Last reviewed: 7 November 2026
Updated November 2026. These Grade 9 dentition and modes of nutrition notes cover how animals obtain food (holozoic, parasitic, saprophytic and symbiotic nutrition), homodont and heterodont dentition, the structure and functions of incisors, canines, premolars and molars, and how dentition differs in carnivores, herbivores and omnivores. Key fact: an adult human usually has 32 teeth, made up of 8 incisors, 4 canines, 8 premolars and 12 molars.
The questions are original practice for Kenyan junior school learners, not an official paper. For other Grade 9 science topics, see the Grade 9 Integrated Science revision guide and the Grade 9 notes hub. Digestion in the human body is covered in our human digestive system notes.
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What the Grade 9 Curriculum Covers
Nutrition in animals is a sub-strand under Living Things and the Environment in the Kenya Institute of Curriculum Development’s Grade 9 Integrated Science design. It covers modes of nutrition, dentition (homodont and heterodont; carnivorous, herbivorous and omnivorous), types of teeth with their structure and functions, and digestion in humans. The design is listed on the KICD Grade Nine curriculum designs page. This page focuses on modes of nutrition and dentition.
Modes of Nutrition in Animals
- Holozoic: taking in solid food and digesting it inside the body, as humans, cows and lions do.
- Parasitic: feeding on or in a living host and harming it, such as ticks, lice and tapeworms.
- Saprophytic: feeding on dead, decaying matter by digesting it outside the body. This is mainly seen in fungi and bacteria.
- Symbiotic: two organisms living together and both benefiting, such as the microorganisms in a cow’s stomach that help digest cellulose.
OpenStax Biology’s section on digestive systems explains how herbivores, carnivores and omnivores differ in their digestive systems, including the role of microbes in ruminants.
Homodont and Heterodont Dentition
Homodont animals have teeth that are all similar in shape, as in most fish and reptiles such as crocodiles; the teeth mainly grip prey. Heterodont animals, which include most mammals, have different types of teeth for different jobs.
Types of Teeth
| Tooth | Shape | Function |
|---|---|---|
| Incisors | Chisel-shaped, at the front | Cutting and biting |
| Canines | Pointed and long | Tearing and gripping |
| Premolars | Broad with cusps | Crushing and grinding |
| Molars | Broad with several cusps, at the back | Grinding |
Structure of a tooth
The crown is above the gum and is covered by enamel, the hardest substance in the body. Below the enamel is dentine. The pulp cavity in the centre contains blood vessels and nerves. The root is held in the jawbone by cement. Sugary foods help bacteria produce acids that can damage enamel, which is why brushing and limiting sweets matter.
Dentition in Carnivores, Herbivores and Omnivores
A dental formula counts the teeth in one half of the upper jaw over one half of the lower jaw, in the order incisors, canines, premolars, molars. Multiply the total by 2 for the whole mouth.
| Animal | Dental formula | Total | Features |
|---|---|---|---|
| Human (omnivore) | i 2/2, c 1/1, pm 2/2, m 3/3 | 32 | All four types; suited to mixed diet |
| Dog (carnivore) | i 3/3, c 1/1, pm 4/4, m 2/3 | 42 | Long canines; sharp carnassial teeth for slicing meat |
| Cow (herbivore) | i 0/3, c 0/1, pm 3/3, m 3/3 | 32 | No upper incisors (horny pad instead); gap called the diastema; ridged molars for grinding grass |
Worked example: using a dental formula
For the dog: (3 + 1 + 4 + 2) + (3 + 1 + 4 + 3) = 10 + 11 = 21 teeth on one side. Total = 21 × 2 = 42.
Original Practice Questions With Worked Answers
- Name the mode of nutrition of a tapeworm. Parasitic.
- Which teeth are used for tearing flesh? Canines.
- What is the diastema and what is its use in herbivores? A gap between the front teeth and the cheek teeth; it lets the tongue move and turn grass during chewing.
- Use i 2/2, c 1/1, pm 2/2, m 3/3 to find the total number of teeth. (8 + 8) × 2 = 32.
- Which part of a tooth contains nerves? The pulp cavity.
Cover the answers and attempt each question first. For timed practice, use the Grade 9 revision papers or the Grade 9 CBC Challenge. These notes are free; full revision access is available with the KSh 20 Day Pass or the KSh 500 Monthly Pass.
Frequently Asked Questions
What are the four types of teeth?
Incisors (cutting), canines (tearing), premolars (crushing and grinding) and molars (grinding).
What is the difference between homodont and heterodont dentition?
Homodont animals have teeth of one shape; heterodont animals have different types of teeth for different functions.
How many teeth does an adult human have?
Usually 32: 8 incisors, 4 canines, 8 premolars and 12 molars.
Why do cows lack upper incisors?
They have a hard dental pad instead, which the lower incisors press against to cut grass.