Biology (microscopes, cells, and specialised cells)

Microscopes

Key Concepts: Lenses, Microscopes, and Staining

• Lens: A clear glass or plastic disk that focuses light. Lenses are fundamental components in eyeglasses, telescopes, cameras, and many other optical instruments.

• Microscope: A device that utilizes lenses to magnify an object. The term is derived from two words:

  • Micro: Meaning small.

  • -scope: Meaning to view or look at.

• Function: Microscopes enable the observation of thin layers of cells, which are the basic building blocks of living organisms.

• Magnify: The process of making small objects look bigger.

• Enlarge: To make bigger.

• Microscopes and Dyes:

  • Because many cells are almost transparent or have components that are difficult to distinguish, coloured dyes or stains are applied to make them more visible.

  • The staining process makes different parts of the cell easier to see when the sample is magnified and lit up.

  • Common Stain Colours: Pinks, blues, purples, greens, and browns are frequently used.

Anatomy of a Microscope: Lenses and Magnification

• Dual Lens System: A microscope contains two distinct types of lenses that work together to magnify an image.

• 1. Eyepiece Lens: This is the black lens located at the top that the user looks through. It has a standard magnification of $10\times$.

• 2. Objective Lenses: These are the three silver lenses located nearest to the object being viewed. There are typically three different magnification options:

  • Low power: $40\times$

  • Medium power: $100\times$

  • High power: $400\times$

• Understanding Magnification: Magnification is described similarly to multiplication in mathematics. A magnification of $10\times$ means the object looks 10 times larger than its actual size.

Anatomy of a Microscope: Observation and Support Parts

• Slide: A thin piece of glass where samples (specimens) are placed for observation.

• Stage: The flat platform that holds the slide. It is equipped with clips to secure the slide in place.

• Light: This component shines light through the glass slide and the sample to make it visible.

  • Illuminate: To make something visible or bright by shining light on it.

• Focusing Dials: "Focusing" refers to making an image clear. There are two dials for this purpose:

  • Coarse focus (large dial): Moves the stage up or down to bring the sample into general focus.

  • Fine focus (small dial): Used for fine-tuning the focus to increase the detail and sharpness of the image.

• Support Structures:

  • Arm: Supports the lenses and connects them to the base.

  • Base: Supports the entire weight of the microscope and houses the light source.

Procedural Guide: Using a Microscope Safely

To ensure safety and the protection of the equipment, follow these seven steps:

1. Carry the microscope with two hands: This ensures stability and prevents dropping the instrument.

2. Place the microscope on a flat surface: A stable, level surface is necessary for proper operation.

3. Ensure the smallest objective lens is in place: Always start with the lowest magnification ($40\times$).

4. Lower the stage and put the slide on it: Create space before placing the specimen on the stage.

5. Looking from the side, raise the stage to the top: Do this while looking from the side to ensure the lens does not hit the slide.

6. Look through the eyepiece lens and turn the coarse focus knob: Move the dial until a general image becomes visible.

7. Use the fine focus knob to sharpen the image: Adjust the small dial to bring out the fine details of the sample.

Relevance and Biological Context

• Biology: The study of living things and what it means to be alive.

• Application: Understanding microscopes is essential because biology involves looking at cells and body systems that allow living things to function. Microscopes are specifically used to examine the cells of both plants and animals

Cells

What is a Cell?

The basic unit of life. It is called this because it is the smallest unit of an organism that is considered living. Some living things are unicellular, while others are multicellular.

Key Features of Cells

Cells can be all different shapes and sizes and contain different things, however they all share:

1. Cytoplasm–Fluid inside the cell that contain structure & contains part of the cell.

2. Cell Membrane–The cell membrane forms a barrier around a cell, controls what comes in and out.

3. DNA–Genetic material found in a double-helix structure.

Animal Cells:

Vacuole (small)

Mitochondria

Cell membrane

Cytoplasm

Plant Cells:

Vacuole (large)

Mitochondria

Cell Membrane

Cytoplasm

Cell Wall

Chloroplast

Functions of Organelles

Cells are made up of organelles (little organs), which are smaller parts of the cell, each one serving a different function;

1. Nucleus–Contains DNA.

2. Mitochondria–Releases energy from food.

3. Ribosomes–Produces proteins.

4. Lysosomes–Gets rid of waste.

5. Endoplasmic Reticulum–Allows materials to move through the cells.

6. Golgi Body–Packages protein inside the cell before they are sent to its designated area.

7. Vacuole–Stores water, nutrients and wastes

A plant cell has the 2 extra organelles in cell walls to provide structure and chloroplasts, which contain chlorophyll vital for photosynthesis. Fungi cells have a cell wall, but not a chloroplast.

Types of Cells

There are 2 main cell types, prokaryotic and eukaryotic

Prokaryotic Cells

• These are the most primitive cell forms on Earth

• Only possesses a few organelle

• Their DNA is in the cytoplasm, leaving no nucleus

• All bacteria are prokaryotic

• Vary in shapes and sizes, usually small (0.1-5µm)

Eukaryotic Cells

• These are more complex than prokaryotic cells, generally also having more organelles

• They can be unicellular or create multicellular organisms

• Contain a nucleus

• Larger in size (10-100µm)

Unicellular Organisms

• Many of the living things on Earth have one cell.

• Each one has a shape and size (structure) to suit their lifestyle

• They have evolved depending on the organism’s environment.

• Most live in water environments

Unicellular Structure

Specialised Cells in the Human Body

• The human body has ~37 trillion cells in total, including over 200 different types of cells

• Specialised cells have unique structures and characteristics to carry out their particular role

Muscle Cells

• Large number of Mitochondria, releasing more energy because of contractions

• Cells are long and tubular, helping them contract and relax

There are 3 muscle types:

1. Skeletal (voluntary muscles)–moves the skeleton’s bones

2. Smooth (involuntary muscles)–help our internal organs carry out functions such as breathing and digesting

3. Cardiac (heart muscles)–allow heart to continuously beat, non-stop

Nerve Cells/ Neurons

• Carry messages throughout the body.

• A majority of them are found in the brain and spinal cord.

• Some nerve cells have very long tail-like fibres called axons extending from the cell. These allow the cell to carry messages over long distances.

• Axons are insulated by myelin sheaths to allow messages to pass along them very quickly.

• Uses electricity travelling through synaptic links; when you think a synapse sparks.

Red Blood Cells (erythrocytes)

• Carry oxygen from the lungs around the cells of the body where it is used to release energy.

• Contain Haemoglobin to help them carry oxygen

• Have no organelles so they can carry more haemoglobin

• They are still considered as Eukaryotic because of specialisation

• Specialised shape (biconcave) to increase surface area allowing oxygen to enter the cell easier

Fat Cells

• Store energy that can be used to produce heat, and to form an insulating layer.

• Fat cells:

                    -Have a flattened disc-shaped nucleus to allow more room for fat

                    -Contain a specialised vacuole called a fat reservoir to allow more fat to be stored

                    -Have a specialised cell membrane to allow the cell to expand more easily

Reproductive Cells (Sperm and Ova)

• Sperm (spermatozoa) and eggs (ova) are cells that contain half the amount of DNA of a normal cell which combine during fertilisation for sexual reproduction

• Sperm uses flagella for mobility, to travel to the ovum

• Ovum contains a large amount of cytoplasm to provide the new organism with nutrients.

Specialised Cells in Plants

Guard Cells and Stomata

• Found on the leaves and stems of plants.

• Work in pairs to open and close very tiny pores called stomata (plural for stoma)

• Gases needed by the plant enter through open stomata and unwanted gases leave the same way

Photosynthetic Cells

• Cells near the surface of the green parts of stems and leaves have large number of chloroplasts

• Chloroplast contains chlorophyll

• Chlorophyll traps the sun’s energy, which the plant then uses in photosynthesis

• Carbon Dioxide→Oxygen+Glucose

• Plant cells unexposed to the sun have no chloroplasts

Conducting Cells–Phloem and Xylem

• Plants take in water from the soil through their roots. This water is needed in the leaves for photosynthesis

• The water is transported from the roots to the leaves via xylem

• The food made through photosynthesis then needs to return to the roots & stems for the plant to live

• The food is transported from the leaves to the roots via phloem

Root hairs

• Water comes into plants from the soil through roots of plants have extensions called root hairs