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Page No 109:

Question 1:

In a unicellular organism, one cell performs all life activities. Do you agree?

Answer:

A unicellular organism is composed of a single cell. This single cell performs all the biological processes required for the maintenance of life activities of a cell. Thus, in case of unicellular organisms, all life activities are performed by a single cell.

Page No 109:

Question 2:

In a multicellular organism, all cells have the capability to perform all life functions. Do you agree? Give reasons.

Answer:

Multicellular organisms are composed of large number of cells and every cell is destined for a specific function. For example, a Red Blood Cell (RBC) can transport oxygen across the body, but it can not perform the functions of a nerve cell. Thus, in case of multicellular organisms, all cells do not have the capability of performing all life functions.

Page No 109:

Question 3:

The cell is the basic structural unit of living organisms. What does this statement mean?

Answer:

Cell is the smallest and fundamental unit of life. All living organisms are essentially made up of cells and the functions carried out by cells is responsible for the perpetuation of life. This is the reason why cells are also referred to as basic structural unit of living organisms.



Page No 112:

Question 1:

What part of the cell can be called the 'brain' of the cell? Why?

Answer:

Nucleus of a cell is also referred to as the brain of the cell. This is because nucleus regulates all the processes within the cell and it also controls all the cellular activities. 

Page No 112:

Question 2:

A cell requires water, minerals and other substances to stay alive. But the cell is covered with a cell membrane. How do these things reach inside the cell?

Answer:

The cell membrane forms a selective barrier around a cell and restricts the entry of many substances. However, cell membrane allows entry of water, minerals and other substances, which are essential for the survival of a cell.

Page No 112:

Question 3:

The cells in a tissue have identical shapes and perform identical functions. Do you agree? Give reasons.

Answer:

Cells that constitute tissues generally have similar structure and function. This is because the concerted functioning of these cells is required for the proper functioning of a tissue. Thus, it can be asserted that cells in the tissues have identical shapes and perform identical functions.

Page No 112:

Question 4:

How does growth in an organism occur- by growth in the size of cells or by growth in the number of cells?

Answer:

Growth in an organism occurs by the process of cell division. In this process, the cells divide to increase the number of cells. 

Page No 112:

Question 5:

Organelles that contain a green pigment are only found in plants and not in animals. What are the organelles and the green pigment called?

Answer:

The organelles that contain a green pigment and are selectively found in plants are called chloroplasts. These organelles contain chlorophyll pigment, which allows them to capture solar energy to prepare food. 



Page No 114:

Question 1:

Which of these is multicellular?
(a) Paramecium
(b) Amoeba
(c) bacteria
(d) mushroom

Answer:

(d) mushroom

Multicellular means made of more than one cells. Mushroom is a multicellular organism. All the other organisms mentioned here, are unicellular.

Page No 114:

Question 2:

The egg of a hen is a
(a) cell.
(b) tissue.
(c) organ.
(d) organ system.

Answer:

(a) cell

The egg of a hen is a cell. It divides repeatedly and differentiates into various tissues to develop into a chicken.

Page No 114:

Question 3:

Which of these is not present in an animal cell?
(a) mitochondria
(b) nucleus
(c) cell membrane
(d) chloroplasts

Answer:

(d) chloroplasts

In an animal cell, chloroplasts are not present. Chloroplasts are present in green plants and serve as the sites of photosynthesis in plants.

Page No 114:

Question 4:

Which of these is the control centre of the cell?
(a) nucleus
(b) cytoplasm
(c) mitochondria
(d) protoplasm

Answer:

(a) nucleus

The control centre of the cell is nucleus. The nucleus contains chromosomes, which divide during cell division.

Page No 114:

Question 5:

Which organelles are responsible for energy production in a cell?
(a) vacuoles
(b) chloroplasts
(c) mitochondria
(d) golgi bodies

Answer:

(c) mitochondria

Mitochondria is responsible for energy production in a cell.

Page No 114:

Question 6:

Which of these is not stated by the cell theory?
(a) Cells are the basic structural units of living organisms.
(b) All cells are identical.
(c) New cells are formed due to division in old cells.
(d) The way an organism functions depends on the way the cells work.

Answer:

(b) All cells are identical.

Cell theory states that all cells are similar in their basic structure and function but not identical.

Page No 114:

Question 7:

In which of these does a single cell NOT perform all life functions?
(a) Amoeba
(b) mosquito
(c) bacteria
(d) Euglena

Answer:

(b) mosquito

Mosquito is a multicellular organism where different organs perform different functions.

Page No 114:

Question 8:

Which of these unicellular organisms has no definite shape?
(a) Amoeba
(b) Paramecium
(c) Euglena
(d) bacteria

Answer:

(a) Amoeba

Amoeba is an unicellular organism that has no definite shape. It keeps changing its shape.

Page No 114:

Question 1:

All living organisms are made up of one or more __________

Answer:

All living organisms are made up of one or more cells.

Page No 114:

Question 2:

Which is the largest known single cell?

Answer:

The egg of an ostrich (measuring 170 mm 130 mm) is the largest known single cell.

Page No 114:

Question 3:

What is the jelly-like substance present in cells called?

Answer:

The jelly-like substance present in cells is called the cytoplasm.

Page No 114:

Question 4:

The cell membrane which surrounds the cell does not allow anything to pass through it. True or false?

Answer:

False.

The cell membrane, which surrounds the cell, is porous and allows the passage of specific molecules both inward and outward of the cell.

Page No 114:

Question 5:

The cytoplasm and the nucleus together make up the __________

Answer:

The cytoplasm and nucleus together make up the protoplasm.

Page No 114:

Question 6:

Name the cell organelles that help to get energy from food.

Answer:

Mitochondria is the cell organelle that helps to get energy from food.

Page No 114:

Question 7:

Which of these has a cell wall−Plant cell or animal cell?

Answer:

Plant cell has a cell wall, which gives shape and rigidity to the cells of a plant.

Page No 114:

Question 8:

Name the process by which new cells are formed.

Answer:

Cell division is the process by which new cells are formed.

Page No 114:

Question 9:

Which structure in the nucleus is a storehouse for information needed by the cell to function?

Answer:

Chromosomes present in the nucleus act as a storehouse for information needed by the cell to function.

Page No 114:

Question 10:

Plant cells have large vacuoles as compared to animal cells. True or false?

Answer:

True.

In mature plant cells, the small vacuoles fuse to form a single large central vacuole that occupies up to 90% of the volume of the cell. In animal cells, vacuoles are usually small in size.



Page No 115:

Question 1:

What are the 'building blocks of life'? Why are they so called?

Answer:

Cells are the building blocks of life. They are called so because large number of cells assemble to make the body of a multicellular organism.

Page No 115:

Question 2:

Differentiate between unicellular and multicellular organisms.

Answer:

 

Unicellular Organism Multicellular Organism
A unicellular organism is made up of a single cell. A multicellular organism is made up of more than one cell.
All the functions of the organism such as respiration, digestion and reproduction are preformed by a single cell. Different organs are present to perform different functions of the organism.

Page No 115:

Question 3:

What is cytoplasm?

Answer:

Cytoplasm is the basic component of the cell. It is a jelly-like substance present between the cell membrane and nucleus. Various organelles of cell such as mitochondria, ribosomes, and Golgi complex are present in the cytoplasm.

Page No 115:

Question 4:

What do you mean by protoplasm?

Answer:

Protoplasm is the entire content of a living cell. It includes the cytoplasm and the nucleus of a cell.

Page No 115:

Question 5:

What is a tissue?

Answer:

A tissue is a group of one or more type of cells and their intercellular substance that performs a particular function.

Page No 115:

Question 6:

What are organelles?

Answer:

Organelles are organised cell components present in the cytoplasm. Each organelle has a specific function to perform inside the cell.
Examples: Ribosomes, mitochondria, vacuoles, etc.

Page No 115:

Question 1:

What are the lower levels of organization in a multicellular organism? Are these levels also present in unicellular organisms?

Answer:

The lower levels of organisation in a multicellular organism are as follows:

(a) Cellular level
(b) Tissue level
(c) Organ level
(d) Organ system level

These levels are not present in unicellular organisms because their body is made up of a single cell.

Page No 115:

Question 2:

Draw a labelled diagram to show the general structure of a cell.

Answer:

Page No 115:

Question 3:

What are the differences between plant and animal cells?

Answer:

 

Plant Cell Animal Cell
Cell wall is present. Cell wall is absent.
Plastids are found in plant cell. Plastids are absent in animal cell.
A mature plant cell has a large central vacuole. An animal cell has many small vacuoles.

Page No 115:

Question 4:

What is meant by the term 'cell division'? Why is cell division necessary?

Answer:

Cell division is the process of formation of new cells from parent cells. Cell division is necessary for the growth and development of a multicellular organism because new cells are needed to replace the old and dead cells.

Page No 115:

Question 1:

What are the main points of the cell theory of life?

Answer:

Following are the main points of the cell theory of life:

(a) All living organisms are composed of cells and their products.
(b) Each cell is made up of a small mass of protoplasm containing a nucleus on its inside and a plasma membrane with or without a cell wall on its outside.
(c) All cells are alike in chemistry and physiology.
(d) Activities of an organism are the sum total of activities and interactions of its constituent cells.

Page No 115:

Question 2:

What are the functions of the following in a cell?
(a) cell membrane
(b) cytoplasm
(c) nucleus
(d) chromosomes
(e) mitochondria
(f) vacuoles

Answer:

(a) Cell membrane: It separates the cells from their external environment. Cell membrane also protects the cell from injury.

(b) Cytoplasm: It contains raw materials and provides the same to cell organelles for their functioning.

(c) Nucleus: It stores genetic information in chromosomes that can be passed on to daughter cells. Nucleus controls the overall cell metabolism and other activities.

(d) Chromosomes: These contain genes. All the hereditary information is located in the genes. Chromosomes control the cell division and cell growth.

(e) Mitochondria: These are called powerhouses of the cell because food is oxidised inside them and energy that is liberated from it helps in performing various energy-requiring processes.

(f) Vacuoles: They play an important role in cell enlargement. Vacuoles store food, waste and water.

Page No 115:

Question 3:

With the help of examples, show the variation in shapes and sizes of cells.

Answer:

Generally, cells are round, spherical or elongated in shape. Some cells such as nerve cells are quite long and have extensive branching. Some cells such as Amoeba has no fixed shape. It keeps changing its shape. White blood cells in humans can also change its shape. The cell membrane provides shape to the cells of animals and plants.

There is a wide variation in the size of the cells also. Most of the cells cannot be seen with naked eye. The smallest cell (a bacterium) is 0.1–0.5 μm in size while the largest cell measuring 170 mm 130 mm is the egg of an ostrich. Longest cells of human body are the nerve cells, which may reach a length of 90 cm.

Page No 115:

Question 1:

In general, cell sizes are not related to the size of an organism. However, will there be a difference in the length of the nerve cells in a rat and a giraffe?

Answer:

It is not necessary that nerve cells, which are the longest cells in the body of a multicellular organism, have difference in the length in a rat and a giraffe.

Page No 115:

Question 2:

White blood cells (WBC) can squeeze through walls of blood vessels and get into intercellular spaces to fight against germs. Which property of WBCs allows them to do this?

Answer:

White blood cells like Amoeba can change their shape. This property allows them to squeeze through the walls of blood vessels and get into intercellular spaces to fight against germs.

Page No 115:

Question 3:

Why do plant cells need a cell wall, and animal cells do not?

Answer:

Plant cells, unlike animals, do not have skeleton to support them. Therefore, they need a cell wall, which provides support and protection to them.

Page No 115:

Question 4:

Why do you think parents and doctors get very worried if a child gets a head or spinal injury?

Answer:

Spinal injury results in destruction of nerve cells. Since, nerve cells cannot be replaced if they are once destroyed, doctors and parents get worried if a child gets a head or spinal injury.

Page No 115:

Question 5:

Living things are made up of cells while non-living things are made up of atoms and molecules. Do you agree? Give reasons.

Answer:

Yes, I agree with the statement. Non-living things cannot reproduce on their own, do not respire and cannot move because they are made up of atoms and molecules. Living things respire, reproduce and move because they are made up of cells, which are the basis of life.

Page No 115:

Question 1:

Study the diagram. Label the structures A, B and C. What is the function of C? Is this a plant cell or an animal cell? Draw and label 3 extra structures that would change this cell into:
1. a plant cell if it is an animal cell
2. an animal cell if it is a plant cell.

Answer:

A - Nucleus
B - Chloroplast
C - Cell wall

It is a plant cell as it has a cell wall. Cell wall is a structure found only in plant cells. It supports and protects the plant cells.

Figure of an animal cell -



 



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