EXCRETION AND HOMEOSTASIS (PLANT AND ANIMAL)

Biology

EXCRETION AND HOMEOSTASIS (PLANT AND ANIMAL)

Introduction

  • Excretion is the process by which living organisms separate and eliminate waste products of metabolism from body cells.
  • If these substances were left to accumulate, they would be toxic to the cells.
  • Egestion is the removal of undigested materials from the alimentary canals of animals.
  • Secretion is the production and release of certain useful substances such as hormones, sebum and mucus produced by glandular cells.
  • Homeostasis is a self-adjusting mechanism to maintain a steady state in the internal environment

Excretion in Plants

  • Plants have little accumulation of toxic waste especially nitrogenous wastes.
  • This is because they synthesise proteins according to their requirements.
  • In carbohydrate metabolism plants use carbon (IV) oxide released from respiration in photosynthesis while oxygen released from photosynthesis is used in respiration.
  • Gases are removed from the plant by diffusion through stomata and lenticels.
  • Certain organic products are stored in plant organs such as leaves, flowers, fruits and bark and are removed when these organs are shed.
  • The products include tannins, resins, latex and oxalic acid crystals.
  • Some of these substances are used illegally.
  • Khat, cocaine and cannabis are used without a doctor’s prescription and can be addictive.
  • Use of these substances should be avoided.

Plant Excretory Products, their source and uses

Excretion and Homeostasis in Unicellular Organisms

  • Protozoa such as amoeba depend on diffusion as a means of excretion.
  • They have a large surface area to volume ratio for efficient diffusion.
  • Nitrogenous waste and carbon (IV) oxide are highly concentrated in the organism hence they diffuse out.
  • In amoeba excess water and chemicals accumulation in the contractile vacuole.
  • When it reaches maximum size the contractile vacuole moves to the cell membrane, bursts open releasing its contents to the surroundings.
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Excretion in Human Beings

  • Excretion in humans is carried out by an elaborate system of specialised organs.
  • Their bodies are complex, so simple diffusion cannot suffice.
  • Excretory products include nitrogenous wastes which originate from deamination of excess amino acids.
  • The main excretory organs in mammals such as human beings include lungs, kidneys, skin and liver.

Structure and function of the human skin

Nerve Endings:

  • These are nerve cells which detect changes from the external environment thus making the body to be sensitive to touch, cold, heat and pressure.

Subcutaneous Fat:

  • Is a layer beneath the dermis.
  • It stores fat and acts as an insulator against heat loss.
  • The skin helps in elimination of urea, lactic acid and sodium chloride which are released in sweat.

The Lungs

  • Carbon (IV) oxide formed during tissue respiration is removed from the body by the lungs.
  • Mammalian lungs have many alveoli which are the sites of gaseous exchange.
  • Alveoli are richly supplied with blood and have a thin epithelium.
  • Blood capillaries around the alveoli have a high concentration of carbon (Iv) oxide than the alveoli lumen.
  • The concentration gradient created causes carbon (IV) oxide to diffuse into the alveoli lumen.
  • The carbon (IV) oxide is eliminated through expiration.

See also

FACTORS AFFECTING RATE OF BREATHING IN HUMANS

GASEOUS EXCHANGE IN A MAMMAL – HUMAN

GASEOUS EXCHANGE IN AN AMPHIBIAN – FROG

GASEOUS EXCHANGE IN INSECTS

GASEOUS EXCHANGE IN ANIMALS

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