Reproduction

a) Aquatic animals such as fishes and frogs reproduce through sexual reproduction by external fertilization i.e. the fertilization occurs outside the female’s body.

b) In external fertilization, since the chances of fertilization, or the development and survival of the zygote are totally dependent on nature, large number of eggs and sperms are produced and released every cycle.

c) Most of the times, the unfertilized or the fertilized eggs are lost to predators, water currents, and other environmental factors, so in order to compensate for the loss, a huge number of eggs are produced.

a) External fertilization can be defined as the fertilization that takes place outside the female’s body.

b) External fertilization is mostly common in aquatic organisms such as fishes and amphibians.

c) During the time of mating, the female lays a large number of eggs in the water and male releases millions of sperms on them in water. The zygote thus formed after the fusion of gametes is protected in a jelly-like structure where it grows and develops.

d) Since the chances of fertilization or the development and survival of the zygote are totally dependent on nature, a large number of eggs and sperms are produced and released every cycle.

e) For example: Fishes, frogs and other amphibians.

Grafting – layering

Stamen – carpel

a) The pollen grain reaches the stigma of the flower called pollination.

b) The pollen tube starts germinating, the pollen contains 2 cells- generative cell and a vegetative cell.

c) Both the cells travel through the pollen tube which leads them to the embryo sac.

d) The embryo sac is a 7 celled 8 nuclei structure.

e) One of the male gametes fuses with the female egg- called syngamy, while the other fuses with the 2 polar nuclei forming a triploid- called triple fusion.

f) Since 2 kinds of fertilization take place in a plant, it is also called double fertilization.

g) After fertilization, the triploid central cell develops into endosperm while the zygote develops into an embryo.

The different modes of asexual reproduction are as follows:

Fission: The splitting of unicellular organisms into daughter cells is called fission. If the parent cell splits into two daughter cells, it is called binary fission whereas splitting of parent cells into more than 2 cells is called multiple fission. For example binary fission in Amoeba and multiple fission in Plasmodium.

Budding: An outgrowth called bud starts forming on the body of the parent organisms. When the bud is fully grown, it detaches itself from the parent body and starts acting as an individual. For example Yeast.

Fragmentation: Fragmentation is a mode of reproduction in which an organism divides into 2 or more fragments and each fragment acts as a new individual. It is more common in simpler organisms such as algae, fungi, and flatworms.

Regeneration: The ability of an organism to grow from a part is called regeneration and is useful in case the organism gets cut up into pieces. For example Planaria.

Parthenogenesis: The process of reproduction where there is a shift from sexual to asexual mode of reproduction due to various environmental changes. It can be both natural such as in bees, wasps or induced such as in various seedless fruits.

Vegetative propagation: The mode of reproduction in which vegetative propagules rather than seeds are used to grow plants. It is useful to grow seedless plants, the plant who have lost the ability to produce seeds or to grow a number of plants in a short duration. It can be both natural such as in Bryophyllum, strawberries, or artificial such as grafting, layering etc.

Spore formation: Spores are microscopic unicellular structures produced inside sporangium in various fungi, bacteria and non-flowering plants. These spores are produced in very large number.

a) The major function of the sperm is to travel to the egg cell so as to fertilize it.

b) For this, sperm has to travel a large distance in short amount of time. The sperm cell consists of a long tail that helps in its movement.

c) Also, in order to introduce its nucleus into the female cell for fusion, the sperm has to break through the various layers enveloping the egg. For this, acrosome is present on the head of the sperm which releases enzymes that help in dissolving the layers around the egg.

a) An average menstrual cycle extends between a period of 28-30 days from the onset of puberty in girls.

b) It starts with the end of the previous menstruation.

c) One of the ovaries develop an egg and release it on the 14^th day. This process is called ovulation.

d) The uterus prepares itself for receiving a zygote if fertilization takes place.

e) The walls of the uterus get thick and richly supplied with blood vessels. The uterus also increases in its size.

f) If the egg is not fertilized between the 14^th-18^th day, the egg is shed off the body.

g) As there is no use of the uterine lining, it too comes off the vagina around 28^th day in the form of menstrual flow.

a) While the fetus is growing inside the uterus, it receives nutrition from the body of the mother itself through the placenta.

b) The placenta is a tissue formed by the cells of both the mother and the embryo around the 12th week of pregnancy.

The foetus absorbs substances such as oxygen and various other nutrients from the mother through the placenta. The blood travels through the membranes surrounding the placenta and the nutrients along with oxygen and other things are diffused in the foetus.

a) Amniotic sac develops from an embryonic membrane called amnion.

b) The amnion grows around the embryo covering it entirely into a cavity.

c) This cavity is filled with a fluid called the amniotic fluid in which the embryo develops.

d) The amniotic fluid along with amniotic cavity helps in keeping the embryo moist and safe from minor mechanical injuries.

e) The amniotic sac provides cushioning whereas the fluid-filled cavity acts as shock absorber.

Advantages of sexual reproduction:

a) Sexual reproduction involves the combining of gametes of both the parents to form a zygote. Hence, this zygote consists of the combination of characteristics of both the parents.

b) Every time a new zygote is formed, new combinations take place giving rise to various variations.

c) Accumulation of such variations helps the organisms to adapt and survive better in the environmental conditions and also helps in bringing new characteristics.

a) Every organism in a population has a certain life span. In that particular time period, it takes birth, grows, develops and after fulfilling its life expectancy dies.

b) Reproduction ensures that the population of a particular species keeps on surviving by the production of new offspring’s of the same kind.

c) If reproduction does not take place, no new organisms will be produced while the old ones keep on perishing. A time will come when all the organisms are dead and the population of particular species will cease to exist.

d) Hence, reproduction is important for providing stability to a population.

a) If the fertilization does no take place, the egg or ova is shed out of the body. The thick uterine lining that developed to receive the embryo also gets wasted.

b) During menstruation, this thick uterine lining/wall is shed out of the body and comes out of the vagina in the form of blood and mucus.

Yes, all unicellular organisms undergo mitotic cell division during favorable conditions in order to increase their population. Whether it be through fission, budding, etc., they reproduce to form daughter cells.

I will suggest the method of either grafting or cross-pollination.

Grafting method:

•In this method, two plants are joined together in such a way that the two stems join and grow as a single plant.

•This technique is used to produce plants with desirable characteristics and is helpful for propagating improved varieties of various flowers and fruits.

•In this technique, the plant attached to the soil is called stock whereas the team attached to it is called Scion.

•Using this technique, we can attach the two plants with desirable characteristics of colourful flowers and big fruits together to get the single plant.

Cross-pollination method:

•In this method, 2 plants of the same species but different characteristics can be cross-pollinated.

•The pollen from one plant having the characteristic of colourful flower can be used to pollinate another plant that bears big fruits.

•The resulting zygote will have the characteristics of both the pants.

Onion root tip consists of meristematic tissues which consist of cells that are continuously dividing. Hence, by observing those cells we can see the various stages of mitosis.

i. Through leaves- Bryophyllum

ii. Through stems-

•Stolon’s- Jasmine, strawberry

•Bulbs- onion

•Tuber- potato

iii. Through roots- carrot, radish

iv. Through corms- ginger

Cell cycle:

Cell cycle consists of two stages- interphase and mitotic phase

a) Interphase: it is the period between two cell divisions. This is a period where genetic material makes its copy such that it is equally divided among the two daughter cells formed during cell division. It consists of three stages-

•G1 phase: this is the linking period between completion of mitosis and the beginning of DNA replication (Gap1 phase). The cell size increases during this period.

•S-phase: this is the period of DNA synthesis (synthesis phase) leading to duplication of chromosomes.

•G2 phase: this is the time between the end of DNA replication and beginning of mitosis (Gap2 phase). Cell organelles divide and the cell prepares for mitosis.

b) M-phase: It is the phase of cell division or mitosis and consists of 2 stages- karyokinesis (nuclear division) and cytokinesis (cytoplasmic division). Karyokinesis is further divided into 4 stages namely- prophase, metaphase, anaphase, and telophase.

Mitosis:

It consists of karyokinesis (nuclear division) and cytokinesis (cytoplasmic division). Karyokinesis is further divided into four stages:

Male reproductive part:

Female reproductive part:

a. This is the structure of the female reproductive part of the flower known as pistil or carpel.

b. It consists of 3 main parts- stigma, style, and ovary.

c. Stigma is the flattened structure on the top that is sticky or hairy to receive and trap the pollen grains.

d. The style is the long stalk that connects the stigma to the ovary.

e. Ovary consists of the female gamete or egg. The ovaries consist of one or more ovules which further develop to form a 7-celled, 8-nucleated embryo sac that contains the egg cell or female gamete.

The male reproductive system of the flower consists of the stamen that produces the male gametophyte- pollen grains

The female reproductive system consists of carpel which consists of stigma, style, and ovary. Ovary consists of the female game in the ovules.

Pollination is the process in which the pollen grains are transferred from the anther of the stamen to the stigma of the carpel

The germination of pollen produces pollen tube which travels down the stigma towards the ovary

The ovary consists of 1 or more ovules. The ovule develops into embryo sac which is a 7-celled, 8-nucleated structure.

The pollen consists of 2 male gametes- generative cell and vegetative cell which travel down to the embryo sac

One of the cells fuses with the female gamete to form zygote while the other fuses with the polar nuclei to form a triploid. This is called double fertilization.

After fertilization the embryo sac gets converted into seed coat, polar nuclei form endosperm, ovary forms the fruit and zygote forms embryo

h) The pollen grain reaches the stigma of the flower called pollination.

i) The pollen tube starts germinating, the pollen contains 2 cells- generative cell and a vegetative cell.

j) Both the cells travel through the pollen tube which leads them to the embryo sac.

k) The embryo sac is a 7 celled 8 nuclei structure.

l) One of the male gametes fuses with the female egg- called syngamy, while the other fuses with the 2 polar nuclei forming a triploid- called triple fusion.

m) Since 2 kinds of fertilization take place in a plant, it is also called double fertilization.

n) After fertilization, the triploid central cell develops into endosperm while the zygote develops into an embryo.

Pollen grain:

a) Pollen grains are the structures or male gametophytes produced in the anthers of the flower which contain the mail gametes.

b) They are coarse powdery grain-like structure.

c) They have double walls with pores. The outer wall is made up of sporopollenin which is one of the hardest substance known.

d) Pollen grain travels from the anthers of the stamen to the stigma of the pistil through various agents to deliver the male gamete by the process called pollination.

a) Organisms reproducing sexually undergo reduction division to form gametes which are haploid i.e., they contain half the number of chromosomes than their parents.

b) This is to ensure that when the 2 gametes fuse to form a zygote, the original chromosome number is restored in the organism and the species remains constant.

c) If meiosis does not take place, the ploidy will double with every other fertilization leading to disruption or imbalance in the number of chromosomes causing many harmful changes, some of which can be fatal for the growing zygote

a) Cell division is an important step for the succession of life.

b) According to the improvised Cell Theory- All new cells arise from the pre-existing cells.

c) These new cells arise due to cell division whether it be mitotic or meiotic. The new cells or daughter cells inherit the information and characteristics from their parent cells.

d) Mitotic cell division helps in increasing the number of cells and hence making sure that the population of the species remains stable.

e) Whereas meiotic division helps in keeping the number of chromosomes constant during sexual reproduction, thus maintaining the accuracy of species and enriching them with variations.

f) Hence, we can say that cell division is very useful for the perpetuation of life.

Precautions to avoid sexually transmitted diseases:

a) Avoid multiple/unknown sexual partners.

b) Avoid unsafe sexual practices.

c) Usage of mechanical barriers such as condoms or diaphragms during any sexual activity.

d) Get a regular checkup from qualified doctors for any sexually transmitted diseases.

e) Avoid sharing of undergarments, towels etc.

Child marriage-

•Child marriage is very common in most parts of rural India.

•Children especially girls below 18 years of age are married to elder men on confines of bonds between their parents.

•This leads to one of the major problems i.e. teenage pregnancy. It is extremely harmful to the girl as well as the baby as the young girl’s body is not prepared to bear a child.

•It causes severe deficiencies to the mother as well as the baby and the child birth can be extremely complex. The children born out of these young pregnancies are weak, undernourished, and sometimes mentally retarded as well.

Female foeticide:

•The girl child is still deemed to be a burden in India and many of the times, these fetuses are aborted in the womb itself.

•This has led to drastic decline in the male-female sex ratio.

•To combat this, prenatal sex determination has been banned in India and any trained individual practicing it is punishable by law.

A pair of ovaries are present in the lower abdomen of females which produce mature eggs each month. The ovaries are also responsible for secreting female hormones and promoting the growth of secondary sexual characteristics.

Fertilization is the process in which male and female gametes fuse together to form a zygote.

Seminiferous tubules are highly coiled tubules present in the lobules of testis which consists of cells that undergo meiosis to form spermatozoa.

The head of the sperm consists of acrosome that releases chemicals on reaction that dissolve the layers surrounding the egg cell so that the sperm can fertilize it.

Egg cells are larger in size as they store food to nourish the zygote till it gets implanted into the mother’s body through placenta.

All of these- cigarettes, alcohol and drug abuse can cause physical, mental damage to the growing foetus and is extremely harmful for the health of both, mother and baby.

The baby grows into a child and then reaches its adolescence and finally grows into an adult.