6. LIFE PROCESSES
Events in photosynthesis:
- Absorption of light energy by chlorophyll.
- Conversion of light energy to chemical energy and splitting of water molecules into hydrogen & oxygen.
- Reduction of CO2 to carbohydrates.
Experiment to show that chlorophyll is essential for photosynthesis:
- Take a potted plant with variegated leaves (e.g. money plant or crotons).
- Keep it in a dark room for 3 days to use up all the starch (destarch).
- Keep the plant in sunlight for about 6 hours.
- Pluck a leaf and mark the green areas in it and trace them on a paper.
- Dip the leaf in boiling water for a few minutes.
- Then immerse it in a beaker containing alcohol. Place the beaker in a water-bath and heat to boil the alcohol.
- The leaf becomes colourless. Chlorophyll is dissolved in alcohol and the alcohol turns green.
- Dip the leaf in a dilute iodine solution for a few minutes.
- The green areas of leaf turn dark blue. It indicates the presence of starch. Colourless part of leaf shows no formation of starch.
Experiment to show that CO2 is essential for photosynthesis:
- Take 2 healthy potted plants having nearly same size.
- Keep them in a dark room for 3 days.
- Now place each plant on separate glass plates. In one, place a watch-glass containing potassium hydroxide (KOH). KOH is used to absorb CO2.
- Cover both plants with separate bell-jars.
- Using Vaseline, seal the bottom of the jars to the glass plates to make it air-tight.
- Keep the plants in sunlight for about two hours.
- Test the leaves from both plants using iodine.
- Leaf of plant kept without KOH turn blue. It indicates the presence of starch. Plant with KOH does not turn blue.
Experiment to show that sunlight is essential for photosynthesis:
- Keep a plant in dark room for 3 days to destarch leaves.
- Cover a leaf partially with a black paper.
- Expose the plant to sunlight for 3-4 hours.
- Remove chlorophyll from the leaf and perform a starch test with iodine.
- Covered leaf part shows brown colour. Exposed leaf turns dark blue due to the presence of starch.
- Some organisms break down food outside the body and absorb it. E.g. fungi like bread moulds, yeast and mushrooms.
- Some take in food and break down inside the body.
- Some organisms take food from organisms without killing them (parasitism). E.g., Cuscuta (amar-bel), ticks, lice, leeches and tape-worms.
Human alimentary canal is a long tube extending from the mouth to the anus.
It is the breakdown of complex food with the help of enzymes into smaller absorbable molecules.
- Take 1 mL starch solution (1%) in test tubes A & B.
- Add 1 mL saliva to test tube A and leave both test tubes undisturbed for 20-30 minutes. Now add a few drops of dilute iodine solution to the test tubes.
- In test tube B, blue colour develops. It indicates presence of starch. In test-tube A, no colour change occurs because starch is digested by salivary amylase.
- Herbivores have a longer small intestine for cellulose digestion.
- Meat is easier to digest. So carnivores have a shorter small intestine.
- Emulsifies fat. It is the breakdown of large fat globules into the smaller globules with the help of bile salts. It increases the efficiency of enzyme action. This is similar to emulsifying action of soaps on dirt.
- Makes the acidic food (from stomach) alkaline.
- Proteins → amino acids.
- Complex carbohydrates → glucose.
- Fats → fatty acids & glycerol.
Dental caries (Tooth decay):
It is the gradual softening & demineralisation of enamel & dentine due to the production of acids by bacteria. They convert sugary foods to acids.
Bacteria invade the pulp causing inflammation & infection.
Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. It prevents saliva reaching the tooth surface to neutralise the acid.
Brushing the teeth after eating can remove plaque.
Experiment to prove release of CO2 during respiration in human
- Take some freshly prepared lime water in 2 test tubes.
- In one, blow air through lime water. It immediately turns lime water milky.
- In other test tube, pass air using a syringe or pichkari. It takes much time to turn the lime water milky.
- It shows that the breath-out air contains more CO2 as compared to atmospheric air.
Experiment to prove release of CO2 during respiration in Yeast
- Add some yeast to fruit juice or sugar solution. Take this mixture in a test tube fitted with a one-holed cork.
- Fit the cork with a bent glass tube. Dip its free end into a test tube containing freshly prepared lime water.
- Air taken out through the tube makes lime water milky. It is due to the production of CO2 in the mixture of yeast & sugar solution. Here, fermentation occurs.
Anaerobic respiration: It is the respiration in the absence of air (oxygen). It releases less energy. E.g.
- In yeast, the pyruvate is converted into ethanol & CO2. It occurs during fermentation.
- Sometimes, when there is no oxygen in our muscle cells, the pyruvate breaks down into lactic acid (3-carbon). This build-up of lactic acid in muscles during sudden activity causes cramps.
ATP is used to fuel all other cellular activities. When the terminal phosphate linkage in ATP is
broken using water, energy (30.5 kJ/mol) is released. It drives
the endothermic reactions in the cell.
Gas exchange in plants:
It occurs through stomata. Here, CO2 & oxygen are exchanged by diffusion. The large intercellular spaces in leaves help the cells in contact with air.
During day, CO2 formed by respiration is used for photosynthesis. So, CO2 is not released but oxygen is released. At night, photosynthesis does not occur. So, CO2 is released out but oxygen is not released.
Gas exchange in animals:
Aquatic animals breathe dissolved oxygen in water.
In fishes, the respiratory organ is gills with gill slits behind their eyes. They may be covered by operculum.
During breathing, fishes open and close mouth & gill slits (or operculum) in a coordinated manner and timing. They take in water through mouth and pumps over the gills. From the gills, dissolved O2 is taken up by blood.
The amount of dissolved O2 is lower than that in the air. So, the rate of breathing in aquatic organisms is faster than that in terrestrial organisms.
In terrestrial animals, there are different types of organs to breathe atmospheric oxygen. They increase surface area which is in contact with the atmosphere.
Surface of respiratory organs is very fine and delicate for easy gas exchange. To protect this surface, it is placed within the body. So, some passages are necessary to carry air in and out of respiratory organ.
Human respiratory system
It involves lungs & air passage.
Tobacco or tobacco products affect tongue, lungs, heart and liver. Smokeless tobacco also causes heart attacks, strokes, pulmonary diseases & cancers.During the breathing cycle, the lungs always contain a residual volume of air so that there is sufficient time to absorb oxygen and release CO2.
Oral cancer is highly reported in India due to tobacco chewing in the form of gutkha.
Smoking destroys cilia on the upper respiratory tract. As a result, germs, dust, smoke etc. enter lungs and cause infection, cough & lung cancer (common cause of death).
Human circulatory system: Blood, Heart & Blood vessels.
- In men: 14 to 17 g/ 100 ml.
- In women: 12 to 15 g/ 100 ml.
- In children: 11 to 16 g/ 100 ml.
Our pump – the heart
Pumping process of heart:
- Oxygenated blood from the lungs → left atrium relaxes → blood enters left atrium → left atrium contracts & left ventricle relaxes → blood enters left ventricle → left ventricle contracts → blood is pumped out to the body.
- Deoxygenated blood from the body → right atrium relaxes → blood enters right atrium → right atrium contracts & right ventricle dilates → blood transfers to right ventricle → right ventricle contracts → blood is pumped into the lungs for oxygenation.
Since ventricles have to pump blood into various organs, they have thicker muscular walls than that of atria.
Heart has valves to prevent the backflow of blood when the atria or ventricles contract.
Schematic representation of transport and exchange of oxygen and CO2
Oxygen enters the blood in the lungs
The separation of right side and left side of the heart prevents mixing of oxygenated and deoxygenated blood. This allows a highly efficient supply of oxygen to the body. It is useful in animals that need high energy (birds & mammals) to maintain body temperature.
Animals like amphibians & many reptiles do not use energy to maintain temperature. They depend on the temperature in the environment. Such animals have 3-chambered heart, and tolerate some mixing of the oxygenated and deoxygenated blood.
Fishes have only 2-chambered heart. Here, circulation occurs as follows:
Deoxygenated blood enters the heart → pumped to gills → blood is oxygenated in gills → blood to rest of the body.
Thus, blood goes only once through the heart during one cycle of passage through the body.
In other vertebrates, blood goes through the heart twice during each cycle. This is called double circulation.
The tubes – blood vessels
It includes arteries, veins and capillaries.
Maintenance by platelets
Leakage or loss of blood due to injury leads to reduction in pressure and efficiency of circulatory system.
To avoid this, the platelet cells plug these leaks to clot the blood at the points of injury.
Lymph (Tissue fluid):
Through the pores in the capillary walls, some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form lymph.
It is similar to blood plasma but colourless and contains less protein.
From intercellular spaces, lymph drains into lymphatic capillaries, which join to large lymph vessels that finally open into larger veins.
Lymph carries digested fat from intestine and drains excess fluid from extracellular space back into the blood.
- Xylem: It moves water & minerals from the soil.
- Phloem: It transports products of photosynthesis (energy stores) from leaves to other parts.
Transport of water
In xylem tissue, vessels & tracheids of the roots, stems and leaves are interconnected to form water-conducting channels reaching all parts.
- Take two small same sized pots with same amount of soil. One should have a plant in it. In other pot, place a stick of the same height as the plant.
- Cover the soil in both pots with a plastic sheet so that moisture cannot escape by evaporation.
- Cover both sets with plastic sheets and place in bright sunlight for half an hour.
- In pot with plant, water droplets are found in plastic sheet. It is due to condensation of water vapour released by transpiration. In other pot, water droplets are not formed.
Transport of food & other substances
Transport of soluble products of photosynthesis (food) from leaves to other parts is called translocation.
Kidneys are located in the abdomen, one on either side of the backbone.
At the end of each nephron, a cup-shaped structure called Bowman’s capsule is seen. It encloses a cluster of very
thin-walled blood capillaries called glomerulus.