Topic: Digestive system.
Instructional Materials. Model, specimen, pictures,
Aim of the Lesson: To help the learner understand
the digestive system
Anticipated Problems: Because of advancement in
class, most themes might be new to the learner and might result to difficulty
in understand.
Possible Solution: The teacher explains the concept in details
using illustrations and real objects.
Content Objectives: By the of the lesson, learner should be
able to;
1. Define
digestive system
2. Identify the different types of
alimentary tracts.
3. Explain the parts and functions of
the mammalian digestive tract.
4. Identify dentition in line with mode
of nutrition.
5. Explain the different feeding habits
of the different life forms.
6. Explain the structural adaptations of
different life forms to these feeding habits.
Time
Table fit/ previous knowledge: The learners know about the digestive system from personal experience
Differentiation
Method/Multiple Intelligence: The teacher uses different
teaching technique such as discussion, role playing, questioning and use of
picture to ensure all the learner benefit from the lesson.
Digestive system
Digestive system involves
all the organs associated with breaking down and utilization of food substances
in the body.
Alimentary Canal
Alimentary canal, also called digestive tract, is a
pathway by which food enters the body and solid wastes are expelled. The
alimentary canal includes the mouth, pharynx, esophagus, stomach, small
intestine, large intestine, and
anus.
Structure of the alimentary canal
ORGANS OF THE ALIMENTARY CANAL AND
THEIR FUNCTIONS
Mouth: Consists of lips, teeth, tongue,
salivary glands. Food is broken down to pieces by teeth, lubricated by saliva,
tongue rolls food into bolus for easy swallowing. Saliva makes food alkaline.
Ptyalin converts cooked starch to maltose.
Esophagus is a muscular tube connecting mouth to
the stomach. Passes food from mouth to stomach by peristalsis. Action of ptyalin continues.
Stomach: Single chamber (monogastric),
muscular, having cardiac and pyloric sphincters. Food is stored, churned and
mixed with gastric juice becoming a paste (chyme).Saliva is neutralized by HCL;
which kills bacteria and provides medium for pepsin. Rennin curdles milk, pepsin
changes proteins to peptides.
Duodenum: First part of the small intestine.
Food is churned with further digestive more digestive enzymes. Region of active
digestion. More peristalsis. Bile emulsifies fats and neutralizes acidity of
food. Carbohydrates, proteins and lipids changed to simple sugars, amino acids,
fatty acids and glycerol respectively.
Ileum: Second part of small intestines lined
with villi Food turned to semifluid. More peristalsis and mixing of
food. Absorption of simple sugars, amino acids, fatty acids and glycerol.
Large intestines: No villi but has mucous glands. Water
absorbed from unabsorbed residue and passes into rectum as feces
Anus is muscular, Expels feces.
TYPES OF FEEDING AND ALIMENTARY
TRACTS
Here, let us consider the digestive tracts of round
worms (earthworms), arthropods(cockroach),aves (bird) and mammals (rabbit).
ROUND WORMS (EARTHWORM)
(Lumbricusspp)
The digestive tract which begins with the mouth and
ends in the anus is divided into specialized compartments. Food mixed with soil
is sucked into the
mouth, passes through a short passage way into the
pharynx and then through the esophagus into the thin-walled crop that functions
as a storage chamber.
Then it enters the gizzard where the food is churned
and ground. The pulverized food suspended in water, passes into the long
intestine where enzymatic digestion and absorption occur.
COCKROACH
The food is softened by a digestive juice secreted by
the salivary glands. Then it passes through the esophagus into the crop and the
gizzard which has thick walls. The food is ground in the gizzard into which the
caecum secretes digestive enzymes. The digested food is passed into the
mesenteron (mid-gut) where absorption takes place. The mid-gut is followed by
the colon, end of which forms the rectum
BIRD
Although birds do not have teeth, they have the
mechanism for grinding up the food swallowed before it is digested. The food is
stored in the crop and later passed on to the gizzard through the glandular
proventiculus. The strong wall of the gizzard and the small stone often
swallowed by the bird help in grinding up the food. Pancreatic ducts in the
pancreas and bile ducts from the liver open into the loop shaped duodenum. This
leads to the ileum and colon. At the posterior end of the rectum are the cloaca
and the anus.
RABBIT
The small intestine in rabbit is very long and coiled
due to the difficulty of digesting plant materials because of the presence of
the cellulose cell wall. The long intestine enables the herbivore to extract
the maximum amount of nutrients from the food. The wall of the large intestine
forms numerous folds.
The caecum is long. This creates more surface area for
the slow action of bacteria which converts cellulose to sugars. The rectum is
long and contain solid pellets of feces.
DENTITION
TYPES OF MAMMALIAN TEETH
1. Incisors: the front teeth used for biting off
small pieces of food. Chisel shaped.
2. Canine: used for tearing off food. E.g.
flesh from bone. Usually long and pointed.
3. Premolars: flat topped with broad surfaces for
grinding food.
4. Molars: like premolars. They are absent in
the milk teeth of young mammals. They also have broad surfaces and are used for
crushing food.
Dentition of a herbivore:
Dental formula: I 2/1, c0/0, pm 3/2, m 3/3
Adaptations:
- Incisors are sharp for cutting grass.
- Canines absent leaving a space (diastema).
- Diastema allows for mixing of food.
- Molars and premolars have transverse ridges for
grinding food
Dentition of a carnivore:
Dental formula: I 3/3, c1/1, pm 4/4, m 2/3
Adaptation:
- Sharp incisors for catching and holding prey.
- Long pointed and curved canines for attacking and
holding prey. Molars and premolars have pointed cusps for crushing bones.
The dentition of an omnivore:
Dental formula: I 2/2, c 1/1, pm 2/2, m 3/3
Adaptation:
- Sharp incisors
for cutting food.
- Premolar and molars have broad surfaces for grinding
food.
Note that human teeth are not all that
specialized as they are used for various plant and animal food materials.
FEEDING HABITS
FEEDING IN PROTOZOA
Protozoan show a holozoic
mode of nutrition. They prey on ciliates by engulfing along with water after
which enzymes are secreted to digest the ciliate. On digestion, it diffuses
into the cytoplasm.
FEEDING IN
COELENTRATES
Coelenterates like jelly
fish sting preys using their tentacles before ingestion. Others like hydra
possess hollow sac, some of which have linings with flagella that mix the
content in the enteron. The digestion is extracellular, it has no anus.
FILTER FEEDING
Clams, prawn, ducks, mosquito larva and whales are
examples of filter feeders. This feeding method occurs mainly in aquatic
organisms. The feed by mere filtration or sifting of smaller diatoms inside the
aquatic environment into their mouth. In mosquito larva, 2 small hairy brushes
near the mouth beat in a circular motion thus setting up water currents near
the mouth. The water and food particles pass through the mouth into the pharynx
where the water is eliminated while filtering out food particles. Mosquito
larva eats bacteria and other small particles of organic matter.
FLUID FEEDING
Most insects feed on fluids like nectar from flowers,
plant juice or blood. They make use of special mouth parts called proboscis.
Examples are insects like bees, mosquitoes, tsetse flies, butterflies, etc. the
mouth parts of the anopheles are modified for piercing and sucking blood and
nectar. As soon as the stylets pierce the skin of the victim, blood is sucked
up through the tubular proboscis.
INSECTS FEEDING ON SOLIDS
Insects that feed on solid food have cutting and
chewing mouth parts. The cockroach for example, has chewing mouth parts,
consisting of a pair of lips and 2 pairs of jaws all arranged around the mouth.
While the food is held in position by the lips, the jaws are used to cut off
pieces of the food.
CARNIVOROUS
PLANTS
These
plants have special devices for attracting and trapping insects. The devices
usually have bright colors, scents and sugary liquids. Once an insect is
trapped, the plant secretes enzyme rich digestive juices o kill and digest it.
The soluble nitrogenous compounds are assimilated by the plants. In the pitcher
plant for instance, the leaf is modified
into a pitcher containing digestive fluid. The rim of the pitcher
is colorful and smooth, and nectar is secreted near it. Insects are attracted
to the nectar, and while they get at it, they slip and fall into the digestive
fluid in the pitcher. Similar mechanisms are employed by the other carnivorous
plants.
Assessment
plan. The teacher uses the following to assess the learners
Class
work
What is digestive system
what are the types of
dentitions?
Home
work
Draw the structure of the
alimentary canal in your note
Multiple
choice questions.
- The
structure in alimentary canal where absorption of water takes place is the
- Mouth
- stomach
- ileum
- large
intestine
- Example
of filter feeders are all except
- Clams
- Prawn
- Ducks
- mosquito larva
- Most insects feed on fluids like
nectar from flowers, plant juice or blood. They make use of special mouth
parts called
- Proboscis
- Antenna
- Mandible
- Mouth
parts
- What’s
the formula for Dentition
in a carnivore?
- I 3/3, c1/1, pm 4/4, m 2/3
- I 3/3, c1/1, pm 4/4, m 2/6
- I 4/3, c1/1, pm 4/4, m 2/3
- I 3/3, c1/1, pm 5/4, m 2/3
Evaluation
1. Define
digestive system
2. Identify the different types of
alimentary tracts.
3. Explain the parts and functions of
the mammalian digestive tract.
4. Identify dentition in line with mode of
nutrition.
5. Explain the different feeding habits
of the different life forms.
6. Explain the structural adaptations of
different life forms to these feeding habits.
Glossary
Alimentary
canal: Digestive tract
Ileum: small
intestine
Dentition:
Arrangement of teeth
Conclusion: Digestive
system involves all the organ associated with break down and utilization of
food substances in the body.
Very helpful for teaching and learning 💪👏👏
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