaning worm, describing their flattened body shape.
• 😀 Most Platyhelminthes are endoparasites, meaning they live inside the bodies of their hosts, like the tapeworm in the human small intestine.
• 😀 Tapeworms use specialized structures like hooks and suckers to cling to the intestinal wall and avoid being washed away by digestive movements.
• 😀 The suckers of tapeworms create a partial vacuum to hold them in place, providing an effective adaptation for parasitic life.
• 😀 Platyhelminthes have a unique excretory system that includes flame cells, which help with osmoregulation and excretion of nitrogenous wastes.
• 😀 Flame cells are named for their cilia, which move like flames, drawing in water and solutes and regulating the body's salt-water balance.
• 😀 Tapeworms are hermaphrodites, meaning they possess both male and female reproductive organs, allowing internal fertilization.
• 😀 After fertilization, tapeworm eggs are laid outside the body, and the species undergoes multiple larval stages in its life cycle.
• 😀 Some species in the Platyhelminthes phylum, like planaria, can regenerate: if cut into pieces, each piece can grow into a complete organism.

Q & A

What are the symptoms that Costa experienced before discovering he had a tapeworm?

Costa experienced abdominal pain, loss of appetite, upset stomach, nausea, weight loss, fatigue, and weakness.

What is the scientific classification of the tapeworm?

The tapeworm belongs to the phylum Platyhelminthes.

Why is the phylum called Platyhelminthes?

The name Platyhelminthes comes from the words 'platy' meaning flat and 'helminth' meaning worm. These worms are flat and are dorsoventrally flattened, meaning they are flattened from top to bottom.

What is meant by 'dorsoventrally flattened' in the context of Platyhelminthes?

'Dorsoventrally flattened' means that the body of the worm is flattened from the top (dorsal) to the bottom (ventral), which is a characteristic feature of this phylum.

Are all Platyhelminthes parasitic?

No, while many Platyhelminthes are parasitic, there are also free-living species like planaria that do not parasitize other organisms.

How does the tapeworm adhere to the wall of the small intestine?

The tapeworm uses hooks and suckers to cling to the wall of the small intestine. The hooks help it to hook onto the wall, and the suckers create a partial vacuum to prevent it from being washed away.

What is the function of the flame cell in the excretory system of Platyhelminthes?

The flame cell helps in osmoregulation and excretion. It regulates the salt-water balance by drawing in water and solutes and excreting excess water or salt. It also helps in removing nitrogenous waste.

What does osmoregulation mean?

Osmoregulation refers to the regulation of the osmotic pressure, which is the concentration of solutes in water. It involves maintaining the balance of salt and water in the body.

How does reproduction occur in Platyhelminthes?

Platyhelminthes are hermaphrodites, meaning each individual has both male and female reproductive organs. Fertilization occurs internally, and the fertilized eggs are laid outside the body. The animals also undergo one or more larval stages during their life cycle.

Why do Platyhelminthes like tapeworms go through multiple larval stages?

Tapeworms and similar Platyhelminthes often require more than one host during their life cycle. This is why they have multiple larval stages to adapt to the different environments and hosts they inhabit, such as both pigs and humans in the case of the tapeworm.