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Life Processes

Unicellular vs Multi cellular Organism

Living things vs non living things

Difference between Plants and Animals


Types of Nutrition

Nutrition In Plants


Steps Involved in Photosynthesis

Raw Materials for Photosynthesis

Structure of Leaf


Exchange of Gases In Plants

Significance of Photosynthesis

Starch – Iodine Test

Carbon dioxide is essential for photosynthesis

Chlorophyll is essential for photosynthesis

Sunlight is essential for photosynthesis

Nutrition In Animals

Nutrition in Amoeba

Nutrition In Humans

Important Organs in Digestive System

Mouth or Buccal Cavity


Small Intestine





Steps in Respiration

Types of Respiration


Exchange of gases in Animals

Human Respiratory System









Breathing Mechanism

Intercostals muscles

Gaseous Exchange In Human Beings

Transportation In Animals

Composition of Blood

Blood Vessels


Double Circulation and Its Benifits

Blood pressure


Transportation In Plants



Transportation of Water/Ascent of Sap

Transport of Food


Human Excretory System



Artificial kidney (Hemodialysis)

Excretion In Plants



Life Processes:

Various functions carried out by living beings; which are necessary to maintain and continue life are called life processes.

Following are some of the life processes in living beings,

Unicellular vs Multi cellular Organism

In the case of a 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 oxygen of all the cells.

In case of multi cellular organism, the body size increases and the body design is more complex. There is division of labour. There are specialised cells and tissues for performing various necessary functions of the body such as intake of food and oxygen.

Living things vs non living things

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 and the molecular movement is the fundamental criterion that can be used to decide whether something is alive or not.

A living 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.

Difference between Plants and Animals



Plants are generally rooted in one place and do not move on their own

Most animals have the ability to move fairly freely.

Plants contain chlorophyl and can make their own food

Animals cannot make their own food and are dependent on plants and other animals for food. 

Plants give off oxygen and take in carbon dioxide given off by animals.

Animals give off carbon dioxide which plants need to make food and take in oxygen which they need to breathe.

Plants cells have cell walls and other structures differ from those of animals.

Animal cells do not have cell walls and have different structures than plant cells

Plants have either no or very basic ability to sense.

Animals have a much more highly develped sensory and nervous system.


The process by which an organism takes food and utilizes it is called nutrition.

Need of nutrition

Organisms need energy to perform various activities like growth and maintenance of cells, tissues. The energy is supplied by the nutrients. Organisms need various raw materials for growth and repair. These raw materials are also provided by nutrients.


Materials which provide nutrition to organisms are called nutrients. Carbohydrates, proteins and fats are the main nutrients and are called macronutrients. Minerals and vitamins are required in small amounts and hence are called micronutrients.

Types of Nutrition:



Green plants prepare their own food in the presence of sunlight using carbon dioxide and water as raw materials. The process by which green plants prepare food is called photosynthesis.

During this process; the solar energy is converted into chemical energy and carbohydrates are formed.

Green leaves are the main sites of photosynthesis. The green portion of the plant contains a pigment chloroplast; which contains chlorophyll.

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Steps Involved in Photosynthesis

  1. Absorption of light energy by chlorophyll.

  2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

  3. Reduction of carbon dioxide to carbohydrates.

These steps need not take place one after the other immediately. 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.

How do raw materials for photosynthesis become available to the plants?

Water and carbon dioxide are raw materials needed for photo synthesis.

Structure of Leaf

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The leaf has vascular bundle (xylem and phloem), which are needed for transportation of water and food.

It contains chloroplasts, which contain green pigment called chlorophyll, required for photosynthesis.

It has stomata, which exchange gases with the atmosphere.

Stomata: The stomata are tiny pores present on the surface of the leaves responsible for gaseous exchange

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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.

Exchange of Gases

The exchange of gases occurs across the surface of stems, roots and leaves. This is based on the principle of diffusion.

During the day oxygen is produced as a byproduct of photosynthesis. Some of the oxygen is utilized in respiration and rest is exchanged with the atmosphere.

CO2 is produced during respiration in the day as well as night. CO2 produced during the day is utilized in photosynthesis, whereas the CO2 produced during night is given out.

Significance of Photosynthesis

How to find out whether the photosynthesis has taken place?

During the photosynthesis, starch is stored in the leaves. Hence if we can test for the presence of starch in the leaf, we can tell that the photosynthesis has taken place.

Activity to find whether the leaf contains starch

Activity to show that sunlight is essential for photosynthesis

  1. Take the potted plant and keep it in a dark place for 2-3 days so that the leaves get destarched.

  2. Cover a part of one of its leaves with the strip of black paper. Make sure that you cover both the sides of the leaf.

  3. Now place this plant in sunlight for 3-4 hours.

  4. Pluck the selected covered leaf and remove the black paper covering it.

  5. Place this leaf in the beaker containing water and boil it for about 10 minutes.

  6. Take out the leaf and now boil it in alcohol, using the water bath, for 10 minutes. This removes the chlorophyll.

  7. Take out the leaf and wash it under running water.

  8. Place this leaf in the Petri dish and put a few drops of iodine solution on it. Now observe the change in colour.

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The leaf turns blue-black except in the covered region. As this covered region did not receive light, photosynthesis did not occur. Hence no starch was formed there. The uncovered region received light and starch was formed there due to photosynthesis.



  1. Before starting the experiment, the leaf must be distracted.

  2. The leaf must be covered with black paper properly to prevent the entry of light.

  3. Boiling the leaf in alcohol should be done in the water bath

Activity to show that Carbon dioxide is essential for photosynthesis

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The leaf taken from the plant placed in the bell jar without KOH turns blue-black whereas the one placed with KOH does not show blue-black colour. As the later leaf did not receive CO2, photosynthesis did not occur. Hence no starch was formed and no colour was shown by this leaf.


Carbon dioxide is essential for photosynthesis.

Activity to show that chlorophyll is essential for photosynthesis

  1. Take a potted plant like croton whose leaves are partly green and partly white. The green part of the leaf has chlorophyll but the white part of the leaf does not have chlorophyll.

  2. Place this plant in a completely dark place for about three days to destarch its leaves.

  3. Take out the potted plant from the dark place and keep it in bright sunshine for three to four days.

  4. Pluck the variegated leaf from the plant and test for starch.


We find that the part of leaf that was originally white (without chlorophyll) does not turn blue-black on adding iodine solution showing that no starch is present in this part of the leaf. The part of leaf which was originally green (contained chlorophyll) turns blue-black on adding iodine solution showing that starch is present in this inner part of the leaf.


From this observation we conclude that chlorophyll is essential for photosynthesis.

How are other raw materials taken by plants ?


Steps of Holozoic Nutrition

  1. Ingestion: The process of taking food into the body is called ingestion.

  2. Digestion: the process in which the food containing large, insoluble molecules is broken down into small, water soluble molecules is called digestion.

  3. Absorption: The process in which the digested food passes through the intestinal wall into blood stream is called absorption.

  4. Assimilation: The process in which the absorbed food is taken in by the body cells and used for energy, growth and repair is called assimilation.

  5. Egestion: The process in which the undigested food is removed from the body is called egestion.

Nutrition in Simple Animals:

Amoeba and paramecium are two very simple unicellular animals. In unicellular animals, all the processes of nutrition are performed by the single cell.

Nutrition in Amoeba:

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Steps involved in the nutrition of Amoeba:

Ingestion: Amoeba ingests food by forming temporary finger-like projections called pseudopodia around it.

The food is engulfed with a little surrounding water to form a food vacuole (‘temporary stomach’) inside the Amoeba.

Digestion: In Amoeba, food is digested in the food vacuole by digestive enzymes which break down the food into small and soluble molecules by chemical reactions.

Absorption: The digested simple and soluble substances pass out of food vacuole into the surrounding environment.

Assimilation: The absorbed food materials are used to obtain energy through respiration and make the parts of Amoeba cell which leads to the growth of Amoeba.

Egestion: The remaining undigested material is moved to the surface of the cell and thrown out of the body of Amoeba.


Human beings are complex animals; which have a complex digestive system.

Structure of the Human Digestive System

The human digestive system is composed of an alimentary canal and some accessory glands. The alimentary canal is divided into several parts, viz. oesophagus, stomach, small intestine, large intestine, rectum and anus. Salivary gland, liver and pancreas are the accessory glands which lie outside the alimentary canal.

The lining of alimentary canal has muscles that contract rhythmically in order to push the food forward. This is called peristaltic movement and occurs all along the gut.

Food is digested with the help of biological catalysts called enzymes.


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Mouth or Buccal Cavity

The mouth has teeth and tongue. Salivary glands are also present in the mouth. The tongue has gustatory receptors which perceive the sense of taste. Tongue helps in turning over the food, so that saliva can be properly mixed in it.

Teeth help in breaking down the food into smaller particles so that swallowing of food becomes easier.

There are four types of teeth in human beings. The incisor teeth are used for cutting the food. The canine teeth are used for tearing the food and for cracking hard substances. The premolars are used for coarse grinding of food. The molars are used for fine grinding of food.

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.

Salivary glands secrete saliva. Saliva makes the food slippery which makes it easy to swallow the food. Saliva also contains the enzyme salivary amylase or ptyalin. Salivary amylase digests starch and converts it into sucrose.


Stomach is a bag-like organ. Highly muscular walls of the stomach help in churning the food. The walls of stomach secrete hydrochloric acid, enzyme pepsin and mucus.

Hydrochloric acid kills the germs which may be present in food. It also makes the medium inside stomach as acidic. The acidic medium is necessary for gastric enzymes to work.

The enzyme pepsin does partial digestion of protein.

The mucus saves the inner lining of stomach from getting damaged from hydrochloric acid.

The exit of food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine.

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. In humans, the small intestine is about 6 meters or 20 feet long.

The small intestine in human beings is the site of complete digestion of food (like carbohydrates, proteins and fats). It receives the secretions of the liver and pancreas for this purpose.


Liver is the largest internal organ in the human body. Liver makes bile juice which gets stored in gall bladder. From the gall bladder, bile is released as and when required.

Bile performs two functions


Pancreas is situated below the stomach. The pancreas secretes pancreatic juice which contains enzymes like pancreatic amylase for breaking down starch, trypsin for digesting proteins and lipase for breaking down emulsified fats.

The inner wall of small intestine is projected into numerous finger-like structures called villi. Villi increase the 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, where it is utilised for obtaining energy, building up new tissues and the repair of old tissues

Large Intestine

Undigested food goes into the large intestine. Some water and salt are absorbed by the walls of the large intestine. After that, the undigested food goes to the rectum; from where it is expelled out through the anus. The large intestine in humans is about 1.5 meters or 5 feet long.


Enzymes are biological molecules (proteins) that act as catalysts and help complex compounds break down into simpler substances, which are easy to absorb into blood.

Secreting Organ /Juice

Enzyme/ Substance

Site of Action


Salivary Glands

Salivary Amylase


Converts starch to maltose




Helps movement of food

Stomach, Gastric juice

Hydrochloric acid


Provides acidic medium and kills microbes


Protects stomach from pepsin and HCl


Initiates digestion of proteins (long chains of amino acids) to polypeptides and peptides (shorter chains of amino acids)



Small Intenstine

Provides basic medium and emulsifies fat (large globules into smaller ones for lipase to work)

Pancreas, Pancreatic Juice

Pancreatic amylase

Small Intenstine

Converts starch (a polysaccharide) to maltose (a disaccharide)


Converts proteins into peptides


Converts lipids (eg. triglycerides) into glycerol and fatty acids

Small Intestine, Intestinal Juice


Small Intestine

Converts maltose (a disaccharide) into two glucose (a monosaccharide)


Converts sucrose (a disaccharide) into glucose and fructose (monosaccharides)


Converts lactose (a disaccharide) into glucose and galactose (monosaccharides)


The process by which a living being utilizes the food to get energy is called respiration.

Respiration is an oxidation reaction in which carbohydrate is oxidized to produce energy. Mitochondria are the site of respiration and the energy released is stored in the form of ATP (Adenosine Tri Phosphate). ATP is stored in mitochondria and is released as per need.


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.

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This is an endothermic processes in the cell use this ATP to drive the reactions. When ATP changes tp ADP, the energy equivalent to 30.5 kJ/mol is released.

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ATP can be used in the cells for the contraction of muscles, protein synthesis, conduction of nervous impulses and many other activities

Steps in Respiration

Breaking down glucose into pyruvate: 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 and small amount of energy is released.

Further breakdown takes place in three ways depending upon the type of respiration in a particular organism.

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The reactions can be written as,

Types of Respiration:

Exchange of gases In Animals

For aerobic respiration; organisms need a continuous supply of oxygen, and carbon dioxide produced during the process needs to be removed from the body. Different organisms use different methods for intake of oxygen and expulsion of carbon dioxide.

Diffusion is the method which is utilized by unicellular and some simple organisms for this purpose. In plants also, diffusion is utilized for exchange of gases.

Fishes take oxygen dissolved in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood. Since 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.

Terrestrial organisms have developed lungs for exchange of gases. Availability of oxygen is not a problem in the terrestrial environment so breathing rate is slower compared to what it is in fishes.


The human respiratory system is composed of a pair of lungs. These are attached to a system of tubes which open on the outside through the nostrils.

Main Organs in Human Respiratory System:

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Nostrils: The two nostrils converge to form a nasal passage. The inner lining of the nostrils is lined by hairs and remains wet due to mucus secretion. The mucus and the hairs help in filtering the dust particles out from inhaled air. Further, air is warmed up when it enters the nasal passage.

Pharynx: It is a tube like structure which continues after the nasal passage.

Epiglottis: The epiglottis is a flap made of elastic cartilage tissue covered with a mucous membrane, attached to the entrance of the larynx. It projects obliquely upwards behind the tongue and the hyoid bone, pointing dorsally. It stands open during breathing, allowing air into the larynx. During swallowing, it closes to prevent respiration, forcing the swallowed liquids or food to go down the esophagus instead. It is thus the valve that diverts passage to either the tracheaor the esophagus.

Larynx: This part comes after the pharynx. This is also called the voice box.

Trachea: This is composed of rings of cartilage. Cartilaginous rings prevent the collapse of trachea in the absence of air.

Bronchi: A pair of bronchi comes out from the trachea; with one bronchus going to each lung.

Bronchioles: A bronchus divides into branches and sub-branches; inside the lung.

Alveoli: These are air-sacs at the end of bronchioles. Alveolus is composed of a very thin membrane and is the place where blood capillaries open. The oxygen mixes with the blood and carbon dioxide exits from the blood. The exchange of gases in alveoli takes place due to pressure differential.

Breathing Mechanism: The breathing mechanism of lungs is controlled by the diaphragm and the intercostals muscles. Diaphragm is a membrane which separates the thoracic chamber from the abdominal cavity. When diaphragm moves down, the lungs expand and air is inhaled. When diaphragm moves up, the lungs contract and air is exhaled.

Intercostals muscles are several groups of muscles that run between the ribs, and help form and move the chest wall.

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Gaseous Exchange In Human Beings

De-oxigenated blood contains higher concentration of CO2 compared to the inhaled air. As a result the CO2 gets diffused out through the memberane of capilliaries. On the other hand the inhaled air has higher concentration of oxygen than the blood and the oxygen goes into the blood. The haemoglobin in the blood combines with oxygen and forms oxyhaemoglobin and transported to the cells. Haemoglobin has higher affinity towards CO compared to oxygen. As a result , if CO is present in the inhaled gas, it combines more readily with the haemoglobin and reduces the oxygen carrying capacity of blood. This may result in lack of oxygen in the cells and may cause death.


Circulatory System

The circulatory system is responsible for transport of various substances in human beings. It is composed of the heart, arteries, veins and blood capillaries.

Composition of Blood and Its Function

Blood plays the role of the carrier of substances.

Blood transports food, oxygen and waste materials in our bodies. Blood is a connective tissue which plays the role of the carrier for various substances in the body. Blood is composed of plasma, blood cells and platelets.

Blood Plasma: Blood plasma is a pale coloured liquid which is mostly composed of water. Blood plasma forms the matrix of blood.

Blood Cells: There are two types of blood cells, viz. Red Blood Cells (RBCs) and White Blood Cells (WBCs).

Red Blood Corpuscles (RBCs): These are of red colour because of the presence of haemoglobin which is a pigment. Haemoglobin readily combines with oxygen and carbon dioxide. The transport of oxygen happens through haemoglobin. Some part of carbon dioxide is also transported through haemoglobin.

White Blood Corpuscles (WBCs): These are of pale white colour. They play important role in the immunity.

Platelets: Platelets are responsible for blood coagulation. Blood coagulation is a defense mechanism which prevents excess loss of blood in case of an injury. They plug the leaks in the blood vessels.

Blood Vesseles

Arteries: These are thick-walled blood vessels which carry oxygenated blood from the heart to different organs. Pulmonary arteries are exceptions because they carry deoxygenated blood from the heart to lungs; where oxygenation of blood takes place.

Veins: These are thin-walled blood vessels which carry deoxygenated blood from different organs to the heart. Pulmonary veins are exceptions because they carry oxygenated blood from lungs to the heart. Valves are present in veins to prevent backflow of blood.

Capillaries: These are the blood vessels which have single-celled walls at the end of arteries or veins.


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The heart is a muscular organ which is as big as our fist. The heart is a pumping organ which pumps the blood. 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 human heart is composed of four chambers, viz. right atrium, right ventricle, left atrium and left ventricle.

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.

Systole: Contraction of cardiac muscles is called systole.

Diastole: Relaxation of cardiac muscles is called diastole.

Double Circulation and Its Benifits

In the human heart, blood passes through the heart twice in one cardiac cycle. This type of circulation is called double circulation. One complete heart beat in which all the chambers of the heart contract and relax once is called cardiac cycle. The heart beats about 72 times per minute in a normal adult.

The separation of the right side and the left side of the heart is useful to keep oxygenated and deoxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in warm blooded animals such as birds and mammals, which constantly use energy to maintain their body temperature.

On the other hand in cold blooded animals that do not use energy for this purpose, the body temperature depends on the temperature in the environment. In such animals, like amphibians or many reptiles which have three-chambered hearts, some mixing of the oxygenated and de-oxygenated blood streams happens and oxygen carrying capacity of blood is reduced. Fishes, on the other hand, 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.

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Blood pressure: The force per unit area 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.

Lymph: It is also called tissue fluid. Lymph is formed when the fluid containing 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. Lymph also plays an important role in the immune system.


Plants have specialized vascular tissues for transportation of substances. There are two types of vascular tissues in plants, viz. xylem and phloem.


Xylem is responsible for transportation of water and minerals. It is composed of trachieds, xylem vessels, xylem parenchyma and xylem fibre. Trachieds and xylem vessels are the conducting elements. The xylem makes a continuous tube in plants which runs from roots to stem and right up to the veins of leaves.


Phloem is responsible for transportation of food. Phloem is composed of sieve tubes, companion cells, phloem parenchyma and bast fibres (fibrous material from a plant, in particular the inner bark of a tree). Sieve tubes are the conducting elements in phloem.


The upward movement of water and minerals from roots to different plant parts is called ascent of sap. Many factors are at play in ascent of sap and it takes place in many steps.

Root Pressure: The walls of cells of root hairs are very thin. Water from soil enters the root hairs because of osmosis. Root pressure is responsible for movement of water up to the base of the stem.

Capillary Action

A very fine tube is called capillary. Water or any liquid rises in the capillary because of surface tension and this phenomenon is called capillary action. Water in stem rises upto some height because of capillary action.

Adhesion-Cohesion of Water Molecules

Water molecules make a continuous column in the xylem because of forces of adhesion and cohesion among the molecules.

Transpiration Pull

Loss of water vapour through stomata and lenticels in plants is called transpiration. Transpiration through stomata creates vacuum which creates a suction called transpiration pull. The transpiration pull sucks the water and minerals from the xylem tubes and thus water is able to rise to great heights in even the tallest plants. Transpiration also helps in maintaining the temperature.


Transport of soluble products of photosynthesis is called translocation and it occurs in the phloem. The phloem also transports amino acids and other substances. These substances are delivered to the storage organs of roots, fruits, seeds and also to growing organs.

Transport of food in plants happens because of utilization of energy. For example 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.

In the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

Thus, unlike the transport through xylem it is a form of active transport.

The flow of substances through phloem takes place in both directions, i.e. it is a two-way traffic in phloem.


The biological process involved in the removal of the harmful metabolic wastes from the body is called excretion.

Different organisms use varied strategies to do this. Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water.

Complex multi-cellular organisms use specialised organs to perform this function.


Image result for human excretory system

The human excretory system is composed of a pair of kidneys. A tube called ureter comes out of each kidney and goes to the urinary bladder. Urine is collected in the urinary bladder, from where it is expelled out through urethra as and when required.

Important components of excretory system are,


Kidney is a bean-shaped organ which lies near the vertebral column in the abdominal cavity. The kidney is composed of many filtering units called nephrons.


Nephron is called the functional unit of kidney. It is composed of a tangled mess of tubes and a filtering part called glomerulus. Glomerulus is a network of blood capillaries to which renal artery and renal vein are attached. It collects the filtered urine. The cup shaped structure is called Bowman’s capsule.

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 urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder. The amount of water reabsorbed depends on how much excess water there is in the body and on how much of dissolved waste is to be excreted.

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 and it is under nervous control. As a result, we can usually control the urge to urinate.

The human urine is mainly composed of water and urea.

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Artificial kidney (Hemodialysis)

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.

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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 reabsorbed in the kidney tubules.


Oxygen is a waste product generated during photosynthesis. CO2 is generated during respiration. Gases are exchanged through stomata and also across the surface of stems, roots and leaves.

Excess water is excreted by transpiration.

Many plant waste products are stored in cellular vacuoles.

Waste products are 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.