Reproductive and Excretory System
- Asexual reproduction is the process of multiplication of individuals without the formation or fusion of gametes.
- The hydra produces buds, starfish can generate an entire body from a fragment of the original body.
- Asexual reproduction occur in several ways :
- Binary Fission : it involves the division of the nucleus followed by that of the cytoplasm, breaking the body into two young ones. It occurs in unicellular organisms. Example: amoeba, euglena, paramecium, etc.
- Multiple Fusion : in this the nucleus divides into several daughter nuclei, followed by the simultaneous division of the cytoplasm. It occurs in protozoa example : plasmodium.
- Sporulation : in many protozoa and bacteria the asexual reproduction occurs by the division of nucleus into several daughter nuclei, and then then each daughter nucleus gets enclosed by small amount of cytoplasm to form a spore.
- Budding : budding is an unequal division of the parent where the identity of the parent body is still maintained. It contrasts with binary fission where the parent body divides equally into two and no identity of the parent is left. It is common in hydra.
- Fragmentation : the body may break into two or more fragments, and each fragment develops into a complete individual. Example: filamentous algae, spirogyra.
- The process of sexual reproduction involves the formation and fusion of gametes and results in the formation of new organisms genetically different from parents.
- In certain animals, the male and female sex organs are present in the same individual. Such species are called monoecious or bisexual. E.g., earthworm, leech.
- Parthenogenesis is a specialised reproduction in which eggs develop without fertilization e.g., bees, ants, wasps, etc.
- Flowers : The reproductive parts of the flower are the stamen (male androecium) and capel (female gynoecium).
- Pollen : pollen grains contain the male gametophyte phase of the plant. They are produced by meiosis of microspore mother cells that are located along the inner edge of the other sacs (microsporangia).
- Pollination : the transfer of pollen from the anther to the female stigma is termed pollination.
- Entomophily is the transfer of pollen by an insect.
- Anemophily is the transfer of pollen by wind.
- The pollen tube grows through stigma and style toward the ovules in the ovary.
- Fruit : the ovary wall, after fertilization has occurred develops into a fruit.
The Excretory System
- components of this system in mammals include the kidneys, liver, lungs and skin.
- Kidney :
- Left kidney is higher than the right kidney.
- A kidney is composed of 1.2 million microscopic structural and functional units called nephrons or uriniferous tubules.
- Kidney functions :
- Maintain volume of extracellular fluid.
- Maintain ionic balance in extracellular fluid.
- Maintain PH and osmotic concentration of the extracellular fluid.
- Excrete toxic metabolic byproducts such as urea, ammonia and uric acid.
- Nephron : functional unit of kidney. It is a long tube differentiated into 4 regions.