Biology Reproduction PDF

# Chapter-7: How do Organisms Reproduce? ## Reproduction - It is the biological process to create new individuals that look similar to parents. - This process is important for the survival of species on Earth and it ensures the continuity of life. ## Types of Reproduction There are two types o...

# Chapter-7: How do Organisms Reproduce? ## Reproduction - It is the biological process to create new individuals that look similar to parents. - This process is important for the survival of species on Earth and it ensures the continuity of life. ## Types of Reproduction There are two types of reproduction: 1. **Asexual** 2. **Sexual** ### Asexual Reproduction 1. It involves a single parent. 2. No gamete formation. 3. No zygote is formed. 4. The new individual formed is a xerox copy of the parent called a clone. 5. Examples: Budding in Yeast, Binary Fission in Amoeba ### Sexual Reproduction 1. It involves two parents of the opposite sex: male and female. 2. Gamete formation occurs. 3. Zygote is formed. 4. The new individual formed is identical to the parent, but with a lot of variations. 5. Examples: Bat, Dog, Mango Plant, Humans, etc. ## Asexual Reproduction in Detail ### Budding - Occurs in **Hydra** - A bud detaches from the parent and grows as an individual ### Regeneration - Occurs in **Starfish**, **Planaria** ### Spore Formation - Common in **Rhizopus** - The fungal stem is called a hyphae. - The hyphae bear knob-like structures called sporangia that produce spores. - These spores develop into new individuals on the arrival of favorable conditions like humidity and moisture. - Spores are well protected by a thick wall cyst. ### Binary Fission - Occurs in **Amoeba** - The nucleus elongates and divides into two daughter cells. ### Multiple Fission - Occurs in **Plasmodium** - The nucleus of the cell divides repeatedly producing many nuclei. - The nuclei are surrounded by cytoplasm and are enclosed in a hard covering called a cyst. - On arrival of favorable conditions, the cyst breaks open and spores are released to produce new individuals. - Multiple fission is also seen in algae. ### Fragmentation - Multicellular organisms with a simple body design show this method. - The body can be broken into two or more pieces, or fragments. - Each fragment grows as a new individual. ### Regeneration - It is the ability of fully differentiated organisms to give rise to a new individual from its body parts. - Small cut or broken parts of the body can regenerate or grow itself. - Examples: **Hydra**, **Planaria** - Regeneration is common in organisms with simpler body designs. - In organisms with higher levels of organization, regeneration ability decreases. ## Vegetative Propagation - New plants are obtained from vegetative parts of old plants without the use of reproductive organs. - Vegetative parts of a plant are the stem, roots and leaves. ### Natural Vegetative Propagation - Occurs in nature by itself. - Examples: 1. By root: Sweet potato 2. Stem: Potato 3. Leaves: Bryophyllum ### Artificial Vegetative Propagation - Occurs with the help of humans - Examples: 1. Cutting: Rose, Sugarcane 2. Grafting: Apple, Mango, Rose 3. Layering: Strawberry, Jasmine, Guava ## Advantages of Vegetative Propagation 1. It is a cheap, easy and rapid method of propagation 2. Important in producing seedless plants: Banana, Tomato, Grapes. 3. Plants produced by this method bear fruit and flowers early than those produced by seeds. 4. New plants are genetically identical to the parents (clone) 5. Better quality and characteristics can be maintained by this method. ## Disadvantages of Vegetative Propagation 1. No new characteristics can be produced. 2. No unwanted characteristics can be removed 3. No genetic variation, so adaptation to the physical environment becomes less. ## DNA Copying (Replication) - DNA present in the cell's nucleus and carries hereditary information. - DNA forms protein that regulate all the body functions. - DNA: Deoxyribonucleic Acid - The basic event in reproduction is DNA copying. - It is done just before the cell divides. - Doubling the amount of DNA by enzyme DNA polymerase. - It ensures that daughter cells formed after cell division have the same amount of genetic material as present in the parent cell. - While DNA copying, enzymes make errors which leads to variation. - In case of asexual reproduction, variation is less (single parent involved) - In case of sexual reproduction, variations could be many (involve two parents) - DNA copying leads to variation, which further results in evolution and speciation (formation of new species) ## Sexual Reproduction in Plants - The reproductive part of a plant is the flower. - There are four parts arranged in whorls. ### Parts of a Flower: 1. _**Calyx** or **Sepal**_: Usually green in color and protects the bud. 2. _**Corolla** or **Petal**_: The colorful part of the flower that attract insects for pollination. 3. _**Androecium** or **Stamen**_: It is the male reproductive part and is formed of filaments and anther. The male gamete, pollen grains, are produced inside the anther. 4. _**Pistil** or **Carpel** or **Gynoecium**_: The female reproductive part and is formed of stigma, style and ovary. - **Stigma**: The sticky part that receives pollen grains. - **Style**: The middle elongated part that connects the stigma to the ovary. - **Ovary**: The swollen bottom part that contains the female gamete ovule. - Sepal and Petal are non-essential parts of the flower as they are not involved directly in reproduction. - Androecium and Gynoecium are essential parts as they are involved directly in reproduction by forming gametes. ## Types of Flower: 1. **Unisexual flower**: It contains either stamen or carpel. - Examples: Papaya, date palm, coconut 2. **Bisexual flower**: Contains both stamen and carpel within it. - Examples: China rose, mustard, railway creeper ### Diagrams: - Stamen - Carpel