CBSE Class 10 Biology Life Processes Notes Set 08

Life Processes and Modes of Nutrition

Life processes are the basic functions every living organism performs to stay alive: nutrition, respiration, transportation and excretion. Energy comes from food, and this energy is needed for repair and to prevent breakdown of the body. Molecular movement, growth, response to stimuli and reproduction are the signs of life. A virus shows no molecular movement outside a host cell, so it behaves as non-living there.

Nutrition means taking in food and using it. Carbohydrates and fats give energy, proteins build and repair the body, and vitamins and minerals regulate body functions.

Photosynthesis

Green plants combine carbon dioxide and water in the presence of sunlight and chlorophyll to form glucose and release oxygen: \(6CO_2+12H_2O\rightarrow C_6H_{12}O_6+6H_2O+6O_2\). Excess glucose is stored as starch. Carbon dioxide enters through stomata, water and minerals come from the soil through the roots.

1. Light reaction in the grana: chlorophyll absorbs light, water splits (photolysis) and ATP and NADPH2 are made. Oxygen is released.
2. Dark reaction in the stroma: ATP and NADPH2 are used to reduce carbon dioxide to sugar. No light is needed directly.
3. Stomata are pores surrounded by two guard cells. Turgid guard cells open the pore and flaccid guard cells close it. Desert plants open stomata at night to save water.
4. Experiments: destarch the plant in the dark first, test with iodine (blue-black means starch), decolourise the leaf in warm spirit. Variegated leaf shows that chlorophyll is needed. KOH in a bell jar removes CO2 and shows that carbon dioxide is needed. A covered part of a leaf shows that light is needed.

Nutrition in Amoeba and Humans

Amoeba engulfs food with pseudopodia, forms a food vacuole where digestion takes place, absorbs the digested food and throws out the undigested remains at any point of the surface.

Peristalsis is the wave of muscle contraction that pushes food along the alimentary canal. Long small intestine in herbivores helps in the digestion of cellulose. Dental caries start when acids made by bacteria in plaque dissolve the enamel.