Combustion

Do Plants Breathe

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Do Plants Breathe

Respiratory system in plants
In plants, food that is manufactured in the form of starch needs to be broken down to release energy. So, respiration is a vital function in plants. It is represented as
Starch (Sugar) + Oxygen —► Energy + Carbon dioxide + Water
Plants respire through tiny holes or openings called stomata present on the underside of leaves. Stomata trap air (containing gases like oxygen and carbon dioxide) and the exchange of gases takes place inside plant cells.

plants-breathe-1
Open Stomata

Even roots buried in the soil require oxygen for the plant to survive. Plant roots typically take in oxygen that is available in the small spaces between soil particles, and give off carbon dioxide. If roots cannot respire, they cannot produce the energy necessary to actively take up minerals from the soil. For proper root respiration, farmers plough or till the soil so that tiny air spaces are created around the soil particles.

Activity
Aim: To demonstrate that plants respire through stomata
Materials needed: Petroleum jelly, a leafy plant, e.g., geranium, dahlia, or rose
Method:
1. Keep the plant in the dark for a few days.
2. Choose two leaves and coat their underside with petroleum jelly.
3. Place the plant on a sunny window sill for a week and observe.
Observation The two leaves begin to die as time goes by.
Conclusion: This is because there is no way for air to enter.

How do plants/animals live in water?
Aquatic plants and animals survive in water by utilizing dissolved oxygen. The sources of dissolved oxygen are direct absorption from the atmosphere and release during photosynthesis by aquatic plants. Aquatic animals breathe through their skins, whereas many have gills. Aquatic plants directly exchange gases with the water surrounding their leaves, stems, and roots.

Activity
Aim: To show that heat is released during respiration
Materials needed: Two thermos flasks, seeds, formalin or carbolic acid, cottonwool, and two thermometers
Method:
1. Take two thermos flasks and mark them (1) and (2).
2. Take a glassful of seeds and soak them in water for more than 24 hours.
3. Divide the seeds into two equal groups.

plants-breathe-2
4. Boil one group of seeds and then wash them with dilute formalin or carbolic acid to prevent decay.
5. Put the live germinating seeds in flask (1) and the killed ones in flask (2).
6. Insert a thermometer in each flask and plug their mouths with cotton wool.
Observation: After a few hours, the thermometer in flask (1) shows a higher reading. The thermometer in flask (2) does not show any rise in temperature.
Conclusion: This indicates that the germinating seeds give out heat because they are alive and are respiring.

Aerobic and anaerobic respiration
Respiration is primarily of two types: aerobic and anaerobic.
1. Aerobic Respiration
The process of respiration that takes place in the presence of oxygen is called aerobic respiration. This results in the release of energy, and in the formation of carbon dioxide and water.
Aerobic respiration is represented by the equation:
Sugar + Oxygen —► Energy + Carbon dioxide + Water
Aerobic respiration is the most efficient form of respiration. The reaction involved in this process is similar to that of combustion or burning. However, there are some differences between the two.
Table Differences between aerobic respiration and combustion

Aerobic RespirationCombustion
1. Energy is given out gradually.1. Energy is given out suddenly
2. Energy is given out in the form that can be used by the organism.2. Energy is given out in the form of heat or light.
3. Energy is stored inside the body in the form of ATP (adenosine triphosphate, energy-rich molecules) which can be used whenever needed3. Energy is not stored as ATP.

2. Anaerobic Respiration
The process of respiration that takes place in the absence of oxygen is called anaerobic (“an” means “without”) respiration. This results in the release of energy, and in the formation of carbon dioxide and ethyl alcohol (an organic compound). It is represented by:
Sugar —► Energy + Carbon dioxide + Ethyl alcohol
In humans, anaerobic respiration can be carried out only for a short period of time. It occurs in our muscle cells when there is not enough oxygen supply. This happens when we are doing heavy work or exercise, running fast, etc. However, many microorganisms such as yeast, bacteria, and fungi can only respire anaerobically.

Activity
Aim: To demonstrate that oxygen is used up during aerobic respiration
Materials needed: Laboratory stand, a round-bottomed glass flask, KOH pellets, mercury, a glass tube, a beaker, and some seeds.
1. Take a few germinating seeds in the flask and arranged the apparatus as shown in the figure.

plants-breathe-3
2. The glass tube is inverted into a beaker containing Seeds mercury.
3. KOH pellets are kept inside the glass tube as shown.
This helps to absorb the carbon dioxide so that it is not used up by the seeds.
4. Another similar setup without KOH pellets is set up alongside to act as control.
Observation: The mercury level rises in the setup with KOH pellets after a day. No change can be seen in the setup without KOH pellets.
Conclusion: When the oxygen in the apparatus is used up, it lowers the pressure inside the bulb, causing the level of mercury to rise up in the glass tube. This shows that oxygen is used by the seeds for aerobic respiration.

What are the Types of Combustion

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What are the Types of Combustion

Combustion

The process of burning of a substance in the presence of air or oxygen with the liberation of heat and light is called combustion. Substances can be classified as combustible or non-combustible, depending on whether or not they can be burnt.

Substances that burn in air or oxygen to produce heat and light are called combustible substances. Paper, wood, kerosene, and LPG are examples of combustible substances.

Substances that do not burn in air or oxygen to produce heat and light are called non-combustible substances. Water, sand, glass, and cement are examples of non-combustible substances.

Types of Combustion

Combustion can be divided into three types:

  1. Rapid combustion
  2. Explosion, and
  3. Spontaneous combustion.

1. Rapid combustion: In this type of combustion, large amount of heat and light are released in a very short span of time. Combustion of LPG, which produces heat and light instantly, is an example of rapid combustion.

2. Explosion: This type of combustion is characterized by sudden release of heat, light, and sound accompanied by the liberation of a large amount of gas. Bursting of firecrackers is an example of an explosion. An explosion can also occur upon the application of pressure.

3. Spontaneous combustion: In this type of combustion, substances catch fire on their own, without the application of heat. For example, white phosphorous.
Combustion of hydrocarbons (compounds of hydrogen and carbon, e.g., LPG, petrol, and natural gas) can be divided into two types: complete combustion and incomplete combustion.

  • Complete combustion: This type of combustion takes place in adequate amount of air or oxygen. It results in the formation of carbon dioxide, water, heat, and light.
  • Incomplete combustion: This type of combustion takes place in inadequate amount of air or oxygen. It results in the formation of carbon monoxide, soot, water, heat, and light.

Chemical Properties of Carbon Compounds

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Chemical Properties of Carbon Compounds

Though we have millions of organic compounds, the reactions they undergo are limited. Some important reactions among them are discussed here.
They are:
1) Combustion reactions
2) Oxidation reactions
3) Addition reactions
4) Substitution reactions

1. Combustion reactions
Carbon, and its compounds burn in presence of oxygen or air to give CO2, heat and light.
The process of burning of carbon or carbon compound in excess of oxygen to give heat and light is called the combustion reaction. In the reactions carbon is in its maximum oxidation state of 4+ in the product.
Eg: 1) C + O2  →  CO2 + Energy
2) 2C2H6 + 7O2  →  4CO2 + 6H2O + Energy
3) CH3CH2OH + 3O2  →  CO2 + 3H2O + Energy
Generally, saturated hydrocarbons burn with a clear light blue flame, whereas unsaturated hydrocarbons burn with yellow flame with soot(carbon). If air is not sufficiently available during combustion, even saturated hydrocarbons give sooty flame. When Coal, Petroleum etc., burn in air they give oxides of sulphur and nitrogen in addition to CO2 and H2O which pollute the environment. When Coal or Charcoal is burnt sometimes they just glow red without flame. This is because to get a flame gaseous
fuels should burn.
Most of the aromatic compounds burn with sooty flame.
Because of the inlets of air getting closed, the fuel gases donot completely undergo combustion. Hence, it forms a sooty carbon form which gets coated over the vessels.A combustion reaction is generally defined as any reaction that sustains a flame. It usually involves burning with oxygen, though some exceptions
are there, combustion reaction is always exothermic, that is energy is liberated during combustion reaction.

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2. Oxidation reactions
Though combustion is generally oxidation reaction, all oxidation reactions are not combustion reactions. Oxidation reactions may be carried out using oxidizing agents. Oxidizing agents or Oxidants are substances that oxidize other substances. They themselves undergo reduction.
Eg: Alkaline Potassium permanganate or Acidified Potassium dichromate in solutions act as oxidizing agents and supplies oxygen to convert alcohols into carboxylic acids. Ethyl alcohol undergoes oxidation to form the product Acetaldehyde and finally Acetic acid.(see following equation).
Chemical Properties of Carbon Compounds 1

3. Addition reactions
Unsaturated organic compounds that contain multiple bonds (=, ≡ bonds) like alkenes and alkynes undergo addition reactions to become saturated. During the reactions addition of the reagent takes place at the double bonded or triple bonded carbon atoms.
Chemical Properties of Carbon Compounds 2
In the above reactions ‘Ni’ acts as ‘catalyst.’
Catalyst: A catalyst is a substance which regulates (increase/decrease) the rate of a given reaction without itself finally undergoing any chemical change.
These reactions are commonly used in the hydrogenation of vegetable oils using nickel as catalyst. Vegetable oils generally have long unsaturated carbon chains, while animal fats have saturated carbon chains.
Fats and oils are both of fatty acids. Oils are generally liquids at room temperature due to unsaturated fatty acids but fats are solids due to saturated fatty acids.

4. Substitution reactions
A reaction in which an atom or a group of atoms in a given compound is replaced by other atom or group of atoms is called a substitution reaction.
Alkanes, the saturated hydrocarbons are chemically least reactive.
Therefore they are also called paraffins (parum = little; affins = affinity,  i.e., no affinity towards chemical changes). However they undergo some chemical changes under suitable conditions which are substitution reactions.
For example, methane (CH4) reacts with chlorine in the presence of sunlight. Hydrogen atoms of CH4 are replaced by chlorine atoms.
Chemical Properties of Carbon Compounds 3

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