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Yogita Ingle 6 years, 3 months ago
- Amoeba is a microscopic single-celled organism found in pond water which has a cell membrane, a round, dense nucleus and many bubble like vacuoles.
- The shape of amoeba is variable.
- It has tiny finger like projections called pseudopodia or false feet for movement and capture of food.
- It eats tiny organisms by spreading out its pseudopodia around its food particle and then engulfing it.
- The food gets trapped inside food vacuole, into which digestive juices are secreted and convert them into simpler substances.
- The digested food is then absorbed which is required for growth, maintenance and multiplication.
- The undigested food is expelled out by vacuole.
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Meghna Thapar 5 years, 8 months ago
An angiosperm ovule contains an egg cell and a diploid fusion nucleus, which is created through the joining of two polar nuclei within the ovule. When a pollen grain comes into contact with the stigma, or top of the pistil, it sends a pollen tube down into the ovary at the pistil's base. First, pollen falls on a flowers stigma. In time, the sperm cell and egg cell join together in the flowers ovule. The zygote develops into the embryo part of the seed. Embryonic development starts with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon). ... The zygote undergoes mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of a multicellular embryo.
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∂Αяѕнαиαα ყα∂Αѵ ??? 6 years, 3 months ago
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Marsh gas is produced when vegetation decomposes naturally within some geographical marshes, swamps, and bogs. Methane is called as Marsh Gas. The main process for the production of methane is anaerobic digestion.
Posted by Sakshi Singh 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
Pollen grains
Each pollen grain is a tiny spherical structure, surrounded by 2 layers:
Exine
- Hard, outer layer
- Composed of sporopollenin
- Highly resistant
Intine
- Thin inner layer
- Composed of cellulose & pectin
Formation of a pollen grain from microspore involves the following changes:
- Expansion of the microspore
- Formation of a large vacuole
- Microspore nucleus displaced to an eccentric position against microspore wall
- Nucleus undergoes first pollen mitosis
- A large vegetative cell & a small generative cell are formed. This is the 2-cell stage. In many plants, pollen grains are released at this 2-celled stage. However, in some others, they are released at a 3-celled stage.
- Generative cell detaches from pollen grain wall
- Generative cell is engulfed by the vegetative cell
- ‘Cell within a cell' structure is formed
- Generative cell again undergo mitosis
- Two sperm cells are formed enclosed within the vegetative cell cytoplasm
Posted by Mulla Gaus 6 years, 3 months ago
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Meghna Thapar 5 years, 8 months ago
The eye is our organ of sight. The eye has a number of components which include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous. Cornea: the clear front window of the eye that transmits and focuses light into the eye.
The front part (what you see in the mirror) includes:
- Iris: the colored part.
- Cornea: a clear dome over the iris.
- Pupil: the black circular opening in the iris that lets light in.
- Sclera: the white of your eye.
- Conjunctiva: a thin layer of tissue that covers the entire front of your eye, except for the cornea.
Posted by Mo Khari 6 years, 3 months ago
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Meghna Thapar 5 years, 8 months ago
Leydig cells are interstitial cells located adjacent to the seminiferous tubules in the testes. The best-established function of Leydig cells is to produce the androgen, testosterone, under the pulsatile control of pituitary luteinizing hormone (LH). Leydig cells release a class of hormones called androgens (19-carbon steroids). They secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone luteinizing hormone (LH). Androgens are synthesized from cholesterol and are produced primarily in the gonads (testicles and ovaries) and also in the adrenal glands.
Posted by Hija Godak 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
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Darwin’s theory |
Hugo de Vries theory |
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Posted by Hija Godak 6 years, 3 months ago
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Meghna Thapar 5 years, 8 months ago
- Meiosis a reduction cell division which takes places in the reproductive cells (Sperms , eggs).
- In this division, the diploid number of chromosomes is reduced to haploid number of chromosomes.
- At the end of meiosis, four haploid daughter cells are formed.
- It is essential for sexual reproduction in all eukaryotes.
- It occurs in two stages including meiosis I and meiosis II.
- Meiosis I include Prophase I, Metaphase I, Anaphase I, Telophase I , Cytokinesis I.
- Meiosis II include Prophase II, Metaphase II, Anaphase II, Telophase II , Cytokinesis II.
- In Prophase I, there are 5 stages including Leptotene, zygotene, pachytene, diplotene, and diakinesis.
- In Pachytene stage, crossing over takes place between non-sister chromatids of two homologous chromosomes which results in genetic variation.
Posted by Jyoti Mishra 6 years, 3 months ago
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Meghna Thapar 5 years, 8 months ago
- Translation involves translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis.
- It is the process in which ribosomes in the cytoplasm or ER synthesize proteins after the process of transcription of DNA to RNA.
Each prokaryotic ribosome, shown schematically, has three binding sites for tRNAs.
- The aminoacyl-tRNA binding site (or A site) is where, during elongation, the incoming aminoacyl-tRNA binds.
- The peptidyl-tRNA binding site (or P site) is where the tRNA linked to the growing polypeptide chain is bound.
- The exit site (or E site) is a binding site for tRNA following its role in translation and prior to its release from the ribosome.
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All three sites (A, P and E) are formed by the rRNA molecules in the ribosome.
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Gregor Johann Mendel: Father of Genetics • Known as the father of modern genetics • Gregor Mendel developed the principles of heredity while studying seven pairs of inherited characteristics in pea plants. • Although the significance of his work was not recognized during his lifetime, it has become the basis for the present-day field of genetics.
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Sarcolemma is a specialized cell membrane which surrounds striated muscles fibre. This play a very important role in muscle contraction process.
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Amaan Ansari 6 years, 3 months ago
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