CLASS: SS2

SUBJECT: BIOLOGY                          PERIODS 3:

DURATION:                                       45 MINUTES

TOPIC:                      EXCRETION

SUBTOPIC 1:             TYPES OF EXCRETORY ORGANS AND WASTE PRODUCTS  

SUBTOPIC 2:             EXCRETION IN HUMAN BEINGS

SUBTOPIC 3:             STOMATA AND LENTICELS IN FLOWERING PLANTS

PREVIOUS KNOWLEDGE: STUDENTS AND FAMILIAR WITH THE

TOPIC

 

OBJECTIVES:    At The End Of The Period(s), students should be able to:

 

PERIOD 1: Identify and describe the different types of excretory systems in animals and plants

PERIOD 2: Explain the mechanism of some of the excretory organs.

PERIOD 3: Describe the mechanism of excretion in plants

REFERENCES: Modern Biology for senior secondary schools pg. 335 – 341.

Essential Biology for senior secondary schools Pg 313 – 319

 

CONTENTS

Excretion can be defined as the processes by which waste products of metabolism are removed from the body of a living organism. These waste products include by products formed as a result of metabolism, unwanted materials in food and excess food substances that cant be stored. Glucose is oxidized to produce energy in a reaction which produces water, carbon dioxide, and heat which are by products and must be excreted.

 

Below is a table showing organisms, their excretory organs and the waste products produced.

 

 

Organisms

Excretory organs

Waste products excreted

1.

Protozoa e.g. amoeba

Contractile vacuole buy diffusion

Carbon dioxide, ammonia and water

2

Annelids e.g. Earthworm

Nephridia

Water, urea, carbon dioxide, and nitrogenous waste.

3

Flatworms e.g. tapeworm

Flame cells

Carbon dioxide, ammonia and water

4.

Insects

Malphighan bubbles

Water, carbon dioxide, uric acid

5.

Crustaceans

Green glands

Water, urea, ammonia salts and carbon dioxide

6.

Fishes

Kidneys

Urine containing urea, salts, water, hormones, and uric acid

7.

Amphibians

Kidneys

Urine containing urea, salts, water, hormones, and uric acid

8.

Reptiles

Kidneys

Urine containing urea, salts, water, hormones, uric acid

9.

Birds

Kidneys and lungs

Uric containing urea, salts, water, hormones and uric acid, carbon dioxide, and water vapour.

10.

Mammals

Kidneys, lungs, skin, liver

Urine containing urea, salts and water), liver, (bile, salts, water and urea)

11.

 Flowering plants

Stomata and lenticels

Water, carbon dioxide and oxygen

12.

Plants (trees)

Bark of trees

Tannins, mucilage, gum, crystals, anthocynanins, alkaloid, resin, oil and latex

 

CONTRACTILE VACUOLE IN AMOEBA

The contractile vacuole serves as a water pump for the removal of excess water in Amoeba. Amoeba is a fresh water organism and its environment is hypotonic to its cell content, therefore, water enters the selective permeable membrane. The contractile vacuole (a small sac lined with membrane) acts as a osmo-regulator since it regulates the water content of the cell, other excretory products produced by Amoeba, carbon dioxide and ammonia are excreted by diffusion since the surface area to volume ratio of Amoeba is large.  

 

FLAME CELL IN FLATWORM

Flame cells are specially hollow structures found at the ends of numerous branched tubules which make up two longitudinal excretory canals. These canals open to the exterior on the body surface. It excretes carbon dioxide, water and ammonia.

 

Malphibian tubules in insects.

Insects are capable of conserving water due to their waterproofing exoskeleton (because of a layer of wax) spiracles which prevent water loss and an extremely efficient excretory system.  The malphibian tubules can be found between the mid gut and rectum. One end of the tubule opens into the gut while the other floats freely in the haemoeocel which absorbs nitrogenous waste and water. The nitrogenous wastes is converted to uric acid as it moves along the malphibian tubules to the gut. The uric acid is changed to solid crystals due to water re-absorption in the gut and even in the hind gut by the rectal glad. Thus, the urine which is eventually excreted is very concentrated almost like a dry solid.

 

KIDNEYS IN HUMAN BEINGS

The kidneys are a pair of bean shaped reddish brown organs located in the posterior end of the abdomen which remove unwanted nitrogenous substances (urea and other ammonium compounds) in  the blood and maintain  the osmotic pressure of the blood (osmoregulation – water and salts) The kidney consists of anouter corter and an inner medulla. Numerous urinary tubules open at the tips of triangular shaped masses of tissues called pyramids. Each urinary tubule serves as a functional unit of the kidney and it begins in the cortex as a cup like structure called the Brownian’s capsule which opens into a short coiled tube, the proximal convoluted tubule. These tubule passes into the medulla where it makes a U shaped loop, the Henle’s loop  before reentering the cortex in which it becomes coiled organ to form the distal convoluted tubule. The tubule pour their contents into wider man collecting ducts  which join up and open into the pelvis at the apices of the pyramids. The tubule associate with the several networks of blood capillaries. The renal artery branches in the kidney and each branch break into a mass of blood capillaries (glomerulus) in the Bowman’s capsule. Both the capsule and glomerulus form the malphighian corpuscle. The renal artery provides the kidneys with oxygenated blood rich in dissolved food substances and the renal vein carries deoxygenated blood away from the kidneys.

          The mechanism of excretion by the kidneys (urine formation) occurs in 3 phases namely:

  1. Ultrafiltration: The blood brought by the renal artery circulates the capillaries (glomerulus) of the Bowman’s capsule and water, urea, mineral salts, nitrogenous compounds, sugars, glucose and plasma solutes are filtrated into the Bowman’s capsule (glomerulus filtrate)
  2. Selective re-absorption: The fluid in the capsule(glomerular filtrate) flows down the tubule. At the proximal convoluted tubule and Henle’s loop, some water, sugars, amino acids and salts which are use reabsorbed into the blood capillaries by active transport (against concentration gradient). The process of reabsorbing useful materials back into the blood is called selective re-absorption.
  3. Hormonal secretion: The glomerular filtrate becomes more concentrated as it flows the distal tubule where more water is reabsorbed by the action of antidiuretic hormone (AOH) and urine is formed  which trickles into the renal pelvis and propelled by peristalsis through the ureter into the urinary bladder. The urine is discharged through the urethra when the bladder is full.

STOMATA AND LENTICELS IN FLOWERING PLANTS

The main excretory organs of plants is the stomata and lenticels, although other parts play excretory roles too e.g. in the roots, gases pass out through the general root surface. In plants like tomato and potato, excess water in droplet form dew drops which form at the tips and margins of leaves, they enlarge and drop off eventually (gutation)

          The waste products of plants include water, carbon dioxide, oxygen, tannins, alkaloids, acids, resins, mucilage, latex, salts, crystals, oils, gum and anthocynanins. Some of the waste products can be converted to harmless insoluble forms and stored in the plants e.g. calcium carbonate and calcium oxalate. Plants oils (cinnamon, eucalyptus, turpenture and camphor), glycosides, alkcaloids (cocaine, morphene and quinine) and tannis may be stored in the cell vacuoles and cell walls of leaves.

 

INSTRUCTION MATERIALS: Video showing the mechanism of excretion in animals.

 

TEACHING METHODS PROCEDURES.

Step I:         Teacher rev9ices last term topic with the students.

Step II:       Teacher introduces the new topic by defining excretion

Step III:      Teacher lists excretory organs and their waste products

Step IV:      Teacher explains the process of mechanism of excretory organs.

Step V:       Teacher allows students to ask question and writes note under content on the board.

 

ACTIVITIES.

PERIOD 1:           Students discuss the excretory organs found in animals and mention the waste products produced.

PERIOD 2:           Students describe how excretion is carried out in some animals.

PERIOD 3:           Students describe excretion in flowering plants.

 

EVALUATION.

PERIOD 1:           1.      What is excretion?

  1. Mention the excretory organs in insects, prawns and toads

PERIOD 2:           What is the organelle responsible for water elimination from a protozoan body?

PERIOD 3:           What are the organs responsible for excretion in plants?

SUMMARY:          Teacher summarizes the topic, marks the students notes and makes corrections where necessary.

 

ASSIGNMENT(S)

PERIOD     1:      Mention the phases of excretion in humans

  1. Describe excretion in an earthworm

PERIOD 2:

How does the composition of blood in the renal vein of a mammal differ from that of a renal artery? Explain in details the part played by the kidney in achieving these changes.

 

PERIOD 3: State five products of excretion in plants.