Summary of the Topic:
The mammalian dentition is a reflection of dietary habits and ecological niches. Understanding the structure, types, and functions of teeth in mammals is crucial for comprehending feeding mechanisms and adaptations.
Key aspects include:
- Types of Teeth: Incisors, canines, premolars, and molars.
- Dental Formula: Represents the number and types of teeth in mammals.
- Tooth Structure: Comprises enamel, dentine, pulp cavity, cement, and periodontal ligament.
- Dentition Types: Heterodont (different types of teeth) and homodont (same type of teeth).
- Adaptations: Variations in dentition among herbivores, carnivores, and omnivores.
Key Concepts Explained:
1. Types of Teeth:
- Incisors: Located at the front; used for cutting or biting food.
- Canines: Pointed teeth next to incisors; used for tearing food.
- Premolars: Located behind canines; used for grinding and crushing food.
- Molars: Found at the back; have broad surfaces for grinding food.
2. Dental Formula:
Represents the number of each type of tooth in one half of the upper and lower jaws. For example:
- Human Adult:
I 2/2, C 1/1, P 2/2, M 3/3
Total teeth = 32 - Rabbit:
I 2/1, C 0/0, P 3/2, M 3/3
Total teeth = 28
3. Tooth Structure:
- Enamel: Hard, protective outer layer.
- Dentine: Beneath enamel; less hard.
- Pulp Cavity: Contains nerves and blood vessels.
- Cement: Covers the root; helps anchor the tooth.
- Periodontal Ligament: Connects tooth to jawbone.
4. Dentition Types:
- Heterodont: Presence of different types of teeth (e.g., humans).
- Homodont: All teeth are similar in shape and function (e.g., lizards).
5. Adaptations:
- Herbivores: Have well-developed molars for grinding plant material; may lack canines.
- Carnivores: Possess sharp canines and carnassial teeth for tearing flesh.
- Omnivores: Exhibit a combination of tooth types for a varied diet.
Example WAEC-Style Questions (With Explanations):
Q1: The dentition belongs to:
A. Rabbit
B. Cat
C. Frog
D. Man
Answer: B. Cat
Explanation: The presence of pronounced canines and carnassial teeth indicates a carnivorous animal like a cat.
Q2: The function of the teeth labeled X is for:
A. Biting and grasping
B. Chewing and grinding
C. Tearing and grasping
D. Chewing and tearing
Answer: C. Tearing and grasping
Explanation: Canines are designed for tearing and grasping food, typical in carnivores.
Q3: The teeth which are absent in the young of the organism are labeled:
A. W
B. X
C. Y
D. Z
Answer: D. Z
Explanation: Molars (labeled Z) are usually absent in the milk dentition and develop later.
Q4: An herbivore cannot feed on a piece of meat because it has no:
A. Incisors to cut the meat
B. Canines to tear up the meat
C. Premolars to grind the meat
D. Molars to mash the meat
Answer: B. Canines to tear up the meat
Explanation: Herbivores lack prominent canines, making it difficult to tear meat.
Q5: Which of the following dental formulae represents the dentition in rabbits?
A. I 2/2 C 0/0 P 3/2 M 3/3
B. I 2/2 C 2/2 P 3/2 M 3/3
C. I 2/2 C 0/0 P 2/3 M 3/3
D. I 2/1 C 0/0 P 3/2 M 3/3
Answer: D. I 2/1 C 0/0 P 3/2 M 3/3
Explanation: Rabbits have a dental formula reflecting their herbivorous diet, lacking canines.
Q6: Which of the following parts of the tooth is first damaged during dental decay?
A. Cement
B. Enamel
C. Dentine
D. Root
Answer: B. Enamel
Explanation: Enamel is the outermost layer and is the first to be affected by decay.
Q7: Which of the following teeth are well-developed to form the carnassial teeth of carnivorous mammals?
A. First lower premolar and third upper molar
B. First lower molar and third upper premolar
C. Second lower premolar and first lower molar
D. First lower molar and last upper premolar
Answer: D. First lower molar and last upper premolar
Explanation: These teeth form the carnassial pair, specialized for shearing flesh in carnivores.
Q8: Which of the following organisms has homodont dentition?
A. Rabbit
B. Man
C. Sheep
D. Lizard
Answer: D. Lizard
Explanation: Lizards have teeth that are similar in shape and function, characteristic of homodont dentition.
Q9: The teeth used for tearing and cutting are:
A. Canine and molars
B. Premolar and incisors
C. Molar and incisors
D. Canine and incisors
Answer: D. Canine and incisors
Explanation: Incisors cut food, while canines tear it.
Q10: The dentition of a herbivore is distinct from that of other animals due to the presence of:
A. Diastema
B. Cusps on molar teeth
C. Canines
D. Ridges on molar teeth
Answer: A. Diastema
Explanation: A diastema is a gap that allows for the manipulation of plant material, common in herbivores.
Q11: Tooth decay is usually caused by:
A. Undigested and absorbed food
B. Eating limited amount of sweetened food
C. The bacteria in the mouth that metabolize sugar to acids
D. Eating a lot of proteinous foods
Answer: C. The bacteria in the mouth that metabolize sugar to acids
Explanation: Bacteria produce acids from sugars, leading to enamel erosion and decay.
Study Tips:
- Create Comparative Charts: Highlight differences in dentition among herbivores, carnivores, and omnivores.
- Use Diagrams: Practice drawing and labeling the structure of a tooth and dental formulas.
- Understand Functions: Relate each type of tooth to its specific function in feeding.
- Memorize Dental Formulas: Know the dental formulas of common mammals for quick recall.
- Practice Past Questions: Regularly attempt past WAEC questions to familiarize yourself with exam patterns.
Conclusion:
A thorough understanding of mammalian dentition is essential for mastering topics related to nutrition and adaptation in biology. To reinforce your learning, proceed to the WAEC past questions provided below, which offer practical application of the concepts discussed.
OBJECTIVES
The diagrams below are illustrations of the dentition of an organism. Study them and answer questions 1 to 3.
1. The dentition belongs to
A. rabbit.
B. cat.
C. Frog.
D. man.
2. The function of the teeth labeled X is for
A. biting and grasping.
B. chewing and grinding.
C. tearing and grasping.
D. chewing and tearing.
3. The teeth which are absent in the young of the organism are labelled
A. W.
B. X.
C. Y.
D. Z.
4. An herbivore cannot feed on a piece of meat because it has no
A. incisors to cut the meat.
B. canines to tear up the meat.
C. premolars to grind the meat.
D. molars to mash the meat.
Which of the following dental formulae represents the dentition in rabbits?
A. I 2/2 C 0/0 P 3/2 M 3/3
B. I 2/2 C 2/2 P 3/2 M 3/3
C. I 2/2 C 0/0 P 2/3 M 3/3
D. I 2/1 C 0/0 P 3/2 M 3/3
6. Which of the following parts of the tooth is first damaged during dental decay?
A. Cement.
B. Enamel
C. Dentine.
D. Root.
7. Which of the following teeth are well-developed to form the carnassial teeth of carnivorous mammals? The
A. firsts lower premolar and third upper molar.
B. first lower molar and third upper premolar.
C. second lower premolar and first lower molar.
D. first lower molar and last upper premolar.
8. Which of the following organisms has homodont dentition?
A. Rabbit.
B. Man.
C. Sheep.
D. Lizard.
9. The teeth used for tearing and cutting are
A. canine and molars.
B. premolar and incisors.
C. molar and incisors.
D. canine and incissors.
10. The dentition of a herbivore is distinct from that of other animals due to the presence of
A. diastema.
B. cusps on molar teeth.
C. canines.
D. ridges on molar teeth.
11. Tooth decay is usually caused by
A. undigested and absorbed food.
B. eating limited amount of sweetened food.
C. the bacteria in the mouth that metabolize sugar to acids.
D. eating a lot of proteinous foods.
THEORY
1. Explain briefly how the dentition of herbivores is adapted for feeding.
2. What is dentition in animals? Describe briefly the generalized structure of a tooth in animals.
3. State: (i) three differences between the dentition of a herbivore and a carnivore; (ii) four differences between the dentition of a human and a goat. (c) What are milk teeth?
