Grade 8 Science Study Guide: Cells & Microscopes

Vocabulary flashcards for Grade 8 Science covering cells, organelles, cell theory, characteristics of living things, and microscopes.

Cell

The smallest unit of life. All living things are made of one or more cells.

Cell theory

Three postulates: (1) All living things are made of one or more cells. (2) The cell is the basic unit of structure and function in living things. (3) All cells come from pre-existing cells.

Magnification

How many times larger an image appears than the actual object.

Field of view

The circular area visible through a microscope.

Organelle

A small structure inside a cell that performs a specific function.

Cytoplasm

Watery fluid in which organelles are suspended; materials move through it and many chemical reactions occur. It is not an organelle.

Cell membrane (plasma membrane)

Surrounds the cell contents and controls movement of substances into and out of the cell.

Nucleus

The cell's control centre; regulates cell activities and stores genetic information.

Chromosomes

Structures in the nucleus that contain genetic information, including genes.

Vacuole

A membrane-surrounded storage compartment for water, nutrients, food, and wastes. Plant cells usually have one large central vacuole.

Cell wall

Rigid cellulose structure around plant cells that provides support and protection; substances pass through small pores.

Chloroplast

Green organelle in plant cells; site of photosynthesis. Chlorophyll inside absorbs sunlight.

Chlorophyll

Substance inside chloroplasts that absorbs sunlight to help make food from carbon dioxide and water.

Flagella (singular: flagellum)

Long, tail-like structures that propel cells through fluids; cells usually have one or two.

Cilia (singular: cilium)

Numerous short, hair-like projections that move a cell or substances around it.

Electron microscope

A microscope that uses electrons instead of visible light to see very small details.

Nutrition

Obtaining food or nutrients for energy, growth, and repair.

Respiration

Chemical reactions that release energy from food; not simply the same as breathing.

Excretion

Removing metabolic wastes, such as carbon dioxide and urea.

Response to stimuli

Reacting to changes in the environment, such as light, sound, or temperature.

Growth

Increasing in size or number of cells.

Reproduction

Producing offspring to continue the species.

Mitochondria

Organelles found in both plant and animal cells that release usable energy through cellular respiration.

Photosynthesis

Process in chloroplasts that uses energy from sunlight, absorbed by chlorophyll, to help make food from carbon dioxide and water.

Cellulose

A substance that makes up plant cell walls. Paper and the stringy strands in celery contain cellulose.

Compound light microscope

Uses visible light and glass lenses to view living or dead specimens in colour; common in school labs.

Scanning electron microscope (SEM)

Uses an electron beam to scan a specimen's surface, showing detailed surface texture and a 3D-like image; specimens cannot be alive during viewing.

Transmission electron microscope (TEM)

Passes electrons through an extremely thin specimen to show detailed internal structures in a 2D image; specimens cannot be alive during viewing.

Total Magnification Formula

$$\text{Total magnification} = \text{eyepiece magnification} \times \text{objective magnification}$$

Coarse adjustment knob

Microscope control used for large focusing movements, generally used on low power.

Fine adjustment knob

Microscope control used for small focusing movements to sharpen the image, especially on high power.

Diaphragm

Microscope part that controls the amount of light.