Biology 3 Marks Question

Meiosis is a process of reductional division in which the amount of genetic material is reduced. Gametogenesis is the process of the formation of gametes. Gametes produced by organisms are haploids (containing only one set of chromosomes), while the body of an organism is diploid. Therefore, for producing haploid gametes (gametogenesis), the germ cells of an organism undergo meiosis. During the process, the meiocytes of an organism undergo two successive nuclear and cell divisions with a single cycle of DNA replication to form the haploid gametes.

Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).

1. Ovary 2n.
2. Anther 2n.
3. Egg n.
4. Pollen n.
5. Male gamete n.
6. Zygote 2n.

A flower that contains both the male and female reproductive structure (stamen and pistil) is called a bisexual flower. Examples of plants bearing bisexual flowers are:

• Water lily (Nymphaea odorata).
• Rose (Rosa multiflora).
• Hibiscus (Hibiscus Rosa-sinensis).
• Mustard (Brassica nigra).
• Petunia (Petunia hybrida).

External fertilisation is a type of fertilization that occurs outside the female body, in external medium, such as water.Disadvantages of external fertilisation are:

• Very less chance of fusion of male and female gametes.
• Offspring are vulnerable to predators because of no parental care.

Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from the vegetative parts of plants. It does not involve the production of seeds or spores for the propagation of new plants. Vegetative parts of plants such as runners, rhizomes, suckers, tubers, etc. can be used as propa gules for raising new plants.Examples of vegetative reproduction are:

1. Eyes of potato:

The surface of a potato has several buds called eyes. Each of these buds when buried in soil develops into a new plant, which is identical to the parent plant.

2. Leaf buds of Bryophyllum:

The leaves of Bryophyllum plants bear several adventitious buds on their margins. These leaf buds have the ability to grow and develop into tiny plants when the leaves get detached from the plant and come in contact with moist soil.

Differences between gametogenesis and embryogenesis are as follows:

	Gametogenesis	Embryogenesis
1	It is the formation of male and female gametes.	It is the formation of embryo from the zygote.
2	Gametes are the haploid cells.	Embryo is a diploid cell.
3	Both mitotic & meiotic cell division take place.	Only mitotic division occur.

Sexual reproduction involves the fusion of the male and the female gamete.
This fusion allows the formation of new variants by the combination of the DNA from two (usually) different members of the species. The variations allow the individuals to adapt under varied environmental conditions for better chances of survival. However, it is not always necessary that the offspring produced due to sexual reproduction has better chances of survival. Under some circumstances, asexual reproduction is more advantageous for certain organisms. For example, some individuals who do not move from one place to another and are well settled in their environment. Also, asexual reproduction is a fast and a quick mode of reproduction which does not consume much time and energy as compared to sexual reproduction.

1. Totipotency.
2. Extract the disease free meristem, in vitro culture to get virus free plants.

Anemophily/ wind pollination.Unisexual flower, large quantity of pollen, pollen small/ smooth/ dry, devoid of scent/ nectar, inconspicuous/ not showy.

Annual: complete their life cycle in one season/normally planted in spring and produce grain before end of growing season/planted in autumn and harvested around mid summer e.g. wheat/barley/rye/rice.
Biennial: They are (monocarpic) plants flower and die in the second season/complete their life cycle in two seasons/show vegetative growth in one season and reproductive growth in second season.
e.g.- Sugarbeet/cabbage/carrot/radish.

1. a - unlimited food and space.

b - limited food and space.

2. Curve a.
3. Carrying capacity/a given habitat has enough resources to support maximum possible number - beyond which no further growth is possible.

1. Vegetative/Juvenile, Reproductive/Mature, senescence (old age)
2. vegetative propagules in flowering plants are:

• Eye, of potato.
• Rhizome, of ginger.
• Bulbil, of Agave.
• Leafbuds, of Bryophyllum.
• Offset, of water hyacinth.

1. Exine - It can withstand high temperature/strong acids/alkali.
2. Intine - It is thin and continuous layer made up of cellulose and pectin.
3. Vegetative cell - It is bigger, has abundant food reserve and a large irregularly shaped nucleus.
4. Generative cell - It divides mitotically to give rise to the two male gametes.

Plasma membrane, acrosome, nucleus, mitochondria tail/centriole/head/neck/middle piece.

Polygonum type embryo sac: Embryo sac in angiosperms is eight nucleate structure (seven - celled structure). Out of the eight nuclei formed by three successive divisions of the functional megaspore three get organised at the micropylar end as egg apparatus, three at the chalazal end as antipodals, and two at the centre as polar nuclei or secondary nucleus (2n), The egg apparatus consists of two synergids and an egg cell (This is monosporic type of development generally referred to as the Polygonum type). Only one megaspore of the tetrad becomes functional/viable that develops into the embryo sac.

1. Agamospermy: Seeds are formed from nucellus/ without fusion of gametes.
2. Parthenogenesis: Seeds/ embryo develop from unfertilized female gametes.
3. Parthenocarpy: Development of fruit in an unfertilized flower/ no viable seeds are formed.

In most plants, flowers need to be pollinated and fertilized to produce fruits. However, some plants can produce fruits before fertilization or without fertilization. Parthenocarpy is the process which produces fruits from unfertilized ovules in plants. Unfertilized ovules develop into fruits prior to fertilization. These fruits do not contain seeds.
Parthenogenesis is a type of reproduction commonly shown in organisms mainly by some invertebrates and lower plants. It can be described as a process in which unfertilized ovum develops into an individual (virgin birth) without fertilization. Therefore, it can be considered as a method of asexual reproduction.
It is seen in organism like rotifers, honeybees and even some lizards and birds (turkey).
The key difference between parthenogensis and parthenocarpy is, parthenogenesis is shown by animals and plants while pathenocarpy is shown only by plants.

1. Vegetative propagules are the units of vegetative reproduction. These are the vegetative parts of the plants which give rise to new plants, when they come into contact with damp soil or water.

Examples:

• Eyes in potato.
• Rhizome of banana and ginger.
• Leaf bud, in Bryophyllum.
• Bulbils in Agave.

2. There three natural methods of vegetative propagation are:

• From Root.
• From stem.
• By leaves.

1.  

1. Algae and bryophytes.
2. Pteridophytes, gymnosperms, angiosperms.

2. Gamete transfer refers to the process by which male and female gametes are physically brought together to facilitate their fusion.

Reduction division (meiosis) is associated with sexual reproduction. The reasons for this are:

• Since sexual reproduction involves the fusion of two types of gametes (male and female), they must have haploid number of chromosomes.
• The cell (meiocyte) which gives rise to gametes often has diploid number of chromosomes and it is only by reducing the number by half that we can get haploid gametes.
• Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.

Reptiles	Frogs
In reptiles, fertilisation is internal.	In frogs, fertilisation is external
They lay fertilised eggs in safe places.	Both male and female gametes are laid in water.
Eggs have a calcareous shell for protection.	Eggs have no calcareous shell, but have a mucilaginous covering.

Homogametes	Heterogametes
When the two fusing gametes are similar in appearance and cannot be categorised into male and female gametes, they are called homogametes, e.g. Cladophora.	When the two fusing gametes are dissimilar in morphology and/or physiology and can be categorised into male and female gametes, they are called heterogametes, e.g. human beings.

1. Isogametes.
2. Fertilisation is taking place and zygote is the resultant structure.
3. Cladophora/ Chlamydomonas.

1. S- seeds, P- pericarp.
2. Ovule-Seeds, Ovary-Fruit.
3. Pericarp.
4. Diploid (2n).
5. It has thick wall which helps in protection.

The process of fusion of male gamete with the female gamete is called fertilisation or syngamy. It results in the formation of a diploid cell called zygote.It is mainly of two types:

1. External Fertilisation:

In majority of the aquatic organisms, e.g. algae, fish and in amphibians, the process of fertilisation takes place outside the body of the organism, i.e. in water. This type of gametic fusion is called external fertilisation.
To enhance the chances of fertilisation, the organisms exhibiting external fertilisation discharge a large number of gametes in water, e.g. bony fishes, frogs, etc.
By this process, a large number of offsprings are produced with the disadvantage of them being vulnerable to predator. This threatens their survival upto adulthood.

2. Internal Fertilisation:

In most of the terrestrial organisms, e.g. fungi, higher animals (reptiles, birds and mammals) and majority of plants such as bryophytes, pteridophytes, gymnosperms and angiosperms, the process of fertilisation takes place inside the body of the organism. This type of gametic fusion is called internal fertilisation.

• Flowering plant- Inside plant body, internal fertilization.
• Frogs- Outside body, external fertilisation.

In some plants and fungi, male and female reproductive structures may be present on the same plant, such plants are called homothallic or monoecious, e.g. chara, cucurbita, coconut palm, etc. While, in some lower plants, male and female reproductive structures may be present on different plants. These plants are known as heterothallic or dioecious, e.g. Marchantia, date palm, etc.

The embryonal protection and care are better in viviparous species because development of zygote takes place inside female and proper nutrients are provided to developing embryo through mother's body.

Juvenile phase, Reproductive phase, Senescent phase
Juvenile phase: The phase of growth in the organisms before reproductive maturity.
Reproductive phase: In this phase organism attains reproductive maturity.
Senescent phase: The phase between reproductive maturity and death.

1. Meiocyte is a type of cell that differentiates into a gamete through the process of meiosis. Through meiosis, the diploid meiocyte divides into four genetically different haploid gametes.

• The diploid number in potato is 48.
• The diploid number in housefly is 12.

2. S. No.	chromosome numbers in gametes	Species Name
   1.	23	Human begin
   2.	6	Housefly
   3.	24	Potato
   4.	17	Apple
   5.	39	Dog
   6.	10	Maize

1. Life span is the period of time from birth to natural death of an organism.
2.  

1. 60 years.
2. 15 years.
3. 140 years.
4. 1-2 weeks.

Dissimilarities: Zoospores are motile whereas conidia are non-motile. Zoospores are produced in a sporangium whereas conidia are produced externally.
Common feature: Both are the means of asexual reproduction.

In those plants, water is the medium through which gamete transfer takes place. A large number of the male gametes, however, fail to reach the female gametes.
To compensate this loss of male gametes during transport, they are produced in large numbers.

• Yes it is also applicable in animals.

Vegetative propagation is also a type of asexual reproduction because,

1. This is uniparental.
2. Clone formation takes place.
3. There is no fertilisation.
4. There is no gamete formation.

Gemmules are internal buds formed inside the parent's body.
Example: Fresh water sponges (Spongilla).

Yes, it is observed in parthenocarpic fruits. The ‘seedless fruits’ that are available in the market such as pomegranate, grapes etc., are infact good examples. Flowers of these plants are sprayed by a growth hormone that induces fruit development even though fertilisation has not occurred. The ovules of such fruits, however, fail to develop into seeds.

There are some benefits for the organism which reproduces through spore formation such as:

1. Reproduction through spores is simple as well as faster mode of reproduction.
2. he spores are light in weight thus, keep floating in the air. This helps in their dispersal.

Vegetative propagation in certain plants; like Bryophyllum, water hyacinth, ginger, etc. can be termed as asexual reproduction. Following are some to the reasons for this:

• Reproduction involves a single parent.
• Meiosis does not happen during any stage of reproduction.
• Offspring get the set of DNA from a single parent.

Organism	Modes of Reproduction
Sycon	External budding
Penicillium	Conidia
Spongilla	Internal budding (Gemmule)
Paramecium	Binary fission (transverse)
Yeast	Budding (External)
Marchantia	Gemmae
Amoeba	Binary fission (Simple)
Chlamydomonas	Zoospores

The number of male gametes produced is more than the female gametes because male gametes are usually motile and they have to compete with one another for their existence. While the female gamete is stationary. At the end only one male gamete fuses with the female gamete for the fertilization to take place.

Parthenocarpy can be natural or artificial process. In this, the process of fertilization (fusion of gametes) does not take place and fruit formed is seedless. Fusion of gametes is not needed in this process and fruit formation is direct.

1.	Ovary	Fruit
2.	Ovary wall	Pericarp (fruit wall)
3.	Ovule	Seed
4.	Outer integument	Testa (Outer seed coat)
5.	Inner integument	Tegmen (Inner seed coat)
6.	Secondary nucleus	Endosperm
7.	Egg	Zygote
8.	Synergids and antipodals	Degenerate
9.	Hilum, funicle and micropyle	Shows no changes

Development of female gamete (ovum) into a complete organism without fertilization is known as parthenogenesis.
Examples:

1. Rotifers.
2. Drones of honeybee.

1. Sexual reproduction brings about variation in the offspring.
2. Since gamete formation is preceded by meiosis, genetic recombination occurring during crossing over (meiosis-I), leads to a great deal of variation in the DNA of gametes.
3. The organism has better chance of survival in a changing environment

1. The given diagram shows a bulbil of Agave.
2. Two other plants which reproduce by same method are Oxalis and lily.
3. The plant parts which help in vegetative (asexual) reproduction are referred to as vegetative propagules.

When the offspring is produced by a single parent without the involvement of gametic fusion, the reproduction is called as asexual reproduction. It involves only mitotic cell division. Meiosis does not occur in asexual reproduction. Offsprings produced by asexual reproduction are identical to one another and exact copies of their parents. Such a group of morphologically and genetically similar individuals are called clone.

Asexual reproduction occurs in unicellular organisms (monerans and protists), some lower animals (sponges, coelenterates, certain worms) plants and tunicates. It is absent in higher invertebrates and vertebrates.

In a pea pod, the pericarp is not differentiated into many layers. In a tomato fruit, the pericarp is differentiated into epicarp, mesocarp and endocarp. Most of the edible part or tomato is composed of mesocarp which is juicy and fleshy. Moreover, placentation is responsible for arrangement of seeds in a fruit. A pea flower shows marginal placentation, while a tomato shows axial placentation.

External fertilisation	Internal fertilisation
When fusion of gametes (syngamy) occurs outside the body of the organism, it is called external fertilisation.	When fusion of gametes (syngamy) occurs inside the body of the organism, it is called internal fertilisation.
A large number of gametes are released in the surrounding medium by such animals.	The number of ova produced is less, but a large number of male gametes are formed, as they have to travel towards the ovum.
Chances of survival of offspring are less. e.g. frog and bonyfish.	Chances of survival of offspring are high. e.g, birds, human beings, etc.

• During embryogenesis, the zygote undergoes a number of mitotic divisions; this is to increase the number of cells.
• The cells thus formed undergo differentiation; this process helps groups of cells to undergo modifications to form specialised tissues and organs.