SC.7.L.16.1: Understand and explain that every organism requires a set of…
Understand and explain that every organism requires a set of instructions that specifies its traits and that this hereditary information (DNA) contains genes located in the chromosomes of each cell (partial; the strawberry DNA lesson).
The Florida's State Academic Standards for Science (NGSSS) outcome SC.7.L.16.1 (Life Science) for Grade 7 says: “Understand and explain that every organism requires a set of instructions that specifies its traits and that this hereditary information (DNA) contains genes located in the chromosomes of each cell (partial; the strawberry DNA lesson).” This Fieldbook unit teaches it hands-on, with everyday materials and a printable teacher guide and student sheet for every lesson. Official wording: Florida's State Academic Standards for Science (NGSSS).
Cells: The Smallest Living Things Grades 7–8
How small is a cell, how does water get in, what's inside, and why are cells so tiny? Four lessons with potatoes, strawberries and gelatin that work with a microscope or without one.
- How big is a cell? 50–60 min
Students measure tiny things they can see, count how many fit across a millimetre, and build a scale ladder from a hand down to a single cell. With a microscope or a phone and a drop of water, they look at real onion cells and estimate their size.
- How do things get in and out of a cell? Two sessions: 45 min, then 30 min the next day
Students weigh potato strips, soak them in plain and salty water, and measure how their mass and stiffness change. They use the results to explain diffusion and osmosis, and why a wilted salad goes limp.
- Can you pull DNA out of a strawberry? 50–60 min
Students mash strawberries with dish soap and salt, filter the juice, and watch a cloudy white tangle of DNA appear when the teacher layers cold rubbing alcohol on top. They explain what each ingredient did to the cell, and test what happens without soap.
- Why are you made of many small cells, not one big one? 50–60 min, with cubes soaking for at least an hour
Students soak gelatin cubes of 1, 2 and 3 cm in food colouring, cut them open and measure how far the colour got in. They calculate surface area to volume and explain why cells stay small.
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