Cell Structure

What distinguishes one cell from another?

Inquiry Question

Prokaryotes vs Eukaryotes Cells

Prokaryotic cells have a much simpler structure than Eukaryotic cells. Although these two types of cells have many differences, they share basic similarities such as a Cell Membrane, Cytoplasm and Ribosomes.

Prokaryotes

• Characterised by a membrane-bound nucleus that contains genetic material of the cell and also consists of membrane-bound organelles.
• Each organelle has a specific function within the cell including the Cell Membrane (controls what enters and leaves the cell) which is not an organelle.
• All organelles contribute to the overall functioning of the cell.
• Eukaryotes are mostly multicellular but also can be unicellular.
• Examples of unicellular Eukaryotes can be known as Paramecium, Amoeba, Euglena, Algae and Protozoans.

Eukaryotes

• Cells which do not have a membrane-bound nucleus and organelles.
• 2 types
  • Bacteria
  • Archae – only found in harsh environments, e.g. volcanoes, deep sea
• 4 main structures
  • Ribosome
  • Cytoplasm
  • Cell Membrane
  • Genetic Material
• Unicellular.

Technologies to Determine the Structure and Function of a Cell

Light Microscope

• A light source passes through a condenser lens and then through a very thin specimen (slide)
• The light passes through the objective lens to be magnified and viewed through the eyepiece.
• Magnification varies from 8x to 1500x.
• Magnification: How big something is.
• Resolution: How clear or sharp an object is. It is the smallest distance between two objects where each can be observed as separate.
• Both living and nonliving specimens can be viewed under a light microscope.
  

Fluorescence Microscopy

• Similar to the light microscope however it has extra features that enable scientists to view specific parts of a cell.
• The sample to be viewed is labelled with a fluorescent substance
• The sample is illuminated with a high-intensity source of light that causes the fluorescence substance to emit light.
• The fluorescent light is directed through a filter which blocks out any other light only allowing top view the specimen that is fluorescent.

Electron Microscope

• The microscopes use electron beams and electromagnets instead of glass and lenses.
• The use of electrons gives better magnification than light and also have better resolving power(resolution) because electrons have shorter wavelengths.
• Reveals more about a cell than any other microscope in the world.
• There are two types of Electron microscopes Scanning Electron Microscopes and Transmission Electron Microscopes(S.E.M)(T.E.M).

Transmission Electron Microscope

• The electrons are transmitted through the specimen and the microscope produces a two-dimensional image.
• Magnification- 8- 1.5 million times
• Resolution- 2 nanometres

Scanning Electron Microscope

• Hits the specimen with a beam of electrons which causes secondary electrons to be emitted from the surface layers of the specimen.
• The SEM has poorer resolution but gives excellent 3D imaging of a specimen.

Computer-Enhanced Technology to Study Cells

• Different types of digital software processes images produced by microscopes that allow scientist to view cells in new ways.
• Cell Scan software produces three-dimensional representations of cell structure, allowing a much greater understanding of cell structure and function.

Confocal Laser Scanning Microscopy

• A laser produces a narrow intense beam of light that is focused a pinpoint on the sample while the surrounding, out-of-focus are not included in the image.
• A different reconstruction software puts together a three-dimensional image of different parts of the specimen.

Features and Functions of Cell Organelles

Cell Organelle	Function and Features
Cell membrane	A large oval-shaped structure around the cell. It controls what enters and leaves the cell.
Protoplasm	A broad term used to categorise the nucleus and the cytoplasm.
Nucleus	A large spherical structure which is colourless and jelly-like. Nucleus stores the information needed to control all cell activities. They consist of pores which is the communication line between the nucleus and cytoplasm. DNA is also stored in the nucleus.
Endoplasmic reticulum	Consists of flattened interconnected membranes it provides a pathway between the nucleus and the cell’s environment. ER also produces proteins for the cell to function.
Ribosomes	They produce proteins which are essential for the function and structure of the cell. Ribosomes are found in the cytoplasm and on the ER.
Golgi bodies	They are made of flattened membranes which do not have ribosomes attached to them like the ER. They are arranged in stacks of four to ten. Golgi bodies process, package and sort cell products.
Lysosomes	Lysosomes recycle and reuse the organelles within the cell which have died out. They contain digestive enzymes which are responsible for the breaking up of the chemical compounds. Apoptosis is the process of killing the cell entirely.
Mitochondria	Mitochondria produces energy in the form of molecules through the process of cellular respiration. The number of mitochondria in a cell varies on how much energy is needed for the cell. E.G muscles cells will have a lot of mitochondria.
Vacuoles	Vacuoles are large sacs which are mainly used to store foods and other essential objects.
Chloroplasts	Chloroplasts are responsible for photosynthesis which is the production of food for the plants. A membrane surrounds the chloroplast which is used to control what enters inside the organelle.
Cell wall	A cell wall is used to give cells strength and support. It consists of fibres which resist the pressures of certain things.
Centrioles	Found near the nucleus in animal cells, it plays a huge part in the process of cell division.
Cytoskeleton	Organelles are distributed and organised within the cell, they are held in place by the cytoskeleton. It is the framework for cell movement, organelle movement and cell division.

Fluid Mosaid Model

• Controls the exchange of material between the internal and external environments of the cell.
• This model depicts (copies) ‘fluid’ phospholipid bilayer with different types of proteins embedded in it, creating a ‘mosaic’ effect.
• Some membrane proteins form pores(temporary).
• Some form active carrier systems or channels for transport.
• Others have carbs attached to them for cell recognition.

Adhesion Proteins: Help link cells together and help maintain a three-dimensional structure.

Transport Proteins: Passageways that allow specific substances to move across the membrane.

Receptor Proteins: They cause cells to respond only to certain signals from substances such as hormones that bind to them, giving them specific functions.

Glycoproteins: A protein molecule with a carb attached to identify the cell and they are called marker molecules. They also help immune systems distinguish between foreign particles.