AP Class 8 Biological Science
1. Cell — Structure and Functions
Discovery: Robert Hooke (1665) — observed CORK cells. Named them 'cells' (little rooms).
Cell Theory
- All organisms are made of cells. 2. Cell = basic unit of structure and function. 3. All cells arise from pre-existing cells.
Prokaryotic vs Eukaryotic
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No nuclear membrane | True nucleus |
| Organelles | No membrane-bound | Present |
| Size | 1-10 μm | 10-100 μm |
| Example | Bacteria | Plants, Animals |
Parts of a Cell
| Part | Function |
|---|---|
| Cell Membrane | Selectively permeable. Controls entry/exit. |
| Cell Wall (Plants only) | Cellulose. Rigid — gives SHAPE and SUPPORT. |
| Nucleus | Control centre. Contains chromosomes (DNA). |
| Cytoplasm | Jelly-like. Site of chemical reactions. |
| Mitochondria | Powerhouse. Respiration → ATP. |
| Chloroplast (Plants) | Photosynthesis. |
2. Microorganisms — Friend and Foe
Major Groups
Bacteria (Lactobacillus — curd). Fungi (Yeast — bread. Penicillium — antibiotic). Protozoa (Amoeba, Paramecium). Algae (Chlamydomonas). Viruses (NOT cellular — border of living/non-living. Common cold, COVID-19).
Friendly Microorganisms
- Food: Curd (Lactobacillus). Bread (Yeast — fermentation → CO₂ makes dough rise). Cheese, idli, dosa.
- Medicine: Antibiotics (Penicillin — from Penicillium fungus. Streptomycin). Vaccines (weakened/dead pathogens → body produces antibodies).
- Agriculture: Nitrogen fixation (Rhizobium in legume root nodules). Decomposition (recycle nutrients).
- Cleaning the Environment: Decomposers break down dead matter → nutrients return to soil.
Harmful Microorganisms — Diseases
| Pathogen | Diseases |
|---|---|
| Virus | Common cold, Flu, COVID-19, Polio, Measles, AIDS (HIV) |
| Bacteria | Typhoid (Salmonella), Cholera (Vibrio), Tuberculosis (Mycobacterium) |
| Protozoa | Malaria (Plasmodium — female Anopheles mosquito). Amoebic dysentery. |
| Fungi | Ringworm. Athlete's foot. |
Food Preservation — Methods to KILL or STOP microbial growth
Heating (pasteurisation — milk). Cooling/Freezing. Adding salt (pickles). Adding sugar (jams). Drying (cereals, pulses — remove moisture). Chemical preservatives (sodium benzoate). Vacuum packing (remove air/oxygen).
3. Reproduction in Animals
Sexual Reproduction
Fusion of MALE GAMETE (sperm) + FEMALE GAMETE (egg/ovum) → ZYGOTE → EMBRYO.
Asexual Reproduction
Binary Fission (Amoeba — splits into two). Budding (Hydra — outgrowth detaches).
Metamorphosis — Complete Transformation
Frog: Egg → Tadpole (aquatic, gills, tail) → Froglet (legs develop, tail shrinks) → Adult frog (lungs, four legs). Silk Moth: Egg → Larva (caterpillar/silkworm — eats mulberry leaves) → Pupa (cocoon — silk thread produced) → Adult moth.
4. Ecosystems and Biodiversity
Ecosystem = Biotic (living) + Abiotic (non-living) components interacting.
Food Chain: Grass → Grasshopper → Frog → Snake → Eagle.
Energy FLOWS one way (Sun → producers → consumers → decomposers → HEAT lost). Only ~10% energy transfers to the NEXT level.
Biodiversity Hotspots
India has 4: WESTERN GHATS. Himalayas. Indo-Burma. Sundaland (Nicobar Islands). 'The Eastern Ghats of Andhra Pradesh are part of a BIODIVERSE landscape — home to the Red Sanders (rakta chandan), slender loris, and great Indian bustard.'
Conservation
Protected Areas: National Parks. Wildlife Sanctuaries. Biosphere Reserves. AP Protected Areas: Sri Venkateswara Wildlife Sanctuary. Nagarjunasagar-Srisailam Tiger Reserve (LARGEST tiger reserve in India). Papikonda National Park. Coringa Wildlife Sanctuary (mangroves — Godavari delta). Red Data Book: IUCN list of ENDANGERED species.
Exam Strategy
| Unit | Key Focus |
|---|---|
| Cell | Prokaryotic vs Eukaryotic. Organelles. |
| Microorganisms | Diseases (pathogen + vector). Food preservation methods. |
| Reproduction | Metamorphosis. Asexual types with examples. |
| Ecosystems | Food chain vs Food web. AP wildlife. |
