Onion & Blood Cells Lab

ONION CELLS The thick, juicy layers of the onion are separated from each other by a protective skin. The onion skin is only one cell in thickness. The cells can be seen very easily through a microscope. Around the cell is a protective cell wall. Just inside the cell wall and very close to it is the cell membrane. Inside the cell membrane is a liquid called cytoplasm. The dark, round body floating in the cytoplasm is the nucleus of the cell. All the cells in the onion skin are alike. They are shaped somewhat like bricks and fit neatly together to make a protective wall. That is their job—to separate the layers of the onion.

Draw what you see. Label the cell wall, the cell membrane, the cytoplasm, and the nucleus.

Structure of onion cell Complete the chart: Structure of onion cell Function of structure Cell wall Gelatin-like substance that flows inside the cell membrane Important chemical reactions occur here Cell membrane Directs all cell activities Contains hereditary material made of DNA.

Infer: why you don’t you see any chloroplasts? Be aware that some cells are SPECIALIZED – this means that they have a special job or function. Think about the location of the actual onion in relation to the ground. Would the leaf have chloroplasts?

BLOOD CELLS The cells that are most numerous in an animal and that look like doughnuts are red blood cells. They are flat disks, thinner in the middle than at the edge. Because of this, the red blood cells look light in the middle and darker at the edge. A red blood cell has no nucleus and never reproduces; rather, it is produced in bone marrow. Red blood cells contain a special chemical called hemoglobin. This chemical makes it possible for the red blood cells to do their most important job—to carry oxygen from the lungs to other parts of the body. White blood cells are larger than red cells, and have nuclei. All white blood cells keep blood clean by eating bacteria and other foreign particles. In a drop of blood, there are approximately 5,000,000 red blood cells and 7,500 white blood cells.

Draw what you see. Label the cell membrane and the cytoplasm

Explain: why can’t a red blood cell reproduce? Specialized cells (like the onion cell seen previously) don’t always have all the structures you would see in other cells. Red blood cells lack an important organelle that contains the genetic material needed for reproduction – if you can figure this out, you’ll get the answer!

Recall: What is the function of red blood cells? Hint: re-read the paragraph at the beginning of the lab

Compare: How are white blood cells like lysosomes? Hint: Think about the FUNCTION of each of these two things. What purpose do they serve?

Why is it important for each cell structure to have its own individual function? This answer won’t be found in the textbook or in your notes… it’s in your head already! This is your ticket out the door!

Our Plant Cell Drawing

Our Animal Cell Drawing