Lesson 3 - Introduction to Digestion

Question 1

How does unicellular holozoan feed?

Answer 1

• Obtain nutrients such as O2 and glucose via diffusion, facilitated diffusion or active transport
• Large molecules/bacteria consumed via endocytosis
• Indigestible remains egested via exocytosis

Question 2

How is the hydra adapted for nutrition?

Answer 2

• Stinging cells on tentacles to paralyse prey
• Tentacles can grab and pull prey into body cavity where it is digested
• They only have one opening in their digestive system meaning food is both ingested and egested via the mouth

Question 3

Why must food be digested?

Answer 3

Because molecules are too large to pass through membranes so they must be broken down to monomers and be rebuilt (assimilated) into molecules needed by cells

Question 4

Describe the 4 main functions of the gut

Answer 4

• Ingestion - Passing food through the mouth
• Digestion - Breaking down of large food molecules until small enough to be absorbed by blood
• Absorption - Passage of soluble molecules and ions through the gut wall into the blood.
• Egestion - Elimination of indigestible waste e.g. cellulose (dietary fibre).
• Egestion -

Question 5

What is the gut?

Answer 5

Long, hollow and muscular tube which transports food through it in on direction via peristalsis

Question 6

What is peristalsis?

Answer 6

Wave of muscular contractions and relaxations of the gut wall to propel the contents along the whole length of the gut.