Cell Structure and Organization | Grade 7 Science Lesson

Cell Structure and Organization

In the world of biology, understanding the structure and organization of a cell is fundamental. As a teacher, it is essential to effectively communicate this complex topic to students in a way that is engaging and educational. This article will guide you through a teacher-student conversation on cell structure and organization, providing insights and explanations that will help both educators and learners grasp this crucial concept.

Harry has always been curious about what made up living things. He went to his biology teacher and asked her.

Harry: I wonder what makes up living things, Mrs. Griggs. Is there a basic constituent?

Mrs. Griggs: Yes of course. Living things are made up of cells. Do you know who coined the term ‘cells’ first?

Harry: No, please tell me.

Mrs. Griggs: It was Robert Hooke, in 1665. What he did was to look at thin slices of cork. He used one of the earliest microscopes to look at them. Of course, he saw only dead cells.

Harry: Wow! So as early as the 17th century, people were interested in this!

Mrs. Griggs: Yes, of course. It was very clear that cells were too small to be seen by the naked eye. So, microscopes were essential. The modern microscope had a predecessor, developed by a Dutch scientist named Anton van Leeuwenhock. He developed a tube-like device made up of many glass lenses. Interestingly, this device was good enough to observe yeast, blood cells and microscopic organisms.

Harry: Can you show me a picture of the modern microscope?

Mrs. Griggs: Sure. Here, look at the different parts of a modern microscope.

Harry: Wow. What do these parts do?

Mrs. Griggs: The mirror of a microscope reflects light into the microscope.

Harry: Amazing! What are those knobs for?

Mrs. Griggs: Large knob moves the stage for a clearer image. Small knob adjusts the focus for a sharper image. Eye piece contains the lenses that increase the magnification of the objective lenses.

Harry: What do these objective lenses do?

Mrs. Griggs: Objective lenses control the magnification for viewing.

Harry: And the tube and clips?

Mrs. Griggs: Tube connects the eye piece to the objective lenses. Clips hold the microscope slide in place. A microscope slide holds the specimen for microscopic study.

Harry: It is all so awesome! Mrs. Griggs, you told us that all living things are made up of cells. And that cells are visible under a microscope. Can you explain a little more about cells? Are all animals and plants made up of cells?

Mrs. Griggs: Of course. I will show you a diagram of an animal cell. Look here.

Harry: So interesting! What do these things do?

Mrs. Griggs: The cell membrane is a thin membrane and it surrounds the cell.

Harry: How about the cytoplasm?

Mrs. Griggs: That is where all chemical reactions take place.

Harry: Vacuoles?

Mrs. Griggs: Vacuoles store water and other nutrients. Nucleus controls cell activities and is needed for the cells to reproduce. And the Mitochondrion generates most of the chemical energy that is needed to power the cell's biochemical reactions.

Harry: So that is the animal cell. How about a plant cell?

Mrs. Griggs: Let me show you.

Harry: Oh! I can see some different structures.

Mrs. Griggs: Yes, the cell wall protects and gives the cell a regular shape. Chloroplasts contain a green pigment called chlorophyll which helps to absorb light energy to make food for the cell during photosynthesis. The rest have the same functions as that of the animal cell.

Harry: So, there are some important differences between the animal cell and plant cell, right?

Mrs. Griggs: Yes, Harry. Look at this table.

	animal cell	plant cell
shape	irregularly shaped	regular shaped or fixed shape
cell wall	has no cell wall	has a cell wall
chloroplasts	does not contain chloroplasts	contains chloroplasts
vacuole	small and numerous. Some animal cells have no vacuoles.	usually large and only one vacuole present

Harry: Mrs. Griggs, how do these cells do all the things that our body does, like respiration etc.?

Mrs. Griggs: I will explain to you. Cells of the same kind that perform the same function are grouped together to form a tissue.

Harry: Ok. Let me guess. Perhaps an organ is made up of several tissues. Am I right?

Mrs. Griggs: Excellent. You are right. And organs work together to form systems.

Harry: By systems do you mean digestive system, respiratory system etc.?

Mrs. Griggs: Yes, Harry.

Harry: What does the digestive system do?

Mrs. Griggs: Can you guess?

Harry: Let me try. It breaks down food into simpler substances that the body can absorb. Am I right?

Mrs. Griggs: Yes, you are. Can you guess what the transport system does?

Harry: I think it transports blood which carries digested food and oxygen to all parts of the body. Am I right?

Mrs. Griggs: Yes. It also transports carbon dioxide and other waste products from all parts of the body to excretory organs.

Harry: Respiratory system?

Mrs. Griggs: It supplies blood with oxygen.

Harry: And the reproductive system?

Mrs. Griggs: That is the system responsible for the continuation of our species. It ensures that new offspring will be born. You will learn more about the organs involved in sexual reproduction in eighth grade.

Harry: Wow! I have learnt a lot today. Thanks a bunch, Mrs. Griggs!