Types of reproduction • Reproduction: is a characteristic of living organisms which is essential for continuity of life due to production of new individuals. • Types of reproduction: • Asexual reproduction. • Sexual reproduction.
Asexual reproduction • Definition: it is a type of reproduction which involves only one parent and the off springs are identical to the parent. • Cell division: this type occurs by mitosis cell division. The new cell contains the same number of chromosomes as the main cell. • Sexual reproduction • Definition: it is a type of reproduction which involves male and female where their gametes fuse to form zygote which develops into a new individual. • Cell division: this type occurs by meiosis where gametes are produced containing half number of chromosomes
Sexual • Two parents are involved • Gametes (male, female cells)are formed • Meiotic cell division • Zygote is formed from fertilization . • Slow • Animals and flowering plants. • One parent involved • No gametes are formed • Mitotic cell division • Identical to the parent. • Rapid • Simple organisms, some plants Asexual
Sexual reproduction in : Flowering Plants • The flowering plant is good example of sexual reproduction and the flower is the reproductive organ of the plant, the flower may contain both male and female organs and it is called bisexual. • Other flower may contain only female or male organ it is called unisexual.
Pollination Pollination: it is the transfer of pollen grains from anther to stigma. Types of pollination: self pollination and cross pollination.
Methods of pollination: There are many agents that can cause pollination such as wind, insects, water, animals, and humans.
Fertilization Fertilization: it is the union of pollen grain of the male and egg cell of the female producing the zygote. Steps of fertilization: • The pollen grain falls on the stigma which produces a sticky liquid for nutrition of the pollen helping its germination. • The pollen grain enlarges protruding a pollen tube from it, where the nucleus of the pollen which is the male gamete passes through this tube. • The pollen tube extends toward the ovule and reaches the micropyle. • The tip of the pollen tube will rupture then the nucleus of the male gamete fuses with the female gamete producing the zygote.
When all these steps are completed the flower undergoes many changes which are: • Sepals, petals, stamens, stigma and style with dry and drop off. • The zygote will develop into the embryo of the seed and the ovule will develop into the seed. • The ovary will get bigger to form the fruit which: • Covers and protects the seed. • Helps in dispersal. • Stores food. Dispersal of seeds and fruits: -Dispersal: the scattering or spreading of seeds and fruits away from the main plant. • Prevent overcrowding that increase the chance for diseases. • Prevent competition between plants for space, water and light. • Increase in the growth of plants in different areas. In the mean time the spreading may increase the hazards of growing unwanted plants between crops or growing plants which may unhealthy properties.
Types of dispersal: • Wind dispersal: • They have certain structures that increase the surface area and they are light to be easily carried by winds for a long distance. Examples of those plants: • Poppy plant: the stem is long and the ovary is dry having halls to allow the seeds out, by the action of the wind and they will be scattered around. • Parachute fruits as Dandelion: they have feathery hear which come out of the fruit and seed that flow in air to different areas. • Sycamore: it has a wing structure to prevent its falling on the ground and so it will be easily carried by wind to different areas. • Animal dispersal: Animal can help in dispersal by: • Carrying the seeds on their fur (hooked seeds like Burdock.) • Eating of the fruit containing the seeds which will be excreted by the animal(blackberry)