Life Processes in Living Organisms Class 10 Science Notes Maharashtra State Board
Living Organisms and Life Processes
Various organ systems are continuously performing their functions in the human body. Along with the various systems like digestive, respiratory, circulatory, excretory, and control systems, different external and internal organs perform their functions independently but through complete coordination. This overall system is in action in more or less the same way in all the organisms. Those need a continuous source of energy for this purpose.
Carbohydrates, fats, and lipids are the main sources of this energy and it is harvested by the mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy production but oxygen is also necessary. All these i.e. foodstuff and oxygen are transported up to the cell via the circulatory system. Besides, it is coordinated by the control system of the body. i.e. each life process contributes in its way in the process of energy production. Functioning of all these life processes also requires energy.
Humans and other animals consume fruits and vegetables. Plants are autotrophs. They prepare their food. They utilize some of the food for themselves whereas the remaining is stored in various parts like fruits, leaves, stems, roots, etc. We consume all these various plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, minerals, etc. Which food materials do we consume to obtain these nutrients? We obtain carbohydrates from milk, fruits, jaggery, cane sugar, vegetables, potatoes, sweet potatoes, sweetmeats, and cereals like wheat, maize, ragi, jowar, millet, rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which this energy is obtained. Many players are seen consuming some foodstuffs during breaks of the game.
Living Organism and Energy Production
In living organisms, respiration occurs at two levels body and cellular level. Oxygen and carbon dioxide are exchanged between the body and surroundings in case respiration occurs at the body level. In the case of respiration at the cellular level, foodstuffs are oxidized either with or without the help of oxygen.
Carbohydrates of the food that we consume every day are mainly utilized for the production of the energy required for daily needs. This energy is obtained in the form of ATP. For this purpose, glucose, a type of carbohydrate is oxidized step by step in the cells. This is called cellular respiration. Cellular respiration occurs among living organisms by two methods. Those two methods are aerobic respiration (oxygen is involved) and anaerobic respiration (oxygen is not involved). In aerobic respiration, glucose is oxidized in three steps.
1. Glycolysis
The process of glycolysis occurs in the cytoplasm. A molecule of glucose is oxidized step by step in this process and two molecules of each i.e. pyruvic acid, ATP, NADH2, and water are formed. Molecules of pyruvic acid formed in this process are converted into molecules of acetyl-Coenzyme-A. Two molecules of NADH2 and two molecules of CO2 are released during this process.
2. Tricarboxylic Acid Cycle
Both molecules of acetyl-CoA enter the mitochondria. A cyclic chain of reactions called the tricarboxylic acid cycle is operated on in the mitochondria. Acetyl part of acetyl-CoA is completely oxidized through this cyclical process and molecules CO2, H2O, NADH2, and FADH2 are derived.
3. Electron Transfer Chain Reaction
Molecules of NADH2 and FADH2 formed during all the above processes participate in the electron transfer chain reaction. Due to this, 3 molecules of ATP are obtained from each NADH2 molecule and 2 molecules of ATP from each FADH2 molecule. Besides ATP, water molecules are also formed in this reaction. The electron transfer chain reaction is operated in mitochondria only. Thus, a molecule of glucose is completely oxidized in aerobic respiration, and molecules of CO2 and H2O are produced along with energy.
NADH2 – Nicotinamide Adenine Dinucleotide
FADH2 – Flavin Adenine Dinucleotide
Both enzymes are formed in the cells and used in cellular respiration.
ATP:
Adenosine triphosphate is an energy-rich molecule and energy is stored in the bonds by which phosphate groups are attached. These molecules are stored in the cells as needed. Chemically, ATP is a triphosphate molecule formed from adenosine ribonucleoside. It contains a nitrogenous compound adenine, pentose sugar-ribose, and three phosphate groups. As per the need, energy is derived by breaking the phosphate bond of ATP; hence ATP is called as ‘energy currency’ of the cell.
If there is an insufficient amount of carbohydrates in the body due to exceptional conditions like fasting and hunger, then lipids and proteins are used for energy production. In the case of lipids, they are converted into fatty acids whereas proteins are into amino acids. Fatty acids and amino acids are converted into acetyl-CoA and energy is obtained through complete oxidation of acetyl-CoA by the process of Krebs cycle in mitochondria.
The process of glycolysis was discovered by three scientists Gustav Embden, Otto Meyerhof, and Jacob Parnas along with their colleagues. For this purpose, they performed experiments on muscles.
Hence, glycolysis is also called as Embden-Meyerhof-Parnas pathway (EMP pathway). The cyclical reactions of the tricarboxylic acid cycle were discovered by Sir Hans Kreb. Hence, this cyclical process is also called Kreb’s cycle. He was awarded the Nobel Prize in 1953 for this discovery.
Process of energy production through aerobic respiration of carbohydrates, proteins, and Fats.
Anaerobic respiration in living organisms/cells
Energy Production in Microorganisms through Anaerobic Respiration
Some organisms cannot live in the presence of oxygen. Ex. Many bacteria. Such living organisms have to perform anaerobic respiration for energy production. Glycolysis and fermentation are two steps of anaerobic respiration. Glucose is incompletely oxidized and less amount of energy is obtained in this type of respiration. Pyruvic acid produced through glycolysis is converted into other organic acids or alcohol with the help of some enzymes in this process. This is called fermentation.
Some higher plants, animals, and aerobic microorganisms also perform anaerobic respiration instead of aerobic respiration if there is a depletion in oxygen levels in the surroundings. Ex. Seeds perform anaerobic respiration if the soil is submerged under water during germination. Similarly, our muscle cells also perform anaerobic respiration while performing the exercise. Due to this, less amount of energy is produced in our body and lactic acid accumulates due to which we feel tired.
Energy from Different Food Components
Excess carbohydrates are stored in the liver and muscles in the form of glycogen.
What is the source of proteins? What are they made up of?
Proteins are the macromolecules formed by bonding together many amino acids. Proteins of animal origin are called as ‘first class’ proteins. We get 4 Kcal of energy per gram of proteins. Amino acids are obtained after the digestion of proteins. Those amino acids are absorbed in the body and transported up to each organ and cell via blood. From these amino acids, organs and cells produce various proteins necessary for themselves and the whole body. Those examples are given in the following diagram.
Excess amino acids obtained from proteins are not stored in the body. They are broken down and the ammonia formed is eliminated out of the body. If necessary, excess proteins are converted into other useful substances like glucose through the process of gluconeogenesis. Plants produce the necessary amino acids from minerals Lenovo and thereby produce different proteins. An enzyme RUBISCO present in the plant chloroplasts is the most abundant protein found in nature.
From where do we obtain the lipids?
The substances formed by specific chemical bonds between fatty acids and alcohol are called as lipids. Digestion of lipids consumed by us is nothing but their conversion into fatty acids and alcohol. Fatty acids are absorbed and distributed everywhere within the body. From those fatty acids, different cells produce various substances necessary to themselves. Ex. the molecules called phospholipids which are essential for producing plasma membranes are formed from fatty acids. Besides, fatty acids are used for producing hormones like progesterone, estrogen, testosterone, aldosterone, etc., and the covering around the axons of nerve cells. We get 9 KCal of energy per gram of lipids. Excess lipids are stored in adipose connective tissue in the body.
Vitamins are a group of heterogeneous compounds of which, each is essential for the proper operation of various processes in the body. There are main six types of vitamins, e.g. A, B, C, D, E, and K. Out of these, A, D, E, and K are fat-soluble whereas B and C are water-soluble. We have seen that FADH2 and NADH2 are produced in the processes like glycolysis and Krebs cycle. Vitamins like riboflavin (Vitamin B2) and nicotinamide (Vitamin B5) respectively are necessary for their production. There is about 65-70% water in our body. Each cell contains 70% water weight by weight. Blood plasma also contains 90% of water. The functioning of cells and thereby whole body is disturbed even if there is a little loss of water from the body. Hence, water is an essential nutrient. Along with all the above-mentioned nutrients, fibers are also essential nutrients. We cannot digest the fibers. However, they help in the digestion of other substances and the digestion of undigested substances. We obtain the fibers from leafy vegetables, fruits, cereals, etc.
Cell Division: An Essential Life Process
Cell division is one of the very important properties of cells and living organisms. Due to this property only, a new organism is formed from an existing one, a multicellular organism grows up and an emaciated body can be restored. There are two types of cell division mitosis and meiosis. Mitosis occurs in somatic cells and stem cells of the body whereas meiosis occurs in germ cells. Before the study of cell division, we should know the structural organization of cells that we have studied earlier. Each cell has a nucleus. Besides, other cell organelles are also present. Let us study the cell division with the help of this information. Before any type of cell division, the cell doubles up its chromosome number present in its nucleus i.e. if chromosome number is 2n, it is doubled up to 4n.
A pair of each type of chromosome is present in the 2n condition whereas a single chromosome of each type is present in the n condition and their structure is like the one shown in the figure given beside.
Mitosis
Somatic cells and stem cells divide by mitosis. Mitosis is completed through two main steps. Those two steps are karyokinesis (nuclear division) and cytokinesis (cytoplasmic division). Karyokinesis is completed through four steps.
A. Prophase:
In prophase, condensation of basically thin thread-like chromosomes starts. Due to this, they become short and thick and they start to appear along with their pairs of sister chromatids. Centrioles duplicate and each centriole moves to opposite poles of the cells. The nuclear membrane and nucleolus start to disappear.
B. Metaphase:
The nuclear membrane completely disappears in metaphase. Chromosomes complete their condensation and become visible along with their sister chromatids. All chromosomes are arranged parallel to the equatorial plane (central plane) of the cell. Special types of flexible protein fibers (spindle fibers) are formed between the centromere of each chromosome and both centrioles.
C. Anaphase:
In anaphase, centromeres split, and thereby sister chromatids of each chromosome separate and they are pulled apart in opposite directions with the help of spindle fibers. Separated sister chromatids are called daughter chromosomes. Chromosomes being pulled appear like a bunch of bananas. In this way, each set of chromosomes reaches two opposite poles of the cell.
D. Telophase:
The chromosomes that have reached opposite poles of the cell now start to decondense due to which they again become thread-like thin and invisible. A nuclear membrane is formed around each set of chromosomes reaching the poles. Thus, two daughter nuclei are formed in a cell. A nucleolus also appears in each daughter nucleus. Spindle fibers completely disappear. In this way, karyokinesis completes and cytokinesis begins.
The cytoplasm divides by cytokinesis and two new cells are formed which are called daughter cells. In this process, a notch is formed at the equatorial plane of the cell which deepens gradually, and thereby two new cells are formed. However, in the case of plant cells, instead of the notch, a cell plate is formed exactly along the midline of the cell and thus cytokinesis is completed.
Mitosis is essential for the growth of the body. Besides, it is necessary for restoration of the emaciated body, wound healing, formation of blood cells, etc.
Meiosis:
Meiosis is completed through two stages. Those two stages are meiosis-I and meiosis-II. In meiosis-I, recombination/crossing over occurs between homologous chromosomes and thereafter those homologous chromosomes (Not sister chromatids) are divided into two groups and thus two haploid cells are formed.
Meiosis-II is just like mitosis. In this stage, the two haploid daughter cells formed in meiosis-I undergo division by separation of recombined sister chromatids, and four haploid daughter cells are formed. The process of gamete production and spore formation occurs by meiosis. In this type of cell division, four haploid (n) daughter cells are formed from one diploid (2n) cell. During this cell division, crossing over occurs between the homologous chromosomes and thereby genetic recombination occurs. Due to this, all four daughter cells are genetically different from the parent cell and each other.
Apparatus: Microscope, watch glass, etc.Conical flask, glass slides, cover slips, forceps, compound microscope, watch glass, etc.
Materials: a medium-sized onion, iodine solution, etc.
Procedure: Take a medium-sized onion. Keep it in a conical flask filled with water in such a way that the roots of the onion will be in contact with the water. Observe the roots of the onion after 4-5 days. Cut the tips of some of the roots and put them in a watch glass. Pour some drops of iodine into the watch glass. Take one of the root tips on the glass slide and press it with the help of forceps. Add 1-2 drops of water and carefully place the cover slip over it in such a way that air will not be trapped between. Observe the prepared glass slide under the compound microscope. Which phase of cell division did you observe? Sketch its figure. Various phases of cell division occurring in the root tips of onions are shown in the following figure. Which one of those could you see in the slide?
We have studied various life processes in previous classes. All those life processes i.e. nutrition, respiration, excretion, sensation & response (control & coordination), etc. are essential to each living organism to remain alive. Besides these life processes, one more life process occurs in living organisms; it is reproduction. However, reproduction does not help the organism to remain alive but it helps to maintain the continuity of the species of that organism.
The formation of new organisms of the same species by earlier existing organisms is called reproduction. Reproduction is one of the various important characteristics of living organisms. It is also one of the various reasons responsible for the evolution of each species. In living organisms, reproduction occurs mainly by two methods. Those two methods are asexual and sexual reproduction.
Asexual Reproduction
The process of formation of a new organism by an organism of the same species without the involvement of gametes is called asexual reproduction. As this reproduction does not involve the union of two different gametes, the new organism has an exact genetic similarity with the reproducing organism. This is uniparental reproduction and it occurs by mitotic cell division. The absence of genetic recombination is a drawback whereas the fast process is an advance of this reproductive method.
A. Asexual Reproduction in Unicellular Organisms
1. Binary Fission
Take a conical flask and collect the water in it from a pond having stagnant water and aquatic plants. Add some wheat grains and aquatic plants to it. Keep it for 3-4 days so that wheat grains & plants will decompose. Early in the morning on the fourth day, take a glass slide and put a drop of that water over it. Carefully, put a cover slip on that drop and observe under a compound microscope. You will be able to see many paramecia performing binary fission. Prokaryotes (Bacteria), Protists (Amoeba, Paramoecium, Euglena, etc.), and eukaryotic cell-organelle like mitochondria and chloroplasts perform asexual reproduction by binary fission.
In this process, the parent cell divides to form two similar daughter cells. Binary fission occurs either by mitosis or amitosis. The Axis of fission/division is different in different protists. Ex: Amoeba divides in any plane due to lack of specific shape; hence it is called a ‘simple binary fission’. Paramoecium divides by ‘transverse binary fission’ whereas Euglena by ‘longitudinal binary fission’. Binary fission is usually performed by living organisms during favorable conditions i.e. availability of abundant food material.
2. Multiple Fission
Asexual reproduction by multiple fission is performed by Amoeba and other similar protists. Amoeba stops the formation of pseudopodia and thereby movements whenever there is a lack of food or any other type of adverse condition. It becomes rounded and forms a protective covering around the plasma membrane. Such encysted Amoeba or any other protist is called a ‘Cyst’. Many nuclei are formed by repeated nuclear divisions in the cyst. It is followed by cytoplasmic division and thus, many amoeba are formed. They remain encysted till there are adverse conditions. Cyst breaks open on arrival of favorable conditions and many amoeba are released.
3. Budding:
Bring the active dry yeast powder from the market. Take 50 ml of lukewarm water in a conical flask. Add 5 gm of active dry yeast powder and 10 gm table sugar to that water and mix well the mixture. Keep the flask in a warm place and after an hour take a drop of that mixture on a clean glass slide. Put a cover glass on that drop and observe it under the compound microscope.
You will see the yeast cells performing budding i.e. a small bud coming out of many parent cells. Asexual reproduction occurs by budding in yeast – a unicellular fungus. Yeast cell produces two daughter nuclei by mitotic division, to reproduce by budding. This yeast cell is called a parent cell. A small bulge appears on the surface of the parent cell. This bulge is a bud. One of the two daughter nuclei enters this bud. After sufficient growth, the bud separates from the parent cell and starts to live independently as a daughter yeast cell.
B. Asexual Reproduction in Multicellular Organisms
1. Fragmentation:
This type of asexual reproduction occurs in multicellular organisms. In this type of reproduction, the body of the parent organism breaks up into many fragments and each fragment starts to live as an independent new organism. This type of reproduction occurs in algae like Spirogyra, and sponges like Sycon. Whenever there is plenty of water and nutrients are available to Spirogyra, its filaments grow very fast and break up into many small fragments. Each fragment starts to live independently as a new Spirogyra fiber. If the body of Sycon breaks up accidentally into many fragments, each fragment develops into a new Sycon.
2. Regeneration
You may know that the wall lizard breaks up and discards some part of its tail in an emergency. The discarded part is regenerated after a period. This is an example of limited regeneration. However, under certain situations, an animal – Planaria breaks up its body into two parts, and thereafter each part regenerates the remaining part of the body, and thus two new Planaria are formed. This is called regeneration.
3. Budding
In the case of Hydra, under favorable conditions, at a specific part of its body, an outgrowth is formed by repeated divisions of regenerative cells of the body wall. This outgrowth is called a bud. Bud grows up progressively and finally forms a small hydra. The dermal layers and digestive cavity of the budding hydra are in continuity with those of the parent hydra. Parent hydra supplies nutrition to the budding hydra. Budding hydra separates from the parent hydra and starts to lead an independent life when it grows up and becomes able to lead an independent life.
4. Vegetative Propagation
Reproduction in plants with the help of vegetative parts like roots, stems, leaves, and buds is called as vegetative reproduction. Vegetative propagation in potatoes is performed with the help of ‘eyes’ present on the tuber whereas in Bryophyllum it is performed with the help of buds present on the leaf margin. In the case of plants like sugarcane & grasses, vegetative propagation occurs with the help of buds present on nodes. Plants like carrots and radishes perform vegetative propagation with the help of roots.
5. Spore Formation
Take a piece of wet bread or ‘bhakari’ and keep it in a humid place. The fungus will grow on it within 2-3 days. Observe the fungus under a compound microscope and draw its diagram. Fungi like Mucor have filamentous bodies. They have sporangia. Once the spores are formed, sporangia burst and spores are released. Spores germinate in moist and warm places and new fungal colony is formed.
Sexual Reproduction
Sexual reproduction always occurs with the help of two germ cells. The female gamete and male gamete are those two germ cells. Two main processes occur in the sexual reproduction.
1. Gamete Formation:
Gametes are formed by the meiosis. In meiosis, chromosome number is reduced to half; hence haploid gametes are formed.
2. Fertilization:
A diploid zygote is formed in this process by the union of haploid male and female gametes. The zygote divides by mitosis and the embryo is formed. The embryo develops to form a new individual. Two parents i.e. male parent and female parent are involved in this type of reproduction. Fusion of the male gamete of the male parent and female gamete of the female parent occurs. Due to this, a new individual always has the recombined genes of both parents. Hence, the new individual shows similarities with the parents for some characters and has some characters different than both parents. Diversity in living organisms occurs due to genetic variation. Genetic variation helps the organisms to adjust to the changing environment and thereby maintain their existence. Due to this, plants and animals can save themselves from becoming extinct.
A. Sexual Reproduction in Plants
Flower is a structural unit of sexual reproduction in plants. It consists of four floral whorls calyx, corolla, androecium, and gynaecium; arranged in sequence from outside to inside. Androecium and gynoecium are called ‘essential whorls’. They perform the function of reproduction whereas calyx and corolla are called ‘accessory whorls’ because they are responsible for the protection of inner whorls. Members of the calyx are called ‘sepals’ and they are green colored. Members of the corolla are called ‘petals’ and they are variously colored.
A flower is called as ‘bisexual’ if both whorls i.e. androecium and gynoecium are present in the same flower. Ex. Hibiscus. A flower is called ‘unisexual’ if any one of the above-mentioned two whorls is present in the flower. If only androecium is present, it is a ‘male flower’ and if only gynoecium is present, the flower is a ‘female flower’. Ex. Papaya.
Many flowers have a stalk for support, called a ‘pedicel’, and such flowers are called a ‘pedicellate’ whereas a flower without a stalk is called a ‘sessile’. The androecium is a male whorl and its members are called stamens. Gynaecium is a female whorl and its membranes are called carpels. Members of gynaecium are called carpels. These may be separate or united. The ovary is present at the basal end of each carpel. A hollow ‘style’ comes up from the ovary. Stigma is present at the tip of style. The ovary contains one or many ovules. The embryo sac is formed in each ovule by meiosis. Each embryo sac consists of a haploid egg cell and two haploid polar nuclei.
Pollen grains from another are transferred to the stigma. This is called pollination. Pollination occurs with the help of abiotic agents (wind, water) and biotic agents (insects and other animals). The stigma becomes sticky during pollination Pollens germinate when they fall upon such sticky stigma i.e. a long pollen tube and two male gametes are formed. The pollen tube carries male gametes.
The pollen tube reaches the embryo sac via style. The tip of the pollen tube bursts and two male gametes are released in the embryo sac. One male gamete unites with the egg cell to form a zygote. This is fertilization. The second male gamete unites with two polar nuclei and the endosperm is formed. As two nuclei participate in this process, it is called double fertilization.
When pollination involves only one flower or two flowers borne on the same plant, it is called self-pollination whereas if it involves two flowers borne on two plants of the same species, it is cross-pollination. While discovering the new high-yielding and resistant varieties of plants, scientists bring about pollination with the help of brush.
Take a suitable glass vessel like a conical flask or beaker. Add some garden soil in it and sow some pulse grains in it in such a way that you can observe them through glass. Water it every day and record the changes.
Ovule develops into seed and ovary into fruit after fertilization. Seeds fall upon the ground when fruits break up and they germinate in the soil under favorable conditions. Zygote develops at the cost of food stored in the endosperm of seed and thus a new plantlet is formed. This is called seed germination.
B. Sexual Reproduction in Human Being
We have studied in the chapter on heredity and variation that men have XY sex chromosomes and women have XX sex chromosomes. The reproductive system with specific organs develops in the body of men and women due to these sex chromosomes only. X-chromosome is present in men and women whereas Y-chromosome is present in men only. Now we shall study the structure and functions of the human reproductive system.
Human Male Reproductive System
The male reproductive system of humans consists of testes, various ducts, and glands. Testes are present in the scrotum, outside the abdominal cavity. Testes contain numerous seminiferous tubules. Germinal epithelium present in the tubules divides by meiosis to produce sperm. Those sperms are sent forward through various tubules. The sequence of those tubules is as – rete testes, vas deference, epididymis, vas deferens, ejaculatory duct, and urinogenital duct. As the sperms are pushed forward from one duct to the next, they become mature and able to fertilize the ovum.
Seminal vesicles secrete their secretion in ejaculatory ducts whereas prostate glands and Cowper’s glands secrete their secretions in the urinogenital duct. Semen is formed by sperms and secretions of all these glands. Semen is ejaculated out through the penis. All the organs of the male reproductive system are paired except the urinogenital duct, penis & scrotum.
Human Female Reproductive System
All organs of the female reproductive system are in the abdominal cavity. It includes a pair of ovaries, a pair of oviducts, a single uterus, and a vagina. Besides, a pair of bulbourethral glands is also present. Generally, every month, an ovum is released in the abdominal cavity alternately from each ovary. The free end of the oviduct is funnel-like. An opening is present at the center of it. Oocyte enters the oviduct through that opening. Cilia are present on the inner surface of the oviduct. These cilia push the oocyte towards the uterus.
Gamete Formation
Both gametes i.e. sperm and ovum are formed by meiosis. Sperms are produced in the testes of men from the beginning of maturation (puberty) till death. However, in the case of women, at the time of birth, there are 2-4 million immature oocytes in the ovary of a female fetus. An oocyte matures and is released from the ovary every month from the beginning of maturity up to the age of menopause (approximately 45 years of age). Menopause is the stoppage of the functioning of the female reproductive system. At the age of about 45-50 years, the secretion of hormones controlling the functions of the female reproductive system either stops or becomes irregular. This causes the menopause.
Fertilization
The formation of a zygote by the union of sperm and ovum is called fertilization. Fertilization is internal in humans. Semen is ejaculated in the vagina during copulation. Sperms, in the numbers of a few million, start their journey by the route of vagina – uterus – oviduct. One of those few million sperm fertilizes the only ovum present in the oviduct. From the age of puberty up the menopause (from 10-17 years of age up to 45-50 years), an ovum is released every month from the ovary. i.e. out of 2-4 million ova, approximately only 400 oocytes are released up to the age of menopause. The remaining oocytes undergo degeneration.
Oocytes released from ovaries during the last few months nearing the age of menopause are 40-50 years old. Their ability to divide has been diminished till now. Due to this, they cannot complete meiotic division properly. If such oocytes are fertilized, the newborns produced from them may have some abnormalities like Down’s syndrome.
The chromosome number in germ cells producing the gametes is diploid i.e. 2n. It includes 22 pairs of autosomes and 1 pair of sex-chromosomes i.e. (44 + XX or 44 + XY). These germ cells divide by meiosis. Due to this, gametes contain only haploid (n) number of chromosomes i.e. (22 + X or 22 + Y). Two types of sperms are produced as (22 + X) or (22 + Y) whereas oocytes are produced of only one type as (22 + X).
Both sperm and oocytes are produced by meiosis. In the case of sperms, the process of meiotic division is completed before the sperms leave the male reproductive tract. However, in the case of oocytes, the process of meiotic division completes after ovulation; during fertilization in the oviduct.
Development and Birth
The zygote formed after fertilization in the oviduct, undergoes repeated mitotic divisions, and the embryo is formed. Meanwhile, it is pushed towards the uterus. Once it reaches the uterus, it is implanted and further development occurs after implantation. An organ called as placenta is formed for the supply of food material during the growth of the uterus. Embryonic development is completed approximately within nine months after fertilization.
The man is responsible, for whether the couple will have a boy or a girl child. During zygote formation, man contributes either an X or Y chromosome to the next generation But females transfer only the X-sex chromosome to the next generation. At the time of fertilization, if X-chromosomes come from a male, the child will be a girl and if Y-chromosome comes then the child will be a boy. Thinking of this, is it right to consider the mother responsible for a girl child? We all must make efforts to stop female foeticide.
Menstrual Cycle:
The female reproductive system undergoes some changes at puberty and those changes repeat at the interval of every 28-30 days. These repetitive changes are called as menstrual cycle. The menstrual cycle is a natural process, controlled by four hormones. Those four hormones are follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. One of the several follicles in the ovary starts to develop along with the oocyte present in it, under the effect of follicle-stimulating hormone. This developing follicle secretes estrogen.
The endometrium of the uterus starts to develop (during the first cycle) or regenerate (during subsequent cycles) under the effect of estrogen. Meanwhile, the developing follicle completes its development. It bursts under the effect of luteinizing hormone and an oocyte is released. This is called ovulation. The remaining tissue of the burst follicle forms the corpus luteum. Corpus luteum starts to secrete progesterone. Endometrial glands secrete their secretion under the effect of progesterone. Such endometrium is ready for implantation of the embryo.
If the oocyte is not fertilized within 24 hours, the corpus luteum becomes inactive and transforms into corpus albicans. Due to this, the secretion of estrogen and progesterone stops completely. Endometrium starts to degenerate in the absence of these two hormones. Tissues of degenerating endometrium and unfertilized ovum are discarded out through the vagina. This is accompanied by continuous bleeding. Bleeding continues approximately for five days. This is called menstruation.
Unless the oocyte is fertilized and the embryo is implanted, this process is repeated every month. If the embryo is implanted, repetition of this cycle is temporarily stopped till the parturition and thereafter period of breastfeeding. The menstrual cycle is a natural process and women experience severe pains during this period. Severe weakness is felt due to heavy bleeding. There is a higher possibility of infections too during this overall period. Due to all such reasons, there is a need for rest along with special personal hygiene.
Reproduction and Modern Technology
Many couples cannot have children due to various reasons. In the case of women, irregularity in the menstrual cycle, difficulties in oocyte production, obstacles in the oviduct, difficulties in implantation in the uterus, and many other reasons are responsible for this. The absence of sperms in the semen, the slow movement of sperms, and anomalies in the sperms are the reasons in the case of males. But now with the help of advanced medical techniques like IVF, Surrogacy, and Sperm banks, childless couples can have a child.
In Vitro Fertilization (IVF)
In this technique, fertilization is brought about in the test tube and the embryo formed is implanted in the uterus of a woman at the appropriate time. IVF technique is used for having the child in case of those childless couples who have problems like less sperm count, obstacles in the oviduct, etc.
Surrogacy
Some women have problems with the implantation of embryos in the uterus. Such women can take the help of the modern remedial technique called surrogacy. In this technique, an oocyte is collected from the ovary of the woman having a problem with implantation in the uterus. That oocyte is fertilized in a test tube with the help of sperm collected from her husband. The embryo formed from such fertilization is implanted in the uterus of some other woman with having normal uterus. Such a woman, in whose uterus the embryo is implanted, is called a surrogate mother.
Sperm Bank/Semen Bank
There are various problems in sperm production as mentioned above, in the case of many men. To have the children in case of such couples, a new concept of sperm bank has been introduced. This concept is similar to the blood bank. Semen ejaculated by the desired men is collected after their thorough physical and medical check-ups and stored in the sperm bank. As per the wish of the needful couple, the oocyte of a woman of the concerned couple is fertilized by IVF technique using the semen from the sperm bank. The resultant embryo is implanted in the uterus of the same woman. The name of the semen donor is strictly kept secret as per the law.
Twins
Two embryos develop simultaneously in the same uterus and thus two offspring are delivered simultaneously. Such offspring are called twins. Many couples have twins. There are two main types of twins – monozygotic twins and dizygotic twins. Monozygotic twins are formed from a single embryo. During the early period of embryonic development (within 8 days of zygote formation), cells of that embryo divide into two groups. Those two groups develop as two separate embryos and thus monozygotic twins are formed. Such twins are genetically exactly similar to each other. Due to this, such twins are exactly similar in their appearance and their gender is also the same i.e. both will be either boys or girls.
In the case of monozygotic twins, if the embryonic cells are divided into two groups 8 days after the zygote formation; there is a high possibility of the formation of conjoined twins (Siamese twins). Such twins are born with some parts of the body joined to each other. Some organs are common in such twins. Occasionally, two oocytes are released from the ovary of a woman and both oocytes are fertilized by two separate sperms and thus two zygotes are formed. Two embryos are formed from those two zygotes and both of those embryos are separately implanted in the uterus and thus dizygotic twins are delivered after complete development. Such twins are genetically different and may be the same of different by gender.
Reproductive Health
A person’s state of physical, mental, and social strength is called health. In our country, there seems to be a lack of awareness regarding reproductive health due to various reasons like social customs, traditions, illiteracy, shyness, etc. Especially, since there seems to be indifference toward the reproductive health of women. The occurrence of the menstrual cycle is related to the reproductive and overall health of women. Nowadays, women are working at par with men. Due to this, they have to stay outdoors for the whole day. Bleeding occurs during the menstrual cycle. Due to this, private organs (genitals) need to be maintained clean from time to time, otherwise, problems regarding reproductive health may arise. Some problems regarding reproductive health may arise in men too. It is essential to maintain the cleanliness of their genitals.
Among the various sexual diseases, syphilis and gonorrhea occur on a large scale. Both of these diseases are caused by bacteria. The occurrence of chancre (patches) on various parts of the body including genitals, rash, fever, inflammation of joints, alopecia, etc. is the symptom of syphilis. Painful and burning sensations during urination, oozing of pus through the penis and vagina, and inflammation of the urinary tract, anus, throat, eyes, etc. are symptoms of gonorrhea.
Population Explosion
| Year | Population |
| 1901 | 238396327 |
| 1911 | 252093390 |
| 1921 | 251321213 |
| 1931 | 278977238 |
| 1941 | 318660580 |
| 1951 | 358142161 |
| 1961 | 439234771 |
| 1971 | 548159652 |
| 1981 | 683329097 |
| 1991 | 846421039 |
| 2001 | 1028610328 |
| 2011 | 1210854977 |
Excessive growth of population within a short duration is called a population explosion. You may have realized from the table given about the fast population growth of India. We have to face various problems like unemployment, decreasing per capita income and increasing loans, stress on natural resources, etc. There is only one solution for all such problems and it is population control. Family planning is essential for this.
Detailed Maharashtra State Board Class 10 Science Notes Life Processes in Living Organisms are particularly useful for answering essay questions.