Cells are the basic units of life. The cell theory, built from the work of many scientists after microscopes were invented, has three parts: all living things are made of one or more cells, the cell is the basic unit of structure and function, and all cells come from existing cells. Inside, cells have parts called organelles, each with a job. The nucleus holds DNA and controls the cell, mitochondria release energy from food, ribosomes build proteins and the cell membrane controls what enters and leaves. Plant cells also have a cell wall, chloroplasts and a large central vacuole.
The NGSS performance expectations MS-LS1-1, MS-LS1-2 and MS-LS1-3 ask middle schoolers to gather evidence that living things are made of cells, model how the parts of a cell work together and explain how cells build tissues, organs and organ systems. A useful way to remember organelles is to link each one to its function, like jobs in a factory. Work through the questions, then read each explanation to lock the facts in.
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Answer: B) Nucleus
The nucleus holds the cell's DNA, which carries the instructions for everything the cell does.
Answer: mitochondria (also accepted: mitochondrion)
Mitochondria break down glucose to release usable energy, which is why they are called the powerhouse of the cell.
Answer: C) Cell wall
Plant cells have a rigid cell wall made of cellulose. Animal cells have only a flexible membrane.
Answer: cell membrane (also accepted: membrane, plasma membrane)
The cell membrane is selectively permeable: it lets some substances in and keeps others out.
Answer: A) All cells come from existing cells.
The cell theory states that all living things are made of cells, cells are the basic unit of life and all cells come from existing cells.
Answer: prokaryotic (also accepted: prokaryote, prokaryotes)
Prokaryotic cells have DNA but no nucleus around it.
Answer: C) cell, tissue, organ, organ system, organism
Cells form tissues, tissues form organs, organs work together in organ systems, and systems make up the whole organism.
Answer: ribosome (also accepted: ribosomes)
Ribosomes read instructions from DNA (via RNA) and assemble proteins.
Answer: B) central vacuole
The central vacuole fills with water and presses against the cell wall, keeping the plant upright.
Answer: tissue (also accepted: a tissue)
A tissue is a group of similar cells doing the same job.
Answer: B) Microscope
Most cells are too small to see with the naked eye. Robert Hooke used a microscope to observe and name cells in 1665.
Answer: chloroplast (also accepted: chloroplasts)
Chloroplasts contain chlorophyll and carry out photosynthesis.
Answer: A) cytoplasm
Cytoplasm fills the cell, and many chemical reactions happen in it.
Plant cells have both chloroplasts AND mitochondria. They make glucose and also need to release its energy.
All cells have a membrane. Only some (plants, fungi, bacteria) also have a rigid wall outside it.
Bacteria are prokaryotes: their DNA floats in the cytoplasm with no nucleus around it.
The order is cell, tissue, organ, organ system, organism. Tissues are made of cells; organs are made of tissues.
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Open the student portal βProkaryotic cells, like bacteria, have no nucleus or membrane-bound organelles. Eukaryotic cells, like plant and animal cells, have a nucleus and organelles surrounded by membranes.
Robert Hooke named cells in 1665 after looking at thin slices of cork under a microscope.