bio notes o level

Chapter 1: Cell Structure and Organisation

How can we study parts of cells? -Most cells are too small to be seen -Microscopes are thus used to see these cells Types of microscopes -Light microscopes (1000x) -Electron microscope (200000x) -The mitochondria, smooth and rough endoplastic reticulum, ribosomes, golgi apparatus and chromosomes can only be seen under an electron microscope as they are too small Viewing cells from different perspectives Longitudinal section (L.S.) -Cut along the length of the cell Transverse section (T.S.) -Cut along the right angles of the cell

What does a cell consist of? -A cell consists of a mass of living matter called protoplasm -Protoplasm of a cell is made of of three parts: -Cell membrane -Cytoplasm -Nucleus -If a cell is dead there is no protoplasm Cell membrane -The cell membrane surrounds the cytoplasm of a cell -It is a partially permeable membrane, thus controlling substances moving in and out of the cell Cell wall -Plant cells have a cell wall which fully encloses the cell -It is fully permeable and made of cellulose, allowing all substances to move in and out of the cell -It protects the cell from injury and gives the plant cell a fixed shape Cytoplasm -The cytoplasm is a jelly-like substance which fills the inside of the cell, where most cell activities occur -It contains many organelles, which perform specific jobs inside the cell

What are the parts of the cytoplasm? -The cytoplasm contains tiny structures called organelles, which are specialised for a specific function -e.g. nucleus, endoplasmic reticulum, ribosomes, golgi body, mitochondria, chloroplasts, vacuoles Nucleus -The nucleus is surrounded by a membrane called the nuclear membrane -It contains genetic information in the form of chromosomes -It controls cell activities such as cell growth and the repair of worn out parts -It is essential for cell division Chromosomes -Chromosomes are long thread like structures found inside the nucleus -It is made up of proteins and deoxyribonucleic acid (DNA) which stores hereditary information and carries instructions that a cell needs while carrying out its activities -When the cell is dividing, the chromosomes condense to form thick, rod shaped structures -A human cell has 46 chromosomes Rough Endoplasmic Reticulum (RER) -It consists of a network of flattened spaces lined with a membrane -Its surface appears rough when viewed under an electron microscope as small particles called ribosomes are attached to its outer surface -The outer surface of the RER is continuous with the nuclear membrane, so it seems to be connected or very near to the nucleus under an electron microscope -The RER transports polypeptides made by the ribosomes to the golgi body for secretion out of the cell

Ribosomes -Ribosomes are small round structures which are either attached to the membrane of the RER or lie freely inside the cytoplasm -They are needed t