Reproduction In Organisms - Class 12 Medical Biology - Extra Questions

Menstruation, also known as a period or monthly, is the regular discharge of blood and mucosal tissue (known as menses) from the inner lining of the uterus through the vagina. The first period usually begins between twelve and fifteen years of age, a point in time known as menarche. However, periods may occasionally start as young as eight years old and still be considered normal. The average age of the first period is generally later in the developing world, and earlier in the developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).  Bleeding usually lasts around 2 to 7 days.

Transfer of pollen grain from anther to stigma is called pollination.

• Regeneration is a form of asexual reproduction. It is the ability of a simple organism to re-grow its lost parts. 
• Planaria can be cut into pieces, and each piece can regenerate into a complete organism. Cells at the location of the wound site proliferate to form a blastema that will differentiate into new tissues and regenerate the missing parts of the piece of the cut planaria.
  

The ability to give rise to new individuals from their body parts is called regeneration. If the body of Planaria is somehow cut or broken up into many pieces, each piece grows into a complete organism. Regeneration is not possible in all types of animals because it is only possible in animals with specialized cells which cells proliferate and make large numbers of cells. 

The importance of reproduction are as follows:

• With the help of reproduction genes are transmitted from the parents to the offspring.
• Reproduction maintains the balance between the birth rate and the death rate.
• The new individuals replace the old and the dying population.
• It also helps in increasing the number of species in the ecosystem.
• This leads to the evolution of the species. Variations in the species and their ability to survive in different environments as a result of reproduction.

Regeneration is defined as organism's ability to regrow damaged or lost body parts. It is a type of asexual reproduction which is shown by many fully differentiated organisms. Organism such as Hydra uses regenerative cells for reproduction in the process of budding. When Hydra reaches maturity and is well fed, its body wall begins to form a rounded growth from the stalk of the adult. This growth is called a bud which develops in time into a miniature Hydra. The body layers, body cavity and digestive cavity of the young Hydra are continuous with that of the parental Hydra. The young Hydra gets its nourishment from the parent. When the young Hydra is sufficiently developed to take up an independent existence, the base of the new Hydra seals off and thus allows the new individual to break off from the parent Hydra.

Other organism in which a similar process occur are: Hydra, Starfish etc.

(a) Internal fertilization is a type of sexual fertilization. It is the union of an egg cell with a sperm during sexual reproduction inside the body of a female. For this process, male sperms are required to enter into the female reproductive system.

Tissue culture is an artificial method of culturing plants. In this method, a small part of the plant is used to grow cells in a nutrient solution in the sterile condition of the laboratory. Tissue culture is a very fast technique.

Advantages of Tissue Culture

1. The new plantlets can be grown in a short period of time. 
2. The new plantlets and plants are more likely to be free of viruses and diseases. 
3. The process can be performed throughout the year.

(a) Human testes lie outside the human body because it helps in spermatogenesis as the process of sperm formation requires a temperature (2 - 2.5 $${^0}$$C) lower than the body temperature. 

Parthenogenesis is the process in which egg development into individual organism occurs without fertilization by a male gamete. In certain animals, parthenogenesis occurs regularly, constantly and naturally in their life cycles and is known as natural parthenogenesis which is observed in the honeybees.

Regeneration is the ability to replace the lost or damaged body parts. Regeneration is defined as the reconstruction of external appendages and internal organs that got injured. Injury is rapidly followed by complete, successful re-growth of the lost parts. Plants can regenerate all body parts from the precursor cells. So, regeneration is a process of restoration and growth and also a process of renewal.

Parthenogenesis is a form of asexual reproduction that involves the development of the female gamete into a new individual without being fertilized by a male gamete. In certain animals, parthenogenesis occurs regularly, constantly and naturally in their life cycles and is known as natural parthenogenesis. It is seen in honeybees, some fishes, gastropods and nematodes.

Regeneration is the development of a complete organism from the parts of the body of the organism which are accidentally cut during an injury. This process is found in organism like-starfish, hydra, planaria etc.

Parthenogenesis is the method of reproduction in which ovum develops into an embryo and forms a new plant , without fertilisation. It has been observed that pollination is necessary, for parthenogenesis. It stimulates the process. Example, Ulothrix, Spirogyra and Solanaceae family plants reproduce by this method.

Asexual reproduction	Sexual reproduction
One parent is involved	Two parents are involved
New generation is identical or true copy of the parent	New generation is similar to its parents
Original parent disappears after reproduction	Original parents remain alive after reproduction
Process of gamete formation fertilization is absent	Fertilization of gametes give rises to zygote
Characteristics of only parent is inherited	Characteristics of both parents are inherited
Special organs for reproduction are not required	Special organs for reproduction are required
Examples: jasmine, rose, potato, etc.	Examples: Hibiscus, coconut, papaya, etc.

$$\textbf{Solution:}$$

Oestrous Cycle	Menstrual Cycle
Occurs in non-primates.	Occurs in primates only.
There is estrus/heat production at the time of ovulation and copulation occurs only during that period.	There is no heat period and copulation occurs during any time of the cycle.
The broken endometrium is reabsorbed.	The broken endometrium is passed out during menstruation.
Examples- cow, sheep, rat, deer, dog, tiger, etc	Examples: monkeys, apes and human beings

In hologamy, true gametes are not formed, but two mature individuals fuse together to form a zygote. On the other hand, in autogamy, the male and female gametes produced by the same unicell fuse to form a diploid zygote.

The importance of syngamy and meiosis in the sexual life cycle of an organism :

Parthenogenesis is a form of asexual reproduction in which an unfertilized egg develops into a new individual. It is a method in which a new individual developed without fertilization. Here, males do not have any role to play and only female gametes develop into new offspring. Examples of plants showing parthenogenesis include honey bees, ants, birds. 

Internal fertilization	External fertilization
Internal fertilization is when the male deposits his sperm directly into the female's body.	External fertilization is when the male and female's gametes unite outside the female's body.
The chances of survival of offspring are more.	The chances of survival of offspring are less.
For example, Humans	For example, Fish

The fertilized egg contains the genetic material of both the parent i.e. it has the best genetic composition out of the two available genes sets. This fertilized egg cell, after maturation, i.e. after growing into an adult will exhibit the same characters present in that fertilized egg. That's why a fertilized egg is the blueprint of future development.

Parthenogenesis is a method of reproduction where the development of the female gamete occurs without fertilisation. It is seen in several insect species including aphids, bees, and ants.

External fertilisation	Internal fertilisation
1. Fertilisation takes place outside the body. And the chance of forming zygote is minimum.	1. Fertilisation takes place inside the body. And the chance of forming zygote is maximum.
2. A large number of male gametes are released in the surrounding medium. Examples- Fish, Amphibians and Algae.	2. Male gametes are released inside the female body. Examples- Reptiles, Birds, Mammals, and Bryophytes.

Fertilization is the process by which the male and female gametes fuse to form the zygote.
There are two types of fertilization-

Isogamous is a type of sexual reproduction in which male and female gametes have similar morphology. They have similar shape and size. Anisogamous is a type of reproduction in which male and female gamete have different morphology. They differ in size and shape. Oogamous is a type of anisogamous in which female gamete is significantly larger than the male gamete. In this, the female gamete is non motile and male gamete is motile.

Internal Fertilization	External Fertilization
The internal fertilization is the process occurs within the body of a female	In external fertilization fusion of sperm and egg occurs externally of the female body
Internal fertilization facilitates the survival of the embryo, selective fertilization	External fertilization does not facilitate the survival of embryo and selective fertilization does not occur
Internal fertilization produce only a few offsprings	The advantage of external fertilization is that it produces a large number of offspring due to the external hazards
Internal fertilization occurs in humans	External fertilization occurs in fish

The ovulatory phase of the menstrual cycle occurs in the middle of the menstrual cycle i.e it occurs between the 10$$^{th}$$ and the 18$$^{th}$$ day of the menstrual cycle.
During this period there is an increase in the luteinizing hormone (LH) level which causes the mature follicle to burst and release the egg (usually around day 14). This is called ovulation.
The best days for conception generally is 11$$^{th}$$ to 17$$^{th}$$ days leading up to and immediately following ovulation. It is also called the fertile period.

Formation of an embryo from an unfertilized egg is called Parthenogenesis. It is a type of asexual reproduction.  In lower plants both the types of gametes can undergo parthenogenesis but in higher plants, usually the female gamete shows the parthenogenesis.

$$\textbf{Solution:}$$ 

$$\bullet$$ $$\textbf{Reproduction:}$$ Reproduction is the generation of offspring from parents. It is the biological process in which new individuals are developed in the population. 

$$\textbf{Necessity of reproduction:}$$

$$\bullet$$ New offspring is developed similar to the parents to maintain the population of organisms. After maturation, these offspring also perform reproduction to produce new offspring. 

$$\bullet$$ The natality or birth rate should balance out the mortality which is the death rate in the given population. This is the way of maintaining a balance in the population. 

$$\bullet$$ Therefore, reproduction maintains the continuation of species and ensures that the population stays stable from one generation to the next. 

• A menstrual cycle begins from the first day of the period and ends when the next period begins. Hormone signals are sent between the brain and the ovaries, causing changes in the ovaries that contain the eggs.
• The first phase of the menstrual cycle prepares an egg to be released from the ovary and builds the lining of the uterus. The second phase prepares the uterus and body to accept a fertilized egg during pregnancy or to start the next menstrual cycle if pregnancy doesn’t happen.

Seasonal breeders mate only during particular time of a year. The reproductive cycle that occurs in them is oestrous. Cycle. Eg, In non-primate animals like cow such cyclical changes occur.

Tissue culture is a technique of growing new plants from cells or tissue from the growing tip of already existing plant, in an artificial medium. The process of tissue culture is as follows:
 1. Cells or tissue from the growing tip of a plant are removed or separated. 
2. These cells are placed in an artificial medium, where they divide to form a group of cells called callus. 
3. The callus is then transferred to a medium. which has hormones for growth and differentiation. 
4. This results in growth of small plantlets, which are then placed in the soil to grow into mature plants.
This technique is finding its application in the propagation of ornamental plants, or for growth of plants from a single parent, in disease-free condition. 

Those small plants may grow up because of the seed dispersal. The seed from the tree can fall down and sprout into smaller plants. 

Internal fertilization occurs in hens. Fertilized egg is enclosed in a protective shell covering in the hen's body and is laid outside for development.
In frogs, fertilization and development of zygote both takes place outside of their body, that is, external fertilization.

The ornamental plants are usually propagated by vegetative reproduction methods for faster growth, obtaining a certain produce or for retaining a certain trait. This form is also known as artificial propagation. Some of the methods included are  layering, budding, cutting, grafting, etc. 
The method of propagation of given plants is: 
(I) Jasmine - layering 
(ii) Rose — cutting 
(iii) Bougainvillea — layering 
(iv) Hibiscus- layering 

During this process the fusion of sperm and egg nucleus takes place, also known as fertilization. Zygote is formed as a result of this process.

The male reproductive system consists of the following organs: 
1. Testes, 
2. Vas deferens, 
3. Seminal vesicle, 
4. Urethra. 

1. Testes: The male reproductive organs consist of two tests, lying in a special pouch of skin called scrotum sac, outside the body between the two legs. They are specialised for the production of spermatozoa. Each testis is made of the number of coiled tubes called seminiferous opens in the collecting duct, called the epididymis. The sperms are produced by cells of the epithelium layer of the seminiferous tubules and are stored in the epididymis. Each sperm consists of three parts- the anterior end of the sperm is called ahead. The nucleus containing chromosomes is located in the head. Behind the head is the middle portion. The third part is the tail, which helps in its movement. 

2. Vas deferens: From each epididymis arises a duct called vas deferens, which opens in the broad structure called seminal vesicles. 

3. Seminal vesicle: It is situated on the anterior part of the urethra. From seminal vesicle arises a tube called ejaculatory duct. Before ejection, the sperms are stored in this duct. 

4. Urethra: The ejaculatory duct opens in a duct called the urethra, which passes through a long and muscular path, present in the penis. This long path opens outside the body through a small opening. The urine and sperms pass out through this opening hence, it is called the urinogenital aperture. 

The female reproductive organs are as follows: 
(1) a pair of ovaries 
(2) a pair of oviducts or fallopian tubes 
(3) Uterus 

1. Ovaries: The female reproductive system consists of two ovaries, located in the abdominal cavity, just below the kidney. The ovaries are white or cream-coloured. They are of an oval shape. The inner layer is made up of germinal epithelium cells, which by the process of oogenesis produces eggs. In front of each, there is a funnel-shaped structure called ostium. 

2. Oviducts or Fallopian tubes: The posterior end of the ostium is in the form of a duct called oviduct. The Female reproductive organ's walls of the ovary are muscular and made up of ciliated epithelium. The action of cilia and the peristaltic act of the duct walls, help the egg to move towards the uterus. 

3. Uterus: The posterior part of the oviduct opens into a hollow sac-like structure called the uterus. The walls of the uterus expand according to need, during the development of an embryo. The anterior tubular part of the uterus is called the vagina and the posterior part is called the vulva. 

Answer:

There is no relationship between the size of an organism and its life span. For example; both Mango and Peepal tree are similar in size but a Mango tree has a much shorter life span compared to a Peepal tree. A tortoise is much smaller than an Elephant, the Tortoise lives for 80-120 years, while the Elephant lives for about 48 - 60 years.

The spores look like tiny dots or particles of dust. Under the microscope the may appear to have various shapes and a certain form of ornamentation.

Importance of vegetative reproduction: 
1. Vegetative reproduction is the only method to maintain and multiply the desired varieties at commercial level, of those plants which are naturally non-seed-producing that is seeds are not produced in them. For example banana, sugarcane, rose etc. and seedless varieties of grapes and orange etc. 
2. Sufficient time is required in the production of flowers in those plants which are produced by the germination of seeds. Further  the development of a plant from seeds is not always definite. On the contrary the development of a plant by vegetative propagation is definite and the time required for flowering and fruiting is very small. 
3. The new plants produced by vegetative propagation are exactly similar in characters to that of mother plant. Thereby the desired characters are maintained true generation after generation. However, the plants produced from seeds often become inferior in characters as compared to the parent plants. 
4. The production is high in the plants produced by vegetative propagation. 

(a) Flower having both the male and the female parts is known as a bisexual flower.
(b) Flower having only male or female parts is known as a unisexual flower.
(c) Transfer of pollen grains from the anther to the stigma is known as pollination.
(d) Fusion of a male cell with the female cell is called fertilisation.

One menstrual cycle completes in 28 to 30 days

Explanation:

• Underground stems are present under the soil surface which stores food and nutrition and helps in the perennation (survival of plant up to the next season). In strawberries and grass runners and stolon are the main units of their propagation as it spreads along the ground.

 Answer:

$$\textbf{Explanation:}$$

Personal hygiene is necessary for girls, because due to unhygiene, different bacteria may cause odour and infection in their body.

No.	Characteristics
1.	Large investment required for incubating and feeding the young for prolonged time	c	I
2.	Lactating females, internal fertilization	b	II
3.	External fertilization, females exhibit territorial behaviour	a	II

(a) The gamete contains haploid set of chromosomes while the meiocyte contains a diploid set.

The process of growing many plants from one plant by man-made methods is called artificial propagation of plants. Artificial reproduction/propagation is the creation of a new life by other than the natural means available to an organism.

The male reproductive organ consists of mainly 3 accessory glands, i.e. seminal vesicles, prostate gland, and the bulbourethral gland. The secretions from the seminal vesicles are viscous and contain fructose, calcium, and prostaglandins. These stimulate uterine contractions, which helps the sperm to move towards the ampulla. The prostate glands secrete a milky fluid, which contains a little citric acid, lipids, bicarbonates, enzymes, and fibrinogen. Prostatic fluid increases sperm motility. The bulbourethral gland is two in number and it secretes mucus for lubrication. 

Fertilization occurs at the ampullary- isthemic junction of the Fallopian tube when both the male and female gametes reach there simultaneously. 

INTERNAL FERTILIZATION	EXTERNAL FERTILIZATION
1) The fusion of male and female gamete inside the body of the female is called internal fertilization. 2) Eg- Mammals.	1) The fusion of male and female gamete in the external environment (water bodies)  is called external fertilization. 2) Eg- Fishes.

• Vegetative reproduction is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment of a parent plant or a specialised reproductive structure. 
• Advantages of practising this process-

Production of fruits or the absence of fruits in these plants is the result of human intervention through horticulture. To understand this issue, we first need to keep in mind the specific purpose for which a particular plant is grown by humans.
Rose plants are mainly grown for ornamental purposes. Rose flowers are considered to be the epitome of beauty. Additionally, most varieties of Rose produce nice fragrance with further adds to its value. Seeds or fruits are not important for Rose plants. Rose is grown by horticulturists worldwide through vegetative propagation. Usually, a portion of the stem is cut off and is put in the soil to produce a new plant. Sometimes, the stem is peeled off at a small section, and clay is applied to produce a new plantlet. Since producing a plant through vegetative propagation requires less time, so it is much beneficial for growing ornamental plants. 

• Rose is a natural seed-bearing plant but in domestically grown varieties, the petals are so tightly fit that they may not permit pollination and hence fruits do not develop in these plants.
• Rose plants may not produce viable cell or functional egg.
• Rose plants may have abortive ovules.
• They may be self-incompatible
• There may be internal barriers to pollen tube growth and /or fertilization.

Tomato, on the other hand, is produced for its juicy fruits. Hence, cultivators have to follow a method that enables them to get as many fruits as possible.
In both cases, the number or size of flowers on a particular plant is not the deciding factor. But the purposes for which a particular plant is grown is the main deciding factor of whether a plant will produce fruit or not.