A2.2 - Cell Structure

Outline cell theory and describe the structure and components of a typical cell

Outline cell theory and describe the structure and components of a typical cell

Cell theory states that all living things are made of individual units, cells, which are the basic units of life, and that all cells arise from other cells.

ComponentKey Function

Plasma Membrane

Regulates entry/exit, communication

Nucleus

Stores DNA, controls cell activities

Cytoplasm

Medium for reactions, supports organelles

Mitochondria

ATP production (energy)

ER	Protein (Rough) and lipid (Smooth) synthesis

Golgi Apparatus

Modifies, sorts, packages molecules

Lysosomes

Digestive enzymes for waste

Cytoskeleton

Structure, movement

Ribosomes

Protein synthesis

Summarise how to make and stain temporary mounts of cells and tissues

1. Using a sharp scalpel, cut a small square of onion.

2. Using tweezers, peel off a thin inside layer of the onion.

3. Transfer the thin layer of onion onto a glass slide.

4. Using a pipette, add a small drop of iodine onto your specimen.

5. Starting with the

   cover slip

    at a 90° angle, gently lower the cover slip over the specimen to avoid bubbles.

6. If bubbles do occur, gently press the cover slip with the eraser end of a pencil to push out the bubble.

To help visualise certain structures, we use stains. Stains bind preferentially to particular structures or areas on a cell, making that structure easier to see.

Describe how to use an eyepiece graticule and stage micrometre to measure the sizes of a specimen

Often, the eyepiece lens of light microscopes will be fitted with an eyepiece graticule. Eyepiece graticules contain a scale or grid. When we look through the eyepiece lens this scale will be superimposed on the image of the specimen. To be able to work out the size of the specimen we are viewing, we can use a stage micrometre to calibrate an eyepiece graticule. Stage micrometres are small, calibrated rulers that are mounted onto the stage of the microscope.

Equation involving actual size, image size and magnification

Magnification = image size (usually in nm/um) /actual size (what we measure ourselves)

Nanometer, micrometer, millimeter, meter

A student observes and draws an amoeba. The diameter of the amoeba in the drawing is 90 mm. The actual diameter of the amoeba is 100 µm. What is the magnification of the drawing?

1. change the units. 100um/1000 = 0.1mm

2. 90/0.1 = x900 magnification

How many millimetres are found in 76 000 μm?

76000um/1000 = 76mm

A white blood cell is viewed under a microscope using a magnification of ×400. The graticule measures the actual size of the cell to be 11 μm. Calculate the size of the image produced in mm.

1. 400 × 11um = 4400um

2. 4400/1000 = 4.4mm

A type of bacterium called Escherichia coli is viewed under the microscope using a magnification of ×50 000. The size of the image produced is 70 mm.

Calculate the actual size of this cell. Give your answer in micrometres.

1. 70/50000 = 0.0014mm

2. 0.0014mm x 1000 = 1.4um

Outline the applications of electron microscopy