Some questions and their answers

Plants are indeed astounding. They not only feed us and are crucial for water cycle but also provide material for our attire, shelter, fuel, and written communication. They also take care of our cosmetic needs. Whenever we suffer from a disease they can come to our rescue. Aren’t they really prodigious. But unfortunately, like our usual self we hardly understand them and often are confounded with many doubts. Let’s face some of them.



Plants and Light:
· Why are most of the plants green in color?
· Why is the upper surface of a leaf greener than the lower surface?
· How do non-green plants like croutons synthesize food when they do not have the chlorophyll?
· Some leaves are half yellow and half green, which part of such a leaf contains chlorophyll?
· How do plants make their food on a cloudy day?
· What is the effect of ultraviolet rays on plants?
· Do plants take oxygen at night for their respiration?
· Is the amount of carbon dioxide taken in by plants during daytime is equal to that released by them during night?
· When stomata closes during night how do plants respire?
· Can plants grow in light other than sunlight e.g. from an electric lamp?
· Will keeping a plant in light for a longer duration or for a period of 24 hours make any difference to its growth?

Photosynthesis is the process, which enables plants to collect energy for their growth from air and sunlight. It is a enzyme catalyzed photochemical reaction. Photochemical reactions are chemical reactions, which require the presence of light to take place. Light is an essential reactant for such reactions. Intensity of light controls the speed of such reactions, lesser the intensity of light slower the reaction. When the intensity of sunlight is low, as on a cloudy day, photosynthesis is slower but it does occur.

Light is electromagnetic radiation in a certain frequency range, whether it is from the Sun or an electric lamp. They differ from each other in their intensity and the distribution of wavelengths in their spectrum (colour composition of its spectrum). Photosynthesis can indeed take place in the light emitted by an electric lamp if has enough intensity of red and blue light. This is so because it is only the light having wavelengths/frequency corresponding to blue and red colors, which participates actively in the photosynthesis. One can than understand the reason why most plants are green. A substance, which appears green in white light, absorbs red and blue parts of the white light and reflects the green light to our eyes. The photosynthetic machinery of a plant is located in an organelle known as chloroplasts. The green colour is due to the presence of a particular green coloured organic compound known as chlorophyll in them. Because the upper surface of a leave faces the sunlight there is a larger concentration of chloroplasts on it, this surface of a leave therefore appears darker green.

But the apparent colour of a plant (like any other object) does not necessarily reveal its composition of pigments. Thus even though croutons do not appear green in colour it does not imply that they do not contain any chlorophyll. The color due to chlorophyll molecules can be very easily camouflaged by molecules which reflect light of a different wavelength composition. Plants also produce carotenoid pigments, which range from lemon yellow to tomato red and anthocyanins, which range from palest pink through red to flamboyant purple. Carotenoids also absorb light for photosynthesis and are frequently found in chloroplasts. Thus the non green croutons can also photosynthesize and an apparently yellow coloured leaf is not devoid of chlorophyll molecules-- it is just due to the presence of some yellow or red carotenoids also in the chloroplasts that it appears yellow rather than green.

The misconception that plants respire only during night is very common amongst most of us. Respiration, as some of us may know, is the process by which a living being processes molecules like glucose etc. to get energy to drive many other biochemical reactions necessary for growth of the organism. It often requires oxygen as a reactant and carbon dioxide is the product. But photosynthesis and respiration are not the only two active processes that take place in a plant. A plant synthesizes vitamins, proteins, cellulose, lipids and chlorophyll etc. etc. almost all the time for its growth and security. All these compounds are synthesized from the inputs – carbon dioxide, oxygen, nitrogenous compounds, phosphorus and many trace elements like magnesium and iron. Obviously all the carbon dioxide taken in during the day is not given off in the night. Respiration is active all through, whether it’s day or night, even when the photosynthesis becomes very slow in the night. Thus plants act as a nett sink of carbon on the Earth’s surface. Even when a large proportion of stomata closes at night, plants do take in oxygen through the ones still open. In addition plants can indeed take up oxygen through other surface structures in the green stems or fruits.

The duration of night and day is not the same all over the Earth. Thus there are places where the duration of day may be as much as 23 hours a day during a particular period of the year. Plants do grow in such places also as they do in caves where there is little or no sunlight. Various kinds of plants have evolved to survive in different physical conditions of environment. Thus while some plants like beets, lettuce or clover can survive only after many days of long hours of sunshine, short day plants occur in regions where the duration of the day is usually short. Usually plants can adapt to a change in duration of light. Ultraviolet, and to a certain extent the shorter wavelengths of light as well, tend to promote the formation of anthocyanins. They can also affect the phototropic phenomena, and can check the stem elongation by inactivating certain growth-promoting hormones.



Plants and Water
· How can plants attract clouds?
· Why do drops of water appear on the leaves of a peepul tree in the morning?
· How does the water from the soil reaches the top of a coconut tree and get inside the coconut?
· How does water rise up in plants against the gravity of Earth?
· Why do leaves of some plants droop at sunset?
· Why does a sensitive plant like mimosa folds its leaves on getting any type of little stimulus?

Water does indeed rise up the body of a plant regardless of its height. The mechanism of this phenomenon has engaged the attention of scientists for very many years. However, there seems to be some consensus on this issue now. The water in a plant is pushed up by the root pressure and is also pulled up due to transpiration (evaporation of water from its leaves ). A plant has an intricate network of veinlets through which water is transported from the soil through the roots to its body. The roots because of osmosis absorb water. Cells in the roots of a plant accumulate many organic compounds and inorganic ions as they grow, this leads to the movement of water into them from the soil due to osmotic pressure. As some of the synthesized food moves up the body of a plant, a pressure gradient for water is generated within the plant body, which pushes the water up. Concurrently as a plant loses water to the atmosphere from its leaves due to transpiration, and as the chloroplasts synthesizes more glucose molecules, water is pulled up to the leaves, branches and fruits due to capillary action. As we know, the capillary action is due to the difference in the adhesive forces between water molecules and the molecules that constitute the walls of a capillary and forces due to hydrogen bonds between water molecules. In a peepal tree water pushed up due to root pressure is not lost to the surroundings rapidly enough due to cooler atmosphere at night/dawn and accumulates as droplets at the tip of leaves. A young coconut fruit is made up of cells, which are rather rich in water content. As the fruit grows this water gets separated from the cells and is accumulated in the center of the fruit.
The stiffness of the branches and leaves of a plant is due to such an inner water pressure in a plant cell, called turgor. An abrupt change in the turgor in the cells at the joints of leaflets and leaf stalk is indeed responsible for the folding up of leaves of a sensitive plant like mimosa. The abrupt change is brought about by the presence of certain molecules in these plants, which are very sensitive to touch. It is speculated that this folding up of leaves is a protective mechanism such plants have evolved to prevent their being eaten by grazing animals. The drooping of leaves at sunset in some plants is also due to similar changes in turgor.

Plants do not attract clouds like a magnet attracts the iron filings or Earth attracts a falling apple. The water vapors produced by transpiration from the plants rise up in the atmosphere. This helps the precipitation of clouds, because as the concentration of water in the clouds increase they are more prone to precipitation.

Flowers, Seeds, Fruits

• Why is the colour of flowers different for different plants?
• Why are seeds dried before sowing, by doing so aren’t the cells killed?
• Why is it that a seed with an intact coat can germinate while a seed without its coat does not germinate?
• Is it correct to assume that seeds preceded plants in evolution?
• Is tomato a fruit or a vegetable?
• A male papaya plant cannot bear fruit, so can we graft a female papaya plant on to a male plant to get a fruit bearing tree?
• Why do flowers smell?
• Why are most of the fruits sour in taste before they ripen but taste sweet after ripening?
• Most fruits become yellow or red only on ripening. How does the change of color, from green to yellow, occur and why?
• Some fruits and vegetable have insects inside them but if we inspect that particular fruit or vegetable we do not find any entry point. How does that insect gets inside and how does it breathe?
• Why don't tinned fruits rot?
• Which plant yields fruit only once in its life?
• How are the seedless varieties of grapes cultivated?
• Why do fruits fall off from a tree only when they are ripe?
  
  Flowers have a special function for the propagation of plants. It is in the flowers that fertilization takes place through pollination. Many plant species depend on an interaction with insects for pollination. The male reproductive cells of such plants are located in a particular part of a flower known as anther. The pollens in the anthers are in fact the male sperm cells. These cells have to combine with the female reproductive structures called ovules present at the base of another flower organ known as pistil -- for fertilization in a plant. Pollen grains must be passed from the anthers to the top of pistils before they can reach the ovule, which then grows into a seed. This can be achieved when an insect sits on the flower and carries some pollen on its limbs to another flower. This kind of fertilization is known as cross pollination. Cross pollination has several advantages for the evolution of the genetic pool of a plant over self pollination. It is therefore advantageous for a plant to attract insects towards its flowers. Bright colours and fragrant smells help a plant in this respect. If an insect lays its eggs on the ovule of a flower which later develops into a fruit, the insect larvae develop inside the body of the fruit as it ripens.
  The journey from a seed to a plant is arduous, to say the least. Most often a fertilized seed does not germinate for a long time after separation from its mother plant. Often it is stored before being sown. If during this period it has sufficient moisture it can easily fall prey to many insects and bacteria. It is to prevent such infestations that seeds are normally dried. The normal drying process does not remove all the water from the cells of a seed. Thus cells in a seed can remain alive even after drying. The seed coat also help prevent insect infestations. But it may not be always true that a seed without a seed coat cannot germinate. In fact, many times external assistance is necessary to break the seed coat.
  Grafting is a method of vegetative propagation where two plants are joined together in such a manner that they unite and continue growth as one plant. It is fairly successful as a method of propagation of pear, peach, plum, mango, guava and sapota trees. However for one reason or the other grafting has not proved useful for the propagation of a papaya tree.
  The term ‘fruit’ in common parlance has a different connotation than the strict botanical term. In botany, fruit means that part of a flower, which develops further and usually, contains seeds for further propagation. Thus tomatoes, peas and beans are really fruits. Strictly speaking, we should reserve the word “vegetable” for edible parts of a plant not derived from the pistil. Thus a potato or an artichoke is a vegetable because they are tubers—the underground parts of the stem. Lettuce, cabbage and spinach are vegetable because they are leaves of plants. Fruits help a plant to disperse its seeds farther away. This is desirable for the propagation of a particular plant species, as it prevents heightened competition for space, light, water and soil nutrients that would result if the seeds sprouted in the immediate vicinity of the parent plant. Thus it is essential that a fruit must separate from its parent plant. The natural falling of a ripe fruit from a tree is just a part of this grand design. Often the seeds are embedded in a thick coat of flesh of the fruit. The seeds inside such fruits to sprout need external help. Birds, humans and animals that consume these fruits and help in dispersing the seeds provide this help. Fruits become sweeter on ripening to make them more inviting for its potential friends, the birds and animals. Many cultivated varieties of plants have become seedless or practically so. In some instances there are only traces of seeds in the fruits, such as black specks of banana. Plant breeders have deliberately developed seedless varieties of grapes and oranges. Since such fruits have no seeds, new plants can be only grown from stem or root cuttings or by some other means of vegetative propagation, e.g. tissue culture.
  A Banana tree bears fruit only once. Tinned fruits don’t rot because we make sure that its syrup is sterile that is it has no bacteria which can grow in it. Both seeds and plants are high up in the evolutionary tree. So if we look back it would not be a seed tr a tree in its present form which preceded the other. Most likely both of them have evolved from a common ancestor: a primitive form of photosynthesizing organism.
  
  Trees:
  
• Why don’t coconut and banana trees have branches?
• How is the age of a tree determined?
• How is ecosphere balanced in the deserts without any trees?
• How do seedlings that sprout on dried tree trunks get their nutrition for growth?
• Why big trees like `Neem' (Margo), `Peepal' have long leaves?
• How do trees make their food in winter or autumn when there are no green leaves present on them?
• Which is the oldest tree on the earth, How old is it?
• Why are mountaintops devoid of trees?
• Can a full-grown tree be planted?
• What is a Bonsai?
• Can the age of a tree be counted without cutting it?
• Why do all trees have a cylindrical trunk?

A trees trunk is as much cylindrical on the average as the cross section of any other living being. This is so because the growth of a living organism is from within-- due to the increase in number of cells by cell division. Unless there is a structural reason for preferred growth in a particular direction the growth is symmetric radialy. But some plants do have stems having a triangular cross section. The shape and size of the leaves or the branches of a tree is determined by its history of evolution. Like all living beings any particular tree has undergone a long evolutionary process, which has resulted in its characteristic traits.

Just like we can survive without food for several days because we have a store of carbohydrates and proteins in our body. Plants also can survive without synthesizing more food through photosynthesis. During winters or autumn when some plants shed almost all leaves, they survive using the carbohydrates stored in their tissue. They also grow much more slowly to conserve food.
Bonsai is the art of growing miniature trees or other plants in a tray or other container. Most bonsai trees range in height from 5 cm. to 95 cm. The art of bonsai requires much skill, time and patience. The trees are kept small by pruning the roots and branches and repotting the trees, as the size of the container also partly determines the final size of a bonsai tree. Pinching off the new growth, wiring the branches, careful watering and fertilizing can also control the size and shape of a bonsai. Some trees are better suited for bonsai than others. Popular trees used for bonsai include cherry, plum, bamboo and maple.
The number of annular rings in its trunk determines the age of a tree. The rings are formed due to uneven growth of the trunk in different seasons from summer to winter. To count these rings one does not have to necessarily cut the trunk. A small cylindrical section can be obtained with the help of certain kind of drilling machines. Bristlecone pine trees are known to be the longest living trees. It is a stunted and knurled plant which flourishes on the wind swept, rock-strewn slopes of White Mountains, in western United States. The oldest such tree is the Methuselah Tree: more then 4600 years old, it was already a sapling when Egyptians started building the pyramids. The age of such very old trees is determined by radio carbon dating method.
Deserts are not totally devoid of plants. A desert ecosystem usually has lesser rainfall and the soil is more siliceous. Different varieties of plants have evolved which are well adapted to such an environment. The three different types of plants found in deserts are: the annuals, which avoid draught by growing only when there is adequate moisture; the succulents such as cacti -- which store water; and the desert shrubs which have numerous branches with thick leaves that are shed during prolonged dry periods.
Full-grown trees can indeed be transplanted. In fact city administrations in metropolitan cities like Delhi have to often resort to it because cutting trees is prohibited but the space occupied by a tree may be required for certain metropolitan development. Not all mountaintops are devoid of trees, only very high rocky mountain are devoid of trees because a tree cannot access water through its roots at such places.

Other miscellaneous questions
· Can plants talk?
· Can vaccination be done in case of plants?
· How do plants cure and prevent diseases?
· Is it possible to make petrol from herbal plants and water, as was reported some years ago? · Why do creeping plants coil over a stick or plant in an anti-clockwise direction only?
· If the branches or even the stem of a tree are cut they continue to grow but if the limbs of an animal are cut they do not grow again, why?
· Are microbes considered to be plants or animals?
· What is plant tissue culture, can we save the medicinal plants through this technique?
· Why hybridization is possible in case of plants but not between mammals?
· Do plant excrete?
· Do plants feel pain?
· If insectivorous plants trap insects for obtaining food, then why are they green in colour?

According to the biological classification, living organisms made up of cells with a cell wall -- made up of cellulose, are called plants. The cells of many microbes like algae do have cell walls hence they are classified as plants. A tree or for that matter any plant does not have a central nervous system. A branch of a tree or a stem of a plant has enough food and cellular machinery for it survive for some time or even grow and reproduce as long as it has access to a nutrients, water and minerals. In fact some of the cells of a part of a plant can even be used to propagate the plant without the intervention of the seeds. Tissue culture is a biotechnological technique like cloning developed to achieve this. A new plant can be grown either by proliferation of the shoot apex or auxiliary bud or from callus – an unorganized mass of cells from any explant. The callus can be made to regenerate a plant with the help of suitable growth regulator chemicals. Plants do not feel pain the same way as we do, but they do sense injury to their body and can communicate it to other plants by releasing certain chemicals, which the other plants can interpret as a message. Thus plants do feel injuries and can talk with other plants but their medium of communication is not sound waves it is through chemicals like our sense of smell.
Plants can indeed be vaccinated. But the immune system in plants is somewhat different from that in humans. In mammals, every time an infectious agent challenges the immune system, it continues to produce antibodies that are highly specific for the agent long after the invader has been defeated. This confers specific immunity to the disease. Individual plants by contrast have only a limited repertoire of resistance genes. And thus produce a hypersensitive response against a fixed set of infectious agents. Yet plants that do not possess resistance against a particular infectious organism can still acquire immunity through being exposed to some other organism. Unlike animals, plants infected with one disease can acquire immunity to a wide range of other diseases. They do this by producing some very specific organic compounds. Thus the wide range of plants present in nature produce many more organic compounds than all organic chemists have conceptualized or synthesized so far. Some of such compounds have reactions in a human body, which may cure certain diseases. No wonder we find that some plants have medicinal value.

Not all creepers coil counter clockwise, if one observes carefully one can surely find creepers, which coil clockwise also. Some creepers do change direction of their coiling midway, i.e. they coil clockwise initially and then anti clockwise or vice versa.
It is not true that hybridization of species is not possible among mammals; the most common example is the mule (a hybrid of a horse and a donkey. Hybridization is possible only between closely related species and this holds true in case of plant hybridization also. Insectivorous plants do not devour insect to obtain carbohydrates, the basic energy source for their growth. The insect body acts mainly as a source of nitrogen, which these plant cannot procure from the soil.

Plants may be prodigious but they cannot transmute one element into other. Petrol is a mixture of hydrocarbons -- having a certain proportion of carbon and hydrogen atoms (about 1:3). Mixing a few hundred grams of any herb to a few liters of water cannot convert the hydrogen and oxygen atoms present in water to carbon atoms to produce hydrocarbons (petrol). Thus the claim by an Indian charlatan to this effect was nothing but a hoax. However some plants indeed produce sap which is rich in hydrocarbons and they have indeed been called petrocrops, but that is a totally different matter and has been scientifically analyzed.