CLASS 10 Science CHAPTER 6 Life Processes (NCERT Solution)

CLASS 10 Science 
CHAPTER 6  
Life Processes (NCERT Solution)

Question 1: Why is diffusion insufficient to meet the oxygen requirements of multi-cellular  organisms like humans?                                                                                                                Answer: Multicellular organisms such as humans possess complex body designs. They have  specialised cells and tissues for performing various necessary functions of the body such as intake of food and oxygen. Unlike unicellular organisms, multicellular cells are not in direct contact with the outside environment. Therefore, diffusion cannot meet their oxygen requirements.

Question 2: What criteria do we use to decide whether something is alive?

Answer: Any visible movement such as walking, breathing, or growing is generally used to

decide whether something is alive or not. However, a living organism can also have movements,

which are not visible to the naked eye. Therefore, the presence of life processes is a fundamental

criterion that can be used to decide whether something is alive or not.

Question 3: What are outside raw materials used for by an organism?

Answer: An organism uses outside raw materials mostly in the form of food and oxygen. The raw

materials required by an organism can be quite varied depending on the complexity of the organism

and its environment.

Question 4: What processes would you consider essential for maintaining life?

Answer: Life processes such as nutrition, respiration, transportation, excretion, etc. are essential

for maintaining life.

Question 5: What are the differences between autotrophic nutrition and heterotrophic nutrition?

Answer: Autotrophic nutrition

(i) Food is synthesised from simple inorganic raw materials such as CO2and water.

(ii) Presence of green pigment (chlorophyll) is necessary.

(iii)Food is generally prepared during daytime.

(iv)All green plants and some bacteria have this type of nutrition.

Heterotrophic nutrition

(i) Food is obtained directly or indirectly from autotrophs. This food is broken down with the help of enzymes.

(ii) No pigment is required in this type of nutrition.

(iii)Food can be prepared at all times.

(iv)All animals and fungi have this type of nutrition.

Question 6: Where do plants get each of the raw materials required for photosynthesis?

Answer: The following raw materials are required for photosynthesis:

• The raw material CO2 enters from the atmosphere through stomata.

• Water is absorbed from the soil by the plant roots.

• Sunlight, an important component to manufacture food, is absorbed by the chlorophyll and other

green parts of the plants.

Question 7: What is the role of the acid in our stomach?

Answer: The hydrochloric acid present in our stomach dissolves bits of food and creates an acidic

medium. In this acidic medium, enzyme pepsinogen is converted to pepsin, which is a protein digesting enzyme.

Question 8: What is the function of digestive enzymes?

Answer: Digestive enzymes such as amylase, lipase, pepsin, trypsin, etc. help in the breaking down of complex food particles into simple ones. These simple particles can be easily absorbed by the blood and thus transported to all the cells of the body.

Question 9: How is the small intestine designed to absorb digested food?

Answer: The small intestine has millions of tiny finger-like projections called villi. These villi

increase the surface area for more efficient food absorption. Within these villi, many blood vessels

are present that absorb the digested food and carry it to the blood stream. From the blood stream,

the absorbed food is delivered to each and every cell of the body. Enlarged view of a villus

Question 10: What advantage over an aquatic organism does a terrestrial organism have with

regard to obtaining oxygen for respiration?

Answer: Terrestrial organisms take up oxygen from the atmosphere whereas aquatic animals need

to utilize oxygen present in the water. Air contains more O2 as compared to water. Since the content of O2 in air is high, the terrestrial animals do not have to breathe faster to get more oxygen. Therefore, unlike aquatic animals, terrestrial animals do not have to show various adaptations for better gaseous exchange.

Question 11: What are the different ways in which glucose is oxidized to provide energy in

various organisms?

Answer: Glucose is first broken down in the cell cytoplasm into a three carbon molecule called

pyruvate. Pyruvate is further broken down by different ways to provide energy. The breakdown of

glucose by different pathways can be illustrated as follows.

In yeast and human muscle cells, the breakdown of pyruvate occurs in the absence of oxygen whereas in mitochondria, the breakdown of pyruvate occurs in the presence of oxygen.

Question 12: How is oxygen and carbon dioxide transported in human beings?

Answer: Haemoglobin transports oxygen molecule to all the body cells for cellular respiration. The haemoglobin pigment present in the blood gets attached to four O2 molecules that are obtained from breathing. It thus forms oxyhaemoglobin and the blood becomes oxygenated. This oxygenated blood is then distributed to all the body cells by the heart. After giving away O2 to the body cells, blood takes away CO2 which is the end product of cellular respiration. Now the blood becomes de oxygenated. Since haemoglobin pigment has less affinity for CO2, CO2 is mainly transported in the dissolved form. This de-oxygenated blood gives CO2 to lung alveoli and takes O2 in return.  Transportation of O2 and CO2 in blood

Question 13: How are the lungs designed in human beings to maximize the area for exchange of

gases?

Answer: The exchange of gases takes place between the blood of the capillaries that surround the

alveoli and the gases present in the alveoli. Thus, alveoli are the site for exchange of gases. The

lungs get filled up with air during the process of inhalation as ribs are lifted up and diaphragm is

flattened. The air that is rushed inside the lungs fills the numerous alveoli present in the lungs.

Each lung contains 300-350 million alveoli. These numerous alveoli increase the surface area for

gaseous exchange making the process of respiration more efficient.

Question 14: What are the components of the transport system in human beings? What are the

functions of these components?

Answer: The main components of the transport system in human beings are the heart, blood, and

blood vessels. Heart pumps oxygenated blood throughout the body. It receives deoxygenated blood from the various body parts and sends this impure blood to the lungs for oxygenation. Being a fluid connective tissue, blood helps in the transport of oxygen, nutrients, CO2, and nitrogenous wastes.

The blood vessels (arteries, veins, and capillaries) carry blood either away from the heart to various organs or from various organs back to the heart.

Question 15: Why is it necessary to separate oxygenated and deoxygenated blood in mammals

and birds?

Answer: Warm-blooded animals such as birds and mammals maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, these animals require more oxygen (O2) for more cellular respiration so that they can produce more energy to maintain their body temperature. Thus, it is necessary for them to separate oxygenated and de-oxygenated blood, so that their circulatory system is more efficient and can maintain their constant body temperature.

Question 16: What are the components of the transport system in highly organised plants?

Answer: In highly organised plants, there are two different types of conducting tissues − xylem

and phloem. Xylem conducts water and minerals obtained from the soil (via roots) to the rest of

the plant. Phloem transports food materials from the leaves to different parts of the plant body.

Question 17: How are water and minerals transported in plants?

Answer: The components of xylem tissue (tracheids and vessels) of roots, stems, and leaves are

interconnected to form a continuous system of water-conducting channels that reaches all parts of

the plant. Transpiration creates a suction pressure, as a result of which water is forced into the

xylem cells of the roots. Then there is a steady movement of water from the root xylem to all the

plant parts through the interconnected water-conducting channels.

Question 18: How is food transported in plants?

Answer: Phloem transports food materials from the leaves to different parts of the plant body. The

transportation of food in phloem is achieved by utilizing energy from ATP. As a result of this, the

osmotic pressure in the tissue increases causing water to move into it. This pressure moves the

material in the phloem to the tissues which have less pressure. This is helpful in moving materials

according to the needs of the plant. For example, the food material, such as sucrose, is transported

into the phloem tissue using ATP energy.

Question 19: Describe the structure and functioning of nephrons.

Answer: Nephrons are the basic filtering units of kidneys. Each kidney possesses large number of

nephrons, approximately 1-1.5 million. The main components of the nephron are glomerulus,

Bowman’s capsule, and a long renal tubule.

Structure of a nephron

Functioning of a nephron:

The blood enters the kidney through the renal artery, which branches into many capillaries associated with glomerulus.

The water and solute are transferred to the nephron at Bowman’s capsule. In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine.

The filtrate then moves down into the loop of Henle, where more water is absorbed. From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct.

Collecting duct collects urine from many nephrons.

The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.

Question 20: What are the methods used by plants to get rid of excretory products?

Answer: Plants can get rid of excess of water by transpiration. Waste materials may be stored in

the cell vacuoles or as gum and resin, especially in old xylem. It is also stored in the leaves that

later fall off.

Question 21: How is the amount of urine produced regulated?

Answer: The amount of urine produced depends on the amount of excess water and dissolved

wastes present in the body. Some other factors such as habitat of an organism and hormone such

as Anti-diuretic hormone (ADH) also regulates the amount of urine produced.

Question 22: The kidneys in human beings are a part of the system for

(a) nutrition.   (b) respiration.       (c) excretion.              (d) transportation.

Answer:  (c) In human beings, the kidneys are a part of the system for excretion.

Question 23: The xylem in plants are responsible for

(a) transport of water.

(b) transport of food.

(c) transport of amino acids.

(d) transport of oxygen.

Answer: (a) In a plant, the xylem is responsible for transport of water.

Question 24: The autotrophic mode of nutrition requires

(a) carbon dioxide and water.

(b) chlorophyll.

(c) sunlight.

(d) all of the above.

Answer: (d) The autotrophic mode of nutrition requires carbon dioxide, water, chlorophyll and

sunlight.

Question 25: The breakdown of pyruvate to give carbon dioxide, water and energy takes place in

(a) cytoplasm.

(b) mitochondria.

(c) chloroplast.

(d) nucleus.

Answer: (b) The breakdown of pyruvate to give carbon dioxide, water and energy takes place in

mitochondria.

Question 26: How are fats digested in our bodies? Where does this process take place?

Answer: Fats are present in the form of large globules in the small intestine. The small intestine

gets the secretions in the form of bile juice and pancreatic juice respectively from the liver and the

pancreas. The bile salts (from the liver) break down the large fat globules into smaller globules so

that the pancreatic enzymes can easily act on them. This is referred to as emulsification of fats. It

takes place in the small intestine.

Question 27: What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer: Autotrophic nutrition takes place through the process of photosynthesis. Carbon dioxide,

water, chlorophyll pigment, and sunlight are the necessary conditions required for autotrophic

nutrition. Carbohydrates (food) and O2 are the by-products of photosynthesis.

Question 28: What are the differences between aerobic and anaerobic respiration? Name some

organisms that use the anaerobic mode of respiration.

Answer: Aerobic respiration

1.It occurs in the presence of O2.

2.It involves the exchange of gases between the organism and the outside environment.

3.It occurs in cytoplasm and mitochondria.

4.It always releases CO2 and H2O.

5.It yields 36 ATPs.

Anaerobic respiration

1.It occurs in the absence of O2.

2.Exchange of gases is absent.

3.It occurs only in cytoplasm.

4.End products vary.

5.It yields only 2 ATPs.

Anaerobic respiration occurs in the roots of some waterlogged plants, some parasitic worms,

animal muscles, and some micro-organisms such as yeasts.

Question 29: How are the alveoli designed to maximise the exchange of gases?

Answer: The alveoli are the small balloon-like structures present in the lungs. The walls of the

alveoli consist of extensive network of blood vessels. Each lung contains 300−350 million alveoli,

making it a total of approximately 700 million in both the lungs. The alveolar surface when spread

out covers about 80 m2area. This large surface area makes the gaseous exchange more efficient.

Alveoli and capillaries

Question 30: What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer: Haemoglobin is the respiratory pigment that transports oxygen to the body cells for

cellular respiration. Therefore, deficiency of haemoglobin in blood can affect the oxygen

supplying capacity of blood. This can lead to deficiency of oxygen in the body cells. It can also

lead to a disease called anaemia.

Question 31: Describe double circulation in human beings. Why is it necessary?

Answer: The human heart is divided into four chambers − the right atrium, the right ventricle, the

left atrium, and the left ventricle.

Flow of blood in the heart:

The heart has superior and inferior vena cava, which carries de-oxygenated blood from the upper and lower regions of the body respectively and supplies this de-oxygenated blood to the right atrium of the heart.

Flow of blood in the human heart

The right atrium then contracts and passes the de-oxygenated blood to the right ventricle, through an auriculo-ventricular aperture.

Then the right ventricle contracts and passes the de-oxygenated blood into the two pulmonary arteries, which pumps it to the lungs where the blood becomes oxygenated. From the lungs, the pulmonary veins transport the oxygenated blood to the left atrium of the heart. Then the left atrium contracts and through the auriculo-ventricular aperture, the oxygenated blood enters the left ventricle.

The blood passes to aorta from the left ventricle. The aorta gives rise to many arteries that distribute the oxygenated blood to all the regions of the body.

Schematic diagram of blood circulation in humans

Therefore, the blood goes twice through the heart. This is known as double circulation.

Importance of double circulation:

The separation of oxygenated and de-oxygenated blood allows a more efficient supply of oxygen

to the body cells. This efficient system of oxygen supply is very useful in warm-blooded animals

such as human beings.

Warm-blooded animals have to maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, they require more O2 for more respiration so that they can produce more energy to maintain their body temperature. Thus, the circulatory system of humans is more efficient because of the double circulatory heart.

Question 32: What are the differences between the transport of materials in xylem and phloem?

Answer: Transport of materials in xylem

(i) Xylem tissue helps in the transport of water and minerals.

(ii)Water is transported upwards from roots to all other plant parts.

(iii)Transport in xylem occurs with the help of simple physical forces such as transpiration pull.

Transport of materials in phloem

(i) Phloem tissue helps in the transport of food.

(ii)Food is transported in both upward and downward directions.

(iii)Transport of food in phloem requires energy in the form of ATP.

Question 33: Compare the functioning of alveoli in the lungs and nephrons in the kidneys with

respect to their structure and functioning.

Answer: Alveoli 

(i) Alveoli are tiny balloon-like structures present inside the lungs.

(ii) The walls of the alveoli are one a long renal tube. It also contains a cluster of thin-walled cell thick and it contains an capillaries.

(iii) Alveoli are the site of gaseous exchange.

(iv) The exchange of O2 and CO2 takes place between the blood of the capillaries that surround the alveoli.

Structure of Alveoli 

Nephron

(i) Nephrons are tubular structures present inside the kidneys.

(ii) Nephrons are made of glomerulus, bowman’s capsule, and extensive network of blood capillaries. 

(iii) Nephrons are the basic unit of filtration.

(iv) The blood enters the kidneys through the renal artery which alveoli and the gases present in the branches into many capillaries in the glomerulus. The water and solute are transferred to the nephron at Bowman’s capsule .Then the filtrate moves through the proximal tubule and then down into the loop of henle. from the henle's loop, filtrate passes into the distal tubules and then too the collecting duct. The collecting duct collects the urine from many nephrons and passes it to the ureter. During the flow of filtrate, some substances such as glucose, amino acids, and the water are selectively re-absorbed.

Structure of  Nephron

( From www.ncrtsolutions.in )

CLASS 10 Science CHAPTER 15 Our Environment (NCERT Notes)

CLASS 10 Science  

CHAPTER 15 

Our Environment (NCERT Notes)

Substances that are broken down by biological processes are said to be biodegradable. For example vegetable waste, manure etc.

Substances that are not broken down by biological processes are said to be non-biodegradable.  For example human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time. 

ECO-SYSTEM — WHAT ARE ITS COMPONENTS?

All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. 

An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. Example of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and an aquarium ,crop-fields are human- made (artificial) ecosystems.

Organisms can be grouped as producers, consumers and decomposers according to the manner in

which they obtain their sustenance from the environment.

All green plants and certain blue-green algae which can produce food by photosynthesis come under this category and are called the producers.

Organisms depend on the producers either directly or indirectly for their sustenance. These organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers are the consumers. Consumers can be classed variously as herbivores, carnivores, omnivores and parasites. 

The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.

Food Chains and Webs

A series of organisms feeding on one another. This series or organisms taking part at various biotic levels form a food chain.

Each step or level of the food chain forms a trophic level. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level.

The interactions among various components of the environment involves flow of energy from one component of the system to another. The autotrophs capture the energy present in sunlight and

convert it into chemical energy. This energy supports all the activities of the living world. When one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again. 

The flow of energy between various components of the environment: –

The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.

When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for

the next level of consumers.

Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step an reaches the next level of consumers.

Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.

The energy flow diagram states that:-

The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert

back to the solar input and the energy which passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels it is no longer available to the previous level. 

The use of several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up

by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification. 

Ozone Layer and How it is Getting Depleted

Ozone (O3) is a molecule formed by three atoms of oxygen. While O2, which we normally refer to as oxygen, is essential for all aerobic forms of life. Ozone, is a deadly poison. At the higher levels of the

atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O)atoms. These atoms then combine with the molecular oxygen to form ozone as shown— 

The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.

Managing the Garbage we Produce                                                                                      Improvements in our life-style have resulted in greater amounts of waste material generation.      Changes in attitude also have a role to play, with more and more things we use becoming disposable. Changes in packaging have resulted in much of our waste becoming non-biodegradable.

( From NCERT Book )

CLASS 10 Science CHAPTER 6 Life Processes (NCERT Notes)

CLASS 10 Science  

CHAPTER 6 

Life Processes (NCERT Notes)

The basic processes of life include organization, metabolism, responsiveness , movements and reproduction. 

In single-celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed because the entire surface of the organism is in contact with the environment.

In multi-cellular organisms, all the cells may not be in direct contact with the surrounding

environment. Thus, simple diffusion will not meet the requirements of all the cells.

NUTRITION

How do living things get their food?

Organisms which use simple food material obtained from inorganic sources in the form of carbon

dioxide and water. These organisms are called  the autotrophs, include green plants and some bacteria. Other organisms utilise complex substances.

Organisms which depends on the other for food are called heterotrophs survival depends directly or indirectly on autotrophs. Heterotrophic organisms include animals and fungi.

Autotrophic Nutrition

Carbon and energy requirements of the autotrophic organism are fulfilled by photosynthesis. It is the process by which autotrophs take in substances from the outside and convert them into stored forms of

energy. This material is taken in the form of carbon dioxide and water which is converted into carbohydrates in the presence of sunlight and chlorophyll. Carbohydrates are utilised for providing energy to the plant.

The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant. Some of the energy derived from the food we eat is stored in our body in the form of glycogen.

The following events occur during the photosynthesis process –

(i) Absorption of light energy by chlorophyll.

(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

(iii) Reduction of carbon dioxide to carbohydrates.

Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants. Other materials like nitrogen, phosphorus, iron and magnesium are taken up from the soil. Nitrogen is an essential

element used in the synthesis of proteins and other compounds. This is taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.

For example, desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day.

If we observe a cross-section of a leaf under the microscope we will notice that some cells contain green dots. These green dots are cell organelles called chloroplasts which contain chlorophyll. 

Stomata are tiny pores present on the surface of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis. Exchange of gases occurs across the surface of stems, roots and leaves as well. Since large amounts of water can also be lost

through these stomata, the plant closes these pores when it does not need carbon dioxide for photosynthesis. The opening and closing of the pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink.

Heterotrophic Nutrition

Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organism.

Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes. Those that depend on living plants and animals are called parasites. They can also live as symbionts – in association with algae as lichens and with roots of higher plants as mycorrhiza.

Detritivores are the organisms that feed orally on the dead matter, to gain nutrients and energy.

Decomposer are the organisms that carry out the process of decay or break down of the dead organism are known as decomposers and the process of breaking down complex organic matter into its simpler form.

How do Organisms obtain their Nutrition?

In single-celled organisms, the food may be taken in by the entire surface. As the complexity of the organism increases, different parts become specialised to perform different functions. 

For example, Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole. Inside the food-vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested

material is moved to the surface of the cell and thrown out.

In Paramoecium, which is a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface

of the cell.

Nutrition in Human Beings

The alimentary canal is basically a long tube extending from the mouth to the anus.

Food which has to pass through the same digestive tract. Naturally the food has to be processed to generate particles which are small and of the same texture. This is achieved by crushing the food with our teeth. Since the lining of the canal is soft, the food is also wetted to make its passage smooth. When we eat something we like, our mouth ‘waters’. This is actually not only water, but a fluid called saliva secreted by the salivary glands.

Food we ingest is its complex nature. It has to be absorbed from the alimentary canal, it has to be broken into smaller molecules. This is done with the help of biological catalysts called enzymes. The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give sugar. 

The food is mixed thoroughly with saliva and moved around the mouth while chewing by the muscular tongue. It is necessary to move the food in a regulated manner along the digestive tube so that it can be processed properly in each part. The lining of canal has muscles that contract rhythmically in order to push the food forward. These peristaltic movements occur all along the gut. From the mouth, the food is taken to the stomach through the food-pipe or oesophagus. The stomach is a large organ which expands when food enters it. The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices.

These digestion functions are taken care of by the gastric glands present in the wall of the stomach.

These release hydrochloric acid, a protein digesting enzyme called pepsin, and mucus. The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin. The mucus protects the inner lining of the stomach from the action of the acid under normal conditions. 

Food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine. From the stomach, the food now enters the small intestine. This is the longest part

of the alimentary canal which is fitted into a compact space because of extensive coiling. The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.

The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas. The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act.

Bile juice from the liver acting on fats. Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules increasing the efficiency of enzyme action. Which help in the emulsification of fat.  

The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats. 

The walls of the small intestine contain glands which secrete intestinal juice. The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.

The digested food is taken up by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi which increase the surface area for absorption. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body, where it is utilised for obtaining energy, building up new tissues and the repair of old tissues.

The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is removed from the body via the anus. The exit of this waste material is regulated by the anal sphincter.

Dental caries

Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins when bacteria acting on sugars produce acids that softens or demineralises the enamel. Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers the teeth. Brushing the teeth after eating removes the plaque before the bacteria produce acids. If untreated, microorganisms may invade the pulp, causing

inflammation and infection.

RESPIRATION

The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen . 

In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. The pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. 

Break- down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than in the anaerobic process. 

When there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is

taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise

to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.

ATP is the energy currency for most cellular processes. The energy released during the process of respiration is used to make an ATP molecule from ADP and inorganic phosphate.

Endothermic processes in the cell then use this ATP to drive the reactions. When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released. It can be

used to obtain mechanical energy, light energy, electrical energy and so on. Similarly, ATP can be used in the cells for the contraction of muscles, protein synthesis, conduction of nervous impulses and many other activities.

Plants exchange gases through stomata and the large inter-cellular spaces ensure that all cells are in contact with air. Carbon dioxide and oxygen are exchanged by diffusion. They can go into   cells, or away from them and out into the air. The direction of diffusion depends upon the environmental conditions and the requirements of the plant. 

At night, when there is no photosynthesis occurring, CO2 elimination is the major exchange. During the day, CO2 generated during respiration is used up for photosynthesis, hence there is no CO2 release instead, oxygen release.

Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced.

Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water. The amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. 

Fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood. Terrestrial organisms use the oxygen in the atmosphere for respiration. This oxygen is absorbed by different organs in different animals. All these organs have a structure that increases the surface area which is in contact with the oxygen-rich atmosphere. Since the exchange of oxygen and carbon dioxide has to take place across this surface.

In human beings air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage. The passage is also lined with mucus which helps in

this process. The air passes through the throat and into the lungs. Rings of cartilage are present in the throat. These ensure that the air-passage does not collapse.

Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli. The alveoli provide a surface where the exchange of gases can

take place. The walls of the alveoli contain an extensive network of blood-vessels.  

When we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result. Because air is sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. 

Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it. In human beings, the respiratory pigment is haemoglobin which has a very high affinity for oxygen. This pigment is present in the red blood corpuscles. Carbon dioxide is more soluble in water than oxygen is and transported in the dissolved form in our blood.

TRANSPORTATION

Transportation in Human Beings

Blood consists of a fluid medium called plasma in which the cells are suspended. Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form. Oxygen is carried by the red blood cells. Many other substances like salts, are also transported by the blood. 

Our pump — the heart

The heart is a muscular organ  as big as our fist . Because both oxygen and carbon dioxide have to

be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The carbon dioxide-rich blood has to reach the lungs for the carbon dioxide to be removed, and the oxygenated blood from the lungs has to be brought back to the heart. This oxygen-rich blood is then pumped to the rest of the body.

Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium. The left atrium relaxes when it is collecting this blood. It then contracts, while the next chamber, the left ventricle, expands, so that the blood is transferred to it. When the muscular left ventricle contracts in its turn, the blood is pumped out to the body. De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. Since ventricles have to pump blood into various

organs, they have thicker muscular walls than the atria do. Valves ensure that blood does not flow backwards when the atria or ventricles contract.

Oxygen enters the blood in the lungs

The separation of the right side and the left side of the heart is useful to keep oxygenated and de-

oxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the

body. This is useful in animals that have high energy needs, such as birds and mammals, which

constantly use energy to maintain their body temperature. 

Animals, like amphibians or many reptiles have three-chambered hearts, and tolerate some mixing of the oxygenated and de-oxygenated blood streams. 

Fishes have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body. Thus, blood goes only once through the heart in the fish during one cycle of passage through the body.

In vertebrates blood has to move twice in the heart without mixing of the blood twice during each cycle. This is known as double circulation.

Blood pressure

The force that blood exerts against the wall of a vessel is called blood pressure. This pressure is much greater in arteries than in veins. The pressure of blood inside the artery during ventricular systole (contraction) is called systolic pressure and pressure in artery during ventricular diastole (relaxation) is called diastolic pressure. The normal systolic pressure is about 120 mm of Hg and diastolic pressure is 80 mm of Hg. Blood pressure is measured with an instrument called sphygmomanometer. High blood pressure is also called hypertension and is caused by the constriction of arterioles, which results in increased resistance to blood flow. It can lead to the rupture of an artery and internal bleeding.

The tubes – blood vessels

Arteries are the vessels which carry blood away from the heart to various organs of the body. Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls. 

Veins collect the blood from different organs and bring it back to the heart. They do not need thick walls because the blood is no longer under pressure, instead they have valves that ensure that the blood flows only in one direction.

The artery divides into smaller and smaller vessels to bring the blood in contact with all the individual cells. The smallest vessels have walls which are one-cell thick and are called capillaries. Exchange of material between the blood and surrounding cells takes place across this thin wall. The capillaries then join together to form veins that convey the blood away from the organ or tissue.

Maintenance by platelets

When we are injured and start bleeding. Naturally the loss of blood from the system has to be minimised. Leakage would lead to a loss of pressure which would reduce the efficiency of the pumping system. To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at these points of injury.

Lymph

Is type of fluid  involved in transportation. This is called lymph or tissue fluid. The pores present in the walls of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the tissue fluid or lymph. It is similar to the plasma of blood but colourless and contains less protein. Lymph drains into lymphatic capillaries from the intercellular spaces, which join to form large lymph vessels that finally open into larger veins. Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood.

Transportation in Plants

Plants take in simple compounds such as CO2 and photosynthesise energy stored in their chlorophyll-containing organs, namely leaves. For plants, the soil is the nearest and richest source of raw materials like nitrogen, phosphorus and other minerals. The absorption of these substances therefore occurs through the part in contact with the soil, namely roots.

If the distances between soil-contacting organs and chlorophyll-containing organs are small, energy and raw materials can easily diffuse to all parts of the plant body. But if these distances become large because of changes in plant body design, diffusion processes will not be sufficient to provide raw material in leaves and energy in roots.

Plant transport systems will move energy stores from leaves and raw materials from roots. These two pathways are constructed as independently organised conducting tubes. The xylem moves water

and minerals obtained from the soil. Phloem transports products of photosynthesis from the leaves where they are synthesised to other parts of the plant.

Transport of water

In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant. At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil. Water, therefore moves into the root from the soil to eliminate this difference. This means that there is steady movement of water into root xylem, creating a column

of water that is steadily pushed upwards. However, this pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants. 

Plants use another strategy to move water in the xylem upwards to the highest points of the plant body.

Provided that the plant has an adequate supply of water, the water which is lost through the

stomata is replaced by water from the xylem vessels in the leaf. Evaporation of water molecules from

the cells of a leaf creates a suction which pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.

Transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation. The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

Transport of food and other substances

Transport of soluble products of photosynthesis is called translocation and it occurs in the part of the vascular tissue known as phloem. Besides the products of photosynthesis, the phloem transports amino acids and other substances. These substances are especially delivered to the storage organs of roots, fruits and seeds and to growing organs. The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.

Transport in xylem can be largely explained by simple physical forces, 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 the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

EXCRETION

Metabolic activities generate nitrogenous materials which need to be removed. The biological process involved in the removal of these harmful metabolic wastes from the body is called excretion. 

Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water. 

Excretion in Human Beings

The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. 

Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.

How is urine produced? 

The purpose of making urine is to filter out waste products from the blood. Nitrogenous waste such as urea or uric acid are removed from blood in the kidneys. kidney is basic unit of  filtration. It is a cluster of very thin-walled blood capillaries. Each capillary cluster in the kidney is associated with the cup-shaped end of a tube that collects the filtered urine. Each kidney has large numbers of these filtration units called nephrons packed close together. Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube. The amount of water re- absorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted. 

The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder. Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra. The bladder is muscular, so it is

under nervous control.

Artificial kidney (Hemodialysis)

Kidneys are vital organs for survival. Several factors like infections, injury or restricted blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of poisonous wastes in the body, which can even lead to death. 

In case of kidney failure, an artificial kidney can be used. An artificial kidney is a device to remove

nitrogenous waste products from the blood through dialysis.

Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialysing fluid. This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient’s blood is passed through these tubes. During this passage, the waste products from the blood pass into dialysing fluid by diffusion. The purified blood is pumped back

into the patient. This is similar to the function of the kidney, but it is different since there is no re-

absorption involved. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily.

However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is re-

absorbed in the kidney tubules.

Excretion in Plants

Oxygen is a waste product generated during photosynthesis. 

They can get rid of excess water by transpiration.

For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves. 

Many plant waste products are stored in cellular vacuoles. 

Waste products may be stored in leaves that fall off. 

Other waste products are stored as resins and gums, especially in old xylem. 

Plants also excrete some waste substances into the soil around them.

( From NCERT Book )