IB MYP Biology Cells Study Notes

IB myp 4-5 Biology – Notes- All Topics

Topic :Cells-Tissues

Topic :Cells– Weightage : 21 % 

All Questions for Topic : Tissues,Organs,System,Structure and Function,Life processes,Factors affecting human health,Vaccination


  • Biology is the study of living organisms and their interactions with the environment.

There are SEVEN characteristics of living organisms:

  • Movement
  • Respiration
  • Sensitivity
  • Growth and development
  • Reproduction
  • Excretion
  • Nutrition


  • Cells are the smallest units of life, but are capable of surviving in mediums free of life.
  • There are 2 main types of cells:
  • Prokaryotic (Before Nucleus): In unicellular organisms. They have no membrane-bound organelles.
  • Eukaryotic (True Nucleus): In multicellular bodies. They have complex organelles and are located in plants, animals

Classification of cells
There are two types of cells, characterized by the presence of or absence of a nucleus, and by its internal organisation:
Prokaryotic cells are simple cells that do not have a true nucleus. They have simple organelles, but lack membranous organelles, and they have a cell wall.
Eukaryotic cells are those which do have a true nucleus. They are larger than prokaryotes, do not always have a cell wall, and have organelles which perform specialized functions.

Size of Structures

Examples of relevance:
A virus can fit into a cell because it is 500x smaller.

Cell Theory

● All living things are composed of one or more cells.
● The cell is the basic unit of life.
● New cells arise from pre-existing cells.

Functions of a cell include:

  • Containing DNA
  • Sensitivity
  • Nutrition
  •  Making enzymes /proteins
  •  A cell contains organelles, mini-organs that carry out these functions.
Animal Cell v/s Plant Cell

Animal Cell

Plant Cell

Difference in Plant cell and Animal Cell

Structure and Function Of Cells

Structure is how it looks and  Function is how it acts

Cell or plasma membrane: Formed by a phospholipid bilayer that surrounds the cytoplasm. It functions as a selective barrier which separates the cell’s contents from its surroundings. It controls the exchange of materials such as nutrients and waste products.

The plasma membrane is a partially permeable membrane, allowing some substances to cross freely, but not others. The molecules which can pass through the membrane are relatively small. Large molecules, or those with the incorrect electrical charge, are unable to pass through the membrane but when required; they can cross via a special transport system.                                                              

Cytoplasm: The cytoplasm is the cellular content excluding the nucleus. It is formed by an aqueous solution with organelles embedded in it.

Mitochondrion: The mitochondrion is an elongated-shaped organelle enclosed in an envelope of two membranes. It is the site for cellular respiration, the process by which the cell obtains energy (ATP- Adenosine triphosphate).

Endoplasmic reticulum: The endoplasmic reticulum (ER) is a series of connected flattened sacs and membranous tubules. If the endoplasmic reticulum has ribosomes attached, it is called rough ER, and if not, smooth ER. Its function is the production of several substances, such as lipids in the smooth ER and proteins in the rough ER.

Ribosomes: Ribosomes are tiny organelles found free in the cytoplasm or attached to the membranes of the endoplasmic reticulum. Ribosomes are made of RNA (ribonucleic acid) and proteins, and are the site of protein synthesis.

Golgi apparatus: A series of flattened stacks of membrane-bound sacs (disclike compartments called cisternae), surrounded by small vesicles. In these vesicles, lipids and proteins synthesized in the ER are chemically changed and prepared for secretion (export to the outside of the cell).

Lysosomes: These are membrane-bound vesicles that contain digestive enzymes. They carry out the digestion of large molecules or old organelles.

Cytoskeleton: System of protein filaments that form complex networks in the cytoplasm of the cell. It gives a cell its shape and is very important in cell division (or mitosis).

Centrioles: Centrioles are small hollow cylinders made up of bundles of microtubules. They direct the movements of the cytoskeleton and are involved in cell division (or mitosis).

Nucleus: The nucleus, which is usually spherical, is found in the centre of the cell. It contains the genetic material (DNA) with the information to control all cellular processes.

  How a cell compares to a factor:

  • Nucleus – Head office
  •  DNA – Manager
  •  Proteins – Product
  •  Smooth Endoplasmic Reticulum + Ribosomes – Machinery
  • Cytoplasm – Free space
  • Vacuole-Storage Room
  •  Cell membrane – Guards 
  •  Mitochondria – Power House
  • The cell membrane is a sheet like protective surface. It is selectively permeable, and lets only some particles pass through. It is made of a phospho-lipid bilayer.
  •  Ribosomes are small globular structures that produce proteins. Ribosomes are made in the Nucleolus. There are two types of Ribosome es free and membrane-bound ribosomes. Free ribosomes roam around freely in the cytoplasm. They synthesize proteins for the use of the cell, while the other type, membrane – bound (attached to Rough Endoplasmic Reticulum) synthesize them for external use.
  •  The Nucleus is the Head office of the cell. It contains the DNA. The Nucleus have 5 components:
  • The Nucleolus makes Ribosomes. The Chromatin contains DNA, and it condenses to form Chromosomes
  • The Cytoplasm is the jelly-like substance inside a cell that counts as free space.
  • The Rough Endoplasmic Reticulum (RER) is right outside the -Nucleus. It is a flattened structure, and is joint to the Nucleus Envelope. It synthesizes and modifies proteins (polypeptides) – It has ribosomes attached to it, giving it a “rough” appearance.
  • The Smooth Endoplasmic Reticulum (SER) synthesizes lipids and removes harmful! substances. This process is known as detoxification. The SER also creates vesicles.
  • The Golgi Apparatus (also called Golgi Body) is a flattened disk-like structure. It has the same membrane as the Cell Membrane. It processes and packages proteins in vesicles. Vesicles are thus mo diffed with in. Then, they (the vesides) merge with the Cell Membrane. The flattened shape of the Golgi Body gives a higher surface Area: volume Ratio.
  • Mitochondria is the “power house of the cell. They carry out cellular Respiration. They have their own ONA. Th of create ATP (Adenine Triphosphate), which helps create and send energy whee ATP is a currency. They have 2 membranes, so enzymes are attached to them?
  • The chloroplast is the other organelle with a double membrane. It contains a pigment called Chlorophyll, which gives the chloroplast its green colour and helps in photosynthesis (which is why chloroplasts are only present in plants and algae).
  • Vacuoles are large fluid filled spaces enclosed by membranes. Plants have any large, central vacuole, while animals have several temporary and small vacuoles. Their membranes are called tonoplasts. It is permeable to water. vacuoles contain salt and glucose.
  • Centrioles are small, round structures that help in coll division. They are only present in animal cells. They  appear in pairs. In any cell, there is only one pair of centrioles. They have a copy of the DNA and are protenin nature.
  • The Cell Wall is an external layer only present in planks. It is made up of cellulose. It has a rigid structure and is completely permeable. It provides support and prevents bursting. It can withstand water pressure.
  • Lysosomes are Digestive Plants for proteins, fats and carbs. They transport undigested material to the cell membrane for its removal. The cell can break down if the Lysosome explodes.
  •  Some cells are specialized. They are modified and have particular structures and functions. They are formed through a process called “Cell Differentiation”.
  • Classic examples of specialized cells are Red Blood cells (RBCS). They transport oxygen throughout the body and remove Carbon Dioxide. It needs storage, which is why they have no nucleus. It needs to store haemoglobin (a metalloprotein). They are created in the bone marrow. At the time of creation, they have a nucleus, but they remove it for Increased storage. They have a biconcave shape to increase the surface Area to volume patio.
  •  Stem cells are cells that have not yet differentiated. They are raw cells, and can order for the growth of the Liver, Heat, Kidney etc. Although the Heart, Liver etc. are organs, stem cell’s can order for their growth because:

CELL MEMBRANE (Phospho -Lipid Bilayer)






Levels of Organization

In unicellular organisms, such as paramecium, an individual cell needs to carry out all the life processes. However, in multicellular organisms, cells become specialised and work together, unable to survive on their own. Humans are multicellular organism composed of eukaryotic cells. Even though the size and shape of our cells vary according to function, we could say that they all share the same basic structures, having three main parts: the cell membrane, the cytoplasm and the nucleus.

The cells of multicellular organisms are differentiated, specialized and contain different organelles. They are grouped together to form more complex structures. This happens the following way:

Cells that perform the same function can work together and form tissues. A tissue is a group of similar cells that together, carry out a specific function. There are different tissues in our bodies which perform specific functions; for example, epithelial tissue covers the outside of the body, and muscle tissue is the main component of muscles and it is responsible for movement.

Histology is the study of tissues. There are 4 types of tissues:

(1) Ephithelial- Cover surfaces
(2) Connective -support, Transport, Storage
(3) Muscles – contract
(4) Neural-Cary Signals

Antagonistic muscles are pairs of muscles working in opposite directions.

To perform different functions, different tissues can work together and make organs. An organ is formed by the functional grouping of several tissues to perform a new function. The brain, heart, stomach and liver are examples of important organs in our body.

In the same way, different organs work together to make systems. A system is a collective functional unit made of several organs which work in complete coordination with one another to perform a complex function. The digestive, the circulatory and the respiratory systems are some examples of the systems that make up our bodies.

Multicellular organisms are made of many different organs and systems that are coordinated.

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