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 to synthesise polypeptides in the cell -The ribosomes attached to the RER make polypeptides which are usually transported out of the cell -The ribosomes in the cytoplasm make polypeptides that are used inside the cytoplasm of the cell Smooth endoplasmic reticulum (SER) -The SER does not have ribosomes attached to its membrane and is more tubular than the RER -It is connected to the RER -It synthesises substances such as fats and steroids and converts harmful substances to harmless substances through detoxification Golgi apparatus -The golgi apparatus, also known as the golgi body, is shaped like a disc and contains a stack of flattened spaces surrounded by membranes -Vesicles can be seen fusing with one side of the golgi apparatus and pinching off from the opposite side -It chemically modifies substances made by the RER and the SER and stores and packages these substances in vesicles for secretion out of the cell

Mitochondria (singular: mitochondrion) -It is a small oval or sausage shaped organelle where aerobic respiration occurs -Food substances are broken down to release energy, which may be used by the cell to perform cell activities such as growth and reproduction -aerobic respiration equation: glucose (C6H12O6) + oxygen (6O2) = carbon dioxide (6CO2) + water (6H2O) + energy Chloroplasts -Chloroplasts are oval structures found in plant cells which contain a green pigment called chlorophyll -Chlorophyll is essential for photosynthesis, the process by which plants make food

-Photosynthesis equation: carbon dioxide (6CO2) + water (6H2O) = glucose (C6H12O6) + oxygen (6O2) Vacuole -The vacuole is a fluid filled space enclosed by a partially permeable membrane -The vacuole stores substances within the cell -Plant cells contain a large, central vacuole which contains a liquid called cell sap -Cell sap contains dissolved substances such as sugars, mineral salts and amino acids -Animal cells contain small, numerous vacuoles which contain food and water substances -These vacuoles usually exist temporarily Differences between plant and animal cells Animal cell Plant cell No cell wall Has a cell wall Many small vacuoles One large central vacuole No chloroplasts Has chloroplasts How are cells adapted to their functions? -Some cells develop or lose certain structures to enable them to carry out specific functions -This process of development is called differentiation Red blood cell -The red blood cell contains haemoglobin, which binds reversibly to oxygen and transports it around the body -It has a biconcave shape, increasing the surface area to volume ratio so that oxygen can diffuse in and out at a higher rate -It lacks a nucleus, allowing it to store more haemoglobin to transport more oxygen -It is flexible to allow it to squeeze through capillaries easily -Haemoglobin chemical equation: Hb + O2 = HbO2 (lungs) HbO2 = Hb + O2 (cells)

Muscle cell -The muscle cell is elongated and cylindrical in shape, containing many nuclei and mitochondria -It has many mitochondria to provide energy for the contraction of the muscle cell -It has contractile protein fibers to allow for contraction and relaxation of the cell to bring about movement -It has many nuclei to allow for cell division Root hair cell -The root hair cell has a long and narrow root hair to increase the surface area to volume ratio to absorb water and mineral salts at a higher rate -It has a large amount of mitochondria to provide energy for the active transport of mineral sats

Chapter 2: Movement of Substances

Diffusion -Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration without the need for energy Concentration gradient -A concentration gradient is the difference in concentration between two regions -If the concentration gradient is steeper, the rate of diffusion is faster -Two substances must have a concentration gradient in order for diffusion to occur Diffusion across a membrane -Diffusion can occur across a membrane as long as both molecules can pass through the membrane Factors that affect the rate of diffusion Concentration gradient -If the concentration gradient is steeper, the rate of diffusion is faster Diffusion distance -Diffusion distance is the distance through which a substance diffuses -The shorter the diffusion distance, the less time needed for the substance to travel, and thus the higher the rate of diffusion Surface area to volume ratio