Chapter 7


Q1. Why do we classify organisms?


By classifying organisms, it is easier and more convenient to study their characteristics. Similarities exhibited by various entities allow us to categorize different entities into a class and hence study the group as a whole.

Q2. Give three examples of the range of variations that you see in life-forms around you.


Listed below are a few ranges of variations observed in life-forms:

(a) Small frog to big whale

(b) Creeper to the eucalyptus tree

(c) Black cuckoo to colourful peacock.

Q3. Which do you think is a more basic characteristic for classifying organisms?

(a) the place where they live.

(b) the kind of cells they are made of. why?


The most basic classification of organisms should be established on the kind of cells they are made up. This is because the habitat can have species with different characteristics living harmoniously whereas the entities with similar cell arrangement will exhibit equivalent characteristics.

Q4. What is the primary characteristic on which the broad division of organisms is made?


The basic characteristic on which organisms are primarily divided is the nature of cells. It is broadly classified as prokaryotic cells and eukaryotic cells which furthermore is classified into subclasses.

Q5. On what basis are plants and animals put into different categories?


The following is the basis for categorization of plants and animals:

(a) The most fundamental consideration of classification is the presence and absence of a cell wall.

(b) The next important criterion is the mode of nutrition. The mechanism through which entities acquire their nutrients is used as the base for classification.

Q6. Which organisms are called primitive and how are they different from the so-called advanced organisms?


Primitive organisms are the organisms that exhibit a very simple and basic cell arrangement, mechanism and structure and no division of labour is observed. Advanced organisms, on the other hand, are the organisms possessing millions of cells that are grouped into various organs performing different functionality such as mammals.

Q7. Will advanced organisms be the same as complex organisms? Why?


Yes. Complex organisms are the same as advanced organisms. The consequence of advancement leads to multiple cell arrangements that operate uniquely.

Q8. What is the criterion for classification of organisms as belonging to kingdom Monera or Protista?


One of the most significant differences in classification is the development of the nucleus. The ones with no nuclear membrane are defined to be Monera while the ones that have well-defined nuclei walls are Protista.

Q9. In which kingdom will you place an organism which is single-celled, eukaryotic and photosynthetic?


Since the cell is photosynthetic, it must have a well-defined nucleus wall. Therefore it needs to be placed in Protista kingdom.

Q10. In the hierarchy of classification, which grouping will have the smallest number of organisms with maximum common characteristics and which will have the largest number of organisms?


(a) The organisms belonging to the Kingdom Monera will have the smallest number of organisms and with maximum characteristics in common.

(b) The organisms belonging to the Kingdom Animalia will have the largest number of organisms.

Q11. Which division among plants has the simplest organisms?


Algae or Thallophyta has the simplest organisms among the plants.

Q12. How are pteridophytes different from the phanerogams?


The following are the differences:



They possess a naked embryo

They possess a covered embryo

Exhibit unclear reproductive organ

Exhibit well-defined reproductive organ

Q13. How do gymnosperms and angiosperms differ from each other?


In gymnosperms, the seeds are naked while in angiosperms the seeds are covered.

Q14. How do poriferan animals differ from coelenterate animals?


Listed below are the differences:



Division of labour is not noticed

Division of labour is observed

Cellular level of organization exhibited

Tissue level of organization exhibited

Coelom absent

Coelom present

Q15. How do annelid animals differ from arthropods?


Listed below are the differences:



The entire body is segmented into rings

Segmentation of body into head, abdomen and the thorax region

Skeleton is absent

Presence of exoskeleton


Presence of different sexes, bisexual present

Q16. What are the differences between amphibians and reptiles?


Listed below are the differences:



Skin is moist and soft

Skin is hardened

In water, they breathe through their skin

Can exist in water. They come to land to intake oxygen

Respire through lungs or gills

Respire through lungs

Capable of jumping

They crawl

Indirect development is noticed

Direct development observed

Q17. What are the differences between animals belonging to the Aves group and those in the mammalian group?


Listed below are the differences:


Q1. What are the advantages of classifying organisms?


Listed below are the advantages of classification of organisms:

  • When organisms are classified, their common features can easily be studied.
  • The study of scientific experiments is simplified.
  • The interrelation of humans with other entities can be interpreted. Their dependence and interactions can be studied.
  • When entities are crossbred and modified genetically, it paves the way for commercial applications.

Q2. How would you choose between two characteristics to be used for developing a hierarchy in classification?


The basis of the start of the hierarchy will be formed by the Gross character while the basis of steps further will be taken care of by the fine character.

For instance:

  • Human beings are categorized under vertebrates as they possess the vertebral column
  • For categorization of tetrapods,
  • For Tetrapods, the existence of four limbs is taken into consideration.
  • In the case of mammals, the mammary gland is the required part.

Q3. Explain the basis for grouping organisms into five kingdoms.


The following factors govern the basis of grouping organisms into five kingdoms,

  • The number of cells present forms the first criteria.
  • Next is the arrangement and the number of layers present.
  • Another important factor for classification is the existence of cell wall
  • Classification of complex organisms is also based on the mode of intake of nutrition
  • To classify, we consider the organization level too.

Q4. What are the major divisions in the Plantae? What is the basis of these divisions?


The following table depicts plant division and the basis of classification for each division.


Basis of Classification

Thallophyta or Algae

Like body


The body is divided into leaf and stem


The body is separated into root, stem and leaf


Seed-bearing, naked seeds


Seed bearings covered seeds

Q5. How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals?


  • One of the major specifications to categorize plants into Thallophytes and Bryophytes is the basic cell structure.
  • Gymnosperms and Angiosperms are classified on the basis of visibility of seeds.

Hence, morphological characteristics play a key role in plant classification. In animal classification, cytology is considered primarily as more minute structural variations are taken into account.

  • The cell layers, cytology, morphology are significant features to be considered in the classification of animals.
  • The presence and absence of various features decide the classification of higher hierarchies.

Q6. Explain how animals in Vertebrata are classified into further subgroups.


Vertebrata has two subclasses namely

  • Pisces
  • Tetrapod

Wherein, organisms belonging to Pisces subclass have a streamlined body with tails and fins which help them in their movement (swim) whereas, the Tetrapoda species have four limbs for their movement.

Furthermore, The tetrapod animals are classified as:

1. Amphibia: The animals belonging to this group are adaptive in nature. They dwell both in the land as well as in water. They show the presence of specialized organs which allows them to breathe underwater.

2. Reptilia: The animals belonging to this class crawl. Their skin is very thick and withstands extreme temperatures.

3. Aves: The forelimbs of these organisms are modified which help them in their flight. They lack teeth and instead have a beak and feathers that cover up their body.

4. Mammalia: The animals belonging to this group show nurturing skills as they contain mammary glands to support them. Their skin is covered with hair and most of them are viviparous in nature.




Q1. Who discovered cells, and how?


In 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The miniscule boxes are referred to as cells.

Q2. Why the cell is called the structural and functional unit of life?


Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

Q3. How do substances like CO2 and water move in and out of the cell? Discuss.


CO2 moves by diffusion – This cellular waste accumulates in high concentrations in the cell, whereas the concentration of CO2 in the external surroundings is comparatively lower. This difference in the concentration level inside and out of the cell causes the CO2 to diffuse from a region of higher(within the cell) to a lower concentration.

H2O diffuses by osmosis through the cell membrane. It moves from a region of higher concentration to a lower concentrated region through a selectively permeable membrane until equilibrium is reached.

Q4. Why is the plasma membrane called a selectively permeable membrane?


The plasma membrane is called a selectively permeable membrane as it permits the movement of only a certain molecule in and out of the cells. Not all molecules are free to diffuse.

 Q5. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Prokaryotic Cell

Eukaryotic Cell

1.   Size: Generally small (1-10 μm)

1 μm = 10-6m

2.   Nuclear region:



and known as ___________________

3.  Chromosome: single

4.  Membrane-bound cell organelles absent.

1.  Size: Generally large (5-100 μm)

2.  Nuclear region: well defined and 

surrounded by a nuclear membrane.

3. More than one chromosome.

4. ______________________________




Prokaryotic Cell

Eukaryotic Cell

1.  Size: Generally small (1-10 μm)

1 μm = 10-6m

2.  The nuclear region is poorly defined due to the absence of a nuclear membrane and known as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

2. Nuclear region: well defined and 

surrounded  by a nuclear membrane.

3. There are more than one 


4. Membrane-bound cell organelles 


Q6. Can you name the two organelles we have studied that contain their own genetic material?


The two organelles which have their own genetic material are:

  1. Mitochondria
  2. Plastids

Q7. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?


In the event of any damage to cells and when the revival of cells is not possible, Lysosomes burst and enzymes digest such cells. This is why lysosomes are often referred to as ‘suicide bags’.

Q8. Why are lysosomes known as suicide bags?


When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

Q9. Where are proteins synthesised inside the cell?


Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

Q1. Make a comparison and write down ways in which plant cells are different from animal cells.


The following table depicts the differences between plant cells and animal cells.


Plant Cell

Animal Cell

Cell wall



Shape of cell

Distinct edges, shape is either rectangular or square shaped.

Round and irregular 



Present. Lies on one side of the cell

Present. Lies in the 

center of the cell


Rarely present

Always present




Structure of Vacuoles

Single or a few large vacuole that is centrally located

Presence of numerous and small vacuoles

Q2. How is prokaryotic cell different from a eukaryotic cell?


Prokaryotic Cell

Eukaryotic Cell

1.  Size: Generally small (1-10 μm)

1 μm = 10-6m

2.  The nuclear region is not well defined as the nuclear membrane is absent and is referred to as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

2. Nuclear region: well defined and girdled by a nuclear membrane.

3. There are more than one chromosomes.

4. Membrane-bound cell organelles present.

The following are the differences between prokaryotic and eukaryotic cells.

Q3. What would happen if the plasma membrane ruptures or breaks down?

Solution: If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.

Q4. What would happen to the life of a cell if there was no Golgi apparatus?


The Golgi apparatus consists of stacks of membrane-bound vesicles whose functions are as follows:

  • storage of substances
  • packaging of substances
  • manufacture of substances

Without the golgi apparatus, the cells will be disabled from packing and dispatching materials that were produced by the cells. The golgi apparatus is also involved in the formation of cells. Hence, in the absence of golgi apparatus, cells will not be produced.

Q5. Which organelle is known as the powerhouse of the cell? Why?


Mitochondria are known as the powerhouse of the cell. It is because it releases the energy required for different activities of life. Mitochondria releases energy in the form of ATP(Adenosine triphosphate) molecules, essential for numerous chemical activities of life. Hence ATP is often referred to as ‘energy currency of the cell’.

Q6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Ans: Lipids and proteins are synthesised in the ER [Endoplasmic Reticulum].

Q7. How does an Amoeba obtain its food?


Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed forming a food vacuole girdling it which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once food is trapped.

Q8. What is osmosis?


The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

Q9. Carry out the following osmosis experiment:
Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then observe the four potato cups and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed out portions of A and D.


(i) Water accumulates in the hollowed portions of B and C as a difference in the water concentration

is observed. Thereby, endosmosis occurs as the cells act as a semipermeable membrane.

(ii) Potato A is essential in this experiment as it is significant to compare different scenarios seen in

potato cups B, C and D. The potato A in this experiment clearly shows that the potato cavity on its

own cannot bring about water movement.

(iii) Cup in A does not show any change in the water flow concentration for osmosis to occur, which

requires the concentration to be higher than the other. Cells in cup D are dead, thus there is no

existence of a semipermeable membrane for water flow. Consequently, osmosis does not occur.

Q10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?


There are two ways in which a cell divides:

  • Mitosis
  • Meiosis

Mitosis is the type of cell division that is involved in the growth and repair of body whereas meiosis is a type of cell division which results in the formation of gametes.