Cell Biology

1.1 Introduction to Cells

The Cell Theory

Rules of Cell Theory:

Additional statements added as microscopes improved:

7 functions all cells carry out for life: Mrs H Gen:

  1. Metabolism – Living things undertake essential chemical reactions
  2. Reproduction – Living things produce offspring, either sexually or asexually
  3. Sensitivity/response – Living things are responsive to internal and external stimuli
  4. Homeostasis – Living things maintain a stable internal environment
  5. Growth – Living things can move and change shape or size
  6. Excretion – Living things exhibit the removal of waste products
  7. Nutrition – Living things exchange materials and gases with the environment

Exceptions to The Cell Theory

Striated Muscle Cell

4.4 Muscle tissue is responsible for body movement | Human anatomy ...

Multinucleated Cell: It challenges the idea that a cell has one nucleus, as the muscle cell (fibre) has more than one nucleus per cell (multinucleated). Additionally, the average muscle fibre cell is about 30 mm long, which is much larger than a typical cell. 

Giant algae: Acetabularia

Juvenile, adult and reproductive morphologies of Acetabularia ...

Not simple and large: As a single-celled organism, Acetabularia challenges two widely accepted notions about cells: that they must be simple in structure and small in size.


Aseptate fungal hyphae 

Fungi Hyphae | Medical Laboratories

Multinucleated Cell with a shared Cytoplasm: This challenges the idea that a cell is a single unit as the fungal hyphae have many nuclei, are very large and possess a continuous, shared cytoplasm.

Microscope Magnification

Magnification = size of drawing / actual size

The scale bar represents the actual size of the sample in the image. It can be used to work out the magnification factor or to simply specify the actual length of the specimen or any component within the image.

Microscope Measurement - презентация онлайн

Cell Differentiation

Specialized tissues can develop by cell differentiation in multicellular organisms

Differentiation involves the expression of some genes and not others in a cell's genome

Stem Cells

Stem cells are unspecialised cells that can give rise to a wide range of body cells by differentiating along different pathways. They retain the capacity to divide indefinitely and have the potential to differentiate into specialised cell types when given the right stimulus.

Types of stem cells: 

Type of Cell Differentiated cells produced

Can differentiate into any type of cell including placental cells.

Can give rise to a complete organism.
Pluripotent Can differentiate into all body cells, but cannot give rise to a whole organism
Multipotent Can differentiate into a few closely related types of body cell.
Unipotent Can only differentiate into their associated cell type. For example, liver stem cells can only make liver cells

Use of stem cells to treat diseases

Treating Stargardt's disease with stem cells

Stargardt's disease is a disease of the eye. It generally appears in late childhood to early adulthood. It is caused by a recessive genetic mutation in gene ABCA4, which causes an active transport protein on photoreceptor cells to malfunction. This ultimately causes the photoreceptor cells to degenerate.

Macular degeneration - Wikipedia

To treat it, patients are given retinal cells derived from human embryonic stem cells, which are injected into the retina. The results obtained have been quite positive as the inserted cells attach to the retina and become functional, suggesting that it may be possible to restore sight to affected individuals using stem cells.

Treating Leukaemia with stem cells

Leukemia, a type of cancer of the blood or bone marrow, is caused by high levels of abnormal white blood cells. People with leukaemia have a higher risk of developing infections, anaemia and bleeding.

Image result for Leukemia

Treatment, in this case, involves harvesting hematopoietic stem cells (HSCs), which are multipotent stem cells. HSCs can be taken from bone marrow, peripheral blood or umbilical cord blood. The HSCs may come from either the patient or from a suitable donor. The patient then undergoes chemotherapy and radiotherapy to get rid of the diseased white blood cells. The next step involves transplanting HSCs back into the bone marrow, where they differentiate to form new healthy white blood cells.

Ethics of Stem Cell Research

Evaluators Embryo Umbilical cord blood Adult
Ethics of extraction Involves the death of the embryo which is unethical. The umbilical cord is discarded whether or not stem cells are taken from it. Does not harm or kill an adult, so it is still ethical
Ease of extraction Must be attained from an embryo  Easily attainable and storable Difficult to attain as there are very few of them and they are buried deep in tissues
Tumour risk More risk of becoming tumour cells than others Medium chance of malignant tumours developing Low chance of malignant tumours developing

1.2 Ultrastructure of cells


They are simple unicellular organisms, with no internal compartmentalisation, no nucleus and no membrane-bound organelles. All metabolic processes thus occur within the cytoplasm. They have 70S Ribosomes.

Prokaryotic Cells | BioNinja

Cell division in Prokaryotes

Prokaryotes reproduce by binary fission (a type of cell division) to produce two genetically identical cells.

Stages of binary fission.

1. We see the intact bacterial chromosome (which is circular). It has two regions called the origin of replication and the terminus of replication, which are located diametrically opposite to one another on the chromosome.

2. The chromosome opens at the origin of replication, and the two DNA strands are copied, with replication proceeding in opposite directions on the two strands.

3. Copying continues, and the cell elongates. The new origins of replication move apart, towards opposite ends of the cell.

4. A septum (wall) forms down the middle of the cell, partitioning it into two new cells, each with one of the two (now-complete) bacterial chromosome copies.

5. The cell pinches in two. We now have two new bacteria!

Image Sourced from: Khan Academy 

Eukaryotic cell Ultrastructure

Animal Cell.

Animal Cell - Biology Experts Notes - Medium

A Plant Cell (palisade mesophyll cell of a leaf)

Plant Cell - Definition, Parts and Functions | Biology Dictionary

Electron microscopy

Electron microscopes have a much higher resolution than light microscopes. The resolution of a light microscope is 200 nm compared to 0.1 nm for an electron microscope.

Microscope resolution is the shortest distance between two separate points in a microscope’s field of view that can still be distinguished as distinct objects

It can differentiate objects as small as 0.001 µm. It played a part in understanding the structure of organelles, such as the thylakoid membranes of chloroplasts, and the actin and myosin filaments of muscle.

Eukaryotic cells can be observed using a light microscope. At this magnification, only larger structures such as cell membrane, cell wall, nucleus, central vacuole and chloroplasts can be seen.

For a detailed view of cells, an electron microscope is usually used.

Electron Microscopy | BioNinja

1.3 Membrane structure

Phospholipid bilayers 

Phospholipid Bilayer - an overview | ScienceDirect Topics


Phospholipid Bilayer ( Read ) | Biology | CK-12 Foundation

The Fluid Mosaic Model

Image result for Fluid mosaic model

Typical exam drawing question: 

Image result for membrane structure labeled

Cholesterol in membranes

Cholesterol is a type of liquid, but is not a fat or oil. It belongs to the group called steroids. 

Its role in the phospholipid bilayer: 

1.4 Membrane transport


The fluidity of membranes allows materials to be taken into cells by endocytosis

Passive methods of transport across membranes

Simple diffusion 

Simple diffusion occurs in a gas or liquid medium and only requires a concentration gradient. Simple diffusion across membranes involves particles passing between the phospholipids in the membrane. It can only happen if the phospholipid bilayer is permeable to the particles. Non-polar particles such as oxygen can diffuse through easily. 

Facilitated diffusion 

Ions and particles that cannot diffuse between phospholipids can pass into or out of cells if there are channels for them through the plasma membrane. Because these channels help particles to pass through the membrane, from a higher concentration to a lower concentration, the process is called facilitated diffusion. 


Water is able to move in and out of most cells freely. This net movement is osmosis.

Diagrams showing the movement of water through cells

Osmolarity refers to the concentration of a solution in terms of moles of solutes per litre of solution.


1.5 The Origin of Cells

Pasteur's Experiment

Louis Pasteur (1822–1895), a famous French microbiologist,  gave crucial evidence to support the hypothesis that cells must come from pre-existing cells. His experiment disproved the theory of spontaneous generation, which stated that life could appear from a combination of dust, air and other factors. 

This imagine shows French Physician Louis Pasteur's experiment in ...

Miller–Urey experiment

Miller and Urey recreated the conditions of early Earth in a closed system by including a reducing atmosphere (low oxygen) with high radiation levels, high temperatures and electrical storms. After running the experiment for a week, some simple amino acids and complex oily hydrocarbons were found in the reaction mixture. This experiment proved that the non-living synthesis of simple organic molecules was possible.

Miller–Urey experiment - Wikipedia

The Endosymbiotic Theory

The theory of endosymbiosis helps to explain the evolution of eukaryotic cells. It states that mitochondria were once free-living prokaryotic organisms that had developed the process of aerobic cellular respiration. Larger prokaryotes that could only respire anaerobically took them in by endocytosis. They allowed them to live in their cytoplasm. As long as the smaller prokaryotes grew and divided as fast as the larger ones, they could persist indefinitely inside the larger cells. The cells evolved to develop a mutualistic relationship turning it into a eukaryote with membrane-bound organelles. In plant cells, the same thing happened with chloroplasts. If a prokaryote that had developed photosynthesis was taken in by a larger cell and was allowed to survive, grow and divide, it could have developed into the chloroplasts of photosynthetic eukaryotes. From prokaryotes to eukaryotes

1.6 Cell division


Cell cycle


The Cell Cycle, Mitosis and Meiosis — University of Leicester


Cyclin - Wikipedia


Image result for mitosis


It is the division of the parental cytoplasm between the two daughter cells after mitosis (though it often starts in telophase).Mitosis ( Read ) | Biology | CK-12 Foundation


Chromatography Review

Chromatography: A technique for separating the components, or solutes, of a mixture on the basis of the relative amounts of each solute distributed between a moving fluid stream, called the mobile phase, and a contagious stationary base. The mobile phase may be either a liquid or a gas, while the stationary phase is either a solid or a liquid

Image result for chromatography RF



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