Weekly Revision Notes
Subject: Science | This Week's Topics Combined
For TLT, ECT, PST, JEST & All Competitive Exams
This week we covered five connected topics in General Science, building from the smallest unit of life all the way up to a fully working body system. Use this page as a quick revision before your weekly test — every topic is summarized with its most important, exam-relevant points.
📋 This Week's Topics
Cell Structure and Function
The cell is the basic structural and functional unit of all living organisms. Every living thing is made up of one or more cells, and each cell carries out the life processes needed for survival.
Main Cell Parts
- Cell Membrane — Controls what enters and leaves the cell.
- Cytoplasm — Jelly-like substance where most cell activities occur.
- Nucleus — Controls the cell's activities and contains DNA/chromosomes.
- Mitochondria — The "powerhouse" of the cell; produces energy.
- Ribosomes — Make proteins for the cell.
- Cell Wall — Found only in plant cells; gives extra rigidity and support.
- Chloroplast — Found only in plant cells; site of photosynthesis.
- Vacuole — Stores water, food, and waste; usually larger in plant cells.
Tissues, Organs and Organ Systems
A tissue is a group of similar cells performing the same function. Animal tissues are of four main types:
- Epithelial Tissue — Covers and lines body surfaces (e.g., skin).
- Connective Tissue — Connects and supports body parts (e.g., bone, blood).
- Muscular Tissue — Produces movement (skeletal, smooth, cardiac).
- Nervous Tissue — Receives and sends signals; made of neurons.
When different tissues work together, they form an organ (e.g., the heart). When several organs work together, they form an organ system (e.g., the digestive system).
Cell Division: Mitosis and Meiosis
Cell division is how a parent cell divides into new cells, essential for growth, repair, and reproduction. There are two main types:
| Feature | Mitosis | Meiosis |
|---|---|---|
| Daughter cells | 2 | 4 |
| Chromosome number | Same as parent | Half of parent |
| Occurs in | Body (somatic) cells | Sex cells (gametes) |
| Purpose | Growth, repair | Sexual reproduction, variation |
The four stages of mitosis, in order, are: Prophase, Metaphase, Anaphase, Telophase (remembered as "PMAT").
Organ Systems of the Human Body
The human body has eleven major organ systems, each with its own organs and job:
| System | Main Function |
|---|---|
| Skeletal | Support, protection |
| Muscular | Movement |
| Digestive | Breaks down food, absorbs nutrients |
| Respiratory | Breathing (oxygen in, CO₂ out) |
| Circulatory | Transports blood, oxygen, nutrients |
| Nervous | Controls and coordinates the body |
| Excretory | Removes waste |
| Endocrine | Releases hormones |
| Reproductive | Produces offspring |
| Integumentary | Covers/protects body, regulates temperature |
| Immune (Lymphatic) | Defends against disease |
The Human Digestive System
The digestive system breaks down food into nutrients the body can absorb. Path of food through the alimentary canal:
Mouth → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus
- Mouth — Chewing + saliva begins starch digestion.
- Esophagus — Food pipe; moves food via peristalsis.
- Stomach — Churns food with gastric juices into chyme.
- Small Intestine — Main site of digestion and absorption (via villi).
- Large Intestine — Absorbs water; forms solid waste.
- Liver & Pancreas — Accessory organs; release bile and digestive enzymes.
The digestive process in order: Ingestion → Digestion → Absorption → Assimilation → Egestion.
Final Revision Tips
- Revise the sequence: Cell → Tissue → Organ → Organ System → Organism — it connects almost every topic this week.
- Compare Mitosis vs Meiosis side by side — this is a very common MCQ pattern.
- Match each organ system to its correct organs and function — exams love this format.
- Learn the digestive tract order and the role of each organ — a frequently repeated question type.
- Re-attempt the quizzes for each topic and review any wrong answers before the test.
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