Animal and Plant Reproduction Cycles
Reproduction and Life Cycles
The Reproduction Function
The function by which progenitor individuals give rise to new individuals, like themselves. There are two types:
- ASEXUAL: Takes place with only one individual who creates identical individuals.
- SEXUAL: Involves two individuals who originate descendants similar but not identical.
The Organic Cycle
These are the stages an organism passes through throughout its life, from zygote to adult. It has a few phases: REPRODUCTION, EMBRYONIC DEVELOPMENT, and GROWTH.
Animal Reproduction
Asexual Reproduction in Animals
Can be:
Division or Fragmentation
Breakage of the parent into one or more parts, each giving rise to a new individual. E.g., starfish.Budding
Consists of the formation of a bud on the animal’s body that gives rise to another individual. E.g., corals.
Sexual Reproduction in Animals
It takes two individuals of different sexes: male and female. In males, there are gonads called testicles, which produce male gametes or sperm. In females, the gonads are the ovaries, which produce female gametes or eggs. The eggs are motionless and larger.
Individual Sex Types
Hermaphroditic Individuals
Each individual has both sexes or male and female gonads, although it is rare for them to self-fertilize.Gonochorism
Each individual has separate sexes: male or female. They are differentiated by their appearance. E.g., lion and lioness.
Fertilization
It is the union of a sperm and an ovum to form a zygote. Can be:
Internal Fertilization
Takes place within the female reproductive tract.External Fertilization
The eggs and sperm are released externally where fertilization occurs.
Embryonic Development
It is formed from the zygote until the birth of the new individual. Can be:
Oviparous Development
Development of the embryo in an egg outside the mother.Viviparous Development
Develops inside the mother.Ovoviviparous Development
Develops inside an egg but inside the mother.
Postembryonic Development
Growth to the adult state. Can be:
Direct Development
They grow progressively.Indirect Development
The offspring becomes adult through metamorphosis. E.g., butterfly.
Plant Reproduction
Sporophyte vs Gametophyte
The sporophyte is the part of a plant that forms spores. The gametophyte is the part of a plant that forms sexual gametes.
Asexual Reproduction in Plants
Creates a new individual from a fragment of the same plant. Types:
Stolons
Low-lying stems touch the ground to take root and create new individuals. E.g., strawberries, spades.Bulbs
Underground stems wrapped in leaves. E.g., onions.Tubers
Underground stems containing storage substances. E.g., potatoes.Spores
New individuals originate from spores.
Sexual Reproduction in Plants
The reproductive organs are flowers. They are:
Reproductive Organs
- Pistil: The female reproductive organ, bottle-shaped. The upper part is called the stigma, the neck is the style, and the base is the ovary which produces the female gametes.
- Stamens: The male reproductive organ. It has a filament with a bulge called the anther, where pollen grains are found, giving the male gametes.
Pollination
The passage of pollen grains from the anther of a flower to the pistil of the same flower (self-pollination) or of another flower (cross-pollination). Can also be due to insects or by wind.Fertilization and Seed Formation
When the pollen grain reaches the pistil, it goes down to fertilize the ovum. The fertilized ovum becomes the seed, which contains the embryo.Fruit Formation
After fertilization, the ovary becomes the fruit, which protects the seed and assists in its dispersion. They can be:- Fleshy: With juicy and sweet walls due to the nutrients and water they contain.
- Dried: Wall hardened by the loss of water.
Seed Dispersion and Germination
When the fruit is mature, it leaves the plant and falls. Some animals may feed on them, assisting in dispersion. If they find appropriate conditions of temperature, humidity, etc., germination occurs, and the embryo begins its development, creating a new plant.
Reproduction Pros and Cons
Asexual Reproduction Pros and Cons
Advantages: Fast, requires a single individual, less energy, and creates many descendants.
Disadvantages: Individuals are identical to the original; any negative environmental change can lead to the death of all.
Sexual Reproduction Pros and Cons
Advantages: The descendants are different, so some are more likely to survive environmental changes.
Disadvantages: It is slower and more complex, and requires more energy from individuals.