Cells and Cell Clusters Class 8 Questions and Answers Notes Basic Science Chapter 9 Kerala Syllabus

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Class 8 Basic Science Chapter 9 Cells and Cell Clusters Question Answer Notes

Class 8 Basic Science Chapter 9 Notes Kerala Syllabus Cells and Cell Clusters Question Answer

Cells and Cell Clusters Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
Identify the word pair relationship and fill the blanks.
a) compound microscope : visible light
……………….. : electron beam
b) Plant cells : eukaryote
………………… : prokaryote
c) Endoplasmic reticulum : Material transport in the cytoplasm
………………….. : Centre for production and distribution of energy
Answer:
a) Electron microscope
b) Bacteria
c) Mitochondria

Question 2.
Choose the statements related to plant cell from the following.
(a) Centrosome is present
(b) Plasma membrane is absent
(c) Plastids are present
(d) Presence of comparatively large vacuoles
Answer:
(c) Plastids are present and (d) Presence of comparatively large vacuoles

Question 3.
Information related to certain cell organelles are given in the table. Complete it by selecting suitable terms from the box.

Answer:
A – f) Golgi apparatus
B – e) Chloroplast
C – d) Ribosome
D – b) Leucoplast

Basic Science Class 8 Chapter 9 Question Answer Kerala Syllabus

Answers to the indicators on page no. 136
Question 1.
Where should the slide be placed in a microscope?
Answer:
The Slide should be placed on the stage of the microscope, and the stage clip is used to keep the slide in place.

Question 2.
Which is the part that regulates the light on the slide?
Answer:
The diaphragm in the condenser controls the amount of light. The condenser lens above this focuses the light onto the object being observed. Mirror- Reflects light from the light source onto the diaphragm.

Question 3.
Which are the lenses used in microscopes?
Answer:
The eyepiece, objective lens, and condenser are the main parts of a microscope that are attached to the lens.

Question 4.
Completed illustration 9.2

Answer:

Question 5.
Completed table 9.1

Answer:

Part of a microsope	Function
Eye piece lens	The image formed by the objective lens is again magnified
Knobes	Used to focus the lenses on the object being observed. The larger knob is called coarse adjustment and the smaller knob is called fine adjustment
Objective lens	The image of the object being observed is magnified and projected into the inner surface of the eyepiece. The part where the objective lenses are mounted is called the nosepiece.
Stage	Used to place slide
Clip	Used to keep the slide in place
Diaphragm in condenser	Control the amount of light
Condenser lens	Helps focus light onto the object.
Mirror	Light from the light source is reflected onto the diaphragm

Question 6.
Completed table 9.2 comparing the peculiarities of different types of microscopes.

Answer:

Peculiarity	Compound microcope	Electron microscope
Need of light	Light is needed	Electron beam is used instead of light
Magnifying power	Up to a thousand times	It magnifies objects more than a million times more than a normal microscope
Lens	Using multiple lenses	Electro magnets are used

Question 7.
Note prepared based on the illustration 9.3 page 140

Answer:
A normal microscope can observe mitochondria, bacteria, red blood cells, yeast, animal cells, plant cells, paramecium, and ova. An electron microscope is an instrument that magnifies objects more than a million times larger than a normal microscope. It helps in the detailed observation of living cells, viruses, and molecular structures. An electron microscope helps in the detailed observation of DNA, viruses, and proteins, which cannot be observed under a normal microscope.

Answers to the indicators on page 141
Question 8.
While preparing the slide:
Answer:

• Use a sharp blade for smooth, thin sections.
• Take the thinnest sections possible. Thin sections allow light to pass through easily.
• Cut straight across to get a proper cross-section.
• Place the thin section on a clean glass slide.
• Add a few drops of water or glycerin to prevent drying.
• Cover with a cover glass using a needle to prevent air bubbles from entering.

Question 9.
Staining:
Answer:

• Use a suitable stain such as safranin or methylene blue.
• Stain for only a few seconds
• Rinse gently with water to remove excess stain before covering with a coverslip.

Question 10.
Observing in high power and low power:
Answer:
Low Power: Observe with a low-power objective lens. Helps to see the epidermis, cortex, pith, etc. Adjust the mirror for a clear view.
High Power: Switch to high power to see things like xylem and phloem. Use the fine adjustment knob to adjust the clarity. Do not move the slide when switching from low power to high power.

Question 11.
Observing and illustrating:
Answer:

• Observe carefully and patiently.
• Draw neatly with a pencil.
• Draw only what you see.
• Use arrows for labelling and write names neatly.

Question 12.
Practical record on page 142 of the textbook:
Answer:
Experiment Name: Plant Stem Observation
Objective: Observe the cells in a plant stem through a microscope.
Materials Required: Microscope, plant stem, Petri dish, glass slide, cover glass, glycerin, blade, tissue paper, needle, brush, water, safranin stain, watch glass.

Procedure:
To prevent dehydration of the object to be observed, place it in Water in a Petri dish. Take thin cross-sections of the object to be observed. Transfer the sections to the water in a watch glass using a brush. Place the thinnest and most complete sections in a diluted stain taken in another watch glass. Add one or two drops of glycerin to prevent the object from drying out. Use a brush to pick up the stained section gently, then wash it in clean water and place it in glycerin on the slide. Cover it with a cover glass using a needle to prevent air bubbles from entering. Wipe off excess glycerin with tissue paper. Observe under a microscope.

Observation:

Conclusion:
Various types of cells are found in plant stems.

Question 13.
Completed illustration 9.5 page 143

Answer:

Question 14.
Completed illustration 9.7 page 147

Answer:

Question 15.
Completed table 9.3 page 149

Answer:

Plant tissues	Characteristics	Functions
Parenchyma	Contain living cells. Thin cell wall. Intercellular spaces are present. Cells in some parts have the ability to divide.	Perform functions such as photosynthesis and food storage.
Collenehyma	A tissue made up of living cells. The cell wall is made of substances such as cellulose and pectin. The cell wall is thicker only in some parts.	Helps in maintaining the shape of plant parts.
Selerenehyma	A tissue consists of dead cells. Thick-cell-wall. The cell wall is of uniform thickness throughout.	Providing strength and support to plant parts.
Xylem	Made up of cells of different shapes and sizes.	Conduction of water and salt to the leaves take place through xylem.
Phloem	Made up of cells of different shapes and sizes.	Carries food synthesised by the leaves to different parts of the plant body.

Question 16.
Completed illustration 9.9 page 151

Answer:

Question 17.
Completed illustration 9.10 page 152

Answer:

Question 18.
Completed table 9.4 page 153

Answer:

Part	Plant cell	Animal cell	Function
Cell wall	present	Absent	Provides protection and shape to the cell
Centrioles	Absent	Present	Helps in cell division
Plastids	Present	Not present	Helps in the production and storage of food.
Lysosome	Absent	Present	Destroying foreign objects

Class 8 Basic Science Chapter 9 Question Answer Extended Activities

Question 1.
Prepare models of Plant cell and Animal cell using materials available in your surroundings.

Question 2.
Prepare a picture chart showing the diversity of cells and exhibit it in the class.
Answer:

Question 3.
Prepare a timeline showing the development of cytology and present it in the class.
Answer:

Cells and Cell Clusters Class 8 Notes

Class 8 Basic Science Cells and Cell Clusters Notes Kerala Syllabus

• Cell biology is the study of cells.
• Human eye can distinguish two spots having a distance of 0.2 mm in adequate light. This distance is called resolution of the eye.
• A simple microscope in which a single lens is used, can magnify an object upto 10 times than the original size, while in a compound microscope, in which more than one lens is used, can magnify an object up to 1000 times.
• Magnification power of a lens is its ability to magnify objects.
• Electron microscope is an instrument that magnifies objects more than a million times. It helps to observe cells, viruses and molecular structure in detail.
• In electron microscope electron beam is used instead of light.
• In 1934 German scientists Ernest Raska and Max Knoll invented electron microscope.
• The various parts of a plant cell are the cell wall, cell membrane or plasma membrane, cytoplasm, and cell organelles.
• Organelles are parts found in the cytoplasm that perform functions necessary for the survival of the cell.
• The organelles in plant cells are nucleus, Golgi apparatus, endoplasmic reticulum, and mitochondria, chloroplast, ribosome, vacuole, etc.
• Plastids are specialized parts of plant cells that help produce and store food. Chloroplast, chromoplast and leucoplasts are different forms of plastids.
• The group of similar type of cells are known as tissues. Tissues that are composed of similar type of cells are known as simple tissues. Xylem and phloem are composed of cells with different shape and size. So they are called complex tissues.
• Meristermatic tissues are composed of cells that are capable of continuous division. Meristematic cells cause growth of plants. Cell clusters or tissues that have lost their ability to divide are known as permanent tissues, Parenchyma, sclerenchyma, collenchyma, xylem arid phloem are examples for permanent tissues.
• Some organelles, such as lysosomes and centrioles, are found in animal cells that are not found in plant cells.
• Tissues composed of group of similar cells perform various functions in the body of animals are called animal tissues. Epithelial tissue, Connective tissue, Muscle tissue, and Neural tissue are different types of animal tissues.
• Stem cells are specialised cells that can develop into various types of cells such as muscle cells, nerve cells, blood cells, etc. Stem cells help to eliminate damaged cells, promote the growth of new cells and maintain healthy tissues.

INTRODUCTION

Imagine looking at your hand, or a leaf from a tree, or even a tiny ant. Have you ever wondered what these living things are made of? Well, just like a building is made of many bricks, all living organisms, from the smallest bacteria to the largest elephant, are made up of tiny basic units called cells.

Cells are often called the “building blocks of life” because they are the smallest units that can perform all the functions necessary for life, like taking in nutrients, growing, and reproducing. They are so tiny that you can’t see them with your naked eye; you need a special instrument called a microscope to observe them.

In this chapter, we’re going to explore the amazing world of cells. We’ll learn about what a cell looks like and its different parts, how different cells come together to form cell clusters (Tissues), Cell theory, and contributions of different scientists in this field.

HISTORY OF CELL BIOLOGY

• Cell biology is the study of cells.
• Matthias Jakob Schleiden discovered that all plants are composed of cells.
• Theodor Schwann discovered that all animals are composed of cells.
• Rudolf Virchow introduced the concept that new cells are formed from pre-existing cells.

Cell Theory

• • All organisms are made up of one or more cells.
  • The cell is the basic unit of life.
  • New cells originate from pre-existing cells.
• Different types of microscopes are used to observe very small or tiny cells. In simple microscopes, lenses are used to magnify objects.
• The human eye can distinguish two spots having a distance of 0.2 mm in adequate light. This distance is called the resolution of the eye.
• A lens is required to distinguish spots having a distance of less than 0.2 mm.
• A simple microscope in which a single lens is used can magnify an object upto 10 times than its original size.
• A compound microscope, in which more than one lens is used, can magnify an object up to 1000 times.
• The magnification power of a lens is its ability to magnify objects. If eye piece lens magnifies the object to 10 x (10 times) and objective lens magnifies it into 40 x (40 times), the magnification power of the lens is 400 x.

Electron microscope

• An instrument that magnifies objects more than a million times.
• It helps to observe cells, viruses and molecular structure in detail.
• In an electron microscope electron beam is used instead of light.
• In 1934, German scientists Ernest Raska and Max Knoll invented the electron microscope.
• In an electron microscope, electromagnetic lenses are used to focus a beam of electrons onto the specimen, allowing for much higher resolution imaging compared to light microscopes.

LET’S OBSERVE CELLS

• Living organisms have cells of different shapes and sizes in their bodies.
• The basic structure of all the different cells in a leaf and a stem is the same.

• Cell Wall – The cell wall is the rigid outer layer of the cell membrane.
• The cell membrane, or plasma membrane – Thin, flexible layer that surrounds the cell. Substances enter and leave the cell through the cell membrane.
• The plasma membrane does not allow all substances to pass through. Therefore, the plasma membrane is known as the semi-permeable membrane.
• Protoplasm – It consists of all the components inside the cell membrane, including the nucleus and cytoplasm.
• Cytoplasm – A jelly-like fluid that fills the cell. It maintains all the organelles in their place and serves as the medium for chemical reactions.
• Organelles are the parts found in the cytoplasm and perform the functions necessary for the survival of the cell.
• The organelles of a plant cell are the cytoplasm, Golgi apparatus, endoplasmic reticulum, and mitochondria.
• Nucleus – The centre that controls the cell. The chromatin network is the structure that appears like a network of threads within the nucleoplasm. During cell division, these chromatin networks condense into chromosomes.
• Golgi Apparatus – Cell organelles that appear as stacked membrane layers. These organelles transport proteins and lipids to various parts of the cell and outside the cell, wrapped in membranous sacs.
• Endoplasmic Reticulum – Organelles appear as a network of tubules within the cell, and serve as pathways for conducting materials. It helps in the synthesis and removal of materials required by the cell.
• Mitochondria – The energy production centre of the cell.
• Plastids – Specific parts in the plant cells that help in the synthesis and storage of food materials. They have a two-layered membrane. Different types of plastids perform different functions.

• Vacuole – Stores water, nutrients and wastes. Usually, large vacuoles are seen in plant cells.
• Ribosome – Found in the cytoplasm either freely or attached to the endoplasmic reticulum. They function as the centre for protein synthesis.

TISSUES
PLANT TISSUES

• The group of similar type of cells are known as tissues.

• Tissues that are composed of similar types of cells are known as simple tissues.
• Xylem and phloem are composed of cells with different shapes and sizes. So they are called complex tissues.
• The transport of water and salts to the leaves takes place through the xylem.
• The food produced by the leaves is transported to various parts by the phloem tissue.
• Meristematic tissues are composed of cells that are capable of continuous division. Meristematic cells are responsible for the growth of plants.

• Cell clusters or tissues that have lost their ability to divide are known as permanent tissues. Parenchyma, sclerenchyma. Collenchyma, xylem and phloem are examples of permanent tissues.

ANIMAL TISSUES

• The animal body is also made up of different types of cells (Animal tissues).
• Some organelles, such as lysosomes and centrioles, are found in animal cells that are not found in plant cells.

Stem cells are specialised cells that can develop into various types of cells, such as muscle cells, nerve cells, blood cells, etc.

• Stem cells help to eliminate damaged cells, promote the growth of new cells and maintain healthy tissues.
• In modern medicine, stem cells have great significance.
• Despite these differences, there are many similarities among living organisms.
• These common characteristics of living things lead us to the reality that the basis of life is one and the same.