NCERT Exemplar for Class 8 Science Solutions Chapter 8 Cell—Structure and Functions

Multiple Choice Questions

1. Choose the correct statement with respect to unicellular organisms:

(a)In unicellular organisms, tissues work in co-ordination to perform different functions.

(b) unicellular organisms do not require food.

(c) unicellular organisms respire and reproduce.

(d) all unicellular organisms move by cilia.

Ans: Option C is the correct answer.

Explanation: Unicellular organisms reproduce by asexual method of reproduct and respire through their surface. Unicellular organisms require food to perform activities. The division of labor is absent in them as they are made up of single cells (not tissue).

2. Majority of cells cannot be seen directly with our naked eyes because:

(a) organisms are generally unicellular

(b) cells are microscopic

(c) cells are present only inside the body

(d) cells are grouped into tissues

Ans: Option B is the correct answer

Explanation: Majority of the cells can be seen only on a microscopic level. These cells are very small and can not be seen with naked eyes.

3. Read the different combinations of terms given below:

(a) cell wall, cell membrane, nucleus, plastid

(b) cell wall, nucleus, ribosome, chromosome

(c) cell membrane, mitochondria, ribosome, chromosome

(d) cell membrane, ribosome, mitochondria, chloroplast. 

The correct combination of terms with reference to an animal cell is _____.

Ans: Option C is the correct answer

Explanation: Cell membrane, Mitochondria, ribosome and chromosome are present in an animal cell. The cell wall and chloroplast characteristics features of a plant cell.

4. Which one of the following terms is not a part of the nucleus?

(a) ribosome

(b) nucleolus

(c) chromosome

(d) gene

Ans:  Option A is the correct answer

Explanation: Ribosomes are often found attached to the endoplasmic reticulum and floating in the cytosol.

5. A suitable term for the various components of cells is

(a) tissue

(b) cell organelles

(c) chromosomes

(d) genes

Ans: Option B is the correct answer

Explanation: Cell organelles are the various components of a cell such as nucleus, golgi apparatus and mitochondria etc.

6. The jelly-like fluid substance present in cells is called

(a) protoplasm

(b) chromosome

(c) chloroplast

(d) cytoplasm

Ans: Option D is the correct answer

Explanation: Cytoplasm fills the space between membrane and nucleus. The structure of cytoplasm is jelly-like fluid.

7. Read the following pairs of examples of organisms:

(a) moss and sponge

(b) yeast and Amoeba

(c) bacteria and blue-green alga

(d) penicillium and Spirogyra

The pair that belongs to the group prokaryotes is_____

Ans: Option C is the correct answer

Explanation: Prokaryotic cells are typically unicellular, rarely multicellular. These cells do not contain cell organelles and chromosomes. Bacteria and blue green algae belong to the group of prokaryotes. 

8. Read the following terms and select the pair that is related to inheritance of characters.

(a) cell wall and cell membrane

(b) chromosome and mitochondria

(c) chloroplast and cell membrane

(d) chromosome and genes

Ans: Option D is the correct answer

Explanation: Chromosomes are found in nucleus and contain genes. Genes are the hereditary unit. Genes and chromosomes possess inheritance characters.

9. Choose the correct statement:

(a) Genes are located in the chromosomes.

(b) Cell is located in the nucleus.

(c) Chromosomes are located in the nucleolus.

(d) Cell membrane surrounds the nucleus.

Ans: Option D is the correct answer

Explanation: Genes are the unit of heredity and responsible for inheritance. The genes are located in the chromosomes. Cell membrane surrounds the cytoplasm which contains cell organelles such as ribosomes, nucleus and golgi apparatus etc. Nucleus is located in the cell. Chromosomes are located in the nucleus. 

10. Green colour of leaves is due to presence of the pigment_____

(a) chlorophyll

(b) ribosomes

(c) mitochondria

(d) chloroplast

Ans: Option A is the correct answer

Explanation: Chlorophyll is responsible for the green colour of leaves. It absorbs solar energy and helps to make food for trees through the photosynthesis process.

11. The unit of measurement used for expressing dimension (size) of cells is:

(a) centimeter

(b) millimeter

(c) micrometer

(d) metre

Ans: Option C is the correct answer

Explanation: Most cells are small in size and the unit of measurement of cell size is micrometer.

12. The most important function of cell membrane is that it:

(a) controls the entry and exit of materials from cells.

(b) controls only the entry of materials into cells.

(c) controls only the exit of materials from cells.

(d) allows entry and exit of materials without any control.

Ans:  Option A is the correct answer

Explanation: Cell membrane is a semipermeable membrane, controls the outgoing and incoming of the materials. It helps to give shape to the cells and protects it also.

13. Paheli accidentally placed her hand over a flame and immediately pulled it back. She felt the sensation of heat and reacted due to the action of

(a) blood cells

(b) skin surface

(c) nerve cells

(d) nucleus of cells

Ans: Option C is the correct answer

Explanation: Nerve cells help to transmit and receive the messages from the brain and body. Nerve cells play a vital role in feeling the sensation and other stimuli such as heat, pain and temperature.

14. Of the following parts of a cell listed below, name the part that is common to plant cell, animal cell and a bacterial cell.

(a) chloroplast

(b) cell wall

(c) cell membrane

(d) nucleus

Ans:  Option C is the correct answer

Explanation: Cell membrane is common in plant cells and animal cells. Chloroplast and Cell wall are characteristic of plant cells but not present in animal cells. Nucleus is a common characteristic of plant and animal cells but absent in bacterial cells.

15. The thread-like structures present in the nucleus are

(a) nucleolus

(b) chromosomes

(c) genes

(d) ribosomes

Ans:  Option B is the correct answer

Explanation: Chromosomes are the thread-like structure. They’re found in the nucleus.

16. Identify the statement which is true for cells.

(a) Cells can be easily seen with naked eyes.

(b) Insect’s egg is not a cell.

(c) A single cell can perform all the functions in a unicellular organism.

(d) The size and shape of cells is uniform in multicellular organisms

Ans: Option C is the correct answer

Explanation: Unicellular organisms can perform every function.

17. Which of the following is not a cell?

(a) Red Blood Corpuscle (RBC)

(b) bacterium

(c) spermatozoa

(d) virus

Ans: Option D is the correct answer

Explanation: Virus is not a cell. In cell theory it is an exception, it is not included in living organisms nor non-living organisms because they use host machinery to synthesize their protein and to reproduce.

18. Which of the following features will help you in distinguishing a plant cell from an animal cell?

(a) cell wall

(b) cell membrane

(c) mitochondria

(d) nucleus

Ans:  Option A is the correct answer

Explanation: Cell wall is different between a plant and an animal.

19. Under a microscope Paheli observes a cell that has a cell wall but no distinct nucleus. The cell that she observes is

(a) a plant cell

(b) an animal cell

(c) a nerve cell

(d) a bacterial cell

Ans:  Option D is the correct answer

Explanation: A prokaryotic cell possesses a cell wall but no distinct nucleus. This cell is found only in bacteria. So, high chances are that the cell observed by Paheli is a bacterial cell.

20. Cheek cells do not have _______

(a) cell membrane

(b) nucleus

(c) golgi apparatus

(d) plastids

Ans: Option D is the correct answer

Explanation: Cheek cells are animal cells which do not have plastids. Plastids are found in plant cells.

21. Identify the correct statement.

(a) Tissue is a group of dissimilar cells.

(b) An organ consists of similar cells.

(c) Vacuoles are not found in plant cells.

(d) Prokaryotes do not have nucleus.

Ans: Option D is the correct answer

Explanation: Prokaryotic cells do not have nucleus thus their genetic material is  concentrated in nucleoid. The prokaryotic cells do not contain cell organelles which are found in animal cells.

22. Which of the following statements are true for eukaryotic cells?

(i) They do not have a nuclear membrane.

(ii) They have a well organised nucleus.

(iii) They have a nuclear membrane.

(iv) Blue green algae are eukaryotic cells.

(a) ii and iv

(b) ii and iii

(c) i and ii

(d) i and iv

Ans: Option B is the correct answer

Explanation: Eukaryotic cells have a well organized nucleus and a nuclear membrane. Blue green algae comes under prokaryotes which are found in bacteria and they also do not have a nuclear membrane.

23. Identify the correct statement about cells.

(a) All the cells have a nucleus.

(b) Cells of an organ have similar structure.

(c) Cells of a tissue have similar structure.

(d) Shape of all types of cells is round.

Ans: Option C is the correct answer

Explanation- Tissues are the group of cells which are similar in structure and perform the same function.

24. The table given below has certain terms and four blank spaces named A, B, C and D. From the options given below choose the correct combination of terms.

(a) A-Pseudopodia; B-Respirations; C-Muscle cell; D-Branched

(b) A-Pseudopodia; B-Photosynthesis; C-Muscle cell; D-Branched

(c) A-Contractile vacuole; B-Photosynthesis; C-Blood cell; D-Spindle shaped

(d) A-Pseudopodia; B-Photosynthesis; C-Cheek cell; D-Spindle shaped

Ans: Option B is the correct answer

Very Short Answer Questions

25. In leaves, name the cell organelle and pigment that is responsible for green colour.

Ans: Chloroplasts contain chlorophyll which is  responsible for the green colour of leaves. Chlorophyll enables plants for photosynthesis.

26. The instrument used to observe cells is ________

Ans: Microscope is used to observe structure of the cells because cells are very small in size, and can not be seen with naked eyes.

27. We do not sense any pain when we clip our nails or cut our hair. Why?

Ans: Nails and hairs are the dead cells of the human body and do not connect with the nerve cell. That’s why we don’t feel any kind of sensation.

28. In a cell, where are the genes located?

Ans: Genes are located in chromosomes and called the units of heredity. Chromosomes are present in the nucleus of  a cell.

29. Amoeba and Paramecium belong to which category of organisms?

Ans: These belong to the protozoan category.

30. What are the functions of the cell wall in plant cells?

Ans: Cell wall gives shape to cells and also protects plant cells from mechanical damage.

Short Answer Questions

31. Is the following statement correct? If it is wrong, correct the statement Statement : 

“Unicellular organisms do not respire, only multicellular organisms respire”

Ans: The given statement is wrong as all the species or organisms respire. 

Explanation: Respiration is a metabolic process by which organisms obtain energy to perform various activities. And energy is required by all organisms whether unicellular or multicellular organisms. 

In unicellular organisms respiration occurs  by diffusion through their surface. Whereas in multicellular organisms, specialised organs are found.

32. Match the terms given in column I with their functions given in column II and fill the blanks given below the table:

A-_____; B-______; C-______; D-______

Ans: A - iii ; B- iv ; C - ii ; D- i .

33. Observe the following diagram given as Fig. 8.1.

Answer the following questions.

A. Does it represent a plant cell or an animal cell?

Ans: The given figure cell wall is not present thus it is an animal cell. The plant cells have a cell wall which is absent in the animal cell. 

B. Does it represent a prokaryotic cell or an eukaryotic cell?

Ans: The given figure is an eukaryotic cell because it contains a well defined nucleus and other organelles which are absent in prokaryotic cells.

34. Label the parts A to E in the given as Fig. 8.2 diagram.

Ans: A- Cell wall

B- Cell membrane

C- Nucleus

D- Cytoplasm

E- Vacuole  

35. Classify the following terms into cells, tissues and organs and write in the tabular column given below. RBC, WBC, Nerve cell, blood, muscle, blood vessels, brain, heart, hand

Ans: 

36. Read the following statements and write the appropriate term against each statement.

A. I control the functions of a cell. Who am I? ...................

Ans: Nucleus

B. I am like a policeman. I do not allow anything and everything to get in and out of the cell. Who am I? ...................

Ans: Cell Membrane

C. I transfer characters from parents to offspring. Who am I?

Ans: Genes

37. Fill in the blanks with the terms given in the box below: 

Nucleus, chromosomes, cell wall, cell membrane, protoplasm, cytoplasm, ribosome, cell organelles

The outermost layer of plant cells is the      (a)         beneath which is the      (b)        The term      (c)        refers to the jelly-like substance containing all the      (d)        .The      (e)        contains thread-like structures called      (f)        .

Ans: The outermost layer of plant cells is the cell wall beneath which is the cell membrane. The term cytoplasm refers to the jelly-like substance containing all the cell organelles .The  nucleus contains thread-like structures called chromosomes.

Long Answer Questions

38. Cells consist of many organelles, yet we do not call any of these organelles as structural and functional units of living organisms. Explain.

Ans: Cell organelles like ribosome, mitochondria, nucleus etc. possess specific functions and perform specific functions. However, referring to them as functions won't be right. This is due to their behavioural performance in any living cell. They do not act unitarily. However, the nuclei possess independent existence. This is the tiniest, useful and structural unit of life.

39. Why do plant cells have an additional layer surrounding the cell membrane? What is this layer known as?

Ans: Plants are an immovable species. Thus, they need protection against high wind, variation of temperature, and atmospheric moisture. For this, plants have a special cell membrane to protect them from these. This also helps a plant to gain their shape.

40. The size of the cells of an organism has no relation with the size of its body. Do you agree? Give reason for your answer.

Ans: The size of the cell is independent of  the size of the body. Let us understand this by taking an example of an elephant and a rodent (rat). The cells of the elephant and rats are similar in size irrespective of their body size. 

The size of a cell only depends on its performance. 

The nerve system of elephants and rats performs the same function of receiving and transferring stimulus from body to brain because the structural and functional unit of the nerve system is the ‘neuron’.  These cells are long and branched in both organisms. The nerve system helps to coordinate the functions of different parts of the body.

NCERT Exemplar for Class 8 Science Solutions Chapter 8 Cell

There are Two Sorts of Organisms:

1. More than one cell makes for a multicellular organism. Mango Tree and Frog, for example.

2. A single cell makes up a unicellular organism. Amoeba and Paramecium are two examples.

Shape of Cells

• The single-celled organism amoeba does not have a defined form. As it travels or feeds, it changes shape, projecting sections of its body to generate 'pseudo' (meaning 'false') 'podia' (meaning 'feet'). Pseudopodia are the term for this kind of venture.

• Humans have millions of cells, including white blood cells (found in the blood), muscle cells, and nerve cells. Their forms differ depending on the functions they carry out.

• The majority of cells are round, spherical, or elongated in shape. Some have a spindle form with long, pointed points on both ends. Nerve cells, also known as neurons, are long and branching structures that receive and transmit signals. The Cell Membrane or Plasma Membrane coating preserves the cells' shapes.

• A Cell Wall is an extra stiff coating found on bacterial and plant cells.

Size of Cells

The cells range in size from a millionth of a meter (known as a micron) to a few centimeters, although the vast majority are invisible to the naked eye. Microscopes are required to observe these minuscule cells.

The size of cells in a huge animal (such as an elephant) does not have to be larger than cells in a small species (such as a rat). The cell's size is determined by the function it performs. The nerve cells of a rat and an elephant, for example, perform the same job and are hence the same size.

Cell Structure and Function

A single cell in a unicellular creature performs all of life's essential processes. However, there is a division of labor in multicellular organisms.

Plants and Animals contain the Following Organelles:

1. Endoplasmic Reticulum

The Endoplasmic Reticulum (ER) is a network of membrane-enclosed canals surrounding a fluid-filled lumen. There are two types:

• The Rough Endoplasmic Reticulum (RER) is lined with ribosomes, rough appearance. Because ribosomes are linked to it, it performs an essential function in protein synthesis.

• The Smooth Endoplasmic Reticulum (SER) lacks ribosomes and so appears smooth. It is essential for the production of lipids.

2. Ribosomes

Ribosomes are spherical entities that contain RNA (ribonucleic acid) and a protein enzyme. They lack membranes and exist independently in the cytoplasm. The place where proteins are synthesized is the ribosome.

3. Golgi Bodies

Cisternae are smooth, flattened sac-like structures that stack in parallel rows to produce Golgi bodies. Endoplasmic reticulum protein is received by the Golgi Cis face, which alters, packages, and stores it. It also transports proteins in vesicles to other locations. The Golgi apparatus controls the secretion of enzymes, hormones, and proteins.

4. Mitochondria

Mitochondria are double-membraned rod-shaped organelles. The exterior membrane is smooth, while the inner membrane folds into cristae. Cristae enhance the inner membrane's surface area by many times. The matrix is the fluid that surrounds the mitochondria. Mitochondria are renowned as the "Powerhouses of the Cell" because they produce energy.

5. Lysosome

Lysosomes are sac-like structures with single-layered membranes surrounding them. They include potent digestive enzymes capable of breaking down all organic matter. Within the cell, it functions as a miniature digestive system. Damaged cells, as well as extra- and intracellular debris, are digested by lysosomes. Suicidal Bags are named because they remove worn-out or malfunctioning cell organelles and may even devour entire cells (that are damaged or dead).

6. Vacuoles

Vacuoles are fluid-filled organelles that are surrounded by a membrane. A big vacuole in plant cells is frequently filled with a liquid termed 'cell sap.' Sugar and salts are dissolved in the cell sap.

Vacuoles may or may not exist in animal cells. They don't contain vacuoles, and if they do, they're far smaller than those seen in plant cells. Plant cells have vacuoles that keep them stiff or controlled. They hold a variety of compounds (including waste products of the cell). Animal cells have vacuoles that store food, water, sugar, minerals, and waste materials. Food vacuoles are referred to as Amoeba because they contain food particles.