How Do Organisms Reproduce?

a. Placenta
Explanation:
The disc shaped tissue known as placenta, which is embedded in the uterine wall provides nutrition to the embryo.

b. Lining of the uterus.

Explanation:
The site where the fertilized egg gets implanted is the lining of the uterus. It is the inner lining of the womb and is shed off the body in the form of blood and mucous during the menstrual cycle.

DNA copying is a basic event in reproduction wherein the cell replicates its own DNA to make its copies by using various chemical processes. This creates two copies of a single DNA molecule in a reproducing cell which are later separated by additional cellular apparatus that are created after the process of DNA copying.

The sperm is made up of two regions that determine its shape. The head region is oval to which a thin and long tail is attached. This shape helps the sperm in its motility to swim very fast towards the egg.

The diagram of sperm is given below:

The two contraceptive methods practices only by women are:

1. Oral contraceptive pills to prevent pregnancy by changing the hormonal balance of the female body.

2. Insertion of Copper-T in the uterus to provide a mechanical barrier so that the sperm does not reach the eggs.

Papaya flowers are called unisexual because the flowers only contain one of the two reproductive parts of the plant and never both. Therefore, the flowers of papaya either consist of the male reproductive part, the stamens or the female reproductive part, the carpels.

i) Testes

Explanation:

Male germ cells are made in the Testes. The testes produces and stores the sperms and also secretes the hormone testosterone for maintaining the secondary sexual characters in male.

ii) Ovaries

Explanation:

Female germ cells are made in the Ovaries. They are known as eggs or oocytes and are stored in the ovaries. The ovaries protect the eggs and release them every month for the purpose of fertilization.

i) Some plants follow the asexual or vegetative mode of reproduction wherein, the plants can reproduce via the root, stem, leaves etc of the plant and do not need the male and female reproductive parts to propagate.

ii) Bryophyllum is one such type which follows the vegetative mode of reproduction. It reproduces via the buds present along the notches of the leaf margin.

iii) These buds when fall off on the soil are able to grow into a new plant through vegetative reproduction.

iv) In case of the rose plant, the leaves do not produce such buds and hence this type of vegetative reproduction cannot take place. Rose plant follows the sexual mode of reproduction.

v) In the rose plant, the stamens and carpels which are the reproductive parts of the plant that contain the germ cells, are the ones responsible for its propagation.

i) Once the sperm has fertilised the egg, the zygote that forms is embedded in the lining of the uterus. This lining thickens considerably and is richly supplied with blood from which the growing embryo gets the nutrition needed for its growth and development.

ii) The embryo gets its nourishment from the mother’s blood via the tissue known as the placenta.

iii) The placenta is a disc shaped tissue which is embedded in the uterine walls.

iv) This disc contains villi on the side facing the embryo and blood spaces on the mother’s side that surround the villi. Due to this arrangement of the villi and the blood spaces, the surface area is increased for the transfer of glucose and oxygen from the mother to the embryo.

i) The menstruation cycle results when the fertilization of the egg by the sperm does not take place.

ii) The ovaries release an egg every month and hence the walls of the uterus already prepare itself for embedding and nourishing the embryo. This causes the uterine walls to thicken and become spongy.

iii) When the egg does not get fertilized, it remains viable for a day after which it does not survive.

iv) Since the egg does not get embedded in the walls of the uterus, the thick lining is not needed anymore and it sheds off in the form of blood and mucous which comes out of the vagina.

v) This process takes place every month and is known as the menstrual cycle which lasts for about 2-8 days every month.

. Production of egg - Ovary

Explanation:

Ovaries are the female reproductive organs in which the female germ cells or eggs are produced. They are also the organs responsible for the secretion of the hormones estrogen and progesterone that maintain the eggs and impart the secondary sexual characters in females.

ii.The siteof fertilization - Fallopian tube

Explanation:

The fallopian tube is the region that receives the egg after it is released from the ovary for fertilization. The sperm travels through the vagina and the uterus towards the fallopian tube in which the egg is present for fertilization by the sperm. The fallopian tube then transfers the fertilized egg to the uterus for implantation.

iii.Siteof implantation - Inner lining of the Uterus

Explanation:

The inner lining of the uterus is the site where the fertilized egg, known as the zygote gets implanted. The tissues in the inner lining are modified to implant the zygote and have many blood vessels to nourish the embryo that grows from the zygote

iv. Entry of the sperms – Vagina

Explanation:

The vagina provides the opening for the entry of sperms through the male penis after sexual intercourse. The sperms travel through the vagina and then the uterus towards the fallopian tube where fertilization of egg takes place.

i) Regeneration is a type of asexual propagation of an organism.

ii) In this phenomenon, if a part of the organism is cut out from its body, then that part and the remaining body of the organism is able to grow into 2 new whole organisms.

iii) For example, Planaria is a type of organism that is capable of regeneration. When a planaria is cut into pieces, each piece is able to regenerate and grow into a complete new organism.

iv) Difference between regeneration and reproduction.

i) Vegetative propagation is a type of asexual reproduction in plants.

ii) In this mode of reproduction, parts of the parent plant, like the root, stem, leaf etc are used to grow a new plant. Sexual reproductive parts are not involved in the propagation of the plants.

Advantages:

i) Plants like bananas, grapes etc which are seedless can be efficiently reproduced via vegetative propagation.

ii) The plants produced through vegetative propagation are genetically identical to their parent plant.

Disadvantages:

i) Since vegetative propagation produces genetically identical plants, no variations can be seen and this sometimes makes the plants more susceptible to diseases.

ii) New desirable traits arising due to genetic variation cannot be achieved.

Fission is a mode of asexual reproduction seen in unicellular organisms. In this type, the organism simply splits or divides into two or more equal parts during cell division. Depending on how many cells it splits into, fission can be divided into binary fission, wherein the organism splits into two or multiple fission in which the unicellular organism splits into more than two cells.

Examples: Binary fission in Amoeba& multiple fission in Plasmodium

Diagram of germination of pollen on the stigma

i) Ovary– The ovary is part of the carpel which is the female reproductive part of a plant. The ovary encloses the ovules that get fertilized by the pollen grains.

ii) Male germ cell– The male germ cells are present in the pollen grains. After pollination, the male germ cells travel towards the female germ cells in the ovary through the pollen tube germinating from the pollen grains.

iii) Female germ cell– Female germ cells are present in the ovary of the plant. These cells fuse with the male germ cells to give rise to a zygote that eventually forms the embryo.

iv) Ovules – The ovule is present inside the ovary and it grows into a seed after it is fertilized by the male germ cells.

(a) Longitudinal section of a flower:

(b) The structures that develop into the embryo and seed are zygote and ovule respectively.

Functions:

A) Stigma– Stigma is the terminal sticky part of the carpel and it functions to trap the pollen grains on its sticky surface.

B) Pollen tube- The pollen tube helps to transfer the male germ cells from the pollen grains to the female germ cells inside the ovary at the base of the flower.

C) Female germ cells– The female germ cells of a flower get fertilized by the male germ cells and develop into a zygote.

i) Reproduction is phenomenon by which living organisms produce new organisms (offspring) from the parent organisms for its continuity and to make sure that it does not go extinct. It is either sexual or asexual in nature.

ii) The two advantages of sexual reproduction over asexual reproduction are as follows:

1. Sexual reproduction produces more variation and thus more unique characteristics in the organisms than asexual reproduction as the characteristics of both the parents are transferred to the offspring.

2. There is a better chance of survival and an increase in the organism’s ability to adapt due to the favourable traits acquired through genetic diversity.

i) Sexually transmitted diseases are infections that spread by any form of sexual contact between affected individuals through the male and female genital regions of the body.

ii) Examples of sexually transmitted diseases are AIDS, syphilis etc.

iii) The measures to prevent these diseases would be to have safe sexual contact between individuals. Using condoms during intercourse, Avoid sharing of wash cloths and under garments and vaccination for some of these diseases are few of the measures that can be adopted to prevent the spread of sexually transmitted diseases.

Diagram: Pistil showing pollen tube growth and its entry into the ovule.

i) The menstruation cycle is the time period during which the unfertilized egg and the uterine wall linings are discharged through the vagina when the fertilization of the egg by the sperm does not take place in the female body.

ii) The changes that take place in a woman are as follows:

iii) The ovaries release an egg every month and hence the walls of the uterus already prepare itself for embedding and nourishing the embryo. This causes the uterine walls to thicken and become spongy.

iv) When the egg does not get fertilized, it remains viable for a day after which it does not survive.

v) Since the egg does not get embedded in the walls of the uterus, the thick lining is not needed anymore and it sheds off in the form of blood and mucous which comes out of the vagina.

vi) The process takes place every month and is known as the menstrual cycle which lasts for about 2-8 days every month.

vii) Females experience some changes in their body during the menstrual cycle. Apart from the bleeding from the vagina during this period, there is fluctuation in the level of certain hormones in the body which sometimes lead to mood swings. Abdomen cramps are also common during the menstrual cycle.

i) Meiosis is a type of cell division wherein the number of DNA of the germ cells is reduced to half and the full number of DNA is restored only after the male and female germ cells have fused together.

ii) Species that reproduce sexually rely on the fertilization of the eggs in the female by the sperms from the male.

iii) DNA from both the parent germ cells combines during sexual reproduction.

iv) If the copies of DNA are to be combined then this would result in double the amount of DNA every time a new individual is born. This is not possible as the individual would not survive.

v) Since the two germ cells need to fuse together for the production of an offspring, it is necessary that the number of DNA in both the cells is half so that when the cells fuse, the correct full number can be restored.

vi) For this reason, meiosis is needed during sexual reproduction so that the amount of DNA can be reduced into half in the germ cells which makes it possible for the two germ cells to fuse and have a stable amount of DNA in the offspring.

i) The process wherein pollination of flowers from one plant is done by the pollens from another flowers or plants of the is known as cross pollination.

ii) Agents like wind, insects, birds etc are required for cross pollination as they transfer the pollens from one flower to another.

iii) Some plants show various adaptations for the purpose of cross pollination. Production of more nectar, Bright colour and large size of the petals, longer stamens, sticky pollen grains etc are a few of the adaptation that help in cross pollination of these plants.

iv) Flowers are brightly coloured to attract insects and birds towards them so that the pollens can stick on them while they feed on the nectar.

v) Such plants produce many pollen grains as compared to the plants that exhibit self pollination. Sometimes the pollen grains are sticky so they can easily get attached to the pollinating agents.

vi) They have longer stamens so that the pollen grains can easily stick on the stigma.

i) Fertilization is process involved in the sexual reproduction of organisms.

ii) It takes place when the male gamete sperm comes in contact with female gamete, the egg and fertilizes it.

iii) For this to take place, the sperms from a male enter the female vagina during sexual intercourse after which the sperms travel upwards till the fallopian tube where it fertilizes the egg.

iv) In females, one egg is released every month from either of the ovaries. This egg travels till the fallopian tube where it encounters the sperm.

v) The sperm now fuses with the egg and a single cell is formed, which is known as a zygote. This zygote has a complete set of DNA copies by receiving half from each of the male and female gametes.

vi) The formation of zygote completes the process of fertilization after which the zygote multiplies and grows into an embryo in the uterus.

i) Ovary –The ovary in female human is the site where the female gametes, the eggs, are made and also an organ that produces female sex hormones like estrogen and progesterone.

ii) Uterus – Uterus in a female human is the organ where the fertilized egg is implanted. It also provides nourishment to the growing embryo and nurtures the fetustill it is mature enough for birth.

iii) Fallopian tube – The fallopian tube helps in the transfer of the ovum or the egg from the ovaries to the uterus and also acts as a site where the sperm fertilizes the egg.

i) The placenta is a disc like tissue embedded in the uterus. It has small projections called villi on its side facing the embryo and blood spaces that cover these villi on the maternal side.

ii) The main function of the placenta is to transfer the nutrients like glucose and oxygen from the mother to the embryo through these blood spaces and villi. The villi increase the surface area for the transfer of these nutrients.

iii) The placenta also acts as the tissue that transfers the waste generated by the developing embryo to the mother’s blood.