Evolution of the Gut

Question 1

What are the six main functions of the gut?

Answer 1

• Receive ingested food
• Store food temporarily
• Reduce food physically
• Reduce food chemically
• Absorb products of digestion
• Eliminate undigested waste

Question 2

What was the first invertebrate to develop an alimentary canal (one way movement from mouth - anus)?

Answer 2

Nematodes

Question 3

What do most invertebrates possess?

Answer 3

Gastrovascular cavity

Question 4

What is a protostome?

Answer 4

Mouth developed from blastopore(Most inverts)

Question 5

What is a deuterostome?

Answer 5

Anus developed from blastopore (Echinoderms and chordates)

Question 6

What was the first multicellular gut like?

Answer 6

Like a bag - food flowed in through mouth and waste flowed back out the same way - bacteria helped digest food within these two cell thick structures

Question 7

What is Cnidarian gut structure like?

Answer 7

Mouth and a blind Gastrovascular cavity - lined with phagocytic, secretory and ciliated cells

Question 8

What is Nematoda gut structure like?

Answer 8

Evolved a more efficient system - tubular so that food flowed in the same direction and exited the anus

Question 9

What is a Mussel’s gut structure like?

Answer 9

Filter feeders - take in water and their gills strain particles.
Gill sheets with cilia, mouth and stomach

Question 10

What is Annelia gut structure like?

Answer 10

Consists of a head gut (mouth, buccal cavity, muscular pharynx) - secretion and digestion and foregut (oesophagus, crop and gizzard) and the intestine.

Question 11

What is Arthropoda gut structure like?

Answer 11

Most crustaceans are filter feeders and their foreguts are lined with chitinous ridges. Their midgut contains glandular ceca.

Question 12

What are most insect’s guts like?

Answer 12

Headgut, foregut, midgut and hind gut.

The headgut is specialised for sucking, chewing or piercing.

Question 13

What is the role of the crop and proventriculus in insects?

Answer 13

Food storage and controlling the passage of food into the midgut - can contain teeth in some species.

Question 14

What were ancestral vertebrates guts like?

Answer 14

Probably filter feeders such as: lampreys. They had simple digestive systems and mucus moved to gut by cilia.

Question 15

Why are lancelets good indicators of evolutionary origins of vertebrates?

Answer 15

Genomes hold clues of how vertebrates have employed old genes for new function

Question 16

What is a lancelets gut like?

Answer 16

Gut is a simple tube from mouth to anus with a diverticulum which secretes digestive enzymes into lumen. Absorption occurs by diffusion into epithelial cells.

Question 17

What advantage did fish have over earlier organisms?

Answer 17

Evolved teeth, livers and kidneys which could remove poisons. These specialised parts prepared the food for the body, their cells were able to get more energy out of the food with less work

Question 18

What is an Agnathan gut like?

Answer 18

No jaws but have cyclostomes (rasping organs like tongues) No stomach or oesophagus but have a straight intestine

Question 19

What is an amphibian’s digestion like?

Answer 19

Frogs evolved to have a tongue to help catch and digest their food. They also evolved to have a pancreas, gallbladder and separated intestines. They also separated their faeces from urine. The tongue and saliva helped to predigest food so cells could get more energy from molecules of food. Frogs have more energy to jump around on land

Question 20

What are the main characteristics of a tetrapod digestive system?

Answer 20

Increased lubrication and then limited chemical and physical digestion. Salivary glands lubricate and predigest food. Fleshy and movable tongue usually present.

Question 21

What are the characteristics of a reptilian gut?

Answer 21

Similarly to amphibians. Birds possess gizzards rather than teeth. Evolved to have beaks instead.
Longer ciliated oesophagus, stomach is simple and curved.

Question 22

What are some characteristics of a birds gut?

Answer 22

Storage organ called a crop.
Stomach is separated into two parts - anterior proventriculus: produces enzymes
Posterior ventriculus or gizzard - muscular for grinding food which is sometimes aided by pebbles eaten by bird

Question 23

What are the characteristics of a mammals gut?

Answer 23

Long oesophagus, stomach is sac like or compartmentalised, 2-6 body lengths intestine in carnivores and insectivores and 20-25 body lengths in marine mammals.

Question 24

Which diet comprises the longest intestines?

Answer 24

Herbivores

Question 25

What gut adaptation does an organism that eats nutritious food but is slow eating?

Answer 25

Short gut with no storage organs e.g. nectar, filter feeders.

Question 26

What gut adaptation does an organism that eats nutritious food but is quickly eats?

Answer 26

Short gut with storage - stomach of carnivores or scavengers

Question 27

Which diets possess a strong muscular stomach?

Answer 27

Carnivores and Omnivores

Question 28

Which diets possess a moderate gut with large storage?

Answer 28

Herbivores and ruminants.

Question 29

What is the oral cavity made up of?

Answer 29

Secondary palate, tongue, teeth and salivary glands

Question 30

What is the role of the oral cavity?

Answer 30

Grasping and ingestion of food, grinding, moistening and lubrication, formation of boluses to push into the pharynx for swallowing

Question 31

What is the role of the secondary palate?

Answer 31

Dual mastication and breathing - separates the nasal passages from mouth

Question 32

What is the role of the tongue?

Answer 32

Mobile and muscular structure that can manipulate food in the oral cavity. Also used as taste receptors.

Question 33

What is the role of teeth?

Answer 33

Specialised to meet the needs of the diet. They tear, cut and masticate food.

Question 34

What are the role of salivary glands?

Answer 34

Produce saliva which facilitate mastication and swallowing of food.

Question 35

Describe the oesophagus

Answer 35

Muscular tube that moves boluses from pharynx to stomach. Circular and longitudinal muscle layers contract to move food

Question 36

Describe the stomach

Answer 36

Cardiac sphincter is the opening of the stomach. Mucus is secreted in the cardiac portion of the stomach and the next region: fundus, secretes digestive enzymes that are responsible for chemical breakdown. The pyloric region also secretes mucus.

Question 37

Describe the small intestines

Answer 37

Longest part of the alimentary canal. Site of most enzymatic digestion and all nutrients are absorbed here.

Question 38

Describe the large intestine

Answer 38

Important for the conservation of water, it also consolidates the faeces.