Life cycles of organisms range in complexity from extremely simple as with unicellular bacteria which begin with fission building the parent and ends once the parent asexually divides into two daughter cells to increasingly complex as with multicellular animals that start with sexual reproduction and morph via developmental stages in which their bodies go through extreme changes.
Simple vs Complex Life Cycles
Life cycles are described as either complex or simple. Many mammals and birds possess simple life cycles because they do not undergo main morphological changes via their development.
A Simple Life Cycle
Bladder wrack algae could be used to show a simple life cycle. This life cycle starts when reproductive receptacles form on the plants within autumn. Eggs form on the female while sperm forms on the male.
A Complex Life Cycle
Other kinds of algae have fairly complex life cycles where greater than one generation can take place within a developmental stage and every generation changes radically in look. Surprisingly, the simplicity of the organism does not always correspond with the simplicity of the life cycle.
Life Cycle Pressures
Numerous multicellular species should overcome ecological and practical obstacles to effectively complete a life cycle. For instance, many species release sperm and eggs to the water where they must fulfill to form what are called free spawned fertilized gametes. The fertilized gametes or zygotes, must then find nutrients for energy to develop into pelagic larvae.
The life cycle of an animal, contains all of the stages from the finish of the last generation to the starting of the next. Life cycles differ in time according to the species of animal and can be as quick as just several weeks for insects, to approximately 200 years for sea urchins.
Despite the time differences, all animal cycles start with the development and growth procedure, which is then followed by reproduction. The reproduction stage within the cycle of life marks the end of the cycle and numerous animals often pass away after they have reproduced just once.
Living Life: Based on the animal species, several animals live very solitary lives and only meet up with other animals from the identical species to mate, in which other animal species including termites and monkeys are very sociable animals and spend their life in a group.
Starting Life: Many animal species start life as a single egg cell which is then fertilised through a sperm cell. The growth procedure varies in speed according to the species as some animals are born in under a week of conception, where others could be born nearly two years afterwards.
Animal Sexes: All animals that require another animal to reproduce are separated into females and males, both of which have very various reproductive organs that have to be combined in order for those animals to make offspring. A small number of animals are asexual which means that they have both female and male reproductive organs and are thus able to self-fertilise. Slugs, snails and barnacles all are asexual animals.
A plant's life cycle explains how long a plant lives or how long it takes to develop, set seed and flower. Plants can be either an annual, perennial or biennial.
Perennial: A plant that lives for three or more years. It can grow, flower and set seed for several years. Underground parts may regrow new stems as in the case of herbaceous plants or the stems may live for many years such as woody plants (trees). Examples: Chrysanthemums, Daisies and roses.
Annual: A plant that finishes its life cycle in one developing season. It will grow, set seed, flower and die. Examples: Tomatoes, petunias and marigolds.
Biennial: A plant that wants two growing seasons to finish its life cycle. It grows vegetatively (produces leaves) one season. Then it goes dormant or rests over the winter. In the spring, it will start to grow again and grow flowers, set seed and die. The seed that is left behind on the ground germinates and the cycle starts again. Examples: Carrots, parsley and foxglove.