This guide covers the fundamental unit of all living things—the cell. Knowing the parts of a cell and their functions is essential for all of biology.

1. Short Notes: Core Concepts

A. The Cell Theory This is the foundation of modern biology.

1. The cell is the basic structural and functional unit of life.

2. All living organisms are made up of one or more cells.

3. New cells are formed from pre-existing cells.

B. Key Differences: Plant vs. Animal Cells This is a very common exam topic. The three main differences are:

C. Cell Organelles: The "Organs" of the Cell Each organelle has a specific job.

• Nucleus: The "control center". Contains the chromosomes (DNA), which carry genetic information and control all cell activities.

• Cell Membrane: Found in BOTH plant and animal cells. It is a semi-permeable barrier that controls what enters and leaves the cell.

• Cell Wall (Plants only): A strong outer layer that provides structural support and protection to the plant cell.

• Cytoplasm: The jelly-like substance that fills the cell and surrounds the organelles. Many chemical reactions happen here.

• Mitochondrion (plural: Mitochondria): The "powerhouse" of the cell. This is where cellular respiration occurs to release energy for the cell to use. Cells that need a lot of energy (like muscle cells) have many mitochondria.

• Chloroplasts (Plants only): The site of photosynthesis, where sunlight, water, and CO₂ are converted into food (glucose).

• Vacuole: A storage sac. In plants, the large central vacuole is crucial for storing water and maintaining turgor pressure (keeping the cell firm).

• Ribosomes: Tiny structures responsible for making proteins (protein synthesis).

D. Cell Growth and Division

• Cell Growth: An irreversible increase in the size of the cell.

• Cell Division: The process where one parent cell divides to form new daughter cells. There are two types:

  1. Mitosis:

     • Purpose: For growth, repair of damaged tissues, and replacing old cells.

     • Process: One parent cell divides once to produce two genetically identical daughter cells.

     • Chromosome Number: The daughter cells have the same number of chromosomes as the parent cell (e.g., in humans, 46 -> 46).

  2. Meiosis:

     • Purpose: To produce gametes (sex cells: sperm and eggs) for sexual reproduction.

     • Process: One parent cell divides twice to produce four genetically different daughter cells.

     • Chromosome Number: The daughter cells have half the number of chromosomes as the parent cell (e.g., in humans, 46 -> 23). This is crucial so that when the sperm (23) and egg (23) fuse, the baby has the correct total of 46.

2. Tips & Tricks for the Exam

• Remember the 3 C's for Plants: Cell wall, Chloroplasts, Central vacuole (large). If a diagram has these, it's a plant cell.

• Diagrams are Key: You will almost certainly be asked to label a diagram of a plant or animal cell. Practice drawing and labeling them from memory.

• Mitosis vs. Meiosis:

  • Mitosis = Makes Identical Twins. Used for Tissues.

  • Meiosis = Makes Eggs (and sperm). Halves the chromosomes.

3. Important Points & Common Exam Questions

• Labeling: Be prepared to identify the nucleus, mitochondrion, cell wall, cell membrane, cytoplasm, vacuole, and chloroplasts on a diagram.

• Compare and Contrast: A classic question is: "State three differences between a plant cell and an animal cell." Use the table above for your answer.

• Function Questions:

  • "What is the function of the mitochondrion?" (Answer: To release energy through cellular respiration).

  • "Why would a leaf cell have many chloroplasts?" (Answer: Because the leaf is the primary site of photosynthesis, which occurs in chloroplasts).

• Significance of Cell Division:

  • "What is the importance of mitosis in a multicellular organism?" (Answer: For growth by increasing the number of cells and for repairing damaged tissues).

  • "What is the main purpose of meiosis?" (Answer: To produce gametes with half the number of chromosomes for sexual reproduction).