# The Microscope

## The Microscope

Using the microscope

1. Mount slide on stage using stage clips

2. Turn on light source – adjust so it is bright but doesn’t hurt your eyes

3. Adjust diaphragm – try it out

4. Put the stage to the lowest setting and put the slide in

5. Start with lowest power objective lens and focus using coarse adjustment knob (turn it until the stage reaches the top then go back one turn)

6. Adjust focus on eyepiece for your eyes

7. Move the slide around the stage adjustment knobs

8. If you wish, move up to a higher magnification and use the fine adjustment knob ONLY to focus – IMPORTANT

9. Make further adjustments if necessary

10. To put the microscope away turn to the lowest lens, put the stage to the lowest setting and take the slide out.

11. Cover, tie up the cord and put back in the cupboard as you found it

Magnification and Measurements

 Measurement Symbol Power/m How many in proportion to 1m? How many in 1m? Written as a number 1 millimetre mm 10-³ metre 1/1000m One thousand 1 micrometre μm 1/1 000 000m 1 nanometre nm 10-⁹ metre One billion 0.000000001

Calculation of sizes and magnification values in biology questions

Magnification = measured size divided by actual size

Magnification

Measured size

Actual size

÷

x

If two of the figures are available then these can be used to work out the third one. Numbers on the top are divided by number on the bottom. Numbers beside each other are multiplied.

So:

· If you know the magnification and the actual size you can multiply them to give the measured size

· If you know the measured size and the actual size you can divide the measured size by the actual size to give the magnification

· If you have measured the size in the picture and know the magnification you can divide the measured size by the magnification to give the actual size

Drawing for Biology

· Use a pencil

Figure 1: The Eukaryotic Cell.

Magnification x400

· Draw in two dimensions (unless 3D is needed to make a point clearer for example for SEM)

· Blank paper

· Lines should not have breaks

· Drawings should be approximately half an A4 page

· Use line to annotate. The lines should not cross

· Drawings should have:

· A figure number – at the bottom

· A title – at the bottom after the figure number

· A legend (not always required)

· Magnification or size (required for microbiology assessment)

· Annotations and labels

Drawings should ‘stand alone’, there should be enough information for the reader to understand what is going on in the picture without having to refer to the main text.

BUT in reports and essays drawings are referred to in the main text to make the text clearer. For example, an essay text contains the sentence: eukaryotic cells contain a number of organelles (see figure 1).

Note, figure number and title at the bottom

Figure 1. The eukaryotic cell.

Some organelles are labelled.

Original magnification x400

Note figure number, title and legend at the bottom

Cells

There are resources below to get you started and you can visit these websites for more information:

https://www.centreofthecell.org/learn-play/games/explore-a-cell/ – interactive but basic

https://www.britannica.com/science/organelle

 Tissue Types Features & Functions Examples Epithelium   Usually forms a barrier between the external and internal environment or between two internal tissues or organs. Endothelium is a type of epithelium which lines the blood vessels. Squamous Thin, paving stone appearance. These cells are adapted for diffusion as they are thin and this reduces the diffusion distance. Squamous epithelium in the lungs: squamous epithelium lines the alveoli – the small sacs at the end of the airways where gas exchange occurs. Cuboidal These cells can be both secretory and for absorption. They resemble rounded cubes. Found in the kidneys and other organs. Columnar Columnar epithelium is where the height of the cell is four times the width. They usually have a secretory function such as mucus in the lungs and digestive enzymes in the small intestine. They also can also be involved in absorption, particularly in the digestive tract. Stratified epithelium in the oesophagus. The cells are being continuously made at the basement membrane and move upwards. The upper layers of cells are dead and full of the protein keratin. When food passes the top cells can be sloughed off without damaging the tissue below. Stratified Stratified epithelium has multiple layers of cells. The layers provide a strong protective surface. pseudostratified Pseudostratified epithelium appears to be stratified columnar cells but in fact all cells are attached to the basement membrane. It has a secretory function. Pseudo stratified ciliated epithelium in the upper respiratory tract. The secretory goblet cells produce mucus which traps unwanted microorganisms. The cilia aid movement of the mucus back up the respiratory tract. Ciliated Ciliated epithelium has tiny hair-like cilia on the top (apical) surface. Cilia can move and are involved in the movement of substances such as mucus. Connective tissue   Mostly tissue with a structural component such as fibres. Blood is included in this category as it is made in the bone marrow. Loose: areolar, reticular, adipose Areolar connective tissue has cells and fibres creating a loose matrix. It connects skin to the surrounding tissue; holds organs in place and provides support for nervous tissue. Elastic tissue. The fibres in this tissue can stretch without breaking when needed. They can be found in the larger blood vessels such as the aorta which expands when blood is pumped through from the heart. Dense: fibrous & elastic Fibrous connective tissue is found in tendons and ligaments. It contains bundles of the protein collagen which are very strong. Blood: red and white cells, lymph White blood cells fight pathogens either by engulfing them (phagocytes) or by producing neutralizing antibodies (B-lymphocytes) Red blood cells are adapted to carrying oxygen around the body. The middle is thinner than the outside giving them a donut like shape. They are flexible and can squeeze through the smallest blood vessels. As they mature they lose their nucleus so they can pack in more of the oxygen carrying protein haemoglobin. Structural: cartilage & bone Cartilage is a smooth but flexible layer which covers the end of the bones and provides the structure for organs such as the ear. Bone has calcium deposits and collagen fibres which makes it very strong. Nervous tissue   Neuronal cells present in the CNS and the PNS Neurons: sensory, relay and motor Sensory neuron: detects changes in the environment. Conveys impulse to the brain or spinal cord To convey electrical impulses, which act as communication, between the body and the brain. Relay neuron: connects sensory and motor neurons Motor neuron: conveys impulse to effector organs such as muscle and glands Muscle tissue   Cell are adapted for movement Smooth muscle Smooth muscle is found in sheets surrounding the tubes of the body such as the digestive system and the blood vessels. The sheets are often layered with the cells organised in different directions. Smooth muscle responds to the autonomic nervous system. In the digestive system it causes peristalsis which moves the food through the digestive tract. In blood vessels it controls how much blood flows through various tissues. Striated muscle Striated muscle is skeletal muscle which, along with the skeletal system, allows movement. The cells fuse end to end during development to form long fibrils. Multiple fibrils form a muscle. These are packed with the proteins actin and myosin which slide against each other to lengthen or shorten the fibril and so the muscle. The stripes or striations formed by actin and myosin can be seen under the light microscope. Cardiac muscle Cardiac muscle cells also have striations but the cells are not fused. They have intercalated discs which are linked to the nervous system and ensure all of the muscle cells contract at the same time.

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