The benefit of introducing genetic variation into the species , however, outweighs this disadvantage. If a disease were to hit the rabbit population, then perhaps not all of the rabbits would be affected because of the variation in the population.
This means that some individuals would survive and be able to reproduce and generate more offspring. Some fungi are able to reproduce both sexually and asexually. Fungi reproduce using spores which they release into the environment. A new fungus will grow from the spore. The Coprinus cinereus fungus can produce spores by sexual reproduction to help create variation in the species.
This method of reproduction is advantageous when the environment is changing because the variation introduced leads to an increase in the probability that a variant that can deal with the change. Normal cell division is also the basis for asexual reproduction.
Only one type of cell is involved, with no input from another individual. Because no new genetic material is introduced, there is no variation in the resulting offspring. Since the offspring from this process contain the same genetic material as one another and the same as the original single parent , they can be described as a clone.
Many plants used for food can be propagated , i. Fruits and seeds are produced as a result of sexual reproduction. Each of the examples of food plants below uses asexual and sexual reproduction in different ways. More about strawberries More about bananas More about potatoes More about onions More about apples. Bacteria reproduce asexually by a simpler process known as binary fission. Asexual reproduction is much less common in animals, but it is often seen in simpler animals e.
Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant. Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination occurs in flowers where the stamen and carpel mature at the same time.
This method does not require the investment required to produce a flower, attract pollinators, or find a means of seed dispersal. To start plant tissue culture, a part of the plant such as a stem, leaf, embryo, anther, or seed can be used. The plant material is thoroughly sterilized using a combination of chemical treatments standardized for that species. Under sterile conditions, the plant material is placed on a plant tissue culture medium that contains all the minerals, vitamins, and hormones required by the plant.
The plant part often gives rise to an undifferentiated mass known as callus, from which individual plantlets begin to grow after a period of time. These can be separated and are first grown under greenhouse conditions before they are moved to field conditions. Figure 6. The bristlecone pine, shown here in the Ancient Bristlecone Pine Forest in the White Mountains of eastern California, has been known to live for 4, years.
The length of time from the beginning of development to the death of a plant is called its life span. The life cycle, on the other hand, is the sequence of stages a plant goes through from seed germination to seed production of the mature plant. Some plants, such as annuals, only need a few weeks to grow, produce seeds and die.
Other plants, such as the bristlecone pine, live for thousands of years. Some bristlecone pines have a documented age of 4, years Figure 6. Even as some parts of a plant, such as regions containing meristematic tissue—the area of active plant growth consisting of undifferentiated cells capable of cell division—continue to grow, some parts undergo programmed cell death apoptosis.
The cork found on stems, and the water-conducting tissue of the xylem, for example, are composed of dead cells. Plant species that complete their lifecycle in one season are known as annuals, an example of which is Arabidopsis , or mouse-ear cress. Biennials such as carrots complete their lifecycle in two seasons. Commercial growers harvest the carrot roots after the first year of growth, and do not allow the plants to flower.
Perennials, such as the magnolia, complete their lifecycle in two years or more. In another classification based on flowering frequency, monocarpic plants flower only once in their lifetime; examples include bamboo and yucca. During the vegetative period of their life cycle which may be as long as years in some bamboo species , these plants may reproduce asexually and accumulate a great deal of food material that will be required during their once-in-a-lifetime flowering and setting of seed after fertilization.
Soon after flowering, these plants die. Polycarpic plants form flowers many times during their lifetime. Fruit trees, such as apple and orange trees, are polycarpic; they flower every year. Other polycarpic species, such as perennials, flower several times during their life span, but not each year.
By this means, the plant does not require all its nutrients to be channelled towards flowering each year. As is the case with all living organisms, genetics and environmental conditions have a role to play in determining how long a plant will live.
Susceptibility to disease, changing environmental conditions, drought, cold, and competition for nutrients are some of the factors that determine the survival of a plant. Plants continue to grow, despite the presence of dead tissue such as cork.
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