The Jobs Inside a Cell

By the end of this lesson, you will be able to name the main parts of plant and animal cells and explain what each one does.

Think about your school on a busy day. The building has walls and doors, a front office, a cafeteria, a custodial closet, and workers making things happen. A cell works the same way. It is packed with organelles, which are tiny structures that each do one special job so the whole cell stays alive.

The cell membrane is the thin outer layer that surrounds every cell and controls what enters and leaves, like the doors of your school letting some people in and keeping others out. Plant cells also have a cell wall outside that membrane, a stiff layer that gives the plant support and shape, which is why a stalk of Texas corn can stand up straight. Inside, the nucleus acts as the office, storing the cell's instructions and directing activities.

Floating in the cell is cytoplasm, the jelly-like fluid that fills the space and holds the organelles in place. Ribosomes work in the cytoplasm like a kitchen crew, building proteins the cell needs to grow and repair itself. Mitochondria are the power plants; they release energy from food so the cell can do work, which is why your muscle cells are loaded with them during football practice.

Plant cells have chloroplasts, green organelles that capture sunlight and make sugar for the plant, a process that keeps pastures and oak trees fed. Both plant and animal cells have vacuoles, storage spaces for water, food, or waste. A plant's large vacuole stays full of water, which is why a wilting tomato plant perks back up after you water it.

Try it: if a plant cell lost its chloroplasts but kept everything else, what job could that cell no longer do?