Phylum Platyhelminthes

Question 1

Symmetry;

This animal displays bilateral symmetry, what is this?

Answer 1

The body can be divided into two equal
halves on each side of a central axis (one
side of the animal is a mirror image of the
other, there are left and right sides).

Question 2

Symmetry;

How does bilateral symmetry benefit?

Answer 2

• The animals have a ‘front’ where the sensory receptors are concentrated,
  allowing the animal to test the new environment they are entering.

Question 3

How does bilateral symmetry help movement?

Answer 3

• The streamlined bilaterally symmetrical shape makes movement much easier
  compared to the radial symmetry of the cnidarians.

Question 4

Support;

If the flatworm lives in water, support can come from the aqueous medium.

Where else can they get support?

Answer 4

All flatworms get support from the additional tissue that fills the space between the
outer surface and the gut.

Question 5

Dorso-ventral flattening;

Having this additional tissue means ____, so there is a higher demand for oxygen and glucose.

What does dorso-ventral flattening achieve?

Answer 5

‘many more cells are involved in metabolic activity’.

The dorso-ventral flattening increases the surface area to volume ratio.

Question 6

Dorso-ventral flattening;

What are 2 advantages of this?

Answer 6

1. Increases the uptake of oxygen (due to the high SA:V ratio)
2. Decreases the diffusion distance for oxygen from the body surface to the
   body cells

Question 7

Gut/feeding;

Have a single opening to the gut, meaning ____

Have a branched gut to faciliate ____ (no circulatory system).

Answer 7

‘the undigested remains of food
are passed out through the same body opening it enters.’.

‘distribution of products of digestion to all cells’.

Question 8

Gut/feeding;

Digestion is ____, with soluble products absorbed into the cytoplasm.

Answer 8

‘both extracellular in the gut cavity and intracellular’.