Reproduction In Organisms

In Sexual reproduction, gamete fusion occurs and the genetic material transfers from both the parents after which reduction division (meiosis) takes place to reduce the diploid body (2n) into a haploid body(n). The progeny resembles the parents.

In asexual reproduction fusion of gametes does not take place, genetic material transfers from the parent body to the new born but no reduction division takes place. The progeny is similar to the parent.

In sexual reproduction the offspring do not have the exact copies of parental DNA, because the fusion of male and female genetic material takes place and a new combination is formed.

All the prokaryotes carry out reproduction through binary fission, as prokaryotes are single celled organisms which can only reproduce through cell division and binary fission is a type of cell division.

I. Sexual reproduction does not always require two individuals. In certain bisexual plants and hermaphrodite animals which have both male and female reproductive parts in one requires an individual only.

II. Sexual reproduction always involves the fusion of male and female gametes to produce a zygote.

III. Meiosis or reduction division takes place occurs during sexual reproduction. Meiosis reduces the diploid gamete (2n) of the gametes to haploid gamete (n) in the zygote.

IV. External fertilisation is not a rule during sexual reproduction. In mammals and many other animals fertilisation takes place inside the female body that is internal fertilisation.

Hence only i and ii statements are true.

A multicellular, filamentous alga exhibits haplontic life cycle. In which meiosis or reduction division takes place after zygote formation. Which is why the adult filament of this alga has haploid vegetative cells and haploid gametangia.

The chromosome number in female gamete would be same as the male gamete. So, the number of chromosomes would be 12. Zygote would have double the parent’s chromosome as it is a diploid (2n) so 24 chromosomes would be there in a zygote. The cells of the seedling will be 24. The seedling is developed from the zygote so it would be a diploid.

i. The male and female gametes are formed and released simultaneously. Due to which the chances of fusion of the gametes increases.

ii. Many gametes are produced at once which increases the chances of fusion of the gametes. Even if some gametes are lost or are immotile.

iii. Water is the medium in most organisms exhibiting external fertilization as shown by fish, coral and sea anemone etc.

iv. Offspring formed as a result of external fertilization have lesser chances of survival than those formed inside an organism. They are born in open environment and are exposed to many predators all the time.

Hence, only statements i and iii holds true.

1. A pistil may have more than one carpel. For example: Papaver

2. Each carpel may have more than one ovule.

I. Both angiosperm and humans remain active during their reproductive phase. So, eggs of both are formed many times during their lifetime not just once.

II. Human eggs are not stationery. Once the egg is released from the ovary. It reaches the uterus.

III. In angiosperms both the gametes are non-motile in nature.

IV. The egg after releasing from the ovary reaches the uterus which shows that the human egg and the angiosperm egg both undergoes syngamy of the male and female gamete to form an embryo.

Hence, only statement iv stands true.

The appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger are mainly because of the presence of meristematic cells. These nodes help in growth and development.

During organic evolution the lower plants had simple body organisation. They adapted the asexual mode of reproduction. When they evolved to form higher plants, it had complex body organisation. They adapted the sexual mode of reproduction.

In asexual reproduction the young one is the exact same copy of its parent. This is because its genetic composition is same as of its parent.

In sexual reproduction the gametes of both the parents have qualitatively different genetic composition, so greater variation is seen.

Dioecious(unisexual) organisms are seen in both plants and animals for example, dioecious plant is Marchantia and dioecious animal is cockroach.

There is no natural death in single celled organisms like Amoeba and bacteria because the parent body itself gets distributed into new fragments.

The type of reproduction depends upon habitat which is the place an organism resides, physiology and genetic makeup.

Simple plants and the members of kingdom fungi reproduces through special reproductive structures. Zoospores are one such motile sexual reproductive structure.

Post fertilisation events are those which occur after the process of fertilisation. Transfer of pollen grains, Formation of flower and pollen grains occurs before fertilisation hence they are pre-fertilisation events. Embryo development occurs after the process of fertilisation hence it is a post fertilisation event.

The body of a maize plant has a diploid state I.e. (2n) state. The microspore mother cell is the part of the reproductive system; hence it also remains in a diploid state. This shows that the number of chromosomes in the microspore mother cells of the same plant shall be 20.

Characteristics of Amoeba and yeast that enable them to reproduce asexually are:

1. Their structural organisation is simple.

2. Only single parent is involved that is they are uni parental.

Clones are genetically and morphologically similar organisms. In the process of asexual reproduction only single parent is involved so no genetic and morphological variation takes place, that is why we refer to offspring formed by asexual method of reproduction as clones.

Although potato tuber is an underground part, it is considered as a stem because:

1. They have leaf shoots arising from the nodes.

2. The tuber has internodes.

These characters are seen in stems.

A plant has three phases in its life cycle which are:

1. Juvenile Phase: This is the phase in which the plant grows and develop.

2. Reproductive Phase: During this phase the plants starts to reproduce.

3. Senescence Phase: This the last phase of a plant’s life cycle, after which the plant dies.

As the annual plant has shorter life span than the perennial plants, its juvenile phase is also shorter than the perennial plants.

The following events of sexual reproduction occur in the following sequence:

1. Pollination: The transfer of pollen to stigma takes place by an agent or self-pollination.

2. Gametogenesis: Formation of male and female gametes takes place.

3. Fertilisation: The fusion of male and female gametes take place to form an embryo.

4. Embryogenesis: The fusion of the gametes forms an embryo.

A bisexual flower has both male and female flowers in the same plant so, the transfer of the pollen to stigma is easier as compared to dioecious plant which are unisexual and requires an agent for the transfer of pollens like birds, insects, wind or water so, the probability of fruit set formation decreases as external help is required.

The basis of sexual reproduction is the generation of haploid gamete only so, the presence of a greater number of gametes do not affect the reproduction. For example: Fern plant has 1260 chromosomes but still it reproduces sexually.

There is no relationship between the size of an organism and its life span this can be justified by giving two examples:

1.The size of birds like crow and parrot is similar but the life span of crow is 15 years and the life span of parrot is 140 years this shows there is no such relation between the size and age.

2.Both Mango and Banyan tree have same size, but their life spans are different.

Cell division takes place in unicellular organisms because each of the parent body forms a daughter cell, but in multicellular organisms no such differentiation occurs. Cell division would be an impractical method.

1. After fertilization takes place, the zygote develops to form an embryo. The ovule develops into seeds.

2. The pericarp develops from the wall of the ovary. It protects the seed.

Gametes produced in large numbers in organisms exhibit external fertilisation because gametes are released in open environment. Due to which they are constantly exposed to factors like predators, desiccation etc. This leads to reduced number of gametes.

2.Increased number of gametes increases the chances ofsyngamy. Which is the fusion of the male and female gametes. Increased number of gametes increases the probability of syngamy.

a. Earthworm “monoecious”

Earthworms are monoecious organisms as both male and female reproductive structures are in the same organisms.

b. Chara “monoecious ”

Chara are monoecious organisms as both male and female reproductive structures are in the same organisms.

c. Marchantia ”dioecious”

Marchantia are dioecious as both male and female reproductive structures are in different individuals.

d. Cockroach ”dioecious”

Cockroach are dioecious organisms as both male and female reproductive structures are in different individuals.

a. Ovary “Fruit”

b. Ovules” Seeds”

After the fertilisation,the ovary develops into a fruit and the ovules inside it develops into a seed.

Haploid organisms are those which have half the number of chromosomes than their parents. These organisms do not undergo meiosis, as only diploid cells undergo meiosis. These haploid cells only show meiotic division when the formation of zygote takes place as the zygote is the only diploid cell in their life cycle.

The higher plants that are the angiosperms, and the higher animals that are the vertebrates have complex structural organisation, this allows them to use sexual mode of reproduction. It allows them to have:

1. Genetically variable offspring are produced.

2. They have more superior survival and adaptation capability than those which are produced asexually.

Lower plants and animals do not have these variations as they produce by asexual reproduction.

A honeybee hive has three kinds of members which are

1. Diploid Queen which are fertile females.

2. Worker bees which are sterile females.

3. Drones which are haploid males.

4. When the male and female gametes combine to produce off springs they could either produce diploid female or haploid males.

1. Meiosis is known as reduction division because, Meiosis occurs in sexual reproduction, as it is involved in the production of gametes. The gametes are haploid by nature which means that the gametes have half the number of chromosomes than the parents. Hence, the name reduction division.

Vegetative reproduction is a type of asexual reproduction because:

1. It involves only one parent.

2. No gamete formation takes place.

3. The off spring has the same genetic composition as the parent.

4. Only mitotic division takes place in this reproduction.

5. Clone formation takes place.

These evidences prove vegetative reproduction is a type of asexual reproduction.

‘Fertilisation is not an obligatory event for fruit production in certain plants' because in some plants unfertilized egg grows into an embryo, this process is known as parthenogenesis. In some fruits chemical fertilisers are also given to enhance the growth.

If in a developing embryo, cell divisions are not followed by cell differentiation the embryo would not grow into an organism as the cells would not differentiate to forms tissues and then organs and would remain as a mass.

After an angiosperm flower undergoes pollination and fertilization certain changes are seen in the flower:

This is due to the different types of placentation shown by the pea and the tomato plants. Placentation is the term used to describe the type of arrangement of ovules inside the ovary. The pea plant shows Marginal Placentation which means that the ovules are arranged into two rows along the rigid ventricular suture, whereas the tomato plant shows Axileplacentation, that means the ovules are arranged along the central axis of the ovary. Hence, the arrangement.

(a) ZOOSPORE (b) CONIDIUM

Dissimilarities

Similarities

1. They both reproduce asexually.

Asexual reproduction is the kind of reproduction in which only one parent is involved, which reproduces asexually to produce similar young ones. Vegetative reproduction is also a type of asexual reproduction because of the following reasons.

1. It involves only one parent.

2. Clone formation takes place that is the young one is exact copy of the parent.

3. No gamete formation takes place.

4. The off spring has the same genetic composition as the parent.

5. Only mitotic division takes place.

These evidences prove that vegetative reproduction is a type of asexual reproduction.

Asexual reproduction is the type of reproduction in which there is only one parent is involved and no fusion of gametes take place. The various kinds of asexual reproduction are as follows:

1. Binary Fission: In this type of asexual reproduction, the parent cell divides its DNA into two, these DNA than incorporates into two identical daughter cells produced from the parent body, example: Amoeba

2. Budding: A small nod or growth on the surface of the parent body derives nutrition from the parent, then detaches and grow into another being. Example: Hydra, Yeast.

3. Fragmentation: In this, the parent body divides into many fragments and every fragment develops into off springs. Example: starfish, sponges etc.

4. Parthenogenesis: The unfertilized eggs develop into an embryo to form an invertebrate like fish, frog and other reptiles.

The gametes formed from a parent organism do not have the same genetic composition (identical DNA copies of the parental genome) because in sexual reproduction the fusion of male and female gamete takes place. The male gamete has different genetic makeup and female gamete has different genetic makeup their recombination leads to the formation of a gamete that has different DNA composition.

Sexual reproduction is the fusion of male and female gametes to produce genetically variant offspring. The sexual reproduction leads to:

1. Genetically varied offspring due to the recombination of the qualitatively different male and female DNA.

2. Due to recombination of DNA genetical variations are seen in the off springs.

3. This type of reproduction is useful as due to genetical variation the adaptation and survival compatibility increases.

Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. On the other hand, a tomato plant produces plenty of fruits though they have small flowers, because of the following possibilities:

1. The pollens produced by the rose plants may not be viable that means they may not have the compatibility to germinate, hence fertilisation does not take place.

2. They may be self-incompatible that means pollen-pistil interaction may not take place.

3. They may have non-functional ovules, that does not produce viable eggs.

4. As the rose plants are hybrid the mitotic division in them may be abnormal, which may produce non-viable gametes.

5. The pollen tubes may have barrier inside of it which restricts the male gamete to reach the ovule.