Cell Structure and Organisation

Cell Structure and Organisation

  • The basic unit of life is cells. There are two different types of organisms; unicellular and multicellular.
  • Unicellular organisms – have only one cell. The cell does not depend on other cells. E.g. bacteria
  • Multicellular organisms – have more than one cell. The cells are interdependent on one another for the functioning. E.g. human.


  • Cells are very tiny they could be seen only through microscope. We have two types of cells:
    1. Plant Cells
    2. Animal Cells

structure of a plant cell

Structure of a plant Cell

Structure of an animal cell
Structure of an animal cell


  1. Structure and functions of Animal and Plant cell




  • This is a thin layer of skin which forms the outer boundary of the cell
  • Controls the passage of substance into and out of the cell. In general, oxygen, waste products (CO2 and urea) are allowed to leave and harmful substances are kept out the cell. Hence, cell membrane is called a selectively permeable membrane (partially permeable / differentially permeable).

*Note: do not use the term semi-permeable. 



  • Refers to all cell contents expcet the nucleus.
  •  This is a jelly-like substance found in the all cells.
  • It contains living structures, which have a particular function in the cell called organelles (e.g. mitochondria) and non-living structures called inclusions (e.g. enzymes, oil droplets).
  • All the chemical reactions of the cell (metabolic reactions) take place within the cytoplasm.


  •  Site of respiration, which releases energy. Also known as the power house of the cell.


  • Control all the cellular activities.
  • Inside there are thread-like structures called chromosomes containing genetic materials (DNA). The chromosomes carry hereditary information from one generation to another. The nucleus also initiates the cell division.


  • Made up of cellulose (a carbohydrate).
  • It is found outside the cell membrane in plant cells.
  • Unlike the cell membrane, the cell wall is fully permeable to all fluids.
  • It allows all molecules to pass through it.
  • Cell wall gives the plant cell a definite shape. The presence of this wall around every cell in plant gives a great deal of support to the plant.

*Note: The cell membrane in plant cell fit tightly against the cell wall and is often difficult to see.




  • All mature plants have a large fluid filled space called a vacuole.
  • The vacuole is filled with watery fluid made up of sugar and salt. This fluid is called the cell sap.
  • The vacuole is also sometimes known as the sap vacuole.
    The vacuole helps to maintain the shape of the cell and also stores food
  • The vacuole is lined with a selectively permeable membrane called vacuolar membrane similar to the cell membrane. The vacuolar membrane separates the vacuoles from the cytoplasm.


  • Chloroplasts are green colored bodies lying in the cytoplasm. These organelles are green, because they contain a green pigment called chlorophyll. The chlorophyll absorbs light energy, and this energy is used for photosynthesis. The chloroplasts are the sites of photosynthesis.
STARCH GRANULES Starch granules are the min energy storage material in plant cells.


  1. Similarities and differences between Animal and Plant cell

2.1 Similarities


Both plant and animal have cell membrane, cytoplasm, nucleus, ribosomes mitochondria, vacuoles, endoplasmic reticulum, and golgi bodies.
2.2 Differences

Plant cell Animal cell
Regular shape Irregular shape
Cell wall present No cell wall
Glycogen granules present Starch granules present
Large, permanent vacuole Small, temporary vacuole
Chloroplast present Chloroplast absent

Specialized cells

In multicellular organisms, most cells when they finished diving and growing, they become specialized. When they have specialized, they do one particular job, their shape and size and content becomes different from other cells. This enables specialized cells to do its functions efficiently.

a) Root hair cell

root hair cell
Root hair cells, absorbs water and mineral salts from the outer layer of young roots and present a vast surface.

b) Xylem Xylem conducts water and mineral ions from roots to stem, leaves, flowers and fruits. Also provides support for the parts of the plant above the ground.


c) Phloem


Phloem transport organic products of photosynthesis (sugar and amino acid). It contains sieve tubes and companion cells.

d) Red blood cells

Red Blood Cells

Red blood cell the most abundant cells in the bloodstream and contains hemoglobin, the compound that carries oxygen through the body.

Levels of organization in multicellular organism

In unicellular organisms, the single cell performs all life functions. It functions independently. However, multicellular organisms have various levels of organization within them. Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:

Level 1: Cell

Cells are the basic units of structures and function in living cell. It my serve a specific functions within the organism.
e.g. blood cells, nerve cells, white cells, etc.

Cell Cell2

Level 2: Tissue

Tissue made up of cells that are similar in structure and function and which works together to perform a specific activity.
e.g. blood, nervous, bone, etc.

Tissue Tissue

Level 3: Organs

Organs made up of tissues that work together to perform a specific activity.
e.g. heart, kidney, lung.


Level 4: Organ systems

Organ system is groups of two or more tissues that work together to perform a specific function for the organism.
e.g. digestive system, circulatory system, skeleton system, etc.

Organ systems

Level 5: Organisms

Organism’s entire living things that can carry out all basic life processes. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce. Organisms are usually made up of organ systems, but an organism may also be made up of only one cell such as bacteria or protest.
Examples of organisms are:- human, mushroom, flower, etc.