EXCRETION AND HOMEOSTASIS (PLANT AND ANIMAL)
- 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.
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
- These are nerve cells which detect changes from the external environment thus making the body to be sensitive to touch, cold, heat and pressure.
- 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.
- 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.