The Cell | Biology Form 1

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The Cell - Biology Form 1

Background Information

In the topic Classification I you learnt about the use of a hand lens. The hand lens is a device used to magnify objects in order to see them much more clearly.

Test yourself to see how much of the hand lens you can remember by naming the parts of the hand lens in the figure below.

LESSON OBJECTIVES

By the end of this lesson you should be able to:

  • State the purpose of the light microscope.
  • Identify parts of the light microscope and state their functions.
  • Use and care for the light microscope.
  • Calculate magnification when using the light microscope







The Cell

Cells

A Light Microscope

The Light Microscope

In Primary Science, you learnt about water-borne diseases which are caused by tiny living things in water. The tiny living things cannot be seen by the unaided eye or the hand lens. The microscope, an instrument with greater magnifying power, is used. A microscope gives finer details of tiny objects. The commonly used microscope in schools is the light microscope.

The light microscope uses light for illumination of the specimen to be viewed. It is therefore important to know the parts of the light microscope, functions of these parts and care for the microscope.

FUNCTIONS OF PARTS OF LIGHT MICROSCOPE


PART                                         FUNCTION

Eye piece lens:                           Used to magnify the specimen under view
Coarse adjustment knob:           Raises or lowers the body tube for focusing
Fine adjustment knob:                Raises or lowers the body tube for sharp focusing.

Body tube:                                  Holds the eye piece lens and the revolving nose piece in position.
Revolving nose piece:               Holds the objective lens in position enabling changes from one objective lens to the other.
Objective lens:                            Magnifies the specimen.
Limb:                                           Supports the body tube and the stage

Base/Stand:                                Provides steady support.
Stage:                                        Where specimen on a slide is placed. It has two clips to hold slide in position during viewing.
Diaphragm:                                An opening which regulates the amount of light passing through condenser to illuminate the specimen.
Mirror:                                         Reflects light through condenser to the specimen.

Use of the Light Microscope

The microscope is used as follows:

  • Prepare the specimen to be observed.
  • Place the microscope on the bench, with the stage facing away from you.
  • Turn the low power objective lens into position. Ensure that the diaphragm is fully open.
  • Look through the eye piece lens with one eye while adjusting the mirror under the stage to allow enough light.
  • Place the slide with the specimen (already prepared) on the stage and clip the slide into position.
  • Look through the eye piece while ensuring enough light passes through the specimen.
  • Bring the low power objective lens to the lowest point using coarse adjustment knob until the specimen comes into focus.
  • Use fine adjustment knob to bring image into sharp focus.
  • Turn the medium power objective lens in position and adjust the focus using the coarse knob. For sharper images, use the fine adjustment knob.
  • If more details are required, turn the high power objective lens into position then use only the fine adjustment knob to bring the image into sharp focus.
  • Observe and draw what you see under the microscope. Work out and write the magnification beside the drawing

The videos next illustrate how to use and care for a light microscope.







.
















Magnification

You are able to see microscopic structures under the microscope because such structures are magnified. The extent of the magnification is a a product of eyepiece and objective lens magnifications.

Thus when using the microscope the magnification of the object/specimen viewed is given by multiplying the eyepiece lens magnification by the objective lens magnification.

Eyepiece lens magnification X Objective lens magnification = Total Magnification.

However the term magnification is broader. It refers to the extent to which the specimen size has been changed. Image observed may be smaller or larger than the actual specimen. In either case, it is still a
magnification.


CARE FOR THE MICROSCOPE

When using the microscope the following points should be observed:

  • Do not place the microscope too close to the edge of the bench/table.

 
  • When carrying the microscope, always use two hands.

To clean dirty lenses, special soft lens tissue paper or tissue  paper moistened with ethanol is used.


The low power objective lens should click into position before and after use of a microscope. This helps to avoid damaging of objective lenses.

Clean and store the microscope in a safe place free from moisture and dust.

BACKGROUND INFORMATION

In Primary science you studied about water borne diseases such as typhoid and cholera. You learnt that such diseases are caused by tiny living organisms which cannot be seen using the unaided eye. These are therefore called microscopic organisms or microorganisms.

The microscope is used to observe such organisms.

LESSON OBJECTIVES

By the end of the lesson you should be able to:

  • Identify the components of a cell as seen under the light microscope.
  • Identify the components of a cell as seen under the electron microscope and relate their structure to functions.
  • Compare plant and animal cells as seen under the microscope.

Cell Structure

The basic unit of a living organism is the cell. A cell is a microscopic structure, that is, it can not be seen using the unaided eye. A microscope is used to observe cells.

Unicellular organisms, for example amoeba and bacteria are made up of only one cell. Multicellular organisms, for example humans, elephants and trees are made up of billions of cells. The main features of a plant and animal cell, as seen through a light microscope, is given next.

Cell Structure


A living organism is made up of tiny microscopic units called cells. The cell is the basic structural and functional unit of a living organism. Unicellular organisms, for example Amoeba and Bacteria are made up of only one cell. Multicellular organisms, for example humans, elephants and trees are made up of billions of cells. The main features of a plant and animal cell, as seen through a light microscope, is given next.

Using the light microscope the following parts of the cell above are seen:

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Nucleolus
  • Vacuole
  • Cell wall
  • Chloroplast

Cell Structure as Seen Under the Light Microscope

Under the light microscope only a few parts of the cell can be seen, as in the animal and plant cells below.

Cell Structure as Seen Under the Electron Microscope

Under electron microscope, great detail of the cell can be seen (See next panel).
An electron microscope has high resolving and magnification power and uses electron beam to illuminate the specimen.

Click on the icons above to see the structures of cells seen under electron microscope.

Cell Structure as seen under the electron microscope

Activity 2

Drag and place the name on respective structures illustrated below.

  • Cell membrane
  • Cell wall
  • Chloroplast
  • Nucleus
  • Cytoplasm
  • Vacuole

Activity

Below is a generalization plant cell as seen under the electron microscope. Label the cell using names given by dragging and dropping them on the correct structure.

Name of the parts:
Cell wall
Nucleus
Nucleolus
Nuclear membrane
Plasma membrane
Cytoplasm
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Ribosome
Golgi apparatus
Tonoplast
Cell sap
Chloroplast
Lysosomes

 Cell Membrane

This is a very thin and flexible membrane that surrounds each cell. It is also known as the plasma membrane.

This membrane has tiny pores which allow movement of some materials in and out of the cell. For example, it allows only small particles such as those of water to move across it but not the relatively large sugar molecules. It is therefore referred to as a semi permeable membrane

Activity

Pick the correct organelle from the list given to fill the blanks in the given statement.
Chloroplast
Centriole
Tonoplast
Cell wall
Lysosome
Golgi apparatus
Cell sap/ sap vacuole

Check for answers:

  1. Centriole
  2. Chloroplast
  3. Tonoplast
  4. Cell wall
  5. Cell sap/sap vacuole.

Chloroplast


The chloroplast is the site for photosynthesis. Chloroplasts are found in plant cells but are absent in animal cells. Chloroplast is an organelle enveloped/enclosed in a double membrane that is similar to the plasma membrane.

Within the chloroplasts are granal lamellae or membranes containing chlorophyll (green pigment) molecules that trap light for photosynthesis.

GAME-QUIZ

  • Cell Vacuole (Sap Vacuole)

  • Cell vacuole is also referred to as sap vacuole.
  • It is surrounded by a single membrane called tonoplast.
  • Tonoplast is permeable to water. The size of sap vacuole varies according to the condition of the cell.

Cell vacuole contains cell sap which is a solution of sugars, ions and waste products. Sap vacuole provides mechanical support to the cell when it is full. It also acts as storage organelle for sugars, ions and pigments.

GAME-QUIZ

Mitochondrion

A mitochondrion appears as a sausage-shaped organelle. Each cell contains several mitochondria.It has a smooth outer membrane and extensively infolded inner membrane. These infoldings, called cristae, project into the matrix (fluid filled space) of the mitochondrion.

A Mitochondrion

This organelle is responsible for production of energy through the process of respiration. Cristae increase surface area for increased enzyme attachment and respiration. Mitochondria are numerous in very active cells such as sperm cells and intestinal cells.

Cell Wall

The cell wall is a rigid outer cover of plant cells. It is made of cellulose fibres. Cell wall gives plant cells its definite shape and provides mechanical support.It allows passage of gases, water and other substances. Cell wall is completely permeable. Due to its rigidity it prevents bursting of plant cells, even when they take in a lot of water.

GAME-EXERCISE


 With reference to plant cells, complete the table below by filling in column II the name of the structure that corresponds with the statement in column I.


COLUMN I

COLUMN II


1.Contains the pigment that traps solar energy



2. Contains the chemical compound that is responsible for transmitting hereditary information.



3. Acts as a selective barrier between the cell and its surroundings



4.Is composed mainly of a high molecular weight polysaccride (cellulose)



5. contains the enzymes responsible for synthesis of most of the cellular ATP


6. Contains most of the cellular solutes


 
Pick and drop in the right box from the list
Nucleus, cell membrane, cytoplasm, cell wall, mitochondria, chloroplast.

Answers
Column I       Column II

  1. chloroplast
  2. nucleus
  3. cell membrane
  4. cell wall
  5. mitochondria
  6. cytoplasm

Golgi Body

These are complex organelles composed of a stack of closely packed flattened cavities. Numerous spherical vesicles are found at the ends of the cavities. These vesicles contain secretions. Secretions are substances made in glands and taken to other tissues to perform specific functions. A Vesicle moves to the surface of the cell and discharges its contents to the exterior, in tissue fluid.

Golgi Body

The Golgi apparatus is where packaging of glycoprotein and other materials occur. It also produces lysosomes which contain enzymes that break down worn-out organelles or entire cell.

Golgi bodies are abundant in glandular/secretory cells such as liver and salivary gland.

GAME-QUIZ


Lysosome

These are small spherical bodies. They arise from golgi bodies.Lysosomes contain lytic enzymes which carry out the digestive processes or lysis. They digest lipids, proteins and carbohydrates. They also digest unwanted organelles and destroy old and damaged cells.

A Lysosome

Cytoplasm

Cytoplasm is the fluid part of the cell in which materials and organelles are found. It consists of a fluid medium where chemical reactions occur. It contains organelles and other inclusions such as starch, glycogen, fat droplets and other dissolved materials.

Nucleus

The nucleus is bound by a double unit called a nuclear membrane which has pores to allow exchange of materials between nucleus and cytoplasm. The outer membrane is continuous with endoplasmic reticulum. The nucleus is made up of a viscous fluid called nucleoplasm in which chromatin materials are suspended. Chromatin makes up chromosomes which carry genetic information. Nucleus carries hereditary materials and also controls the activities of the cells.

Ribosomes

They are spherical in shape, scattered within the cytoplasm and on the surface of rough endoplasmic reticulum.
They are sites for protein synthesis.

Ribosomes

Centrioles

Centrioles are rod-shaped structures located outside the nuclear membrane, in animal cells.
In each cell, two centrioles are found, situated at right angles to each other.
Centrioles take part in cell division and in the formation of cilia and flagella.

Centrioles

Endoplasmic Reticulum (ER).

These appear as a series of interconnected channels running throughout the cytoplasm. It is continuous with outer membranes of the nucleus. Some endoplasmic reticulums have ribosomes on their surface and are called Rough Endoplasmic reticulum (RER). RER facilitates transport of proteins synthesized in the cells.

Rough Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

Endoplasmic reticulum without ribosomes on its surface is called Smooth Endoplasmic Reticulum (SER). It is concerned with the synthesis and transport of lipids and steroids

Smooth Endoplasmic Reticulum

These appear as a series of interconnected channels running throughout the cytoplasm. It is continuous with outer membranes of the nucleus. Some endoplasmic reticulums have ribosomes on their surface and are called Rough Endoplasmic reticulum (RER). RER facilitates transport of proteins synthesized in the cells.

Rough Endoplasmic Reticulum

Endoplasmic reticulum without ribosomes on its surface is called Smooth Endoplasmic Reticulum (SER). It is concerned with the synthesis and transport of lipids and steroids

Smooth Endoplasmic Reticulum

Centrioles

Centrioles are rod-shaped structures located outside the nuclear membrane, in animal cells.
In each cell, two centrioles are found, situated at right angles to each other.
Centrioles take part in cell division and in the formation of cilia and flagella.

BACKGROUND INFORMATION

You have learnt about the structure, functions and use of a light microscope. You have also learnt about the cell structure as seen under the light microscope and electron microscope. In this lesson, you will learn how to prepare and observe temporary slides.

LESSON OBJECTIVE

By the end of this lesson you should be able to

prepare, mount and stain temporary slides of plant cells such as onion epidermal cells.

QUIZ-GAME



 

State whether true or false for the following statements about the previous activity.
 

True      or     False

  1. Cell membrane, cytoplasm, chloroplast, cell wall, nucleus, tonoplast, and lysosomes are observed both in the stained and unstained temporary slides
  2. Staining makes the cells more clear when viewing under the light microscope
  3. The specimen is placed in a drop of water to keep cells turgid.
  4. Lysosomes are visible under both light and electron microscopes.

Answers.


1. False     
2. True
3. True

4. False  

Temporary and Permanent Slides

We may observe cells on a permanent slide, or we can prepare a temporary slide of cells. Temporary slides are also called fresh slides and are used during a laboratory activity and then discarded.

A Temporary Slide seen under a light microscope

A Permanent Slide

Materials for Preparing Temporary Slides

You have already learnt about two types of microscopes. You will now learn how to prepare and observe temporary slides.
To prepare temporary slides you need the following materials and apparatus:

  • Microscope
  • Clean microscope slides
  • Cover slips
  • Scalpel / new razor blade
  • Distilled water
  • Onion bulb
  • A pair of forceps
  • Mounting needle
  • Dropper
  • Iodine solution

Microscope

Clean microscope slides

Scalpel / new razor blade

Cover slips

Distilled water


Onion bulb

A pair of forceps

Mounting needle

Dropper

Iodine solution

Procedure for Preparation of Temporary Slides:

  • Follow the following procedure for preparation of temporary slides.
  • Cut the onion bulb vertically into two parts. This gives you a longitudinal section through the bulb.

  • Separate a fleshy leaf from one of the parts
  • Remove a thin piece of epidermis from this leaf using forceps.
  • Place a drop of water on a clean slide and quickly spread the piece of epidermis onto the drop of water.
  • Gently lower a clear cover slip onto the epidermis strip using a mounting needle to avoid trapping of air bubbles.
  • Observe this temporary slide under the low and then medium power objective lens of the microscope
  • Repeat the above procedure using another epidermal strip. Use a drop of dilute iodine solution instead of distilled water, to stain the cells, then observe under the microscope.

BACKGROUND INFORMATION


  1. Count and estimate the number of millimeter markings that fit into the diameter of the circular field of view.

Type your answer


 


  
 Estimate the diameter/ length of the cells in micrometers 
Type in your answer
  

Diameter/ length of one cell= Diameter of field in micrometer
        Number of cells across the field

Answer


(i) 3.5mm (3.3    -    3.7mm)
(ii) 15 cells

  1. field of view in mm= 3.5mm

field of view in m = 3.5 X 1000= 3500m
         
Diameter/ length of the cells= Diameter of field in micrometer
          Number of cells across the fields

      = 3500
         15

        
= 233.33m         

LESSON OBJECTIVE

By the end of this lesson you should be able to observe and estimate the size of a plant cell.


GAME 2

Activity: Two
A piece of squared graph paper was placed on the stage of a microscope and its edge viewed through a *10 objective lens and *4 eye piece lens.
A slide carrying several cheek cells were also placed alongside the ruler on the microscope stage.
The viewer observed that each cheek cell covered about one eighth of a millimeter square (mm2).

Answer
Each cheek cell is 1/8 of a millimeter
1mm== 1000m
1/8mm== (1000/8) m
Diameter of cheek cells = 1000/8
               = 125m

Estimation of Cell Size

A cell is very tiny. To estimate the size of this structure we need to use a microscope. The length and width of a fairly large organism can be measured with a ruler in millimeters. Most cells are shorter than a millimeter and therefore their sizes are measured in smaller units such as micrometers.



A Microscope

To measure this a transparent ruler with mm markings is mounted on the stage of a light microscope and the markings brought into focus in a similar procedure as when observing a specimen on a slide. The marks observed are noted and recorded to indicate the span of the field of view in millimetrs e.g. 3mm as in the figure below.

Microscope Field of View with ruler mm markings

Convert the milimetres into micrometres by multiplying the millimetres observed by 1000 e.g. (3mm X 1000 = 3000micrometres).This is the diameter of the field of view in micrometers.

Remove the plastic rule and mount an onion skin epidermis and observe under the same magnification. Count the number of cells along the diameter of the field of view.(e.g. 4 cells in the figure)

Estimate the width/length of one cell in micrometers by dividing the diameter of the field of view by the number of cells across the the field of view. (e.g. 3000 divide by 4 = 750 micrometers in the figure.) This is the estimated length of one cell.

Activity



1mm = 1000m
1cm = 10mm = 10000m
Convert 1m to micrometer

Answer
1m=100cm
1cm=10000m
1m= 100*10000m
   =1000000m

1m = 1/1000 of a millimeter

= 0.001mm

Convert 1 micrometer to:


  1. Centimeter
  2. Meter

Answer

  1. 1m = 1/1000000 th of a centimeter.
  2. 1m = 1/1000000 th of a meter
  
=0 .000001m

Materials Required for Estimation of Cell size


To estimate the size of a cell the following materials are required:

  • Transparent ruler marked in millimeters

Microscope

Epidermal cells from onion bulb.

Iodine stain

Glass slide

A razor blade

Razor blade

Scalpel

Forceps

Procedure for Cell Estimation

  • With the low power objective in place keep the transparent ruler on the stage of the microscope
  • Focus the microscope so that the millimeter markings are visible as thick dark lines
  • Determine the diameter of the field by counting the number of millimeter spaces with the field.
  • Express the diameter of the field in m by multiplying by 1000.
  • Remove the ruler and place the slide containing the onion epidermis on the stage.
  • Identify a row of cells that spans the diameter of the field.
  • Count the number of cells in the row.
  • Estimate the diameter/ length of the cells in micrometer using the following formula:

Diameter / length of the cells  =  Diameter of field in micrometer
                                                     Number of cells across the field


 

Video tape all these stages: counting of the number of the cells from the screen.

BACKGROUND INFORMATION
You have learnt about the structure and functions of the cell. You have

also estimated the size of a cell from a temporary slide.

Earlier you learnt characteristics of living organisms in the topic "Introduction to Biology".

In this lesson, you will learn about cells that are modified to carry out specific functions. Such cells develop a special structure which enables them to be more efficient.

Activity: 1
Match each of the plant tissues in column A with its major function in column B.

COLUMN A

COLUMN B

a. Meristematic


1. Transport water, salts and food materials

b. Photosynthetic


2. To make new tissues

c. Parenchyma


3. To make food for plants

d. Epidermal


4. To support and strengthen plants.

e. Vascular


5. Protect the inner delicate tissues.

f. Supportive

6. Fill spaces between other tissues.


Answers
a 2    c 6    e 1
b 3    d 5    f 4

LESSON OBJECTIVE

By the end of this lesson you should be able to state

the differences between cells, tissues, organs and organ systems.

Activity

 
 
Answers
Heart.               Organ
Chloroplast       Organelle
Nuclear.            Organelle
Cheek cell.        Cell
Onion                Epidermis Tissue
Onion bulb         Organ
Mitochondrion   Organelle
Lung..                Organ
Blood                Tissue

CELL SPECIALISATION

In multicellular animals and plants cells from different parts of the body differ in size, shape and contents. Each cell type has special features that enable it perform a particular function efficiently. This is described as cell specialization.

Specialised Plant Cells

The diagrams shown below are some types of plant cells that develop from an undifferentiated cell.

Specialised Plant Cells

Activity 2


GAME- Background

Activity 2:



Activity

  1. Arrange the following in the correct order from the simplest to the most complex organ, cell, organelle, organ, organism, tissue.

Check answer


If correct reinforce positively and if incorrect try again (only twice).

Specialised Animal Cells

The illustrations below are of some types of specialized animal cells that develop from undifferentiated cells:

Sperm Cell (Spermatozoon)

Nerve Cell (Neurone)

Egg Cell (Ovum)

Tissues
A tissue is made up of cells of a particular type that are grouped together to perform the same functions.Below are examples of tissues.

Plant Tissues


Animal Tissues

 

 

 


 

 

 

 

 

Plant Tissues

The table below shows plant tissues, their description and functions. (Show illustration of each part)

Name of tissue

Description

Function

Epidermal

Single thin layer of cells covering the outer surface of plant parts.

Protects plants from mechanical damage and infection.

Photosynthetic

Cells rich in chloroplasts containing chlorophyll.

Absorb light energy and manufacture food (photocy)

Vascular (conducting tissue)

Consists of xylem and phloem.

Xylem Conduct water and salts up the plant
Phloem Transport food substances.

Parenchyma

Thin walled, irregularly shaped cells

Packaging and storage functions

Meristematic

Small, thin walled cells which retain ability to divide throughout their life.

To make new cells


Animal Tissues

The following table shows some animal tissues.

Name of tissue

Description

Functions

Epithelial

Thin continuous layer of cells.

Lining and protection of internal and external body surfaces.

Muscle

Bodies/ sheets of elongated cells with fibers that can contract.

Contract and relax to bring about movement.

Blood

Fluid containing red and white blood cells, platelets and dissolved substances.

Transport gases, nutrients and other dissolved substances.
Protect the body against Functions.

Connective

Consists of strong fibres.

Connects other tissues and organs holding others together in position.

Organs

An organ is a group of different tissues working together to perform a specific function, for example the mammalian heart.

The heart is made up of the following tissues:

Epithelial tissue

Muscular tissue,

Connective tissue


Blood tissue

Mammalian Heart

The heart pumps blood around the body. It is made up of various tissues.

Epithelial tissue         Muscular tissue

               

HEART

        

 


    Blood tissue     Nerve tissue     Connective tissue

Functions of Tissues of Mammalian Heart

The table below is a summary of the various tissues which form the heart.

(Let each tissue appear as it is mentioned).

Tissue

Role


1. Connective tissue

Binds other tissues together


2. Blood tissue

Transports oxygen and nutrient needed for energy production. Also removes carbon dioxide and nitrogenous wastes.


3. Muscular tissue

Contracts and relaxes causing the pumping action of the heart.


4. Epithelial tissue

Protects the inner tissues


5. Nerve tissue

Receives signals and informs the heart about the heartbeat rate



This is an example of different tissues functioning together in an organ. The organ is then able to perform its functions.

  Other Human Organs

Other organs composed of several tissues in animals include liver, brain, stomach, kidneys, lungs, gills and skin.



PLANT ORGANS

Plant organs include the leaf, roots, and stems.
The root is composed of epidermal tissue, vascular tissue and parenchyma tissue.

 

Organ Systems

An organ system is a system consisting of several organs working together to perform a specific function.

An example of an organ system is the digestive system in humans.

This system is composed of the following organs:

  • Mouth
  • Oesophagus
  • Liver
  • Stomach
  • Pancreases
  • Intestines

        •  

           

          Human Digestive System

          Other human organ systems include:

        • Circulatory system

        • Excretory system

        • Respiratory system (Breathing/Gaseous Exchange)

        • Reproductive system
        • Female

          Male

        • Nervous system
        • Organs and organ systems work together to form an independent, whole organism.


ASSIGNMENT

Project Work

Find out the organ systems which make up a plant. State the main functions of each organ system.

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