9-2: Why and How We Eat

Question 1

feeding mechanisms in animals

Answer 1

• suspension feeder
• substrate feeders
• fluid feeders
• bulk feeders

Question 2

suspension feeders

Answer 2

sift small food particles from the water (humpback whale, clams, oysters, etc.)

Question 3

substrate feeders

Answer 3

live in or on their food source (caterpillars, moth larvae, fly larvae, termites, etc.)

Question 4

fluid feeders

Answer 4

suck nutrient-rich fluid from a living host (mosquitoes, aphids, bees, hummingbirds, etc.).

Question 5

bulk feeders

Answer 5

eat large pieces of food, and have many adaptations

to kill their prey (majority of animals).

Question 6

digestive systems

Answer 6

• No specialized digestive systems (sponges)
• Gastrovascular cavity with just one opening (cnidarians)
• Alimentary canal with two openings (animals with more complex body plans)
• Digestion in animal bodies within these systems can occur in the
following ways:
-Intracellular digestion
-Extracellular digestion
- Combination of intra and extracellular digestion

Question 7

Intracellular digestion

Answer 7

-occurs within individual cells inside vacuoles
-brings the whole food
particles inside the cell by
phagocytosis.
-Animals that perform
intracellular digestion are
sponges (sedentary feeders
with no specialized digestive
system

Question 8

Extra/intracellular digestion in gastrovascular cavity

Answer 8

-Gastrovascular cavity is a chamber within the
body, which has only one opening.
-It is found in cnidarians (jellyfish, hydra, sea anemones)
-Even though digestion begins extracellularly
in gastrovascular cavity by enzymes secreted
from the gland cells, it is the nutritive cells
that engulf these food particles, so most of
the hydrolysis of macromolecules occurs
intracellularly.
• The undigested remains are eventually
expelled through the same opening by which
the food entered.

Question 9

Extracellular digestion in alimentary canals

Answer 9

-more complex body plan have a digestive tube with two openings, which allows animals to feed more frequently.
- mechanical grinding of food into smaller pieces, and
• chemical breakdown, until food is small enough for absorption, which mostly
occurs in intestine.
• Digestion in alimentary canals is extracellular (enzymes break the food into small
molecules outside of cells, and then they pass the cell membranes)

Question 10

Stages of food processing in alimentary canals

Answer 10

• Ingestion: the act of eating
• Digestion: the process of
breaking food down into soluble
molecules - small enough to
absorb
• Absorption: uptake of nutrients
by body cells
• Elimination: the passage of
undigested material out of the
digestive compartment

Question 11

Liver Functions

Answer 11

1. Regulates distribution of
   nutrients to the rest of the body
2. Detoxifies substances before they spread widely

Question 12

Lipids

Answer 12

• lipids go into the lymphatic system first. The main
  reason is that, even after being digested into smaller components by the lipase in the small intestine, they are still too big to enter the capillaries. So they enter the lymphatic system before they are carried to the capillaries
  -note that this lymphatic system is within the small intestine
  itself (lymphatic vessels called lacteals are found at the core of each villus)

Question 13

mouth

Answer 13

Mechanical and chemical processing

Question 14

pharynx + esophogus

Answer 14

Food transport

Question 15

stomach

Answer 15

Mechanical and chemical processing

Question 16

small intestine

Answer 16

Chemical processing and absorption

Question 17

large intestine

Answer 17

Absorption of water and compressing undigested material

and bacteria into feces

Question 18

rectum

Answer 18

holding feces

Question 19

anus

Answer 19

eliminating feces

Question 20

salivary glands

Answer 20

secretes enzymes, lubricates

Question 21

liver

Answer 21

secretes bile salts, detoxifies digested food

Question 22

gallbladder

Answer 22

stores bile

Question 23

pancreas

Answer 23

secretes enzymes

Question 24

pancreas enzymes

Answer 24

• function in small intestine
  1) Breaking peptide bonds
• carboxypeptidase
• chymotrypsin
• trypsin
• pepsin
  2) Breaking carbs
• pancreatic amylase
  3) Breaking nucleic acids
• nucleases
  4) Breaks lipids
• pancreatic lipase

Question 25

salivary glands enzymes

Answer 25

salivary amylase

Question 26

stomach enzymes

Answer 26

HCl

Question 27

liver enzymes

Answer 27

bile salts which emulsify fats in small intestine

Question 28

beginning of digestion

Answer 28

• Saliva from salivary glands lubricates;
• Teeth chew;
• Tongue shapes them into a bolus and
provides help with swallowing;
• Carbohydrates break down by salivary amylase;
• Some fats start to break down by lingual lipase

Question 29

Bolus in pharynx and esophogus

Answer 29

• The throat, or pharynx, is the junction
that opens to both the esophagus and
the trachea.
• The esophagus connects to the stomach.
• The trachea (windpipe) leads to the
lungs.
• The esophagus conducts Timbits from
the pharynx down to the stomach by
peristalsis.
• Swallowing causes the epiglottis to block
entry to the trachea, and the bolus is,
therefore, guided to the digestive system
and not to the respiratory system

Question 30

in stomach

Answer 30

• Coordinated contraction and
relaxation of stomach muscle
churn the stomachʼs contents.
• Sphincters prevent Timbits from re-entering the esophagus and regulate their entry into the
small intestine.
• Both, mechanical and chemical digestion happens here
• Secretes gastric juice: 
- Contains HCl and enzymes 
-Turns food to chyme 
• Chemical: 
-Proteins (by pepsin) 
- Some lipids (by gastric lipase)
• pH is ~ 2 (kills bacteria and
denatures proteins)

Question 31

gastric gland cells

Answer 31

• Goblet (mucus) cells
• Chief cells (produce inactive pepsinogen)
• Parietal cells (produce H+ and Cl- separately)
• Gastric juice is made up of hydrochloric acid (HCl) and pepsin.
• Pepsin is a protease, or protein-digesting enzyme, that cleaves
proteins into smaller peptides.

Question 32

parts of small intestine

Answer 32

• Duodenum digests more than it absorbs
• Jejunum absorbs most of the nutrients
• Ileum absorbs certain left overs

Question 33

Duodenum

Answer 33

-is the first and the shortest segment of the small intestine. It receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine. Most digestion occurs here, and not much absorption.

Question 34

Jejunum

Answer 34

is the middle segment of the small intestine found between the duodenum and the ileum. Most of the nutrients present in food are ABSORBED by the jejunum before being passed on to the ileum for further absorption.

Question 35

Ileum

Answer 35

is the third and final part of the small intestine. Its function is to mainly absorb vitamin B12 and bile salts and
whatever products of digestion were not absorbed by the jejunum. The pH
in the ileum is more neutral.

Question 36

Functions of liver

Answer 36

• Detoxifies the blood;
• Stores some vitamins, iron, and
glycogen as sugar reserve;
• Coverts glycogen to usable
sugar when needed;
• Breaks down hemoglobin,
insulin and other hormones;
• Coverts ammonia to urea;
• Destroys old erythrocytes.

Question 37

small intestine summary

Answer 37

• The small intestine is the longest compartment of the alimentary canal.
• Most enzymatic hydrolysis of
macromolecules from ex-Timbits
occurs here.
• The first portion of the small intestine is the duodenum, where chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself.
• The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen.
• The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption.

Question 38

large colon

Answer 38

• Colon begins with the cecum • aids in the fermentation of plant material;
-connects where the small and large intestines
meet.
• The human “cecum” is an appendix
-plays a minor role in immunity • •The colon
-completes the reabsorption of water that
began in the small intestine;
-houses bacteria necessary for our digestion.