Students by the time they reach Class 9 are already familiar with the topic of cells, its discovery, shapes and sizes, unicellular and multicellular organisms. However, in Andhra Board Class 9 Biology Chapter 1, students will recall the terms related to cells as well as study the diagrams of models of the cell. The chapter includes topics like;
- Different parts of Cells
- Cell Organelles
- Where Do Cells come from?
What is a Cell?
A cell is defined as the fundamental unit of life.
Different Parts of Cells
Cell membrane: It is a thin, flexible layer surrounding the cells of all living things and it basically separates the inside of cells from the outside. It is also known as a cytoplasmic membrane or plasma membrane.
Cell wall: It is an outer layer surrounding certain type of cells and is usually present outside of the cell membrane.
Nucleus: It is a spherical-shaped organelle present in almost all the eukaryotic type of cell.
Cytoplasm: It is the fluid content inside the plasma membrane and usually contains many specialised cell organelles.
Important Cell Organelles
Some of the important cell organelles are Mitochondria, Plastids, Ribosomes, Endoplasmic reticulum, Golgi apparatus, Lysosomes, and vacuoles.
- Mitochondria are small, spherical or cylindrical organelles and are often referred to as the powerhouse of the cell.
- Ribosomes are small granule-like structures present in the cytoplasm of the cell.
- The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
- Lysosomes or commonly know as suicidal bags are membrane-bound sacs which are filled with digestive enzymes.
- Vacuoles, on the other hand, are the storage sacs used for storing liquid or solid contents.
- The Golgi apparatus or Golgi body is a collection of stacks of membranes bound vesicles that are for shipping certain cellular products.
Where Do Cells Come From?
Rudolf Von Virchow a German biologist was the first one to explain that cells divided and new cells formed only by the division of the pre-existing cells. Therefore, it has been concluded that all cells arise from pre-existing cells.
Students can have a glimpse of important questions below and learn about some of the additional chapter topics.
Question 1: State whether cells are flat or not.
Answer: If we observe cells under a microscope, the image appears as flat and two-dimensional. The reality though is that cells have a definite length, breadth and thickness. Cells are not flat.
Question 2: Write down the main characteristic of a plasma membrane?
Answer: Plasma membrane is a selectively permeable membrane and it consists of lipids and proteins.
Question 3: Where are plastids found? Name the different types of plastids.
Answer: A plastid is a self-reproducing cell organelle that is usually present in plants and algae. Plastids are divided into chromoplasts (coloured) and leucoplasts (colourless).
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