B1.1 - Cell structures

Which of Light microscopes and Electron are optical and which isn’t ?

Light Microscopes - Optical

Electron Microscopes - Non - Optical

Why do we use microscopes ?

Many Biological structures are too small to be seen by the naked eye so scientists use optical microscopes to see tissue, cells and organelle

Summary of how optical microscopes work:

Light is directed through a thin layer of biological material that is supported on a glass slide

Then light is focused through several lenses so an image is visible through the eyepiece

Name the components of a Light (optical) Microscope:

• The eyepiece lens

• The objective lenses

• The stage

• The light source (can be external also)

• The coarse and fine focus

What other external apparatus is used when prepping a light microscope?

• Forceps

• Scissors

• Scalpel

• Coverslip

• Slides

• Pipette

What are each of these labels referring to?

What is the setup - prep - calibration of a light microscope?

Specimens must be placed on a slide to be observed under the light microscope.

• Is carefully done to avoid damaging specimen + structures within it

How to prep a liquid specimen for a light Microscope?

1. Add few drops of sample to slide using a pipette

2. Place coverslip on top and gently press down to remove air bubbles

• Wear gloves to prevent cross contamination

How to prep a solid specimen for a light Microscope

1. Cut a small sample of tissue

2. Then peel a very thin layer of cells from tissue using scalpel/forceps and place on a slide

• (Some samples may need chemicals to make tissue rigid (kill))

3. Place coverslip on top and gently press down to remove air

• (Some tissues may need a stain to make structures visible, (if transparent/colourless))

• ex: methylene blue to stain cheek cells and iodine to stain onion cells

How to prevent dehydration of a tissue?

Thin layers of material placed on slide can dry up rapidly

• So adding a drop of water to specimen (beneath coverslip) can prevent cell damage by dehydration

How to view a specimen on Light Microscope?

Always start with low power objective lens:

• Easier to find what you’re looking for

• This helps prevent damage to lens or coverslip if stage is raised too high

Why is an image unclear/blurry on Light microscope?

Switch to low power objective lens and use coarse focus to get a clearer image

Consider if sample is thin enough for light to pass through to see structures

Could be cross-contamination with foreign cells

Limitations of Light Microscopy:

1. Size of cells/structures may appear inconsistent in different specimen slides: cell structures are 3d and different tissue samples will have been cut at different planes resulting in inconsistencies when viewed on a 2D slide

2. Optical Microscopes aren’t the most powerful so some structures can’t be seen

3. Treatment of specimens when preparing slides could alter cell structures

How to get smaller units and how to get bigger units in unit conversion?

to get smaller units you x

to get bigger units you /

1m = 1000mm

1mm = 1000µm

1µm = 1000nm

Calculating Magnification formula and triangle: (with sizes)

Magnification = Image size / Actual Size

Calculating Magnification of light microscope: (with lens)

Magnification of light microscope = Magnification of eyepiece lens x Magnification of objective lens (picture the triangle with this formula asw)

Do m to mm to micrometres to nanometers

1m = 1000mm

1mm = 1000µm

1µm = 1000nm

What are organisms made of?

made of cells which are the smallest unit with the basic properties of life

Name the 2 types of cellular organisms

eukaryotes or prokaryotes 

Define a Eukaryote:

A eukaryote is a larger and more complex organism than Pro-K whose cells contain a nucleus and membrane‑bound organelles to help efficiently carry out functions within the cell (ex: animal and plant cells)

Define a Prokaryote:

Only Unicellular and is an organism whose cells do not have a nucleus or membrane‑bound organelles (ex: bacteria)

What’s the Prokaryote cell structure like?

KEY: NO NUCLEUS IN PROKARYOTE

Cytoplasm - contains gel like substance where most chemical reactions take place

Cell Membrane - encloses the cytoplasm, acts as a selective barrier, controlling what goes in + out of cell.

• Receptors in membrane help prokaryotes sense their environment

Cell Wall - The outside of the cell is surrounded by a cell wall which Helps provide strength and maintain the shape of the cell

One long circular chromosome in Pro-K which floats free in cytoplasm (no nucleus), controls cell activities and replication

Plasmids - Small loops of DNA called plasmids may be present: - Can be exchanged between bacteria and give additional benefits ex: antibiotic resistance

Ribosomes - For protein Synthesis

Label this Animal Cell

Name the Structures and Functions in Animal Cell: (also what do Animal cells have similar to Pro-K and what do animal cells have that Pro-K don’t have)

(b) Cytoplasm - Gel-like substances composed of water and dissolved solutes , supports internal cell structures, site of many chemical reactions including anaerobic respirations

(b) Cell membrane - Holds cell together separating inside of cell from outside , controls which substances can enter and leave cell

(a only) Nucleus - Contains Genetic Material (DNA) which controls the activities of the cell

(a only) Ribosomes - Site of Protein Synthesis, Found in cytoplasm

(a only) Mitochondria - Site of most of the reactions involved in aerobic respiration, cells with high metabolism (carry out many different cell reactions) have significantly higher numbers of mitochondria than cells with lower metabolism

Label this Plant cell:

Name the Structures and Functions in Plant Cell: (also what do Animal cells have that Plant cells don’t have) (all other sub-cellular structures both animal and plant have)

(p only) Cell Wall - Rigid Cell wall made of cellulose to provide additional support for the cell, defining its shape

(p only) Chloroplasts - Site of Photosynthesis providing food for plants, they contain green chlorophyll pigment absorbs light energy needed for the reaction to occur

(p only) Vacuole - Contain cell sap, used for storage of certain material, also helps support cell shape

(b) Cytoplasm - Gel-like substances composed of water and dissolved solutes , supports internal cell structures, site of many chemical reactions including anaerobic respirations

(b) Cell membrane - Holds cell together separating inside of cell from outside , controls which substances can enter and leave cell

(b) Nucleus - Contains Genetic Material (DNA) which controls the activities of the cell, controls cell division

(b) Ribosomes - Site of Protein Synthesis, Found in cytoplasm

(b) Mitochondria - Site of most of the reactions involved in aerobic respiration, cells with high metabolism (carry out many different cell reactions) have significantly higher numbers of mitochondria than cells with lower metabolism

Why are Electron microscopes?

Light microscopes have limited resolution and magnification

Electron microscopes help address this limitation with beams of electrons, not light, to visualise specimens

• Wavelength of electron beams are much smaller than visible light which give electron microscopes a much higher resolution and magnification. so we can see smaller structures in detail

Why aren’t Electron Microscopes found in schools?

Very expensive and not portable

Electron Microscopes vs Light Microscopes: (differences)

EM:

Large + once installed, can’t be moved

Vacuum needed

Complicated sample prep

Over x500 000 Mag

Resolution of 0.5nm

Specimens are dead

LM:

Small + easy to carry

No Vacuum needed

Easy sample prep

up to x2000 Mag

Resolution of 200nm

Specimens can be living/dead