Grade 6 Science Practice Test: Cell Structures, Organelles and Microscopes

The cell theory says all living things are made of cells, cells are the basic unit of life, and new cells come from existing cells. Cells forming from nonliving matter is an old idea that experiments disproved.

The nucleus holds the DNA, which carries the instructions for the cell's work. The membrane controls what enters and leaves, but it does not hold the instructions.

Mitochondria break down sugar to release energy the cell can use. Chloroplasts do the opposite job: they capture light energy to make sugar.

Plant cells have a stiff cell wall outside the membrane; animal cells do not. Both kinds of cells have a membrane, a nucleus and mitochondria.

The membrane lets some substances in and out and keeps others out. A stiff shape comes from the cell wall in plant cells, not from the membrane.

Chloroplasts carry out photosynthesis, using light energy to make sugar from carbon dioxide and water. They are why leaves look green.

Total magnification is eyepiece times objective: 10 x 40 = 400. Adding the two numbers gives 50x, a common mistake.

The central vacuole stores water, and when it is full it presses outward so the plant stands up straight. A plant that wilts has lost water from its vacuoles.

Ribosomes build proteins using instructions that come from the DNA. They are tiny and found in both plant and animal cells.

Similar cells form a tissue, tissues form an organ, and organs working together form an organ system. For example, muscle cells form muscle tissue, which is part of the heart.