Week 10 · Unit 3 Living Organisms, Their Structure and Processes, opener; Lesson 1 Cells and Life: the cell as the unit of life, prokaryotes and eukaryotes, unicellular and multicellular organisms, stem cells · 3 lessons
1
The cell: the building unit of life
Science Prep 1 Term 1, Unit 3: pp. 55–63
GoalExplain that the cell is the unit of life and order cells, tissues, organs and systems.
New words
cell · the unit of structure and function of living thingstissue · a group of similar cells that do the same joborgan · a part of the body made of different tissues working togethersystem · a group of organs that work together
Explanation
The atom is the unit of matter, and the cell is the unit of structure and function of living things. A living organism is built in levels. Similar cells form a tissue. Different tissues form an organ. Several organs working together form a system, and the systems together make the whole organism. Scientists also group living things by their similarities and differences. This is called classification. Think of a city: houses are cells, streets of houses are tissues, buildings with a job such as a school or a hospital are organs, and districts are systems. The way a cell is built suits its job: a muscle cell is long, so it can shorten and lengthen.
cells→tissue→organ→system→organism
Worked examples
heart muscle cells→heart muscle tissue→the heart→circulatory system
In your body, heart muscle cells form heart muscle tissue. This tissue and others (such as blood vessels) make the heart, which is an organ. The heart, blood and blood vessels work together as the circulatory system.
A muscle cell is long and thin, like a thread. Its shape suits its job: it can shorten (contract) and lengthen (relax) to move a part of the body. Structure fits function.
Scientists group living things by similarities and differences. A camel and a horse are both animals that feed milk to their young, but a date palm is a plant. Grouping like this is classification.
Class activity
Paper city of the body. On a big sheet draw four labelled boxes, one inside the other: cell, tissue, organ, system. Choose an example for each level, for example a stomach muscle cell, muscle tissue, the stomach, the digestive system. Then make a second chain for a plant: a leaf cell, leaf tissue, the leaf, and the whole plant.
Practice
1
What is the unit of structure and function of living things?
The cell.
2
Put in order from smallest to largest: organ, cell, system, tissue.
Cell, tissue, organ, system.
3
Why is a muscle cell long?
So that it can shorten and lengthen to move a body part.
4
What is classification?
Grouping living things by their similarities and differences.
