Coconut Water: Nutritional Value and Health Benefits

Ans. Coconut water is formed by the process of double-fertilization in plants. It is the liquid endosperm which results due to free-nuclear division of the primary endosperm nucleus. The PEN undergoes Karyokinesis which is not followed by cytokinesis. This leads to the formation of liquid triploid endosperm which nourishes the growing embryo in the plants.

As plants grow and mature, cell formation takes place and the liquid endosperm turns into a white flesh called Coconut Meat. However, a little amount of liquid endosperm still remains in the cavity of the mature fruit.

Ans. Double-fertilization is the process in which two male gametes are released into the female gametophyte. Out of the two gametes, one male gametes fuses with an egg cell resulting in the formation of a diploid zygote. The other male gamete fuses with the two haploid polar nuclei resulting in a triploid Primary Endosperm Nucleus (PEN). 

The PEN undergoes free-nuclear divisions but cell wall formation does not take place. This results in a highly nutritious liquid endosperm. The endosperm continues to nourish the growing embryo in the plant. As the plant matures, cell wall formation begins that turns liquid endosperm into white flesh. 

Ans. There are mainly three types of endosperm development, found in angiosperms-

1. Nuclear type - In this type, the nuclear division is not followed by cell wall formation. The nuclei are not bounded by cell-wall and remain free in the cytoplasm of the embryo sac. Cytokinesis may or may not take place depending upon the plant and in some it is even incomplete like coconut. 
2. Cellular type - In this type of development, each nuclear division is accompanied by cell-wall formation. There are no free nuclei in the cytoplasm.
3. Helobial type - In this type, the first nuclear division is followed by cytokinesis but subsequent nuclei remain free and do not undergo cell-wall formation.

Ans. Pollination is the process of transfer of pollen grains from anther to stigma of a plant. After depositing on the stigma, the pollen grains form a tube through the style through which male gametes enter into female gametophyte. It is a physical process.

Whereas, Fertilization is the term used to describe the process of fusion of male and female gametes resulting in the formation of a diploid zygote. The zygote then develops into an embryo. It is a biological process.

Ans. In asexual reproduction, plants give rise to individuals which are genetically identical to their parent but do not involve fusion of male and female gametes. There are different ways of asexual reproduction seen in plants. Broadly, asexual reproduction in plants takes place in two ways:

1. Natural Methods
2. Artificial Methods

Natural Methods - In this, plants reproduce through self-propagation. This may take place in below mentioned ways:

1. Budding - In this type, a new individual develops from a bud. A bud is generally an outgrowth on a plant formed due to cell division at a particular site. 
2. Fragmentation - In this, each part or fragment of the plant develops into a whole new individual. 
3. Vegetative Propagation - In this, new plants arise from vegetative parts like root, stem and leaves of a plant. This can occur naturally as well as can be artificially induced.
4. Spore Formation - In this, plants produce asexual reproductive structures called spores which germinate and give rise to new individuals under favourable conditions.

Artificial Methods - Asexual reproduction in plants can be induced artificially in following ways:

1. Grafting - In this method, parts of two different plants are cut and joined together. This is then grown under favorable conditions to form a new plant.
2. Layering - This is a method in which the stem grows roots while being attached to the parent plant and then detaches from it when fully grown.
3. Micropropagation - This is a technique used to grow a large number of plants at the same time under laboratory conditions. This is done by cutting a part of a plant called an explant (like shoot tip, root tip etc.) and growing it in laboratory conditions to produce a mature, fully grown plant.

Ans. During sexual reproduction, the processes which occurs before fertilization takes place are termed as pre-fertilization events. These are-

1. Gametogenesis - It is the process of formation of gametes from male and female gametocytes. It takes place either by meiosis or mitosis. Haploid cells produce gametes through mitosis, whereas diploid cells undergo meiosis to produce gametes. 
2. Gamete Transfer - The process by which male and female gametes come together for the purpose of fertilization is called gamete transfer. In some cases, male gamete is motile and approaches towards female gamete for fertilization while in some both are motile. In plants, pollen grains are transferred from anther to stigma by pollination.

Ans. The two types of pollination observed in plants are-

1. Self-Pollination - It is the process of transfer of pollen grains from anther to stigma of the same flower or different flower of the same plant. It can cause inbreeding depression and also decreases genetic diversity. 
2. Cross-Pollination - It is the process of transfer of pollen grains from anther to stigma of a different flower. It is carried out by pollinating agents like wind, insects etc. It increases genetic diversity.

Ans. There are two types of self-pollination:

1. Autogamy - In autogamy, pollen is transferred from anther to stigma of the same flower.
2. Geitonogamy - In geitonogamy, pollen is transferred from anther to the stigma of another flower of the same plant.

The advantages of self-pollination are given below:

1. Since it occurs within the same flower or plant, it does not require pollinating agents.
2. It prevents wastage of pollen grains as found in cross-pollination.
3. It helps to maintain the genetic traits of a species and allow lesser genetic variations.
4. It produces pure lines rather than giving hybrid varieties.

Ans. The presence of starch in leaves can be tested by the Iodine test. When we remove chlorophyll from the leaf by boiling it in alcohol and then putting 2 drops of iodine solution, its colour change to blue indicates the presence of starch.

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A typical angiosperm ovule

A typical angiosperm ovule is a small structure that is formed in the ovary. Ovule first develops as a projection on the placenta and is composed of multilayered cellular tissue called the nucellus. The hypodermal cell of the die nucellus enlarges and is transformed into a megaspore mother cell. This cell undergoes meiosis to produce four haploid cells only one of which develops & forms an embryo sac (female gametophyte). An ovule may be surrounded by one or two protective layers called integuments, leaving a small opening at one end termed as micropyle which acts as a passage for the entry of the pollen tube into the ovule. Thus, a typical ovule consists of a fully developed embryo sac with the nucellus and integuments.