class: SS 2:
Subject: Biology Period(s) 3
Duration: 45 minutes
Topic: Feeding in Amoeba, Hydra and man
Subtopic 1: Feeding in Amoeba and Hydra
Subtopic 2: Structure of a tooth
Subtopic 3: Dental formula
Previous knowledge: Students are familiar with the topic:
Objectives: At the end of the period(s) students would be able to:
Period 1:
- Describe the feeding process in a unicellular organism.
- Describe the feeding process in hydra
period 2:
- State the two major types of dentition
- Mention the types of teeth, incisors, canines, premolars and molars
iii. Describe the structure of a tooth.
Period 3:
- State the dental formular of man, dog and rabbit
- State the adaptations of dentition to mode of nutrition in different organisms.
References Essential Biology for Senior Secondary Schools M.C. Michaels Pg 121-125. Modern Biology for senior secondary schools 1 -3pg 290 – 296
CONTENT
FEEDING IN AMOEBA
Amoeba is a holozoic organism which feeds on microorganism such as demids, diatoms and other organic particles. Amoeba surrounds the food particles by forming a cup like shape with its pseudopodia and engulfs its food. The pseudopodia bouching, fuse and enclose the food into the body with little drop of water forming a food vacuole. The engulfed food particles in the food vacuole is digested in the vacuole and absorbed in the body.
FEEDING IN HYDRA
It feeds mainly on small crustaceans or other smaller acquatic organisms. Hydra captures its prey by the action of nematocysts borne on the tentacle. The food is then conveyed into the mouth by the tentacles. Digestive enzymes are secreted into the enteron by the gland cells. The digested food is absorbed into the body while the undigested parts are sent back to the enteron and forced out through the mouth.
TEETH
Dentition can be defined as the number and kinds of teeth present in an organism and their arrangement in the lower and upper jaws bones. Dentition of an organism is related to the type of food a mammal eats. There are two major types of dentition namely:
- Homodont dentition: This involves the same type of teeth. No set of teeth is spcialized for any function. All the teeth are of the same shape, size and functions e.g. reptiles, amphibians and fishes.
- Heterodont dentition: This involves teeth of different shape, size and functions. This type of dentition can be found in mammals and rabbits, cattle, dog, cat, man etc. There are 4 different types of teeth namely incisors, canines, premolars and molars.
Human beings are omnivores and they possess 2 sets of teeth in their life time. The first set, the milk teeth grows when the child is few months old. It si made up of the incisor, canine and premolar teeth. It may be up to 20 in number and lasts for only a short time after which it falls off and becomes replaced by the second set, the permanent teeth, which is 32 in number and consists of the incisors, canines, premolars and molars.
- Incisors: are flat and chisel shaped teeth located in front of the jaw. They are used for biting off pieces of food, cutting and holding on to the prey. It has just a root each.
- Canines – They are conical or sharp and pointed at the tips. They are located next to the incisors. They are used for tearing flesh and for catching the prey. It has just a root each.
iii. Premolars have large, ridges flat surfaces or cusps located at the back of the jaw after the canines. They are used for grinding and chewing food. It may have 2 or 3 roots each.
- Molars – are located after the premolars at the extreme back of the jaws. They are closely packed with ridged surfaces. Molars are also used for chewing and grinding. It may have 2 or 3 roots each.
STRUCTURE OF A TOOTH
All teeth have the same basic structure and its made up of three regions namely:
- The crown – It projects above the gums
- The root – it is embedded in the gum socket or jawbone
iii. The neck – it is the junction between the crown and the root.
The external part of the tooth consists of enamel a white layer which is manufactured by the gum cells and is the hardest material made by animals. It is a non-living and it contains calcium salts. The enamel protects the pulp and dentine a hard bonylike material which contains the living pulp cells. The dentine encloses the pulp The pulp cavity which is at the centure of the tooth is made up of blood capillaries, sensory nerves and connective tissues. A hole at the tip of the root connects the pulp capillaries and nerves to those of the bones and gums. The sensory nerves enables the tooth respond to cold, heat and pair. At the root region, the totoh is not covered by enamel but by a thing layer of a bonelike material called cement which is surrounded by the periodontal numbers which fixes the tooth to the jawbone. The tooth is embedded in the jaw bone of maxilla upper jaw) and mandible (lower jaw)
DENTAL FORMULA
The dental formula shows the number and types of teeth an animal has in one half od each jaw. Dental formula is a reflection of special adaptation of mammalian teeth for feeding. Different animals have different dental formula depending on their diet.
The dental formula of man is
(upper jaw) I= 2, C =1, Pm = 2, M = 3, = 16
(lower jaw) 2 1 2 3
Each of the four types of teeth is indicated by its initial letter. The total number of teeth is 32 and is obtained by multiplying the total number of teeth in the dental formula by 2. Man as an omnivore, possesses sharp and broad incisors for cutting food, bluntly pointed canines for gripping and tearing food, premolars and molars for chewing and grinding food.
Dog as a carnivore posses teeth adapted for eating meat. Dog possess small and pointed incisors for cutting a meat piece from bones, long, curved, large and pointed canine used for defence, attack, seize and tear flesh from bones, premolars and moalrs that are broad and thick to cut up, tear away from the bone and grind. The last premolar in the upper jaw and the first molar in the lower jaw and large modified to form carnassials teeth for cracking bones and any other functions) The dental formular of Dog is
I= 3 C=1 Pm =4 M = 2 = 21
3 1 4 3
The total number of Dog’s teeth is 42
Rabbit, a herbivore, possess long chisel shaped incisors with sharp cutting edges for cutting grasses, diastems instead of can. For manipulationof grasses in the mouth, large closely paved premolars and molars which have large ridged surface area for cutting and grinding. The dental formula of rabbit is I = 2 pm 3 m = 3 = 14
1 2 3
The total number of a rabbit’s teeth is 28
Note: The teeth of rabbit wear away fast due to the grind effect against one another, however, they grow continuously to the good supply of blood into the pulp cavity and are known as open teeth (teeth that grow continuously). Teeth whose supply of blood is minimal are called closed teeth because the blood is just enough to keep both alive but not enough to keep growing e.g. in man.
INSTRUCTION MATERIALS: A model of the mammalian teeth pictures and videos
Teaching methods procedures
Step 1: Teacher introduces the topic and revises the previous topic with the students.
Step II: Teacher explains how Amoeba and Hdyra feeds
Step III: Teacher describes the structure of the tooth.
Step IV: Teacher describes in details the dentition of an omnivore, carnivore and herbivore.
Step V: Teachers allows the students to ask questions and write notes under content on the board.
CLASSROOM: (Activites)
Period 1: Students discuss the feeding habits of unicellular organisms and Hydra.
Period 2: Students discuss the structure of the tooth.
Period 3: Students discuss with the help of the teacher, the adaptation of teeth in a named herbivore, carnivore and omnivore.
EVALATION:
PERIOD 1: DEFINE DENTITION? Mention the types of dentition
PERIOD 2: Differentiate between closed teeth and open teeth
Period 3: State the total number of a Dog’s teeth
Summary/conclusion: Teacher summarizes the topic, marks the students notes and makes correction where necessary.
ASSIGNMENT(S):
Period 1: Describe the role of the teeth in mammalian nutrition
Period 2: Describe the general arrangement of the viscera of a named mammal
Period 3: With the aid of appropriate diagrams, describe the dentition of
- Carnivore
- a herbivore