Samacheer Kalvi 8th Science Solutions Chapter 18 Pdf

Samacheer Kalvi 8th Science Solutions Chapter 18 Pdf

Tamilnadu Board Samacheer Kalvi 8th Science Solutions Chapter 18: Tamilnadu State Board Solution Class 8 Science Chapter 18 – Organisation of Life.

Samacheer Kalvi 8th Science Solutions Chapter 18: Overview

Board

Samacheer Kalvi
Class

8

Subject

Science
Chapter

18

Chapter Name

Organisation of Life


Samacheer Kalvi 8th Science Solutions Chapter 18 Pdf

(I) Choose the best answer .

( 1) Sclera is tough and thick white sheath that protects the inner parts of the eye.

a ) Sclera  

b) Conjunctiva

c) Cornea

d) Iris

(2) Stem cells are specialised cells that can be transformed into any kind of cells.

a ) Nerve

b) Stem

c) Heart

d) Bone

(3) Maintenance of constant internal environment of the body is known as homeostasis.

a) homeostasis

b) homeophytes

c) homeokinesis

d) homeophilics

(4) In the absence of oxygen, glucose is broken down into lactic acid .

a ) lactic acid 

b) citric acid

c) acetic acid

d) nitric acid

(5) The process of air passing in and out the lungs is called breathing.

a ) inhalation

b) exhalation

c) breathing

d) None of these

(6) Osmosis is the movement of water molecules from lower concentration to a region of higher concentration.

a ) higher concentration to a region of lower concentration.

b) lower concentration to a region of higher concentration.

c) Both of these

d) None of these

7 ) The erythrocyte is placed in hypotonic solution which has lesser concentration of solutes and greater concentration of water than in the cytoplasm.

a ) hypotonic 

b) hypertonic

c) neutral

d) acidic

(II) Fill in the blanks.

1 ) Cell is the structural and functional unit of living organisms.

2)  The largest cell is egg of an ostrich.

3) Yeast is a good example for anaerobic respiration.

4) Optic nerve is located at the end of the eyes behind the retina.

5) The size of the cells are measured in units of microns.

(III) Match the following .

Carbohydrates CO2, Water and Heat
Glucose Amino acid
Protein Glucose
Amino acids Cholesterol and other steroid
Fatty acids Enzymes, hormone, protein

Answer

Carbohydrates Glucose
Glucose CO2, Water and Heat
Protein Amino acid
Amino acids Enzymes, hormone, protein
Fatty acids Cholesterol and other steroid

(IV) State true or false. If false, correct the statement.

1 ) In hypotonic condition, concentration of the external and internal solution of the organism are same.

This statement is false.

Explanation:

In hypotonic condition, concentration of the external and the internal solution of the organism are not same but rather, concentration of the external solution is less in comparison to the concentration of internal solution of the organism.

2) Diffusion is the movement of particles from an area of lower concentration to higher concentration.

This statement is false.

Explanation:

Diffusion does not refer to the movement of particles from an area of lower concentration to higher concentration but rather , diffusion depicts the movement of particles from an area of higher concentration to lower concentration.

3) Human beings are warm blooded in nature.

This statement is true.

4) The larynx has fold of tissue which vibrate with the passage of air to produce sound.

This statement is true.

5) Aqueous humour plays an important role in maintaining the shape of the eye.

This statement is false.

Explanation:

Aqueous humour does not play an important role in maintaining the shape of the eye but rather, it is vitreous humour that performs an essential role in maintaining the shape of the eye.

(V) Answer very briefly.

1 ) What is cell differentiation?

Zygote refers to a single cell from where our body is developed. The zygote goes through the process of constant mitotic  division which leads to the formation of foetus that contains multiple of cells of varying size ,shape and content. Therefore, a gradual change is acquired in the structure and function of the foetal cells and this process is termed as cell differentiation.

2) State different types of tissues.

Tissues can be categorized into fourtypes on the basis of their structure and function.

1 ) Epithelial ( covering) tissue -performs an important role in rendering protection.

2) Muscular ( contractile) tissue – functions in such a manner that facilitates movement and locomotion.

3) Connective ( supporting) tissue -The main role of this tissue is to bind the different structures of the body.

4) Nervous tissue -plays an important role in conducting nerve impulses.

So, these are the four basic types of tissues that are contained in almost all the complex organisms.

3) Mention the function of ‘Alveoli ‘.

Alveoli are extremely small air sacs in the lungs that are situated at the terminal point of bronchial tubes ,which depicts a microscopic nature . It’s primary function is to permit the rapid exchange of oxygen and carbon dioxide during the process of inhalation and exhalation.

4) Name the processes by which air enters and comes out of our lungs.

Inspiration or inhalation refers to the process of taking air into the lungs. This process ultimately facilitates in transporting oxygen into our body. Expiration or exhalation on the other hand, refers to the process of expelling air from the lungs. This process renders support in giving out carbon dioxide.

5) Differentiate osmoconformers and osmoregulators .

Osmoconformers

  • In order to maintain the osmolality of their body, these organisms try to match up with their surrounding environment. Invertebrates and marine organisms depicts a perfect example.

Osmoregulators

  • These organisms goes through physiological process for the purpose of maintaining their internal osmolality, irrespective of their surrounding environment. Freshwater fish is one of the most relevant example.

6) Define- Metabolism

Metabolism refers to the sum total of chemical reaction that facilitates the sustenance of living organisms. Metabolism is composed of anabolism and cetabolism . Metabolism refers to the process of breaking down of food and its conversion into energy, cellular products and elimination of waste matter .

( VI) Answer briefly .

1 ) Define – Prokaryotic cell

Organisms can be categorized into prokaryotes and eukaryotes, on the basis of their structural organization. Bacteria, cyanobacteria and mycoplasm are for instance those organisms that does not possess true nucleus and these organisms are known as prokaryotes .

2) Tabulate the differences between aerobic and anaerobic respiration.

The differences between aerobic and anaerobic respiration are as follows :

Aerobic respiration

  • Oxygen plays an important role in executing aerobic respiration.
  • Carbon dioxide and water represents the end products of aerobic respiration.
  • Aerobic respiration occurs in almost all higher plants and animals.

Anaerobic respiration

  • Oxygen does not play an important role in executing anaerobic respiration,which means this process take place without the presence of oxygen.
  • CO2, ethanol or lactic acid represents the end product of anaerobic respiration.
  • Anaerobic respiration occurs in specific microorganisms and human muscle cell, during the course of their strenuous activity.

3) Why the human eye is compared with camera ?

Iris

The main function of iris is to regulate the size of the pupil on the basis of the quantity of light entering it.

Pupil

Pupil acts as the eyehole of a camera by permitting light to enter within it.

Lens

Lens is a transparent medium that is composed of protein. The light is refracted by the lens with the aid of cornea, which after converging on the retina leads to the formation of images on it.

Retina

The primary function of retina is to convert light into impulses. The optic nerve then performs an important role by transporting the signals to the brain. Therefore, the film in a camera can be compared with the retina.

Due to the above reasons, human eye is compared with camera.

4) Which organ and organ system help to maintain homeostasis.

Homeostasis refers to any self-regulating process, that are utilised by living things for the purpose of maintaining their stable conditions that is essential for existence. There is an occurrence of regulation in a  defined internal environment. Mammals possesses the ability to maintain their constant body temperature, regardless of the changes in the external temperature. The stability of homeostasis can be maintained with the help of behavioral and physiological responses and these responses are regarded as two important regulating mechanisms. Nervous and hormonal system plays a significant role in mediating all the processes of integration and coordination of function. The liver, kidney and brain, autonomic nervous system and the endocrine system performs an essential part for the purpose of maintaining homeostasis.

( VII) Answer in detail.

2) Explain osmosis with an example.

Osmosis

The tendency of solvent particles to move across a semipermeable membrane from a less concentrated solution into a more concentrated solution and this process is known by the term of osmosis. There is an occurrence of movement because solvent tries to equate the concentration on both sides of the membrane by trying to dilute the concentrated solution. There is a dependency of liquids that is moving in and out of the cells, on the concentration of the surrounding solution. Isotonic, hypotonic and hypertonic are mainly the three types of solution in which this could differ to a certain extent.

Isotonic

In this case, an equivalency prevails in the concentration of external and internal solution of the organism.

Hypotonic

In this case, the concentration of external solution is less in comparison to the concentration of the internal solution of the organism. So in this situation, water will depict the tendency to flow into the organism.

Hypertonic

In this situation, the concentration of external solution is greater in comparison to the concentration of the internal solution of the organism. So in this case, water will tend to flow out of the organism.

3) Differentiate between inhalation and exhalation.

The differences between inhalation and exhalation are as follows:

Inhalation :

  • Inhalation occurs with the contraction of the diaphragm muscles.
  • The diaphragm moves in a downward direction.
  • The ribs tends to proceedboth upward and outwards.
  • There is an expansion in the volume of thoracic cavity.
  • Air reaches the lungs with the help of nose.

Exhalation

  • Exhalation occurs with the relaxation of the diaphragm muscles.
  • The diaphragm proceeds in a upward direction.
  • The ribs depicts the tendency to move in a downward direction.
  • There is a reduction in the volume of thoracic cavity.
  • In exhalation, nose performs an opposite role, which means it helps to expel the air from the lungs.

4) List out the different types of metabolism with an example.

Metabolism refers to the sum total of chemical reaction that facilitates the sustenance of living organisms. Metabolism is composed of anabolism and cetabolism . Metabolism refers to the process of breaking down of food and its conversion into energy, cellular products and elimination of waste matter .

a ) Anabolism

Anabolism is also called constructive metabolism, whose main concern is to laid emphasis on building and storing. It not only facilitates the growth of new cells but it also renders  support for the maintenance of body tissues. It helps to store the energy which could be utilised in the subsequent time period. During anabolic process, small molecules are transformed into relatively large and complex molecules.

The breakdown of glucose into glycogen and other sugars portrays one of the most relevant example.

b) Catabolism

Catabolism is also called destructive metabolism . Catabolism refers to the production of energy that is essential for executing all activity in the cells. In this procedure, large molecules are broken down for the purpose of releasing energy. This energy not only supplies fuel for  anabolism but also facilitates muscles contraction ,which in turn promotes the movement of the body. During catabolic process, complex units are transformed into simple substances. Thus, skin ,kidneys lungs and intestines plays an important role in removing the waste produces that are released during the process of catabolism.

The breakdown of carbohydrates into glucose depicts a perfect example.

5) Explain the mechanism of breathing .

Inspiration (Inhalation)

Inspiration or inhalation refers to the process of taking air into the lungs. This process ultimately facilitates in transporting oxygen into our body. During the process of inhalation, the sternum tends to move upwards and outwards and the diaphragm on the other hand,depicts the tendency to proceed in a downward direction. This leads to an expansion in the volume of thoracic cavity, that ultimately contributes in reducing the pressure. The air reaches the lungs with the help of nose. Therefore, there is an occurrence of gaseous exchange between the air and the blood.

Expiration( Exhalation)

Expiration or exhalation refers to the process of expelling air from the lungs. This process renders support in giving out carbon dioxide. During the process of exhalation, there is an expulsion of air from the lungs. The relaxation of the inner costal muscles enables the chest wall to return to its actual position. During the process of exhalation, the diaphragm tends to move in an upward direction. This leads to a reduction in the volume of thoracic cavity that ultimately contributes in enhancing the pressure. This pressure gradient performs an essential role in expelling the air out of the lungs. So, this movement of air out of the lungs is considered as a passive event.

(VIII) Higher Order Thinking Questions.

1 ) Why do we need instant energy? Does glucose give that energy? Explain.

Energy is essential for executing several activitiesof the body and this energy is obtained through consumption of food. Hence ,in this way energy is supplied to the entire organ systems. In order to perform physical activities, energy is required, which will facilitate smooth functioning of the activities. Glucose represents a simple form of sugar. Hence, glucose plays an important role, as it can be dissolve quickly into the blood. In this way it reaches the organs of the body which ultimately helps in providing the instant energy that is required for performing all the activities of the cell.

2) How are we preparing pickles? What are the steps involved in that?

An excessive amount of salt is added in the preparation of pickles. So as a result of which, a higher concentration is created by the salty solution in the outer coverage of the vegetable that is used for the purpose of making pickles. When vegetable begins to shed water, then it goes through the process of plasmolysis which leads to it’s  shrinkage. Therefore, the pickle can be stored for quite a long period of time ,the moment it loses the water content.

(IX) Value Based Questions.

1 ) Dr. Usha is a pulmonologist ( Doctor for respiratory diseases) . One day, a school student named Arjun, met her with respiratory problems. After diagnosis, the doctor advised him to go to playground daily and play football or basketball. She also advised him to do pranayamam in the morning.

a ) Why did the doctor advised him to go to the playground?

The doctor recommended him to go to the playground because if he will indulge himself in playing then it will contribute to enhance his breathing process and will also improve the circulatory system in the body. So, this in turn will help him to get rid of his respiratory diseases.

b) What is the use of pranayamam?

Pranayamam helps in improving the circulation of the blood. We should always follow a proper mechanism for breathing and this technique is included in pranayamam. Pranayamam contributes in enhancing the capability of the lungs, which will facilitate in providing sufficient amount of oxygen into the body.Pranayamam is very effective for those persons who is having difficulty in breathing and undergoing respiratory problems.

2) Explain why you are not able to breathe normally when you are in closed and crowded places?

It is difficult to breathe normally in a closed and crowded places because the gathering of  people are much more in crowded areas. As we all know that, we breathe oxygen and give out carbon dioxide, soall the people will also excel carbon dioxide. As a result of which, the quantity of carbon dioxide in the air will exceed in comparison to the quantity of oxygen that is available for breathing. Therefore, there will be shortage of oxygen for breathing.

3) Shylesh is a school going kid studying standard VIII . He is crazy about playing video games in mobile phones. After couple of months, his eyes turned red and he felt severe pain in his eyes. His science teacher enquired about this and advised his parents to take him to an eye doctor.

i ) How does excessive usage of mobile phone affect our eyes?

The radiation that comes out of the mobile phone poses a severe damage to the eyes ,which can ultimately lead to the occurrence of early cataracts. Excessive usage of cell phone can prove to be very harmful, as it can  blurry the vision and exert pressure on the eye muscles. It can also lead to several problems like dryness of the eye, causing itchiness and tremendous pain in the eyes. Apart from these problems, mobile phones can also bring about a negative effect on our nervous system. An excessive usage of cell phone can also cause disturbance in sleeping pattern.

(ii) What are the values shown by teacher?

Care and responsibility are for instance, some of the values that are shown by the teacher.

  • The science teacher recommended his parents to take him to an eye care specialist, as he was facing severe problem in his eyes due to the excessive usage of mobile phone. So, this point clearly portrays the value of care.
  • After enquiring about the particular issue, the science teacher took an initiative to inform his parents about the problem. So, this point clearly depicts the value of responsibility.
Updated: December 6, 2021 — 12:28 pm

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