Lesson: Life Processes

# Question 1

Which of the following statements about the autotrophs is incorrect?

(a) They synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll.

(b) They store carbohydrates in the form of starch.

(c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight.

(d) They constitute the first trophic level in food chains.

(c)

# Question 2

In which of the following groups of organisms, food material is broken down outside the body and absorbed?

(a) Mushroom, green plants, Amoeba

(c) Paramecium, Amoeba, Cuscuta

(d) Cuscuta, lice, tapeworm

(b)

# Question 3

Select the correct statement

(a) Heterotrophs do not synthesise their own food

(b) Heterotrophs utilise solar energy for photosynthesis

(c) Heterotrophs synthesise their own food

(d) Heterotrophs are capable of converting carbon dioxide and

water into carbohydrates

(a)

# Question 4

Which is the correct sequence of parts in human alimentary canal?

(a) Mouth → stomach → small intestine → oesophagus → large intestine

(b) Mouth → oesophagus → stomach → large intestine small intestine

(c) Mouth → stomach → oesophagus → small intestine → large intestine

(d) Mouth → oesophagus → stomach → small intestine → large intestine

(d)

# Question 5

If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected?

(a) Proteins breaking down into amino acids

(b) Starch breaking down into sugars

(c) Fats breaking down into fatty acids and glycerol

(d) Absorption of vitamins

(b)

# Question 6

The inner lining of stomach is protected by one of the following from hydrochloric acid. Choose the correct one

(a) Pepsin

(b) Mucus

(c) Salivary amylase

(d) Bile

(b)

# Question 7

Which part of alimentary canal receives bile from the liver?

(a) Stomach

(b) Small intestine

(c) Large intestine

(d) Oesophagus

(b)

# Question 8

A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains

(a) complex proteins

(b) simple proteins

(c) fats

(d) starch

(d)

# Question 9

In which part of the alimentary canal food is finally digested?

(a) Stomach

(b) Mouth cavity

(c) Large intestine

(d) Small intestine

(d)

(d)

(b)

# Question 12

The correct sequence of anaerobic reactions in yeast is

(d)

# Question 13

Which of the following is most appropriate for aerobic respiration?

(d)

# Question 14

Which of the following statement(s) is (are) true about respiration?

(i) During inhalation, ribs move inward and diaphragm is raised

(ii) In the alveoli, exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air

(iii) Haemoglobin has greater affinity for carbon dioxide than oxygen

(iv) Alveoli increase surface area for exchange of gases

(a) (i) and (iv)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (ii) and (iv)

(d)

# Question 15

Which is the correct sequence of air passage during inhalation?

(a) Nostrils → larynx → pharynx → trachea → lungs

(b) Nasal passage → trachea → pharynx → larynx → alveoli

(c) larynx → nostrils → pharynx → lungs

(d) Nostrils → pharynx → larynx → trachea → alveoli

(d)

(b)

# Question 17

Which of the following statement (s) is (are) true about heart?

(i) Left atrium receives oxygenated blood from different parts of body while right atrium receives deoxygenated blood from lungs

(ii) Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs

(iii) Left atrium transfers oxygenated blood to right ventricle which sends it to different body parts

(iv) Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body

(a) (i)

(b) (ii)

(c) (ii) and (iv)

(d) (i) and (iii)

(c)

(a)

# Question 19

Single circulation i.e., blood flows through the heart only once during one cycle of passage through the body, is exhibited by

(a) Labeo, Chameleon, Salamander

(b) Hippocampus, Exocoetus, Anabas

(c) Hyla, Rana, Draco

(d) Whale, Dolphin, Turtle

(b)

# Question 20

In which of the following vertebrate group/ groups, heart does not pump oxygenated blood to different parts of the body?

(a) Pisces and amphibians

(b) Amphibians and reptiles

(c) Amphibians only

(d) Pisces only

(d)

# Question 21

Choose the correct statement that describes arteries.

(a)   They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart

(b)   They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body

(c)   They have thick elastic walls, blood flows under low pressure; carry blood from the heart to various organs of the body

(d)   They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

(d)

(d)

# Question 23

Oxygen liberated during photosynthesis comes from

(a) water

(b) chlorophyll

(c) carbon dioxide

(d) glucose

(a)

(a)

# Question 25

Which of the following is an incorrect statement?

(a) Organisms grow with time

(b) Organisms must repair and maintain their structure

(c) Movement of molecules does not take place among cells

(d) Energy is essential for life processes

(c)

# Question 26

The internal (cellular) energy reserve in autotrophs is

(a) glycogen

(b) protein

(c) starch

(d) fatty acid

(c)

# Question 27

Which of the following equations is the summary of photosynthesis?

(a) $6\text{\hspace{0.17em}}C{O}_{2}+12\text{\hspace{0.17em}}{H}_{2}O\to {C}_{6}{H}_{12}{O}_{6}+6\text{\hspace{0.17em}}{O}_{2}+6\text{\hspace{0.17em}}{H}_{2}O$

(b) $6\text{\hspace{0.17em}}C{O}_{2}+{H}_{2}O+Sunlight\to {C}_{6}{H}_{12}{O}_{6}+{O}_{2}+6\text{\hspace{0.17em}}{H}_{2}O$

(c) $\begin{array}{l}6\text{\hspace{0.17em}}C{O}_{2}+12\text{\hspace{0.17em}}{H}_{2}O+Chlorophyll+Sunlight\\ \text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\to {C}_{6}{H}_{12}{O}_{6}+6\text{\hspace{0.17em}}{O}_{2}+6\text{\hspace{0.17em}}{H}_{2}O\end{array}$

(d) $\begin{array}{l}6\text{\hspace{0.17em}}C{O}_{2}+12\text{\hspace{0.17em}}{H}_{2}O+Chlorophyll+Sunlight\\ \text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\to {C}_{6}{H}_{12}{O}_{6}+6\text{\hspace{0.17em}}C{O}_{2}+6\text{\hspace{0.17em}}{H}_{2}O\end{array}$

(c)

(c)

(c)

(b)

(c)

(c)

# Question 33

Lack of oxygen in muscles often leads to cramps among cricketers. This results due to

(a) conversion of pyruvate to ethanol

(b) conversion of pyruvate to glucose

(c) non-conversion of glucose to pyruvate

(d) conversion of pyruvate to lactic acid.

(d)

(c)

(a)

# Question 36

Name the following

(a) The process in plants that links light energy with chemical energy

(b) Organisms that can prepare their own food

(c) The cell organelle where photosynthesis occurs

(d) Cells that surround a stomatal pore

(e) Organisms that cannot prepare their own food

(f) An enzyme secreted from gastric glands in stomach that acts on proteins.

# Question 37

“All plants give out oxygen during day and carbon dioxide during night”. Do you agree with this statement? Give reason.

## Solution:

Plants give out oxygen due to photosynthesis. Photosynthesis is a process where plants use the Sun’s energy to convert water and minerals into oxygen and various organic matter. Therefore, during daytime, plants release oxygen. At night, plants give out carbon dioxide due to lack of Sun’s energy.

# Question 38

How do the guard cells regulate opening and closing of stomatal pores?

## Solution:

Guard cells surround each stoma. When water enters the guard cells, they become turgid and the stomatal pores opens. When water exits from guard cells, they become flaccid and the stomatal pores close. This is how guard cells help regulate opening and closing stomatal pores.

# Question 39

Two green plants are kept separately in oxygen free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons.

## Solution:

The plant which is kept in continuous light will live longer, because it will be able to produce oxygen required for its respiration by the process of photosynthesis.

# Question 40

If a plant releases carbon dioxide and takes in oxygen during daytime, does it mean that photosynthesis is not occuring? Justify your answer.

## Solution:

Plants breathe throughout day and night.  Photosynthesis takes place only in presence of sunlight. Therefore, during day time, plants release oxygen and at night they release carbon dioxide. However, if a plant releases carbon dioxide and takes in oxygen during daytime, it means that the rate of photosynthesis is slow. The carbon dioxide released during respiration is used up for photosynthesis.

# Question 41

Why do fishes die when taken out of water?

## Solution:

Fishes breathe with the help of gills. Gills are designed to specifically inhale oxygen that is dissolved in water, but are not designed to inhale oxygen from air. Therefore, when a fish is taken out of water, it is unable to inhale oxygen in the air and dies quickly.

# Question 42

Differentiate between an autotroph and a heterotroph.

## Solution:

 Autotroph Heterotroph They prepare their own food. They depend on other organisms for food. They have chlorophyll. They lack chlorophyll.

# Question 43

Is ‘nutrition’ a necessity for an organism? Discuss.

## Solution:

Yes, nutrition is necessary for all organisms.

Importance of nutrition

·         It provides energy for various activities.

·         It is required for growth of new cells.

·         It is required for repair of damaged cells.

·         It helps fight against various diseases.

# Question 44

What would happen if green plants disappear from Earth?

## Solution:

Green plants are the direct or indirect sources of energy for all organisms. Green pants help transfer solar energy to other organisms. If all green plants disappear from Earth, all the herbivores will die of starvation and as a ripple effect, all the carnivores will also die.  This will eventually lead to extinction of life from Earth.

# Question 45

Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your answer.

## Solution:

The vaseline coat will create an impermeable layer on the leaves. This will clog the stomata and the leaves will not get oxygen for respiration. Also, photosynthesis will not occur. As a result, the plant will not be able to prepare its food. Eventually, the plant will slowly die.

# Question 46

How does aerobic respiration differ from anaerobic respiration?

## Solution:

 Aerobic respiration Anaerobic respiration Occurs in the presence of oxygen. Occurs in the absence of oxygen. Takes place in cytoplasm (glycolysis) and inside mitochondria (Krebs cycle) Takes place only in cytoplasm. End products are carbon dioxide and water. End products are lactic acid or ethanol and carbon dioxide. More energy is released. Less energy is released.

# Question 47

Match the words of Column (A) with that of Column (B)

 Column (A) Column (B) (a) Phloem (i) Excretion (b) Nephron (ii) Translocation of food (c) Veins (iii) Clotting of blood (d) Platelets (iv) Deoxygenated blood

(a) (ii)

(b) (i)

(c) (iv)

(d) (iii)

# Question 48

Differentiate between an artery and a vein.

## Solution:

 Artery Vein Have thick elastic, muscular walls. Have thin, non-elastic walls. Valves are absent. Valves are present. Carry blood from heart to all body parts. Carry blood from all body parts to heart. Carry oxygenated blood (except pulmonary artery). Carry deoxygenated blood (except pulmonary vein)

# Question 49

What are the adaptations of leaf for photosynthesis?

## Solution:

Leaves show following adaptations for photosynthesis:

(a)   Leaves provide large surface area. This helps absorbing maximum light.

(b)   Leaves are arranged at right angles to the light source. This helps in absorbing maximum light.

(c)    Leaves have extensive network of veins. This enables quick transport of substances to and from the mesophyll cells.

(d)    Leaves have numerous stomata for gaseous exchange.

(e)   The upper surface of leaves have more number of chloroplasts. Chloroplasts enable photosynthesis.

# Question 50

Why is small intestine in herbivores longer than in carnivores?

## Solution:

Digestion of cellulose takes longer time. Herbivores eat grass, and therefore need a longer small intestine to allow complete digestion of cellulose. In case of carnivores, cellulose is not present in their diet, because they eat a protein rich diet that can be easily digested. Therefore, the small intestine of herbivores is longer than that of carnivores.

# Question 51

What will happen if mucus is not secreted by the gastric glands?

## Solution:

Mucus protects the inner lining of stomach from hydrochloric acid. If mucus is not secreted, the inner lining of stomach will be corroded by hydrochloric acid leading to acidity and ulcers.

# Question 52

What is the significance of emulsification of fats?

## Solution:

Food, fats are present in the form of large molecules that make it difficult for the digestive enzymes to act on them. Emulsification of fat breaks down large fat molecules into small molecules, making it easy for the digesting enzymes to digest the fat.

# Question 53

What causes movement of food inside the alimentary canal?

# Question 54

Why is digested food absorbed mainly in the small intestine?

## Solution:

The wall of the small intestine contains glands that secrete intestinal juice. This intestinal juice contains a number of enzymes that help in digestion.

Liver provides villi to the inner lining of the small intestine. This increases the surface area for absorption. The blood vessels in the walls of small intestine take the absorbed food to each cell of the body.

# Question 55

Match Group (A) with Group (B)

 Group (A) Group (B) a) Autotrophic nutrition (i) Leech (b) Heterotrophic nutrition (ii) Paramecium (c) Parasitic nutrition (iii) Deer (d) Digestion in food vacuoles (iv) Green plant

## Solution:

(a)  $—$ (iv)

(b)  $—$ (iii)

(c)  $—$ (i)

(d)  $—$ (ii)

# Question 56

Why is the rate of breathing in aquatic organisms faster than in terrestrial organisms?

## Solution:

Air is not available in large quantity under water and aquatic organisms obtain oxygen in a dissolved state. Since the amount of dissolved oxygen is fairly low, aquatic organisms have to put more effort to breathe oxygen to meet their needs. On the other hand, because of good availability of oxygen in air, terrestrial organisms do not need to put too much effort to breathe. Therefore, aquatic organisms breathe much faster than terrestrial organisms.

# Question 57

Why is blood circulation in human heart called double circulation?

## Solution:

During one cardiac cycle, blood passes through a human heart twice. Once through the right half in the form of deoxygenated blood and secondly through the left half in the form of oxygenated blood. Thus, blood circulation in human heart is called double circulation.

# Question 58

What is the advantage of having a four chambered heart?

## Solution:

A four chambered heart prevents oxygenated and deoxygenated blood from mixing. Blood is received by the upper chambers from rest of the body and is pumped out back to the body by the lower chambers. This segregation between blood received by the heart and then sent out again increases the efficiency of the heart.

# Question 59

Mention the major events during photosynthesis.

## Solution:

The major events during photosynthesis are:

(a) Absorption of sunlight (energy) by chlorophyll.

(b) Conversion of light energy into chemical energy and splitting of water into hydrogen and oxygen.

(d) Reduction of carbon dioxide by hydrogen to form carbohydrates.

# Question 60

In each of the following situations what happens to the rate of photosynthesis?

(a) Cloudy days

(b) No rainfall in an area

(c) Good manuring in an area

(d) Stomata get blocked due to dust

(a) Decreases

(b) Decreases

(c) Increases

(d) Decreases

# Question 61

Name the energy currency in all living organisms. When and where is it produced?

## Solution:

Adenosine triphosphate (ATP) is the energy currency in all living organisms. It is produced during respiration in the mitochondria. It is also produced during photosynthesis.

# Question 62

What is common for cuscuta, ticks and leeches?

## Solution:

The given examples belong to parasites. They derive nutrition from plants or animals without killing them.

# Question 63

Explain the role of mouth in digestion of food.

## Solution:

Mouth plays the following roles in the digestion of food:

(a)      Food is crushed into smaller pieces by the teeth. So that it become easier to swallow the food.

(b)     The smaller food particles are then mixed with saliva. The enzyme amylase (found in saliva) breaks down the starch into sugars.

(c)      Tongue plays the important role of mixing food with saliva.

# Question 64

What are the functions of gastric glands present in the wall of a stomach?

## Solution:

Functions of gastric glands:

(a)   They produce gastric acid.

(b)   They release gastric enzyme pepsin to digest proteins.

(c)   They secret mucus to protect the inner lining of a stomach.

# Question 65

Match the terms in Column (A) with those in Column (B)

 Column (A) Group (B) a) Trypsin (i) Pancreas (b) Amylase (ii) Liver (c) Bile (iii) Gastric glands (d) Pepsin (iv) Saliva

## Solution:

(a) $—$ i

(b) $—$ iv

(c) $—$ ii

(d) $—$ iii

# Question 66

Name the correct substrates for the following enzymes

(a) Trypsin

(b) Amylase

(c) Pepsin

(d) Lipase

## Solution:

(a)$—$ Protein

(b)$—$ Starch

(c)$—$ Protein

(d)$—$ Fats

# Question 67

Why do veins have thin walls as compared to arteries?

## Solution:

Arteries are thick-walled blood vessels. It carries blood from heart to all parts of a body. The blood that emerges from heart is under high pressure. Therefore, to control the pressure, the walls of the arteries have to be thick. Veins collect blood from different organs of the body and carry it to the heart. Veins do not need thick walls as the blood is no longer under high pressure.

# Question 68

What will happen if platelets were absent in blood?

## Solution:

Platelets in blood help in blood clotting. Therefore, absence of platelets will reduce blood clotting causing excessive blood flow during an injury. This might lead to death.

# Question 69

Plants have low energy needs as compared to animals. Explain.

## Solution:

Animals need to move from one place to another in search of food. Plants, on the other hand, do not move. Therefore plants require less energy as compared to animals.

# Question 70

Why and how does water enter continuously into the root xylem?

## Solution:

Root cells are in close contact with soil. They actively take up ions. The osmotic pressure at the roots of a plant is more than the pressure at the leaves due to high ion concentration inside the root. This pressure difference continuously increases the movement of water from the soil into the root xylem.

# Question 71

Why is transpiration important for plants?

## Solution:

Transpiration helps in absorption and upward movement of water and minerals from roots to leaves. It prevents plant parts from heating up. Also, it is a way for plants get rid of excess water.

# Question 72

How do leaves of plants help in excretion?

## Solution:

Many plants store their waste materials in leaves, barks, and fruits. When dead leaves fall off from a plant, these waste materials also get excreted. Apart from this, gaseous waste in plants is removed through stomata in leaves.

# Question 73

Explain the process of nutrition in Amoeba.

## Solution:

Amoeba is a unicellular organism which follows holozoic mode of nutrition. The cell membrane of an amoeba keeps on protruding into temporary finger-like extensions, which surrounds food particles and form a food vacuole. Inside the food vacuole, complex food substances are digested into simpler substances with the help of digestive enzymes. After that, the digested food is diffused into the cytoplasm. Finally, the remaining undigested food material is moved to the surface of the cell and expelled out.

# Question 74

Describe the alimentary canal of man.

## Solution:

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

Mouth: It consists of oral cavity, through which food is ingested. It contains teeth, tongue and three pairs of salivary glands.

Oesophagus: It is also known as food pipe. It begins from the neck and ends in the stomach. The muscular movement of the oesophagus called peristalsis carries the food down to the stomach.

Stomach: Stomach is a bag-like organ. It is a large organ which expands when food enters into it. The highly muscular walls of the stomach help in churning the food thoroughly with more digestive juices.

Small Intestine: It is a highly coiled tube-like structure. It is divided into three parts, namely duodenum, jejunum and ileum.

Large Intestine: The ileum passes into large intestine. It is smaller than the small intestine and the undigested food goes into it. The large intestine is further divided into two parts as anterior colon and posterior rectum. The terminal part of rectum is called anal canal. It opens into the anus, guarded by sphincter muscles. It allows the waste matter to be excreted.

# Question 75

Explain the process of breathing in man.

## Solution:

Breathing is the process of taking in oxygen-rich air and giving out carbon dioxide-rich air.

Breathing in humans involves following steps:

·         Inhalation: When we breathe in, the muscles between the ribs contract causing the ribcage to move upward and outward. Simultaneously, the diaphragm contracts and moves downward. As the chest cavity size increases, air is sucked in from outside into the lungs, the lungs get filled up with air and expand. Thus, the size of our chest increases. Breathing is the process of taking in oxygen-rich air and giving out carbon dioxide-rich air.

·         Gaseous exchange: Haemoglobin in the red blood cells binds with oxygen and carries it through blood. During respiration, blood passes through the tissues of a body, the oxygen from the blood diffuses into various cells and carbon dioxide produced diffuses into the blood. The carbon dioxide-rich blood is carried to the lungs.

·         Exhalation: When we breathe out, the muscles between the ribs relax causing the ribcage to move back and the diaphragm relaxes and moves upward. As the chest cavity becomes smaller, carbon dioxide-rich air is pushed out from the lungs.

# Question 76

Explain the importance of soil for plant growth.

## Solution:

Soil provides the base on which all terrestrial plants and even some aquatic plants grow. Soil is the reservoir of water and minerals essential for all metabolic activities of a plant. The roots of a plant take oxygen required for respiration from soil by process of diffusion. Some plants form symbiotic relationship with soil microbes and absorb minerals such as nitrogen. For example, leguminous plants form symbiotic relationship with the soil because it absorbs minerals from soil.

# Question 77

Draw the diagram of alimentary canal of man and label the following parts.

Mouth, Oesophagus, Stomach, Intestine

# Question 78

How do carbohydrates, proteins and fats get digested in human beings?

## Solution:

Digestion of carbohydrates:

Digestion of carbohydrates starts from the mouth cavity. The saliva secreted in the mouth cavity contains the salivary amylase. It breaks down starch into simple sugar.

$Starch\stackrel{Sali\mathrm{var}y\text{\hspace{0.17em}}\text{\hspace{0.17em}}Amylase}{\to }Sucrose$

Other forms of carbohydrates are digested in small intestine.

Digestion of Proteins:

Partial digestion of protein takes place in stomach with the help of a gastric enzyme called pepsin. Further digestion of protein happens in small intestine.

$\begin{array}{l}Protein+Pepsin\to Peptone+Proteose\\ \left(Protein+Peptone+Proteose\right)+\left(trypsin+chymotrypsin\right)\to Dipeptides\end{array}$

Digestion of Fat:

Fat is at first emulsified by bile and then digested by small intestine.

# Question 79

Explain the mechanism of photosynthesis.

## Solution:

Photosynthesis is a process by which green plants prepare their own food.

During photosynthesis,

·         Sunlight is absorbed by chlorophyll.

·         Light energy is then converted into chemical energy.

·         Water is absorbed from soil and transported to leaves with the help of roots and stem. Then water molecule splits into hydrogen and oxygen.

·         Oxygen, which is the by-product of photosynthesis is released into air.

·         Hydrogen is used for reduction of carbon dioxide to form carbohydrate (glucose) by utilizing the chemical energy. Carbon dioxide enters the leaves from air through tiny pores called stomata.

·         The extra glucose is stored as starch in the leaves of a plant.

The whole process of photosynthesis can be shown by following equation:

# Question 80

Explain the three pathways of breakdown in living organisms.

## Solution:

In the process of respiration, the first step is breakdown of glucose into pyruvate. This process takes place in the cytoplasm. The molecules formed depend on the type of respiration in a particular organism. Respiration is of two types, aerobic respiration and anaerobic respiration.

·         Anaerobic Respiration: This process takes place in absence of oxygen. For example, during yeast fermentation, pyruvate is converted into ethanol and carbon dioxide.

·         Aerobic Respiration: In this type of respiration, breakdown of pyruvate takes place in the presence of oxygen. Hence, optimum output of energy is achieved. The release of energy in aerobic respiration is much more than anaerobic respiration.

# Question 81

Describe the flow of blood through the heart of human beings.

## Solution:

After systemic circulation through-out the body, blood flows into the right auricle of the heart. From the right auricle, the heart, pumps blood into the right ventricle. From the right ventricle, heart pumps blood to lungs through pulmonary artery. Oxygenation of blood takes place in alveoli inside lungs. This oxygenated blood from the lungs flows into the left auricle through pulmonary vein. From left auricle, heart pumps blood into the left ventricle. Finally, from the left ventricle, heart pumps out blood to the body for another round of systemic circulation.

This whole process is repeated continuously. The circulatory system in humans is called double circulation. This is because blood flows twice through the heart during one complete cycle.

# Question 82

Describe the process of urine formation in kidneys.

## Solution:

Urine is formed in the kidneys. Nephrons are the structural and functional 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.

The following steps are involved in the formation of urine:

(i)     Filtration: Blood enters the kidney through the renal artery that branches into many capillaries associated with glomerulus. The filtration of blood takes place in Bowman's capsule under very high pressure. Large molecules remain in the blood.

(ii)  Selective reabsorption: Some molecules are selectively reabsorbed into the blood. Then the filtrate flows through the proximal convoluted tubule, the U-shaped Henle’s loop and distal convoluted tubule. After substances such as glucose, amino acids, and salts are reabsorbed, the filtrate now contains urea, some salts and water. Reabsorption of solutes increases the water concentration of the filtrate.

(iii)            Tubular secretion: Some nitrogenous waste products like creatinine are removed from blood and are added to urine. Then the filterate goes to the collecting duct. The 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.