Overview
This lecture discusses healthy screen habits and focuses on the phases of the cell cycle, including interphase and the mitotic (M) phase, and highlights key differences in cell division between animal and plant cells.
Healthy Screen Habits
- Sit properly with your back supported to prevent neck and back strain.
- Change your sitting position regularly during long screen sessions.
- Use dim lighting to reduce risk of eye damage from screens.
- Use breaks to stretch, walk, and move around.
- Avoid watching TV in bed to prevent back and neck pain.
Introduction to Life Cycles
- A life cycle is a series of developmental steps from birth to reproduction.
- The cell cycle is the life cycle of a cell, involving growth and division.
The Cell Cycle: Overview
- The cell cycle is the process by which cells replicate to produce two new cells.
- In eukaryotic cells (cells with a nucleus), the cell cycle has two major phases: interphase and mitotic (M) phase.
Interphase
- Interphase is when the cell grows and copies its DNA, preparing for division.
- It has three stages: G1 (first gap), S (synthesis), and G2 (second gap).
- G1 phase: Cell accumulates resources and energy; little visible change.
- S phase: DNA is replicated; centrosome is duplicated.
- G2 phase: Cell replenishes energy, produces proteins, duplicates organelles, and prepares for mitosis.
Mitotic (M) Phase
- M phase involves mitosis (nuclear division) and cytokinesis (cytoplasmic division).
- Mitosis has four stages: prophase, metaphase, anaphase, telophase.
- Cytokinesis splits the cytoplasm and forms two new cells.
- Animal cells use a contractile ring (cleavage furrow) to divide.
- Plant cells build a cell plate to divide due to their rigid walls.
Control and Timing of the Cell Cycle
- Some cells divide rapidly (embryonic, cancer cells); others rarely or never divide (nerve cells).
- The G0 phase is a resting state where the cell is not preparing to divide.
- Typical rapidly dividing human cells take about 24 hours per cycle.
Key Terms & Definitions
- Cell Cycle — series of steps from cell formation to division into two daughter cells.
- Interphase — phase of growth and DNA replication (G1, S, G2).
- Mitosis — division of cell nucleus resulting in two identical cells.
- Cytokinesis — division of cytoplasm into two daughter cells.
- G0 phase — non-dividing, resting phase of the cell.
- Centrosome — organelle helping organize spindle fibers during division.
- Cell Plate — structure that forms in plant cells to divide them during cytokinesis.
Action Items / Next Steps
- Complete the assignment: Arrange these events in order—spindle fibers emerge from centrosomes, chromosomes condense, nucleolus disappears, nuclear envelope breaks down—in your biology interactive notebook.