1. Definition of Cell
- The cell
is the basic structural and functional unit of life.
- All living
organisms are made up of cells.
2. Parts of a Cell
A. Cell Membrane
- Semi-permeable membrane.
- Composed
of lipid bilayer with proteins (fluid mosaic model).
- Controls
entry & exit of substances.
Mnemonic:
"LPP" = Lipid-Protein-Permeable
(Lipid bilayer, Proteins, Permeable)
B. Cytoplasm
- Jelly-like
fluid inside the cell.
- Contains
organelles and cytosol.
C. Organelles
(Membranous & Non-Membranous)
- Mitochondria –
powerhouse of the cell (ATP production)
- Endoplasmic
Reticulum (ER)
- RER:
protein synthesis
- SER:
lipid synthesis
- Golgi
apparatus – packing and secretion
- Lysosomes –
digestion
- Ribosomes – protein
synthesis (non-membranous)
- Centrosome – cell
division
- Nucleus –
contains DNA (control center)
Mnemonic for Organelles:
"My Giant Elephant Likes Running Crazy Nights"
(Mitochondria, Golgi, ER, Lysosome, Ribosome, Centrosome, Nucleus)
3. Functions of Cell
Membrane
- Protection
- Transport (active
& passive)
- Communication via
receptors
- Attachment of
cytoskeleton
- Enzymatic
activity
Mnemonic:
"Please Take Care And Eat"
(Protection, Transport, Communication, Attachment, Enzymes)
4. Transport Across
Cell Membrane
A. Passive Transport (No energy
required)
- Simple
diffusion (O₂, CO₂)
- Facilitated
diffusion (glucose via GLUT)
- Osmosis
(water only)
B. Active Transport (Energy
required - ATP)
- Sodium-potassium
pump (Na⁺ out, K⁺ in)
- Endocytosis
(into the cell)
- Exocytosis
(out of the cell)
Mnemonic:
"P-FOS / A-SEE"
(Passive: Facilitated, Osmosis, Simple / Active: Sodium pump, Endo, Exo)
5. Resting Membrane
Potential (RMP)
- Electrical
charge difference across the membrane.
- Inside =
Negative (~ -70 mV)
- Maintained
by Na⁺/K⁺ pump & leaky K⁺ channels.
6. Action Potential
- Sudden
change in membrane potential → nerve impulse.
- Depolarization: Na⁺ in
- Repolarization: K⁺ out
- Hyperpolarization: excess
K⁺ out
- Restoration: via
Na⁺/K⁺ pump
Mnemonic:
"Do Really Hot Roti"
(Depolarization, Repolarization, Hyperpolarization, Restoration)
7. Cell Cycle
- Series of
events for cell division.
- Phases:
- G₁ – growth
- S – DNA
synthesis
- G₂ –
preparation
- M –
mitosis
- G₀ –
resting
Mnemonic:
"Go Study Go Make Grades"
(G₁, S, G₂, M, G₀)
8. Apoptosis
(Programmed Cell Death)
- Normal
cell death for balance.
- Controlled,
no inflammation.
9. Differences Between
Apoptosis and Necrosis
|
Feature |
Apoptosis |
Necrosis |
|
Nature |
Physiological |
Pathological |
|
Energy |
Requires energy |
No energy needed |
|
Inflammation |
No |
Yes |
|
Cell membrane |
Intact |
Ruptured |
FAQs for Exams
Q1. What is the
function of mitochondria?
Ans: Mitochondria produce energy in the form of ATP – hence called the powerhouse of the cell.
Q2. What is the
sodium-potassium pump?
Ans: It’s an active transport mechanism that pumps 3 Na⁺ out and 2 K⁺ in using ATP to maintain RMP.
Q3. What are the types
of transport across cell membrane?
Ans: Passive (simple diffusion, osmosis, facilitated diffusion) and Active (sodium-potassium pump, endocytosis, exocytosis).
Q4. What is the fluid mosaic model?
Ans: It describes the cell membrane as a flexible, lipid bilayer with scattered proteins.
Q5. What is the
difference between apoptosis and necrosis?
Ans: Apoptosis is programmed and physiological; necrosis is accidental and causes inflammation.
