Reproduction in animals notes Class 8 CBSE, Metamorphosis, asexual reproduction
For eg- Penicillium , Aspergillus etc. Planaria shows good example of reproduction by regeneration. For eg:- Amoeba, Euglena etc. Dictyospores: spores with one or more transverse and vertical septa 5. The cells then begin to form groups that develop into different tissues and organs of the body. The meeting of the special sex cells gametes , which carry this information is by no means certain and arranging for them to meet often carries an element of risk, for animals at least. At the time of conjugation two opposite strain are attracted toward each other and lie parallel in close contact under common sheath of mucilage.
These roots can give rise to new plants; when kept under the soil. This post is not the correct place to discuss the advantages and disadvantages of the two types of reproduction. Zoospores Ø Zoospores are a type of sporangiospores endospore Ø They are motile spores with flagella Ø Zoospores are usually produced by lower groups of fungi Ø Example: Phythium, Phytopthora Ø Based on the number and position of flagella, there are three types of zoospores in fungi 1. Offspring are identical replicas of parent. Binary Fusion The type of division, in which two individuals are formed from a single individual, is called binary fusion. The chromosome separation process ensures that each sex cell has a unique combination of genes in its nucleus.
Summary of differences Asexual reproduction Sexual reproduction Number of parents 1 either male or female Usually 2 male and female - see note 1 below Makeup of offspring genetically identical to parent and other offspring genetically different Cell division process normal cell division following nuclear division by mitosis special cell division following nuclear division by meiosis producing sex cells gametes - see note 2 below: after fertilisation subsequent divisions: normal Advantages quick - good for bulking up of numbers to colonise new areas produces variation - the basis of evolution Disadvantages disease may affect all slower - needs special processes to bring together gametes and protect zygote, embryo etc during development Life cycle useful when conditions ideal for growth may be synchronised with end of? Regeneration: Some simple organisms can regenerate a new individual from a part which has been accidentally cut off. These organisms are non-motile single cells with chitinous cell walls that earn them classification as fungi. The genitalia are the external reproductive organs of males or females. The cell of opposite filament behaves as gamentangia and produce a tubular outgrowth called papillae. During copulation, sperms reach the Fallopian tube where a sperm fertilizes the egg.
This is an important advantage of asexual reproduction until living conditions change in some way. The bud grows to a certain size and gets detached from the mother hydra. In the plants, the stigma produces sticky substance so pollen grains get stuck in it. It is a diploid spore and is releases after decay of the female filament. Ann Williamson for their continuous support and encouragement. In addition to being used to duplicate whole organisms, binary fission is also utilized within the cells of eukaryotic organisms by some of the organelles.
Spores can also remain dormant for a long time, till favourable conditions are found. It is a resting spore and resistant to unfavorable environmental condition. Birds, lizards, crocodiles are some examples of oviparous animals. Among two gamete, male gamete is motile and active while female gamete is stationary. Modified roots of Carrot and Sweet Potato: Carrot and sweet potato are examples of modifications of roots; for food storage. The group includes organisms from unicellular yeasts to complex cup fungi.
The offspring produces are almost all genetically identical to the parent organism, and so a successful genetic combination can be passed on without change. Figure %: a Some varieties of Ascomycota. Many plants and fungi reproduce asexually as well. Scientists consider spores are precursors of seeds. The female structure is always a differentiated region known as the ascogonium. The daughter nuclei; in turn; grow into new individuals. The daughter cells are morphologically and genetically identical.
However, the introduction of a new disease to an environment, a change in temperature or human intervention can cause the total destruction of a group of genetically identical organisms, because if one cannot cope with the new environment, neither can all the others. There are 2000 identified genera and 30,000 species of Ascomycota. Those animals which lay eggs are called oviparous animals. Both spend energy but which is better for us humans? The pollen tubes divide and form male gametes which emerge towards the ovule. Conjugation is the process of fusion of two gametes produced by two opposite strain. Young Ones to Adults: 1. Conidiaphores may simply branch off from the mycelia or they may be formed in fruiting bodies.
Sexual Reproduction: The process of reproduction in which two individuals are involved to produce a new individual. Reproduction in Simple Organisms Binary Fission: Most of the unicellular animals prefer this method for reproduction. Most varieties of yeast do not form multicellular filiments like the mycelia and hyphae of other fungi, though they do live in massive groupings called colonies. Both male and female sex cells sperms and eggs in animals, pollen and ovules in plants are produced by a special cell division process which halves the number of chromosomes in each resulting cell. However as each organ develops, the cells within it collectively known as tissues become specialised for their particular tasks, e. So each cell of the embryo, and the adult organism into which it develops, contains cells which are genetically identical.
Reproduction in animals notes Class 8 CBSE, Metamorphosis, asexual reproduction
However, some species like S. How many divisions are there in mitosis? Formation of Egg Shell in Hens: Internal fertilization takes place in hens. They cloned successfully a sheep named Dolly. Yeast and Hydra reproduce by budding. Binary Fission:This method of reproduction is seen in unicellular animals, example- amoeba. So, this conjugation is known as scalariform conjugation. However there are cases of simple organisms where two very similar sized cells fuse, then after nuclear fusion meiosis occurs - and there is the suggestion that sex itself can be seen as the result of evolution.
So morphologically reproduction is Isogamous. If a planaria is cut into several pieces; each piece develops into a new individual. Artificial Vegetative Propagation: Man has used artificial vegetative propagation to grow many plants. Asexual reproduction is the term used for any reproductive strategy that produces genetically identical offspring. Asexual reproduction has many advantages.
