08Class 11 Biology
Cell: The Unit of Life short notes
A quick revision of the cell for NEET and boards. Questions here often test which organelle does what, so learn structure and function together.
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Cell theory and types
- All living things are made of cells, and all cells arise from existing cells. Schleiden and Schwann proposed the theory, and Virchow added the second part.
- Prokaryotes (such as bacteria) have no membrane-bound nucleus or organelles.
- Eukaryotes have a true nucleus and membrane-bound organelles.
- Prokaryotic ribosomes are 70S (50S + 30S), while eukaryotic ones in the cytoplasm are 80S (60S + 40S).
Cell membrane and wall
- The fluid mosaic model of the membrane comes from Singer and Nicolson.
- Plant cell walls are mainly cellulose. Fungal walls contain chitin, and bacterial walls contain peptidoglycan.
- The membrane is selectively permeable. Water moves across it by osmosis.
Organelles
- Mitochondria: site of aerobic respiration and ATP production, with their own DNA and 70S ribosomes.
- Chloroplasts: site of photosynthesis, with thylakoids (grana) and a stroma, also with their own DNA.
- Endoplasmic reticulum: rough ER makes proteins, and smooth ER makes lipids.
- Golgi apparatus: packages and modifies materials, and forms glycoproteins and glycolipids.
- Lysosomes: contain hydrolytic enzymes that work best at an acidic pH.
- Ribosomes: sites of protein synthesis, and have no membrane.
- Vacuole: large in plant cells, and stores sap. Its membrane is called the tonoplast.
- Centrosome: has two centrioles with a 9 + 0 arrangement. Cilia and flagella have a 9 + 2 arrangement.
Nucleus
- It has a double membrane with pores, plus chromatin and a nucleolus.
- The nucleolus is the site of rRNA synthesis.
- Chromosomes are classed by where the centromere sits: metacentric, sub-metacentric, acrocentric or telocentric.
Where students slip up
- Confusing 9 + 2 (cilia and flagella) with 9 + 0 (centrioles).
- Saying ribosomes are membrane-bound. They aren't, so they're found in prokaryotes too.
- Forgetting mitochondria and chloroplasts are semi-autonomous, with their own DNA and ribosomes.
Try it on your weakest chapter.
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