Prokaryotic cells (without a nucleus) like bacteria, and Eukaryotic cells (with a nucleus) like plant and animal cells. The cell theory states three key points: All living things are made of cells, the cell is the basic unit of life, and all cells come from pre-existing cells
Cell membrane (controls entry and exit), Cytoplasm (jelly-like substance), Nucleus (control center with DNA), Mitochondria (powerhouse), Ribosomes (protein factories), and in plants - Chloroplasts (for photosynthesis) and Cell wall (for support).
Osmosis rate ∝ Concentration gradient
RRB Group D frequently asks about cell organelles and their functions (60% questions), differences between plant and animal cells (25% questions), and cell division processes (15% questions). Questions often use diagrams or ask 'odd one out' type problems.
- PORN Method for plant cell organelles: P-Plastids, O-Only in plants, R-Rigid cell wall, N-Nuclear membrane present. For animal cells, remember MEN: M-Mitochondria plenty, E-Endoplasmic reticulum, N-No cell wall.
Total time = 2 hours = 120 minutes
Number of divisions = 120/20 = 6 divisions
Number of cells = 2^6 = 64 cells Answer: 64 cells Worked Example 2: A cell has surface area 600 square units and volume 100 cubic units. What is the surface area to volume ratio?
Surface area = 600 square units
Volume = 100 cubic units
Ratio = 600/100 = 6:1 Answer: 6:1 Most Common Trap: Students confuse chloroplasts with chromoplasts. Remember - CHLOROplasts contain CHLOROphyll for photosynthesis (green color). CHROMOplasts give other colors like red, yellow, orange to fruits and flowers. This confusion appears in 40% of wrong answers. Another major mistake is thinking viruses are cells. Viruses are NOT cells - they cannot reproduce on their own and need host cells. They are non-living particles with genetic material surrounded by protein coat. Cell size is measured in micrometers. Most animal cells are 10-30 micrometers, while plant cells are 10-100 micrometers. Bacteria are much smaller at 1-5 micrometers. The largest single cell is the ostrich egg. Diffusion and osmosis are key transport processes. Diffusion moves particles from high to low concentration without energy. Osmosis specifically moves water across membranes. Active transport requires energy to move against concentration gradient.
12graded MCQs · easy to hard · full solution & trap analysis