Chapter 6 Life Processes
In text Questions
Why is diffusion insufficient to meet the oxygen requirement of multicellular organisms like us ?
Every living cell requires oxygen for performing cellular respiration. In unicellular organisms (e.g., Amoeba), the single cell is in direct contact with environment. Oxygen passes into it through diffusion. In simple multicellular organisms (e.g., Hydra), every cell may also get oxygen through diffusion from environment. This is not possible in complex multicellular organisms like humans. The body is covered by dead cells. The living cells are not in contact with external environment. Air containing intercellular spaces are absent. Therefore, quick diffusion cannot occur. Cell to cell diffusion is a very slow process. Passage of oxygen from lungs to toes through cell to cell diffusion will take about three years. Therefore, diffusion cannot meet the oxygen requirement of multicellular organisms like humans.
What criteria do we use to decide whether something is alive ?
The major criterion which is used to decide whether something is alive is movements. Movements may be that of locomotion (e.g., running of dog), movements of a part (e.g., chewing cud by cow), breathing movements, growth, growth movements (in plants) and movement of molecules in metabolic reactions, maintenance and repair of cellular structures.
Besides movements, other criteria found in living beings that distinguish them from the non-living are presence of protoplasm, self built organisation, self repair, reproduction and various life processes like metabolism, nutrition, respiration, growth, exchange of materials, transportation, excretion and irritability. All living beings have a definite life span and life cycle.
What are outside raw materials used by an organism ?
Food by heterotrophic organisms ; carbon dioxide, minerals, sunlight and water by autotrophic organisms ; oxygen by all aerobic organisms.
What processes would you consider essential for maintaining life ?
Life processes of nutrition, metabolism, respiration, exchange of materials, transportation, excretion and awareness.
What are the differences between autotrophic nutrition and heterotrophic nutrition ?
‘ Heterotrophic Nutrition
1. Food. It is self manufactured.
2. External Energy. An external source of energy is required for synthesis of food.
3. Inorganic Substances. They constitute the raw materials for manufacturing food.
4. Digestion. It is absent.
Food is obtained ready-made from outside.
An external source of energy is not required. The required energy is present in the food obtained from outside.
Inorganic substances are not much required.
An external or internal digestion is required for conversion of complex organic materials into simpler and soluble ones.
Where does the plant get each of the raw materials for photosynthesis ?
- Carbon Dioxide: At through stomata.
- Water: Soil through roots.
- Minerals: Soil through roots. ,
What is the role of acid in our stomach ? (CCE 2012, 2013)
Hydrochloric acid (HCl) is component of gastric juice. It has five functions,
- Softening of food,
- Conversion of pepsinogen and prorennin into active forms of pepsin and rennin
- Acidify the food for proper action of pepsin,
- Killing of microorganisms present in food,
- Stoppage of action of salivary amylase.
What is the junction of digestive enzymes ? (CCE 2011)
Digestive enzymes are hydrolytic enzymes which bring about hydrolytic splitting of complex organic substances into simple, soluble and absorbable substances, e.g.,
How is small intestine designed to absorb digested food ?
Small intestine is lined by epithelium which is specialised to absorb. It has mechanisation to increase its absorbing surface area several times,
- Villi: They are transverse folds of intestine wall that not only increase surface area but also reach deep into the lumen of intestine for absorption of digested food. Villi possess blood capillaries and lacteals (lymph vessels) for quick transport of absorbed food,
- Microvilli: The columnar cells of the intestinal epithelium have fine microscopic outgrowths called microvilli. Microvilli increase the surface area of epithelial cells.
What advantage does a terrestrial organism possess over aquatic organism with regard to obtaining oxygen for respiration ?
Air contains about 21% of oxygen while water haà less than 1% oxygen in dissolved state. A terrestrial organism is able to get several times more oxygen than an aquatic organism.
What are the different ways in which glucose is oxidised to provide energy in various organisms ?
How is oxygen and carbon dioxide transported in human beings ? (CBSE AI2008, CCE 2012)
- 97% in combined state with haemoglobin called oxyhaemoglobin.
- 3% dissolved in plasma.
- 5-7% as dissolved in plasma.
- 70% as sodium bicarbonate in plasma.
- 23% in combined state with haemoglobin called carbaminohaemoglobin.
How are lungs designed in human beings to maximise the area for exchange of gases ?
(CBSE AI 2008, CCE 2011)
Each lung has a highly branched respiratory tract called respiratory tree. A primary bronchus divides into secondary bronchi, secondary into segmental bronchi, segmental bronchus into bronchioles which divide into terminal bronchioles, respiratory bronchioles, alveolar sacs and alveoli. Alveoli are small rounded or polyhedral pouches which are extremely thin walled and possess a network of capillaries over their surface. They function as respiratory surfaces. The total area of all the alveoli is more than 80 m2. It is several times more than the surface area of the whole human body.
What are the components of the transport system in human beings ? What are the junctions of these components ?
Human transport system has two components, blood vascular system and lymphatic system..
Blood Vascular System: It consists of blood, blood vessels (tubes) and heart.
Heart: It is pumping organ of blood vascular system.
Blood is made of plasma and three types of cells — red blood corpuscles, white blood corpuscles and blood * platelets.
Blood Plasma: Transport of nutrients, excretory materials, hormones etc.
- Antibodies in the form of immunoglobins.
- Prothrombin and fibrinogen for blood clotting.
- Red Blood Corpuscles: Transport of oxygen as oxyhaemoglobin. Transport of about 23% carbon dioxide as carbaminohaemoglobin.
- White Blood Corpuscles: Phagocytosis of germ cells, production of antibodies and histamine.
- Blood Platelets: Formation of thromboplastin for blood clotting.
- Arteries: Taking away blood from heart to different body parts.
- Veins: Transporting blood towards heart from various body parts.
- Capillaries: Exchange of materials between blood and living cells through tissue fluid.
Lymphatic System: It consists of lymph, lymph vessels and lymph nodes.
- Collection of extra tissue fluid and passing it back into blood.
- Picking up tissue secretions and passing into blood.
- Attracting and carrying germs to lymph nodes.
Lymph Vessel: Collection of lymph and passing the same into veins.
- Lymph organs specialised to filter germs,
- Maturation of lymphocytes.
Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds ? (CCE 2012)
Mammals and birds are warm blooded animals. They constantly use energy to maintain their body temperature. They have a higher energy need and require more oxygenated blood for their cells. It is important that their oxygenated blood does not mix up with deoxygenated blood.
What are the components of the transport system in highly organised plants ? (CCE 2010)
Transport system of highly organised plants consists of xylem and phloem.
Xylem: It is used in transport of water and minerals. Xylem is made of tracheids, vessels, xylem fibres and xylem parenchyma. Tracheids and vessels constitute the tracheary elements or channels for transport of water and minerals.
Phloem: It is used for transport or translocation of organic solutes or food. Phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma. Sieve tubes constitute the channels for transport of food materials.
How are water and minerals transported in plants ?
Water and minerals absorbed by the plant roots are passed into xylem as sap. Sap present in xylem is under tension or negative pressure as mesophyll and other cells of aerials parts lose water to the outside through transpiration.
Development of Negative Pressure: Loss of water by mesophyll and other cells of aerial parts in transpiration increases their suction pressure. They withdraw water from xylem channels. As there are billions of transpiring mesophyll cells withdrawing water from xylem channels, water present in xylem comes under negative pressure of 10-20 atmospheres. However, water column does not break due to
- Cohesive force amongst water molecules and
- Adhesion force between walls of xylem channels and water moecules.
Rise of Sap (Water and Minerals): Tension or negative pressure of water column results in upward pull just as cold-drink is sucked with the help of straw pipe. Since it develops due to transpiration, it is called transpiration pull. The mechanism of this ascent of sap was put forth by Dixon and Joly in 1894.
How is food transported in plants ?
Unlike animals, some materials pass in and out of plants through diffusion. For rapid gaseous diffusion to occur, the plants possess stomata and lenticels. During the daytime the photosynthetic organs obtain carbon dioxide from outside by diffusion. The same is used for synthesis of food. Oxygen is released as a by-product. It passes out of the plant by diffusion. Simultaneously, a lot of water vapours pass out.
Other materials required for building plant body are obtained from soil, e.g., nitrogen, phosphorus, other minerals, water .They are sent to chlorophyll containing organs where food is manufactured. The manufactured food is passed to all parts for utilisation and storage. If the distance between the two is small, the materials reach there by diffusion. If the distance is large, as in most plants, they have to be transported through a proper system of transportation. However, plants have a large proportion of dead cells. They do not move. Therefore, they have low energy needs.
The transport is slow: Plants possess two independent transport pathways having conducting tubes. One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food and hormones from the region of availability (e.g., leaves, storage organs) to the areas of utilisation (all living cells, growing points, storage organs, developing fruits).
Describe the structure and functions of nephron.
What are the methods used by plants to get rid of excretory products ?
Carbon Dioxide: Land plants obtain it from atmosphere while aquatic plants absorb the same from water. Atmosphere contains over 0-038% carbon dioxide. It enters the leaves through stomata. However, the open stomata also become sites for loss of water in transpiration.
Water: Land plants absorb water from soil through their roots. The absorbed water is transported to photosynthetic areas through xylem. Minerals are also transported alongwith water. They are used in synthesis of different organic substances like sulphur in proteins, phosphorus in nucleic acids, magnesium in chlorophyll, etc. 99% of absorbed water is lost through transpiration. Only a small quantity of water is used in photosynthesis as hydrogen donor. For this, water splits into its components with the help of light energy. The phenomenon is called photolysis of water. Oxygen is evolved.
How is the amount of urine produced regulated ?
Amount of urine is regulated by volume of blood and amount of antidiuretic hormone (ADH). Volume of blood is determined by presence or absence of extra water in the body. More blood volume will increase pressure in the glomerulus. It increases the amount of glomerular or nephric filtrate. ADH is not secreted. Dilute urine is allowed to pass through the kidneys. The amount of urine is higher than the normal.
In case the body has no extra water or is deficient of water, lesser glomerular filtrate will be produced. ADH is secreted. It helps in withdrawing a good amount of water from urine. Therefore, only concentrated urine is passed out. Amount of urine is smaller than the normal.
Chapter 6 Life Processes NCERT Chapter End Exercises
The kidneys in human beings are a part of the system for
The xylem in plants is responsible for
(a) Transport of water
(b) Transport of food
(c) Transport of amino acids
(d) Transport of oxygen.
The autotrophic mode of nutrition requires,
(a) Carbon dioxide and water
(c) Sun light
(d) All of the above.
The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
How are fats digested in our bodies Where does this process take place ? (CCE 2011)
1° infants, fat digestion occurs both in stomach and small intestine. However, fat digestion in stomach is poor as gastric lipase is a weak enzyme. Most of the fat digestion occurs in small intestine (jejunum part). Fat is first emulsified with the help of bile salts. Emulsification converts fat into very fine droplets. They are acted upon by pancreatic and intestinal lipase. Lipase breaks fat into fatty acids and glycerol. The latter are absorbed by villi and passed into their lacterals where fat is again formed.
What is the role of saliva in the digestion of food ? (CCE 2011)
Saliva is the secretion of salivary glands that is poured in the buccal cavity for :
- Moistening and softening of food for easy crushing by the teeth.
- Action of enzyme ptyalin or salivary amylase which converts starch and glycogen of cooked food into sweet sugar maltose.
- Conversion of semisolid food into slippery bolus for easy swallowing.
What are the necessary conditions for autotrophic nutrition and what are its by-products ?
- Carbon dioxide
- Proper temperature. By-products. Glucose (product), oxygen (byproduct).
What are the differences between aerobic and anaerobic respiration ? Name some organisms that use the anaerobic mode of respiration.
1. Method. It is the common method of respiration.
It occurs permanently only in a few organisms. In others it may occur as a temporary measure to overcome shortage of oxygen.
2. Steps. It is completed in 3 steps—glycolysis, Krebs cycle and terminal oxidation.
There are two steps— glycolysis and anaerobic breakdown of pyruvic acid.
3. Oxygen. It requires oxygen.
Oxygen is not required.
Anaerobic Organisms: Yeast (can also perform aerobic respiration), Lactobacillus (bacterium), Ascaris (Roundworm), Taenia (Tapeworm).
How are alveoli designed to maximise the exchange of gases ?
Alveoli are small pouches or sacs. About 300 million alveoli occur inside each lung. The whole surface of an alveolus functions as respiratory surface. As there are about 300 million alveoli in each lung, a very large area of respiratory surface becomes available (about 80 m2) for exchange of gases.
What would be the consequence of deficiency of haemoglobin in our body ?
Deficiency of haemoglobin is called anaemia. In anaemia the blood is unable to carry the amount of oxygen required by the body (hypoxia). Lesser energy will be available to the body. The person will feel weak, pale, lethargic and unable to perform vigorous exercise or physical work.
Describe double circulation in human beings. Why is it necessary ?
Double circulation is the passage of same blood twice through heart, first from right side to lungs and back to left side for passage to rest of the body to be returned to right side. It consists of two components, pulmonary circulation (from heart to lungs and back) and systemic circulation (from heart to different parts of body and back). In pulmonary circulation deoxygenated blood is converted into oxygenated blood. In systemic circulation oxygenated blood is supplied to all parts of the body. It gets changed into deoxygenated form.
Double circulation ensures supply of oxygenated blood to all body parts for efficient release of energy to ensure higher physical activity and thermoregulation of body. It also provides for direct passage of all deoxygenated blood to lungs for oxygenation.
What are the differences between the transport of materials in xylem and phloem ? (CCE 2014)
Differences in Transport of Materials in Xylem and Phloem
Transport in Xylem
Transport in Phloem
1. Components. It consists of water and minerals.
It consists of organic nutrients.
2. Direction. The movement is generally unidirectional.
The movement is multidirectional.
3. Force. It operates through creation of negative tension.
It operates through creation of positive turgor.
4. Active Component. An active component is absent.
An active component is present in the region of loading and unloading.
5. Metabolic Inhibitors. Metabolic inhibitors have no effect on xylem transport.
Metabolic inhibitors inhibit phloem transport.
6. Channels. Tracheary elements are non-living.
Phloem channels are made of living cells.
Compare alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
1. Shape. They are rounded or polyhedral.
They are elongated tubules.
2. Components. Alveoli are single entities.
Each nephron has two components-Malpighian capsule and renal tubule. Renal tubule has three parts – PCT, loop of Henle and DCT.
3. Blood Capillaries. They are of one type and lie all over the alveoli.
Blood capillaries form two patches—glomerulus and peritubular capillaries.
4. Materials. They deal with respiratory gases.
They deal with body fluids.
5. Function. Alveoli perform exchange of gases between blood and inhaled air.
Nephrons bring about separation of waste products from blood.
6. Processes. Gaseous exchange occurs through diffusion.
Urine formation occurs through ultrafiltration, reabsorption, secretion and osmosis.
PRACTICAL SKILL BASED QUESTIONS
Mention any two functions of epidermis. (CCE 2016)
- Covering and protecting the internal tissues.
- Having stomata for gaseous exchange and transpiration.
Explain why only turgid leaf is selected for the preparation of temporary mount of a leaf peel. (CCE 2016)
A peel is removed either by twisting and tearing of a leaf or scraping its lower surface. In both the cases only a turgid leaf can be handled properly. In a wilted or flaccid leaf, a lot of mesophyll remains attached to the surface layer or peel. In a turgid leaf, the compact epidermis is easily separable from loose mesophyll.
In an experiment to prepare temporary stained mount of a leaf epidermal peel, how can extra stain be removed ? What possible outcome would be observed if it is removed with cotton wool ? (CCE 2016)
By means of blotting paper which can soak the extra stain from the sides of the cover slip. Use of cotton wool can spread the stain over the slide as well as cover slip.