ICSE Living Science Biology for Class 7 Solutions Chapter 1 Basic Biology
Check Your Progress
Fill in the blanks.
Question 1.
A ………….. is a device used to see very small objects like cells.
Answer:
A microscope is a device used to see very small objects like cells.
Question 2.
A cell is the basic …………… and …………. unit of life.
Answer:
A cell is the basic structural and functional unit of life.
Question 3.
Robert Hooke observed …………… cells under a microscope.
Answer:
Robert Hooke observed cork (dead) cells under a microscope.
Question 4.
Cells show diversity in …………. and …………..
Answer:
Cells show diversity in shape, size and number.
Question 5.
One …………. is one-thousandth of a millimetre.
Answer:
One micron is one-thousandth of a millimetre.
Question 6
………….. are the smallest cells in the human body.
Answer:
Red blood cells are the smallest cells in the human body.
Practice Question 1.
White blood cells are ………….. shaped.
Answer:
White blood cells are irregularly shaped.
Practice Question 2.
…………. is surrounded by a double membrane called nuclear membrane.
Answer:
Nucleus is surrounded by a double membrane called nuclear membrane.
Practice Question 3.
Every organism is characterized by a ………….. number of chromosomes.
Answer:
Every organism is characterized by a fixed number of chromosomes.
Practice Question 4.
…………… is called the control centre of the cell.
Answer:
Nucleus is called the control centre of the cell.
Practice Question 5.
…………… is a small, non-membranous organelle found very close to the nucleus.
Answer:
Centrosome is a small, non-membranous organelle found very close to the nucleus.
Check Your Progress
State if the following statements are true or false. Correct the statement if it is false.
Question 1.
Cell wall is found in animal cells.
Answer:
False. Cell wall is found in plant cells.
Question 2.
Mitochondria are the carriers of heredity.
Answer:
False. Nuclei are the carriers of heredity.
Question 3.
Nucleus is surrounded by a double membrane called nuclear membrane.
Answer:
True
Question 4.
Every species is characterized by a fixed number of chromosomes.
Answer:
True
Question 5.
Centrosome is called the control centre of the cell.
Answer:
False. Nucleus is called the control centre of the cell.
Question 6.
Lysosomes are also called the powerhouses of the cell.
Answer:
False. Mitochondria are also called the powerhouses of the cell.
A. Tick the most appropriate answer.
Question 1.
The term cell was coined by –
a. Matthias Jakob Schleiden.
b. Robert Hooke
c. Theodor Schwann
d. Rudolf Carl Virchow
Answer:
b. Robert Hooke
Question 2.
The cell wall is made up of –
a. proteins
b. fats
c. cellulose
d. vitamins
Answer:
c. cellulose
Question 3.
Which of the following holds hereditary characters in an organism ?
a. Nucleus
b. Chloroplast
c. Mitochondrion
d. Ribosome
Answer:
a. Nucleus
Question 4.
Which of the following helps in cell division ?
a. Centrosome
b. Ribosome
c. Plasma membrane
d. Lysosome
Answer:
a. Centrosome
Question 5.
In a cell, proteins are formed w ith the help of –
a. nucleus
b. Golgi bodies
c. mitochondria
d. ribosomes
Answer:
d. ribosomes
Question 6.
The foldings of the inner membrane of the mitochondrion are called –
a. matrix
b. cisternae
c. cristae
d. vesicles
Answer:
c. cristae
Question 7.
Which of the following is also called the powerhouse of the cell ?
a. Chloroplast
b. Mitochondrion
c. Centrosome
d. Cell wall
Answer:
b. Mitochondrion
Question 8.
Which of the following organelles is called the ‘suicide bag’ of the cell ?
a. Nucleus
b. Chloroplast
c. Ribosome
d. Lysosome
Answer:
d. Lysosome
Question 9.
The green pigment is present in –
a. chromoplasts
b. amylopiasts
c. chloroplasts
d. leucopiasts
Answer:
c. chloroplasts
Question 10.
The membrane surrounding the vacuole is called –
a. plasma membrane
b. nuclear membrane
c. tonoplast
d. cell wall
Answer:
c. tonoplast
Practice Question 1.
The centrosome has –
a. two centrioles
b. one centriole
c. three centrioles
d. four centrioles
Answer:
a. two centrioles
Practice Question 2.
The green pigment in the chloroplast is present in its –
a. outer membrane
b. matrix
c. grana
d. all of these
Answer:
c. grana
B. Match the following. Column A (Organelle)
1. leucoplast
2. endoplasmic reticulum
3. golgi bodies
4. chloroplast
5. vacuole
Answer:
Column A (Organelle)
1. leucoplast
2. endoplasmic reticulum
3. golgi bodies
4. chloroplast
5. vacuole
4. matrix all of these
Column B (Function)
a. transport of material
b. making food
c. storage of starch and proteins
d. makes the cell turgid
e. synthesis of cell w all in a plant cell
Column B (Function)
c. storage of starch and proteins
a. transport of material e. synthesis of cell wall in a plant cell
4. chloroplast b. making food
5. vacuole d. makes the cell turgid
C. State if the following statements are true or false. Correct the statement if it is false.
Question 1.
The size of a cell is usually measured in centimetres.
Answer:
False. Correct : The size of a cell is usually measured in micrometres.
Question 2.
The nuclear membrane encloses a colourless, dense fluid called nucleoplasm.
Answer:
True
Question 3.
Golgi bodies form a network of tubes which run throughout the cytoplasm.
Answer:
Flase. Endoplasmic reticulum form a network of tubes which run throughout die cytoplasm.
Question 4.
Chromophsts arc the ‘kitchen’ of the cell.
Answer:
False. Correct : Chloroplasts are the ‘kitchen’ of the cell.
Question 5.
Vacuoles are filled with a fluid called nucleoplasm.
Answer:
False. Connect : Vacuoles arc filled with a fluid called cell sap.
Practice Question 1.
At the time of cell division the chromatin network changes into small thread-like structures called genes.
Answer:
False. Correct : At the time of cell division the chromatin network changes into small thread like structures called chromosomes.
Practice Question 2.
Ribosomes are the sites of respiration in a cell.
Answer:
False. Correct : Ribosomes are the sites of protein synthesis in a cell.
Practice Question 3.
A mitochondrion is bound by two membranes.
Answer:
True
Practice Question 4.
Every cell is bound by a cell wall.
Answer:
False. Correct : Only plant cell is bound by a cell wall.
Practice Question 5.
Growth and reproduction are based on cell division.
Answer:
True
D. Answer the following in short.
Question 1.
Why is a cell called the structural and functional unit of a living organism ?
Answer:
A cell is called the structural unit of life because all living organism irrespective of their size, shape and complexity are made up of cells and functions performed by organism is the result of the activity of the cells in its body.
Question 2.
Why is the cell membrane called a selectively- permeable membrane ?
Answer:
Cell membrane is called selectiyely permeable membrane as it allows only selected substances to pass through it, and prevents the passage of other substances.
Question 3.
What is chromatin network ?
Answer:
Chromatin network is a network of thread-like structures present in the nucleus. They form chromosomes at the time of cell division which cany genes.
Question 4.
Why are mitochondria called the powerhouse of a cell?
Answer:
Mitochondria are the sites of respiration in cell. Mitochondria form energy in the form of ATP (Adenosine triphosphate) during the process of respiration. Therefore, they are called power house of the cell.
Question 5.
Define cell division. What is the relationship between growth and cell division ?
Answer:
Cell division is a process by which a cell divides, forming two new cells. It is the basis of growth and reproduction of an organism. The life of all multicellular organisms begin with single cell. This cell divided and redivides, there by forming a cluster of many cells. So cell division is necessary for growth.
Question 6.
Why is papaya yellow, spinach green and the edible part of watermelon red ?
Answer:
Three kinds of plastids are present in plants – chromoplasts, chloroplasts and leucoplasts. Among above three, chromoplasts are of different colours which provide different colours yellow to papaya, green to spinach and red to edible part of watermelon.
Practice Question 1.
Where are the genes located in a cell ?
Answer:
Genes are located on chromosomes inside nucleus of a cell. .
E. Answer the following in detail.
Question 1.
Why was the invention of a microscope important for the study of living beings ?
Answer:
All living organisms, unicellular or multicellular “are made up of cells. Microscope makes it possible to see inside the cells’ that make up all living organisms. Without microscope we could not see or understand, how life works. So the invention of microscope made it possible to see the basic component of life.
Question 2.
What is cell theory ? Name the three scientists whose work led to the formulation of the cell theory.
Answer:
Cell theory was given by Schleiden and Schwann in the year 1838-1839. It was refined further by Rudolf Virchow. The main postulates of cell theory are :
- All living beings are made up of one or more cells.
- Cells are the basic structural and functional unit of all living beings.
- All cells are basically alike in chemical composition and metabolic processes.
- New cells arise by division of pre existing cells. (Rudolf Virchow)
Question 3.
Nucleus is the most important part of a cell. Explain this statement.
Answer:
Nucleus controls all activities of the cell. It is called the control centre of the cell. It helps in cell division and its stores all genetic information of the cell and without it, a cell won’t be able to function. Hence, nucleus is the most important part of a cell.
Question 4.
Which structure of a plant cell is non-living and what are its function ?
Answer:
CELL WALL is non living structure present outside the plasma membrane of plant cell. It is formed of cellulose.
Functions of cell wall :
- Cell wall gives a definite shape to the cell.
- It also provides strength and rigidity to the cell.
- It provides protection to the plant cell.
- It allows the materials to pass in and out of the cell.
Question 5.
Give four main differences between a plant cell and an animal cell. Highlight the differences with well- labelled diagrams.
Answer:
Plant Cell :
- Cell wall is present in plant cells.
- Plastids are present
- Large vacuole is present which keep it turgid.
- Centrosome is absent in plant cell.
- Lysosomes are absent.
Animal Cell :
- Cell wall is absent in animal cell.
- Plastids are absent.
- Vacuoles are absent if present they are very small.
- Centrosome is present in animal cell.
- Lysosomes are present.
Question 6.
Differentiate between mitosis and meiosis.
Answer:
Mitosis :
- It is a kind of cell division in which the two daughter cells fonned have same number of chromosomes as their parent cell.
- It is also called as equational division.
- It helps in multiplication of cells (growth) and repair and replacement of cells.
meiosis :
- It is a kind of cell division in which the two daughter cells fonned have half the number of chromosomes than their parent cell.
- It is also called as reductional division.
- It helps in sexual reproduction, forms gametes and helps in maintaining the chromosomes number.
F. Give reasons for the following.
Question 1.
Cells are called the building blocks of life.
Answer:
Any function performed by an organism is due to the activity of the cells in its body. They are the basic unit of living organisms and mast by present for life to exist. They can exist independently (as in unicellular organisms like bacteria) or can divide and multiply to make multicellular organisms like man. Thats why they are called the building blocks of life they make up all living things.
Question 2.
Lysosomes are called suicide bags of the cell.
Answer:
Under certain conditions, lysosomes release enzymes that digest other cell organelles. That is why, they are called the suicidal bags of the cell.
Question 3.
Cell division forms the basis of growth and reproduction in living organisms.
Answer:
All multicellular animals begin their life with a single cell, which divides and redivides to fonn many cells, leading to growth in size. This process goes on during the life of an organism. Hence, cell division fonns the basis of growth. Cell division also forms the basis of reproduction in living organisms. It leads to formation of two daughter cells from a parent cell in unicellular organisms. In higher living organisms, cell division leads to formation of male and female gametes and sexual reproduction takes place leading to birth of young ones.
G. Identify and label the diagrams given below.
Living Science Biology Class 7 ICSE Solutions