IB Biology option d2

1. OPTION D
D.2 DIGESTION

4. • Digestive juices are only produced when they
are needed.
• For example, the gastric juice is only produced
when food is present in stomach.

5. • The sight or smell of food causes the brain
send nerve impulses via the vagus nerve from
the medulla.
• Impulses from the brain cause the production
of secretions from endocrine cells.
• Gastrin hormone is produced by dudodenum
cells.

6. • Gastrin stimulates the production of HCl and
pepsinogen by stomach cells.
• Secretin and somatostatin hormones inhibit
gastrin secretion.

7. • Exocrine glands secrets their components to
ducts. (mainly enzymes)
• Endocrine glands secrets their components to
blood stream. (mainly hormones)

8. Some juices from different glands
• Saliva video.

18. Answers

21. • https://www.
youtube.com/
watch?v=lnVj
XuyM6xk

28. • https://www.youtube.com/watch?v=jG1VNSC
sP5Q

30. ANSWERS
1. 50%;
2. digestible matter increases mean residence time; reduced fibre
reduces transit rate and extra water is reabsorbed in the colon;