Topic 1 - CELLS

Topic 1

Identify the conversions between Millimetres, Micrometres, and Nanometres.

Milimetre → (x1000) Micrometre → (x1000) Nanometre.

Identify the Magnifying and Resolving Power of an Optical (Light) Microscope.

Magnifying Power: x1500

Resolving Power: 200nm

Identify the Magnifying and Resolving Power of an Electron Microscope.

Magnifying Power: x500,000

Resolving Power: 0.5nm

Why can Ribosomes not be seen using a Light Microscope?

The wavelength of light is too big to interfere with the ribosomes, as they are too small.

Define Magnification.

The magnification of an object is how many times bigger the image is when compared with the object.

Define Resolution.

The resolution (resolving power) of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items.

What is the formula for Magnification?

Magnification = Size of Image / Actual Size

What do TEM and SEM stand for?

TEM: Transmission Electron Microscope.

SEM: Scanning Electron Microscope.

Identify the five features of a TEM.

1. Uses electrons.

2. Allows a greater resolution.

3. Smaller organelles can be observed, with greater detail in organelles.

4. View only dead, dehydrated specimens.

5. Does not show colour.

Identify the differences between TEM and SEM.

TEM:

• Based on Transmitted Electrons.

• Electrons are directly pointed toward the sample and the parts through which electrons are passed are illuminated in the image.

• TEM seeks to see what is inside or beyond the surface.

SEM:

• Based on Scattered Electrons.

• The scattered electrons produced the image of the sample after the microscope collects and counts the scattered electrons.

• SEM focuses on the sample’s surface and its scattered electrons.

Identify the limitations of TEM and SEM.

TEM:

• Cannot look at living material.

• Specimen must be very thin.

• Complex staining method/long preparation time.

• Image only in 2D.

SEM:

• Cannot look at living material.

• (Doesn’t need to be thin.)

• Complex staining method/long preparation time.

• (Can build 3d Image.)

Identify the five features of an Optical Microscope.

1. Uses light.

2. Smaller resolution.

3. Smaller organelles cannot be seen.

4. View live specimens.

5. Shows colour when stained.

List the Cell Structures in an Animal Cell.

• Nucleus (Nucleolus, Chromatin, Nuclear Pore, Nuclear Envelope).

• RER.

• SER.

• Mitochondria.

• Lysosome.

• Centrosome.

• Golgi Body and Vesicles.

• Microtubules (From Centrosome).

• Ribosomes.

• Cell Surface Membrane.

• Cytoplasm.

List the Cell Structures in a Plant Cell.

• Nucleus (Nucleolus, Chromatin, Nuclear Pore, Nuclear Envelope).

• RER.

• SER.

• Mitochondria.

• Golgi Body and Vesicles.

• Microtubules.

• Ribosomes.

• Cell Surface Membrane.

• Cell Wall.

• Cytoplasm.

• Vacuole (Tonplast and Cell Sap).

• Chloroplast (Envelope and Grana).

Identify the features of the Nucleus.

• Largest organelle.

• Surrounded by a double membrane called the Nuclear Envelope.

• This has pores in it called Nuclear Pores.

• Contains DNA which is in the form of Chromatin when not dividing and Chromosomes when it is.

• Contains the Nucleus inside.

Identify the features of the Nucleolus.

• Dense, darker area of the Nucleus.

• Produces Ribosomes and RNA.

Identify the features of a Ribosome.

• They are made of Ribosomal RNA and Protein.

• They are used in the process of Protein Synthesis to assemble the Polypeptide.

• Only 25nm in diameter.

• 80S are found in the cytoplasm and attached to the Rough Endoplasmic Reticulum.

• 70S are found in the Cytoplasm and Mitochondria (As well as in Prokaryotes).

Identify the features of the Rough Endoplasmic Reticulum (RER).

• Endoplasmic reticulum is made from flattened sacs of membrane called Cisternae.

• The RER also has Ribosomes dotted along the surface as this is the location of extracellular protein synthesis.

• Once a protein has been made the membrane can pinch off to form a vesicle and be transported around the cell.

• The RER is usually found next to the Nucleus of the cell, and sometimes joined to the Nuclear Envelope.

Identify the features of the Smooth Endoplasmic Reticulum (SER).

• The function of the SER is to manufacture Lipids and Steroids such as certain Hormones.

• It has the same structure as RER but without Ribosomes.

Identify the features of a Mitochondrion.

• Aerobic Respiration occurs in the Mitochondria to produce ATP.

• Cells that require more ATP have more Mitochondria.

• Capsule-shaped or Spherical made from a double membrane filled with a fluid called Matrix.

• The inner membrane is folded into Cristae to provide a large surface area.

• 1000nm, can be seen using a light microscope.

Identify the features of a Centriole.

• Only found in Animal Cells, NOT Plant Cells.

• Found in a pair near the Nucleus, usually ay right-angles to each other.

• Each one is a bundle of Nine Microtubules.

• They are used when the cell Divides.

• They move to opposite ends and produce the Microtubule Spindle that will attach to the Chromosomes and pull them apart.

Identify the features of a Lysosome.

• Lysosomes are responsible for the breakdown of unwanted structures such as old organelles or even whole cells.

• In White Blood Cells, Lysosomes are used to Digest Bacteria.

• Among the 60+ Enzymes contained in Lysosomes are Proteases, Lipases, and Nucleases which break down Protein, Lipids, and Nucleic Acids respectively.

How are Proteins made in cells?

1. Parts of the RER - vesicles containing proteins - fuse with one side of the Golgi Body membranes.

2. Proteins are modified/changed/processed within the Golgi Body.

3. At the other side, small vesicles - containing modified proteins - bud off and move towards the cell membrane, where the fuse, releasing their contents by exocytosis.

Identify the features of a Golgi Apparatus.

• Stacks of membrane-bound sheets.

• Small membrane-bound transport sacks (Vesicles) fuse with it and also get pinched off.

• The Golgi receives Vesicles containing Proteins made in the RER.

• The Golgi modifies the Proteins, folds them up or adds extra parts to make them ready for their role.

• Then they release them in a Vesicle to be transported around the cell or released at the Cell Membrane by Exocytosis.

Identify the features of a Cytoskeleton.

• A Fibrous network that fills the Cytoplasm.

• Gives cells structure.

• Moves and holds structures like organelles.

• Made from Microtubules and Protein Microfilaments like Actin.

Identify the features of the Cell Wall.

• Surrounds the entire cell giving it a regular shape.

• Provides strength and Support.

• It is freely permeable and does not control what comes in and out of the cell, this is the job of the cell membrane.

• It is made up of a few layers, the Middle Lamella which contains Pectin and the Cellulose Microfibrils.

• Plant cells can be linked together by gaps in the cell walls called Plasmodesmata.

Identify the features of a Chloroplast.

• The site of Photosynthesis.

• Contains Chlorophyll which is green pigment required for Photosynthesis.

• Double membrane bound capsule-like organelle.

• Inner membrane folded into Thylakoids which are stacked up to form Granum.

• This provides a large surface area for chemical reactions to occur.

• These are linked by Lamella and all surrounded by a liquid called the Stroma.

Identify the features of the Vacuole.

• Animal cells sometimes have a small temporary Vacuole, but Plant cells have a large, permanent Vacuole.

• It is filled with Cell Sap, which is dissolved substances in Water.

• Used to help maintain the cell Shape.

• Also used for Storage.

Identify the features of the Tonplast.

• The Tonoplast is the membrane that surrounds the Vacuole.

• It controls what enters and leaves the Vacuole and therefore controls the cell’s Osmotic Potential.

List the Cell Structures in a Bacteria Cell.

Always Present:

• Cell Wall containing Murein (a Peptidogycan).

• Cell Surface Membrane.

• Cytoplasm.

• Circular DNA.

• Ribosomes (70S).

Sometimes Present:

• Flagellum (For Locomotion).

• Capsule (Protection).

• Infolding of Cell Surface Membrane.

• Plasmid (Small Circlet of DNA).

• Pili (For Attachment to other Cells/Surfaces).

List the Features of a Virus.

• Viruses are made up of a Protein Coat (Capsid), Genetic Material (double or single-stranded RNA or DNA), and sometimes an Envelope (made from Lipids taken from the host cell.

• The Capsid is made up of simple repeated units of a Protein called Capsomeres.

• Viruses only reproduce inside a living cell.

• To do this, Viruses must first enter the cell through the Plasma Membrane and (if present) the Cell Wall.

• Viruses do so by either attaching to a Receptor on the cell’s surface or by simple mechanical force.

• The Virus then releases its Genetic Material (DNA or RNA) into the cell.

Identify the differences between a Prokaryotic Cell and a Eukaryotic Cell.

Prokaryote:

• Diameter: 0.5-5nm.

• DNA: Circular and free in Cytoplasm.

• Ribosome Size: About 18nm (70S).

• Endoplasmic Reticulum: None.

• Organelles: Few, and none are Double Membrane.

• Cell Wall: Present.

Eukaryote:

• Diameter: Up to 40nm.

• DNA: Double-helix contained in the Nucleus.

• Ribosome Size: About 22nm (80S).

• Endoplasmic Reticulum: Present and may have Ribosomes.

• Organelles: Many types, some Single Membrane and some Double Membrane.

• Cell Wall: Sometimes present (Plant cells).