Lesson Notes By Weeks and Term - Senior Secondary 2

Digestive system

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TERM – 1ST TERM

WEEK ONE

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Biology

Topic: DIGESTIVE SYSTEM

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Describe the modification of feeding habits in organisms
  2. Describe the mechanism of feeding of organisms

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

The teacher discusses the modification of feeding habits in organisms

Students pay

attention

STEP 2

EXPLANATION

Teacher explain the mechanism of feeding in organisms

Students pay

attention and

participate

 

STEP 3

DEMONSTRATIO

N

Teacher uses specimens and charts of the digestive system of housefly, butterfly, cockroach, tapeworm sheep or dog to illustrate different types of feeding mechanism

Students observe provided specimens noting the various modification found in the animals

STEP 4

NOTE TAKING

The teacher writes a summarized

note on the board

 

The students

copy the note in

their books

 

NOTE

DIGESTIVE SYSTEM

Modification of the feeding habits

filter feeders

Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish.

 fluid feeders:  Fluid feeders are organisms that obtain their nutrition by consuming liquids. Modifications in feeding habits among fluid feeders can vary widely depending on the species. Examples include: Mosquitoes, Butterflies, Hummingbird, Ticks.

insects feeders: Insects feeders refer to organisms within the insect class that consume various types of food to meet their nutritional needs. Insects exhibit diverse feeding strategies based on their mouthparts and dietary preferences. Examples of insects feeders include: Beetles, caterpillar, mosquitoes, aphids, Butterflies, bees, Housefly etc.

parasitic and saprophytic feeders

  1. Parasitic Feeders: Parasitic feeders are organisms that live on or inside a host organism and derive nutrients from the host, often causing harm or damage to the host. Examples in Insects include Fleas, lice, ticks, and parasitic wasps are examples of parasitic insects. They may feed on the blood or tissues of their host.
  2. Saprophytic Feeders: Saprophytic feeders, or saprophytes, are organisms that obtain their nutrients by feeding on dead or decaying organic matter. They play a crucial role in decomposition. Examples in Insects include some beetle larvae which may consume decaying wood, and certain fly larvae (maggots) feed on decomposing organic matter.

Modification and mechanism of feeding habits

Organisms have evolved various feeding mechanisms, including biting and chewing, sucking, and absorbing, depending on their dietary preferences and ecological niches. Examples of animals with these feeding mechanisms are:

Biting and Chewing

  1. Lions (Carnivores): Lions have sharp teeth adapted for biting into the flesh of their prey. Their powerful jaw muscles allow them to chew and tear meat efficiently.
  2. Rabbits (Herbivores): Rabbits have sharp incisors for biting through vegetation, and they chew using a side-to-side motion. They also have a specialized digestive system for processing plant material.

Sucking

  1. Mosquitoes (Blood-sucking Insects): Mosquitoes have specialized mouthparts (proboscis) that pierce the skin of hosts, allowing them to suck blood.
  2. Hummingbirds (Nectar Feeders): Hummingbirds use a long, specialized beak to suck nectar from flowers. Their tongue acts like a tube for efficient sucking.

 Absorbing

  1. Leeches (Blood-sucking Invertebrates): Leeches have a segmented body and use a sucker at each end for attachment. They secrete anticoagulants to prevent blood clotting while absorbing blood.
  2. Tapeworms (Parasites): Tapeworms are intestinal parasites that absorb nutrients through their body wall. They attach to the host's intestinal lining using suckers and hooks.

Feeding in Protozoa

Feeding in protozoa varies among different species. They generally obtain nutrients through processes like phagocytosis, pinocytosis, or absorption. Phagocytosis involves engulfing solid particles, while pinocytosis involves engulfing liquids. Some protozoa are autotrophic and can photosynthesize, while others are heterotrophic, relying on organic matter for nutrition. Examples of Protozoa include amoeba, paramecium, euglena, trypanosoma, plasmodium etc.

Structure of amoeba

Feeding in Hydra

Hydra, a simple freshwater organism belonging to the phylum Cnidaria, feeds primarily through a process called extracellular digestion. The processes are as follows:

  1. Capture of Prey: Hydra use specialized cells called cnidocytes, which contain stinging structures called nematocysts. When prey, such as tiny crustaceans or small organisms, come in contact with the tentacles of Hydra, nematocysts are triggered, injecting toxins and helping in prey capture.
  2. Enzymatic Digestion: Once the prey is captured, Hydra secretes digestive enzymes into the gastrovascular cavity. This extracellular digestion begins breaking down the prey into simpler substances.
  3. Nutrient Absorption: The digested nutrients are then absorbed by the cells lining the gastrovascular cavity. Hydra's body is two-layered, and these cells perform both digestion and absorption.
  4. Waste Elimination: Any undigested or unabsorbed remnants are expelled from the body through the same opening used for ingestion.

       

Feeding habits in Mammals

Feeding in mammals involves several distinct stages:

  1. Ingestion: The process of taking food into the mouth. Mammals have specialized teeth for different functions like cutting, grinding, or tearing, depending on their diet.
  2. Digestion: Food undergoes mechanical and chemical breakdown in the digestive system. Mechanical digestion occurs in the mouth through chewing, while chemical digestion involves enzymes breaking down food in the stomach and small intestine.
  3. Absorption: Digested nutrients are absorbed in the small intestine. Villi and microvilli increase the surface area for efficient nutrient absorption into the bloodstream.
  4. Transportation: Nutrients are transported via the circulatory system (bloodstream) to cells and tissues for energy, growth, and repair.
  5. Assimilation: Cells utilize absorbed nutrients for various metabolic processes, contributing to the organism's overall well-being.
  6. Elimination: Undigested and unabsorbed materials, along with waste products, are expelled from the body as feces through the rectum and anus.

EVALUATION: 1. Describe the mechanism of feeding in Protozoa

  1. Identify the three mechanism of feeding in organisms

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively