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Grade 4
Topic Summary
The World of Living Things

The Cells in Living Things


In this topic you will learn what cells are made of.

Most cells have everything they need to carry out the five basic life functions. Plant and animal cells are not made up of all the same parts. Two major parts of a plant cell include chloroplasts and the cell wall. Chloroplasts are a plant cell's food factory. The cell wall is a thick, stiff structure that protects and supports a plant cell.

Animal cells do not have chloroplasts or cell walls. However, animal and plant cells do have some of the same parts. The nucleus is one of the largest parts of the cell. It is the cell's control center.

A vacuole is a holding bin for food, water, and waste. Plant cells have one or two vacuoles. Vacuoles are small in animal cells. Animal cells have more vacuoles than plant cells. The cell membrane is an animal cell's thin outer covering. In plants it is found beneath the cell wall. Cytoplasm is the jellylike substance that fills the cell. It is mostly water but contains many important chemicals.

Chromosomes are threadlike structures that control an organism's traits. To reproduce, a cell makes a copy of its chromosomes. It then splits to form two new cells. Each new cell gets a copy of the chromosomes.

The basic differences between most plant and animal cells include their covering, color, and shape. A plant cell has a thick wall. An animal cell has a thin covering. Most plant cells have green coloring. An animal cell does not. Most plant cells have a boxy shape. Animal cells have a wide variety of shapes.

There are some other types of cells and organisms. The one-celled microorganisms that live in pond water are called protists. Bacteria are also one-celled organisms. A bacterium has a cell wall but no nucleus. Some bacteria cause illnesses, such as strep throat. Many bacteria are helpful. Some are used to make cheese. Some break down waste materials. A mushroom is a fungus made of many cells. Cells of fungi have a nucleus and a cell wall. Fungi do not have chloroplasts or make food.

Viruses only contain parts of chromosomes. A virus does not make or use food. It does not grow, change, nor respond to an environment. It only reproduces. There are many types of organisms and cells. Learning what different cells look like can help us identify organisms.