Life Processes | Q & A

Life Processes | Q & A


Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Ans: In the case of a single-celled organism, no specific organs for exchange of gases are needed because the entire surface of the organism is in contact with the environment. But in multicellular organism, all the cells may not be in direct contact with the surrounding environment. Thus, diffusion is insufficient to meet the oxygen requirements of large multicellular organisms (human beings) because the volume of human body is so big that oxygen cannot diffuse into all the cells of the human body quickly.

What criteria do we use to decide whether something is alive?

Ans: Following are the standards that decide whether something is alive:

(i) The major criterion is movement. Movement may be incurred through locomotion (running, walking, etc.), action of body parts (e.g., chewing of cud by cow), breathing, growth (in plants), maintenance and repair of cellular structures and molecular movement in metabolic reactions.

(ii) Requirement of food for performing life processes.

(iii) Respiration and utilisation of the inhaled oxygen for oxidation of food.

(iv) Display of growth and development.

(v) Expulsion of metabolic wastes (Excretion).

What are outside raw materials used for by an organism?

Ans: Outside raw materials provide energy to organisms to maintain their body processes. They are needed to prevent damage and break-down in the body.

What processes would you consider essential for maintaining life?

Ans: The important processes essential for maintaining life are: nutrition, respiration, transportation and excretion, and control and coordination.

What are the differences between autotrophic nutrition and heterotrophic nutrition?


Autotrophic Nutrition Heterotrophic Nutrition
The organisms that make their food from simple inorganic substances are called autotrophs, e.g., most green plants. Therefore, autotrophic nutrition refers to the process of nourishing, namely photosynthesis, that they adopt for growth and maintenance. The organisms which cannot make their own food and depend directly or indirectly on autotrophs for their survival are called heterotrophs, e.g., animals and fungi. Heterotrophic nutrition refers to the process of nourishing, namely by obtaining food from other organisms, for their own growth and maintenance.
The raw materials required for preparation of food are CO2 and H2O. Heterotrophs are directly or indirectly dependent on autotrophs.
Chlorophyll and sunlight are essential for photosynthesis and thus nutrition to occur. Chlorophyll and sunlight are not required.

 Where do plants get each of the raw materials required for photosynthesis?

Ans: The raw materials required for photosynthesis are carbon dioxide and water. Terrestrial plants get carbon dioxide from environment and water from the soil. Aquatic plants take up CO2 that is present in dissolved form in water. Water is simply absorbed by the parts of the aquatic plant submerged in water.

What is the role of the acid in our stomach?

Ans: The acid (hydrochloric acid) secreted inside the stomach makes the medium acidic which is necessary for the activation of the enzyme pepsin. It converts inactive propepsin into active pepsin. Also, hydrochloric acid kills any bacteria which may enter the stomach along with food.

What is the function of digestive enzymes?

Ans: Digestive enzymes convert the large and insoluble food molecules into small water soluble molecules in the process of digestion. For example, pancreas secretes enzymes like amylase, trypsin and lipase. The enzyme amylase breaks down the starch, trypsin breaks down the proteins and lipase breaks down the emulsified fats into simple sugars, amino acids and fatty acids, respectively.

How is the small intestine designed to absorb digested food?

Ans: The small intestine is the main region for the absorption of digested food. The inner lining of small intestine has millions of tiny finger-like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area for absorption of digested food. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body.

What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Ans: The organism that lives in water such as a fish obtains oxygen for respiration which is dissolved in water whereas the terrestrial organisms take in oxygen directly from the air. Since, the amount of oxygen dissolved in water is fairly low as compared to the amount of oxygen in the air, breathing rate in aquatic organisms is much faster than terrestrial organisms.

What are the different ways in which glucose is oxidised to provide energy in various organisms?

Ans: Breakdown of glucose takes place by various pathways as given below:


(6-carbon molecule)

In cytoplasm →


(3-carbon molecule)

Absence of oxygen

(in yeast)


Lack of oxygen

(in muscle cells)

Lactic acid + Energy

(3-carbon molecule)

Presence of oxygen

(in mitochondira)

CO+ H2O + Energy

How is oxygen and carbon dioxide transported in human beings?

Ans: During inhalation, oxygen comes into alveoli of the lungs. The alveoli is surrounded by very thin blood vessels called capillaries. So, the oxygen diffuses out from the alveoli walls to the blood in capillaries. The oxygen is carried by blood to all the parts of body by binding it with haemoglobin present in blood.

The blood passes through the tissues of the body and the oxygen present in it diffuses into the cells (due to its higher concentration in the blood). This oxygen combines with the digested food present in the cells to release energy. Carbon dioxide is produced as a waste product during respiration in the cells of the body tissues. This CO2 diffuses into the blood (due to its higher concentration in body tissues). Blood carries CO2 back to the lungs where it diffuses into its alveoli, then into the trachea, nostrils and then out of the body into air. CO2 is more soluble in water than oxygen and hence mostly transported in the dissolved form in our blood.

How are the lungs designed in human beings to maximise the area for exchange of gases?

Ans: In the lungs, the air passage (wind pipe) divides into smaller tubes, called bronchi which in turn form bronchioles. The bronchioles later terminate in balloon-like structures, called alveoli. The presence of alveoli in the lungs provides a very large area for the exchange of gases and this availability of large surface area maximises the exchange of gases. The alveoli have very thin walls and contain an extensive network of blood vessels to facilitate exchange of gases.

What are the components of the transport system in human beings? What are the functions of these components?

Ans: Transport system in human beings consists of heart, blood and blood vessels.

(i) Heart: The muscular organ which pumps and receives the blood.

(ii) Blood: It is a fluid connective tissue. It consists of plasma, RBC, WBC and blood platelets. Plasma transports food, CO2 as nitrogenous wastes in dissolved form. RBCs transport respiratory gases and hormones. WBCs protect the body from infections and platelets prevent the loss of blood at the time of injury by forming blood clots.

(iii) Vessels: They are subdivided into:

(a) Arteries: Carries blood from heart to different body parts.

(b) Veins: Transport blood towards heart from various body parts.

(c) Capillaries: Site of exchange of materials between blood and living cells through tissue fluid.

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Ans: Mammals and birds are warm-blooded animals. They constantly use energy to maintain their body temperature. They have higher energy needs and so they require more oxygen to produce energy. Thus, it is important that their oxygenated blood does not get mixed up with deoxygenated blood.

What are the components of the transport system in highly organised plants?

Ans: The components of the transport system of highly organised plants consist of xylem and phloem. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.

How are water and minerals transported in plants?

Ans: In xylem tissue, vessels and tracheids of the roots, stem and leaves are interconnected to form a continuous system of water- conducting channels reaching all parts of the plant. The root hairs are directly in contact with the film of water in between the soil particles. Water gets into the root hairs by the process of diffusion. At the roots, cells in contact with the soil actively take up ions. This creates a difference in concentration of these ions between the root and the soil. Water, therefore, moves into the root from the soil. Hence, there is steady movement of water into root xylem, creating a column of water that is steadily pushed upwards.

Also, water is lost from the aerial parts of plant (transpiration). Evaporation of water molecules from the cells of the leaf creates a suction which pulls water from the xylem cell of roots (the transpiration pull). Thus, transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.

How is food transported in plants?

Ans: The food manufactured by the leaves of a plant is transported to its other parts through a kind of tube system called phloem. The transport of food from the leaves to other parts of the plant is called translocation. 

The translocation in phloem is achieved by utilising energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to plant’s needs.

Describe the structure and functioning of nephrons.

Ans: Structure of Nephron: Nephron is the structural and functional unit of kidney.

(i) It consists of a long coiled tubule differentiated into proximal tubule, Loop of Henle and distal tubule. The distal tubule opens into the collecting tubule.

(ii) At the proximal end of the nephron lies a double-walled cup-shaped structure called Bowman’s capsule.

(iii) The Bowman’s capsule contains a bundle of blood capillaries which is called glomerulus.

(iv) In the glomerulus, the blood that comes in through afferent arteriole is drained out through efferent arteriole.

Functions of Nephron:

(i) Filtration: Filtration of blood takes place in Bowman’s capsule from the capillaries of glomerulus. This takes place under high pressure. The filtrate passes into the tubular part of the nephron. This filtrate contains glucose, amino acids, urea, uric acid, salts and major amount of water.

(ii) Reabsorption: As the filtrate flows along the tubule useful substances such as glucose, amino acids, salts and water are selectively reabsorbed into the blood by capillaries surrounding the nephron tubule.

(iii) Tubular secretion: Certain substances which are harmful and not needed by the body like ammonia, potassium, creatinine and hydrogen ions are secreted from the capillary blood into the lumen of distal tubule. This is called tubular secretion.

The fluid entering the collecting tubule is called urine. It flows through the ureters into urinary bladder, where it is stored and discharged from time to time through urethra.

What are the methods used by plants to get rid of excretory products?

Ans: To get rid of excretory products, plants use the following ways:

(i) The plants get rid of gaseous waste products through stomata on leaves and lenticels in stems.(ii) The plants get rid of stored solid and liquid wastes by shedding of leaves, peeling of bark and felling of fruits.

(iii) The plants also secrete wastes in the form of gums and resins.

(iv) some waste substances are excreted through roots into the soil around them.

(v) Excess of water is eliminated by the process of transpiration.

(vi) In living cells, many cytoplasmic wastes are shifted to cellular vacuoles.

How is the amount of urine produced regulated?

Ans: The amount of urine produced depends on how much of excess water is there in the body, and on how much of dissolved waste is there to be excreted. More water and dissolved waste in the body will produce more urine and on the other hand, less water and less dissolved waste will therefore, produce less urine.

How are fats digested in our bodies? Where does this process take place?

Ans: The small intestine is the site of the complete digestion of fats. The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act. It is made alkaline by bile juice secreted by the liver. The upper part of small intestine, also called duodenum, receives bile juice from the liver and the enzyme lipase from pancreas. Bile salts break them down into smaller globules thereby increasing the efficiency of enzyme action and lipase breaks down the emulsified fats. The wall of the small intestine contain glands which secrete intestinal juice. The enzymes present in it finally convert the fats into fatty acids and glycerol. These are absorbed by villi and passed to every cell for obtaining energy.

What is the role of saliva in the digestion of food?

Ans: Saliva contains an enzyme called salivary amylase which digests the starch (complex molecule) present in food into sugar (maltose).

What are the necessary conditions for autotrophic nutrition and what are its byproducts?

Ans: The conditions necessary for autotrophic nutrition are sunlight, chlorophyll, carbon dioxide and water.

The byproducts of autotrophic nutrition are water and oxygen.

What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.


Aerobic Respiration Anaerobic Respiration
Aerobic respiration takes place in the presence of oxygen. Anaerobic respiration takes place in the absence of oxygen.
Complete break down of food occurs in it. The end products may be ethyl alcohol and carbon dioxide or lactic acid.
The end products are carbon dioxide (CO2) and water (H2O). The end products may be ethyl alcohol and carbon dioxide or lactic acid.
It produces a considerable amount of energy, due to complete oxidation of food molecules. Much less energy is produced, due to incomplete oxidation of food.

Organisms that use the anaerobic mode of respiration are yeast, some bacteria and some parasitic worms.

How are the alveoli designed to maximise the exchange of gases?

Ans: Alveoli are small pouches or sac-like structure. They are surrounded by blood capillaries. More than millions of alveoli are present in the lungs. The presence of millions of alveoli in the lungs provides a very large surface area for the exchange of gases. When we breathe in, the alveoli expand and maximise the exchange of gases.

What would be the consequence of a deficiency of haemoglobin in our body?

Ans: The deficiency of haemoglobin in our body is called anaemia. In anaemia, the blood is unable to carry the sufficient amount of oxygen required by the body. So, respiration would be less and less energy will be available to the body. The haemoglobin deficient person will feel weak, pale, lethargic and will be unable to perform heavy physical work.

Describe double circulation in human beings. Why is it necessary?

Ans: The blood passes through the heart twice through separate pathways for completing one cycle. This type of circulation is called double circulation.

Necessity of double circulation: In humans, having four-chambered heart (which consists of two auricles and two ventricles) the left side and right side of heart are completely separated to prevent the oxygenated blood from mixing with deoxygenated blood. Such a separation allows a highly efficient supply of oxygen to the body cells which is necessary for producing a lot of energy. This energy is useful in case of human beings that have high energy need because they constantly require energy to maintain their body temperature.

What are the differences between the transport of materials in xylem and phloem?


Transport in Xylem Transport in Phloem
It transports water and minerals. It transports organic nutrients.
The movement is generally unidirectional. The movement is multidirectional.
It is not influenced by metabolic inhibitors. Phloem transport is inhibited by metabolic inhibitors.
It is carried out by xylem vessels and tracheids. Takes place in sieve tubes with the help of adjacent companion cells.
Major operating forces are diffusion and transpiration pull. Energy (ATP) is required for translocation.

 Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.


Alveoli Nephron
Its structure is that of a pouch-like air sac. They are elongated tubules.
The walls of alveoli are very thin. Each nephron has two components—Bowman’s capsule and tubules.
Alveoli’s are surrounded by the thin blood capillaries. Blood capillaries form two patches—glomerulus and peritubular capillaries.
The presence of millions of alveoli in the lungs provides a very large surface area for the exchange of gases between blood and inhaled air. The function of tubular part of nephron is to allow the selective reabsorption of the useful substances into the blood capillaries.