Chapter 18

Earthquakes

Highlights

EXERCISE

A. Fill in the blanks.
B. Match the following column:
C. Tick the correct option.

Answer: vacuole

Answer: a single cell

Answer: nuclear membrane

Answer: cell wall

Answer: cell → tissue → organ → organ system

Answer: cell wall and plastids

D. Answer the following questions in brief.

Answer: The (main) factors that determine the shape of a cell are location and function.

Answer: Distinguish between unicellular and multicellular organisms are

Unicellular organisms are made up of a single cell. e.g., Euglena and Amoeba.

Multicellular organisms are made up of many cells. e.g., Humans and Birds.

Answer: All organisms are made up of cells. A cell is capable of independent existence. Due to this, cell is called the structural and functional unit of life.

Answer: Cell wall is present in plant cell. Due to this, plant cells are more rigid than animal cells.

Answer: Mitochondria is known as the Powerhouse of the cell.

Mitochondria are the site of cellular respiration. Energy is produced during this process. Due to this, mitochondria are called the Powerhouse of the cell.

Answer: Chloroplast is responsible for imparting colour to the leaves. Chromoplast is responsible for imparting colour to fruits.

Answer: Cilia and flagella are extensions on the cell membrane, these help in locomotion and procurement of food in organisms like Amoeba and Paramoecium. Cilia are much smaller than flagella.

Answer: Cilia and flagella are extensions on the cell membrane, these help in locomotion and procurement of food in organisms like Amoeba and Paramoecium. Cilia are much smaller than flagella.

E. Answer the following questions.

Answer: three different cell types found in human beings are:

DAV Solutions for Class 8 Science Chapter 1
Diagram

These figures clearly show that liver cell is irregular in shape, fat cell is spherical and muscle cell is spindle-shaped. This shows that all cells in an organism do not have the same shape.

Answer: Chromosomes are formed in the nucleus during cell division. When the cell is ready to divide, the chromatin (in nucleus) condenses to form thicker, thread-like chromosomes. Chromosomes are responsible for inheritance of characters from one generation to the next generation.

Answer: three differences between a plant cell and an animal cell are:

DAV Solutions for Class 8 Science Chapter 1
plant cell and animal cell
Plant CellAnimal cell
Cell wall is presentCell wall is absent
Chloroplast is presentChloroplast is absent
Vacuole a very largeVacuoles are small

(a) Endoplasmic Reticulum- It is a network of membranes. It provides channels for transport of materials in a cell.

(b) Golgi Complex- They are sac-like structures stacked one above the other. They are involved in the processing and packaging of materials produced by the cell.

(c) Nucleus- a specialised structure in the cells, bound by the nuclear membrane; responsible for controlling all cellular activities.

(d) Chromoplasts- They are responsible for imparting colour (other than green) to the different parts of the plant.

(e) Vacuoles- It appears as an empty space in the cytoplasm. It is generally large in plant cells. It stores excess of water and waste products.

(f) Mitochondria- These are rod-shaped or spherical structures. They are responsible for cellular respiration and for generation of energy for different activities of life.

Answer: When the cell membrane gets damaged, it exposes the cell’s contents to external environment. This results in stoppage of all functions of the cell, and eventually to cell death.

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