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Yogita Ingle 5 years, 5 months ago
Apomixis is a mechanism to produce seeds without fertilization. This mechanism produces clones, hence can be considered as a form of asexual reproduction.
Apomixis can occur in a number of ways, some of which are mentioned below:
Nucellar cells which are diploid & located outside the embryo sac continuously divide and enter inside embryo sac and later develop into embryos. In this way, multiple embryos can exist inside one ovule. This is termed as Polyembryony. It is seen commonly in Citrus, mango etc..
Sometimes, the egg cell is not formed as a result of reduction division, hence diploid. This diploid egg cell later directly develops into an embryo.
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Muzammil Hasan 5 years, 5 months ago
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Meghna Thapar 5 years, 3 months ago
Anatropous ovule is a completely inverted ovule turned back 180 degrees on its stalk. For example, Helianthus and Tridax. Ovule is a small body that contains the female germ cell of a plant; develops into a seed after fertilization. Anatropous ovule - In this type, the body of the ovule becomes completely inverted during the development such that micropyle lies very close to the funicle. For example, gamopetalae members.
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Insha Khalid 5 years, 5 months ago
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Meghna Thapar 5 years, 5 months ago
As the anther develops, the cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad, each one is a potential pollen or microspore mother cell. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. Inside each microsporangium, several thousands of microspores or pollen grains are formed that are released with the dehiscence of the anther.
Posted by Tushar Upadhyay 5 years, 5 months ago
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Yogita Ingle 5 years, 5 months ago
Darwin Darwin had the following ideas regarding the theory of natural selection:
- Species keep on evolving or changing with time. As the environment changes, the requirements of an organism also change and they adapt to the new environment. This phenomenon of changing over a period of time as per the natural requirements is called adaptation.
- As per Darwin’s theory, only the higher changes are naturally selected and the lower ones are eliminated. Thus, not all the adaptations contribute to a progressive evolution. For example, people living in tropical countries have more melanin in their body to protect them from the sunlight.
- Almost all organisms share common ancestry with some organism. According to Darwin, all organisms had one common ancestor at some point in time and kept on diverging ever since. His evolutionary theories support the convergent theory and divergent theory of evolution with examples.
- He also studied that the birds of Galapagos Island (Darwin’s finches) developed different beaks as per the availability of the food. This proved adaptive radiation. Similarly, he also observed the Australian Marsupials which showed a number of marsupials emerging from an ancestor.
- According to Charles Darwin, evolution is a very slow and gradual process. He concluded that evolution took place over a very long period of time. As we talk about the time period in evolution we usually refer to billions of years. The generation of a species from another takes a long period of time. It is a very steady process as the changes and adaptation take a long time to stabilize and give rise to a new species.
Posted by Deepak . 5 years, 5 months ago
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Meghna Thapar 5 years, 5 months ago
Surgical instruments and other material or equipment that will contact the surgical site must be sterile prior to use. The process of sterilization kills all forms of life, including bacterial spores and viruses.
Posted by Aman Sharma 5 years, 5 months ago
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Yogita Ingle 5 years, 5 months ago
Juvenile phase- the period of growth from birth to reproductive maturity in animalsis called juvenile phase and in plants this inter flowering period is known as vegetative phase.
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Yogita Ingle 5 years, 5 months ago
Regeneration is one of the processes in which if an organism is cut into several pieces, each of its parts regrows to the original state. This process is carried out by specialized cells called stem cells. It takes place in organisms that have a very simple structure with very few specialized cells.
The cells divide quickly into a large number of cells. Each cell undergoes changes to form various cell types and tissues. This sequential process of changes is known as development. The tissues form various body parts and organs.
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Meghna Thapar 5 years, 5 months ago
An ectopic pregnancy most often occurs in a fallopian tube, which carries eggs from the ovaries to the uterus. This type of ectopic pregnancy is called a tubal pregnancy. Sometimes, an ectopic pregnancy occurs in other areas of the body, such as the ovary, abdominal cavity or the lower part of the uterus (cervix), which connects to the ******.
Harjinder Singh 5 years, 5 months ago
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Harjinder Singh 5 years, 5 months ago
Aditya Chauhan 5 years, 5 months ago
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Meghna Thapar 5 years, 5 months ago
The main difference between testa and tegmen is that testa is the outer seed coat whereas tegmen is the inner seed coat. Furthermore, testa is smooth, thick, impermeable, and may be colored while tegmen is a thin membranous and hyaline. Testa and tegmen are the two seed coats found in the bitegmic seed of dicots.
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Yogita Ingle 5 years, 5 months ago
Many organisms occupy positions in different food chains, and several food chains become interconnected to form a food web.
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Meghna Thapar 5 years, 3 months ago
Semelparous organisms reproduce by a single reproductive act. Annual and biennial plants are semelparous, as are many insects and a few vertebrates, notably salmon and eels. Other semelparous animals include many insects, including some species of butterflies, cicadas, and mayflies, many arachnids, and some molluscs such as some species of squid and octopus. Semelparity also occurs in smelt and capelin, but is very rare in vertebrates other than bony fish.
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Meghna Thapar 5 years, 3 months ago
Dehiscence is the splitting, at maturity, along a built-in line of weakness in a plant structure in order to release its contents, and is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part. Structures that open in this way are said to be dehiscent. The most commonly type of dehiscence pattern in another is the pollen grains is commonly released from the anther through a longitudinal slitlike opening in the anther wall but other method also occur.
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Insha Khalid 5 years, 6 months ago
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Meghna Thapar 5 years, 4 months ago
Flagella and cilia consist of 9 fused pairs of protein microtubules with side arms of the motor molecule dynein that originate from a centriole. These form a ring around an inner central pair of microtubules that arise from a plate near the cell surface. The arrangement of microtubules is known as a 2X9+2 arrangement.
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