- Do Organisms Create Exact Copies of Themselves?
- Reproduction and its Significance
- Reproduction in Unicellular and Multicellular Organisms
- Reproduction in Animals
- Sexual Reproduction in Plants
1. Do Organisms Create Exact Copies of Themselves?
Yes! organisms create copies of themselves by Reproduction process.
Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should be similar. Thus, reproduction involves making copies of the blueprints of body design.
Though all of us have similar organs, none of us is the same. Eye colour and blood type differ among individual humans. Differences in these traits are due to genetic differences, or genetic variation. The human gene pool carries alternative alleles that affect blood type and many other traits. Other species also have variation in their gene pools.
Examples:
Though all human beings belong to the species, Homo sapiens, the first upright mammal, no two individuals are exactly alike. Even identical twins have slight differences in their DNA(Deoxyribo Nucleic Acid), which contain information for an inheritance of features from one generation to another.
Apple trees are all members of one species, but the fruit produced by different trees can be red or yellow, hard or soft, sweet or taste, large or small.
Cell:
The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, and cells are often called the “building blocks of life“.
Important parts of a Cell:
- DNA(Deoxyribo Nucleic Acid) : DNA is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms.
- Gene : A gene is a locus or region of DNA which is made up of nucleotides and is the molecular unit of heredity.
- Chromosome : A chromosome is a DNA molecule with part or all of the genetic material (genome) of an organism.
DNA Replication :
It is a complex process whereby the ‘parent’ strands of DNA in the double helix are separated, and each one is copied to produce a new (daughter) strand.
- DNA is responsible for all inherited characters.
- DNA replication of one helix of DNA results in two identical helices.
- If the original DNA helix is called the “parental” DNA, the two resulting helices can be called “daughter” helices.
- Since it is a biochemical process, DNA replication sometimes results in variations in the new molecule. These changes may be viable or non-viable.
- Viable changes are seen as changes in the offspring, while non-viable changes result in death of the new cell..
- This inbuilt tendency for variation is the basis for heredity and evolution
Reproduction is the biological process by which existing organisms give rise to their offspring. Every existing plant, animal or other living organism is the result of biological reproduction. Reproduction maintains the thread of life.
Reproduction can be of two types – Asexual mode and Sexual mode.
Reproduction is carried out by different living organisms to perpetuate their species. Reproduction is an integral feature of all living beings.
Reproduction is important for the survival of all living things. Without a mechanism for Reproduction, life would come to an end.
Reproduction helps in maintaining a proper balance among various biotic constituents of the ecosystem. Moreover, reproduction also facilitates evolution because variations come through reproduction; over several generations.
Reproduction can be of two types – Sexual mode and Asexual mode.
Asexual Reproduction:
When a single parent is involved and no gamete formation takes place; the method is called asexual reproduction. No meiosis happens during asexual reproduction.
Sexual Reproduction:
When two parents are involved and gamete formation takes; the method is called sexual reproduction. Meiosis happens during gamete formation; which is an important step of sexual reproduction.
Significance of reproduction:
- Reproduction prevents all kinds of organisms from becoming extinct.
- Reproduction is not necessary for carrying out life processes of an individual but helps in increasing the individuals in a population.
- Reproduction is essential in creating variations in species through genetic recombination.
- Reproduction is necessary in the process of evolution by carrying favourable variations from one generation to another generation.
Reproduction
Reproduction is the phenomenon which involves the production of an offspring by particular individual or individuals to propagate their species. Reproduction is done during reproductive phase.
Unicellular organisms are single-celled forms whereas multicellular organisms are made up of many cells. Depending upon the complexity of the body, reproduction in unicellular organisms is different from that of multicellular organisms.
Asexual reproduction and Sexual reproduction are the two types of reproduction in a living organism.
Unicellular organisms reproduce by asexual means. This asexual mode of reproduction involves single parent to produce their offspring. Different types of asexual modes of reproduction include binary fission, multiple fission, fragmentation, budding etc.
Multicellular organisms can choose both asexual and sexual modes to reproduce their offspring. The mode of reproduction by organisms depends upon the prevailing conditions.
Types of reproduction:
Asexual and Sexual reproduction are the 2 types of reproduction.
- Asexual mode of reproduction:
It is a mode of reproduction in which a single individual is responsible for creating a new generation of species. Reproductive structures are not involved. Vegetative parts of individuals are used for the process of reproduction. Gametes are not formed. Single parent cell gives rise to daughter cell. Offspring formed are exact individuals of the parents
- Sexual mode of reproduction:
It involves the union of two opposite sex cells by the process of fertilisation to give rise to zygote, the single cell. This type of reproduction involves two organisms, the male and the female.
Reproductive organs in humans produce gametes – eggs and sperms. Egg is the female gamete produced by female reproductive organ. Sperms are male gametes produced by male reproductive organ. A zygote is a future individual formed by the fusion of an egg and a sperm.
Types of asexual reproduction:
- Binary fission:
It involves the longitudinal or transverse splitting of an organism into two equal halves which develop into two separate individuals. Binary fission is generally seen in unicellular organisms such as amoeba and paramecium falling into the category of protozoa.
Amoeba is a simple, unicellular organism which reproduces by transverse binary fission. The division begins with the division of nucleus.
Binary fission can also be observed in multicellular animals like sea anemones and planarians.
Binary fission observed in Leishmania is longitudinal binary fission. Longitudinal binary fission is the division occurring in a definite orientation in relation to the whip-like structures located at one end of the cell.
- Budding:
This is a form of asexual reproduction which involves the development of a small mass of cells as protuberances on the parental body to give rise to new structures called as buds. These buds separate out from the parental body and develop into new individuals.
Two types of budding are external budding and internal budding.
Hydra uses regenerative cells for reproduction in the process of budding. Buds are formed on specific sites on the parent body. Buds detach from parent body and grow into a new individual.
- Fragmentation:
It involves breaking of parent organism into two or many fragments. Each fragment develops into an individual organism. Fragmentation is seen in sea stars which accidentally break their body into fragments. Fragmentation is also observed in annelids, turbellarians and some of the poriferans.
Spirogyra reproduces through fragmentation during which each fragment grows into a new individual.
- Regeneration:
Regeneration is also called Morphallaxis. If the organism is cut up, its pieces can grow into separate individuals. Regeneration is commonly seen in Planaria, Hydra.
Regeneration is referred to tissue repair to a normal state. It is the restoration of normal structure and function of the organ. It is actually the replacement of damaged tissue with the same type of cells. Some organisms like lizards have the power of regenerating their tail.
- Spore formation:
Spore formation is one form of asexual reproduction. Spore formation is the method of developing new individuals by forming reproductive structures called spores.
A spore is a small spherical or oval structure which protects the future individual in a thick protective covering. Spore germinates on a substratum under favourable conditions. Some organisms like ferns, some groups of fungi reproduce by spore formation.
Fungus reproduces by means of spores. Fungus like bread mould produce spores which germinate on moist organic surfaces. The cottony white mass on bread formed by fungus after spore germination is called a mould. Spores can survive in extreme conditions because of the protective hard coat.
- Vegetative propagation:
Vegetative propagation is one mode of asexual reproduction in plants. It is the production of new plants from the vegetative parts of the plant.
Roots, stems and leaves are called the vegetative parts of a plant. Any of these parts serve as vegetative propagules.
Vegetative propagation takes place by different methods like Grafting, Leaf propagation, Root propagation, underground stem propagation etc. Though vegetative reproduction results in the production of varieties of plants, offspring propagated through vegetative propagation are more uniform to parents.
Reproductive phase is a phase in the life of every individual which makes the individual capable of reproducing the offspring.
In the early reproductive phase, individuals acquire changes in the body which result in the formation of germ cells. Sperms is male germ cells and eggs are female germ cells. Reproductive phase involves the changes in appearance and size of the bodily organs.
Important terms:
Puberty: It is the time during which sexual and physical changes occur which allow the transition of a child to an adult. Puberty starts at the beginning of adolescence.
Changes common to girls and boys
- Increase in height and weight.
- Increased activity of sebaceous glands or oil glands and sweat glands and therefore, occurrence of pimples and acne.
- Appearance of hair in armpit and pubic region.
- Development of thinking, reasoning, logic and intelligence.
- Emotional changes like irritability, insecurity, anger, defiance, rebellious tendencies may occur in some boys and girls.
Changes in boys
- Appearance of facial hair (beard and moustache)
- Appearance of body hair on chest, back, arms and legs.
- Deepening of voice and increase in size of Adam’s apple in the throat.
- Broadening of shoulders.
- Sperms are produced by testes. This may be evident as night emission along with seminal fluid.
- Body becomes muscular.
Changes in girls
- Broadening of hips.
- Body becomes soft and rounded.
- Appearance of breasts
- The menstrual cycle begins.
Adolescence: It is the period of life between the onset of puberty and reaching adulthood, that is, the period that leads to reproductive maturity making a person capable of reproduction. An adolescent is a general term for teenagers of both sexes.
Male reproductive system:
This system includes a pair of testis, vas deferens and a muscular organ, the penis.
- Testes:
Testis is the main reproductive organ in males. A pair of testis is placed in a structure called as scrotum which is located outside the abdominal cavity. At lower temperature maintained by the scrotum, testes produce sperms by the process of spermatogenesis. Sperms are the male gametes possessing a head, body and a tail.
- Vas deferens:
Sperm duct is also known as vas deferens. They are two in number, each one arising from testis placed on either side. They transport sperms into the penis. They also collect fluids secreted by different glands. Sperms along with these secretions form a thick substance called as semen. Semen is conveyed to urethra through which it is discharged outside.
- Urethra:
Urethra forms a common passage for both the sperm and urine as it is just one tube that connects both the glands – urinary bladder and vas deferens.
- Penis:
It is a part of the male reproductive system. Penis is a muscular organ which transfers semen into the female reproductive tract. Penis receives both urinary tube and sperm duct and serves as a common transporting organ for urine and semen. It opens out through a small tube called as the urethra. The penis is underlined by thin blood vessels which give it a continuous supply of blood.
Female reproductive system:
This system includes a pair of ovaries, a pair of oviducts, uterus and vagina opening out through the urethra.
- Ovary:
A pair of ovaries forms the gonads in a female. Ovaries are the female sex organs that lie one on either side of the abdominal cavity. Ovaries by the process of oogenesis form eggs which are released as one per month. Ovaries produce two hormones, namely,
Estrogen controls the changes that occur during puberty, like feminine voice, soft skin and development of mammary glands, the growth of pubic hair and controls the release of mature eggs.
Progesterone controls the uterine changes during the menstrual cycle and helps in the maintenance of pregnancy.
- Oviducts:
A tube like structure arising from each ovary on either side is called as an oviduct. This is also called as the fallopian tube. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube. The two oviducts combine and open into an elastic bag-like structure known as the uterus.
- Uterus:
The uterus is a hollow muscular organ which has the capacity to bear the child. It is otherwise called as the womb. Zygote formed after fertilisation in the fallopian tube travels downward by dividing itself continuously to form an embryo.
Embryo, as it reaches the uterus, gets implanted into the wall of the uterus. After fertilisation, female reproductive hormones bring in many changes to the uterus, so as to bear the growing embryo. As the embryo grows, it transforms into the foetus. Uterus is the organ which bears the foetus.
- Vagina:
It is the reproductive part situated at the end of the uterus in the female reproductive tract. It connects uterus to the outside world. Vagina secretes mucous to keep the tract wet. It opens out through vulva.
Sexual reproduction in humans:
Sexual reproduction is a process through which new organism is created by the fusion of two gametes. The male gamete is known as sperm which is produced inside the testes. The female gamete or ovum is produced inside the ovarian follicle of female.
The following is a step by step basis of how reproduction occurs from beginning to end:
- Fusion of male gamete and female gamete happens inside the female body.
- During sexual intercourse, the sperms enter inside the female body.
- The sperms are motile and they swim towards the ovum which stays inside the uterus. There is a single ovum and numerous sperms swim towards it to fuse with.
- A single sperm gets the opportunity to fuse with the ovum. This is called fertilization.
- After fertilization, the membranes of the ovum become so hard that no other sperm can enter inside.
- The fertilized ovum changes into zygote which further develops into an embryo. Embryo gradually develops and forms a completely developed foetus within 36 months.
- After getting fully developed the foetus comes out of mother’s body as an infant.
Reproductive health:
It is a state of physical, emotional, mental and social well-being in relation to sexuality. Reproductive health requires a positive approach to sexuality and healthiness of the individuals participating in mating.
Reproductive health also refers to the capability of satisfying the partner. It also specifies the ability and freedom to reproduce.
Sexually transmitted diseases:
STD stands for Sexually Transmitted Diseases. These are the diseases which are transmitted from one person to another during the sexual act between two individuals.
STD can be caused by different microorganisms like bacteria, fungi, virus, protozoans etc.
Gonorrhoea, Syphilis, AIDS etc are some of the examples of STDs.
STD can mostly be prevented from transmission from one individual to another by using protective or contraceptive like:
- Copper T or loop placed in the uterus do not allow implantation of an egg.
- Mechanical methods like using a condom or vaginal covers ensures the sperm does not reach the egg
- Hormonal methods like using pills which do not allow the release of eggs
- Surgical methods like vasectomy and Tubectomy create blocks in the oviducts and sperm ducts
Plant reproduction is the production of new individuals or offspring in plants, which can be accomplished by sexual or asexual reproduction. Asexual reproduction produces new individuals without the fusion of gametes, genetically identical to the parent plants and each other. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from the parent or parents.
Unlike animals, plants are immobile, and cannot seek out sexual partners for reproduction. In the evolution of early plants, abiotic means, including water and wind, transported sperm for reproduction. Primitive land plants like liverworts and mosses had motile sperm that swam in a thin film of water or were splashed in water droplets from the male reproduction organs onto the female organs.
Sexual reproduction in flowering plants involves the production of male and female gametes, the transfer of the male gametes to the female ovules in a process called pollination. After pollination occurs, fertilization happens and the ovules grow into seeds within a fruit. After the seeds are ready for dispersal, the fruit ripens and by various means the seeds are freed from the fruit and after varying amounts of time and under specific conditions the seeds germinate and grow into the next generation.
Plants have complex life cycles involving alternation of generations. One generation, the sporophyte, gives rise to the next generation asexually via spores. The alternate generation, the gametophyte, produces gametes, eggs and/or sperm. A gametophyte can be bisexual, producing both eggs and sperm, or unisexual, either female (producing eggs) or male (producing sperm). However, spores and sporophytes are neither male nor female because they do not produce gametes. The sporophyte of a flowering plant is often described using sexual terms (for example, ‘female’ or ‘male’) based on the sexuality of the gametophyte it gives rise to.
Sexual Reproduction in plants:
- The flower is the characteristic structure concerned with sexual reproduction in flowering plants.
- There are two kinds of reproductive cells produced by flowers:
- Microspores, which will divide to become pollen grains, are the ‘male’ cells and are borne in the stamen, which is the male reproductive part of a flower. Stamens are the male reproductive parts of flowers. A stamen consists of an anther (which produces pollen) and a filament. The pollen consists of the male reproductive cells; they fertilize ovules.
- The ‘female’ cells called megaspores, which will divide to become the egg cell are contained in the ovule and enclosed in the carpel, which is the female reproductive part of a flower. Each carpel includes an ovary (where the ovules are produced; ovules are the female reproductive cells, the eggs), a style (a tube on top of the ovary) and a stigma (which receives the pollen during fertilization). The pistil is the collective term for the carpel(s).
- Pollen must fertilise an ovule to produce a viable seed. This process of fertilisation is called pollination.
Types of Flowers:
- Perfect flowers are those flowers with both male and female reproductive organs
- Imperfect flowers have only male reproductive organs or only female reproductive organs.
- Complete flowers have both male and female flowers, while others have males on one plant and females on another. Complete flowers have stamens, a pistil, petals, and sepals.
- Incomplete flowers lack one of these parts.
Fertilisation:
- Sexual reproduction in plants occurs when the pollen from an anther is transferred to the stigma. If plants can fertilise themselves, it is called self-fertilisation. Self-fertilisation occurs when the pollen from an anther fertilizes the eggs on the same flower.
- Cross-fertilisation occurs when the pollen is transferred to the stigma of an entirely different plant.
Pollination:
- Pollination is often aided by animals like bees, which fly from flower to flower collecting sweet nectar. As they visit flowers, they spread pollen around, depositing it on some stigmas. After a male’s pollen grains have landed on the stigma during fertilisation, pollen tubes develop within the style, burrowing down to the ovary, where the sperm fertilises an ovum (an egg cell), in the ovule. After fertilisation, the ovule develops into a seed in the ovary.
- When the ovules are fertilized, they will develop into seeds. The petals of the flower fall off leaving only the ovary behind, which will develop into a fruit. There are many different kinds of fruits, including apples and oranges and peaches. A fruit is any structure that encloses and protects a seed. When you eat a fruit, you are actually eating the ovary of the flower.