• The cell is the basic unit of an organism
  • All living organisms are made up of cells
  • Some organisms are made up of one cell and others are said to be multicellular
  • Other organisms are made of many cells and are said to be multicellular
  • Cells are too little to see with the naked eye
  • They can only be seen with the aid of a microscope

The microscope

The microscope is used to magnify objects


  • The magnifying power is usually inscribed on the lens
  • To find out how many times a specimen is magnified, the magnifying power of the objective lens is multiplied by that of the eye piece lens
  • If the eye piece magnification lens is x10 and the objective lens is x4, the total magnification is x40
  • Magnification has no units
  • It should always have the multiplication sign


Microscope parts and their functions

To View the Object

  • Turn the low power objective lens until it clicks into position
  • Looking through the eye piece, ensure that enough light is passing through by adjusting the mirror
  • This is indicated by a bright circular area known as the field of view
  • Place the slide containing the specimen on stage and clip it into position
  • Make sure that the specimen is in the centre of the field of view
  • Using the coarse adjustment knob, bring the low power objective lens to the lowest point
  • Turn the knob gently until the specimen comes into focus
  • If finer details are required, use the fine adjustment knob
  • When using high power objective always move the fine adjustment knob upwards

Care of a Microscope

  • Great care should be taken when handling it
  • Keep it away from the edge of the bench when using it
  • Always hold it with both hands when moving it in the laboratory
  • Clean the lenses with special lens cleaning paper
  • Make sure that the low power objective clicks in position in line with eye piece lens before and after use
  • Store the microscope in a dust-proof place free of moisture

Cell membrane (Plasma membrane):

  • This is a thin membrane enclosing cell contents
  • It controls the movement of substances into and out of the cell


  • This is a jelly-like substance in which chemical processes are carried out
  • Scattered all over the cytoplasm are small structures called organelles
  • Like an animal cell, the plant cell has a cell membrane, cytoplasm and a nucleus


  • Plant cells have permanent, central vacuole

It contains cell sap where sugars and salts are stored

Cell wall:

  • This is the outermost boundary of a plant cell
  • It is made of cellulose
  • Between the cells is a middle lamella made of calcium pectate


  • With special staining techniques it is possible to observe chloroplasts
  • These are structures which contain chlorophyll, the green pigment responsible for trapping light for photosynthesis

The Electron Microscope (EM)

  • Capable of magnifying up to 500,000 times
  • The specimen is mounted in vacuum chamber through which an electron beam is directed
  • The image is projected on to a photographic plate
  • The major disadvantage of the electron microscope is that it cannot be used to observe living objects
  • However, it provides a higher magnification and resolution (ability to see close points as separate) than the light microscope so that specimen can be observed in more detail

The Plasma Membrane

  • Under the electron microscope, the plasma membrane is seen as a double layer
  • This consists of a lipid layer sandwiched between two protein layers
  • This arrangement is known as the unit membrane and the shows two lipid layers with proteins within
  • Substances are transported across the membrane by active transport and diffusion

The Endoplasmic Reticulum (ER)

  • This is a network of tubular structures extending throughout the cytoplasm of the cell
  • It serves as a network of pathways through which materials are transported from one part of the cell to the other
  • An ER encrusted with ribosomes it is referred to as rough endoplasmic reticulum
  • An ER that lacks ribosomes is referred to as smooth endoplasmic reticulum
  • The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids

The Ribosomes

  • These are small spherical structures attached to the ER
  • They consist of protein and ribonucleic acid (RNA)
  • They act as sites for the synthesis of proteins

Goigi Bodies

  • Golgi bodies are thin, plate-like sacs arranged in stacks and distributed randomly in the cytoplasm
  • Their function is packaging and transportation of glycol-proteins
  • They also produce lysosomes


  • Each mitochondrion is a rod-shaped organelle
  • Made up of a smooth outer membrane and a folded inner membrane
  • The foldings of the inner membrane are called cristae
  • They increase the surface area for respiration
  • The inner compartments called the matrix
  • Mitochondria are the sites of cellular respiration, where energy is produced


  • These are vesicles containing hydrolytic enzymes
  • They are involved in the breakdown of micro-organisms, foreign macromolecules and damaged or worn-out cells and organelles

The Nucleus

  • The nucleus is surrounded by a nuclear membrane which is a unit membrane
  • The nuclear membrane has pores through which materials can move to the surrounding cytoplasm
  • The nucleus contains proteins and nucleic acid deoxyribonucleic acid (DNA) and RNA
  • The chromosomes are found in the nucleus
  • They are the carriers of the genetic information of the cell
  • The nucleolus is also located in the nucleus but it is only visible during the non-dividing phase of the cell

The Chloroplasts

  • These are found only in photosynthetic cells
  • Each chloroplast consists of an outer unit membrane enclosing a series of interconnected membranes called lamellae
  • At various points along their length the lamellae form stacks of disc like structures called grana
  • The lamellae are embedded in a granular material called the stromal
  • The chloroplasts are sites of photosynthesis
  • The light reaction takes place in the lamellae while the dark reactions take place in the stroma

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