Cells: The Basic Unit of Life: Grade 6 Study Guide
All living things are made of cells. Different cells have different jobs.
All living things are made of one or more cells. Some organisms, such as bacteria, are a single cell; others, like humans, have trillions. Cells were first seen using microscopes, which let us see structures too small for the eye.
Cells have parts called organelles that carry out specific jobs. Cells with similar jobs form tissues, tissues form organs, organs form organ systems and systems work together in an organism.
Parts of a cell
| Part | Job | Plant | Animal |
|---|---|---|---|
| Cell membrane | controls what enters and leaves | yes | yes |
| Nucleus | contains DNA; directs the cell | yes | yes |
| Mitochondria | release energy from food | yes | yes |
| Cell wall | rigid support | yes | no |
| Chloroplasts | make food by photosynthesis | yes | no |
| Vacuole | stores water and nutrients | large | small or none |
Levels of organization
A muscle cell is long and packed with mitochondria, giving energy for movement. A nerve cell has long branches that carry signals. A root hair cell has a thin extension that absorbs water. Structure matches function. Cells divide to make new cells for growth and repair.
Basic unit.
Similar cells together.
Tissues working as a unit, like the heart.
Organs working together, like the circulatory system.
Using a microscope
A light microscope magnifies objects by combining an eyepiece lens and an objective lens. Total magnification = eyepiece × objective: 10 × 40 = 400×. Start with the low-power lens, use the coarse focus first, then the fine focus, and carry the microscope with two hands. Make a labeled drawing with a title, magnification and scale.
Worked example and common misconceptions
Example: An onion skin cell under the microscope shows a clear wall and a nucleus, but no chloroplasts because the onion bulb grows underground. Common misconceptions: thinking plants have no mitochondria (they do), that cells are all the same shape and that the nucleus is the only important part. Compare diagrams with real images.
Check your understanding: model answers
1. Cell wall and chloroplasts. 2. They release energy from food. 3. 400×.
✨ Key Takeaways
- All living things are made of cells.
- Organelles have specific jobs.
- Plant cells have a cell wall and chloroplasts.
- Cells → tissues → organs → systems.
💬 Questions for Discussion & Reflection
- Name two parts found only in plant cells.
- What is the job of mitochondria?
- Calculate the magnification: 10× eyepiece and 40× objective.
Print a science observation log →